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Atmospheric Measurement Techniques

Atmospheric Measurement Techniques

Constraining regional greenhouse gas emissions using geostationary concentration measurements: a theoretical studyAtmospheric Measurement Techniques, 7, 3285-3293, 2014Author(s): P. J. Rayner, S. R. Utembe, and S. CrowellWe investigate the ability of column-integrated trace gas measurements from a
geostationary satellite to constrain surface fluxes at regional scale. The
proposed GEOCARB instrument measures CO2, CO and CH4 at a maximum
resolution of 3 km east–west × 2.7 km north–south. Precisions are
3 ppm for CO2, 10 ppb for CO and 18 ppb for CH4. Sampling frequency
is flexible. Here we sample a region at the location of Shanghai every 2
daylight hours for 6 days in June. We test the observing system by
calculating the posterior uncertainty covariance of fluxes. We are able to
constrain urban emissions at 3 km resolution including an isolated
power plant. The CO measurement plays the strongest role; without it our
effective resolution falls to 5 km. Methane fluxes are similarly
well estimated at 5 km resolution. Estimating the errors for a full year
suggests such an instrument would be a useful tool for both science and
policy applications. 2014/10/03 - 12:22

A gas chromatograph for quantification of peroxycarboxylic nitric anhydrides calibrated by thermal dissociation cavity ring-down spectroscopyAtmospheric Measurement Techniques, 7, 3263-3283, 2014Author(s): T. W. Tokarek, J. A. Huo, C. A. Odame-Ankrah, D. Hammoud, Y. M. Taha, and H. D. OsthoffThe peroxycarboxylic nitric anhydrides (PANs, molecular formula:
RC(O)O2NO2) can readily be observed by gas chromatography (PAN-GC)
coupled to electron capture detection. Calibration of a PAN-GC remains a
challenge, because the response factors differ for each of the PANs, and because their
synthesis in sufficiently high purity is non-trivial, in particular for PANs
containing unsaturated side chains. In this manuscript, a PAN-GC and its
calibration using diffusion standards, whose output was quantified by blue
diode laser thermal dissociation cavity ring-down spectroscopy (TD-CRDS), are
described. The PAN-GC peak areas correlated linearly with total peroxy
nitrate (ΣPN) mixing ratios measured by TD-CRDS
(r > 0.96). Accurate determination of response factors
required the concentrations of PAN impurities in the synthetic standards to
be subtracted from ΣPN. The PAN-GC and its TD-CRDS calibration method
were deployed during ambient air measurement campaigns in Abbotsford, BC,
from 20 July to 5 August 2012, and during the Fort McMurray Oil Sands
Strategic Investigation of Local Sources (FOSSILS) campaign at the AMS13
ground site in Fort McKay, AB, from 10 August to 5 September 2013. The PAN-GC
limits of detection for PAN, PPN, and MPAN during FOSSILS were 1, 2, and
3 pptv, respectively. For the Abbotsford data set, the PAN-GC mixing ratios
were compared, and agreed with those determined in parallel by thermal
dissociation chemical ionization mass spectrometry (TD-CIMS). Advantages and
disadvantages of the PAN measurement techniques used in this work and the
utility of TD-CRDS as a PAN-GC calibration method are discussed. 2014/10/01 - 23:45

Simultaneous retrieval of effective refractive index and density from size distribution and light-scattering data: weakly absorbing aerosolAtmospheric Measurement Techniques, 7, 3247-3261, 2014Author(s): E. Kassianov, J. Barnard, M. Pekour, L. K. Berg, J. Shilling, C. Flynn, F. Mei, and A. JeffersonWe propose here a novel approach for retrieving in parallel the effective
density and real refractive index of weakly absorbing aerosol from optical
and size distribution measurements. Here we define "weakly absorbing" as
aerosol single-scattering albedos that exceed 0.95 at 0.5 μm. The
required optical measurements are the scattering coefficient and the
hemispheric backscatter fraction, obtained in this work from an integrating
nephelometer. The required size spectra come from mobility and aerodynamic
particle size spectrometers commonly referred to as a scanning mobility particle
sizer and an aerodynamic particle sizer. The performance of this approach is
first evaluated using a sensitivity study with synthetically generated but
measurement-related inputs. The sensitivity study reveals that the proposed
approach is robust to random noise; additionally the uncertainties of the
retrieval are almost linearly proportional to the measurement errors, and
these uncertainties are smaller for the real refractive index than for the
effective density. Next, actual measurements are used to evaluate our
approach. These measurements include the optical, microphysical, and chemical
properties of weakly absorbing aerosol which are representative of a variety
of coastal summertime conditions observed during the Two-Column Aerosol
Project (TCAP; The evaluation includes
calculating the root mean square error (RMSE) between the aerosol
characteristics retrieved by our approach, and the same quantities calculated
using the conventional volume mixing rule for chemical constituents. For dry
conditions (defined in this work as relative humidity less than 55%) and
sub-micron particles, a very good (RMSE ~ 3%) and reasonable
(RMSE ~ 28%) agreement is obtained for the retrieved real
refractive index (1.49 ± 0.02) and effective density
(1.68 ± 0.21), respectively. Our approach permits discrimination
between the retrieved aerosol characteristics of sub-micron and sub-10-micron
particles. The evaluation results also reveal that the retrieved density and
refractive index tend to decrease with an increase of the relative humidity. 2014/10/01 - 23:45

Retrieval of cirrus cloud optical thickness and top altitude from geostationary remote sensingAtmospheric Measurement Techniques, 7, 3233-3246, 2014Author(s): S. Kox, L. Bugliaro, and A. OstlerA novel approach for the detection of cirrus clouds and the retrieval of
optical thickness and top altitude based on the measurements of the Spinning
Enhanced Visible and Infrared Imager (SEVIRI) aboard the geostationary
Meteosat Second Generation (MSG) satellite is presented. Trained with 8 000 000 co-incident measurements of the Cloud-Aerosol Lidar with Orthogonal
Polarization (CALIOP) aboard the Cloud-Aerosol Lidar and Infrared Pathfinder
Satellite Observations (CALIPSO) mission the new "cirrus optical properties
derived from CALIOP and SEVIRI algorithm during day and night" (COCS)
algorithm utilizes a backpropagation neural network to provide accurate
measurements of cirrus optical depth τ at λ = 532 nm and top
altitude z every 15 min covering almost one-third of the Earth's atmosphere.
The retrieved values are validated with independent measurements of CALIOP
and the optical thickness derived by an airborne high spectral resolution
lidar. 2014/10/01 - 23:45

Calibrating airborne measurements of airspeed, pressure and temperature using a Doppler laser air-motion sensorAtmospheric Measurement Techniques, 7, 3215-3231, 2014Author(s): W. A. Cooper, S. M. Spuler, M. Spowart, D. H. Lenschow, and R. B. FriesenA new laser air-motion sensor measures the true airspeed with a
standard uncertainty of less than 0.1 m s−1
and so reduces uncertainty in the measured component of the relative
wind along the longitudinal axis of the aircraft to about the same
level. The calculated pressure expected from that airspeed at the
inlet of a pitot tube then provides a basis for calibrating the
measurements of dynamic and static pressure, reducing standard
uncertainty in those measurements to less than 0.3 hPa and the
precision applicable to steady flight conditions to about
0.1 hPa. These improved measurements of pressure, combined with
high-resolution measurements of geometric altitude from the global positioning system, then indicate (via integrations of the
hydrostatic equation during climbs and descents) that the offset and
uncertainty in temperature measurement for one research aircraft are
+0.3 ± 0.3 °C. For airspeed, pressure and temperature,
these are significant reductions in uncertainty vs. those obtained
from calibrations using standard techniques. Finally, it is shown
that although the initial calibration of the measured static and
dynamic pressures requires a measured temperature, once calibrated
these measured pressures and the measurement of airspeed
from the new laser air-motion sensor
provide a measurement of temperature that does not depend on
any other temperature sensor. 2014/10/01 - 23:45

The AquaVIT-1 intercomparison of atmospheric water vapor measurement techniquesAtmospheric Measurement Techniques, 7, 3177-3213, 2014Author(s): D. W. Fahey, R.-S. Gao, O. Möhler, H. Saathoff, C. Schiller, V. Ebert, M. Krämer, T. Peter, N. Amarouche, L. M. Avallone, R. Bauer, Z. Bozóki, L. E. Christensen, S. M. Davis, G. Durry, C. Dyroff, R. L. Herman, S. Hunsmann, S. M. Khaykin, P. Mackrodt, J. Meyer, J. B. Smith, N. Spelten, R. F. Troy, H. Vömel, S. Wagner, and F. G. WienholdThe AquaVIT-1 intercomparison of atmospheric water vapor measurement
techniques was conducted at the aerosol and cloud simulation chamber AIDA
(Aerosol Interaction and Dynamics in the Atmosphere) at
the Karlsruhe Institute of Technology, Germany, in October 2007. The overall
objective was to intercompare state-of-the-art and prototype atmospheric
hygrometers with each other and with independent humidity standards under
controlled conditions. This activity was conducted as a blind
intercomparison with coordination by selected referees. The effort was
motivated by persistent discrepancies found in atmospheric measurements
involving multiple instruments operating on research aircraft and balloon
platforms, particularly in the upper troposphere and lower stratosphere,
where water vapor reaches its lowest atmospheric values (less than 10 ppm).
With the AIDA chamber volume of 84 m3, multiple instruments analyzed
air with a common water vapor mixing ratio, by extracting air into
instrument flow systems, by locating instruments inside the chamber, or
by sampling the chamber volume optically. The intercomparison was successfully
conducted over 10 days during which pressure, temperature, and mixing ratio
were systematically varied (50 to 500 hPa, 185 to 243 K, and 0.3 to 152 ppm).
In the absence of an accepted reference instrument, the absolute accuracy of
the instruments was not established. To evaluate the intercomparison, the
reference value was taken to be the ensemble mean of a core subset of the
measurements. For these core instruments, the agreement between 10 and
150 ppm of water vapor is considered good with variation about the reference
value of about ±10% (±1σ). In the region of most
interest between 1 and 10 ppm, the core subset agreement is fair with
variation about the reference value of ±20% (±1σ).
The upper limit of precision was also derived for each instrument from the
reported data. The implication for atmospheric measurements is that the
substantially larger differences observed during in-flight intercomparisons
stem from other factors associated with the moving platforms or the
non-laboratory environment. The success of AquaVIT-1 provides a template for
future intercomparison efforts with water vapor or other species that are
focused on improving the analytical quality of atmospheric measurements on
moving platforms. 2014/09/26 - 15:30

Satellite retrieval of aerosol microphysical and optical parameters using neural networks: a new methodology applied to the Sahara desert dust peakAtmospheric Measurement Techniques, 7, 3151-3175, 2014Author(s): M. Taylor, S. Kazadzis, A. Tsekeri, A. Gkikas, and V. AmiridisIn order to exploit the full-earth viewing potential of satellite
instruments to globally characterise aerosols, new algorithms are required
to deduce key microphysical parameters like the particle size distribution
and optical parameters associated with scattering and absorption from space
remote sensing data. Here, a methodology based on neural networks is
developed to retrieve such parameters from satellite inputs and to validate
them with ground-based remote sensing data. For key combinations of input
variables available from the MODerate resolution Imaging Spectro-radiometer (MODIS) and the Ozone Measuring Instrument (OMI) Level 3 data sets, a grid of 100
feed-forward neural network architectures is produced, each having a
different number of neurons and training proportion. The networks are
trained with principal components accounting for 98% of the variance of
the inputs together with principal components formed from 38 AErosol RObotic NETwork (AERONET) Level
2.0 (Version 2) retrieved parameters as outputs. Daily averaged, co-located
and synchronous data drawn from a cluster of AERONET sites centred on the
peak of dust extinction in Northern Africa is used for network training and
validation, and the optimal network architecture for each input parameter
combination is identified with reference to the lowest mean squared error.
The trained networks are then fed with unseen data at the coastal dust site
Dakar to test their simulation performance. A neural network (NN), trained with co-located
and synchronous satellite inputs comprising three aerosol optical depth
measurements at 470, 550 and 660 nm, plus the columnar water vapour (from
MODIS) and the modelled absorption aerosol optical depth at 500 nm (from
OMI), was able to simultaneously retrieve the daily averaged size
distribution, the coarse mode volume, the imaginary part of the complex
refractive index, and the spectral single scattering albedo – with moderate
precision: correlation coefficients in the range 0.368 ≤ R ≤ 0.514. The network failed to recover the spectral behaviour of the real part
of the complex refractive index. This new methodological approach appears to
offer some potential for moderately accurate daily retrieval of the total
volume concentration of the coarse mode of aerosol at the Saharan dust peak
in the area of Northern Africa. 2014/09/26 - 15:30

Reconstruction of global solar radiation time series from 1933 to 2013 at the Izaña Atmospheric ObservatoryAtmospheric Measurement Techniques, 7, 3139-3150, 2014Author(s): R. D. García, E. Cuevas, O. E. García, V. E. Cachorro, P. Pallé, J. J. Bustos, P. M. Romero-Campos, and A. M. de FrutosThis paper presents the reconstruction of the 80-year time series of daily
global solar radiation (GSR) at the subtropical high-mountain
Izaña Atmospheric Observatory (IZO) located in Tenerife (The Canary
Islands, Spain). For this purpose, we combine GSR estimates from sunshine
duration (SD) data using the Ångström–Prescott method over the
1933/1991 period, and GSR observations directly performed by pyranometers
between 1992 and 2013. Since GSR measurements have been used as a reference,
a strict quality control has been applied based on principles of physical
limits and comparison with LibRadtran model. By comparing with high quality
GSR measurements, the precision and consistency over time of GSR estimations
from SD data have been successfully documented. We obtain an overall root
mean square error (RMSE) of 9.2% and an agreement between the variances
of GSR estimations and GSR measurements within 92%. Nonetheless, this
agreement significantly increases when the GSR estimation is done considering
different daily fractions of clear sky (FCS). In that case, RMSE is reduced
by half, to about 4.5%, when considering percentages of
FCS > 40% (~ 90% of days in the testing period).
Furthermore, we prove that the GSR estimations can monitor the GSR anomalies
in consistency with GSR measurements and, then, can be suitable for
reconstructing solar radiation time series. The reconstructed IZO GSR time
series between 1933 and 2013 confirms change points and periods of
increases/decreases of solar radiation at Earth's surface observed at
a global scale, such as the early brightening, dimming and brightening. This
fact supports the consistency of the IZO GSR time series presented in this
work, which may be a reference for solar radiation studies in the subtropical
North Atlantic region. 2014/09/25 - 13:46

Aircraft validation of Aura Tropospheric Emission Spectrometer retrievals of HDO / H2OAtmospheric Measurement Techniques, 7, 3127-3138, 2014Author(s): R. L. Herman, J. E. Cherry, J. Young, J. M. Welker, D. Noone, S. S. Kulawik, and J. WordenThe EOS (Earth Observing System) Aura Tropospheric Emission Spectrometer (TES) retrieves the
atmospheric HDO / H2O ratio in the mid-to-lower troposphere as well
as the planetary boundary layer. TES observations of water vapor and the HDO
isotopologue have been compared with nearly coincident in situ airborne
measurements for direct validation of the TES products. The field
measurements were made with a commercially available Picarro L1115-i isotopic
water analyzer on aircraft over the Alaskan interior boreal forest during the
three summers of 2011 to 2013. TES special observations were utilized in
these comparisons. The TES averaging kernels and a priori constraints have
been applied to the in situ data, using version 5 (V005) of the TES data.
TES calculated errors are compared with the standard deviation (1σ)
of scan-to-scan variability to check consistency with the TES observation
error. Spatial and temporal variations are assessed from the in situ aircraft
measurements. It is found that the standard deviation of scan-to-scan
variability of TES δD is ±34.1‰ in the boundary layer
and ± 26.5‰ in the free troposphere. This scan-to-scan
variability is consistent with the TES estimated error (observation error) of
10–18‰ after accounting for the atmospheric variations along the
TES track of ±16‰ in the boundary layer, increasing to
±30‰ in the free troposphere observed by the aircraft in situ
measurements. We estimate that TES V005 δD is biased high by an
amount that decreases with pressure: approximately +123‰ at
1000 hPa, +98‰ in the boundary layer and +37‰ in
the free troposphere. The uncertainty in this bias estimate is
±20‰. A correction for this bias has been applied to the TES
HDO Lite Product data set. After bias correction, we show that TES has
accurate sensitivity to water vapor isotopologues in the boundary layer. 2014/09/25 - 13:46

Evaluation of wind profiles from the NERC MST radar, Aberystwyth, UKAtmospheric Measurement Techniques, 7, 3113-3126, 2014Author(s): C. F. Lee, G. Vaughan, and D. A. HooperThis study quantifies the uncertainties in winds measured by the Aberystwyth
Mesosphere–Stratosphere–Troposphere (MST) radar (52.4° N,
4.0° W), before and after its renovation in March 2011. A total of 127
radiosondes provide an independent measure of winds. Differences between
radiosonde and radar-measured horizontal winds are correlated with long-term
averages of vertical velocities, suggesting an influence from local mountain
waves. These local influences are an important consideration when using radar
winds as a measure of regional conditions, particularly for numerical weather
prediction. For those applications, local effects represent a source of
sampling error additional to the inherent uncertainties in the measurements
themselves. The radar renovation improved the signal-to-noise ratio (SNR) of measurements, with a
corresponding improvement in altitude coverage. It also corrected an
underestimate of horizontal wind speeds attributed to beam formation
problems, due to pre-renovation component failure. The root mean square error (RMSE) in
radar-measured horizontal wind components, averaged over half an hour,
increases with wind speed and altitude, and is 0.8–2.5 m s−1
(6–12% of wind speed) for post-renovation winds. Pre-renovation values
are typically 0.1 m s−1 larger. The RMSE in radial velocities is
<0.04 m s−1. Eight weeks of special radar operation are used to
investigate the effects of echo power aspect sensitivity. Corrections for
echo power aspect sensitivity remove an underestimate of horizontal wind
speeds; however aspect sensitivity is azimuthally anisotropic at the scale of
routine observations (≈1 h). This anisotropy introduces random
error into wind profiles. For winds averaged over half an hour, the RMSE
is around 3.5% above 8 km, but as large as 4.5% in the
mid-troposphere. 2014/09/25 - 13:46

Aerosol optical and microphysical retrievals from a hybrid multiwavelength lidar data set – DISCOVER-AQ 2011Atmospheric Measurement Techniques, 7, 3095-3112, 2014Author(s): P. Sawamura, D. Müller, R. M. Hoff, C. A. Hostetler, R. A. Ferrare, J. W. Hair, R. R. Rogers, B. E. Anderson, L. D. Ziemba, A. J. Beyersdorf, K. L. Thornhill, E. L. Winstead, and B. N. HolbenRetrievals of aerosol microphysical properties (effective radius, volume and
surface-area concentrations) and aerosol optical properties (complex index of
refraction and single-scattering albedo) were obtained from a hybrid
multiwavelength lidar data set for the first time. In July 2011, in the
Baltimore–Washington DC region, synergistic profiling of optical and
microphysical properties of aerosols with both airborne (in situ and remote
sensing) and ground-based remote sensing systems was performed during the
first deployment of DISCOVER-AQ. The hybrid multiwavelength lidar data set
combines ground-based elastic backscatter lidar measurements at 355 nm with
airborne High-Spectral-Resolution Lidar (HSRL) measurements at 532 nm and
elastic backscatter lidar measurements at 1064 nm that were obtained less
than 5 km apart from each other. This was the first study in which optical and
microphysical retrievals from lidar were obtained during the day and directly
compared to AERONET and in situ measurements for 11 cases. Good agreement was
observed between lidar and AERONET retrievals. Larger discrepancies were
observed between lidar retrievals and in situ measurements obtained by the
aircraft and aerosol hygroscopic effects are believed to be the main factor
in such discrepancies. 2014/09/25 - 13:46

Aircraft testing of the new Blunt-body Aerosol Sampler (BASE)Atmospheric Measurement Techniques, 7, 3085-3093, 2014Author(s): A. Moharreri, L. Craig, P. Dubey, D. C. Rogers, and S. DhaniyalaThere is limited understanding of the role of aerosols in the formation and
modification of clouds, partly due to inadequate data on such systems.
Aircraft-based aerosol measurements in the presence of cloud particles have
proven to be challenging because of the problem of cloud droplet/ice particle
shatter and the generation of secondary artifact particles that contaminate
aerosol samples. Recently, the design of a new aircraft inlet, called the
Blunt-body Aerosol Sampler (BASE), which enables sampling of interstitial
aerosol particles, was introduced. Numerical modeling results and laboratory
test data suggested that the BASE inlet should sample interstitial particles
with minimal shatter particle contamination. Here, the sampling performance
of the inlet is established from aircraft-based measurements. Initial
aircraft test results obtained during the PLOWS (Profiling of Winter Storms)
campaign indicated two problems with the original BASE design: separated
flows around the BASE at high altitudes and a significant shatter problem
when sampling in drizzle. The test data were used to improve the accuracy of
flow and particle trajectory modeling around the inlet, and the results from
the improved flow model were used to guide design modifications of the BASE to
overcome the problems identified in its initial deployment. The performance
of the modified BASE was tested during the ICE–T (Ice in Clouds Experiment –
Tropics) campaign, and the inlet was seen to provide near shatter-free
measurements in a wide range of cloud conditions. The initial aircraft test
results, design modifications, and the performance characteristics of the BASE
relative to another interstitial inlet, the submicron aerosol inlet (SMAI),
are presented. 2014/09/25 - 13:46

Quality assessment of ozone total column amounts as monitored by ground-based solar absorption spectrometry in the near infrared (> 3000 cm−1)Atmospheric Measurement Techniques, 7, 3071-3084, 2014Author(s): O. E. García, M. Schneider, F. Hase, T. Blumenstock, E. Sepúlveda, and Y. GonzálezThis study examines the possibility of ground-based remote-sensing ozone
total column amounts (OTC) from spectral signatures at 3040 and
4030 cm−1. These spectral regions are routinely measured by the NDACC
(Network for the Detection of Atmospheric Composition Change) ground-based
FTIR (Fourier transform infraRed) experiments. In addition, they are
potentially detectable by the TCCON (Total Carbon Column Observing Network)
FTIR instruments. The ozone retrieval strategy presented here estimates the
OTC from NDACC FTIR high-resolution spectra with a theoretical precision of
about 2 and 5% in the 3040 and 4030 cm−1 regions, respectively.
Empirically, these OTC products are validated by inter-comparison to FTIR OTC
reference retrievals in the 1000 cm−1 spectral region (standard
reference for NDACC ozone products), using an 8-year FTIR time series
(2005–2012) taken at the subtropical ozone supersite of the Izaña
Atmospheric Observatory (Tenerife, Spain). Associated with the weaker ozone
signatures at the higher wave number regions, the 3040 and 4030 cm−1
retrievals show lower vertical sensitivity than the 1000 cm−1
retrievals. Nevertheless, we observe that the rather consistent variations
are detected: the variances of the 3040 cm−1 and the 4030 cm−1
retrievals agree within 90 and 75%, respectively, with the variance of the
1000 cm−1 standard retrieval. Furthermore, all three retrievals show
very similar annual cycles. However, we observe a large systematic difference
of about 7% between the OTC obtained at 1000 and 3040 cm−1,
indicating a significant inconsistency between the spectroscopic ozone
parameters (HITRAN, 2012) of both regions. Between the 1000 cm and the
4030 cm−1 retrieval the systematic difference is only 2–3%.
Finally, the long-term stability of the OTC retrievals has also been
examined, observing that both near-infrared retrievals can monitor the
long-term OTC evolution, consistent with the 1000 cm−1 reference data.
These findings demonstrate that recording the solar absorption spectra in the
3000 cm−1 spectral region at high spectral resolution (about
0.005 cm−1) might be useful for TCCON sites. Hence, both NDACC and
TCCON ground-based FTIR experiments might contribute to global ozone
databases. 2014/09/23 - 08:24

An inverse-modelling approach for frequency response correction of capacitive humidity sensors in ABL research with small remotely piloted aircraft (RPA)Atmospheric Measurement Techniques, 7, 3059-3069, 2014Author(s): N. Wildmann, F. Kaufmann, and J. BangeThe measurement of water vapour concentration in the atmosphere is an ongoing
challenge in environmental research. Satisfactory solutions exist for
ground-based meteorological stations and measurements of mean values.
However, carrying out advanced research of thermodynamic processes aloft as well, above the
surface layer and especially in the atmospheric boundary layer (ABL),
requires the resolution of small-scale turbulence. Sophisticated optical
instruments are used in airborne meteorology with manned aircraft to achieve
the necessary fast-response measurements of the order of 10 Hz (e.g. LiCor
7500). Since these instruments are too large and heavy for the application on
small remotely piloted aircraft (RPA), a method is presented in this study that enhances small capacitive humidity sensors to be able to resolve
turbulent eddies of the order of 10 m. The sensor examined here is a
polymer-based sensor of the type P14-Rapid, by the Swiss company Innovative
Sensor Technologies (IST) AG, with a surface area of less than 10 mm2 and
a negligible weight. A physical and dynamical model of this sensor is
described and then inverted in order to restore original water vapour
fluctuations from sensor measurements. Examples of flight measurements show
how the method can be used to correct vertical profiles and resolve
turbulence spectra up to about 3 Hz. At an airspeed of 25 m s−1 this
corresponds to a spatial resolution of less than 10 m. 2014/09/23 - 08:24

Tropospheric CO vertical profiles deduced from total columns using data assimilation: methodology and validationAtmospheric Measurement Techniques, 7, 3035-3057, 2014Author(s): L. El Amraoui, J.-L. Attié, P. Ricaud, W. A. Lahoz, A. Piacentini, V.-H. Peuch, J. X. Warner, R. Abida, J. Barré, and R. ZbindenThis paper presents a validation of a method to derive the vertical
profile of carbon monoxide (CO) from its total column using
data assimilation.
We choose version 3 of MOPITT CO total columns to validate
the proposed method. MOPITT products have the advantage of providing both the
vertical profiles and the total columns of CO. Furthermore,
this version has been extensively validated by comparison with many
independent data sets, and has been used in many scientific

The first step of the paper consists in the specification of
the observation errors based on the chi-square (χ2) test. The
observations have been binned according to three types: over land during
daytime, over land during night-time, and over sea. Their respective
errors using the χ2 metric have been found to be 8, 11 and 7%.

In the second step, the CO total columns, with their specified errors, are used
within the assimilation system to estimate the vertical profiles. These are
compared to the retrieved profiles of MOPITT V3 at global and regional
scales. Generally, the two data sets show similar patterns and good agreement
at both scales. Nevertheless, total column analyses slightly overestimate CO
concentrations compared to MOPITT observations. The mean bias between both
data sets is +15 and +12% at 700 and 250 hPa, respectively.

In the third step, the assimilation of total column has been compared to the
assimilation of MOPITT vertical profiles. The differences between both
analyses are very small. In terms longitude–latitude maps, the mean bias between the
two data sets is +6 and +8% at the pressure levels 700 and
200 hPa, respectively. In terms of zonal means, the CO
distribution is similar for both analyses, with a mean bias which does not
exceed 12%.

Finally, the two analyses have been validated using
independent observations from the aircraft-based
MOZAIC program
in terms of vertical profiles over eight airports. Over
most airports, both analyses agree well with aircraft profiles. For more than
50% of recorded measurements, the difference between the analyses and
MOZAIC does not exceed 5 ppbv (parts per billion by volume). 2014/09/20 - 18:38

Smoothing error pitfallsAtmospheric Measurement Techniques, 7, 3023-3034, 2014Author(s): T. von ClarmannThe difference due to the content of a priori information between a
constrained retrieval and the true atmospheric state is usually represented
by a diagnostic quantity called smoothing error. In this paper it is shown
that, regardless of the usefulness of the smoothing error as a diagnostic
tool in its own right, the concept of the smoothing error as a component of
the retrieval error budget is questionable because it is not compliant with
Gaussian error propagation. The reason for this is that the smoothing error
does not represent the expected deviation of the retrieval from the true
state but the expected deviation of the retrieval from the atmospheric state
sampled on an arbitrary grid, which is itself a smoothed representation of
the true state; in other words, to characterize the full loss of information
with respect to the true atmosphere, the effect of the representation of
the atmospheric state on a finite grid also needs to be considered. The idea of a
sufficiently fine sampling of this reference atmospheric state is problematic
because atmospheric variability occurs on all scales, implying that there is
no limit beyond which the sampling is fine enough. Even the idealization of
infinitesimally fine sampling of the reference state does not help, because
the smoothing error is applied to quantities which are only defined in a
statistical sense, which implies that a finite volume of sufficient spatial
extent is needed to meaningfully discuss temperature or concentration.
Smoothing differences, however, which play a role when measurements are
compared, are still a useful quantity if the covariance matrix involved has
been evaluated on the comparison grid rather than resulting from
interpolation and if the averaging kernel matrices have been evaluated on a
grid fine enough to capture all atmospheric variations that the instruments are
sensitive to. This is, under the assumptions stated, because the undefined
component of the smoothing error, which is the effect of smoothing implied by
the finite grid on which the measurements are compared, cancels out when the
difference is calculated. If the effect of a retrieval constraint is to be
diagnosed on a grid finer than the native grid of the retrieval by means of
the smoothing error, the latter must be evaluated directly on the fine grid,
using an ensemble covariance matrix which includes all variability on the
fine grid. Ideally, the averaging kernels needed should be calculated
directly on the finer grid, but if the grid of the original averaging kernels
allows for representation of all the structures the instrument is sensitive to, then their
interpolation can be an adequate approximation. 2014/09/20 - 18:38

A comparison of ice water content measurement techniques on the FAAM BAe-146 aircraftAtmospheric Measurement Techniques, 7, 3007-3022, 2014Author(s): S. J. Abel, R. J. Cotton, P. A. Barrett, and A. K. VanceThis paper presents a comparison of ice water content
(qi) data from a variety of measurement techniques on
the Facility for Airborne Atmospheric Measurements (FAAM) BAe-146
research aircraft. Data are presented from a range of cloud types
measured during the PIKNMIX field experiment that include
mixed-phase stratocumulus, cumulus congestus and cirrus clouds. These
measurements cover a broad range of conditions in which atmospheric
ice particles are found in nature, such as the low-ice-water-content
environments typically found in midlatitude cirrus and the environments with much
higher ice water content often observed in cold
convective clouds. The techniques include bulk measurements from (i)
a Nevzorov hot-wire probe, (ii) the difference between the measured
total water content (condensed plus vapour) and the water vapour
content of the atmosphere and (iii) a counterflow virtual impactor
(CVI) (only for cirrus measurements). We also estimate the
qi from integration of the measured particle size
distribution (PSD) with assumptions on how the density of ice
particles varies as a function of size.

The results show that the only bulk ice water content technique
capable of measuring high qi values (several g m−3)
was the method of total water content minus water vapour. For low ice water contents we develop a new parametrisation
of the Nevzorov baseline drift that enables the probe to be
sensitive to qi ± 0.002 g m−3. In cirrus
clouds the agreement between the Nevzorov and other bulk
measurements was typically better than a factor of 2 for the CVI
(qi > 0.008 g m−3) and the method of total water
content minus water vapour (qi >
0.02 g m−3). Good agreement with the bulk measurements
for all cases could be obtained with the estimate from the PSD
provided that appropriate a priori assumptions on the
mass–dimension relationship were made. This is problematic in the
convective clouds sampled because pristine ice particles, heavily
rimed particles and supercooled liquid drops were all present. In
a cirrus case, we show that using a temperature-dependent
mass–dimension relation was required to match the bulk measurement
of qi. 2014/09/20 - 18:38

Validation of XCH4 derived from SWIR spectra of GOSAT TANSO-FTS with aircraft measurement dataAtmospheric Measurement Techniques, 7, 2987-3005, 2014Author(s): M. Inoue, I. Morino, O. Uchino, Y. Miyamoto, T. Saeki, Y. Yoshida, T. Yokota, C. Sweeney, P. P. Tans, S. C. Biraud, T. Machida, J. V. Pittman, E. A. Kort, T. Tanaka, S. Kawakami, Y. Sawa, K. Tsuboi, and H. MatsuedaColumn-averaged dry-air mole fractions of methane (XCH4), retrieved
from Greenhouse gases Observing SATellite (GOSAT) short-wavelength infrared
(SWIR) spectra, were validated by using aircraft measurement data from the
National Oceanic and Atmospheric Administration (NOAA), the US Department
of Energy (DOE), the National Institute for Environmental Studies (NIES),
the HIAPER Pole-to-Pole Observations (HIPPO) program, and the GOSAT
validation aircraft observation campaign over Japan. In the calculation of
XCH4 from aircraft measurements (aircraft-based XCH4), other
satellite data were used for the CH4 profiles above the tropopause. We
proposed a data-screening scheme for aircraft-based XCH4 for reliable
validation of GOSAT XCH4. Further, we examined the impact of GOSAT SWIR
column averaging kernels (CAK) on the aircraft-based XCH4 calculation
and found that the difference between aircraft-based XCH4 with and
without the application of the GOSAT CAK was less than ±9 ppb at
maximum, with an average difference of −0.5 ppb.

We compared GOSAT XCH4 Ver. 02.00 data retrieved within ±2° or ±5° latitude–longitude boxes centered at
each aircraft measurement site with aircraft-based XCH4 measured on a
GOSAT overpass day. In general, GOSAT XCH4 was in good agreement with
aircraft-based XCH4. However, over land, the GOSAT data showed a
positive bias of 1.5 ppb (2.0 ppb) with a standard deviation of 14.9 ppb
(16.0 ppb) within the ±2° (±5°) boxes,
and over ocean, the average bias was 4.1 ppb (6.5 ppb) with a standard
deviation of 9.4 ppb (8.8 ppb) within the ±2° (±5°) boxes. In addition, we obtained similar results when we used
an aircraft-based XCH4 time series obtained by curve fitting with
temporal interpolation for comparison with GOSAT data. 2014/09/20 - 18:38

Overview: Tropospheric profiling: state of the art and future challenges – introduction to the AMT special issueAtmospheric Measurement Techniques, 7, 2981-2986, 2014Author(s): D. Cimini, V. Rizi, P. Di Girolamo, F. S. Marzano, A. Macke, G. Pappalardo, and A. RichterThis paper introduces the Atmospheric Measurement Techniques special issue
on tropospheric profiling, which was conceived to host full papers
presenting the results shown at the 9th International Symposium on
Tropospheric Profiling (ISTP9). ISTP9 was held in L'Aquila (Italy) from 3 to
7 September 2012, bringing together 150 scientists representing of 28
countries and 3 continents. The tropospheric profiling special issue
collects the highlights of ISTP9, reporting recent advances and future
challenges in research and technology development. 2014/09/20 - 18:38

A horizontal mobile measuring system for atmospheric quantitiesAtmospheric Measurement Techniques, 7, 2967-2980, 2014Author(s): J. Hübner, J. Olesch, H. Falke, F. X. Meixner, and T. FokenA fully automatic horizontal mobile measuring system (HMMS) for atmospheric
quantities has been developed. The HMMS is based on the drive mechanism of
a garden railway system and can be installed at any location and along any
measuring track. In addition to meteorological quantities (temperature,
humidity and short-/long-wave down/upwelling radiation), HMMS also measures
trace gas concentrations (carbon dioxide and ozone). While sufficient spatial
resolution is a problem even for measurements on distributed towers, this
could be easily achieved with the HMMS, which has been specifically developed
to obtain higher information density about horizontal gradients in
a heterogeneous forest ecosystem. There, horizontal gradients of
meteorological quantities and trace gases could be immense, particularly at
the transition from a dense forest to an open clearing, with large impact on
meteorological parameters and exchange processes. Consequently, HMMS was
firstly applied during the EGER IOP3 project (ExchanGE processes in mountainous
Regions – Intense Observation Period 3) in the Fichtelgebirge
Mountains (SE Germany) during summer 2011. At a constant 1 m above
ground, the measuring track of the HMMS consisted of a straight line
perpendicular to the forest edge, starting in the dense spruce forest and
leading 75 m into an open clearing. Tags with bar codes, mounted every
metre on the wooden substructure, allowed (a) keeping the speed of the HMMS
constant (approx. 0.5 m s−1) and (b) operation of the HMMS in
a continuous back and forth running mode. During EGER IOP3, HMMS was
operational for almost 250 h. Results show that – due to considerably
long response times (between 4 and 20 s) of commercial
temperature, humidity and the radiation sensors – true spatial variations of
the meteorological quantities could not be adequately captured (mainly at the
forest edge). Corresponding dynamical (spatial) errors of the measurement
values were corrected on the basis of well-defined individual response times
of the sensors and application of a linear correction algorithm. Due to the
very short response times (≤ 1 s) of the applied commercial
CO2 and O3 analysers, dynamical errors for the trace gas data
were negligible and no corrections were done. 2014/09/20 - 18:38

Measuring the atmospheric organic aerosol volatility distribution: a theoretical analysisAtmospheric Measurement Techniques, 7, 2953-2965, 2014Author(s): E. Karnezi, I. Riipinen, and S. N. PandisOrganic compounds represent a
significant fraction of submicrometer atmospheric aerosol mass. Even if most
of these compounds are semi-volatile in atmospheric concentrations, the
ambient organic aerosol volatility is quite uncertain. The most common
volatility measurement method relies on the use of a thermodenuder (TD). The
aerosol passes through a heated tube where its more volatile components
evaporate, leaving the less volatile components behind in the particulate
phase. The typical result of a thermodenuder measurement is the mass fraction
remaining (MFR), which depends, among other factors, on the organic aerosol
(OA) vaporization enthalpy and the accommodation coefficient. We use a new
method combining forward modeling, introduction of "experimental" error,
and inverse modeling with error minimization for the interpretation of TD
measurements. The OA volatility distribution, its effective vaporization
enthalpy, the mass accommodation coefficient and the corresponding
uncertainty ranges are calculated. Our results indicate that existing
TD-based approaches quite often cannot estimate reliably the OA volatility
distribution, leading to large uncertainties, since there are many different
combinations of the three properties that can lead to similar thermograms. We
propose an improved experimental approach combining TD and isothermal
dilution measurements. We evaluate this experimental approach using the same
model, and show that it is suitable for studies of OA volatility in the lab
and the field. 2014/09/20 - 18:38

GOME-2 total ozone columns from MetOp-A/MetOp-B and assimilation in the MACC systemAtmospheric Measurement Techniques, 7, 2937-2951, 2014Author(s): N. Hao, M. E. Koukouli, A. Inness, P. Valks, D. G. Loyola, W. Zimmer, D. S. Balis, I. Zyrichidou, M. Van Roozendael, C. Lerot, and R. J. D. SpurrThe two Global Ozone Monitoring Instrument (GOME-2) sensors operated in
tandem are flying onboard EUMETSAT's (European Organisation for the Exploitation of Meteorological Satellites) MetOp-A and MetOp-B satellites,
launched in October 2006 and September 2012 respectively. This paper
presents the operational GOME-2/MetOp-A (GOME-2A) and
GOME-2/MetOp-B (GOME-2B)
total ozone products provided by the EUMETSAT Satellite
Application Facility on Ozone and Atmospheric Chemistry Monitoring (O3M-SAF).
These products are generated using the latest version of the GOME
Data Processor (GDP version 4.7). The enhancements in GDP 4.7, including the
application of Brion–Daumont–Malicet ozone absorption cross sections, are
presented here. On a global scale, GOME-2B has the same high accuracy as the
corresponding GOME-2A products. There is an excellent agreement between the
ozone total columns from the two sensors, with GOME-2B values slightly lower
with a mean difference of only 0.55±0.29%. First global validation
results for 6 months of GOME-2B total ozone using ground-based measurements
show that on average the GOME-2B total ozone data obtained with GDP 4.7 are
slightly higher than, both, Dobson observations by about 2.0±1.0% and
Brewer observations by about 1.0±0.8%. It is concluded that the
total ozone columns (TOCs) provided by GOME-2A and GOME-2B are consistent
and may be used simultaneously without introducing systematic effects, which
has been illustrated for the Antarctic ozone hole on 18 October 2013.
GOME-2A total ozone data have been used operationally in the Copernicus
atmospheric service project MACC-II (Monitoring Atmospheric Composition and
Climate – Interim Implementation) near-real-time (NRT) system since October 2013.
The magnitude of the bias correction needed for assimilating GOME-2A
ozone is reduced (to about −6 DU in the global mean) when the GOME-2 ozone
retrieval algorithm changed to GDP 4.7. 2014/09/12 - 22:30

Impact of radar data assimilation for the simulation of a heavy rainfall case in central Italy using WRF–3DVARAtmospheric Measurement Techniques, 7, 2919-2935, 2014Author(s): I. Maiello, R. Ferretti, S. Gentile, M. Montopoli, E. Picciotti, F. S. Marzano, and C. FaccaniThe aim of this study is to investigate the role of the assimilation of
Doppler weather radar (DWR) data in a mesoscale model for the forecast of a
heavy rainfall event that occurred in Italy in the urban area of Rome from
19 to 22 May 2008. For this purpose, radar reflectivity and radial
acquired from Monte Midia Doppler radar are assimilated into the Weather
Research Forecasting (WRF) model, version 3.4.1. The general goal is to
improve the quantitative precipitation forecasts (QPF): with this aim,
several experiments are performed using the three-dimensional variational
(3DVAR) technique. Moreover, sensitivity tests to outer loops are performed
to include non-linearity in the observation operators.

In order to identify the best initial conditions (ICs), statistical
indicators such as forecast accuracy, frequency bias, false alarm rate and
equitable threat score for the accumulated precipitation are used.

The results show that the assimilation of DWR data has a large impact on both
the position of convective cells and on the rainfall forecast of the analyzed
event. A positive impact is also found if they are ingested together with
conventional observations. Sensitivity to the use of two or three outer loops
is also found if DWR data are assimilated together with conventional data. 2014/09/12 - 22:30

Derivation of tropospheric methane from TCCON CH4 and HF total column observationsAtmospheric Measurement Techniques, 7, 2907-2918, 2014Author(s): K. M. Saad, D. Wunch, G. C. Toon, P. Bernath, C. Boone, B. Connor, N. M. Deutscher, D. W. T. Griffith, R. Kivi, J. Notholt, C. Roehl, M. Schneider, V. Sherlock, and P. O. WennbergThe Total Carbon Column Observing Network (TCCON) is a global
ground-based network of Fourier transform spectrometers that produce
precise measurements of column-averaged dry-air mole fractions of
atmospheric methane (CH4). Temporal variability in the total
column of CH4 due to stratospheric dynamics obscures
fluctuations and trends driven by tropospheric transport and local surface fluxes
that are critical for understanding CH4 sources and sinks.
We reduce the contribution of stratospheric variability from the total
column average by subtracting an estimate
of the stratospheric CH4 derived from simultaneous
measurements of hydrogen fluoride (HF). HF provides a proxy for
stratospheric CH4 because it is strongly correlated to CH4 in the
stratosphere, has an accurately known tropospheric abundance (of zero), and
is measured at most TCCON stations. The stratospheric partial column of CH4 is
calculated as a function of the zonal and annual trends in the
relationship between CH4 and HF in the stratosphere, which
we determine from ACE-FTS satellite data. We also explicitly take
into account the CH4 column averaging kernel to estimate the
contribution of stratospheric CH4 to the total column. The
resulting tropospheric CH4 columns are consistent with in
situ aircraft measurements and augment existing observations in the
troposphere. 2014/09/11 - 17:26

First results from a rotational Raman scattering cloud algorithm applied to the Suomi National Polar-orbiting Partnership (NPP) Ozone Mapping and Profiler Suite (OMPS) Nadir MapperAtmospheric Measurement Techniques, 7, 2897-2906, 2014Author(s): A. Vasilkov, J. Joiner, and C. SeftorThis paper reports initial results from an Ozone Mapping and Profiler Suite
(OMPS) Nadir Mapper cloud pressure and cloud fraction algorithm. The OMPS
cloud products are intended for use in OMPS ozone or other trace-gas
algorithms. We developed the OMPS cloud products using a heritage algorithm
developed for the Ozone Monitoring Instrument (OMI) on NASA's Aura satellite.
The cloud pressure algorithm utilizes the filling-in of ultraviolet solar
Fraunhofer lines by rotational Raman scattering. The OMPS cloud products are
evaluated by comparison with OMI cloud products that have been compared in
turn with other collocated satellite data including cloud optical thickness
profiles derived from a combination of measurements from the CloudSat radar
and MODerate-resolution Imaging Spectroradiometer (MODIS). We find that the probability density
functions (PDFs) of effective cloud fraction retrieved from OMPS and OMI
measurements are very similar. The PDFs of the OMPS and OMI cloud pressures
are comparable. However, OMPS retrieves somewhat higher pressures on average.
The current NASA total ozone retrieval algorithm makes use of a monthly
gridded cloud pressure climatology developed from OMI. This climatology
captures much of the variability associated with the relevant cloud
pressures. However, the use of actual cloud pressures retrieved with OMPS in
place of the OMI climatology changes OMPS total column ozone estimates
locally (presumably in the correct direction) only in areas with large
differences between climatological and actual cloud pressures. The ozone differences can
be up to 5% in such areas. 2014/09/11 - 17:26

Influence of changes in humidity on dry temperature in GPS RO climatologiesAtmospheric Measurement Techniques, 7, 2883-2896, 2014Author(s): J. Danzer, U. Foelsche, B. Scherllin-Pirscher, and M. SchwärzRadio occultation (RO) data are increasingly used in climate
research. Accurate phase (change) measurements of Global Positioning
System (GPS) signals are the basis for the retrieval of near-vertical profiles of bending angle, microwave refractivity, density,
pressure, and temperature. If temperature is calculated from
observed refractivity with the assumption that water vapor is zero,
the product is called "dry temperature", which is commonly used to
study earth's atmosphere, e.g., when analyzing temperature
trends due to global warming. Dry temperature is a useful quantity,
since it does not need additional background information in its
retrieval. However, it can only be safely used as proxy for physical
temperature, where moisture is negligible. The altitude region above
which water vapor does not play a dominant role anymore, depends
primarily on latitude and season.

In this study we first investigated the influence of water vapor on
dry temperature RO profiles. Hence, we analyzed the maximum altitude
down to which monthly mean dry temperature profiles can be regarded
as being equivalent to physical temperature. This was done by
examining dry temperature to physical temperature differences of
monthly mean analysis fields from the European Centre for
Medium-Range Weather Forecasts (ECMWF), studied from 2006 until
2010. We introduced cutoff criteria, where maximum temperature
differences of −0.1, −0.05, and
−0.02 K were allowed (dry temperature is always lower than
physical temperature), and computed the corresponding altitudes. As
an example, a temperature difference of −0.05 K in the
tropics was found at an altitude of about 14 km, while at
higher northern latitudes in winter it was found at an altitude of
about 9–10 km, in summer at about
11 km.

Furthermore, regarding climate change, we expect an increase of
absolute humidity in the atmosphere. This possible trend in water
vapor could yield a wrongly interpreted dry temperature trend. As
a consequence, we performed a model study, investigating the
increase in height of the transition region between moist and dry
air. We used data from the fifth phase of the Coupled Model
Intercomparison Project (CMIP5), analyzing again monthly mean dry
temperature to physical temperature differences, now from the years
2006 to 2050. We used the highest emission scenario RCP8.5
(representative concentration pathway), studying all available
models of the CMIP5 project, analyzing one internal run per model,
with the goal to identify the altitude region where trends in dry
temperature can be safely regarded as reflecting trends in physical
temperature. From all models we therefore choose a selection of
models ("max 8" CMIP5 models), which showed the largest trend
differences. As a result, our trend study suggests that the lower
boundary of the region where dry temperature is essentially equal to
physical temperature rises about 150 m decade−1. 2014/09/11 - 17:26

Hydrometeor classification from two-dimensional video disdrometer dataAtmospheric Measurement Techniques, 7, 2869-2882, 2014Author(s): J. Grazioli, D. Tuia, S. Monhart, M. Schneebeli, T. Raupach, and A. BerneThe first hydrometeor classification technique based on
two-dimensional video disdrometer (2DVD) data is presented. The method provides
an estimate of the dominant hydrometeor type falling over time
intervals of 60 s during precipitation, using the
statistical behavior of a set of particle descriptors as input, calculated
for each particle image. The employed supervised algorithm is
a support vector machine (SVM), trained over 60 s precipitation time steps labeled by visual inspection. In this way, eight dominant
hydrometeor classes can be discriminated. The algorithm achieved high classification performances, with median overall accuracies
(Cohen's K) of 90% (0.88), and with accuracies
higher than 84% for each hydrometeor class. 2014/09/11 - 17:26

Remote sensing of cloud top pressure/height from SEVIRI: analysis of ten current retrieval algorithmsAtmospheric Measurement Techniques, 7, 2839-2867, 2014Author(s): U. Hamann, A. Walther, B. Baum, R. Bennartz, L. Bugliaro, M. Derrien, P. N. Francis, A. Heidinger, S. Joro, A. Kniffka, H. Le Gléau, M. Lockhoff, H.-J. Lutz, J. F. Meirink, P. Minnis, R. Palikonda, R. Roebeling, A. Thoss, S. Platnick, P. Watts, and G. WindThe role of clouds remains the largest uncertainty in climate
projections. They influence solar and thermal radiative transfer and
the earth's water cycle. Therefore, there is an urgent need for
accurate cloud observations to validate climate models and to
monitor climate change. Passive satellite imagers measuring
radiation at visible to thermal infrared (IR) wavelengths provide
a wealth of information on cloud properties. Among others, the cloud
top height (CTH) – a crucial parameter to estimate the thermal cloud
radiative forcing – can be retrieved. In this paper we investigate
the skill of ten current retrieval algorithms to estimate the CTH
using observations from the Spinning Enhanced Visible and InfraRed
Imager (SEVIRI) onboard Meteosat Second Generation (MSG). In the
first part we compare ten SEVIRI cloud top pressure (CTP)
data sets with each other. The SEVIRI algorithms catch the
latitudinal variation of the CTP in a similar way. The agreement is
better in the extratropics than in the tropics. In the tropics
multi-layer clouds and thin cirrus layers complicate the CTP
retrieval, whereas a good agreement among the algorithms is found for trade wind cumulus,
marine stratocumulus and the optically thick cores of the deep
convective system.

In the second part of the paper the SEVIRI retrievals are compared
to CTH observations from the Cloud–Aerosol LIdar with Orthogonal
Polarization (CALIOP) and Cloud Profiling Radar (CPR)
instruments. It is important to note that the different measurement
techniques cause differences in the retrieved CTH data. SEVIRI
measures a radiatively effective CTH, while the CTH of the active
instruments is derived from the return time of the emitted radar or lidar
signal. Therefore, some systematic differences are expected. On
average the CTHs detected by the SEVIRI algorithms are 1.0 to
2.5 km lower than CALIOP observations, and the correlation
coefficients between the SEVIRI and the CALIOP data sets range
between 0.77 and 0.90. The average CTHs derived by the SEVIRI algorithms are closer
to the CPR measurements than to CALIOP measurements. The biases between SEVIRI and
CPR retrievals range from −0.8 km to 0.6 km.
The correlation coefficients of CPR and
SEVIRI observations vary between 0.82 and 0.89. To discuss the
origin of the CTH deviation, we investigate three
cloud categories: optically thin and thick single layer as well as
multi-layer clouds. For optically thick clouds the correlation
coefficients between the SEVIRI and the reference data sets are
usually above 0.95. For optically thin single layer clouds the
correlation coefficients are still above 0.92. For this cloud
category the SEVIRI algorithms yield CTHs that are lower than CALIOP
and similar to CPR observations. Most challenging are the
multi-layer clouds, where the correlation coefficients are for most
algorithms between 0.6 and 0.8. Finally, we evaluate the
performance of the SEVIRI retrievals for boundary layer clouds.
While the CTH retrieval for this cloud type is relatively accurate,
there are still considerable differences between the
algorithms. These are related to the uncertainties and limited
vertical resolution of the assumed temperature profiles in
combination with the presence of temperature inversions, which lead
to ambiguities in the CTH retrieval. Alternative approaches for the
CTH retrieval of low clouds are discussed. 2014/09/11 - 17:26

The influence of temperature calibration on the OC–EC results from a dual-optics thermal carbon analyzerAtmospheric Measurement Techniques, 7, 2829-2838, 2014Author(s): J. Pavlovic, J. S. Kinsey, and M. D. HaysThermal–optical analysis (TOA) is a widely used technique that fractionates
carbonaceous aerosol particles into organic and elemental carbon (OC and EC),
or carbonate. Thermal sub-fractions of evolved OC and EC are also used for
source identification and apportionment; thus, oven temperature accuracy
during TOA analysis is essential. Evidence now indicates that the "actual"
sample (filter) temperature and the temperature measured by the built-in oven
thermocouple (or set-point temperature) can differ by as much as
50 °C. This difference can affect the OC–EC split point selection and
consequently the OC and EC fraction and sub-fraction concentrations being
reported, depending on the sample composition and in-use TOA method and
instrument. The present study systematically investigates the influence of an
oven temperature calibration procedure for TOA. A dual-optical carbon
analyzer that simultaneously measures transmission and reflectance (TOT and
TOR) is used, functioning under the conditions of both the National Institute of Occupational Safety and
Health Method 5040 (NIOSH) and
Interagency Monitoring of Protected Visual Environment (IMPROVE) protocols. The application of the oven calibration procedure to our dual-optics instrument significantly changed NIOSH 5040 carbon fractions (OC and
EC) and the IMPROVE OC fraction. In addition, the well-known OC–EC split
difference between NIOSH and IMPROVE methods is even further perturbed
following the instrument calibration. Further study is needed to determine if
the widespread application of this oven temperature calibration procedure
will indeed improve accuracy and our ability to compare among carbonaceous
aerosol studies that use TOA. 2014/09/06 - 15:00

Retrieval of sulfur dioxide from a ground-based thermal infrared imaging cameraAtmospheric Measurement Techniques, 7, 2807-2828, 2014Author(s): A. J. Prata and C. BernardoRecent advances in uncooled detector technology now offer the possibility of
using relatively inexpensive thermal (7 to 14 μm) imaging devices
as tools for studying and quantifying the behaviour of hazardous gases and
particulates in atmospheric plumes. An experimental fast-sampling (60 Hz)
ground-based uncooled thermal imager (Cyclops), operating with four spectral
channels at central wavelengths of 8.6, 10, 11 and 12 μm and one
broadband channel (7–14 μm) has been tested at several volcanoes
and at an industrial site, where SO2 was a major constituent of the
plumes. This paper presents new algorithms, which include atmospheric
corrections to the data and better calibrations to show that SO2 slant
column density can be reliably detected and quantified. Our results indicate
that it is relatively easy to identify and discriminate SO2 in
plumes, but more challenging to quantify the column densities. A full
description of the retrieval algorithms, illustrative results and a detailed
error analysis are provided. The noise-equivalent temperature difference
(NEΔT) of the spectral channels, a fundamental measure of the quality
of the measurements, lies between 0.4 and 0.8 K, resulting in slant column
density errors of 20%. Frame averaging and improved NEΔT's can
reduce this error to less than 10%, making a stand-off, day or night
operation of an instrument of this type very practical for both monitoring
industrial SO2 emissions and for SO2 column densities and emission
measurements at active volcanoes. The imaging camera system may also be used
to study thermal radiation from meteorological clouds and the
atmosphere. 2014/09/03 - 20:36

Ecosystem fluxes of hydrogen: a comparison of flux-gradient methodsAtmospheric Measurement Techniques, 7, 2787-2805, 2014Author(s): L. K. Meredith, R. Commane, J. W. Munger, A. Dunn, J. Tang, S. C. Wofsy, and R. G. PrinnOur understanding of biosphere–atmosphere exchange has been considerably
enhanced by eddy covariance measurements. However, there remain many trace
gases, such as molecular hydrogen (H2), that lack suitable analytical
methods to measure their fluxes by eddy covariance. In such cases,
flux-gradient methods can be used to calculate ecosystem-scale fluxes from
vertical concentration gradients. The budget of atmospheric H2 is poorly
constrained by the limited available observations, and thus the ability to
quantify and characterize the sources and sinks of H2 by flux-gradient
methods in various ecosystems is important. We developed an approach to make
nonintrusive, automated measurements of ecosystem-scale H2 fluxes both
above and below the forest canopy at the Harvard Forest in Petersham, Massachusetts, for
over a year. We used three flux-gradient methods to calculate the fluxes: two
similarity methods that do not rely on a micrometeorological determination of
the eddy diffusivity, K, based on (1) trace gases or (2) sensible heat, and
one flux-gradient method that (3) parameterizes K. We quantitatively
assessed the flux-gradient methods using CO2 and H2O by comparison
to their simultaneous independent flux measurements via eddy covariance and
soil chambers. All three flux-gradient methods performed well in certain
locations, seasons, and times of day, and the best methods were trace gas
similarity for above the canopy and K parameterization below it. Sensible heat
similarity required several independent measurements, and the results were
more variable, in part because those data were only available in the winter,
when heat fluxes and temperature gradients were small and difficult to
measure. Biases were often observed between flux-gradient methods and the
independent flux measurements, and there was at least a 26% difference
in nocturnal eddy-derived net ecosystem exchange (NEE) and chamber
measurements. H2 fluxes calculated in a summer period agreed within
their uncertainty and pointed to soil uptake as the main driver of H2
exchange at Harvard Forest, with H2 deposition velocities ranging from
0.04 to 0.10 cm s−1. 2014/09/03 - 20:36

Validation of the Aura High Resolution Dynamics Limb Sounder geopotential heightsAtmospheric Measurement Techniques, 7, 2775-2785, 2014Author(s): L. L. Smith and J. C. GilleThe geopotential height (GPH) product created from global observations by
the High Resolution Dynamics Limb Sounder (HIRDLS) instrument on NASA's
Earth Observing System (EOS) Aura spacecraft is discussed. The accuracy,
resolution and precision of the HIRDLS version 7 algorithms are assessed and
data screening recommendations are made. Comparisons with GPH from
observations, reanalyses and models including European Centre for
Medium-Range Weather Forecasts Interim Reanalysis (ERA-Interim), and
National Centers for Environmental Prediction/National Center for
Atmospheric Research (NCEP/NCAR) Reanalysis illustrate the HIRDLS GPHs have a
precision ranging from 2 to 30 m and an accuracy of ±100 m up to 1 hPa.
Comparisons indicate HIRDLS GPH may have a slight low bias in the tropics
and a slight high bias at high latitudes. Geostrophic winds computed with
HIRDLS GPH qualitatively agree with winds from other data sources including
ERA-Interim. 2014/08/30 - 21:35

Comparing the cloud vertical structure derived from several methods based on radiosonde profiles and ground-based remote sensing measurementsAtmospheric Measurement Techniques, 7, 2757-2773, 2014Author(s): M. Costa-Surós, J. Calbó, J. A. González, and C. N. LongThe
cloud vertical distribution and especially the cloud base height, which is
linked to cloud type, are important characteristics in order to describe the
impact of clouds on climate. In this work, several methods for estimating the
cloud vertical structure (CVS) based on atmospheric sounding profiles are
compared, considering the number and position of cloud layers, with a
ground-based system that is taken as a reference: the Active Remote Sensing
of Clouds (ARSCL). All methods establish some conditions on the relative
humidity, and differ in the use of other variables, the thresholds applied,
or the vertical resolution of the profile. In this study, these methods are
applied to 193 radiosonde profiles acquired at the Atmospheric Radiation Measurement (ARM) Southern Great Plains
site during all seasons of the year 2009 and endorsed by Geostationary Operational Environmental Satellite (GOES) images, to
confirm that the cloudiness conditions are homogeneous enough across their
trajectory. The perfect agreement (i.e., when the whole CVS is estimated
correctly) for the methods ranges between 26 and 64%; the methods show
additional approximate agreement (i.e., when at least one cloud layer is
assessed correctly) from 15 to 41%. Further tests and improvements are
applied to one of these methods. In addition, we attempt to make this method
suitable for low-resolution vertical profiles, like those from the outputs of
reanalysis methods or from the World Meteorological Organization's (WMO) Global Telecommunication System. The
perfect agreement, even when using low-resolution profiles, can be improved
by up to 67% (plus 25% of the approximate agreement) if the thresholds
for a moist layer to become a cloud layer are modified to minimize false
negatives with the current data set, thus improving overall agreement. 2014/08/29 - 02:17

Potential of airborne lidar measurements for cirrus cloud studiesAtmospheric Measurement Techniques, 7, 2745-2755, 2014Author(s): S. Groß, M. Wirth, A. Schäfler, A. Fix, S. Kaufmann, and C. VoigtAerosol and water vapour measurements were performed with the lidar system
WALES of Deutsches Zentrum für Luft- und Raumfahrt (DLR) in October and
November 2010 during the first mission with the new German research aircraft
G55-HALO. Curtains composed of lidar profiles beneath the aircraft show the
vertical and horizontal distribution and variability of water vapour mixing
ratio and backscatter ratio above Germany. Two missions on 3 and
4 November 2010 were selected to derive the water vapour mixing ratio inside
cirrus clouds from the lidar instrument. A good agreement was found with
in situ observations performed on a second research aircraft flying below
HALO. ECMWF analysis temperature data are used to derive relative humidity
fields with respect to ice (RHi) inside and outside of cirrus clouds from the lidar water vapour
observations. The RHi variability is dominated by small-scale fluctuations in
the water vapour fields while the temperature variation has a minor impact.
The most frequent in-cloud RHi value from lidar observations is 98%. The
RHi variance is smaller inside the cirrus than outside of the cloud.
2-D histograms of relative humidity and backscatter ratio show
significant differences for in-cloud and out-of-cloud situations for two
different cirrus cloud regimes. Combined with accurate temperature
measurements, the lidar observations have a great potential for detailed
statistical cirrus cloud and related humidity studies. 2014/08/26 - 18:40

Measurement of gas-phase ammonia and amines in air by collection onto an ion exchange resin and analysis by ion chromatographyAtmospheric Measurement Techniques, 7, 2733-2744, 2014Author(s): M. L. Dawson, V. Perraud, A. Gomez, K. D. Arquero, M. J. Ezell, and B. J. Finlayson-PittsAmmonia and amines are common trace gases in the atmosphere and have a
variety of both biogenic and anthropogenic sources, with a major contribution
coming from agricultural sites. In addition to their malodorous nature, both
ammonia and amines have been shown to enhance particle formation from acids
such as nitric, sulfuric and methanesulfonic acids, which has implications
for visibility, human health and climate. A key component of quantifying the
effects of these species on particle formation is accurate gas-phase
measurements in both laboratory and field studies. However, these species are
notoriously difficult to measure as they are readily taken up on surfaces,
including onto glass surfaces from aqueous solution as established in the
present studies. We describe here a novel technique for measuring gas-phase
ammonia and amines that involves uptake onto a weak cation exchange resin
followed by extraction and analysis using ion chromatography. Two variants –
one for parts per billion concentrations in air and the second with lower (parts per trillion) detection
limits – are described. The latter involves the use of a custom-designed
high-pressure cartridge to hold the resin for in-line extraction. These
methods avoid the use of sampling lines, which can lead to significant inlet
losses of these compounds. They also have the advantages of being relatively
simple and inexpensive. The applicability of this technique to ambient air is
demonstrated in measurements made near a cattle farm in Chino, CA. 2014/08/26 - 18:40

The MUSICA MetOp/IASI H2O and δD products: characterisation and long-term comparison to NDACC/FTIR dataAtmospheric Measurement Techniques, 7, 2719-2732, 2014Author(s): A. Wiegele, M. Schneider, F. Hase, S. Barthlott, O. E. García, E. Sepúlveda, Y. González, T. Blumenstock, U. Raffalski, M. Gisi, and R. KohlheppWithin the project MUSICA (MUlti-platform remote Sensing of Isotopologues for
investigating the Cycle of Atmospheric water) ground- and space-based remote
sensing as well as in situ data sets of tropospheric water vapour
isotopologues are provided. The space-based remote-sensing data set is
produced from spectra measured by the IASI (Infrared Atmospheric Sounding
Interferometer) sensor and is potentially available on a global scale.

Here, we present the MUSICA IASI data for three different geophysical
locations (subtropics, midlatitudes, and Arctic), and we provide a
comprehensive characterisation of the complex nature of such space-based
isotopologue remote-sensing products. The quality assessment study is
complemented by a comparison to MUSICA's ground-based FTIR (Fourier Transform
InfraRed) remote-sensing data retrieved from the spectra recorded at three
different locations within the framework of NDACC (Network for the Detection
of Atmospheric Composition Change).

We confirm that IASI is able to measure tropospheric H2O profiles with a
vertical resolution of about 4 km and a random error of about 10%. In
addition IASI can observe middle tropospheric δD that adds
complementary value to IASI's middle tropospheric H2O observations. Our
study presents theoretical and empirical proof that IASI has the capability
for a global observation of middle tropospheric water vapour isotopologues on
a daily timescale and at a quality that is sufficiently high for water cycle
research purposes. 2014/08/26 - 18:40

The performance of Aeolus in heterogeneous atmospheric conditions using high-resolution radiosonde dataAtmospheric Measurement Techniques, 7, 2695-2717, 2014Author(s): X. J. Sun, R. W. Zhang, G. J. Marseille, A. Stoffelen, D. Donovan, L. Liu, and J. ZhaoThe European Space Agency Aeolus mission aims to measure wind profiles from space. A major
challenge is to retrieve high quality winds in heterogeneous atmospheric
conditions, i.e. where both the atmospheric dynamics and optical properties
vary strongly within the sampling volume. In preparation for launch we aim
to quantify the expected error of retrieved winds from atmospheric
heterogeneity, particularly in the vertical, and develop algorithms for wind
error correction, as part of the level-2B processor (L2Bp).

We demonstrate that high-resolution data from radiosondes provide valuable
input to establish a database of collocated wind and atmospheric optics at
10 m vertical resolution to simulate atmospheric conditions along
Aeolus' lines of sight. The database is used to simulate errors of Aeolus
winds retrieved from the Mie and Rayleigh channel signals. The non-uniform
distribution of molecules in the measurement bin introduces
height assignment errors in Rayleigh channel winds up to 2.5% of the
measurement bin size in the stratosphere which translates to 0.5 m s−1
bias for typical atmospheric conditions, if not corrected. The presence of
cloud or aerosol layers in the measurement bin yields biases in Mie channel
winds which cannot be easily corrected and mostly exceed the mission
requirement of 0.4 m s−1. The collocated Rayleigh channel wind solution
is generally preferred because of smaller biases, in particular for
transparent cloud and aerosol layers with one-way transmission above 0.8.

The results show that Aeolus L2Bp, under development, can be improved by the
estimation of atmosphere optical properties to correct for height assignment
errors and to identify wind solutions potentially detrimental when used in
Numerical Weather Prediction. 2014/08/26 - 18:40

The Sofia University Atmospheric Data Archive (SUADA)Atmospheric Measurement Techniques, 7, 2683-2694, 2014Author(s): G. Guerova, T. Simeonov, and N. YordanovaAtmospheric sounding using the Global Navigation Satellite Systems (GNSS) is
a well-established research field in Europe. At present, GNSS data from 1800
stations are available for model validation and assimilation in
state-of-the-art models used for operational numerical weather prediction
centres in Europe. Advances in GNSS data processing make it possible also to
use the GNSS data for climatic trend analysis, an emerging new application.
In Bulgaria and southeastern Europe, the use of GNSS for atmospheric sounding
is currently under development.

As a first step, the Sofia University Atmospheric Data Archive (SUADA) is
developed. SUADA is a user-friendly database, and includes GNSS tropospheric
products like zenith total delay (ZTD) and derivatives like vertically
integrated water vapour (IWV), as well as observations from radiosonde (RS)
and surface atmospheric data. Archived in SUADA are (1) GNSS tropospheric
products (over 12 000 000 individual observations) and derivatives (over
55 000) from five GNSS processing strategies and 37 stations for the period
1997–2013, with temporal resolutions from 5 min to 6 h, and (2) radiosonde
IWV data (over 6000 observations) for station Sofia (1999–2012).

Presented are two applications of the SUADA data for the study of long- and
short-term variations of IWV over Bulgaria during the 2007 heatwave and
intense precipitation events in 2012. 2014/08/22 - 20:04

Optimized method for black carbon analysis in ice and snow using the Single Particle Soot PhotometerAtmospheric Measurement Techniques, 7, 2667-2681, 2014Author(s): I. A. Wendl, J. A. Menking, R. Färber, M. Gysel, S. D. Kaspari, M. J. G. Laborde, and M. SchwikowskiIn this study we attempt to optimize the method for measuring black carbon
(BC) in snow and ice using a Single Particle Soot Photometer (SP2). Beside
the previously applied ultrasonic (CETAC) and Collison-type nebulizers we
introduce a jet (Apex Q) nebulizer to aerosolize the aqueous sample for SP2
analysis. Both CETAC and Apex Q require small sample volumes (a few
milliliters) which makes them suitable for ice core analysis. The Apex Q
shows the least size-dependent nebulizing efficiency in the BC particle
diameter range of 100–1000 nm. The CETAC has the advantage that air and
liquid flows can be monitored continuously. All nebulizer-types require a
calibration with BC standards for the determination of the BC mass
concentration in unknown aqueous samples. We found Aquadag to be a suitable
material for preparing calibration standards. Further, we studied the
influence of different treatments for fresh discrete snow and ice samples as
well as the effect of storage. The results show that samples are best kept
frozen until analysis. Once melted, they should be sonicated for 25 min,
immediately analyzed while being stirred and not be refrozen. 2014/08/22 - 20:04

Online technique for isotope and mixing ratios of CH4, N2O, Xe and mixing ratios of organic trace gases on a single ice core sampleAtmospheric Measurement Techniques, 7, 2645-2665, 2014Author(s): J. Schmitt, B. Seth, M. Bock, and H. FischerFirn and polar ice cores enclosing trace gas species offer a unique archive
to study changes in the past atmosphere and in terrestrial/marine source
regions. Here we present a new online technique for ice core and air samples
to measure a suite of isotope ratios and mixing ratios of trace gas species
on a single sample. Isotope ratios are determined on methane, nitrous oxide
and xenon with reproducibilities for ice core samples of
0.15‰ for δ13C–CH4,
0.22‰ for δ15N–N2O,
0.34‰ for δ18O–N2O, and
0.05‰ per mass difference for δ136Xe for
typical concentrations of glacial ice. Mixing ratios are determined on
methane, nitrous oxide, xenon, ethane, propane, methyl chloride and
dichlorodifluoromethane with reproducibilities of 7 ppb for CH4, 3 ppb
for N2O, 70 ppt for C2H6, 70 ppt for C3H8, 20 ppt
for CH3Cl, and 2 ppt for CCl2F2. However, the blank contribution for
C2H6 and C3H8 is large in view of the measured values
for Antarctic ice samples. The system consists of a vacuum extraction
device, a preconcentration unit and a gas chromatograph coupled to an
isotope ratio mass spectrometer. CH4 is combusted to CO2 prior to
detection while we bypass the oven for all other species. The highly
automated system uses only ~ 160 g of ice, equivalent to
~ 16 mL air, which is less than previous methods. The
measurement of this large suite of parameters on a single ice sample is new
and key to understanding phase relationships of parameters which are usually
not measured together. A multi-parameter data set is also key to understand
in situ production processes of organic species in the ice, a critical issue
observed in many organic trace gases. Novel is the determination of xenon
isotope ratios using doubly charged Xe ions. The attained precision for
δ136Xe is suitable to correct the isotopic ratios and mixing
ratios for gravitational firn diffusion effects, with the benefit that this
information is derived from the same sample. Lastly, anomalies in the Xe
mixing ratio, δXe/air, can be used to detect melt layers. 2014/08/22 - 20:04