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A comparison of ice water content measurement techniques on the FAAM BAe-146 aircraft

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.

Atmospheric Measurement Techniques 2014/09/20 - 18:38 Czytaj