Version 4 CALIPSO Imaging Infrared Radiometer ice and liquid water cloud microphysical properties – Part II: Results over oceans
2021
Abstract. Following the release of the version 4 Cloud-Aerosol Lidar with Orthogonal
Polarization (CALIOP) data products from Cloud-Aerosol Lidar and Infrared
Pathfinder Satellite Observations (CALIPSO) mission, a new version 4 (V4) of
the CALIPSO Imaging Infrared Radiometer (IIR) Level 2 data products has been
developed. The IIR Level 2 data products include cloud effective
emissivities and cloud microphysical properties such as effective diameter
( De ) and water path estimates for ice and liquid clouds. This paper
(Part II) shows retrievals over ocean and describes the improvements made
with respect to version 3 (V3) as a result of the significant changes
implemented in the V4 algorithms, which are presented in a companion paper
(Part I). The analysis of the three-channel IIR observations (08.65,
10.6, and 12.05 µ m) is informed by the scene classification
provided in the V4 CALIOP 5 km cloud layer and aerosol layer products.
Thanks to the reduction of inter-channel effective emissivity biases in
semi-transparent (ST) clouds when the oceanic background radiance is derived
from model computations, the number of unbiased emissivity retrievals is
increased by a factor of 3 in V4. In V3, these biases caused inconsistencies
between the effective diameters retrieved from the 12 / 10
( β eff 12 / 10 = τ a , 12 / τ a , 10 )
and 12 / 08 ( β eff 12 / 08 = τ a , 12 / τ a , 08 )
pairs of
channels at emissivities smaller than 0.5. In V4, microphysical retrievals
in ST ice clouds are possible in more than 80 % of the pixels down to
effective emissivities of 0.05 (or visible optical depth ∼0.1 ). For the month of January 2008, which was chosen to illustrate the results, median
ice De and ice water path (IWP) are, respectively, 38 µ m
and 3 g m −2 in ST clouds, with random uncertainty estimates of 50 %.
The relationship between the V4 IIR 12 / 10 and 12 / 08 microphysical
indices is in better agreement with the “severely roughened single column”
ice habit model than with the “severely roughened eight-element aggregate”
model for 80 % of the pixels in the coldest clouds ( K) and
60 % in the warmest clouds ( >230 K). Retrievals in opaque ice
clouds are improved in V4, especially at night and for 12 / 10 pair of
channels, due to corrections of the V3 radiative temperature estimates
derived from CALIOP geometric altitudes. Median ice De and IWP are
58 µ m and 97 g m −2 at night in opaque clouds, with again
random uncertainty estimates of 50 %. Comparisons of ice retrievals with
Moderate Resolution Imaging Spectroradiometer (MODIS)/Aqua in the tropics
show a better agreement of IIR De with MODIS visible–3.7 µ m than
with MODIS visible–2.1 µ m in the coldest ST clouds and the opposite
for opaque clouds. In prevailingly supercooled liquid water clouds with
centroid altitudes above 4 km, retrieved median De and liquid water
path are 13 µ m and 3.4 g m −2 in ST clouds, with estimated random
uncertainties of 45 % and 35 %, respectively. In opaque liquid clouds,
these values are 18 µ m and 31 g m −2 at night, with estimated
uncertainties of 50 %. IIR De in opaque liquid clouds is smaller
than MODIS visible–2.1 µ m and visible–3.7 µ m by 8 and 3 µ m,
respectively.
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