Version 4 CALIPSO Imaging Infrared Radiometer ice and liquid water cloud microphysical properties – Part II: Results over oceans
Authors: Garnier Anne , Pelon Jacques , Pascal Nicolas , Vaughan Mark A. , Dubuisson Philippe , Yang Ping , Mitchell David L. 
Published: May 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 µm) 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
(βeff12/10 = τa,12/τa,10)
and 12/08 (βeff12/08 = τa,12/τa,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 µm
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 (<210 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 µm 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 µm than
with MODIS visible–2.1 µm 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 µm 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 µm 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 µm and visible–3.7 µm by 8 and 3 µm,
respectively.