Journal cover Journal topic
Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
https://doi.org/10.5194/acp-2017-1216
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
Research article
31 Jan 2018
Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).
Ice cloud microphysical trends observed by the Atmospheric Infrared Sounder
Brian H. Kahn1, Hanii Takahashi1,2, Graeme L. Stephens1, Qing Yue1, Julien Delanoë3, Gerald Manipon1, Evan M. Manning1, and Andrew J. Heymsfield4 1Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, 91109, USA
2Joint Institute for Regional Earth System Science and Engineering, University of California – Los Angeles, Los Angeles, CA, 90095, USA
3LATMOS/IPSL, UVSQ-CNRS-UPMC, 11 Boulevard D'Alembert, 78280 Guyancourt, France
4National Center for Atmospheric Research, Boulder, CO, 80301, USA
Abstract. We use the AIRS version 6 ice cloud property and thermodynamic phase retrievals to quantify variability and 14-year trends in ice cloud frequency, ice cloud top temperature (Tci), ice optical thickness (τi) and ice effective radius (rei). The trends in ice cloud properties are shown to be independent of trends in information content and χ2. Statistically significant decreases in ice frequency, τi, and ice water path (IWP) are found in the SH and NH extratropics, but trends are much smaller and statistically insignificant in the tropics. However, statistically significant increases in rei are found in all three latitude bands. Perturbation experiments consistent with estimates of AIRS radiometric stability fall significantly short of explaining the observed trends in ice properties, averaging kernels, and χ2 trends. Values of rei are larger at the tops of opaque clouds and exhibit strong dependence on surface wind speed, column water vapour (CWV) and surface temperature (Tsfc) with changes up to 10–12 μm. Transparent clouds exhibit a much smaller change in rei for CWV, while none is observed for Tsfc. Comparisons between DARDAR and AIRS suggest that rei is smallest for single-layer cirrus, larger for cirrus above weak convection, and largest for cirrus above strong convection at the same cloud top temperature. This behaviour is consistent with enhanced particle growth from radiative cooling above convection or large particle lofting from strong convection.

Citation: Kahn, B. H., Takahashi, H., Stephens, G. L., Yue, Q., Delanoë, J., Manipon, G., Manning, E. M., and Heymsfield, A. J.: Ice cloud microphysical trends observed by the Atmospheric Infrared Sounder, Atmos. Chem. Phys. Discuss., https://doi.org/10.5194/acp-2017-1216, in review, 2018.
Brian H. Kahn et al.
Brian H. Kahn et al.
Brian H. Kahn et al.

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Short summary
The Atmospheric Infrared Sounder (AIRS) satellite instrument shows statistically significant global trends in ice cloud properties between September 2002 and August 2016. The trends are not explained by known AIRS instrument limitations. Significant differences in the ice cloud particle size is found between convective clouds and thin ice clouds in the tropics. These results will be a useful benchmark for other studies of global ice cloud properties.
The Atmospheric Infrared Sounder (AIRS) satellite instrument shows statistically significant...
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