Ice cloud microphysical trends observed by the Atmospheric Infrared Sounder
<p>We use the Atmospheric Infrared Sounder (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 (<i>T</i><sub>ci</sub>), ice optical thickness (<i>τ&l...
Main Authors: | , , , , , , , |
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Format: | Article |
Language: | English |
Published: |
Copernicus Publications
2018-07-01
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Series: | Atmospheric Chemistry and Physics |
Online Access: | https://www.atmos-chem-phys.net/18/10715/2018/acp-18-10715-2018.pdf |
Summary: | <p>We use the Atmospheric Infrared Sounder (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 (<i>T</i><sub>ci</sub>), ice
optical thickness (<i>τ</i><sub>i</sub>) and ice effective radius
(<i>r</i><sub>ei</sub>). The trends in ice cloud properties are shown to be
independent of trends in information content and <i>χ</i><sup>2</sup>. Statistically
significant decreases in ice frequency, <i>τ</i><sub>i</sub>, and ice water path
(IWP) are found in the SH and NH extratropics, but trends are of much smaller
magnitude and statistically insignificant in the tropics. However,
statistically significant increases in <i>r</i><sub>ei</sub> 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 <i>χ</i><sup>2</sup> trends. Values of
<i>r</i><sub>ei</sub> are larger at the tops of opaque clouds and exhibit
dependence on surface wind speed, column water vapour (CWV) and surface
temperature (<i>T</i><sub>sfc</sub>) with changes up to 4–5 µm but are only 1.9 %
of all ice clouds. Non-opaque clouds exhibit a much smaller change in
<i>r</i><sub>ei</sub> with respect to CWV and <i>T</i><sub>sfc</sub>. Comparisons between DARDAR
and AIRS suggest that <i>r</i><sub>ei</sub> 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.</p> |
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ISSN: | 1680-7316 1680-7324 |