Ice cloud microphysical trends observed by the Atmospheric Infrared Sounder

Abstract

Abstract. 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 (T ci ), ice optical thickness (τ i ) and ice effective radius (r ei ). The trends in ice cloud properties are shown to be independent of trends in information content and χ 2 . Statistically significant decreases in ice frequency, τ i , 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 r ei 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 χ 2 trends. Values of r ei are larger at the tops of opaque clouds and exhibit dependence on surface wind speed, column water vapour (CWV) and surface temperature (T sfc ) 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 r ei with respect to CWV and T sfc . Comparisons between DARDAR and AIRS suggest that r ei is smallest for singlelayer 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.

Global Statistics of Ice Microphysical and Optical Properties at Tops of Optically Thick Ice Clouds

“…Aside we note that the slight increase of r e near 265 K over ocean, especially in midlatitude winter and at high latitudes, is consistent with laboratory measurements showing a local increase in growth rate at those temperatures (Fukuta & Takahashi, 1999;Jensen et al, 2017). Over land, r e quite abruptly increases with decreasing temperatures below about 225 K at middle and high latitudes, which is also observed using Atmospheric Infrared Sounder measurements and may be consistent with overshooting convection (Kahn et al, 2018). Figures 2 and 3 indicate that cloud top temperature trends of asymmetry parameters, distortion values, and aspect ratios are qualitatively similar over ocean and land.…”

Footprint-scale cloud type mixtures and their impacts on Atmospheric Infrared Sounder cloud property retrievals

“…CC BY 4.0 License. et al 2011;van Diedenhoven et al 2014;Kahn et al, 2018). These Cu cases are likely transient cumulus congestus at altitudes cold enough for cloud top glaciation.…”

“…Ice tests dominate in the Dc cloud scene histogram although a very small proportion of -1, 0, and +1 occur. Inspection of AIRS granules (not shown) demonstrate that the spectral signatures used in thermal infrared phase tests break down in the presence of overshooting convection and other ice clouds within a few Kelvins of the tropopause (e.g., Kahn et al, 2018).…”

The effect of increased resolution of geostationary satellite imageries on predictability of tropical thunderstorms over Southeast Asia

“…Here, the definition of lead time is the time passed from when the cloud was initially detected to the mature point. The minimum BT11 at 230 K can be used as a parameter of the mature point, because when the minimum BT11 is near 230 K, the maximum of ice effective radius occurs (Kahn et al, 2018). The cloud drop size has an impact on the growth rate.…”