Ice water content vertical profiles of high-level clouds: classification and impact on radiative fluxes

Artem G. Feofilov (1) , Claudia J. Stubenrauch (1) , Julien Delanoë (2)

1 LMD - Laboratoire de Météorologie Dynamique (UMR 8539)
2 SPACE - LATMOS

In this work, we discuss the shape of ice water content (IWC) vertical profiles in high ice clouds and its effect on radiative properties of these clouds, both in short- and in long-wave bands (SW and LW). Based on the analysis of colocated satellite data, we suggest a minimal set of primitive shapes (rectangular, isosceles trapezoid, lower and upper triangle), which sufficiently well represents the IWC profiles. About 75% of all high-level ice clouds (P < 440 hPa) have an ice water path smaller than 100 g m−2, with a 10% smaller contribution from single layer clouds. Most IWC profiles (80%) can be represented by a rectangular or isosceles trapezoid shape. However, with increasing IWP, the number of lower triangle profiles (IWC rises towards cloud base) increases, reaching up to 40% for IWP values greater than 300 g m−2. The number of upper triangle profiles (IWC rises towards cloud top) is in general small and decreasing with IWP, with the maximum occurrence of 15% in cases of IWP less than 10 g m−2. We propose a statistical classification of the IWC shapes using ice water path (IWP) as a single parameter. We have estimated the radiative effects of clouds with the same IWP and with different IWC profile shapes for five typical atmospheric scenarios and over a broad range of IWP, cloud height, cloud vertical extent, and effective ice crystal diameter (De). We explain changes in outgoing LW fluxes at the top of the atmosphere (TOA) by the cloud thermal radiance while differences in TOA SW fluxes relate to the De vertical profile within the cloud. Absolute differences in net TOA and surface fluxes associated with these parameterized IWC profiles instead of assuming constant IWC profiles are in general of the order of 1–2 W m−2: they are negligible for clouds with IWP < 30 g m−2, but may reach 2 W m−2 for clouds with IWP >300 W m−2.

Domaines: Météorologie; Physique Atmosphérique et Océanique [physics.ao-ph]

Artem G. Feofilov, Claudia J. Stubenrauch, Julien Delanoë. Ice water content vertical profiles of high-level clouds: classification and impact on radiative fluxes. Atmospheric Chemistry and Physics, 2015, 15 (21), pp.12327-12344. ⟨10.5194/acp-15-12327-2015⟩. ⟨insu-01164245⟩