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Discussion papers
https://doi.org/10.5194/acp-2019-835
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2019-835
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 20 Nov 2019

Submitted as: research article | 20 Nov 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).

Cloud Phase Characteristics Over Southeast Asia from A-Train Satellite Observations

Yulan Hong and Larry Di Girolamo Yulan Hong and Larry Di Girolamo
  • Department of Atmospheric Sciences, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA

Abstract. This study examines the climatological characteristics of cloud phase over Southeast Asia (SEA) based on A-Train satellite observations. Using the combined CloudSat-CALIPSO (CC) data, five main cloud groups are investigated: ice-only, ice-above-liquid, liquid-only, ice-above-mixed and mixed-only clouds that have annual mean frequencies of 27.8 %, 21.9 %, 16.9 %, 7.4 % and 6.2 %, respectively. Liquid-only clouds tend to occur in relatively cold, dry and stable environments. The other four cloud groups appear more frequently in relatively warm, humid and unstable conditions and their seasonal distributions move with large-scale climate systems: Asian monsoon and ITCZ. Liquid clouds are found to be highly inhomogeneous based on the heterogeneity index (Hσ) from Aqua MODIS, while ice-only and mixed-only clouds are often very smooth. Ice-above-liquid clouds are less inhomogeneous than liquid-only clouds due to the thin overlying ice clouds. Undetected subpixel liquid clouds enlarge clear sky Hσ, leading to some inhomogeneous clear sky pixels, which otherwise should be smooth. The reflectance at 0.645 (R0.645) and brightness temperature at 11 μm (BT11) of ice-only, liquid-only and ice-above-liquid clouds show peak frequencies near that of clear sky (R0.645 ~ 0.02, BT11 ~ 294 K), implying that a large population of thin or subpixel clouds over SEA are difficult to see by MODIS. The CC data also show abundant thin clouds over SEA, which indicates 78.3 % ice-only and 89.6 % ice-above-liquid clouds with ice τ < 3. Mixed-only clouds in contrast are thick (top ~ 14 km), bright (R0.645 ~ 0.61) and cold (BT11 ~ 231 K). The intraseasonal and interannual behaviors of all-sky Hσ and spectral signatures follow that of cloud phases and are able to track the MJO and ENSO phases. Climatologies of clouds over SEA provided in this study are useful for the evaluation of large-scale model simulations, as well as for the interpretation of cloud properties derived from passive satellite sensors in this region.

Yulan Hong and Larry Di Girolamo
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Yulan Hong and Larry Di Girolamo
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Short summary
Cloud phase plays a crucial role in Earth radiation budget but is not well understood. Using A-Train satellite observations, this study provides climatological studies of cloud phase characteristics over Southeast Asia on multiple meteorological scales. Results show that ice, liquid and ice over liquid clouds display distinct spatial heterogeneity and spectral radiance features. The intraseasonal and interannual behaviors of cloud phases are useful to track the MJO and ENSO.
Cloud phase plays a crucial role in Earth radiation budget but is not well understood. Using...
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