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Discussion papers
https://doi.org/10.5194/acp-2019-560
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2019-560
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 04 Sep 2019

Submitted as: research article | 04 Sep 2019

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

The Relationship between Low-Level Cloud Amount and Its Proxies over the Globe by Cloud Types

Jihoon Shin and Sungsu Park Jihoon Shin and Sungsu Park
  • School of Earth and Environmental Sciences, Seoul National University, Seoul, South Korea

Abstract. We extend upon previous work to examine the relationship between low-level cloud amount (LCA) and various proxies for LCA – estimated low-level cloud fraction (ELF), lower-tropospheric stability (LTS), estimated inversion strength (EIS), and estimated cloud-top entrainment index (ECTEI) – by low-level cloud types (CL) over the globe using individual surface and upper-air observations. Individual CL has its own distinct environmental structure, and therefore our extended analysis by CL can provide insights into the strength and weakness of various proxies and help to improve them.

Overall, ELF performs better than LTS/EIS in diagnosing the variations in LCA among various CLs, indicating that a previously identified superior performance of ELF to LTS/EIS as a global proxy for LCA comes from its realistic correlations with various CLs rather than with a specific CL. However, ELF as well as LTS/EIS has a problem in diagnosing the decrease in LCA when CL0 (no low-level cloud) is reported and the increase of LCA when CL12 (cumulus) is reported over the deserts where background stratus does not exist. This incorrect diagnosis of CL0 as a cloudy condition is more clearly seen in the analysis of individual CL frequencies binned by proxy values. If CL0 is excluded, all ELF/LTS/EIS have good inter-CL correlations with the amount-when-present (AWP) of individual CLs. In future, an advanced ELF needs to be formulated to deal with the dissipation of LCA when the inversion base height is lower than the lifting condensation level, to diagnose cumulus updraft fraction as well as the amount of stratiform clouds and detrained cumulus, and to parameterize the scale height as a function of appropriate environmental variables.

Jihoon Shin and Sungsu Park
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Jihoon Shin and Sungsu Park
Jihoon Shin and Sungsu Park
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Latest update: 17 Sep 2019
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Short summary
In this work, we showed that the previously identified strong spatiotemporal correlation relationship between the low-level cloud fraction (LCA) and its large-scale environmental proxy, the estimated low-level cloud fraction (ELF), holds for various low-level cloud types over the globe rather than for a specific cloud type. However, we also identified several weaknesses of ELF and suggest a potential pathway to further improve the ELF in future as a global proxy for LCA.
In this work, we showed that the previously identified strong spatiotemporal correlation...
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