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Radiatively Active Hydrometeors Frequencies from CloudSat-CALIPSO Data for Evaluating Cloud Fraction in Global Climate Models
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  • Jui-Lin F. Li,
  • Wei-Liang Lee,
  • Kuan-man Xu,
  • Yu Cian Tsai,
  • Jonathan H Jiang,
  • Jia-Yuh Yu,
  • Graeme Stephens,
  • Eric J. Fetzer,
  • Wei-Ting Chen
Jui-Lin F. Li
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Wei-Liang Lee
Academia Sinica

Corresponding Author:leelupin@gate.sinica.edu.tw

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Kuan-man Xu
NASA Langley
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Yu Cian Tsai
Department of Atmospheric Sciences, National Central University
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Jonathan H Jiang
Jet Propulsion Laboratory, California Institute of Technology
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Jia-Yuh Yu
National Central University
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Graeme Stephens
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Eric J. Fetzer
Jet Propulsion Laboratory
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Wei-Ting Chen
National Taiwan University
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This study derives radiatively-active hydrometeors frequencies (HFs) from CloudSat-CALIPSO satellite data to evaluate cloud fraction in present-day simulations by CMIP5 models. Most CMIP5 models do not consider precipitating and/or convective hydrometeors but CESM1-CAM5 in CMIP5 has diagnostic snow and CESM2-CAM6 in CMIP6 has prognostic precipitating ice (snow) included. However, the models do not have snow fraction available for evaluation. Since the satellite-retrieved hydrometeors include the mixtures of floating, precipitating and convective ice and liquid particles, a filtering method is applied to produce estimates of cloud-only HF (or NPCHF) from the total radiatively-active HF (THF), which is the sum of NPCHF, precipitating ice HF and convective HF. The reference HF data for model evaluation include estimates of liquid-phase NPCHF from CloudSat radar-only data (2B-CWC) and ice-phase THF from CloudSat-CALIPSO 2C-ICE combined radar/lidar data. The model evaluation results show that cloud fraction from CMIP5 multi-model mean (MMM) is significantly underestimated (up to 30 %) against the total HF estimates, mainly below the mid-troposphere over the extratropics and in the upper-troposphere over the midlatitude lands and a few tropical convective regions. The CMIP5 cloud fraction biases are reduced dramatically when compared to the cloud-only HF estimates, but the area of overestimates expands from the tropical convective regions to mid-latitudes in the lower and upper troposphere. There is no CMIP5 standard output snow fraction available for comparison against CloudSat-CALIPSO estimate. The implications of these results show that hydrometeors frequency estimates from CloudSat-CALIPSO provide a reference for GCM’s cloud fraction from stratiform and convective form.