Physical characteristics of convective and non-convective cirrus clouds from CALIPSO data over the South China Sea

Abstract

Studying the characteristics and mechanisms of convective and non-convective cirrus clouds over the South China Sea is vital for their impact on regional climate dynamics, and enhancing predictive models for weather and climate forecasts. This study utilizes eight years of CALIPSO data (from March 2007 to February 2015) to investigate convective and non-convective cirrus clouds. Explicit new insights include the observation that convective cirrus cloud samples are three times more numerous than non-convective cirrus clouds. Convective cirrus clouds are associated with humid conditions and demonstrate higher ice water content (IWC) values ranging from 10⁻³ to 10⁻¹ g m⁻³, whereas non-convective cirrus clouds tend to be drier, exhibiting IWC values ranging from 10⁻⁴ to 10⁻³ g m⁻³. Both cirrus cloud types exhibit a maximum cloud fraction at 10°N. Convective cirrus reach their peak cloud fraction at an altitude of 14 km, while non-convective cirrus typically occur at altitudes between 15 and 16 km. The seasonal variability of the convective cirrus cloud fraction primarily reflects bottom-up positive specific humidity anomalies originating from convective activity, whereas the non-convective cirrus cloud fraction is influenced by top-down negative temperature anomalies.

摘要

南海是陆地, 海洋和大气相互作用强烈的区域, 在此背景下, 深对流活动对于卷云的形成和维持至关重要. 然而, 关于该区域对流性和非对流性卷云物理特征的研究十分有限. 本文基于2007–2015年的CALIPSO数据对南海地区的对流性和非对流性卷云进行了研究. 结果表明, 对流性卷云的样本数是非对流性卷云的三倍; 对流性卷云表现出较高的冰水含量 (IWC) 并伴随着潮湿的环境条件, 而非对流性卷云的冰水含量较低; 此外, 进一步的分析揭示了对流性卷云和非对流性卷云的云量呈现出不同的垂直分布, 对流性卷云的最大云量出现在14 km, 而非对流性卷云则出现在15–16 km; 最后, 阐明了驱动两种类型卷云云量的季节性变化机制, 对流性卷云云量的季节性变化主要受自下而上的正比湿异常影响, 而非对流性卷云则受自上而下的负温度异常驱动.