On the build-up of dust aerosols and possible indirect effect during Indian summer monsoon break spells using recent satellite observations of aerosols and cloud properties,Journal of Earth System Science

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On the build-up of dust aerosols and possible indirect effect during Indian summer monsoon break spells using recent satellite observations of aerosols and cloud properties
Journal of Earth System Science ( IF 1.9 ) Pub Date : 2021-02-17 , DOI: 10.1007/s12040-020-01526-6
V B Arya , Sajani Surendran , Kavirajan Rajendran

Abstract

Association of higher (lower) rainfall with lower (higher) Aerosol Optical Depth (AOD) is consistent with the understanding that increased washout (build-up) and shorter (longer) life-time of aerosols occur in wetter (drier) conditions. Given the life-time of aerosols, it is imperative to examine how aerosols impact active/break (wetter/drier than normal) spells, prominent intraseasonal variability (ISV) of Indian summer monsoon (ISM), through their composite analysis using recent satellite observations of aerosols and cloud properties, circulation and rainfall. Dust aerosols can act as CCN and participate efficiently in cloud processes during active phase. During breaks, build-up of desert dust transported by prevalent circulation, is associated with lower cloud effective radius implying aerosols’ indirect effect where they can inhibit cloud growth in the presence of reduced moisture and decrease precipitation efficiency/rainfall. Correspondingly, correlation albeit small, between intraseasonal anomalies of AOD and rainfall is negative, when AOD leads rainfall by 3–5 days implying that indirect aerosols impact is effective during breaks, though it is not the dominant responsible factor. During breaks, lower shortwave flux at top of atmosphere hints at dust-induced semi-direct effect. As breaks are permanent features of ISM, incorporation of dust-induced feedbacks in models, is essential for improved ISV simulation and ISM prediction.

Highlights

Active (break) spell of summer monsoon is found to be associated with lower (higher) aerosol optical depth over India.
The build-up of desert dust transported to India by prevalent circulation during summer monsoon breaks, is associated with lower cloud effective radius which indicates the indirect effect of aerosols.
Predominant indirect effect induced by dust aerosols along with secondary semi-direct effect can lead to further rainfall reduction during intense and persistent breaks.
Proper incorporation of dust aerosol induced heating during breaks in models, is essential for simulation of intraseasonal variation inherent to Indian summer monsoon and thereby improving its prediction.

中文翻译：

利用最近的卫星对气溶胶和云特性的观测，研究了印度夏季风季风爆发期间尘埃气溶胶的堆积和可能的间接影响

摘要

较高（较低）的降雨与较低（较高）的气溶胶光学深度（AOD）的关联与以下认识是一致的：在潮湿（干燥）的条件下，气溶胶的冲刷（堆积）增加和气溶胶寿命缩短（更长）的寿命。考虑到气溶胶的寿命，必须通过使用最近的卫星观测资料进行综合分析，研究气溶胶如何影响活动/破裂（比正常情况更干燥/干燥），印度夏季风（ISM）的明显季节内变异性（ISV）。气溶胶和云的性质，环流和降雨的影响。在活动阶段，粉尘气溶胶可以充当CCN并有效参与云过程。休息时，由于普遍的循环而积累的沙漠尘埃堆积，这与较低的云有效半径有关，这意味着气溶胶的间接作用，即在水分减少的情况下，它们可以抑制云的生长并降低降水效率/降雨。相应地，当季节内AOD异常与降雨之间的相关性很小，但当AOD领先降雨3-5天时，表明间接气溶胶影响在休息期间是有效的，尽管这不是主要的影响因素。在休息期间，大气顶部的短波通量较低，暗示着灰尘引起的半直接效应。由于中断是ISM的永久特征，因此在模型中纳入粉尘引起的反馈对于改进ISV仿真和ISM预测至关重要。当AOD导致降雨提前3-5天时，AOD的季节内异常与降雨量之间的负值是负的，这表明在休息期间间接气溶胶的影响是有效的，尽管这不是主要的影响因素。在休息期间，大气顶部的短波通量较低，暗示着灰尘引起的半直接效应。由于中断是ISM的永久特征，因此在模型中纳入粉尘引起的反馈对于改进ISV仿真和ISM预测至关重要。当AOD导致降雨提前3-5天时，AOD的季节内异常与降雨量之间的负值是负的，这表明在休息期间间接气溶胶的影响是有效的，尽管这不是主要的影响因素。在休息期间，大气顶部的短波通量较低，暗示着灰尘引起的半直接效应。由于中断是ISM的永久特征，因此在模型中纳入粉尘引起的反馈对于改进ISV仿真和ISM预测至关重要。