arXivDaily arXiv每日学术速递 周一至周五更新
arXiv 2008.08251physics.ao-phcs.CVphysics.geo-ph
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从离散视角看印度季风期间降雨与对流云的时空关系

Spatio-temporal relationships between rainfall and convective clouds during Indian Monsoon through a discrete lens

Cornell University(康奈尔大学);International Centre for Theoretical Sciences (ICTS-TIFR)(国际理论科学中心(TIFR))

Arjun Sharma, Adway Mitra, Vishal Vasan, Rama Govindarajan

AI总结:

本研究基于马尔可夫随机场模型的离散时空表示方法,分析2004-2010年印度季风期降雨与OLR的时空关系,发现少量模式可覆盖超90%日期的情况,揭示了二者的关联及逐日变化规律,为季风过程的简化描述提供工具。

摘要:

印度季风是一个多变量过程,每年6-9月引发强降雨,其时空异质性极强。本研究针对2004-2010年的季风期,探究降雨与射出长波辐射(Outgoing Longwave Radiation,OLR,表征对流云覆盖)之间的关系。为识别、分类并可视化降雨与OLR的空间模式,我们采用了一种离散且时空连贯的数据表示方法,该方法基于马尔可夫随机场(Markov Random Field)的统计模型构建。我们的方法将降雨和OLR空间分布相似的日期聚类为少量空间模式。研究发现,降雨和OLR各有8种日空间模式,二者的联合模式有7种,这些模式可描述超过90%的日期情况。通过这些模式我们发现,OLR总体上与降水呈强负相关,但存在显著的空间差异。具体而言,印度半岛(除西海岸外)大部分时间都被显著的对流云覆盖,但始终无雨。我们还发现,大部分季风降雨与低OLR同时发生,但印度东部和西北部6月的部分降雨出现在高OLR日,推测这类降雨来自浅云。为研究两个量的逐日变化,我们识别了由观测数据计算得到的时间梯度中的空间模式。研究发现,印度全境对流云活动的变化最常见的成因是南北向OLR梯度的建立,该梯度会持续1-2天,使对流云覆盖从浅云转为深云,或反之。这类变化也伴随着降水空间分布的改变。因此,本研究为复杂的空间模式及其逐日变化提供了高度简化的描述,可作为未来对该过程进行简化描述的有用工具。

英文摘要:

The Indian monsoon, a multi-variable process causing heavy rains during June-September every year, is very heterogeneous in space and time. We study the relationship between rainfall and Outgoing Longwave Radiation (OLR, convective cloud cover) for monsoon between 2004-2010. To identify, classify and visualize spatial patterns of rainfall and OLR we use a discrete and spatio-temporally coherent representation of the data, created using a statistical model based on Markov Random Field. Our approach clusters the days with similar spatial distributions of rainfall and OLR into a small number of spatial patterns. We find that eight daily spatial patterns each in rainfall and OLR, and seven joint patterns of rainfall and OLR, describe over 90\% of all days. Through these patterns, we find that OLR generally has a strong negative correlation with precipitation, but with significant spatial variations. In particular, peninsular India (except west coast) is under significant convective cloud cover over a majority of days but remains rainless. We also find that much of the monsoon rainfall co-occurs with low OLR, but some amount of rainfall in Eastern and North-western India in June occurs on OLR days, presumably from shallow clouds. To study day-to-day variations of both quantities, we identify spatial patterns in the temporal gradients computed from the observations. We find that changes in convective cloud activity across India most commonly occur due to the establishment of a north-south OLR gradient which persists for 1-2 days and shifts the convective cloud cover from light to deep or vice versa. Such changes are also accompanied by changes in the spatial distribution of precipitation. The present work thus provides a highly reduced description of the complex spatial patterns and their day-to-day variations, and could form a useful tool for future simplified descriptions of this process.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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