Climatological distribution and diurnal variation of mesoscale convective systems over China and its vicinity during summer |
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Authors: | YongGuang Zheng Jiong Chen PeiJun Zhu |
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Institution: | (1) National Meteorological Center, Beijing, 100081, China;(2) Department of Earth Sciences, College of Science, Zhejiang University, Hangzhou, 310027, China |
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Abstract: | The climatological distribution of mesoscale convective systems (MCSs) over China and its vicinity during summer is statistically
analyzed, based on the 10-year (1996–2006, 2004 excluded) June–August infrared TBB (Temperature of black body) dataset. Comparing
the results obtained in this paper with the distribution of thunderstorms from surface meteorological stations over China
and the distribution of lightning from low-orbit satellites over China and its vicinity in the previous studies, we find that
the statistic characteristics of TBB less than −52°C can better represent the spatiotemporal distribution of MCSs over China
and its vicinity during summer. The spreading pattern of the MCSs over this region shows three transmeridional bands of active
MCSs, with obvious fluctuation of active MCSs in the band near 30°N. It can be explained by the atmospheric circulation that
the three bands of active MCSs are associated with each other by the summer monsoon over East Asia. We focus on the diurnal
variations of MCSs over different underlying surfaces, and the result shows that there are two types of MCSs over China and
its vicinity during summer. One type of MCSs has only one active period all day long (single-peak MCSs), and the other has
multiple active periods (multi-peak MCSs). Single-peak MCSs occur more often over plateaus or mountains, and multi-peak MCSs
are more common over plains or basins. Depending on lifetimes and active periods, single-peak MCSs can be classified as Tibetan
Plateau MCSs, general mountain MCSs, Ryukyu MCSs, and so on. The diurnal variation of multi-peak MCSs is very similar to that
of MCCs (mesoscale convective complexes), and it reveals that multi-peak MCSs has longer life cycle and larger horizontal
scale, becomes weaker after sunset, and develops again after midnight. Tibetan Plateau MCSs and general mountain MCSs both
usually develop in the afternoon, but Tibetan Plateau MCSs have longer life cycle and more active MαCSs. Ryukyu MCSs generally develop after midnight, last longer time, and also have more active MαCS. The abundant moisture and favorable large-scale environment over Indian monsoon surge areas lead to active MCSs and MαCSs almost at any hour all day during summer. Due to local mountain-valley breeze circulation over the Sichuan Basin, MCSs
are developed remarkably more often during the nighttime, and again there are also more active MαCSs. Because of local prominent sea-land breeze circulation over Guangxi and Guangdong, the MCSs over this region propagate
from sea to land in the afternoon and from land to sea after midnight. The statistic characteristics of TBB less than −52°C
clearly display the different climatological characteristics of MCSs owing to the thermal difference among water, land and
rough terrain. Not only the large-scale atmospheric circulation but also the local atmospheric circulation caused by the thermal
difference among water, land and rough terrain, to a great extent, determines the climatological distribution of MCSs over
China and its vicinity during summer.
Supported by the National Major Basic Research “973” Program of China (Grant No. 2004CB418300) and the National Natural Science
Foundation of China (Grant No. 40305004) |
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Keywords: | mesoscale convective systems IR TBB diurnal variation climatological distribution |
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