气候变化领域集成服务门户(CCPortal): Assessing Historical Variability of South Asian Monsoon Lows and Depressions With an Optimized Tracking Algorithm

CCPortal

DOI	10.1029/2020JD032977
	Assessing Historical Variability of South Asian Monsoon Lows and Depressions With an Optimized Tracking Algorithm
	Vishnu S.; Boos W.R.; Ullrich P.A.; O'Brien T.A.
发表日期	2020
ISSN	2169897X
卷号	125 期号:15
英文摘要	Cyclonic low-pressure systems (LPS) produce abundant rainfall in South Asia, where they are traditionally categorized as monsoon lows, monsoon depressions, and more intense cyclonic storms. The India Meteorological Department (IMD) has tracked monsoon depressions for over a century, finding a large decline in their number in recent decades, but their methods have changed over time and do not include monsoon lows. This study presents a fast, objective algorithm for identifying monsoon LPS and uses it to assess interannual variability and trends in reanalyses. Variables and thresholds used in the algorithm are selected to best match a subjectively analyzed LPS data set while minimizing disagreement between four reanalyses in a training period. The stream function of 850 hPa horizontal wind is found to be optimal in this sense; it is less noisy than vorticity and represents the complete nondivergent wind, even when flow is not geostrophic. Using this algorithm, LPS statistics are computed for five reanalyses, and none show a detectable trend in monsoon depression counts since 1979. Both the Japanese 55-year Reanalysis (JRA-55) and the IMD data set show a step-like reduction in depression counts when they began using geostationary satellite data, in 1979 and 1982, respectively; the 1958–2018 linear trend in JRA-55, however, is smaller than in the IMD data set, and its error bar includes 0. There are more LPS in seasons with above-average monsoon rainfall and in La Niña years, but few other large-scale modes of interannual variability are found to modulate LPS counts, lifetimes, or track length consistently across reanalyses. © 2020. The Authors.
英文关键词	Low-pressure system; Monsoon; Reanalyses; South Asia; Track data; Trend
语种	英语
来源期刊	Journal of Geophysical Research: Atmospheres
文献类型	期刊论文
条目标识符	http://gcip.llas.ac.cn/handle/2XKMVOVA/185880
作者单位	Department of Earth and Planetary Science, University of California, Berkeley, CA, United States; Climate and Ecosystem Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, United States; Department of Land, Air, and Water Resources, University of California, Davis, CA, United States; Earth and Atmospheric Sciences Department, Indiana University, Bloomington, Bloomington, IN, United States
推荐引用方式 GB/T 7714	Vishnu S.,Boos W.R.,Ullrich P.A.,et al. Assessing Historical Variability of South Asian Monsoon Lows and Depressions With an Optimized Tracking Algorithm[J],2020,125(15).
APA	Vishnu S.,Boos W.R.,Ullrich P.A.,&O'Brien T.A..(2020).Assessing Historical Variability of South Asian Monsoon Lows and Depressions With an Optimized Tracking Algorithm.Journal of Geophysical Research: Atmospheres,125(15).
MLA	Vishnu S.,et al."Assessing Historical Variability of South Asian Monsoon Lows and Depressions With an Optimized Tracking Algorithm".Journal of Geophysical Research: Atmospheres 125.15(2020).