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【06.15讲座】暖季降水响应全球变暖的新机制
发布时间：Thu Jun 08 08:46:00 CST 2017
主 题：暖季降水响应全球变暖的新机制
时 间：2017年06月15日(星期四) 9:00-11:00
地 点：京师科技大厦B座520,学院南路12号
主讲人：戴爱国 教授
讲座内容介绍：
气候模式模拟结果表明随着温室气体的增加，降水强度增加而降水频率减少。目前降水频率减少的机制尚不明确。基于WRF模式的北美4公里网格小时降水数据，发现模式模拟重现了观测中降水频率的季节变化和空间变化；暖季降水频率的减少主要是由于轻中度降水（0.1-2.0 mm/hr）的减少，而强降水（2-10 mm/hr）和超强降水（10 mm/hr以上）是增加的。暖季的干燥期时间变长并且更加频繁，对流层底部的相对湿度减少，导致了总的降水频率和轻中度降水事件的减少；大气水汽含量增加和潜热释放的正反馈效应导致了强降水的大量增加。预计未来气候中暴雨的强度增加而数量减少。
主讲人简介：
戴爱国，1985年本科毕业于南京大学大气科学专业；1988年硕士毕业于中国科学院大气物理研究所；1996年博士毕业于美国哥伦比亚大学大气科学专业；1997-2012年在美国国家大气研究中心（NCAR）工作；2012年至今就职于美国纽约州立大学奥尔巴尼分校大气与环境科学学院。多年从事降水变率、全球及区域气候变化、水文气象等方面的相关研究，曾担任Journal of Climate编辑和Journal of Hydrology副编辑。在Nature、Nature Climate Change等高水平期刊上发表论文100余篇。截至2017年5月，论文引用率达23660次，H 指数为61。2014-2016年连续三年获得汤姆森路透社高引用科学家（前1%）。
Title: A new mechanism for warm-season precipitation response to global warming
Speaker: Prof. Aiguo Dai, Depeartment of Atmospheric and Environmental Sciences, University at Albany, SUNY, Albany, New York, USA
Abstract: Climate models project increasing precipitation intensity but decreasing frequency as greenhouse gases (GHGs) increase. However, the exact mechanism for the frequency decrease remains unclear. Here we investigate this by analyzing hourly data from regional climate change simulations with 4km grid spacing covering most of North America using the Weather Research and Forecasting (WRF) model. The model was forced with present and future boundary conditions, with the latter being derived by adding the CMIP5 19-model ensemble mean changes to the ERA-interim reanalysis. The model reproduces well the observed seasonal and spatial variations in precipitation frequency and histograms, and the dry interval between rain events over the contiguous U.S. (CONUS). Results show that overall precipitation frequency indeed decreases during the warm season mainly due to fewer light-moderate precipitation (0.1<P£2.0mm/hr) events, while heavy (2<P£10mm/hr) to very heavy precipitation (P>10mm/hr) events increase. Dry spells become longer and more frequent, together with a reduction in time-mean relative humidity (RH) in the lower troposphere during the warm season. The increased dry hours and decreased RH lead to a reduction in overall precipitation frequency and also for light-moderate precipitation events, while water vapor-induced increases in precipitation intensity and the positive latent heating feedback in intense storms may be responsible for the large increase in intense precipitation. The size of intense storms increases while their number decreases in the future climate, which helps explain the increase in local frequency of heavy precipitation. The results generally support a new hypothesis for future warm-season precipitation: Each rainstorm removes ³7% more moisture from the air per 1K local warming, and surface evaporation and moisture advection take slightly longer than currently to replenish the depleted moisture before the next storm forms, leading to longer dry spells and a reduction in precipitation frequency, as well as decreases in time-mean RH and vertical motion.
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