Impact of the Horizontal Heat Flux in the Mixed Layer on an Extreme Heat Event in North China:A Case Study  

作　　者：Ying NA Riyu LU Bing LU Min CHEN Shiguang MIAO 

机构地区：[1]State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics,Institute of Atmospheric Physics, Chinese Academy of Sciences [2]College of Earth and Planetary Sciences, University of the Chinese Academy of Sciences [3]Institute of Urban Meteorology, China Meteorological Administration

出　　处：《Advances in Atmospheric Sciences》2019年第2期133-142,共10页大气科学进展（英文版）

基　　金：sponsored by the Ministry of Science and Technology of China (Grant No.2015DFA20870)

摘　　要：Extreme heat over the North China Plain is typically induced by anomalous descending flows associated with anticyclonic circulation anomalies. However, an extreme heat event that happened in the North China Plain region on 12–13 July 2015,with maximum temperature higher than 40℃ at some stations, was characterized by only a weak simultaneous appearance of an anomalous anticyclone and descending flow, suggesting that some other factor(s) may have induced this heat event. In this study, we used the forecast data produced by the Beijing Rapid Updated Cycling operational forecast system, which predicted the heat event well, to investigate the formation mechanism of this extreme heat event. We calculated the cumulative heat in the mixed-layer air column of North China to represent the change in surface air temperature. The cumulative heat was composed of sensible heat flux from the ground surface and the horizontal heat flux convergence. The results indicated that the horizontal heat flux in the mixed layer played a crucial role in the temporal and spatial distribution of high temperatures.The horizontal heat flux was found to be induced by distinct distributions of air temperatures and horizontal winds at low levels during the two days, implying a complexity of the low-level atmosphere in causing the extreme heat.Extreme heat over the North China Plain is typically induced by anomalous descending flows associated with anticyclonic circulation anomalies. However, an extreme heat event that happened in the North China Plain region on 12–13 July 2015,with maximum temperature higher than 40℃ at some stations, was characterized by only a weak simultaneous appearance of an anomalous anticyclone and descending flow, suggesting that some other factor(s) may have induced this heat event. In this study, we used the forecast data produced by the Beijing Rapid Updated Cycling operational forecast system, which predicted the heat event well, to investigate the formation mechanism of this extreme heat event. We calculated the cumulative heat in the mixed-layer air column of North China to represent the change in surface air temperature. The cumulative heat was composed of sensible heat flux from the ground surface and the horizontal heat flux convergence. The results indicated that the horizontal heat flux in the mixed layer played a crucial role in the temporal and spatial distribution of high temperatures.The horizontal heat flux was found to be induced by distinct distributions of air temperatures and horizontal winds at low levels during the two days, implying a complexity of the low-level atmosphere in causing the extreme heat.

关 键 词：EXTREME HEAT North China Plain HORIZONTAL HEAT FLUX sensible HEAT FLUX WARM advection 

分 类 号：O4[理学—物理]