The Interannual And Interdecadal Variation Of South China Summer Extreme Hot Events And Its Possible Relationship With Sea Surface Temperature

By using 1980-2016 daily maximum temperature data of 753 observation stations in China,NCEP/NCAR reanalysis data and NOAA_ERSST_V4,this study defines extreme hot event days and intensity by ways of Percentiles to discuss the interannual and interdecadal variation of South China summer extreme hot events and its possible causes by observation analysis and NCAR CAM5.1 numerical simulations.Based on simulation results of the Community Earth System Model(CESM)under the global warming of 1.5?/2.0?(relative to the pre-industrial)and its 20 th century historical simulation results to estimate the situation of summer extreme hot events in the future in South China.The results are as follows:(1)The main distribution for the entire district of summer extreme hot events in South China is in the same phase and the corresponding time series appears obvious interannual and interdecadal variation.The interannual variability of summer extreme hot events days in South China show that 1983,1990,1998,2003 and 2007 are hot years and 1982,1997,1999,2002,2008 and 2012 are cold years.The interdecadal transition point is 1992 and 2002,which means 1980-1992,2003-2016 correspond to hot period and 1993-2002 corresponds to cold period;(2)It was found that when the South Asia High was much eastern,larger and stronger than usual and Western Pacific Subtropical High was much more western,larger and stronger than usual,the convergence in 200 hPa wind filed and divergence in 850 hPa lead to descend current in South China,it would be hotter in summer South China;(3)The summer extreme hot events days in South China has a significant interannual correlation with sea surface temperature anomaly(SSTA)over the region in the tropical eastern Indian Ocean and western Pacific(EI-WP).The observation data and NCAR CAM5.1 numerical simulations show possible mechanisms of effect of SSTA in the EI-WP on the interannual summer extreme hot events in South China: when the spring and summer SST in EI-WP is warmer than normal,ascend current would prevail in the key region and it would descend in South China under the effect of 105°E-125°E mean meridional circulation,which is favorable to the maintenance of fine weather in summer South China.(4)In interdecadal timescale,the summer extreme hot events days in South China has a significant correlation with SSTA over the Central South Indian Ocean(CSI).There are two possible mechanisms of SSTA in th CSI on the interdecadal summer extreme hot events: when the CSI spring and summer SST is warmer than usual,(I)abnormal cyclone exists in the North Indian Ocean,under the 15°N-25°N mean zonal circulation influence,the upward airflow in the North Indian Ocean would drop in South China;(II)the upward current contributed by abnormal cyclone in the CSI would descend in the western Australia under the 40°S-20°S mean zonal circulation effect,then the 105°E-125°E mean meridional circulation would cause the downward motion in South China.Both downward current would be favorable to the maintenance of fine weather in summer South China;(5)The 95 percentile threshold of daily maximum temperature in summer South China in the present day simulated by CESM is 30.2 ?.Relative to present day,under the global warming of 1.5/2.0 ?,the probability of exceeding the threshold is 33%,54% respectively,which increases 5.6,9.8 times respectively;the extreme hot events days increases 3.0,3.7 times respectively;the extreme hot events intensity increases 2.4,3.6 times respectively.Thus,the summer extreme hot events would be much more frequent and stronger in 1.5/2 ? scenarios.