North China Summer Drought And Flood Statistical Correlation With Extreme High Temperature

The extreme events show characteristics such as high devastating and hard to predict. Extreme climate event is a hot topic in the research work of climate change. Under the background of global warming, the extreme events of China shows characteristics such as high intensity and hard to predict. Precipitation and temperature are the important parts of climate change, and the extreme events of precipitation-droughts/floods and extreme high and low temperature events, due to its harm is very serious, so it is always the focus of scientists. In this paper, we will research on the two aspects of extreme climate events.At first, the NCEP/NCAR reanalysis data for the period1948-2011is used to calculate NPOI, and then the positive correlation between North Pacific Osillation and summer drought/flood over North China was discovered through studying the relationship between NPOI and PDSI. When in positive NPOI years, summer PDSI is higher than normal, and North China has more summer floods; otherwise, in negative NPOI years, summer PDSI is lower than normal, and North China has more summer droughts. Possible circulation mechanism analysis shows that, when in positive(negative) NPOI years, on lower layer(at850hPa wind field), the common action of anti-cyclonic(cyclonic) in Ural Mountains, the cyclone(anti-cyclonic) of Lake Baikal, and the anti-cyclonic(cyclonic) anomaly circulation in West Pacific, have strengthened(weakened) the convergence of south-west warm and humid air flows of low layer in North China region. And also, when in positive(negative) NPOI years,500hPa geopotential height anomaly shows’+-+’(’-+-’)wave train, and West Pacific subtropical high is stronger(weaker)/shifting northwest(southeast)than normal years, cold and warm air activities make more(less) rainfall over North China. The winter SST of Pacific Ocean has forcing role on May NPO, which then influcences summer drought/flood over North China.There have been more research on extreme temperature events of Ground, but less research on high temperature extremes. So in this article, The high and low days in Eastern China are preliminarily analysed by utilizing daily mean temperature of free atmospheric records of137meteorlogical stations of eight layers from1971to2009. The results show that:the regularity in winter is better than that of summer. Compared with other levels, the statistical regularity of tropopause layer150hPa and bottom of stratosphere100hPa is independent. The days of whole layers are more in low layers and fewer in upper layers. Long term trend analysis show that: regardless of winter low temperature days or summer high temperature days are warming in the lower layers and the colding in upper layers. Correlation analysis show that:the revelance of summer high days is greater than that of winter low days, and the correlation among150hPa/100hPa and other layers is poor. The significant correlation is almost in adjacent level. and low days in low levels(850hPa,700hPa), middle levels(500hPa,400hPa,300hPa,200), and upper levels(150hPa,100hPa) is significant positive correlation, however, the high days is significant positive correlation in850-200hPa.