Climatic Characteristics And Influencing Factors Of Persistent High-Temperature Events In Hunan

It was a hot topic of heat waves, this paper was analyzed,basing on ground observation site daily maximum temperature data for 95 stations in Hunan, NCEP/NCAR reanalysis daily data and monthly daily data, and NOAA global monthly sea surface temperature anomaly data during 1979-2013, the paper was analyzed through the following methods:Mann-Kendall test,Morlet wavelet analysis, empirical orthogonal function decomposition, correlation analysis,singular value decomposition.high temperature strength grade and persistent high temperature events were defined, Climatic characteristics of single station high temperature and persistent high-temperature events in Hunan, and atmospheric circulation anomalies distribution were revealed, then it was explored the relationship between sea surface temperature and persistent high-temperature events, Finally, it was analyzed to select two columns typical column analysis. This article aimed to reveal the temperature and climate characteristics of persistent high temperature events in Hunan, find out the reasons of persistent high-temperature events, and look for some early signals of SSTA.(1) High temperatures were likely to occur in April to October, in generally to begin to develop in late June to July-August vigorous development, in part to the high temperature of sustainable September in Hunan. Distribution of high-temperature weather was presented East Dorsey less, and there were two temperature zones, respectively in Hengyang-Yongzhou-Zhuzhou and Yiyang-Changde, differences in the average daily number of high-temperature weather great, but the distribution of high temperature days and terrain also had a close relationship. There were four kinds of scales cycle change in the process of high temperature days, the scale cycle was the most obvious from 3 to 7 years; there also were four more obvious oscillation cycle, it was a strongest cyclical swing in 32 years. Different decadal also show different strength and scope, especially in the 21st century the most obvious change. In addition, there were significant temperature Hunan interannual and decadal changes in the 1980s, before the total number of hot days was slightly decreasing trend, but in the 21st century, the total number of high temperature days showed significant increase.(2) There had been a total of 22 times high temperature events of Hunan persistent in 1979 to 2013.Before the 1990s, persistent high temperatures often had intermittent incidents occurred after a sustained high temperature events often with 1 to 2 years gap, and a shorter duration of high temperature events; persistent high temperature events existed in the 1990s quasi-two-year cycle, but the duration was significantly lengthened the previous month; the 21st century, persistent high temperatures an increase in the number of incidents, and the duration was also significantly lengthened, the longest duration of a high temperature events up to 45 days. Evolution found before the 1980s, the total number of hot days is a slight downward trend, but in the 21st century, the total number of high temperature days showed a significant increase in temperature trends from the international era.(3)Atmospheric circulation 500hPa field in Hunan swelter,mid-latitudes was more prevalented zonal circulation, low pressure in the low-latitude region of the Bay of Bengal was weaker than normal, while Iran was a strong high pressure Sheng; WPSHP anomalously large bias strong, easterly and northerly location was also deputy high long-term stability control, Hunan,was one of the important causes of persistent high temperature events occur.850hPa wind field maps, Hunan swelters in unusual strong southerly winds, the West Pacific Ocean to strengthen the anti-cyclonic circulation, while the high latitudes north appeared weakened, and the air force was weak; In addition, in the coastal areas of southeast China abnormal north, then tropical ocean system activity was difficult to influence inland northward, which would help the emergence of sustained hot weather in Sea level pressure field. Hunan swelters in high-pressure system in the western Pacific ocean strengthened, and sea level pressure, Hunan and north of the lower, indicating a weak cold air north.(4) The central waters of the Pacific (160°E～140°W,10°N～40°N) of the previous year Feb to October and summer high temperature days had a significant positive correlation, that was, when the key area of the waters of the sea surface temperature anomaly when high, the duration of the summer heat Hunan also anomalously long and easy to produce extreme high temperatures, on the contrary, when the waters of the sea surface temperature anomaly was low key, the duration of the summer heat of Hunan shorter, less prone or summer weather.(5) WPSHP was abnormal strong, westerly, northerly control Hunan of summer in 2003 and 2013, and stable circulation less dynamic situation, was one of the important influence affecting the system Hunan persistent high-temperature. South Asian high continued eastward to strengthen in summer, it was a favorable conditions of west extension, maintaining stable of WPSHP, it was one of the important reasons for sustained high temperatures occur. Furthermore, the great weaken of vertical upward motion, zonal and radial water vapor transport were conducived to the sustainable development of high temperature. At the same time, sea surface temperature anomalies of the key areas from August to October of the previous year can be as a early signals of persistent high-temperature events in summer.