Decadal Characteristics Of Summer Northern Pacific Storm Track And Its Possible Relation To Precipitation And Temperature Over China

On the basis of NCEP/NCAR reanalysis investigation is conducted on the decadal variations in strength, longitude and latitude, as well as its period and abrupt years, of the summer northern Pacific storm track (SNPST). Results show that the SNPST does exist evident decadal characteristics, with its strength, longitude and latitude vary at quasi-13-, 19-, and 14～15- yearly periods, respectively. The years with abrupt change in strength is around 1978 as compared to 1982 and 1989 for latitude, while longitude is slowly changed without significant abrupt shift.Based on China 160 station precipitations and temperatures, examination is further done on the possible concurrent relationships between the decadal variations of SNPST and precipitation and temperature over China. Evidence shows that on the decadal basis, there are tight contemporary correlations between the SNPST and precipitation as well as temperature over China. The years when the storm track is stronger(weaker), the rainfall in Yangtze valley is more(less) than mean, as opposed to that in southeast coastal area;while temperature in south China is higher(lower) than mean, with lower(higher) temperature in the Hetao area. When the storm track is westward (eastward) of mean, the rainfall in southeast coastal area, especially in Fujian, is more(less);while the temperature at northwest China is higher (lower), In the years when the SNPST is northward(southward), the rainfall in southwest and north China is less(more), while the temperature over most of central China and north China is high(lower).In the end, NCEP/NCAR reanalysis in years of significant variations in the SNPST are chosen for compositive study of the possible mechanism of the SNPST influence on summer precipitation and temperature in China on the decadal basis. It shows that in years with strengthened SNPST, it is propitious to stronger southerly anomalies, leading warm and wet winds flowing to the north, encountered with the cold air in the Yangtze valley, which results in more rainfall and lower temperature therein. When the storm track is westward, it is favorable for the southwesterly anomaly to strengthen in the low-latitudes, causing warm and wet winds in thisregion flowing to the north. As a result of this process, precipitation over most area of China is increased and temperature is decreased. Furthermore, when the SNPST is northward, the whole eastern China is under the control of the easterly anomaly, favorable for warm and wet flows gone with the easterly through the Pacific to east China, leading to increased precipitation therein, which undoubtedly makes for decreased temperature. Meantime, northeast China is located in the part of the anticyclonic anomaly, also impacted by the difference easterlies, thus accounting for more rainfall and lower temperature in this area.As a result, the decadal variability of the SNPST can provide a clue for the forecast of precipitation and temperature over China in summer.