The Relationship Between Dipole In Tibetan Plateau And The Westerly Zone

Based on the daily and monthly reanalysis data of the ERA-Interim atmosphere developed by the European Centre(ECMWF)from 1979 to 2015 and the observation data from more than 2,400 Chinese ground meteorological stations,a set of lattice datasets was established by interpolation(The precipitation data in CN05.1)analyzes the changes of the geopotential height field on the south and north sides of the Qinghai-Tibet Plateau in the past 37 years,finds the basis for the existence of the dipole phenomenon,and defines the dipole index,establishing the dipole through analysis.Sub-index critical area physical characteristics.The dipole index was used to study the relationship between the position and intensity of the dipole and the westerly zone,and further analysis was made of the effects of dipole changes on the westerly wind,geopotential height,vorticity,precipitation,temperature,and westerly jet flow in China.The following conclusions:There are obvious seasonal changes in latitudinal flow pattern around the plateau.From March to May,the curvature of the ridge lines on both sides of the plateau gradually increased,and the vorticity values on the south and north sides of the plateau gradually decreased.In the three months of spring,the geopotential height field on the south side of the plateau and the north side of the plateau exhibited negative correlations,and the correlation was best in May.The regions with the best correlation coefficients and the most obvious changes in vorticity on both sides of the May Plateau were selected as the key regions A(10°-26°N,60°-95°E)and B(41°-56°N,85°-108°E),the dipole index is defined as the difference between the average geopotential height in Region A and the average geopotential height in Region B.The dipole index shows a slight growth trend and there is a quasi-4a and a quasi-10 a cycle.The first mode in the temporal and spatial distribution of high in situ height shows a dipole distribution pattern,and the large value area of reverse change appears in the northeast side of the plateau and the eastern part of the south side of the plateau.The change range is from the plateau to the plateau.Both sides increase,and the negative signal changes drastically more than the positive signal.In spring and winter,there are two westerly jets on the south and north sides of the plateau.The south jet west westerly jet stream has increased in spring and was interrupted at the end of May.It was replaced by East wind and reappeared in October.The large value of the North Branch rapids occurred in April and October.23-32 The north and south sides of the plateau have a rapid flow.On the 23 rd side of the plateau,the center of the jet stream gradually moves northward and the wind speed at the low altitude gradually decreases.The south jet rapidly disappears northward,and the low altitude on the south side of the plateau is controlled by the weak easterly wind.The 200 hPa wind speed in the upper troposphere always has a maximum wind speed center on the north side of the plateau.The wind speed on both sides of the troposphere decreases gradually,and it gradually advances to the east and north.At the lower troposphere 600 hPa,the westerly jet at the north of the north plateau has a westerly jet,the intensity of the westerly jet at the north side of the plateau weakens,and the weak easterly wind at 23-26 to control the South China Sea region gradually increases,and the 27 th and 28 th episodes suddenly disappear.It is re-established.The zero wind speed line has a phenomenon of north jump.The ridge zone on the north side of the plateau first increased and then decreased,weakened after 25 th,and the southern side of the plateau began to deepen from late April,weakened after the 27 th time reached its maximum value,but the range of the channel area increased,and there was a conversion to a closed low pressure.System trend.The dipoles have a relatively late northerly jump and a southward pullout time.The dipole and the 600-hPa westerly zone show a significant positive correlation in most of the regions outside the northeastern region of China,while there is a significant negative correlation in the Bay of Bengal region.The dipole and the 200 hPa wind field are positively related to the entire western part of Xinjiang except for a small part of the western part of the country,and they show a negative correlation in Mongolia.The index shows a negative correlation with the temperature field in Inner Mongolia-Mongolia and Northeast China,and a significant positive correlation distribution pattern in most regions south of 40°N.The positive correlation distribution pattern is very significant.Combining the geopotential height field and the variation trend of vorticity field,the dipoles are strong,and the height of the geopotential height on the north side of the high altitude plateau is increased.At this time,the north of the lower plateau is controlled by the negative vorticity and the temperature is increased,while the south side of the high altitude plateau The height of the geopotential height is reduced.At this time,the south side of the lower plateau is controlled by positive vorticity and the temperature is lowered.The difference between strong and weak annual precipitation fields is significant.In the dipole strong years,precipitation in the southwestern and southern parts of China and in a small part of Inner Mongolia increased significantly,while precipitation in other regions decreased to varying degrees.