Dominant Patterns of Winter Temperature Variation in Yunnan and Key Circulation Factors Affecting on Them

Abstract

To reveal the main characteristics of winter temperature change in Yunnan and the key circulation factors affecting on it， the winter temperature variation is first investigated by using monthly mean temperature data of 124 meteorological observation stations in Yunnan， NCEP / NCAR reanalysis data， some atmospheric teleconnection indices and atmospheric circulation characteristic indices provided by CPC （Climate Prediction Center） and NCC （National Climate Center）.The results show that the annual variability of winter temperature is more obvious in the East than that in the West.There are four dominant EOF patterns of winter temperature in Yunnan， i.e.the whole regional consistent pattern， the East-West difference pattern， the meridional triple-like pattern and the northwest-southeast difference pattern.The four dominant patterns account for 90% of the EOF total variance contribution.The interannual changes of the first three patterns show a significant linear trend， but the fourth pattern mainly shows interdecadal fluctuation characteristics.It is found that the situation and trends of wave train in mid-high latitude regions is obvious different corresponding to different temperature patterns.The geopotential height in four key areas related to the anomalous wave trains in mid-high latitude regions at 500 hPa， as well as the atmospheric circulation anomalies in low-high level in the Bay of Bengal（BOB）， have a very important impact on the temperature patterns.The first EOF pattern is closely related to geopotential height difference between in the southern （20°N -30°N， 90°E -120°E） and Northern （45°N -60°N， 90°E -120°E） East Asia.When the geopotential height is low in Southern and high in Northern， the temperature is uniform warming， and vice versa.The second pattern is related to the zonal wave trains in the mid-high latitude regions.When the geopotential height from East Asia to Northwest Pacific region （15°N -25°N， 80°E -100°E） is high （low）， there is a cyclone（anticyclone） occur in 700 hPa in the northern BOB （15°N -25°N， 80°E -100°E）， 300 hPa Uwnd-shear-300 index in Southeast Asia is higher （less） than zero， which is conducive to the cold Western and warm Eastern （warm Western and clod Eastern）.The third pattern is related to the northwest-southeast wave train in the middle and high latitude regions.The geopotential height in plateau area （30°N -50°N， 80°E -110°E） is high （low）， which is conducive to the meridional triple-like pattern， with warm-cold-warm （cold-war-cold） from West to East of Yunnan.The fourth pattern is mainly affected by the changes of local circulation in BOB.The correlation between EOF time coefficients and atmospheric teleconnection indices and key circulation system indices further shows the important role of circulation wave train in mid-high latitude regions.At the same time， it also shows that the change of geopotential height in Plateau is one of the important factors affecting the temperature in winter in Yunnan.

Keywords

• winter temperature in yunnan
• dominant patterns
• key circulation factors
• wave train in mid-high latitude
• geopotential height over plateau
• bob cyclone
• siberian high