Spatial And Temporal Variations Of Air Temperature Over China In Spring And Their Relationships With Atmospheric Circulation Anomalies

By using air temperature data of China meteorological stations and NCEP/NCAR atmospheric reanalysis data from 1951-2010 as well as statistical methods, such as the Gaussian filter, EOF and REOF, etc., the spatial and temporal variations of air temperature over China in the spring of 1951-2010 were analyzed. Furthermore, linear regression method was applied to discuss the relationships between spring air temperature and atmospheric circulation. The main conclusions are as follows:(1)EOF decomposition results indicate that spring temperature over China has three main spatial modes:same anomalies in whole area of China, opposite anomalies in the southern and northern parts of China and, "-、+、-" pattern from north to south. PC1 and PC2 show obvious characteristics of decadal variation, while PC3 shows inter-annual variability. REOF decomposition concluded that there are 5 major regions of temperature anomalies over China in spring. Based on cluster analysis method, the features of spring temperature changes can be divided into two categories, that is, overall gradual warming and temperature increase first and decrease later. A relatively cold period exists in the warm period.(2)Except for the Southwest China, most regions of China experience warming in spring and the situation of temperature "increase-decrease" is presented from northeast to southwest after 1980s. The air temperatures raise 0-1℃ in most regions of China except for some locations of the southwest China in March, April and May. The seasonal process from March to May speeds up in the regions to the south of Yangtze River and the eastern part of the Southwest China, while it slows down in the northeast China, the southern part of the Southwest China and the northern part of the Northwest China. The seasonal process in the Inner Mongolia and the southern part of the South China experienced the changes from fast to slow. On the whole, under the background of global warming, the start and end dates of spring become early in the East China, while change indistinctly in the West China.(3)Compared with the conditions during 1951-1980, the Ural blocking high and East Asian trough have weakened, while the zonal circulation over Asia in the middle and high latitudes, the subtropical high in the western Pacific ocean, and the subtropical westerly jet over East Asia have strengthened since 1980s. Those are disadvantageous to the influences of cold air from polar region and high latitude areas in the northern hemisphere on the climate of China, therefore the temperatures are high over most of China, especially the Northeast China in spring.However, the strengthen of the middle East Jet, the southward of the East Asian Jet, and the activity of the Central Asian Trough are in favor of the cold air from the central-eastern part of Europe influencing the Southwest China and resulting in low air temperature there. In the mean time, the weakened southern branch trough goes against the warm and wet flows from the Indian Ocean and Bay of Bengal influencing the Southwest China, which easily results in low temperature in these areas.(4)On the inter-annual time scale, EOF decomposition concluded that spring temperature over China has three main space modes:unanimous anomalies in the whole area, opposite anomalies in the south and north, and "-、+、-" anomalies from north to south. Further analysis showed that when it is warm in the whole China in spring, main anomalous trough and ridge in the middle-troposphere of atmosphere are three-wave pattern. New land, the Ural mountains, and Alaska are controlled by super long wave troughs, while most of china is controlled by super long wave ridge. The cold Siberian high pressure decreases and the sea level pressures of Okhotsk and the South China Sea increase, which are conducive to the transportations of warm wet vapours from south to north. The subtropical westerly jet over East Asia is located northward anomalously. The southerly wind anomalies at high latitudes in 850hPa and the positive anomalies of subtropical high in the South China Sea are conducive to the transportations of the warm wet vapours from south to north.(5)On the inter-decadal time scale, the main characteristics of spring temperature modes over China is uniformity in the whole area. The time series is at the positive phase before 1960s, negative phase between the middle of 1960s and 1990s, and positive phase after the middle of 1990s. The second characteristics of spring temperature modes over China shows opposite anomalies in the south and north The time series is at positive phase after 1970s, begins to decrease at the beginning of the 21st century, and at negative phase after the year of 2005.