Relationship Between Soil Temperature Change At East Asian Mid-high Latitudes In Late Spring And Early Summer And East Asian Summer Climate Anomaly

This article is supported by the CAS Strategic Priority Research Program Grant No. XDA05110203. Based on northern Eurasia former winter snow and East Asia summer climate correlationship, this paper focuses on effect of East Asia mid-high latitudes soil temperature anomaly on summer atmospheric circulation in East Asia. The main research work and conclusions are as follows.(1) Due to the scarcity of observed soil temperature in East Asia middle and high latitudes, this study investigates the qualities of four soil temperature reanalyses over East Asian middle and high latitudes based on a set of Russian historical soil temperature data(RHSTD). Four reanalyses chosen are ERA-Interim re-analysis, ERA-Interim/Land and MERRA-Land generated by running land surface model offline, and a 20 th century reanalysis(NOAA-CIRES 20CR).More emphasis is put on spring and summer, and the results prove that ERA-Interim/Land, or ERA-Land for short, depicts climatology, seasonal cycle and inter-annual variations of soil temperatures very well, but not for inter-annual variability, i.e. standard deviation.(2) With the 31-year ERA-Land soil temperature mentioned above and the coarse but over 100 years long one, NOAA-CIRES, the paper further analyzes their temporal and space variation in the region in spring and summer. The results show that both spring and summer soil temperatures' EOF1 are characterized by overall warming in recent three decades at this region. Further analysis reveals that spring soil warming at all layers belongs to long-term change, and may be related to the global warming. Summer soil temperature in 0-30 cm is dominated by inter-decadal change which is related to fluctuations of 30-60 years with one inter-decadal mutation around 1998, whereas soil temperature in 100-200 cm is more related to long-term change. And soil temperature in 30-100 cm embodies both mentioned above. On the other hand, after being removed long term trend, spring soil temperature at all layers still contains significant 6-8 years fluctuations, while the counterpart in summer only exhibits obvious inter-annual change without significant period.(3) Finally, this paper analyzes the impact of temperature anomalies at East Asian middle and high latitudes on East Asian atmospheric circulation, and found that when spring soil temperature in Baikal characterizes positive anomaly, homochronous temperature and geopotential height at local middle and upper troposphere are high, with negative anomalies at both north and south sides, zonal wind at middle(high) latitude weakened(enhanced), and westerly jet weakened. Meanwhile, abnormal north wind appears in the lower troposphere along the East Asian coast. Similar but weaker linkage exists between summer soil temperature and circulation. Secondly, the influence of soil temperature anomalies in spring key area, that is Lake Baikal area, on East Asian circulation only last for 1 to 2 months. However, when positive soil temperature anomalies exist at East Asian middle and high latitudes in late spring and early summer, both the subtropical westerly jet and the western Pacific subtropical high are weaker and move to a further south position. Correspondingly, the summer precipitation in Eastern China is more likely to exhibit "- +- +" pattern from north to south. Apart from soil temperature change in phase(EOF1), the anti-phase variation between southern and northern soil temperature at that region(EOF2) affects meridional displacement of westerly jet as well.