Based on monthly mean surface air temperature(SAT) from 71 stations in northern China and NCEP NCAR and NOAA-CIRES(Cooperative Institute for Research in Environmental Sciences) twentieth century reanalysis data, the dominant modes of winter SAT over northern China were explored. The results showed that there are two modes that account for a majority of the total variance over northern China. The first mode is unanimously colder(warmer) over the whole of northern China. The second mode is characterized by a dipole structure that is colder(warmer) over Northwest China(NWC) and warmer(colder) over Northeast China(NEC), accounting for a fairly large proportion of the total variance. The two components constituting the second mode, the individua variations of winter SAT over NWC and NEC and their respective preceding factors, were further investigated. I was found that the autumn SAT anomalies are closely linked to persistent snow cover anomalies over Eurasia showing the delayed effects on winter climate over northern China. Specifically, the previous autumn SAT anomalies over the Lake Baikal(LB; 50–60°N, 85–120°E) and Mongolian Plateau(MP; 42–52°N, 80–120°E) regions play an important role in adjusting the variations of winter SAT over NWC and NEC, respectively. The previous autumn SAT anomaly over the MP region may exert an influence on the winter SAT over NEC through modulating the strength and location of the East Asian major trough The previous autumn SAT over the LB region may modulate winter westerlies at the middle and high latitudes of Asia and accordingly affects the invasion of cold air and associated winter SAT over NWC.
The summer snow anomalies over the Tibetan Plateau （TP） and their effects on climate variability are often overlooked,possibly due to the fact that some datasets cannot properly capture summer snow cover over high terrain.The satellite-derived Equal-Area Scalable Earth grid （EASE-grid） dataset shows that snow still exists in summer in the western part and along the southem flank of the TP.Analysis demonstrates that the summer snow cover area proportion （SCAP） over the TP has a significant positive correlation with simultaneous precipitation over the mei-yu-baiu （MB） region on the interannual time scale.The close relationship between the summer SCAP and summer precipitation over the MB region could not be simply considered as a simultaneous response to the Silk Road pattern and the SST anomalies in the tropical Indian Ocean and tropical central-eastern Pacific.The SCAP anomaly has an independent effect and may directly modulate the land surface heating and,consequently,vertical motion over the western TP,and concurrently induce anomalous vertical motion over the North Indian Ocean via a meridional vertical circulation.Through a zonal vertical circulation over the tropics and a Kelvin wave-type response,anomalous vertical motion over the North Indian Ocean may result in an anomalous high over the western North Pacific and modulate the convective activity in the western Pacific warm pool,which stimulates the East Asia-Pacific （EAP） pattern and eventually affects summer precipitation over the MB region.
This study explores the characteristics of high temperature anomalies over eastern China and associated influencing factors using observations and model outputs.Results show that more long-duration（over 8 days） high temperature events occur over the middle and lower reaches of the Yangtze River Valley（YRV） than over the surrounding regions,and control most of the interannual variation of summer mean temperature in situ.The synergistic effect of summer precipitation over the South China Sea（SCS） region（18°–27°N,115°–124°E） and the northwestern India and Arabian Sea（IAS） region（18°–27°N,60°–80°E） contributes more significantly to the variation of summer YRV temperature,relative to the respective SCS or IAS precipitation anomaly.More precipitation（enhanced condensational heating） over the SCS region strengthens the western Pacific subtropical high（WPSH） and simultaneously weakens the westerly trough over the east coast of Asia,and accordingly results in associated high temperature anomalies over the YRV region through stimulating an East Asia–Pacific（EAP） pattern.More precipitation over the IAS region further adjusts the variations of the WPSH and westerly trough,and eventually reinforces high temperature anomalies over the YRV region.Furthermore,the condensational heating related to more IAS precipitation can adjust upper-tropospheric easterly anomalies over the YRV region by exciting a circumglobal teleconnection,inducing cold horizontal temperature advection and related anomalous descent,which is also conducive to the YRV high temperature anomalies.The reproduction of the above association in the model results indicates that the above results can be explained both statistically and dynamically.
