The Response Of Snow Cover On The Qinghai-Tibet Plateau To Solar Activity

The multi-scale characteristics of the F10.7cm solar flux data?F10.7?and AO Index?AOI?and the relationship between them were analyzed with EEMD method and power spectrum estimation.Not only the interdecadal correlations between snow depth over the Tibetan Plateau?TP?and F10.7,but also the interdecadal correlation between various modes after REOF decomposition of snow depth over TP and F10.7 were discussed.The large-scale circulations related with the distribution of the snow depth were also discussed.The conclusions were showed as follows:?1?During the 18^th-24^th solar cycles,solar activity tended to decrease and AO tended to increase.Both F10.7 and AOI had multi-scale characteristics.The interannual scale,7.8 years,and interdecadal scale,11.0 years,were the main periodic characteristics of solar activity.The main interannual scale of AO was 2.7 years,4.7years and 8.3 years.Solar activity could regulate not only the same scale of the AO component,but also the lower scale of the AO component,which meant solar activity was one of the external causes of multi-scale AO changes.In addition,the EEMD method could effectively extract many potential periodic features,but the length of time series had a certain impact on the extracted periods.Compared with the longer time-scale periodic information,the shorter time-scale information was more credible.When discussing the relationship between climate factors and solar activity,the effective and credible scales were interannual?7.8 years?and interdecadal period?11.0years?.?2?The high correlation area between the snow depth over TP and solar activity was consistent with the trends of mountain range.The positive correlation was concentrated in the line of Kunlun Mountains-Tanggula Mountains-Nianqing Tanggula Mountains-Hengduan Mountains.The large value areas of snow depth over TP were more sensitive to solar activity,but the time scale of the climatic effect of solar activity was limited,and there was a significant positive correlation below 7 years.The correlation field changed obviously after two years later,and gradually developed to the pattern of"positive north and negative south".The snow over the northern part of TP which was above 32°N and the western TP which located the west of 85°E were positively correlated with solar activity.?3?The sensitive areas of the anomalous distribution of snow depth over TP were mostly located in the Kunlun Mountains,Himalayas,Animaqing Mountains and Bayan Kara Mountains,which were roughly opposite to the northern margin areas of TP,such as the north of Kunlun Mountains and Qilian Mountains.After the 21st century,the snow over the western TP in every mode tended to be less,which indicated that the change of the western plateau was relatively stable after the 21^stt century.In the 1980s,the second and third mode tended to be more,while the fourth mode showed a weak negative trend,and all modes changed obviously in 1998.The various distribution of snow depth over TP changed differently with time,which indicated that the spatial and temporal variations of snow were complicated in interannual variations.?4?The PC_S of different modes had different responses to solar activity.PC1 and PC2were most sensitive to solar activity.Regression analysis of PC1 and PC2,the corresponding atmospheric teleconnection was the negative phase of AO,and the correlation between PC2 and AO index was significantly inverse.This indicated that AO had palyed an important role in the process of snow depth over TP responsed to the solar activity,forming a process chain of solar activity-AO-snow depth over TP.?5?The possible mechanism of AO affecting the interdecadal distribution of snow depth over TP was that when AO was in negative phase,the polar region was a high-pressure area with weak cold air,the Ural Mountains high-pressure area,which would block the eastward movement of the trough and cold air in eastern Europe,the trough in East Asia was strong,and the winter monsoon was obvious.The dry and cold air from Siberia invaded TP along the northwest or westerly airflow,and with the uplift of topography,the northern edge of the TP was likely to snow,while the central and eastern regions were affected by subsidence airflow,which couldn't be conducive to snow.The warm and humid airflow influenced parts of the southern edge of the TP under the action of southeast or southerly airflow,resulting in some areas to snow over the southern part of TP,it was unlikely to cause a wide range of snowfall weather,higher temperature over TP formed a circulation background with less snow.On the contrary,in the positive phase of AO,the polar region was a low-pressure area with strong cold air,t he high-pressure ridge of Ural Mountains moved eastward to the vicinity of Lake Baikal.The East Asian trough was weak.The southerly flow was conducive to conveying warm and wet airflow current over TP.The western and eastern parts of TP were ascending motion,prompting a wide range of snowfall weather over TP.Lower temperature help to form more snow.