Font Size: a A A

Variation In Snow Disaster Frequency Over The Qinghai-Tibet Plateau And Its Response To Surface Sea Temperature Forcing

Posted on:2021-05-03Degree:DoctorType:Dissertation
Country:ChinaCandidate:C H LiuFull Text:PDF
GTID:1480306533492374Subject:Climate system and global change
Abstract/Summary:PDF Full Text Request
Snow disaster is the most important,influential and destructive meteorological disaster in Qinghai-Tibet Plateau.Enhancing the researches on the changing characteristics of plateau snow disaster and its driving forces is of great significance for the prevention of climatic and ecological risks in Tibetan areas.This dissertation used the data of snow depth and days with snow cover in winter half year(from October to the mid-March of next year in the Northern Hemisphere)of 72 stations on the Qinghai-Tibet Plateau from 1978 to 2014 to have defined the snow disaster occurrence index and analyzed the changing characteristics of snow disaster,adopted the optimal feedback model analysis method with the combination of general equilibrium feedback assessment and empirical orthogonal function(GEFA-EOF)to have discussed the feedback relationship of snow disaster frequency and sea temperature anomaly mode and revealed the relative contribution of sea temperature anomaly in key areas to plateau snow disaster change in key regions and its influence mechanism,and further confirmed the feedback effect of sea temperature to plateau snow disaster by using ECHAM5 model sensitivity test.The main conclusions were as follows:(1)From 1978 to 2014,the snowfall in winter half year of Qinghai-Tibet Plateau showed regional differences.The snowfall in southeast and southwest of the plateau decreased,while the snowfall in the other areas increased.In winter half year,the average temperature in Qinghai-Tibet Plateau was below zero,at-4.0?.The total days with snow cover decreased,the average snow depth showed no obvious linear changing trend,and the snow disaster frequency mainly showed a quasi-periodic oscillation of 7a.(2)In winter half year,the snow disaster frequency in Qinghai-Tibet Plateau increased from north to south.Its high-value areas were mainly concentrated in the north slope of the Himalayas and the Jiali region,and there totally occurred 80 ? 105 snow disasters.In the northwest of Qinghai and its eastern agricultural areas,there were less than 10 snow disasters.In those snowy disaster years,in the middle and high troposphere,the height field,as a whole,was low from polar to the mid-high latitude area of Asia,and the geopotential height anomaly in the mid-high latitude area of Asia and Europe presented a "+-+" distribution from west to east,which was a typical two-ridge and one-trough type.The Ural trough area led the cold air south,the plateau on its above was the abnormal center.In the middle and low troposphere,the plateau on its above was an abnormal cyclonic circulation,coupled with the abnormal anticyclonic influence near Lake Baikal,and then the easterly humid air flow in the northwest Pacific Ocean and the top of the abnormal anticyclone of the warm and humid air flow in the west southwest in the Bay of Bengal converge over the plateau.As a result,the snowfall increased.In those disaster years with less snow,the geopotential height anomaly in the midhigh latitude area of Asia and Europe presented a "+-+" distribution from west to east,which was a typical two-trough and one-ridge type.The Qinghai-Tibet Plateau was controlled by the fore-ridge northwest airflow system,and no significant water vapor was transported to the plateau area.Therefore the snowfall was reduced.(3)In winter half year,GEFA diagnosis showed that the contribution of the El Nino(TP1)mode sea surface temperature(SST)anomaly in the middle-east equator Pacific Ocean and the tropical Indian Ocean SST dipole mode(IOD)to the snow disaster frequency change was more than 45%,and,in this change,the TP1 contribution was 23.8%.When there is SST forcing of TP1 or IOD-type positive phase in the equatorial Pacific or tropical Indian Ocean SSTA,the frequency of snowstorms increases by 3.6 and 3.9 times,respectively.When El Nino occurred,a "+-+" circulation form of the middle and upper layers of the troposphere was strengthened,the air pressure of the Ural Mountains in the middle and high latitudes were abnormally high.The north of Lake Baikal and China were both abnormally low-value areas,the northwest Pacific surface had an abnormally high-value center,the East Asia major trough was weak and located westward,and there was a low-value center in the western part of the plateau.When the IOD was in the positive phase,the water vapor transport in the middle and lower layers was strengthened.The middle and high latitudes of the Eurasia continent had an abnormal anticyclone.The areas from the Iranian plateau to eastern China had an abnormal cyclone.Humid easterly air currents in the northwest Pacific entered the northern plateau under the action of abnormal anti-cyclones in the middle and high latitudes.Warm and humid air currents above the Arabian Sea were transported to the southern plateau through the Iranian Plateau under the action of the South China Sea-Bay of Bengal-Indian Ocean abnormal anticyclone.Water vapor over the plateau increased and convection was strengthened.The combined effect of the two key sea areas promoted the convergence of the airflow over the plateau,which was conducive to the occurrence of snowfall on the plateau.(4)The results of ECHAM5 model sensitivity test showed that the El Nino mode SST anomalies in the middle-east equator Pacific Ocean forced a Rossby wave train in the middle and upper layers of troposphere,and the geopotential height anomalies ranged from the tropical Pacific,north to the mid-latitude Pacific,then west to the East Asian continent,and finally to the Indian Peninsula,and it was the positive-negative-positive-negative circulation pattern,which were similar to the abnormal circulation pattern of controlling snowfall for many years.Such a circulation pattern weakened the East Asia major trough.The abnormal easterly wind on the south side of the east Asian abnormal anticyclone converged with the southerly wind from the north Indian Ocean on the plateau,which was conducive to the occurrence of snowfall.The abnormal Indian Ocean dipole-type positive phase sea temperature forced the dry and cold air currents from the east side of the Siberian abnormal anticyclone and the humid air currents from the northwest Pacific in the middle and upper layers of the troposphere to enter the plateau,which was easy to cause snowfall on the plateau.
Keywords/Search Tags:Qinghai-Tibet Plateau, snow disaster change, sea temperature anomaly, climate respons
PDF Full Text Request
Related items