| As a typical type of disastrous space weather events,geomagnetic storms have a significant impact on the upper and middle atmosphere.In this theis project,we use the Thermosphere Ionosphere Mesosphere Electrodynamics General Circulation Model(TIMEGCM)to simulate the the effects of the magnetic storm in April 2002 caused by a CME.The simulation results show that the storm-time global temperature and wind variations in the mesosphere and lower thermosphere(MLT)region.By using the diagnostic analysis of outputs of the thermodynamics and dynamics solvers of the TIMEGCM,we,for the first time,describe and understand the physical mechanisms that cause the storm-time temperature and wind changes in the MLT region at both the high latitudes and the middle and low latitudes.In this work,we futher show that not only is the upper and middle atmosphere influenced by storms,but also the signal of the magnetic storms can be found in the troposphere.Using cross-wavelet analysis,GAM,MK,and other statistical methods,we report a possible correlation between the heat source of the Qinghai-Tibet Plateau in summer and solar and geomagnetic activities.Then,we investigate the responses to the lower atmosphere circulation when the heat source of the Qinghai-Tibet Plateau is abnormal in summer.Based on the Sichuan precipitation anomaly events in 2008,we delineate the relationship between the summer heat source anomaly over the Qinghai-Tibet Plateau and the precipitation anomaly events.The main conclusions of this PhD thesis project are as follows:(1)The storm time temperature changes(storm-quite)at high latitudes in the mesosphere and lower thermosphere(MLT)region inclue both increases and decreases.The temperature variations at high latitudes from 0:00 to 12:00 local time(LT)is negative,whereas the temperature changes from 12:00 to 24:00 LT is positive.In the MLT region and high latitudes,adiabatic heating/cooling and vertical advection associated with vertical wind variations are the most important heating processes during geomagnetic storms.Joule heating contributes to the total heating in the aurora oval.The MLT vertical winds in the auroral oval are consistent with the vertical winds in the upper thermosphere.The storm-time vertical wind changes from 0:00-12:00 LT are upward,but downward from 12:00-24:00 LT.However,the storm-time vertical wind variaitons in the polar cap are only consistent with those below 220 km.In the aurora oval,Ion drag is the most important forcing process,both in the meridional and zonal directions.Pressure gradient and Coriolis force also contribute to the storm-time wind changes.Inside the polar cap,the temperature-induced pressure gradient force and the Coriolis force are the most important forcing processes.Ion drag also contributes to the momentum blance.Viscosity and horizontal advection sometimes contribute to the force balance too.(2)Large temperature increases at middle and low latitudes in the MLT region were observed by Lidar during the 04/17/2002 geomagnetic storm.Our TIMEGCM simulations have reporduced the characterictics of the observed temperature changes.A diagnostic analysis of the model outputs has been carried out to understand the physical processes driving the temperature variations during the storm.The storm-time temperature changes are produced mainly by compressional/expansion heating/cooling that is associated with the storm-time varying global neutral wind circulation,with contributions from vertical heat advection.The storm-time temperature variations depend on local time and latitudes.Nighttime temperature changes occur faster than those in the daytime and the time delay of temperature peak relative to the commencement of the storm increases with decreasing latitude.(3)Thermosphere Ionosphere Mesosphere Electrodynamics General Circulation Model(TIMEGCM)simulations are also diagnostically analyzed to investigate the causes of mesosphere and lower thermosphere(MLT)wind changes at middle latitudes during the 17/04/2002 storm.In the early phase of the storm,middle-latitude upper thermospheric wind changes are greater and occur earlier than MLT wind changes.The horizontal wind changes cause downward vertical wind changes,which are transmitted to the MLT region.Adiabatic heating and heat advection associated with downward vertical winds cause MLT temperature increases.The pressure gradient produced by these temperature changes and the Coriolis force then drive strong equatorward meridional wind changes at night,which expand toward lower latitudes.Momentum advection is minor.As the storm evolves,the enhanced MLT temperatures produce upward vertical winds.These upward winds then lead to a decreased temperature,which alters the MLT horizontal wind pattern and causes poleward wind disturbances at higher latitudes.(4)As the third pole on the Earth,the Tibetan Plateau is one of the most sensitive systems to solar activity.In Tibetan Plateau solar shortwave radiation can rapidly be translated directly to long-wave radiation,heating the upper atmosphere and affecting climate and atmospheric circulation in the north hemisphere.Using sunspot number,the geomagnetic Ap index,and NCEP/NCAR reanalysis data,and the Generalized Additive Model(GAM),we investigate the correlation between solar activity and the summer atmospheric heat source over the eastern Tibetan Plateau.The summer atmospheric heat source over the eastern Tibetan Plateau has two cycles that are the same as those solar activity,including the Schwabe cycle(11-year)and the Hale cycle(22-year);the Schwabe cycle plays a dominant role in the summer atmospheric heat source over the eastern Tibetan Plateau;In the interannual time scale,the solar shortwave radiation and the geomagnetic Ap index can make contributions of?34.5%and 27.1%to the summer atmospheric heat source,respectively.However,since 1994,the influence of Ap reaches 63.6%for the summer atmospheric heat source over the eastern Tibetan Plateau,which is stronger than that of the solar short wavelength radiation.(5)Using the NCEP/NCAR reanalysis data and monthly precipitation data from160 stations in China,we analyze the relationship between the summer heat source in the eastern Qinghai-Tibet plateau and 100 hPa,500 hPa and 850 hPa height fields.When summer heat source in the eastern Qinghai-Tibet plateau is strong,100 hPa height field shows anomaly which leads to the abnormal South Asia high pressure.Then,the western Pacific subtropical high responds to the anomaly South Asia high.If 500 hPa and 850 hPa height fields and 500 hPa wind fields are unusual,the abnormal kinetic energy and abnormal tropical convection will happen.As an example,we show the background of rainstorm in the Sichuan basin and explain the relationship between the rainstorm in Sichuan basin and the summer heat source in the eastern Qinghai-Tibet plateau. |
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