磁層頂結構的MHD模擬研究.pdf

1、摘要由于缺少衛(wèi)星觀測數(shù)據(jù)，基于觀測的磁層頂位形模型還不夠理想。隨著計算機技術和數(shù)值模擬方法的發(fā)展，基于對磁層頂位形的物理理論研究構建的數(shù)值模擬數(shù)據(jù)是解決這一問題的有效途徑。本文采用太陽風一磁層一電離層系統(tǒng)全球磁流體力學(MHD)的數(shù)值模擬數(shù)據(jù)，研究磁層頂?shù)慕Y構及單一條件下的位形，主要研究了幾種不同太陽風動壓&和行星際磁場IMF的z分量&條件下，地球赤道面和子午面的磁層頂位置和形狀特征。對赤道面磁層頂?shù)哪M結果顯示：磁層頂日下點高度r。主

2、要由Dp控制。隨著Dp增加，磁層頂被壓縮，r。顯著減小。相同^條件下，在IMF2分量由南向(B:0)逐漸增大的過程中，r。緩慢增大。不同條件下MHD模擬所得磁層頂張角0變化較小，反映了赤道面磁層頂結構的自相似性。與Shueetal.[1998](Shue98)低緯磁層頂經(jīng)驗模型比較發(fā)現(xiàn)，MHD模擬能較好再現(xiàn)磁層頂日下點位置rQ對！^和《的依賴關系。MHD模擬和經(jīng)驗模型給出的磁層頂張角^差別較小但MHD模擬中令隨&的變化趨勢并非經(jīng)驗模型中

3、的簡單線性關系。對子午面的研究發(fā)現(xiàn)：采用以電流密度極大值為判據(jù)MHD模擬數(shù)據(jù)描繪的磁層頂位形和高緯經(jīng)驗模型Boardsenetal.[2000](B00)—致，具有內凹結構特征。論證了由于子午面存在極尖區(qū)，不能簡單利用Shueetal.[1997](Shue97)低緯磁層頂位形函數(shù)擬合計算r。。行星際磁場為南向時，隨磁場強度增強，日下點距離減??；行星際磁場為北向時，隨磁場增強，日下點距離rQ增大。動壓增大，日下點距離&減小。南向磁場增強

4、，背陽面的磁層頂張角變大。在子午面cusp磁尾側的模擬數(shù)據(jù)與Shue97模型符合較好，行星際磁場南向分量越大，磁層頂?shù)膹埥莂越大，磁層頂擴張更加顯著。在磁場為南向增大時，隨)增大aAbstractBecauseofthelackofsufficientsatellitedatatherearefewhighlatitudemagopauseshapemodels.Withthedevelopmentofcomputertechnolog

5、ynumericalsimulationmethodsthesimulationdatabasedonphysicaltheyofmagopauseisbecomingeffectivesubstitutes.Inthispapertheglobalmagohydrodynamics(MHD)numericalsimulationdataofthecoupledmodelofsolarwindmagosphereionospheresy

6、stemareusedtostudythethreedimensionalstructureofthemagopauseitsshapeatdistinctconditions.Westudythepositionshapeofthemagopauseunderseveralsolarwinddynamicpressure(Dp)interplaarymagicfield(IMF)conditions.Thesimulationresu

7、ltsofequatialplaneshowthatthesubsolarposition(r0)ofthemagopauseismainlycontrolledbyDpwithsignificantdecreasingofr0asDpincreases.AtcertainDpwhensouthernIMFB_(B_0)increasesthesubsolarpositionr0keepsgraduallyincreasing.Fall

8、casesstudiedheretheflareangle(p)ofthemagopauseexperiencesverysmallchange.Thisprovidesanevidencefthestructuralselfsimilarityofthemagopauseinequatialplane.ComparedwiththeempiricallowlatitudemagopausemodelofShue98MHDsimulat

9、ioncanreproducethedependenceofthesubsolarpointrQonDpandB:.Astotheflareangle(althoughthedifferencebetweenourMHDsimulationempiricalmodelfeachcaseisverysmallthevariationofwithIMFB_inMHDresultsisnotthelinearrelationshipassho

10、wninempiricalmodel.ItisfoundthatinthenoonmidnightmeridianplanethemagopauseshapehasevidentconcavefeatureswhichisconsistentwiththeexperiencemodelofBoardseal.[2000].Thecuspstructureofthemeridionalplanedoesnotfollowthemodelo

11、fShueetal.[1997]flowlatitudemagopause.Byanalyzingthechangeofthemagopauseshapeparametersonthenoonmidnightmeridianplaneweobtainthesameresultswiththatofempiricalmodel.Thesimulationresultsshowthatinthenoonmidnightmeridianpla