摘要
基于CHAMP卫星资料,分析了2002—2008年267个磁暴期间400km高度大气密度变化对季节、地方时与区域的依赖以及时延的统计学特征,得到暴时大气密度变化的一些新特点,主要结论如下：1）两半球大气密度绝对变化（δρa）结果在不同强度磁暴、不同地方时不同.受较强的焦耳加热和背景中性风共同作用,在北半球夏季,中等磁暴过程中夜侧和大磁暴中,夏半球的δρa强于冬半球;由于夏季半球盛行风环流造成的扰动传播速度快,北半球夏季日侧30°附近大气,北（夏）半球到达峰值的时间早于南（冬）半球.而可能受半球不对称背景磁场强度所导致的热层能量输送率影响,北半球夏季强磁暴和中磁暴个例的日侧,南半球δρa强于北半球;春秋季个例中日侧30°附近大气,北半球先于南半球1～2h达到峰值.2）受叠加在背景环流上的暴时经向环流影响,春秋季暴时赤道大气密度达到峰值的时间最短,日/夜侧大气分别在Dstmin后1h和2h达到峰值.至点附近夜侧赤道大气达到峰值时间一致,为Dstmin后3h;不同季节日侧结果不同,在北半球冬季时赤道地区经过更长的时间达到峰值.3）日侧赤道峰值时间距离高纬度峰值时间不受季节影响,为3h左右.在春秋季和北半球冬季夜侧,赤道大气密度先于高纬度达到峰值,且不同纬度大气密度的峰值几乎无差别,表明此时低纬度存在其他加热源起着重要作用。
During geomagnetic storms,the coupling magnetosphere-ionosphere-thermosphere system is a rather complex phenomenon,and the thermospheric mass density exhibits large deviations from the climatological behavior upon the conjunct effect of Joule/particle heating,Lorentz force,thermal expansion,upwelling,and horizontal wind circulation.Due to different weight effects,thermospheric responses might vary with different storms,and even for the same storm case resulting from unlike methods of data process.In order to know more about theseasonal,magnetic local time（MLT）and latitude dependencies and the time delay characteristic of the thermospheric response to geomagnetic storms,we investigate the thermospheric response to 267 geomagnetic storms in which the Dst minimum,Dstmin,is below-50 nT during 2002—2008.The data of thermospheric mass density normalized to 400 km is derived from the highaccuracy accelerometer on board the CHAMP satellite.Each orbit is first divided into an ascending and a descending half,which are subdivided into five latitudinal segments,namely±60°,±30°and 0°.In order to investigate the dependence of MLT,density data are sorted into 4different MLT sectors：05∶00MLT to 09∶00MLT as the dawn sector,10∶00MLT to 16∶00MLT as the noon sector,17∶00MLT to 21∶00MLT as the dusk sector,and 22∶00MLT to 04∶00MLT as the night sector.To investigate seasonal variations,the available data are subdivided into three local seasons：the northern hemisphere winter（December-February,DJF）,combined equinoxes（March-May,MAM,and September-November,SON）,and the northern hemisphere summer（June-August,JJA）.Dstminis used to identify four categories of geomagnetic storms：weak storms（-30〉Dstmin≥-50nT）,moderate storms（-50〉Dstmin≥-100nT）,intense storms（-100〉Dstmin≥-200nT）and great storms（Dstmin〈-200nT）.By this means the effects of magnetic local time,latitude,season and intensity of storm are separated.Since the quiet-time density（ρq）shows much dependence on th
出处
《地球物理学报》
SCIE
EI
CAS
CSCD
北大核心
2015年第9期3023-3037,共15页
Chinese Journal of Geophysics
基金
国家自然科学基金重点项目(41231065)
国家重点基础研究发展计划项目(2012CB825604)
航天飞行动力学技术重点实验室开放基金项目(2012afdl034)共同资助
关键词
热层大气密度
磁暴
CHAMP卫星
半球不对称性
地方时和纬度依赖
时延
Thermospheric neutral mass density
Geomagnetic storms
CHAMP
Hemisphericasymmetry
Local time and latitude dependencies
Time delay
