热层大气受太阳辐射的影响，其变化与光照时间长短密切相关，在春分、秋分、夏至、冬至期间呈现出不同的特点。通过在中国低轨道航天器上装载大气密度探测器，获得在轨原位探测数据，分析大气密度在两分两至点时的变化关系。结果表明，春分和秋分（两分点）期间全球热层大气密度随纬度对称性变化，但夏至和冬至（两至点）期间则呈现出全球热层大气密度的南北半球不对称性变化；两至点期间南北半球分别处于夏半球和冬半球，在南北高纬地区（纬度80°附近）670 km上空热层大气密度存在显著差异，探测值表示出3~3.6倍的差异，而在560 km高度上探测到两者差异可高达13倍左右，不对称程度与高度和纬度有关；探测值与模式值比较表明，模式值对冬夏半球上空热层大气密度差异变化显著响应不足。
The thermospheric neutral density sees a strong variation during equinoxes and solstices due to the solar insolation variation. The long-term continual data from Chinese Atmospheric Density Detector installed on the satellite are used to study this variation, The main results of this study are that the thermospheric density has an obvious symmetry around March equinox and September equinox; the thermosphere density has an obvious asymmetry around June solstice and December solstice; the variations have an obvious hemispheric asymmetry in high latitude (around 80 degrees); the proportion of the atmospheric density is 3~3.6 times at the height of 670 km, 13 times at the height of 560 km; the latitude and the altitude contribute to this asymmetry; the comparison of the measured data and the NRLMSISE00 data shows that the NRLMSISE00 data cannot fully respond to the summer and winter hemisphere atmospheric density variations.
[1] Daglis I A. Space storms and space weather hazards[M]. Dordrecht:Springer, 2001.
[2] 秦国泰. 强磁暴、能量粒子暴与热层大气密度涨落之间的相关关系[J]. 空间科学学报, 2013, 33(1):39-47. Qin Guotai. Relationship between severe geomagnetic storm, energetic particle storms and thermosphere density strong disturbances[J]. Chinese Journal of Space Science, 2013, 33(1):39-47.
[3] 李永平, 朱光武, 秦国泰, 等. 不同高度和不同地磁扰动期间热层大气密度模式值与探测值的显著差异[J]. 地球物理学报, 2014, 57(11):3703-3714. Li Yongping, Zhu Guangwu, Qin Guotai, et al. Significant differences of thermosphere density between the model and the obvervation values during different altitudes and geomagnetic disturbances[J]. Chinese Journal of Geophysics, 2014, 57(11):3703-3714.
[4] Liu H, Luhr, Henize V. Global distribution of the thermospheric total mass density derived from CHAMP[J]. Journal of Geophysical Research:Space Physics, 2005, 110, A4:301.
[5] Chen G M, Xu J Y, Wang W, et al. A comparison of the effects of CIR-and CME-induced geomagnetic activity on thermospheric densities and spacecraft orbits:Case studies[J]. Journal of Geophysical Research:Space Physics, 2012, 117(A8):315.
[6] Sutton E K, Forbes J M, Nerem R S. Global thermospheric neutral density and wind response to the severe 2003 geomagnetic storms from CHAMP accelerometer data[J]. Journal of Geophysical Research:Space Physics, 2005, 110, A9:S40.
[7] 李永平, 朱光武, 秦国泰, 等. 地磁扰动期间热层大气N2数密度异常增变[J]. 中国科学:技术科学, 2014, 44(8):883-889. Li Yongping, Zhu Guangwu, Qin Guotai, et al. The abnormal variation of N2 number density in thermosphere during geomagnetic disturbance[J]. Science China Technological Sciences, 2014, 44(8):883-889.
[8] 秦国泰, 孙丽琳, 曾宏, 等. 2005年8月24日强磁暴事件对高层大气密度的扰动[J]. 空间科学学报, 2008, 28(2):137-141. Qin Guotai, Sun Lilin, Zeng Hong, et al. Disturbance of the upper atmospheric density during August 24, 2005 severe geomagnetic storm event[J]. Chinese Journal of Space Science, 2008, 28(2):137-141.
[9] Willis P, Deleflie F, Barlier F, et al. Effects of thermosphere total density perturbations on LEO orbits during severe geomagnetic conditions (Oct-Nov 2003) using DORIS and SLR data[J]. Advances in Space Research, 2005, 36(3):522-533.
[10] Bruinsma S, Forbes J M, Nerem R S, et al. Thermosphere density response to the 20-21 November 2003 solar and geomagnetic storm from CHAMP and GRACE accelerometer data[J]. Journal of Geophysical Research:Space Physics, 2006, 111(A6):03.
[11] Qin G, Qiu S, Ye H, et al. The thermospheric composition different responses to geomagnetic storm in the winter and summer hemisphere measured by "SZ" atmospheric composition detectors[J]. Advances in Space Research, 42(7):1281-1287.
[12] Lei J H, Matsuo T, Dou X K, et al. Annual and semiannual variations of thermospheric density:EOF analysis of CHAMP and GRACE data[J]. Journal of Geophysical Research:Space Physics, 2012, 117(A1):310.
[13] Qian L Y, Solomon S C, Kane T J, et al. Seasonal variation of thermospheric density and composition[J]. Journal of Geophysical Research:Space Physics, 2009, 114(A1):312.
[14] Liu J, Liu L B, Zhao B Q, et al. Superposed epoch analyses of thermospheric response to CIRs:Solar cycle and seasonal dependencies[J]. Journal of Geophysical Research:Space Physics, 2012, 117(A9):L10.
[15] Weng L B, Lei J H, Doornbos E, et al. Seasonal variations of thermospheric mass density at dawn/dusk from GOCE observations[J]. Journal of Geophysical Research, 2018, 36(2):489-496.
[16] Xu J Y, Wang W B, Lei J H, et al. The effect of periodic variations of thermospheric density on CHAMP and GRACE orbits[J]. Journal of Geophysical Research:Space Physics, 2011, 116, A2:315.
[17] 李勰, 徐寄遥, 唐歌实, 等. APOD卫星大气密度数据处理与标校[J]. 地球物理学报, 2018, 61(9):3567-3576. Li Xie, Xu Jiyao, Tang Geshi, et al. Processing and calibrating of in-situ atmospheric densities for APOD[J]. Chinese Journal of Geophysics, 2018, 61(9):3567-3576.
[18] Picone J M, Hedin A E, Drob D P, et al. NRLMSISE-00 empirical model of the atmosphere:Statistical comparisons and scientific issues[J]. Journal of Geophysical Research:Space Physics, 2002, 107(A12):15-16.
[19] Picone M, Hedin A E, Drob D. NRLMSISE-00 model 2001[EB/OL].[2018-10-01]. http://ccmc.gsfc.nasa.gov/modelweb/atmos/nrlmsise00.html.
[20] Emmert J T. Thermospheric mass density:A review[J]. Advances in Space Research, 2015, 56(5):773-824.
