Characteristics and mechanisms of the annual asymmetry of thermospheric mass density

• Published in: Science China. Earth sciences Vol. 58; no. 4; pp. 540 - 550
• Main Authors: Ma, RuiPing, Xu, JiYao, Wang, WenBin, Chen, GuangMing, Yuan, Wei, Lei, JiuHou, Burns, Alan G., Jiang, GuoYing
• Format: Journal Article
• Language: English
• Published: Heidelberg Science China Press 01-04-2015; Springer Nature B.V
• Subjects: Aeronomy; Altitude; Earth and Environmental Science; Earth Sciences; Ionosphere; Research Paper; Solar activity; UV辐射; 不对称; 太阳活动; 机制; 热层; 特性; 质量密度; 随机变化; Sun-Earth distance; annual asymmetry of thermospheric mass density; solar EUV radiation
• ISSN: 1674-7313; 1869-1897
• DOI: 10.1007/s11430-014-5020-3

In this paper, globally-averaged, thermospheric total mass density, derived from the orbits of -5000 objects at 250, 400, and 550 km that were tracked from 1967 to 2006, has been used to quantitatively study the annual asymmetry of thermospheric mass density and its mechanism（s）. The results show that thermospheric mass density had a significant annual asymmetry, which changed from year to year. The annual asymmetry at the three altitudes varied synchronously and its absolute value increased with altitudes. The results suggest that there is an annual asymmetry in solar EUV radiation that is caused by the difference in the Sun-Earth distance between the two solstices and the random variation of solar activity within a year. This change in radiation results in an annual change in the thermospheric temperature and thus the scale height of the neutral gas, and is the main cause of the annual asymmetry of thermospheric mass density. The annual asymmetry of mass density increases with altitude because of the accumulating effect of the changes in neutral temperature and scale height in the vertical direction.