Characteristics and mechanisms of the annual asymmetry of thermospheric mass density

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.

在这份报纸，全球性平均， thermospheric 总数团密度，在从 1967 ～ 2006 被追踪的 250， 400，和 550 km 源于 5000 个目标的轨道，习惯于份量上学习 thermospheric 质量的年度不对称现象密度和它的机制。结果证明那 thermospheric 团密度有重要年度不对称现象，它从年改变了到年。在三高度的年度不对称现象同时地变化了，它的绝对值与高度增加了。结果建议在被差别在一年以内在在二至和太阳的活动的随机的变化之间的太阳地球远处引起的太阳的 EUV 放射有年度不对称现象。在在在 thermospheric 温度并且这样的一个年度变化的放射结果的这个变化中立气体的规模高度，并且是 thermospheric 质量的年度不对称现象的主要原因密度。因为变化的积累的效果，集体密度的年度不对称现象在垂直方向在中立温度和规模高度与高度增加。