Global distribution of the thermospheric total mass density derived from CHAMP
Global distribution of the thermospheric total mass density derived from CHAMP
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DOI：
10.1029/2004ja010741
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发表时间：
2004-12
影响因子：
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通讯作者：
Huixin Liu;H. Lühr;V. Henize;W. Köhler
中科院分区：
文献类型：
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作者：
Huixin Liu;H. Lühr;V. Henize;W. Köhler
[1]利用CHAMP卫星上的高精度加速度计获得了400 km高度的热层总质量密度的全球分布，具有良好的时空覆盖。它显示了两个有趣的特征。一是低纬度地区的异常分布。在地磁地方时10点到20点之间，热层密度在赤道两侧地磁纬度20°-25°左右达到最大值，而不是在赤道的白天侧赤道达到最大值。这种纬向分布与赤道电离异常非常相似，从而表明通过电离层-热层耦合对热层质量密度的强磁控制。在午夜前不久，热层密度在赤道的夜侧出现了二次极大值，这让人想起了众所周知的热层午夜温度极大值。另一个值得注意的特征是，热层密度在高纬度地区高度结构化，局部密度增强可能与焦耳/粒子加热有关。然而，这种结构与美国国家大气研究中心在海拔120-300公里处的热层环流模式所认可的细胞结构不同。这表明精确的蜂窝结构可能不一定延伸到400公里。与质谱仪非相干散射1990 （mss90）模式预测结果的比较表明，该模式虽然较好地描述了观测密度的一般结构，但完全忽略了低纬度地区的双峰。这导致在波峰区域总质量密度低估了15-20%。在高纬度地区，午夜扇区和尖峰区出现20-30%的低估。在这些局部区域之外，观测和预测之间的一致性相当好，在安静的地磁条件下平均只有~ 5%的差异。
[1] A global distribution of the thermospheric total mass density at 400 km altitude is derived from the high-accuracy accelerometer on board the CHAMP satellite with good temporal and spatial coverage. It shows two interesting features. One is the anomalous distribution at low latitudes. Instead of maximizing at the dayside equator, the thermospheric density shows maxima at about 20°–25° geomagnetic latitude on both sides of the equator between 10 and 20 magnetic local time. This latitudinal distribution resembles fairly well the equatorial ionization anomaly, thus indicating strong magnetic control of the thermospheric mass density via ionosphere-thermosphere coupling. The thermospheric density shows a secondary maximum at the nightside equator shortly before midnight, in reminiscence of the well-known thermospheric midnight temperature maximum. Another feature to notice is that the thermospheric density is highly structured at high latitudes, with localized density enhancements possibly related to Joule/particle heating. This structure is, however, different from the cellular structure recognized by the National Center for Atmospheric Research thermosphere general circulation model at altitudes of 120–300 km. This indicates that the exact cellular structure may not necessarily extend to 400 km. A comparison between observations and the Mass Spectrometer Incoherent Scatter 1990 (MSIS90) model predictions shows that although the model describes the general structure of the observed density reasonably well, it misses the double peaks at low latitudes completely. This causes an underestimation of the total mass density by 15–20% in the crest region. At high latitudes an underestimation of 20–30% occurs in the midnight sector and the cusp region. Outside these localized areas the agreement between observations and predictions is quite good, with only ∼5% difference on average under quiet geomagnetic conditions.