Zonal winds in the equatorial upper thermosphere: Decomposing the solar flux, geomagnetic activity, and seasonal dependencies
Zonal winds in the equatorial upper thermosphere: Decomposing the solar flux, geomagnetic activity, and seasonal dependencies
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DOI：
10.1029/2005ja011415
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发表时间：
2006-07
影响因子：
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通讯作者：
Huixin Liu;H. Lühr;S. Watanabe;W. Köhler;V. Henize;P. Visser
中科院分区：
文献类型：
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作者：
Huixin Liu;H. Lühr;S. Watanabe;W. Köhler;V. Henize;P. Visser
我们利用CHAMP卫星上的加速计在3年（2002 - 2004年）中的16，400多个轨道上的测量数据，研究了热层上部赤道纬向风的气候学。注意到几个主要特征。最突出的一个是，太阳通量显着影响白天和夜间的风。它覆盖了地磁活动的影响，这被发现是相当有限的夜面。太阳通量水平从F10.7升高？100 × 10？22 W m？2赫兹？1到F10.7？190 × 10？22 W m？2赫兹？1产生一个向东扰动风高达？110米秒？1.因此，这增强了夜间东风，但抑制了白天的西风。季节性变化与较弱的风（超过50米秒？1在晚上）在6月冬至前后比在其他季节已观察到无论太阳通量和地磁活动水平。纬向风在整个晚上都是向东的，除了在6月至日附近，在那里它在午夜后的扇区中在低太阳通量水平下几乎下降到零或甚至转向西。白天的风通常比夜间的风更稳定，特别是对地磁活动没有反应。从水平风模型的预测找到良好的协议与CHAMP？观测风在高太阳通量水平在夜间。然而，在低太阳通量水平，该模型强烈低估了西风在上午的时间由50 - 120米秒？1取决于季节HWM之间的主要区别是什么？预测和CHAMP？观测到的风是在其日变化的相位中看到的。冠军？观测到的风在1200 - 1300 MLT左右向东转，而不是模式预测的1600 - 1700 MLT。与地面FPI观测和NCAR热层的比较？电离层？电动力学大气环流模式（TIEGCM）的模拟结果表明，CHAMP模拟的太阳辐射通量效应与TIEGCM模拟的结果一致。太阳通量的纬向风的依赖性，发现在这里与纬向离子漂移在以前的研究中发现的反映了E的相对重要性？而F？热层中的区域风力发电机？电离层耦合过程此外，这些风的测量表明，地球的大气层超旋转。平均超旋转速度约为22米秒？1对于F10.7的太阳通量水平？100 × 10？22 W m？2赫兹？1，但增加到63 m s？1为F10.7？190 × 10？22 W m？2赫兹？1.最后，在这项研究中提出的风的行为是纵向平均，并可能不同于风测量在一定的经度。
Using 3 years (2002–2004), over 16,400 orbits of measurements from the accelerometer on board the CHAMP satellite, we have studied the climatology of the equatorial zonal wind in the upper thermosphere. Several main features are noticed. The most prominent one is that the solar flux significantly influences both the daytime and nighttime winds. It overrides the geomagnetic activity effect, which is found to be rather limited to the nightside. An elevation of the solar flux level from F10.7 ? 100 × 10?22 W m?2 Hz?1 to F10.7 ? 190 × 10?22 W m?2 Hz?1 produces an eastward disturbance wind up to ?110 m s?1. This consequently enhances the nighttime eastward wind but suppresses the daytime westward wind. A seasonal variation with weaker wind (by over 50 m s?1 at night) around June solstice than in other seasons has been observed regardless of solar flux and geomagnetic activity levels. The zonal wind is eastward throughout the night except around June solstice, where it ebbs to almost zero or turns even westward in the postmidnight sector at low solar flux level. The daytime wind is found to be generally more stable than the nighttime wind, particularly unresponsive to geomagnetic activities. Predictions from the Horizontal Wind Model find good agreement with the CHAMP?observed wind at high solar flux levels during nighttime. At low solar flux levels, however, the model strongly underestimates the westward wind during morning hours by 50–120 m s?1 depending on season. The major difference between the HWM?predicted and the CHAMP?observed wind is seen in the phase of its diurnal variation. The CHAMP?observed wind turns eastward around 1200–1300 MLT instead of 1600–1700 MLT predicted by the model. Comparisons with ground FPI observations and the NCAR Thermosphere?Ionosphere?Electrodynamics General Circulation Model (TIEGCM) predictions show that the solar flux effect obtained from CHAMP is consistent with that modeled by TIEGCM. The solar flux dependence of zonal wind found here together with that of the zonal ion drift found in previous studies reflect the relative importance of the E? and F?region wind dynamo in the thermosphere?ionosphere coupling process. Furthermore, these wind measurements indicate that the Earth's atmosphere superrotates. The average superrotation speed amounts to about 22 m s?1 for a solar flux level of F10.7 ? 100 × 10?22 W m?2 Hz?1 but increases to 63 m s?1 for F10.7 ? 190 × 10?22 W m?2 Hz?1. Finally, the wind behavior presented in this study is longitudinally averaged and may differ from wind measurements at a certain longitude.