A statistical analysis of longitudinal dependences of upper thermospheric zonal winds at dip equator latitudes derived from CHAMP
A statistical analysis of longitudinal dependences of upper thermospheric zonal winds at dip equator latitudes derived from CHAMP
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DOI：
10.1016/j.jastp.2007.04.004
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发表时间：
2007-08
影响因子：
1.9
通讯作者：
K. Häusler;H. Lühr;S. Rentz;W. Köhler
中科院分区：
文献类型：
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作者：
K. Häusler;H. Lühr;S. Rentz;W. Köhler
CHAMP 卫星上的加速计获得的新观测结果揭示了热层纬向风的详细图像。基于三年的数据（2002-2004），我们研究了赤道纬向三角洲风（与纬向平均值的偏差）的纵向依赖性。大量的通道（∼33750）允许同时考虑风特性的多个方面。在本次分析中，我们推导了约 400 公里高度处纬向三角洲风的纵向变化，并研究了其对太阳通量、磁活动和季节的依赖性。主要的纵向依赖性仅限于当地时间 (LT) 上午时间 03-09。三角洲风的幅度大约与磁倾角赤道距地理赤道的纬度位移成正比。三角洲风的方向在六月至十二月之间反转。在春分季节，这些大型特征几乎不存在。太阳能 EUV 的通量水平对纵向变化没有显着影响。仅在日落后的时间内（即 18 至 21 LT）才能发现对磁活动的依赖性。对我们的三角洲风速进行傅里叶变换揭示了一些 LT 扇区的春分数据中波数 4 占主导地位。波 4 结构是缓慢进动卫星框架中的一个主要特征，最近有报道，例如TIMED 卫星上的 SABRE 仪器在中层低层热层 (MLT) 区域进行非迁移潮汐温度测量。因此，这项对纬向风纵向依赖性的统计研究为非迁移潮汐耦合各大气层提供了新的观测证据。
New observations, obtained by the accelerometer onboard the CHAMP satellite, reveal a detailed picture of the thermospheric zonal wind. Based on three years of data (2002–2004) we have studied the longitudinal dependence of the zonal delta wind (deviations from the zonal average) at the dip equator. The large number of passes (∼33750) allows to consider several aspects of the wind characteristics at the same time. For this analysis we derived the longitudinal variation of the zonal delta wind at about 400km altitude and investigated its dependence on solar flux, magnetic activity, and season. Major longitudinal dependences are confined to the morning hours, 03-09 local time (LT). The amplitude of the delta wind is approximately proportional to the latitudinal displacement of the magnetic dip equator from the geographic equator. The direction of the delta wind reverses sign between the June and December Solstices. During Equinox seasons these large scale features are almost absent. The flux level of solar EUV has no significant influence on the longitudinal variations. A dependence on magnetic activity could only be found during the post-sunset hours, 18-21 LT. Performing a Fourier transform of our delta wind velocities revealed a dominance of the wavenumber 4 in the Equinox data at some LT sectors. The wave-4 structure is a prevailing feature in the slowly precessing satellite frame, which has been recently reported, e.g. in nonmigrating tidal temperature measurements of the SABER instrument on the TIMED satellite in the Mesosphere Lower Thermosphere (MLT) region. Therefore, this statistical study of zonal wind longitudinal dependences provides new observational evidence for the coupling of the various atmospheric layers by nonmigrating tides.