A climatology of the F-layer equivalent winds derived from ionosonde measurements over two decades along the 120 -150 E sector
A climatology of the F-layer equivalent winds derived from ionosonde measurements over two decades along the 120 -150 E sector
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DOI：
10.5194/angeo-22-2785-2004
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发表时间：
2004-09
影响因子：
1.9
通讯作者：
X. Luan;Libo Liu;W. Wan;J. Lei;T. Yu
中科院分区：
文献类型：
--
作者：
X. Luan;Libo Liu;W. Wan;J. Lei;T. Yu
本文分析了沿着120 - 150 E经度段F层的垂直等效风（VEW），并着重分析了VEW的纬向依赖性。VEW是由14个电离层探测站20年来的月平均数据得出的。结果表明，VEW对磁纬有很大的依赖性，且关于磁赤道近似对称。在磁赤道区，它们主要受电场漂移的控制，而在中纬度则主要由中性风贡献。这两个动力学因素的相对贡献除了它们自身的大小外，还受磁倾角的调节。在低纬和高纬之间，VEW通常具有相反的方向和不同的震级。在太阳极小期，低纬度VEW的量级仅在20 - 20 m/s之间，而在高纬度VEW往往随纬度增加，通常量级在20-40 m/s之间。在太阳活动极大期，在高纬度的某些地方，VEW的幅度减少了约10-20米/秒。潮汐分析表明，主要潮汐分量的相对重要性在低纬度和高纬度之间也是不同的。VEW还取决于当地时间、季节和太阳活动。在高纬度地区，夜间VEW在午夜后有较大的震级，中午前的白天VEW也有较大的震级。VEW不仅在夜间，而且在白天都与太阳活动成反比关系，这与HWM 93模式预测的纬向风不同。VEW的纬度依赖性有两个主要趋势：一个是在最高纬度（就本工作所涉及的纬度而言）最大值;另一个是中纬度最大值。这两个纬度趋势主要取决于季节，而它们对当地时间和太阳活动的依赖相对较弱。VEW的纬向梯度也有中纬度最大的趋势，只是在某些季节，在南部较高的中纬度地区有更强的纬向梯度。白天的梯度在太阳活动最大时比最小时小得多，而在两个太阳活动水平下，它们在夜间通常相当。
The vertical equivalent winds (VEWs) at the F-layer are analyzed along the 120 -150 E longitude sec- tor with an emphasis on their latitudinal dependence. The VEWs are derived from the monthly median data of four- teen ionosonde stations over two decades. The results show that the VEWs have considerable dependences on the mag- netic latitude with an approximate symmetry about the mag- netic equator. They are mostly controlled by the electric field drifts in the magnetic equatorial region, and shift to be mostly contributed by neutral winds at mid-latitudes. The relative contribution of the two dynamic factors is regulated by the magnetic dip in addition to their own magnitudes. The VEWs generally have opposite directions and different mag- nitudes between lower and higher latitudes. At solar mini- mum, the magnitudes of VEWs are only between 20 and 20 m/s at lower latitudes, while at higher latitudes they tend to increase with latitudes, typically having magnitudes be- tween 20-40 m/s. At solar maximum, the VEWs are reduced by about 10-20 m/s in magnitudes during some local times at higher latitudes. A tidal analysis reveals that the relative im- portance of major tidal components is also different between lower and higher latitudes. The VEWs also depend on local time, season and solar ac- tivity. At higher latitudes, the nighttime VEWs have larger magnitude during post-midnight hours and so do the daytime ones before midday. The VEWs tend to have an inverse rela- tionship with solar activity not only at night, but also by day, which is different from the meridional winds predicted by the HWM93 model. The latitudinal dependence of VEWs has two prevailing trends: one is a maximum at the highest lati- tudes (as far as the latitudes concerned in the present work); the other is a mid-latitude maximum. These two latitudinal trends are mostly dependent on season, while they depend relatively weakly on local time and solar activity. The lati- tudinal gradients of VEWs also show a tendency of a mid- latitude maximum, except that there are much stronger lat- itudinal gradients at southern higher mid-latitudes in some seasons. The gradients during daytime are much smaller at solar maximum than minimum, whereas they are generally comparable at night under both solar activity levels.