Abstract The importance of gravity waves (GWs) in the redistribution of energy and momentum in the Earth's atmosphere is well known. It is extremely important to understand the nature of variation in the GW characteristics to address issues of coupling in the Earth's atmosphere. We have used digisonde measurements to investigate the variation in thermospheric wave dynamics in the daytime over low-latitudes (Ahmedabad, India) during geomagnetic quiet and disturbed times. Vertical phase speeds and wavelengths of GWs are calculated by monitoring the phase offsets in the digisonde derived height variations of constant electron densities throughout the day. During geomagnetic quiet times, the magnitudes of vertical propagation speeds of GWs and their vertical wavelengths show seasonal variation and vary in the range of 10–70 ms−1 and 70–520 km, respectively. The distributions of vertical propagation parameters of GWs for geomagnetic quiet days show two peaks annually and are anti-correlated with the thermospheric horizontal winds. As the winds over a given location flow in different directions in different seasons, this information can be used to infer the season dependent preferential direction of propagation of GWs. Changes in the vertical propagation characteristics of GWs during geomagnetic disturbed days as compared to their average quiet time values show good semblance with the integrated values of the AE index. A linear relation has been obtained between the changes in vertical phase speeds of GWs and the integrated values of AE index during geomagnetic disturbed days. This linear relation, in combination with empirical formulation arrived at for averaged values of vertical propagation speeds during geomagnetic quiet times, yields comprehensive information on propagation characteristics of GWs as a function of day of the year that includes geomagnetic disturbance conditions as well. Such systematic information on the GW characteristics in the daytime thermosphere and their quantification during geomagnetic quiet times and their changes due to enhancement in energy input at high-latitudes (as characterized by the AE index) also provides a strong and direct information on high-to low-latitude coupling.

中文翻译：

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地磁安静和扰动条件下低纬度地区白天热层重力波特征

摘要 重力波 (GW) 在地球大气中能量和动量的重新分配中的重要性是众所周知的。了解 GW 特性变化的性质对于解决地球大气中的耦合问题非常重要。我们已经使用 digisonde 测量来研究低纬度地区（印度艾哈迈达巴德）在地磁平静和干扰时期白天热层波动力学的变化。GW 的垂直相位速度和波长是通过监测全天恒定电子密度的高度变化中的相位偏移来计算的。在地磁安静时期，引力波的垂直传播速度大小及其垂直波长呈现季节性变化，变化范围为 10-70 ms-1 和 70-520 km，分别。地磁平静日引力波的垂直传播参数分布每年呈现两个峰值，与热层水平风反相关。由于给定位置上的风在不同季节沿不同方向流动，因此该信息可用于推断 GW 传播的季节相关优先方向。地磁干扰日期间 GW 的垂直传播特性与其平均安静时间值相比的变化与 AE 指数的积分值显示出良好的相似性。得到了地磁扰动日引力波垂直相位速度变化与声发射指数积分值之间的线性关系。这种线性关系，结合经验公式得出地磁静默时期垂直传播速度的平均值，产生了关于 GW 传播特性的综合信息，作为一年中某一天的函数，其中也包括地磁扰动条件。这种关于白天热层中引力波特征的系统信息及其在地磁安静时期的量化及其由于高纬度能量输入的增强（以 AE 指数为特征）而发生的变化也提供了强有力和直接的信息。低纬度耦合。