Research on thermospheric vertical wind using computer modeling

为了研究热层中垂直风的行为，发展了二维和三维非静力热层模式。计算结果与Fabry-Perol干涉仪观测的热层风进行了比较。当在极光弧附近观测到较大的热层垂直风时，偶尔会出现垂直风的振荡运动。这种变化可以用局部焦耳热驱动的变化来解释。另一方面，垂直风往往表现出非常复杂的行为，这表明热层动力学是由几个过程的组合控制的，如（1）热源的时空变化，（2）在其他地区产生的大尺度重力波的传播，（3）热层背景风的影响，（4）重力波之间的相互作用。在以前的模拟与极光弧有关的热层和电离层动力学，极光弧被假定为是固定的空间。然而，实际上，大多数极光弧的移动非常迅速，表明加热区也在快速移动。利用非静力学的热层-电离层模式研究了包括极光弧在内的热层和电离层动力学。通过与EISCAT观测资料的比较，我们得到以下结果：（1）当极光弧经过EISCAT雷达站上空时，EISCAT观测到的场向离子运动周期为15-40 min，幅度为10 - 30 m/s;（2）数值模拟表明，极光弧的移动产生了周期为15分钟的场向离子运动;（3）该模型还预测了当突然加热时会产生周期为30 - 40分钟的重力波;（4）该模型给出的场向离子速度往往比观测到的离子速度小。

Two- and Three- dimensional nonhydrostatic thermospheric models have been developed in order to study behavior of vertical wind in the thermosphere. The calculated results were compared with the observations of thermospheric wind obtained by the Fabry-Perol interferometers. When large thermospheric vertical wind is observed in the vicinity of an auroral arc, oscillatory motion of the vertical wind occasionally occurs. This kind of variation could be explained by variations driven by local Joule heating. On the other hand, the vertical wind often exhibits very complicated behavior, suggesting that the thermospheric dynamics is controlled by combination of several processes such as (1) temporal and spatial variations of heat sources, (2) propagation of large-scale gravity waves generated in other regions, (3) effects of background wind of the thermosphere, and (4) interaction between gravity waves. In previous modeling of thermospheric and ionospheric dynamics associated with auroral arcs, the auroral arcs are assumed to be fixed in space. In reality, however, most of auroral arcs move very rapidly, indicating the heating regions also move rapidly. We studied the thermospheric and ionospheric dynamics including moving auroral arcs using the nonhydrostatic thermosphere-ionosphere model. By comparing the model results with EISCAT data, we obtained the following results, (1) when an auroral arc passes above the EISCAT radar site, field-aligned ion motion with a period of 15-40 min. and an amplitude of 10 - 30 m/s are often observed by EISCAT ; (2) our numerical model shows that field-aligned ion motion with a period of 15 min. are generated associated with moving an auroral arc ; (3) the model also predicts that a gravity wave with a period of 30 - 40 min. is generated when sudden heating occurs ; (4) the model tends to give smaller filed-aligned ion velocities than the observed ion velocities.