Explicit Global Simulation of Gravity Waves in the Thermosphere

Explicit Global Simulation of Gravity Waves in the Thermosphere

We present a new version of the high‐resolution Kühlungsborn Mechanistic general Circulation Model (KMCM) extended to z ∼ 450 km. This model is called HIAMCM (HI Altitude Mechanistic general Circulation Model) and explicitly simulates gravity waves (GWs) down to horizontal wavelengths of λh ∼ 165 km. We find predominant tertiary GWs in the winter thermosphere at middle/high latitudes. These GWs typically have horizontal wavelengths λh ∼ 300–1,100 km, ground‐based periods ∼ 25–90 min, and intrinsic horizontal phase speeds cIh ∼ 250–350 m s−1. Above z ∼ 200 km, the predominant GW horizontal propagation directions are roughly against the background winds from the diurnal tide; the GWs propagate mainly poleward at midnight, eastward at 6 local time (LT), equatorward at noon, and westward at 18 LT. Wintertime GWs at z ∼ 300 km having 165 km ≤ λh ≤ 330 km create a large hot spot over the Southern Andes/Antarctic Peninsula that agrees well with quiet time satellite measurements. Due to cancelation effects, the time‐averaged zonal mean Eliassen‐Palm flux divergence from the resolved GWs in the thermosphere is negligible compared to that of the tides and compared to the zonal component of the time‐averaged zonal mean ion drag. We also find that the thermospheric GWs dissipate mainly from macroturbulent diffusion and, above z ∼ 200 km, from molecular diffusion, whereas the tides dissipate mainly from ion drag. The averaged dissipative heating in the thermosphere due to tides is much stronger than that due to GWs.

我们提出了一个新版本的高分辨率屈隆斯博恩机制通用环流模型（KMCM），其扩展到了约450公里的高度。这个模型被称为HIAMCM（高海拔机制通用环流模型），它能明确模拟水平波长低至约165公里的重力波（GWs）。我们在中高纬度的冬季热层中发现了主要的三级重力波。这些重力波通常具有水平波长约300 - 1100公里、地基周期约25 - 90分钟以及固有水平相速度约250 - 350米/秒。在约200公里以上，主要的重力波水平传播方向大致与由日潮引起的背景风相反；重力波在午夜主要向极地传播，在当地时间6时向东传播，在中午向赤道传播，在当地时间18时向西传播。在约300公里高度且水平波长在165公里≤λh≤330公里的冬季重力波在南安第斯山脉/南极半岛上空形成了一个大热斑，这与卫星在平静时段的测量结果非常吻合。由于抵消效应，热层中已解析的重力波的时间平均纬向平均伊莱亚森 - 帕尔姆通量散度与潮汐的相比以及与时间平均纬向平均离子阻力的纬向分量相比是可忽略不计的。我们还发现热层中的重力波主要通过宏观湍流扩散耗散，在约200公里以上还通过分子扩散耗散，而潮汐主要通过离子阻力耗散。热层中由潮汐引起的平均耗散加热比由重力波引起的要强得多。