Climatology of medium-scale thermospheric gravity waves simulated by high-resolution Whole Atmosphere Model

Gravity waves (GWs) propagate vertically and horizontally away from their source regions and play an important role in coupling of energy and momentum between different regions of the Earth’s atmosphere. Even though GWs have been widely observed at higher altitudes, there is still a lack of understanding of their characteristics in the ionosphere and thermosphere (IT) region because of lack of direct observations and their broad spatial and temporal spectrum. The improvement in computing resources has led to the development of high-resolution space weather models, enabling the investigation of much larger spectrum of GWs and comparison with observations. In this study, we use the high-resolution Whole Atmosphere Model, WAM (T254), with horizontal resolution of ~0.5o, to investigate the climatology and characteristics of quiet-time medium-scale thermospheric GWs with scale lengths between ~150-620 km. The largest GW activity is observed in the mesosphere and lower thermosphere region. During equinoxes, GW activity is observed at low-mid latitudes and is attributed to upward propagating waves generated in the lower atmosphere from tropical convection and orography. During solstices, GW activity is observed in the mid-latitude winter hemisphere and is attributed to the waves propagating up from the polar winter jet stream. At high latitudes, in all the seasons, thermospheric GWs are generated in situ due to auroral precipitation and Joule heating. When GW activity along only the dawn-dusk sector is extracted, larger values are obtained over the continents further signifying lower atmospheric origin. We also discuss the GW time periods, phase speeds, and local time and height dependence of GW spectrum. Our results in the IT region agree with the previous observations of GWs from TIMED, GOCE and CHAMP satellites and ground-based observations. We also find that T254 version has a larger temporal variability in the thermosphere than the lower-resolution model (T64). Thus, we show that the high-resolution GCM, WAM is able to realistically simulate the generation, propagation and dissipation of GWs and the resulting variability in the IT region.