Medium-scale thermospheric gravity waves in the high-resolution Whole Atmosphere Model: Seasonal, local time, and longitudinal variations

• Main Authors: Malhotra, Garima, Fuller-Rowell, Timothy, Fang, Tzu-Wei, Yudin, Valery, Karol, Svetlana, Becker, Erich, Kubaryk, Adam Marshall
• Format: Journal Article
• Language: English
• Published: 28-06-2024
• Subjects: Physics - Atmospheric and Oceanic Physics; Physics - Data Analysis, Statistics and Probability; Physics - Geophysics; Physics - Plasma Physics; Physics - Space Physics
• DOI: 10.48550/arxiv.2407.00234

This paper presents a study of the global medium-scale (scales<620 km)
gravity wave (GW) activity (in terms of zonal wind variance) and its seasonal,
local time and longitudinal variations by employing the enhanced-resolution
(~50 km) Whole Atmosphere Model (WAMT254) and space-based observations for
geomagnetically quiet conditions. It is found that the GW hotspots produced by
WAMT254 in the troposphere and stratosphere agree well with previously
well-studied orographic and non-orographic sources. In the
ionosphere-thermosphere (IT) region, GWs spread out forming latitudinal
band-like hotspots. During solstices, a primary maximum in GW activity is
observed in WAMT254 and GOCE over winter mid-high latitudes, likely associated
with higher-order waves with primary sources in polar night jet, fronts and
polar vortex. During all the seasons, the enhancement of GWs around the
geomagnetic poles as observed by GOCE (at ~250 km) is well captured by
simulations. WAMT254 GWs in the IT region also show dependence on local time
due to their interaction with migrating tides leading to diurnal and
semidiurnal variations. The GWs are more likely to propagate up from the MLT
region during westward/weakly-eastward phase of thermospheric tides, signifying
the dominance of eastward GW momentum flux in the MLT. Additionally, as a novel
finding, a wavenumber-4 signature in GW activity is predicted by WAMT254
between 6-12 LT in the tropics at ~250 km, which propagates eastward with local
time. This behavior is likely associated with the modulation of GWs by wave-4
signal of non-migrating tides in the lower thermospheric zonal winds.