The primary mechanism through which energy and momentum are transferred from the lower atmosphere to the thermosphere is through the generation and propagation of atmospheric waves. It is becoming increasingly evident that a few waves from the tropical wave spectrum preferentially propagate into the thermosphere and contribute to modify satellite drag. Two of the more prominent and well-established tropical waves are Kelvin waves: the eastward-propagating 3-day ultra-fast Kelvin wave (UFKW) and the eastward-propagating diurnal tide with zonal wave number 3 (DE3). In this work, Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) temperatures at 110 km and Gravity field and steady-state Ocean Circulation Explorer (GOCE) neutral densities and cross-track winds near 260 km are used to demonstrate vertical coupling in this height regime due to the UFKW and DE3. Significant inter- and intra-annual variability is found in DE3 and the UFKW, with evidence of latitudinal broadening and filtering of the latitude structures with height due to the effect of dissipation and mean winds. Additionally, anti-correlation between the vertical penetration of these waves to the middle thermosphere and solar activity level is established and explained through the effect of molecular dissipation.

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Contemporary theory, modeling, and first-principles simulations indicate that dissipation of gravity waves (GW) plays an important role in modifying the mean circulation, thermal structure, and composition of the thermosphere. GW can propagate into the thermosphere from various sources in the lower atmosphere, deposit energy, and momentum into the thermosphere, and thereby modify its mean circulation, thermal structure and composition. However, measurements that verify or constrain predictions of GW propagation well into the thermosphere, especially on a global basis, are extremely limited. In this paper total mass densities and cross-track winds between 230 and 280 km derived from accelerometer measurements on the Gravity Field and Ocean Circulation Earth Explorer (GOCE) satellite between November 2009 and October 2013 are used to reveal the global morphology of horizontal structures between 128 km and 640 km, which are assumed to mainly reflect the presence of GW. The zonal-mean RMS variability at these scales is quantified in terms of seasonal-latitudinal dependences and dawn-dusk differences, which are interpreted in terms of current theoretical and modeling results. Little evidence is found for any longitude variability that can be attributed to specific source regions, except at high latitudes where polar/auroral sources and magnetic control dominate and near the Andes and the Antarctic Peninsula during local winter.

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Meridional winds in the thermosphere are key to understanding latitudinal coupling and thermosphere-ionosphere coupling, and yet global measurements of this wind component are scarce. In this work, neutral and electron densities measured by the Challenging Minisatellite Payload (CHAMP) satellite at solar low and geomagnetically quiet conditions are converted to pressure gradient and ion drag forces, which are then used to solve the horizontal momentum equation to estimate low latitude to midlatitude zonal and meridional "synthetic" winds. We validate the method by showing that neutral and electron densities output from National Center for Atmospheric Research (NCAR) Thermosphere Ionosphere Mesosphere Electrodynamics-General Circulation Model (TIME-GCM) can be used to derive solutions to the momentum equations that replicate reasonably well (over 85% of the variance) the winds self-consistently calculated within the TIME-GCM. CHAMP cross-track winds are found to share over 65% of the variance with the synthetic zonal winds, providing further reassurance that this wind product should provide credible results. Comparisons with the Horizontal Wind Model 14 (HWM14) show that the empirical model largely underestimates wind speeds and does not reproduce much of the observed variability. Additionally, in this work we reveal the longitude, latitude, local time, and seasonal variability in the winds; show evidence of ionosphere-thermosphere (IT) coupling, with enhanced postsunset eastward winds due to depleted ion drag; demonstrate superrotation speeds of ∼27 m/s at the equator; discuss vertical wave coupling due the diurnal eastward propagating tide with zonal wave number 3 and the semidiurnal eastward propagating tide with zonal wave number 2.@en