Monthly Climatologies of Zonal‐Mean and Tidal Winds in the Thermosphere as Observed by ICON/MIGHTI During April 2020–March 2022

Abstract

The uppermost layer of the Earth's atmosphere, the thermosphere, extends from ∼90 up to ∼600 km (e.g., Kato, 2007;Richmond, 1983). Early studies evaluated densities of the thermosphere based on the measurement of orbital decay of artificial satellites. Jacchia (1965) developed a global empirical model of thermospheric densities under the assumption of diffusive equilibrium. A by-product of the model was an estimate of the global distribution of air pressure. Theoretical studies found that the model pressure provides useful information for evaluating the global wind system in the thermosphere (Geisler, 1967;Kohl & King, 1967). It has been demonstrated that global motion of the air above approximately 150 km is primarily driven by solar-induced pressure gradients. That is, horizontal winds blow from the higher-temperature (and higher-pressure) dayside to the lower-temperature (and lower-pressure) nightside. On the other hand, the motion of the air in the lower thermosphere (<150 km) is often dominated by waves from the lower layers of the atmosphere. In particular, atmospheric tides (e.g., Lindzen & Chapman, 1969) are known to play an important role in the meteorology of the mesosphere and lower thermosphere.Theoretical models of the thermosphere were developed and used to explain how solar heating, as well as Joule heating in the polar region, drives the global circulation of the thermosphere under different seasonal conditions (e.g.,

Climatology of Dayside E‐Region Zonal Neutral Wind Shears From ICON‐MIGHTI Observations

“…The other transition occurs at ∼97 km in the 10°S-25°N range, with winds turning from a trend toward westward to eastward direction. This tendency is roughly consistent with the wind pattern shown in the Figure 2 of Yamazaki et al (2023), which estimated the latitudealtitude variation of zonal mean zonal wind using ICON MIGHTI data and compared the observation with HWM14 model. The results show that generally below 110 km, there are prevailing westward winds in the 10°S-10°N latitudes and a transition from eastward to westward winds in the ∼20°N-40°N latitudes.…”

“…The likely wavenumber 4 of the longitudinal variations of positive shears shown in the Figure 5b are consistent with modulation by DE3 zonal winds, which have strong signals at ∼100-110 km near the equator during July-November (Y. Yamazaki et al, 2023). Plotting the mean shears in the longitude versus LT at ∼110 km in 10°S- 10°N during fall (not shown) reveals an eastward inclination close to 3.75°/hr, which might partially suggest modulation by DE3 zonal winds.…”

Large‐Scale Wave‐Driven Interactions and Plasma‐Neutral Coupling in the Low‐Latitude Ionosphere‐Thermosphere

“…CTMT has been successful in interpretating the Michelson Interferometer for Global Highresolution Thermospheric Imaging (MIGHTI) instrument on the Ionospheric CONnections (ICON)-derived zonal and meridional wind diurnal/semidiurnal tidal amplitudes for viscous dissipation and vertical coupling during solar low conditions (Forbes et al, 2022;Gasperini et al, 2023), but without in situ sources of excitation due to tide-tide or tide-ion drag nonlinear interactions. Even though the lower thermospheric tidal amplitudes are often larger in ICON/MIGHTI than CTMT, their structures and seasonal variations are in good agreement (Yamazaki et al, 2023). CTMT tidal components have been used and compared to many observational studies, in particular satellite observations (e.g., Forbes et al, 2012Forbes et al, , 2014Forbes et al, , 2022Gasperini et al, 2023;Lieberman et al, 2013;Molina & Scherliess, 2023).…”

Horizontal structure of convergent wind shear associated with sporadic E layers over East Asia

“…The physics of mid-latitude Es layer formation has been described by the wind shear theory (Whitehead, 1961). The long-lived metallic ions (Fe + , Mg + ) (Plane et al, 2015) are converged into a thin layer in the ionospheric E region by vertical shears (Yamazaki et al, 2023;Zhou BZ et al, 2022) in the horizontal neutral winds. The seasonal and geographic dependence of the occurrence of Es layers, which can be attributed to the combined interaction of global neutral wind shear and the geomagnetic field, has been well explained by simulations (Chu YH et al, 2014;Shinagawa et al, 2017;Yu BK et al, 2019;Qiu LH et al, 2019) and observations (Liu Y et al, 2018;.…”