Dayside Vertical Wind Reversal at Transition Altitude From E to F Regions Observed by the ICON Satellite

The Michelson Interferometer for Global High‐Resolution Thermospheric Imaging (MIGHTI) onboard the Ionospheric Connection Explorer (ICON) mission measures the neutral winds from about 88 to 310 km altitudes, which provides a good opportunity to investigate the vertical distribution of the neutral winds. In this study we used the green line of MIGHTI to focus on the wind reversal due to large vertical shears at the transition altitude from E to F regions (∼120–220 km). For the limitations of green line filter during night‐time, we therefore present only the results on the dayside from 0600 to 1800 local time (LT). Based on more than 2 years data, there were 206 and 96 orbits identified with clear wind reversal in the meridional and zonal components, respectively. These events almost covered the whole altitude of ∼120–220 km. Interestingly, such wind reversal occurs mostly (about 75%) during magnetic quiet periods with Kp less than 2. Their dependences on LT, geographic latitude (Glat) and longitude (Glon) have been further analyzed. Two different trends for the wind reversals on LT dependence have been found, for example, the mean altitude of meridional (zonal) wind reversal is higher at dawn, and then slowly decreases toward dusk; or the mean altitude of wind reversal is higher at dusk and slowly decreases toward dawn. Such two kinds of altitude trends of wind reversal are also found for the dependence on Glat, but not on Glon. In addition, we find that there are about 90% orbits with wind reversal simultaneously observed at the low E and F regions, but the altitude variations of wind reversal can be the same or opposite in the two regions, even for the same orbit. This result suggests that the wind reversals at the low E and low F regions should be different. The climatology of the wind reversals at low F region observed by ICON provides helpful constrain for the neutral wind simulation based on physical models. Key Points Clear wind reversals due to large vertical shears were identified in the meridional and zonal components of ICON wind observations The wind reversal of both meridional and zonal winds show two types of altitude variations on local time and latitude For most orbits with wind reversal identified at low F region, there are wind reversals simultaneously observed at low E region