Vertical Shears of Horizontal Winds in the Lower Thermosphere Observed by ICON

Abstract

Vertical shears of horizontal winds play an important role in the dynamics of the upper atmosphere. Prior observations have indicated that these shears predominantly occur in the lower thermosphere. MIGHTI observations from the Ionospheric Connection Explorer indicate that strong wind shears are a common feature of the lower thermosphere between 100–130 km, varying greatly between orbits. This work focuses on these strong shears, and examines their occurrences, horizontal scales and underlying organization. The wind shears can persist for 1000s km horizontally. Over a large data set, no preferred direction for the strong wind shears is found. The shears that persist for a short horizontal extent are slightly larger in amplitude and more numerous than those that persist across large horizontal scales. The altitude at which the strongest shears occur, regardless of the horizontal extent, show a downward progression with local time, following the climatological winds and upward propagating tides.