High‐Latitude Observations of a Localized Wind Wall and Its Coupling to the Lower Thermosphere

Reversals in the thermospheric zonal winds at altitudes of 140 to 250 km from eastward to westward have been found at southern geographic latitudes between 60° and 70°. These are confined to a narrow region between 100° and 200° in longitude with zonal velocities regularly of −400 m/s, sometimes reaching −600 m/s, so sharply defined that the authors describe it as a “wind wall.” The observations were made by the Wind Imaging Interferometer on National Aeronautics and Space Administration's Upper Atmosphere Research Satellite, and they occur as the field of view crosses the high polar cap wind field. The wind reversals at the wall boundaries create a convergence on the west side of the wall and a divergence on the east side that potentially generate vertical flows, consistent with observed perturbations in the O(1S) emission rate. They are present about one half of the time in local summer and autumn. Plain Language Summary We have an appreciation of the wind that greets us when we step outdoors. These winds are driven by heat from the Sun combined with effects from the Earth's rotation and have velocities of a few tens of miles per hour, exceeding 70 miles/hr during hurricanes. This paper is concerned with different winds, in the polar regions at altitudes above 150 miles. Here the Sun affects the atmosphere in a different way where electrically charged particles from the Sun in what is called the solar wind drive the electrically charged particles (ions) in the Earth's ionosphere to high velocities. The ions in turn collide with neutral atoms, bringing them up to high velocity. For this paper, an instrument called the Wind Imaging Interferometer measured these winds at over 1,000 miles/hr near the Earth's poles, with a very sharp reversal in their direction at the lower‐latitude boundary. These reversals were shown to compress the atmosphere, or decompress it, causing upward and downward flows reaching as low as 60‐mile altitude. In other words, high‐latitude winds cause vertical motions that have huge impact on the composition of the high atmosphere, resulting in effects that have yet to be fully explored. Key Points A “wind wall” of thermospheric zonal wind,up to 600 m/s is observed at 100 degrees to 200 degrees longitude at southern latitudes of 60 degrees to 70 degrees The wall is also present in the Northern Hemisphere; for both hemispheres it is located close to their Magnetic Dip Pole The influence of this thermospheric feature is seen as low as 10