In 2008, scientists reported a “superdisturbance” consisting of extreme east–west variations in wind speed in the upper atmosphere near Australia. It was not an anomaly; similar disturbances occurred in March of three different years. Building on that initial discovery, Shepherd and Shepherd now report the existence of extreme-speed wind features called “wind walls” near Earth’s magnetic poles.
The superdisturbances reported in 2008 surfaced from data captured by the Wind Imaging Interferometer (WINDII) instrument mounted on NASA’s Upper Atmosphere Research Satellite. From 1991 to 2003, WINDII measured wind flow in the lower thermosphere (at altitudes of 80–300 kilometers) by observing airglow, the luminescence of atmospheric molecules resulting from their excitement by solar radiation.
In 2017, analysis of airglow measurements from WINDII revealed perturbations of atomic oxygen levels in the same locations in the atmosphere as the superdisturbances, which prompted further investigation of the WINDII data, including moving the search nearer to the magnetic poles.
The new WINDII analysis reveals vertical wall-like channels where gentle, east flowing winds reverse and give way to extreme westward winds racing at 200–600 meters per second at altitudes of 140–250 kilometers near the south magnetic pole. These high-latitude “wind walls” occur about 50% of the time during the local summer and autumn, and similar wind walls occur near the north magnetic pole in the Northern Hemisphere’s summer and fall.
Sharp wind gradients at the walls’ boundaries result in different airflow patterns on either side of each wall, influencing vertical transport of atmospheric molecules. This airflow accounts for the atomic oxygen perturbations reported in 2017. The wind walls also appear to affect vertical transport of helium, nitrogen, and argon.
Previous research has shown that the interplanetary magnetic field can affect high-altitude, high-latitude winds. The new WINDII analysis suggests that the interplanetary magnetic field may help to shape wind walls, but more research is needed to determine the extent of this influence. (Geophysical Research Letters, https://doi.org/10.1029/2018GL077722, 2018)
—Sarah Stanley, Freelance Writer