Plot showing the latitudinal profile of F-region meridional wind as a function of local time for the day of 4 January 2019.
Latitudinal profile of F-region meridional wind, depicted by the background color hue, as a function of local time for the day of 4 January 2019. The large region of blue colored hue represents the cross-polar jet, which is seen to stall just equatorward of Poker Flat (dashed horizontal line) between approximately 10 to 13 hours UT. The color bar indicates the magnitude of the meridional wind speed, while arrows in the plot show geomagnetically aligned wind vectors as indicated by the wind scale at the bottom right of the figure. Credit: Itani and Conde [2021], Figure 7
Editors’ Highlights are summaries of recent papers by AGU’s journal editors.
Source: Journal of Geophysical Research: Space Physics

In the polar cap region, collisions between the large antisunward flow of ions and neutral particles drives a strong wind from the dayside to the nightside, particularly near the midnight sector. Until now the current belief was that, emerging from the polar cap, this neutral wind would penetrate to sub-auroral latitudes well equatorward of Poker Flat, Alaska at about 65 degrees North. However, ground-based observations by Itani and Conde [2021] of the winds near 240 kilometers in altitude over Alaska have revealed that occasionally the winds behave very differently.

The winds can stall quite abruptly over short distances of 100 to 200 kilometers, long before reaching sub-auroral latitudes. Occurrences of this infrequent phenomenon appear to be favored during mid-winter, and at times of low solar activity and low to moderate geomagnetic activity and is probably the result of the reduced pressure gradients associated with weaker dayside solar heating and the reduced forcing of the winds through collisions with ions when the ion densities are lower.

Simulations conducted with the Thermosphere Ionosphere Electrodynamics General Circulation Model, with approximately 280-kilometer grid point separations, were unable to reproduce the wind stalling pattern.

This observation of unexpected dynamics on small spatial scales is an important result for both the observational and modeling communities with the potential to motivate modeling studies to try to understand this interesting phenomenon.

Citation: Itani, R., & Conde, M. [2021]. Characterizing unexpectedly localized slowing of the thermospheric cross-polar jet of neutral wind over Alaska in the midnight sector. Journal of Geophysical Research: Space Physics, 126, e2020JA028916. https://doi.org/10.1029/2020JA028916

Text © 2021. The authors. CC BY-NC-ND 3.0
Except where otherwise noted, images are subject to copyright. Any reuse without express permission from the copyright owner is prohibited.