edu.ucar.opensky::articles:12902 UCAR/NCAR - Library OpenSky Support PO Box 3000 Boulder CO 80307-3000 opensky@ucar.edu http://opensky.ucar.edu/ homepage pointOfContact 2025-12-26T03:45:09.958482 ISO 19115-2 Geographic Information - Metadata - Part 2: Extensions for Imagery and Gridded Data ISO 19115-2:2009(E) https://n2t.org/ark:/85065/d7pc3383 WINDII observations and TIME-GCM simulations of O(¹S) polar spirals during geomagnetic disturbances 2013-05-28T00:00:00Z publication https://n2t.org/ark:/85065/d7pc3383 https://doi.org/10.1002/jgra.50272 Shepherd, G. author Roble, Raymond G. author Cho, Y. author UCAR/NCAR - Library publisher The daytime O(¹S) emission at 557.7 nm observed at 250 km with the Wind Imaging Interferometer (WINDII) is dominantly excited by photoelectron impact on atomic oxygen, so the volume emission rate is normally a measure of the atomic oxygen concentration. Daily polar maps of the 250 km volume emission rate during geomagnetic disturbances display polar spirals extending out of the auroral region and down to the equator. Since the local time is fixed for a given latitude for a single day, the spiral maps form a spatio-temporal pattern in which the longitudinal variations cannot be distinguished from those in universal time. Simulations for 2 January 1993 implemented with the National Center for Atmospheric Research Thermosphere-Ionosphere-Mesosphere-Electrodynamics General Circulation Model (TIME-GCM) using the equivalent satellite perspective show a remarkably similar spiral pattern. Hourly universal time simulations reveal a rapid equatorward expansion of the spirals during this modest geomagnetic event of Kp = 4.7, which are mirrored in the meridional and vertical winds. Simulations of the electron density show that the emission within the spirals is caused by the recombination of O₂+ ions with electrons, and not the atomic oxygen enhancement itself. All of this strongly suggests that the spirals are in fact large-scale Traveling Ionospheric Disturbances (TIDs), and comparisons of the WINDII data made with TID observations reported in the literature, including those made on the same day, support this conclusion. The TIME-GCM simulations suggest that a component of the spirals originates in the lower atmosphere and appears at thermospheric heights. UCAR/NCAR - Library OpenSky Support PO Box 3000 Boulder CO 80307-3000 opensky@ucar.edu http://opensky.ucar.edu/ homepage pointOfContact PDF Text theme Resource Type 2016-01-01T00:00:00Z publication Copyright 2013 American Geophysical Union. None eng geoscientificInformation