Investigation of the temperature gradient instability as the source of midlatitude quiet time decameter‐scale ionospheric irregularities: 1. Observations. Issue 6 (9th June 2014)

• Record Type: Journal Article
• Authors: de Larquier, S.; Eltrass, A.; Mahmoudian, A.; Ruohoniemi, J. M.; Baker, J. B. H.; Scales, W. A.; Erickson, P. J.; Greenwald, R. A.
• Is Part Of: Journal of geophysical research. Volume 119:Issue 6(2014:Jun.)
• Page Start: 4872
• Page End: 4881
• Publication Date: 2014-06-09
• Subjects: ionosphere -- SuperDARN -- irregularities; Magnetospheric physics -- Periodicals; Space environment -- Periodicals; Cosmic physics -- Periodicals; Planets -- Atmospheres -- Periodicals; Heliosphere (Astrophysics) -- Periodicals; Geophysics -- Periodicals; 523.01
• DOI: 10.1002/2013JA019643
• Languages: English
• ISSNs: 2169-9380

Abstract

Abstract: Super Dual Auroral Radar Network (SuperDARN) radars regularly observe decameter‐scale ionospheric irregularities at midlatitudes during quiet geomagnetic conditions. The mechanism responsible for the growth of such irregularities is still unknown. Previous results based on data from the Wallops SuperDARN HF radar and Incoherent Scatter Radar have suggested that the Temperature Gradient Instability (TGI) could be responsible for only part of the observed irregularities. This conclusion was reached based on the relative orientation of horizontal electron temperature and density gradients. However, the TGI theory requires driving gradients to be perpendicular to perpendicular to the geomagnetic fieldB . Since midlatitude field lines are approximately 20° off vertical, we have reexamined the original data and computed gradients along the meridional direction perpendicular toB . Distinctions have to be made between the topside and bottomside F region due to the strong influence of vertical gradients. We find that the TGI growth is possible in the topside F region for the duration of the experiment, even before irregularities were observed. We show that the absence of observed irregularities during favorable TGI growth conditions is not a consequence of HF propagation but of higher E region electron irregularity growth. We conclude that the TGI is a valid mechanism to explain the generation of all irregularities observed during the experiment. Key Points: The topside subauroral F region is conducive to the growth of the TGI The E region inhibits TGI growth before sunset TGI grows at kilometer scale and cascade to dam scale in the bottomside F region