Bibliography

Investigation of sudden electron density depletions observed in the dusk sector by the Poker Flat, Alaska incoherent scatter radar in summer

This paper investigates unusually deep and sudden electron density depletions (troughs) observed in the Poker Flat (Alaska) Incoherent Scatter Radar data in middle summer of 2007 and 2008. The troughs were observed in the premidnight sector during periods of weak magnetic and solar activity. The density recovered to normal levels around midnight. At the time when the electron density was undergoing its steep decrease, there was usually a surge of the order of 100 to 400 K in the ion temperature that lasted less than 1 h. The Ti surges were usually related to similar surges in the AE index, indicating that the high-latitude convection pattern was expanding and intensifying at the time of the steep electron density drop. The convection patterns from the Super Dual Auroral Radar Network also indicate that the density troughs were associated with the expansion of the convection pattern to Poker Flat. The sudden decreases in the electron density are difficult to explain in summer because the high-latitude region remains sunlit for most of the day. This paper suggests that the summer density troughs result from lower latitude plasma that had initially been corotating in darkness for several hours post sunset and brought back toward the sunlit side as the convection pattern expanded. The magnetic declination of ~22\textdegree east at 300 km at Poker Flat greatly facilitates the contrast between the plasma convecting from lower latitudes and the plasma that follows the high-latitude convection pattern.

Richards, P.; Nicolls, M.; St.-Maurice, J.-P.; Goodwin, L.; Ruohoniemi, J.;

Published by: Journal of Geophysical Research: Space Physics      Published on: 12/2014

YEAR: 2014     DOI: 10.1002/jgra.v119.1210.1002/2014JA020541

ion temperature; plasma convection; plasma troughs

Ionospheric storm time dynamics as seen by GPS tomography and in situ spacecraft observations

During major geomagnetic storms anomalous enhancements of the ionospheric density are seen at high and middle latitudes. A number of physical mechanisms have been invoked to explain these storm time density anomalies including an expansion of high-latitude electric plasma convection to midlatitudes, thermospheric neutral winds, and changes in the ionospheric composition. However, it remains unclear which mechanism plays the dominant role in the formation of storm time density anomalies, partly because of insufficient coverage of the measurements of global electric convection and thermospheric winds at midlatitudes. This paper describes a novel technique for extracting the storm time E × B convection boundary from in situ measurements of plasma bulk motion obtained by LEO DMSP satellites. The convection boundary estimated from the DMSP data during major magnetic storm of 20 November 2003 has been compared with the global distributions of the ionospheric plasma deduced from characteristics of GPS signals acquired by a ground-based network of GPS receivers. The tomographic inversion of GPS data using a three-dimensional time-dependent inversion technique reveals the spatial and temporal evolution of the storm time density anomaly. Comparison between the tomographic reconstructions of the ionospheric plasma distributions and in situ DMSP measurements of plasma bulk motion suggests that the convective flow expanded low enough in latitude to encompass, in part, the formation of the midlatitude TEC anomaly. Some features of the TEC dynamics observed during the 20 November 2003 storm, however, suggest that mechanisms other than the expanded ionospheric convection (such as thermospheric neutral winds) are also involved in the formation of the midlatitude anomaly.

Pokhotelov, D.; Mitchell, C.; Spencer, P.; Hairston, M.; Heelis, R.;

Published by: Journal of Geophysical Research: Space Physics      Published on:

YEAR: 2008     DOI: https://doi.org/10.1029/2008JA013109

Ionospheric storms; Tomography; plasma convection

Undulations on the equatorward edge of the diffuse proton aurora: TIMED/GUVI observations

Undulations on the equatorward edge of the diffuse proton aurora have been identified by using TIMED/GUVI auroral images in the far ultraviolet wavelengths. While undulations have been previously reported on the duskside (Lui et al., 1982), GUVI observations show the undulation also occurs in the dayside, nightside, and morningside. The GUVI proton auroral images provide direct optical evidence that the undulations occur in the proton aurora. It is also the first detection of the undulation in the dayside indicating strong convection shear in the region. The undulation in the nightside, a wavy structure in the whole diffuse proton aurora, is significantly different from those in the duskside and dayside. While almost all of the undulation events are observed during magnetic storms (Dst \< -60 nT), one exceptional case shows undulation in the dayside with Dst = 30 nT. However, the case is associated with a large solar wind speed (650 km/s) and a high dynamic pressure (14 nPa). Coincident DMSP SSIES observations suggest that both large ion drift velocity (\>1000 m/s) and strong velocity shear (\>0.1 s^-1) within the diffuse aurora oval are necessary conditions for the undulation to occur. The SSIES data also indicate the areas with large ion drift velocity and shear move to higher latitudes in the MLT sectors toward midnight. This may explain why the undulation is rarely detected in the nightside.

Zhang, Y.; Paxton, L.; Morrison, D.; T. Y. Lui, A.; Kil, H.; Wolven, B.; Meng, C.-I.; Christensen, A.;

Published by: Journal of Geophysical Research      Published on: 09/2005

YEAR: 2005     DOI: 10.1029/2004JA010668

auroral undulation; K-H instability; Magnetic storm; plasma convection