Stormtime subauroral density troughs: Ion‐molecule kinetics effects

Abstract

[1] We report on subauroral plasma density troughs observed by Defense Meteorological Satellite Program (DMSP) satellites during the major magnetic storm of 6 April 2000. The troughs were embedded within strongly irregular, !500-km wide subauroral convection streams, composed of two distinctive parts. The poleward part coincided with strong wave structures, energetic (ring current) ion precipitations, and enhanced vertical ion flows. One or several narrow density decreases were present here. The equatorward part was marked by a density trough coincident with a local maximum of the electron temperature $7000-9000 K. Here the ion temperatures and downward vertical ion velocities were $2000 K and <20 m/s, respectively. The mean convection velocity was typically 500 m/s. We develop analytical approximations for the rate coefficients of the charge exchange reactions based on recent laboratory experiments. These have been used in local modeling of the equatorward F peak density depletions. Topside steady-state density profiles were evaluated assuming diffusive equilibrium in a given T e profile. A scenario for the transition of an initial density-height profile to a flat profile is described. Substantial agreement between the modeling results and DMSP observations indicates that the vibrational mechanism contributes significantly to the formation of high-T e -related density troughs.

Evaluation of the IRI model using CHAMP observations in polar and equatorial regions

“…Trough formation is mainly due to plasma decay in regions of stagnation or chemical and dynamical processes associated with fast plasma motion in the rest frame of the neutral particles (see the review of Rodger et al, 1992, and references therein). Processes like ion outflows (Anderson et al, 1991;Liu et al, 2001) and strong vibrationally excited N 2 (Mishin et al, 2004) may also rise to further deplete the ionosphere under disturbed conditions. Furthermore, Rodger et al (1992) has pointed out that an anti-correlation normally exists between the electron temperature and density in trough regions caused by stagnation or sub-auroral ion drift (SAID).…”

Prompt response of SAPS to stormtime substorms

“…SAID are considered as a subset of the subauroral polarization streams (SAPS) that include plasma flow events both broad and narrow extents in latitude (Foster and Burke, 2002). Sometimes, SAPS are highly variable and structured (Maynard et al, 1980;Erickson et al, 2002;Mishin et al, 2002Mishin et al, , 2003aMishin et al, , 2004Foster et al, 2004;Mishin and Burke, 2005). Especially strong SAPS-wave structures (SAPSWS), in which V W -oscillations reach AE1-2 km/s and exceed the dc component, follow stormtime substorm onsets.…”

Temporal evolution of pump beam self‐focusing at the High‐Frequency Active Auroral Research Program

“…[9] Mishin et al [2004aMishin et al [ , 2004b have shown that plasma depletion in the ionosphere can occur due to vibrationally excited N 2 in the presence of heated electrons. However, the mechanism is slow and requires minutes at 400 km to 10 or more minutes at 300 km to produce the plasma depletion.…”