Atmospheric Response in Aurora experiment: Observations of E and F region neutral winds in a region of postmidnight diffuse aurora

Abstract

The goal of the Atmospheric Response in Aurora (ARIA) experiment carried out at Poker Flat, Alaska, on March 3, 1992, was to determine the response of the neutral atmosphere to the long-lived, large-scale forcing that is characteristic of the diffuse aurora in the postmidnight sector. A combination of chemical release rocket wind measurements, instrumented rocket composition measurements, and ground-based optical measurements were used to characterize the response of the neutral atmosphere. The rocket measurements were made at the end of a 90-min period of strong Joule heating. We focus on the neutral wind measurements made with the rocket. The forcing was determined by running the •ssimil•ted m•pping of ionospheric electrodynamics (AMIE) •n•lysis procedure developed at the National Center for Atmospheric Research. The winds expected at the latitude and longitude of the experiment were calculated using the spectral thermospheric general circulation model developed at the Danish Meteorological Institute. Comparisons of the observations and the model suggest that the neutral winds responded strongly in two height ranges. An eastward wind perturbation of 00100 m s -1 developed between 140 and 200 km altitude with a peak near 160 km. A southwestward wind with peak magnitude of 00150 m s -1 developed near 115 km •titude. The large amplitude winds at the lower •ltitude are particularly surprising. They appear to be associated with the upward propagating semidiurnal tide. However, the amplitude is much larger than predicted by any of the tid• models, and the shear found just below the peak in the winds was nominally unstable with a Richardson number of 000.08. response of the neutral atmosphere will be especially strong in the region of diffuse aurora characteristic of the morning side. In particular, the broad spatial extent and the long-lived nature of the diffuse aurora are Paper number 95JA01346. 0148-0227/95/95 JA-01346505.00 expected to produce Lorentz forcing and Joule heating over a broad region for an extended period. The discrete aurora which typically characterize the duskside may produce stronger local forcing, but the response of the neutrals will be more limited since the spatial extent of the forcing region is small enough that the neutrals pass through the heating and acceleration regions quickly. Over the years, there have been numerous measurements of the F region neutral flow on the dawn side of the auroral oval. The Dynamics Explorer observa-17,299 17,300 LARSEN ET AL.' OBSERVATIONS OF NEUTRAL WINDS range in the mesosphere and lower thermosphere, and an instrumented rocket was used to measure the neutral composition and particle energies. In addition, an extensive set of ground-based instrumentation provided measurements of the magnetic fields and electron energies throughout the night. In this article, we will focus on the neutral wind measurements made with the chemical release rocket technique. Geophysical Conditions The chemical release experiment took place on March 3, 1992. The launch followed ...

Simulations of the neutral structure within the dusk side aurora

“…Strong winds and wind shears were also observed within the postmidnight recovery phase aurora, during the coordinated ARIA (Atmospheric Response in Aurora) campaigns (Larsen et al, 1995(Larsen et al, , 1997Anderson et al, 1995) and during some pre-ARIA observing campaigns (Larsen et al, 1989). The generation of E-region winds of the observed magnitudes on the dawn or the dusk side is not easily explained by auroral processes alone, and the mechanisms which produce the observed strong vertical structure are not well understood.…”

“…Whilst there was some agreement with the observations, the strong wind structure and wind magnitudes were not well reproduced. Simulations of the winds produced during the ARIA I campaign using a spectral general circulation model (Larsen et al, 1995), generated the characteristics of the observations above 140 km, but the strength of the vertical structure in the E-region was not well reproduced. Simulations of winds generated within the dusk side aurora during the campaign of 28 February 1978, using the same spectral model (Mikkelsen and Larsen, 1993) reproduced some of the main features of the observations, although the simulated wind vectors were rotated relative to the observations, and Eregion maxima were too high in altitude.…”

Sensitivity studies of the E region neutral response to the postmidnight diffuse aurora

“…Zonal and meridional neutral winds measured during the ARIA I campaign are shown in Fig. 1 (see also Larsen et al, 1995Larsen et al, , 1997.…”

“…In this paper, we make use of measurements within the postmidnight diffuse aurora made during the ARIA I campaign (Anderson et al, 1995;Larsen et al, 1995). The ARIA I campaign took place on 3 March 1992, and consisted of coordinated rocket, ground-based and satellite observations made at Poker Flat, Alaska (65.1 • N, 212.5 • E geographic) during, and in the recovery phase of, a substorm which had an onset time of 10:00 UT.…”

“…Johnson et al, 1987). Measurements of neutral structure within the postmidnight diffuse aurora during the ARIA (Atmospheric Response in Aurora) coordinated rocket, ground based and satellite campaigns (Anderson et al, 1995;Larsen et al, 1995), and earlier rocket campaigns (Larsen et al, 1989) show strong vertical structure in the winds, with peak magnitudes of around 200 m/s between 110 and 120-km altitude, and large wind shears above and below. The shear below the peak sometimes appears to be unstable, with Richardson number less than 0.25.…”