Physics
Scientific paper
Dec 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003agufmsa21b0077p&link_type=abstract
American Geophysical Union, Fall Meeting 2003, abstract #SA21B-0077
Physics
0310 Airglow And Aurora, 3369 Thermospheric Dynamics (0358), 3384 Waves And Tides
Scientific paper
Measurements from chemical release experiments within the dusk sector recovery phase diffuse aurora, and observations made during ARIA (Atmospheric Response in Aurora) and pre ARIA rocket campaigns within the dawn side diffuse aurora, reveal very large neutral winds in the E region, with strong vertical shears. Winds of 150 to 200 m/s were found around 110 to 120 km altitude within the dawn sector diffuse aurora, and even larger winds of 350 to 400 m/s were found in the dusk sector around 130 km. Winds of this magnitude are hard to explain in terms of geomagnetic forcing at E region altitudes and the reasons for such large winds are still not fully understood. Both dawn and dusk sector observations show very strong vertical structure, and regions below the vertical shears sometimes appear to be unstable, with Richardson number less than 0.25. Instabilities associated with these shears could produce turbulence, enhanced eddy diffusion and strong localized composition changes, and may feedback into auroral generation processes or produce various types of waves. Recent work suggests that tidal forcing plays an important role in producing the wind structures observed within the dawn sector diffuse aurora during the ARIA I campaign. However, the relative importance of tidal and geomagnetic forcing in producing the strong vertical variations in the winds is not well known. Also it is not known whether the different conditions for accelerating winds in the pre and post midnight sectors of the auroral oval produce significantly different neutral responses on the dawn and dusk sides of the diffuse aurora. Simulations have been performed using a 3-dimensional, high resolution, limited area model developed at UCLA, to try to determine the processes that are responsible for producing the strong vertical variations seen in the neutral atmosphere within both the dawn and dusk side diffuse aurora. Global background winds and tides have been provided by the CTIP (coupled thermosphere ionosphere plasmasphere) model. The sensitivity of the response to varying auroral forcing parameters and to changing background conditions of winds, tides and interplanetary magnetic field have been investigated. ~
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