HR: 1340h
AN: SA23A-0383    [Abstracts]
TI: Investigations of the structure of the neutral atmosphere within the dawn and dusk sector diffuse aurora.
AU: * Parish, H F
EM: helen@atmos.ucla.edu
AF: Department of Atmospheric Sciences,UCLA, 405,Hilgard Avenue, Los Angeles, CA 90095-1565 United States
AB: The neutral thermosphere within the pre and post midnight substorm recovery phase diffuse aurora is found to show very large horizontal winds, and strong vertical structure. In the dusk side diffuse aurora, rocket measurements indicate neutral winds of up to 400 m/s. Rocket, satellite, and ground based observations during the ARIA (Atmospheric Response in Aurora) campaigns, and earlier dawn side rocket observations, show winds of up to 200 m/s, and a characteristic jet like wind maximum around 110 to 120 km altitude. Strong shears are present in the wind structure on both the dawn and dusk sides, and the regions below these shears sometimes have a Richardson number below 0.25, suggesting that they may be unstable. Instabilities may be associated with waves, turbulence, enhanced diffusivity, and changes in local composition. The enhanced auroral precipitation and electric fields associated with substorms may have significant effects on the E region neutral thermosphere, and observed wind magnitudes are found to have a dependence on geomagnetic activity level. However, recent results suggest that propagating tides play a significant role in generating the strong vertical variations in the neutral winds, and the relative importance of auroral and tidal forcing in generating the observed winds is not well known. Significant differences also exist in the acceleration conditions in the pre and post midnight sectors of the auroral oval, and how these affect the neutral responses on the dawn and dusk sides is not well understood. Investigations have been performed using a three-dimensional high resolution limited area thermosphere model developed at UCLA, to understand the processes which generate the observed neutral structure within the diffuse aurora on both the dawn and dusk sides. Auroral forcing parameters for the model have been estimated using values measured during the dawn and dusk observing campaigns. The CTIP (Coupled Thermosphere Ionosphere Plasmasphere) model has been used to specify global background winds and tides. The response of the neutral atmosphere to changes in auroral forcing, IMF orientation, large scale winds, and propagating tides, including the (2,4), (2,5), and (2,6) semidiurnal modes, has been determined for both the dawn and dusk sectors.
DE: 3369 Thermospheric dynamics (0358)
DE: 3384 Waves and tides
DE: 2704 Auroral phenomena (2407)
DE: 0358 Thermosphere--energy deposition
SC: SPA-Aeronomy [SA]
MN: 2004 AGU Fall Meeting