Showing papers on "Winds aloft published in 1993"

The effects of neutral inertia on ionospheric currents in the high-latitude thermosphere following a geomagnetic storm

Abstract: Results of an experimental and theoretical investigation into the effects of the time dependent neutral wind flywheel on high-latitude ionospheric electrodynamics are presented. The results extend our previous work which used the National Center for Atmospheric Research Thermosphere/Ionosphere General Circulation Model (NCAR TIGCM) to theoretically simulate flywheel effects in the aftermath of a geomagnetic storm. The previous results indicated that the neutral circulation, set up by ion-neutral momentum coupling in the main phase of a geomagnetic storm, is maintained for several hours after the main phase has ended and may dominate height-integrated Hall currents and field-aligned currents for up to 4-5 hours. We extend the work of Deng et al. to include comparisons between the calculated time-dependent ionospheric Hall current system in the storm-time recovery period and that measured by instruments on board the Dynamics Explorer 2 (DE 2) satellite. Also, comparisons are made between calculated field-aligned currents and those derived from DE 2 magnetometer measurements. These calculations also allow us to calculate the power transfer rate (sometimes called the Poynting flux) between the magnetosphere and ionosphere. The following conclusions have been drawn: (1) Neutral winds can contribute significantly to the horizontal ionospheric current system in the period immediately following the main phase of a geomagnetic storm, especially over the magnetic polar cap and in regions of ion drift shear. (2) Neutral winds drive Hall currents that flow in the opposite direction to those driven by ion drifts. (3) The overall morphology of the calculated field-aligned current system agrees with previously published observations for the interplanetary magnetic field (IMF) B(sub Z) southward conditions, although the region I and region 2 currents are smeared by the TI(ICM model grid resolution. (4) Neutral winds can make significant contributions to the field-aligned current system when B(sub Z) northward conditions prevail following the main phase of a storm, but can account for only a fraction of the observed currents. (5) DE 2 measurements provide a demonstration of "local" (satellite-altitude) flywheel effects. (6) On the assumption that the magnetosphere acts as an insulator, we calculate neutral-wind-induced polarization electric fields of approx. 20-30 kV in the period immediately following the geomagnetic storm.

Observations of the F-region horizontal and vertical winds in the auroral zone

Abstract: The MICADO instrument consisting of a Michelson interferometer has been designed to observe winds and temperature in the mesosphere and thermosphere. Three winter campaigns were organized at Sodankyla (Finland) and Tromso (Norway) from 1988 to 1991. This paper is mainly dedicated to wind observations in the thermosphere by use of the O( 1 D) oxygen emission line. As a function of magnetic activity and universal time, a mean model of F-region meridional, zonal and vertical neutral wind components is presented, discussed and compared with recent empirical models. Magnetic activity effects are shown on lines intensily, temperature and wind, particularly the numerical relationship of its vertical component with the amplitude of the magnetic perturbation

A comparison between vertical winds and divergence in the high-latitude thermosphere

Abstract: Measurements of thermospheric wind velocities obtained from a Fabry-Perot interferometer (FPI) situated at Halley, Antarctica (75.5°S, 26.6°W, L=4.2) have been used to compare the vertical wind with the divergence of the horizontal flow at an altitude of approximately 240 km. It is found that the ratio between vertical wind and divergence is of the order of five times that predicted by a theoretical model. The likely causes of this discrepancy are discussed. A scale size of approximately 360 km for the vertical wind at this high latitude site is suggested by the results

Mesopause Winds and OH Intensities at Mid-Latitudes-Fabry-Perot Interferometer Observations of the OH Emission at 8430 A from Bear Lake Observatory

Abstract: : Observations were made from Bear Lake Observatory using an Imaging- Fabry-Perot Interferometer Neutral winds were derived from the Doppler shift to the emission line, and relative intensity was also analyzed Results presented are from the period between December 1991 and March 1992 The 8430 A OH data showed remarkable day-to-day variability in the wind pattern Diurnal, semidiurnal, and terdiurnal tidal components all appeared at some point during the observing period with no consistent regularity The OH intensities showed the presence of gravity wave activity with discernible period down to approximately 3 hours The 6300 AO(1D) wind and intensity observations showed a high degree of magnetic activity which correlated positively with Kp and Ap indices We noted a definite presence of auroral and SAR-arc activity almost nightly on nights when the 6300 A O(1D) emission was observed