Showing papers by "Arthur D. Richmond published in 1990"

Global measures of ionospheric electrodynamic activity inferred from combined incoherent scatter radar and ground magnetometer observations

Abstract: An analysis of several global measures of high-latitude ionospheric electrodynamic activity is undertaken on the basis of results obtained from the Assimilative Mapping of Ionospheric Electrodynamics (AMIE) procedure applied to incoherent scatter radar and ground magnetometer observations for January 18–19, 1984. Different global measures of electric potentials, currents, resistances, and energy transfer from the magnetosphere show temporal variations that are generally well correlated. We present parameterizations of these quantities in terms of the AE index and the hemispheric power index of precipitating auroral particles. It is shown how error estimates of the mapped electric fields can be used to correct the estimation of Joule heating. Global measures of potential drop, field-aligned current, and Joule heating as obtained by the AMIE procedure are compared with similar measures presented in previous studies. Agreement is found to within the uncertainties inherent in each study. The mean potential drop through which field-aligned currents flow in closing through the ionosphere is approximately 28% of the total polar cap potential drop under all conditions during these 2 days. We note that order-of-magnitude differences can appear when comparing different global measures of total electric current flow and of effective resistances of the global circuit, so that care must be exercised in choosing characteristic values of these parameters for circuit-analogy studies of ionosphere-magnetosphere electrodynamic coupling.

Comparison of VHF Doppler beam swinging and spaced antenna observations with the MU radar: First results

Abstract: We present a comparison between wind measurements in the 5–21 km altitude range over the middle and upper atmosphere (MU) radar obtained by two different techniques: Doppler beam swinging (DBS) and spaced antenna (SA). The SA data are analyzed by full correlation analysis (FCA) to extract the apparent and true velocities. The period analyzed, December 14–18, 1988, had strong zonal winds that often exceeded 80 m/s at around 11 km altitude and also had substantial (> 1 m/s) vertical winds that existed over extended regions of height and time. It is essential to account properly for the vertical wind when extracting the horizontal winds from the oblique DBS beams, but no obvious influence of the vertical velocity on the FCA is detected. In different altitude regions of the atmosphere (below and above the jet stream peak and above 17.7 km), the DBS amplitude alternately agrees better with the true or the apparent velocity obtained by the FCA method. The directions of all three wind estimations agree well, although the apparent direction displays more variability with altitude than do the true and DBS directions. When a smaller spacing for the receiving array is used, it yields a smaller true velocity estimate.

Electric potential patterns deduced for the SUNDIAL period of September 23-26, 1986

Abstract: High-latitude electric potential and ionospheric conductance patterns are presented and discussed for the Northern Hemisphere during the SUNDIAL period of September 23-26, 1986 using the Assimilative Mapping of Ionospheric Electrodynamics (AMIE) technique of Richmond and Kamide (1988). Data sources used for the model are satellite and ground magnetometers, electron precipitation instruments, incoherent scatter radars, and ionospheric coherent radars. The period was characterized by many substorms, and a wide variety of instantaneous patterns of electrodynamic parameters on a hemispheric scale are derived throughout this period, of which only a few examples are displayed. The entire set of electric potentials and conductances are being made available through the NCAR CEDAR Data Base for further analysis and utilization in simulation models.

Solar cycle variations in F region electrodynamic drifts at Arecibo

Abstract: Plasma drift measurements for the F region of the ionosphere have been made by the Arecibo incoherent scatter radar over the course of more than one solar cycle. The analysis of the data indicates that there are significant differences in the nighttime drifts between solar minimum and solar maximum. In general, these results agree qualitatively with results obtained through previous studies which have been done for incoherent scatter measurements from Jicamarca, Peru, as well as with some characteristics of model simulations.

Electric Potential Patterns Deduced for the SUNDIAL Period of 23-26 September 1986

Abstract: : Reprint: Electrical Potential Patterns Deduced for the SUNDIAL period of 23-26 September 1986.