THERMOSPHERIC MERIDIONAL WIND AT LOW-LATITUDE FROM MEASUREMENTS OF F-LAYER PEAK HEIGHT

Thermospheric meridional winds are calculated in this paper for the lo w-latitude station, Cachoeira Paulista, in Brazil using ionospheric F layer peak height h(max) as the primary database for different seasons and solar activity conditions. A servo model is used that expresses t he ionospheric F layer peak height displacements as a function of chem ical loss, diffusion, thermospheric meridional wind and vertical plasm a drift. The method used is similar to, and an extension of, the one u sed in recent years for midlatitudes, where the effect of vertical pla sma drift is considered negligible. We have included in our analysis t he effect of vertical plasma drift on h(max) over Cachoeira Paulista b y using a vertical drift model which is a field line extension of an e quatorial electric field model developed for our longitude, for which the radar data from Jicamarca, Peru, are complemented, in the sunset s ector, by vertical drift from ionosonde data over Fortaleza. A numeric al model on the electrodynamic coupling of the E and F regions is used to obtain the equatorial height dependence of the vertical drift need ed for its field line mapping to low latitude. Meridional winds were c alculated using the servo equations in which the vertical plasma drift s, and h(max) values deduced from Cachoeira Paulista ionograms, were t he main inputs. The magnetic meridional winds calculated for the summe r equinoctial and winter months of high and low solar activity epochs are compared with the HWM-90 and with the measurements by Fabri-Perot technique available for Cachoeira Paulista. The results show varying a greements. The paper presents details of the method of analysis and th e comparison of the results.