Papers on Ionosphere and Upper Atmosphere
Thermospheric meridional wind at low latitude from measurements of F layer peak height
Thermospheric meridional winds are calculated in this paper for the low-latitude station, Cachoeira Paulista, in Brazil using ionospheric F layer peak height hmax as the primary database for different seasons and solar activity conditions. A servo model is used that expresses the ionospheric F layer peak height displacements as a function of chemical loss, diffusion, thermospheric meridional wind and vertical plasma drift. The method used is similar to, and an extension of, the one used in recent years for midlatitudes, where the effect of vertical plasma drift is considered negligible. We have included in our analysis the effect of vertical plasma drift on hmax over Cachoeira Paulista by using a vertical drift model which is a field line extension of an equatorial electric field model developed for our longitude, for which the radar data from Jicamarca, Peru, are complemented, in the sunset sector, by vertical drift from ionosonde data over Fortaleza. A numerical model on the electrodynamic coupling of the E and F regions is used to obtain the equatorial height dependence of the vertical drift needed for its field line mapping to low latitude. Meridional winds were calculated using the servo equations in which the vertical plasma drifts, and hmax values deduced from Cachoeira Paulista ionograms, were the main inputs. The magnetic meridional winds calculated for the summer 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 agreements. The paper presents details of the method of analysis and the comparison of the results.
The authors acknowledge support in the form of fellowships received from Conselho Nacional de Desenvolvimento Científico e Tecnológico - CNPq and CAPES. The digisonde at Cachoeira Paulista was acquired with partial support from the Fundação de Amparo à Pesquisa do Estado de São Paulo - FAPESP.
The Editor thanks N. Balan and G. J. Bailey for their assistance in evaluating this paper.