Observations of thermospheric neutral winds at 23°S
ABSTRACT Observations of night-time thermospheric neutral wind velocities from measurements of Doppler shifts of the OI 630.0 nm airglow emission line, using a Fabry-Perot interferometer, have been carried out from 23°S geographic latitude in the Brazilian sector, during the period March 1988–December 1989. The observing location is situated inside both the equatorial ionospheric and South Atlantic magnetic anomalies. In this paper we present and discuss salient features of the average nocturnal variations of the thermospheric meridional and zonal wind velocities during autumn, winter, spring and summer seasons. The results are compared with the wind velocities predicted by the HWM-87 and HWM-90 models. The observed and predicted meridional and zonal wind velocities from the HWM-87 and HWM-90 models show a reasonable agreement in terms of tendencies of nocturnal variations during different seasons. However, some discrepancies are observed with regard to the magnitudes and detailed variation in the nocturnal patterns. The observed zonal winds are stronger than the meridional winds. Also the summer zonal winds are stronger than in winter, contrary to the HWM-87 model predictions. The observed thermospheric wind velocities, presented here, are comparable with those reported from other low latitude stations.
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ABSTRACT: 1] An ionospheric sounding station is operational at Palmas (10.2°S, 48.2°W, dip latitude 5.5°S), Brazil, since 2002. Observations of F layer virtual height day-to-day variations during evening hours (1800 LT to 2000 LT) show a strong variability, even during geomagnetically quiet periods. From the ionospheric multifrequency virtual height variations (at 3, 4, 5, 6, 7, and 8 MHz), observed from July 2003 to May 2004, it is found that the virtual height day-to-day variability presents oscillations with periods of days during the evening hours. The thermospheric wind component perpendicular to the magnetic meridian (zonal wind) is one of the primary sources that generate the F region dynamo near sunset, which causes the zonal electric field prereversal enhancement (PRE) that induces the E Â B vertical F layer postsunset height rise. Therefore, the planetary wave (PW) component that flows superposed on the thermospheric wind induces a traveling planetary wave ionospheric disturbance (TPWID) on the vertical F layer displacement. This indicates that the postsunset ionospheric height rise can be strongly modulated by TPWID oscillations. Our study shows that TPWIDs with periods of several days control the strength of the electric field PRE and, therefore, slowly push the F layer heights up or down, according to the TPWID phase. Also, simultaneous virtual height variations at Sao José dos Campos (low latitude) and Palmas (equatorial region) for October and November show similar behavior. This suggests that TPWID oscillation is a manifestation of atmospheric equatorial Kelvin waves that modulate the thermospheric wind. (2009), F layer postsunset height rise due to electric field prereversal enhancement: 1. Traveling planetary wave ionospheric disturbance effects, J. Geophys. Res., 114, A12321, doi:10.1029/2009JA014390.Journal of Geophysical Research 12/2009; 114(A12):A12321. · 3.17 Impact Factor
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ABSTRACT: Trans-equatorial F region plasma bubbles are large-scale ionospheric depleted regions that develop in the bottomside of equatorial F region due to plasma instability processes. Simultaneous all-sky imaging observations of the OI 630.0 nm and OI 777.4 nm nightglow emissions were carried out at São José dos Campos (23.21oS, 45.86oW; dip latitude 17.6oS), Brazil, during the years 2000 and 2001, a period of high solar activity. In this work we present and discuss the height-resolved nocturnal F region zonal drift velocities obtained from plasma bubbles observed in imaging observations of these two emissions for several days of 2000 and 2001. It should be pointed out that the two emissions result from different excitation mechanisms (OI 630.0 nm by dissociative recombination of O2+ and OI 777.4 nm by radiative recombination of O+) and come from different F region heights, separated by ~50-80 km. We have investigated the nighttime zonal plasma drift variations using fixed emission peak altitudes, used by earlier investigators, as well as emission peak altitudes based on simultaneous ionospheric sounding observations. The average maximum and minimum zonal plasma drift velocities inferred for both the emissions, using emission peak altitudes based on simultaneous ionospheric observations, (OI 630.0 nm: 172 2 and 89 15 m/s; OI 777.4 nm: 184 12 and 103 16 m/s) are lower and with less scatter than those using fixed emission peak altitudes (OI 630.0 nm: 185 10 and 104 18 m/s; OI 777.4 nm: 202 19 and 121 20 m/s). Also, the nocturnal variations of the zonal plasma drift velocities obtained for the two emissions with peak altitudes based on simultaneous ionospheric observations show better agreement than for the case with fixed emission peak altitudes (h = 380 km for OI 777.4 nm and h = 300 km for OI 630.0 nm).Journal of Geophysical Research 11/2004; 109(A11):A11308. · 3.17 Impact Factor
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ABSTRACT: Nighttime thermospheric meridional winds aligned to the magnetic meridian have been inferred using h′F and hpF2 ionosonde data taken from two equatorial stations, Manaus (2.9°S, 60.0°W, dip latitude 6.0°N) and Palmas (10.17°S, 48.2°W, dip latitude 6.2°S), and one low-latitude station, Sao Jose dos Campos (23.21°S, 45.86°W, dip latitude 17.26°S), during geomagnetic quiet days of August and September, 2002. Using an extension of the ionospheric servo model and a simple formulation of the diffusive vertical drift velocity, the magnetic meridional component of the thermospheric neutral winds is inferred, respectively, at the peak (hpF2) and at the base (h′F) heights of the F region over Sao Jose dos Campos. An approach has been included in the models to derive the effects of the electrodynamic drift over Sao Jose dos Campos from the time derivative of hpF2 and h′F observed at the equatorial stations. The magnetic meridional winds inferred from the two methods, for the months of August and September, are compared with winds calculated using the HWM-90 model and with measurements from Fabry–Perot technique. The results show varying agreements and disagreements. Meridional winds calculated from hpF2 ionospheric data (servo model) may produce errors of about 59 m/s, whereas the method calculated from the F-region base height (h′F) ionospheric data gives errors of about 69 m/s during the occurrence of equatorial spread-F.Advances in Space Research 07/2008; 41(4):599-610. · 1.18 Impact Factor