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Positive ionospheric storm effects that occurred during the superstorm on 20 November 2003 are investigated using a combination of ground-based Global Positioning System (GPS) total electron content (TEC), and the meridian chain of ionosondes distributed along the Latin America longitude of ~280° E. Both the ground-based GPS TEC and ionosonde electron density profile data reveal significant enhancements at mid-low latitudes over the 280° E region during the main phase of the November 2003 superstorm. The maximum enhancement of the topside ionospheric electron content is 3.2–7.7 times of the bottomside ionosphere at the locations of the ionosondes distributed around the mid- and low latitudes. Moreover, the height of maximum electron density exceeds 400 km and increases by 100 km compared with the quiet day over the South American area from middle to low latitudes, which might have resulted from a continuous eastward penetration electric field and storm-generated equatorward winds. Our results do not support the conclusions of Yizengaw et al. (2006), who suggested that the observed positive storm over the South American sector was mainly the consequence of the changes of the bottomside ionosphere. The so-called "unusual" responses of the topside ionosphere for the November 2003 storm in Yizengaw et al. (2006) are likely associated with the erroneous usage of magnetometer and incomplete data.

The response of the ionospheric F-region in the South American sector during the super geomagnetic storms on 29 and 30 October 2003 is studied in the present investigation. In this paper, we present ionospheric sounding observations during the period 29–31 October 2003 obtained at Palmas (a near equatorial location) and Sao Jose dos Campos (a location under the southern crest of the equatorial ionospheric anomaly), Brazil, along with observations during the period 27–31 October 2003 from a chain of GPS stations covering the South American sector from Imperatriz, Brazil, to Rio Grande, Argentina. Also, complementary observations that include sequences of all-sky images of the OI 777.4 and 630.0 nm emissions observed at El Leoncito, Argentina, on the nights of 28–29 (geomagnetically quiet night) and 29–30 (geomagnetically disturbed night) October 2003, and ion densities observed in the South American sector by the DMSP F13, F14 and F15 satellites orbiting at about 800 km on 29 and 30 October 2003 are presented. In addition, global TEC maps derived from GPS observations collected from the global GPS network of International GPS Service (IGS) are presented, showing widespread and drastic TEC changes during the different phases of the geomagnetic disturbances. The observations indicate that the equatorial ionospheric irregularities or plasma bubbles extend to the Argentinean station Rawson (geom. Lat. 33.1° S) and map at the magnetic equator at an altitude of about 2500 km.

Observations of total ozone at low latitudes in Brazil have been made using Dobson spectrophotometers since 1974 for Cachoeira Paulista (23.1° S, 45° W) and since 1978 for Natal (5.8° S, 35.2° W). Annual averages, 12 months and 36 months running averages have been analyzed. Spectral analyses of the data revealed that the most important periods found (confidence level > 90%) were: for Natal, 2.5 years (93.1%, quasi-biennial oscillation-QBO) and 10 years (98,2%, possibly the solar cycle signal); for Cachoeira Paulista, 2.4 years (96.8%, QBO) and 8 years (99.6%). The difference in total ozone between maximum and minimum solar cycles were estimated, using yearly averages of total ozone. For solar cycle 21, 1.16% and 1.26% for Natal and Cachoeira Paulista were found; for solar cycle 22, a larger difference of 3.8% for Natal and 4.1% for Cachoeira Paulista were found. The corresponding variation in UV-B at 300 nm, using Beer's law, is 8–10% for C. Paulista and 4–5% for Natal, with maxima occurring during the minimum of the solar cycle.

Observations of the OI 630 nm nightglow emission using a wide-angle imaging system have been carried out at Cachoeira Paulista (22.7° S, 45° W, 15.8° S dip latitude), Brazil during the period 1987 to 1999. The OI 630 nm images obtained during this period show frequently the optical signature of the plasma bubble (quasi north-south aligned depleted intensity regions). During the period studied a strong seasonal variation was noticed in the plasma bubble formations. Also, it was observed that, during high solar activity, the plasma bubble bifurcation occurrences were higher than during low solar activity. Important features from this set of observations are presented and discussed in this paper.

With the recent advances in all-sky imaging technology for nightglow emission studies, the F-region OI 630 nm emission has become an important tool for ionospheric/thermospheric coupling studies. At equatorial and low latitude regions, the all-sky imaging observations of the OI 630 nm emission show quasi north-south aligned intensity depletion bands, which are the optical signatures of large scale F-region plasma irregularities. By observing the motion of the intensity depleted bands it is possible to infer the ionospheric plasma zonal velocity of the depletion. The north-south aligned structures seen in the field of view of the all-sky imaging system corotate with the ionospheric plasma, so that by calculating the spatial displacements occurring during successive OI 630 nm emission images we can infer the ionospheric plasma drift velocity. However, the plasma bubbles have their own internal space-time dynamics leading to changes in their shape and dimensions and this may induce some errors in the calculated drift velocities. In this paper we take into account the space-time changes in the plasma bubbles in order to calculate the ionospheric plasma zonal drift velocities using the OI 630 nm nightglow emission.

During the recent past, wide-angle optical imaging observations of F-region nightglow emissions (e.g. OI 630nm) have provided excellent results related to the occurrence, evolution and dynamics of strong large-scale range spread-F irregularities, as they are characterized by large-scale ionospheric plasma depletions, generally known as transequatorial plasma bubbles, which result in quasi north–south aligned intensity depleted bands. The intensity depletions seen in the airglow images are the optical signature, at the height range of the emitting layer of transequatorial magnetic field-aligned plasma bubbles. An all-sky imaging system, observing the OI 630nm emission, was operational at Cachoeira Paulista (22.7°S, 45.0°W; ∼16°S dip latitude), Brazil, during the period March 1987 to October 1991. It was put back in operation again in September 1994 and observations are continuing. These observations have provided an extensive data-base of OI 630 nm images which permitted us to address several aspects related to the formation and development of large-scale spread-F plasma irregularities during both high- and low solar activity periods. An analysis of about 11,000 images from these investigations are presented and discussed in this paper. The seasonal occurrence characteristics are fairly similar for both low and high solar activities. However, the occurrences of intensity depleted bands are much less during low solar activity (33%) as compared with high solar activity (55%). Also, some of the intensity depleted bands in the images (which show the optical signatures at the height of the emitting layer around 250–300 km) indicating that plasma bubbles attaining very high altitudes ( >1500 km ) at the magnetic equator (by mapping the depletion bands along geomagnetic field lines to the equatorial plane (e.g., Mendillo, Tyler, J. Geophys. Res. 88 (1983) 5758), are much less during low solar activity (34% of the images with intensity depleted bands) as compared with high solar activity (66% of the images with intensity depleted bands). The average nocturnal variations of intensity depleted regions show different characteristics during the high and low solar activity periods.

Measurements with Dobson spectrophotometers are used to study ozone trends at Cachoeira Paulista (22.7°S, 45.0°W) and Natal (5.8°S, 35.2°W) in Brazil. The time series are from 1974 to 1997 for Cachoeira Paulista and from 1978 to 1997 at Natal. Using a model that accounts for the quasi-biennial oscillation, seasonal variation, and solar cycle, a trend in total ozone of -2.0±1.2% per decade was found at Cachoeira Paulista for the period 1974 to 1997. At Natal the trend was -0.8±0.8% per decade over the period 1978 to 1997. The annual values of column ozone reported at Cachoeira Paulista are lower in the 1990's than in the previous two decades: total ozone amounts are 12.5 Dobson units (DU), or 4.6%, lower in the 1990s than those observed during the 1970s. From a monthly analysis it is shown that these ozone decreases have occurred in all months of the year. There was no statistically significant change between the 1980s and 1990s at Natal.

During the last few years, a network (6 stations) of Brewer spectrophotometers has been established in different ecosystems in South America by the Brazilian National Institute for Space Research (INPE). A Brewer spectrophotometer permits simultaneous observations of total ozone and UV-B radiation and is operational on a routine basis at Cuiaba (16°S, 56°W), Brazil, since 1991. Surface ozone is also measured at Cuiaba using UV ozone monitor since 1987. In this paper we present and discuss the simultaneous observations from these two instruments obtained in 1995. This study permits comparison of the observations during the biomas burning period (dry season) with the wet season. Although surface ozone levels were considerably higher during the biomass burning season, no effect on the total ozone column could be observed. The UV-B radiation, however, was significantly reduced due to absorption by biomass burning aerosols.

In December 1995, a campaign was carried out to study the day-to-day variability in precursor signatures to large-scale ionospheric F-region plasma irregularities, using optical diagnostic techniques, near the magnetic equator in the Brazilian sector. Three instruments were operated simultaneously: (a) an all-sky (180° field of view) imaging system for observing the OI 630 nm nightglow emission at Alcântara (2.5°S, 44.4°W); (b) a digisonde (256-Lowell) at São Luis (2.6°S, 44.2°W); and (c) a multi-channel tilting filter-type zenith photometer for observing the OI 630 nm and mesospheric nightglow emissions at Fortaleza (3.9°S, 38.4°W). During the period December 14-18, 1995 (summer in the southern hemisphere), a good sequence of the OI 630 nm imaging observations on five consecutive nights were obtained, which are presented and discussed in this study. The observing period was geomagnetically quiet to moderate (Kp = 0+ to 5+; Dst = 18 nT to -37 nT). On four nights, out of the five observation nights, the OI 630 nm imaging pictures showed formations of transequatorial north-south aligned intensity depletions, which are the optical signatures of large-scale ionospheric F-region plasma bubbles. However, considerable day-to-day variability in the onset and development of the plasma depleted bands was observed. On one of the nights it appears that the rapid uplifting of the F-layer in the post-sunset period, in conjunction with gravity wave activity at mesospheric heights, resulted in generation of very strong plasma bubble irregularities. One of the nights showed an unusual formation of north-south depleted band in the western sector of the imaging system field of view, but the structure did not show any eastward movement, which is a normal characteristic of plasma bubbles. This type of irregularity structure, which probably can be observed only by wide-angle imaging system, needs more investigations for a better understanding of its behaviour.Key words. Atmospheric composition and structure (airglow and aurora) · Ionosphere (equatorial ionosphere; ionospheric irregularities)

In recent years, scientists have used wide-angle imaging observations of F-region nightglow emissions (e.g., OI630 nm and OI777.4 nm) to map the F-region equatorial ionospheric irregularity structures, characterized by large scale plasma depletions, generally known as transequatorial plasma bubbles. In Brazil, an OI630 nm all-sky imaging system has been in operation at Cachoeira Paulista (22.7°S, 45.0°W) since March 1987. This has provided an extensive data-base of the OI630 nm all-sky imaging observations in the equatorial ionospheric anomaly region. In this paper, the morphology of large scale equatorial F-region plasma depletions under sunspot maximum and minimum conditions is presented and discussed. It has been observed that the occurrences of plasma depleted regions are relatively lesser during low solar activity than during high solar activity. The seasonal occurrence pattern is fairly similar for high and low solar activities.

During the period March 1987 to October 1991, a wide-angle imaging system to observe the OI 630 nm nightglow emission was operational at Cachoeira Paulista (22.7°S, 45.0°W; dip latitude 15.8°S), Brazil. The OI 630 nm wide-angle imaging observations detect optical signatures of large scale equatorial F-region ionospheric plasma depletions or bubbles and the large data-base (about 4.5 years) permitted studies of their occurrence characteristics in the Brazilian sector. It has been observed that between the months of May and August the occurrence of large scale F-region plasma bubbles is at its minimum. However, during this period on several occasions at times of magnetic disturbances, the presence of large scale plasma bubbles was noted. In this paper we present and discuss several cases of the generation (or absence of generation) of plasma depleted regions during these months with magnetic disturbances. The imaging observations are complemented with ionospheric parameters obtained at Fortaleza (3.9°S, 38.4°W; dip latitude 3.7°S), Brazil. The possible influence of magnetic disturbance effects on equatorial ionospheric fields during the events studied is analysed and presented. It has been observed that on no plasma bubble nights with magnetic disturbances, possibly the storm induced high latitude electric field could not penetrate to the equatorial region due to the shielding charges in the inner magnetosphere, whereas on the nights with plasma bubbles, disturbance drifts result from the prompt penetration of high latitude electric fields.

The 12-month moving averages of total ozone mapping spectrometer (TOMS) total ozone data for 14 years (1979-1992) were examined for quasi-biennial oscillation (QBO) and quasi-triennial oscillation (QTO) and compared with stratospheric low-latitude zonal wind and equatorial eastern Pacific sea surface temperature (SST). The equatorial ozone had a strong QBO with a period of ∼30 months, and its maxima tallied with westerly wind maxima. At other latitudes the ozone maxima spacings were often different from 30 months, more so in the northern hemisphere. A spectral analysis showed that both hemispheres had one peak at ∼20 months and another peak at ∼30 months, only up to ∼50° latitude. At higher latitudes these peaks shifted to ∼23 and ∼36 months. For 0°-50° the ∼30-month periodicity in the northern hemisphere showed abrupt phase changes, while the southern latitudes showed a roughly gradual phase shift. The northern hemisphere had an additional periodicity at ∼4 years, roughly matching the SST. Analysis of the same data without 12-month averaging showed the above characteristics more clearly and revealed additional peaks at ∼0.7 years (8-9 months) and ∼1.30 years (16-17 months). All of these peaks showed shifts (mostly increases) at higher latitudes.

Observations of the OH(8-3) band rotational temperature have been carried out from Calgary (51 °N, 114 °W), Canada, from 1988 to 1990. The measurements have been taken in orthogonal scanning mode and the data set has been analyzed to study salient features of gravity waves in the mesospheric region from this mid-latitude station. Rotational temperature data from 36 nights showed distinct gravity wave activity during this period. The gravity wave characteristics studied include the dominant period, horizontal structure speed, implied horizontal wavelength and horizontal component of direction of propagation. The preferred direction in the horizontal wave propagation at Calgary is towards the north-west. A comparison of the observed horizontal propagation directions with the permitted directions, using model wind profiles for Calgary, shows good agreement. This indicates that the upward flow of wave energy could be modified by the background wind.

We examine the appearance of the ozone hole over a populated area with more than 100,000 inhabitants. The largest population concentrations on the South American continent nearest the ozone hole region are Punta Arenas, Chile (53.0°S, 70.9°W) and Ushuaia, Argentina (54.5°S, 68.0°W), located close to the strait of Magallanes, opposite the Antarctic Peninsula. A special field mission was held in Punta Arenas, in September-October 1995 to investigate the vertical distribution of ozone during the appearance of the Antarctic ozone hole. Previous work has shown that the city of Punta Arenas is located at the edge of the hole area and is affected every year during a few days in the October period. The ozone trend near these locations is −0.5% per year using the yearly averages and −1.2% per year using the October means. This trend is 2 to 5 times larger than the global average. Several ozonesondes of the electrochemical concentration cell type were launched from Punta Arenas to determine the vertical distribution of ozone during “normal” and “perturbed” conditions. The ozone hole passed over Punta Arenas on October 12, 13 and 14, 1995. In addition to the sondes, which were launched once a day, ozone column amounts and UVB radiation were measured with a ground-based ozone Brewer spectrophotometer. The strongest ozone depletion over Punta Arenas in 1995 occurred on October 13, when the ozone column decreased from a “normal” value of about 325 Dobson Units (DU) to 200 DU; the vertical distribution of ozone on October 13 compared with October 6 shows depleted ozone roughly 50% less during hole conditions in the stratosphere. The UVB intensities have increased accordingly. The spectral ratio for October 13 to October 4 is 13 times larger at 297 nm.

The nightglow OH(9, 4) and O 2 atmospheric (0,1) band emission intensities and their rotational temperatures T(OH) and T(O 2 ), respectively, observed at Cachoeira Paulista (23 ° S, 45 ° W), Brazil, during the period from October 1989 to December 1990, have been analyzed to study the nighttime mesospheric energy loss rates through the radiations from the vibrationally excited OH * and electronically excited O 2 * bands. The total emission rates of the OH Meinel bands, O 2 atmospheric (0,0) and O 2 infrared atmospheric ( 1 Δ g ) bands were calculated using reported data for the relative band intensities I (ν '' ,ν ' ) / I (9,4) , I O2A(0,0) / I O2A(0,1) and I O2 ( 1 Δ g )/ I O2A(0,1) . It was found that there is a minimum in equivalent energy loss rate by the OH * Meinel bands during December/January (equivalent energy loss rate of 0.39K/day * , where day * means averaged over the night) and maximum in equivalent energy loss rate during September (equivalent energy loss rate of 0.98K/day * ). Energy loss rate by the O 2 * radiation, on the other hand, is weaker than that by the OH * Meinel bands, showing equivalent energy loss rates of 0.12K/day * and 0.22K/day * during January and September, respectively.

Simultaneous observations of the OI 630.0 nm nightglow emission using an all-sky imaging system, and thermospheric winds and temperatures using a Fabry-Perot interferometer at 630.0 nm, have been recently conducted at Cachoeira Paulista (22.7°S, 45.0°W, dip latitude 15.8°S). The all-sky imaging observations of the OI 630.Onm nightglow emission, which arises from the O 2 + ionospheric dissociative recombination process, are used to monitor the morphology and dynamics of transequatorial ionospheric plasma bubbles in the height range of the nightglow emissions. In this paper we present simultaneous observations from these two instruments obtained in April and August 1991, in which some nights showed the presence of ionospheric plasma bubbles. These observations are also complemented by ionospheric sounding data obtained at the equatorial station Fortaleza (3.9°S, 38.4°W, dip latitude 3.7°S). Significant features of the morphology and time evolution of the plasma depletions as seen through the OI 630.0 nm emission images and possible influence of the thermospheric winds on the generation of the plasma irregularities are analyzed and discussed.

The Mt. Pinatubo eruptions in June 1991 were some of the largest of this century. In addition to causing devastating local effects, they injected large quantities of particles and gases, especially sulfur dioxide, SO 2 , straight into the middle atmosphere. In this paper we present and discuss simultaneous observations of stratospheric O 3 and SO 2 carried out at Cuiaba (16.0 °S, 56.0 °W), Brazil, where an automated Brewer spectrophotometer is operated on a routine basis. The data presented cover both the pre- and post-eruption conditions (October 1990–August 1994). Also, some complementary total ozone observations carried out at Cachoeira Paulista (22.7 °S, 45.0 °W) and Natal (5.8 °S, 35.2 °W) in Brazil have been used in this report. After about two weeks of the major eruption (early July), a strong enhancement (factor of six) in the column SO 2 observations was detected at Cuiaba. The enhanced SO 2 levels continued for about two and half months. The total ozone observations at Cuiaba showed a significant (11%) decrease in the stratospheric ozone levels during the winter months in 1992, possibly associated in part with delayed volcanic injection effects in the stratosphere.

Simultaneous observations of F2-layer peak heights, from an ionosonde, and nighttime thermospheric neutral wind velocities inferred from measurements of Doppler shifts of the OI 630 nm airglow emission line, using a Fabry-Perot interferometer, have been carried out at Cachoeira Paulista (23°S, 45°W, dip latitude 16°S), Brazil. The MSIS-86 neutral density model is used to calculate the F-layer balance heights (H 0 ) due only to diffusion and recombination processes. The observed meridional and zonal wind velocities and H 0 are used to estimate variations in the F2-layer peak heights (H M ). In this paper we present and discuss results from a comparison between the observed F2-layer peak heights and the estimated H M variations produced by the observed meridional wind velocities along the magnetic field lines.

An all-sky (180°) imaging system for observations of the OI 630 nm nightglow emission is in routine operation at Cachoeira Paulista (22.7°S, 45.0°W; 16°S dip latitude), Brazil. This technique permits observations covering a large area, extending from the equatorial region to nearly mid-latitude from this observational site. During February 1995, a relatively good sequence of observations on six consecutive nights were obtained. On five out of the six nights, weak to strong nearly north-south aligned intensity depleted regions, which are the optical signatures of large-scale field-aligned equatorial F-region plasma depletions, were observed. Important features from this set of observations, including vertical and zonal velocities of the plasma bubbles, are presented and discussed in this paper.

Observations of the OH (8-3) band airglow emission, using a multichannel tilting filter type photometer, have been carried out at Calgary (51°N, 114°W), Canada, since 1981. In this paper recent measurements of the nocturnal, seasonal and solar flux variations of the mesopause temperature, obtained from the rotational temperature of the OH (8-3) band observations, are presented. The data presented span the ascending phase of the present solar cycle viz. 1987–1988 (low solar activity) and 1990 (high solar activity). Good correlations (r = 0.73) between the OH (8-3) band rotational temperature and the 10.7 cm solar flux were observed. The mean temperature for the period investigated was about 210 K. The seasonally averaged nocturnal variations show only small irregular excursions, possibly associated with solar tides and the passage of gravity waves in the mesopause region. However, the observed rotational temperatures show considerable night-to-night changes.

Night-time thermospheric temperatures, T63o, and mesospheric rotational temperatures, T (OH) and T (O 2 ), have been measured at Cachoeira Paulista (23°S, 45°W, 16°S dip latitude), located in both the equatorial ionospheric anomaly and the South Atlantic Geomagnetic Anomaly, with a Fabry-Perot interferometer and a multi-channel tilting filter-type photometer, respectively. The thermospheric temperatures are obtained from the Doppler line broadening of the OI 630.0 nm emission and the mesospheric rotational temperatures from the OH(9,4) and O 2 A(0,1) band emissions. Measurements made during three geomagnetic storms showed that the nocturnal mean values of T 630 during the recovery phase of the storms were lower than those observed during quiet time and from model predictions. Also, the nocturnal mean value of the T 630 soon after the SSC event on 27 June 1992 was higher than the quiet time and model predictions. The observed mesospheric nocturnal mean rotational temperatures, T (O 2 ) and T (O 2 ), were unaffected by the storms. A comparison of the night-time observed temperatures T 630 , T (OH) and T (O 2 ) with those calculated using the MSIS-86 model is also presented.

Low-latitude plasma drifts (zonal and meridional) in the F-region are inferred from the observed night-time thermospheric neutral wind velocities and temperature gradients, together with models for the neutral density (MSIS-86 model) and the electron density (IRI model). The thermospheric neutral winds and temperatures are derived from measurements of Doppler shifts and widths of the Oi 630.0 nm airglow emission line, respectively, using a Fabry-Perot interferometer at Cachoeira Paulista (23°S, 45°W), Brazil. The equations considered are the ideal gas law and the momentum equation for the thermosphere, which includes the time variation of the neutral wind, the pressure gradient which is related to the temperature and density gradients and the ion drag force. The present method to infer the night-time plasma drift using observed neutral parameters (time variation of neutral wind velocities and temperature gradients) showed results that are in reasonable agreement with our calculated plasma drifts and those observed in other low-latitude locations. On the other hand, it is surprising that sometimes the winds flow from the observed coldest sector to the hottest part of the thermosphere during many hours, suggesting that plasma drift can drive the neutral winds at low latitudes for a period of time.

It is well-known that, at equatorial and low-latitudes, the OI 557.7 nm emission emanates both from the mesosphere and F-region. Earlier investigations using, in general, ground-based simultaneous observations indicate that the contribution to the OI 557.7 nm emission from the F-region is about 20% of the F-region OI 630.0 nm emission. Both of these emissions are excited by the dissociative recombination process (O 2 + + e → O ∗ ( 1 S, 1 D) + O) in the F-region. The nocturnal intensity variations of these emissions sometimes show large short-lived depletions, associated with the passage of equatorial spread-F plasma bubbles through the field of view of a photometer. Regular observations of these emissions have been carried out at Cachoeira Paulista (22.7°S, 45.0°W), Brazil, since 1973. In this paper, we present and discuss simultaneous observations of these emissions, during periods of strong equatorial spread-F conditions, when both emissions show large intensity drop-outs. Twenty-five nights of measurements from Cachoeira Paulista have been analysed for this study, which indicate that the average ratio of the intensity depletions ( ΔI557.7 nm ΔI630 nm ) is about 0.26±0.07 for F-region altitudes, and this component has a dependence on the height of the electron density profile.

Simultaneous measurements of the 015 57.7 nm, O2 atmospheric (0,1) band, NaD and OH (9,4) band emissions obtained during the period October November 1989 at Cachoeira Paulista (23°S, 45°W), Brazil, have been analysed to study gravity waves in the mesospheric region at a low-latitude station in the southern hemisphere. It was found that, when these emissions showed large temporal intensity variations, there were also short period quasi-coherent temporal variations superposed on them, suggesting a possible passage of internal gravity waves in the emission layers. Cross-correlation analysis indicates that the time lag between the different emissions is smaller for short period variations compared with the long period variations. The wave parameters, namely a vertical wavelength of 12 km, a horizontal derived wavelength of 200 km with a period of 80 min, estimated from one of the observed short-period coherent oscillations, are typical of the internal gravity waves at the airglow emission height.

Observations of nighttime thermospheric neutral wind velocities and temperatures from measurements of Doppler shifts and widths, respectively, of the OI 630.0 nm airglow emission line, using a Fabry-Perot interferometer, have been carried out at Cachoeira Paulista (23°S, 45°W), Brazil, since 1988. In this paper we present observations of thermospheric neutral winds and temperatures during the period July 6–10, 1991, which included the strong magnetic disturbance of July 8–9, 1991 when the Kp value reached 8. During this storm the meridional and zonal neutral wind velocity patterns were strongly modified. On July 9–10, the observed meridional wind during the storm shows a behaviour opposite to that observed during winter and the observed zonal wind at the beginning of the night shows a behaviour similar to its quiet time behaviour (to the east), but at 01:15 LT the zonal wind changes its direction rapidly to the west and at 03:45 LT it reverses to east again. Also, from the observed thermospheric temperatures, inferred from the thermal broadening of the 630.0 nm line emission, we find that during this event there is thermospheric cooling over Cachoeira Paulista. This result is surprising, because we would normally expect thermospheric heating during geomagnetic storms, since a large amount of energy is deposited in the thermosphere at high latitudes.