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Long-term data available from Lidar systems located at three different locations namely São José dos Campos, Brazil (23.2° S, 45.8° W), Gadanki (13.5° N, 79.2° E) and Reunion (20.8° S, 55.5° E) have been used to investigate the long-term variations like Annual, Semi-annual, Quasi-biennial, El Nino Southern Oscillation and solar cycle. These oscillations are also extracted from simultaneous satellite borne measurements of HALogen Occultation Experiment (HALOE) instrument onboard UARS and SABER onboard TIMED over these stations making largest time series covering the entire middle atmosphere. A good agreement is found between the LIDAR and satellite-derived amplitudes and phases between 30 and 65 km altitude, which suggests that satellite measurements can be used to investigate the long-term trends globally. Latter measurements are extended to 80 km in order to further investigate these oscillations. Large difference in the amplitudes between the eastern pacific and western pacific is noticed in these oscillations. Changing from cooling trends in the stratosphere to warming trends in the mesosphere occurs more or less at altitude around 70 km altitude and this result agrees well with that observed by satellite measurements reported in the literature. The peak in the cooling trend does not occur at a fixed altitude in the stratosphere however maximum warming trend is observed around 75 km at all the stations. The observed long-term trends including various oscillations are compared with that reported with various techniques.

Aims. To aid the design of laser guide star (LGS) assisted adaptive optics (AO) systems, we present an analysis of the statistics of the mesospheric sodium layer based on long-term observations (35 years).Methods. We analyze measurements of the Na-layer characteristics covering a long period (1973-2008), acquired at latitude 23 degrees south, in Sao Jose dos Compos, Sao Paulo, Brazil. We note that Paranal (Chile) is located at latitude 24 degrees south, approximately the same latitude as Sao Paulo.Results. This study allowed us to assess the availability of LGS-assisted AO systems depending on the sodium layer properties. We also present an analysis of the LGSs spot elongation over the year, as well as the nocturnal and the seasonal variation in the mesospheric sodium layer parameters.Conclusions. The average values of the sodium layer parameters are 92.09 km for the centroid height, 11.37 km for the layer thickness, and 5 x 10(13) m(-2) for the column abundance. Assuming a laser of sufficient power to produce an adequate photon return flux for an AO system with a column abundance of 4 x 10(13) m(-2), a telescope could observe at low geographic latitudes with the sodium LGS more than 250 days per year. Increasing this power by 20%, we could observe throughout the entire year.

In the absence of aerosol scattering, lidar measurements of the Rayleigh backscattering coefficient can be used to determine atmospheric density profiles. Such density profiles can then be transformed into temperature profiles via the assumption of hydrostatic equilibrium and the perfect gas law. In the presence of aerosols, however, simple elastic scattering measurements are unable to differentiate between the Rayleigh and aerosol components, making it impossible to determine temperature profiles. It is possible to overcome this problem by determining atmospheric density from the rotational Raman scattering from atmospheric nitrogen and oxygen, which is unaffected by the aerosol scattering. This paper describes a lidar receiver designed to implement this technique, making it possible to determine both the atmospheric temperature profile and the aerosol backscattering from a single lidar measurement.

Temperature profiles between 30 and 65 km have been obtained in Sao Jose dos Campos, Brazil (23° S, 46° W) with a lidar operated at 589 nm since 1993. The long-term knowledge of this temperature profile has allowed us to know its average climatology as well as the nighttime evolution. During the period of late September-early October, 2002 we observed profiles which differ considerably from the average for the same period in other years. Specially, a profile obtained on the night of October 2, 2002 called our attention by presenting an unusual stratospheric inversion layer with a decrease of 8-10 K between 38 and 42 km. Subsequent analysis showed that this period coincided with an unprecedented major southern hemisphere stratospheric warming at high latitude. Analysis of additional SABER temperature data showed that inversion layers at the same altitude extends to a wide area at low latitude.

A lidar has been operated in São José dos Campos, Brazil (23.2°S, 45.8°W) since 1972, mainly dedicated to the study of mesospheric sodium at the 589nm resonant line. The molecular Rayleigh scattering can also be used provided we limit the height to ∼75km where the sodium scattering begins. Nevertheless, the weak signal obtained only permits the determination of density and temperature profiles by accumulating a large number of shots giving only nocturnal average profiles. Temporal variations in density and temperature on the scale of hours can however, be obtained by performing a superposed epoch analysis for a given time interval and covering a period of several days. In this way we obtained hourly mean profiles grouped by months, seasons and overall, with data acquired from 1993 to 2004. The difference between the hourly temperatures and the nocturnal means shows for some months, with enough data coverage, downward propagating structures that apparently have tidal origin. The seasonal averages show a recurrent feature with high temperatures before and low temperatures after midnight above 50km. Some similarity is found with the GSWM model, but the observed temperature amplitudes are twice of that for the model.

In a paper published 12 years ago, we showed that the height of the atmospheric sodium layer at our location is about 1 km lower in November than at any other time of the year. We also showed that the decrease in height of the sodium layer was accompanied by an increase in the intensity of the OI 557.7 nm and OH(9,4) band airglow emissions. At that time we suggested that this behavior could be the result of large scale convective transport in the MLT region. We have now had the opportunity to compare the diurnal variations of the sodium layer and airglow emissions with the tidal winds measured by meteor radar over the past 5 years. We find that the amplitude of the diurnal tide is much smaller in November than at other times of the year. Since most of the sodium measurements and all of the airglow observations are for night-time conditions only, a change in the amplitude of the 24-h tide could strongly influence the average measured sodium and airglow parameters. It is shown that the observed changes in the tidal winds are qualitatively consistent with the sodium measurements, but the amplitude of the observed height change is much greater than would be expected from the tidal winds.

In this study we show examples of very special shapes in the height-time evolution of the sodium layers measured by lidar installed at Sao Jose dos Campos (23°, 46°w), Brazil. We selected two nights during the period from 1996 to 1999, in order to analyze the morphology of the Na layer and its relation with gravity wave perturbations. In some cases the Na layer becomes narrower and then broadens whereas in others, the sodium layers bifurcate. Since the linear layer response is not always adequate to describe gravity wave sodium layer interactions (by linear response, it is meant that the layer density perturbations have the same temporal and spatial frequencies as the gravity wave), nonlinear components of the layer density response must be considered in interpreting sodium lidar data. In this work, these observed morphologies are presented and discussed under linear and nonlinear layer density response.

The sporadic occurrence of layers of enhanced concentration of meteoric metals in the vicinity of the mesopause has been observed by lidar at many locations. These layers are much thinner than the background layer, last between a few minutes and many hours, and appear to be related to ionospheric sporadic E. A much more rare type of transient layer has been reported in the literature only once, by Kane et al. [2001]. The layers in question, observed in sodium by a lidar operating at Arecibo (18.3°N, 66.7°W), appear as C‐shaped structures in the lidar height/time display. The structures, which have been observed at around 100 km, with durations around 30 min, appear not to be related to normal sporadic metals layers, and the Arecibo workers suggest that they might be produced by wave‐breaking or Kelvin‐Helmholtz billows. At São José dos Campos (23°S, 46°W) we observe C‐structures in the sodium layer only very occasionally, but an analysis of their formation, together with simultaneous meteor winds measurements, suggests that the observed structures might be the result of wind‐shear distortion of preexisting clouds of enhanced sodium concentration.

La investigación sobre la atmósfera alta en el Instituto de Investigaciones Espaciales de Brasil se concentra en las áreas de fotoquímica y dinámica de la mesopausa y la termosfera baja, climatología de la atmósfera media y aerosol estratosférico. Por el momento el principal énfasis está en la dinámica de la mesopausa. Los estudios experimentales se llevan a cabo con lidar, resplandor atmosférico y radar de meteoros y con técnicas espaciales. El lidar operando en San José de los Campos (23°S, 46°W) mide la distribución vertical del sodio atmosférico entre 80 y 110 km, el perfil de densidad atmosférica, de 35 a 70 km, y el aerosol estratosférico alrededor de los 20 km. El fotómetro de resplandor atmosférico instalado en Cachoeira Paulista (23°S, 45°W) y en San José de Cariri (7°S, 37°W) mide la emisión del oxígeno atómico y molecular del OH y del sodio. La temperatura entre 75 y 95 km se determina a partir de los espectros rotacionales del OH y O2. Con un sistema de imágenes se mide la estructura horizontal de las mismas emisiones en San José de Cariri. Estas observaciones tienen por objeto el estudio de la propagación de ondas internas de gravedad y sus efectos en la mesopausa. Un radar de meteoros instalado en Cahoeira Paulista se usa para determinar la estructura del viento entre 80 y 110 km durante las 24 horas, con el propósito principal de estudiar las mareas atmosféricas y las ondas planetarias. Ocasionalmente se hacen experimentos a bordo de satélites, que se lanzan desde Natal (6°S, 35°W) o Alcántara ("°S, 44.5°W) y se usan para estudiar la distribución vertical de la emisión del resplandor atmosférico y su relación con otros parámetros atmosféricos.

Measurements of the vertical distribution of atmospheric sodium, made at São José dos Campos (23°S, 46°W) from 1972 to 2001 show a negligible net long‐term trend in the layer over this time period. In view of the fact that cooling of the upper atmosphere, as indicated by some experimental studies and predicted by models, would be expected to influence the vertical distribution of sodium, this result can be used to estimate the limits of such cooling. In order to investigate the sensitivity of the sodium layer to changes in the atmospheric temperature profile, and thus estimate an upper limit to the changes it should be possible to detect, we have used a comprehensive model for the mesosphere and lower thermosphere (65–110 km) that includes all species and reactions thought to be relevant to the sodium chemistry. On the basis of this study we find that the sodium layer observations are consistent with model calculations for the global effects of increased CO2 but are not consistent with many of the experimental studies, which show cooling trends much larger than expected from theoretical studies.

In earlier studies, an analysis of the long-term variation in the centroid height of the atmospheric sodium layer suggested the existence of a secular decrease in the height of the layer. The analysis of lidar data obtained between 1972 and 1994 indicated a fall of 740 m over this 22 year time period. A possible solar cycle variation with an amplitude of 170 m was also detected, although with low statistical significance. A new analysis, in which care was taken to exclude days in which sporadic sodium layers were present, and including measurements made up to the end of 2001, shows that the linear trend has not continued. The fall in centroid height observed in the early data is found to be compensated by a higher values observed since 1988, and the overall linear trend for 1972 to the end of 2001 is now only 93±53 metres/decade. This new result strongly suggests that the previously detected trend was not a consequence of long-term global cooling of the upper atmosphere

Rare and sporadic events, caused by unusual conditions in the MLT region may occur such as the sporadic metal layers, observed by lidars, and the more recently detected sharp front in the nightglow emissions imaged with CCD all sky cameras. Few events of this latter kind have been reported in the literature and no simultaneous occurrence of both. In this work, we report the observation of a sporadic sodium layer measured by lidar in São José dos Campos, Brazil (22.5°S,46°W) on the night of July 13–14, 1999 which was followed by a rare “wall” event observed at Cachoeira Paulista (CP) (23°S,45°W) in the OH NIR and OI5577 by a CCD imager, and zenith tilting filter photometers. The wind field was also observed by a SkiYmet meteor radar system also operated at CP. At around 23:45 the sodium layer had an abrupt change in its shape. At the same time unusual situation also had occurred in the airglow data taken in CP both with the imager and with the zenith photometer. A sequence of all sky images for the OI557.7nm and OH NIR showed very clear lines dividing the sky into bright and dark areas, with the first propagating from the NE to SW at ∼70m/s and the second propagating to NNE. Zenith photometer also showed a rapid decrease of the OH(6,2) intensity at around 23:45 and a very large increase in the rotational temperature of O2(0,1) (at ∼94km) from 23:00 to 24:00(∼40K). The meridional and zonal wind structure measured by the meteor radar in CP showed that from 21:00 to 01:00 a wind shear was present both in the meridional and zonal winds with the phase propagating from ∼97 to 80km during this time which were very well correlated with the vertical displacement of the sporadic peak. Large-amplitude gravity wave was also detected. The temperature enhancement above 90km could be responsible for the sodium density increase and also for the set up of the conditions for the airglow events.