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Key Points: 1) Good inter-comparison is obtained between Arecibo observatory spectrometer and Lidar temperatures and results are similar to previous studies. 2) The temperature comparison improves considerably when time varying weighting functions are used instead of a single weighting function. 3) Spectrometer and Lidar temperature comparison provide better estimation of the 20 OH(6,2) peak altitudes in presence of a reference for it. Abstract Rotational temperatures in the Mesosphere-Lower Thermosphere region are estimated by utilizing the OH(6,2) Meinel band nightglow emission observed with an Ebert-Fastie Spectrometer (EFS) operated at Arecibo Observatory (AO), Puerto Rico (18.35 o N, 66.75 o W) during February-April 2005. To validate the estimated rotational temperatures, a comparison with temperatures obtained from a co-located Potassium Temperature Lidar (K-Lidar) and overhead passes of the Sounding of the Atmosphere by Broadband Emission Radiometry (SABER) instrument onboard NASA’s TIMED satellite are performed. Two types of weighting functions are applied on the K-Lidar temperatures to compare them with EFS temperatures. The first type has a fixed peak altitude and a fixed full width at half maximum (FWHM) for the whole night. In the second type, the peak altitude and FWHM vary with the local time. Average temperature difference between the EFS and K-Lidar obtained with both types of weighting functions are comparable with the previously published results from different latitude-longitude sectors. Further, it is found that temperature comparison improves when the time varying weighting functions are considered. On the other hand, we have shown that comparison of temperatures obtained from these two instruments could provide a better estimate of the OH(6,2) peak altitudes if a reference temporal trend of the OH(6,2) peak altitudes is available. Also, it is noticed that there are significant differences between the seasonal mean OH(6,2) peak altitudes obtained from SABER observation and model calculation. Such a detailed study using the AO EFS data has not previously been carried out.

Optical observations of transient luminous events and remote-sensing of the lower ionosphere with low-frequency radio waves have demonstrated that thunderstorms and lightning can have substantial impacts in the nighttime ionospheric D region. However, it remains a challenge to quantify such effects in the daytime lower ionosphere. The wealth of electron density data acquired over the years by the Arecibo Observatory incoherent scatter radar (ISR) with high vertical spatial resolution (300-m in the present study), combined with its tropical location in a region of high lightning activity, indicate a potentially transformative pathway to address this issue. Through a systematic survey, we show that daytime sudden electron density changes registered by Arecibo’s ISR during thunderstorm times are on average different than the ones happening during fair weather conditions (driven by other external factors). These changes typically correspond to electron density depletions in the D and E region. The survey also shows that these disturbances are different than the ones associated with solar flares, which tend to have longer duration and most often correspond to an increase in the local electron density content.

In the last couple of decades, substantial research has been dedicated to understanding the coupling between atmospheric regions. Research on transient luminous events (TLEs) appeared and quickly intensified with the promise of TLEs serving as an optical remote sensing tool of the mesosphere and lower ionosphere. However, to date it remains challenging to obtain quantitative estimates of electron density changes in the ionospheric D region due to underlying lightning and thunderstorms. Arecibo’s incoherent scatter radar (ISR) capabilities for measuring ionospheric electron density with high resolution (300-m spatial resolution in the present study), combined with its tropical location in a region of high lightning incidence rates, indicate a potentially transformative pathway to address this problem. Through a systematic survey, we show that sudden electron density changes registered by Arecibo’s ISR during thunderstorm times are on average different than the ones happening during fair weather conditions (driven by other external factors). Electron density changes happening coincidentally with lightning activity have typical amplitudes of 10–90% between 80–90 km altitude, and in a selected number of cases can be reasonably correlated to underlying lightning activity.

We employ in this work the first airglow dataset registered at the Remote Optical Facility (ROF) in Culebra, Puerto Rico, during the descending phase of the solar cycle #24. From November 4, 2015, ...

We present in this work a method for estimation of equatorial plasma bubble (EPB) mean zonal drift velocities using keograms generated from images of the OI 6300.0 nm nightglow emission collected from an equatorial station&ndash, Cariri (7.4&deg, S, 36.5&deg, W), and a mid-latitude station&ndash, Cachoeira Paulista (22.7&deg, S, 45&deg, W), both in the Brazilian sector. The mean zonal drift velocities were estimated for 239 events recorded from 2000 to 2003 in Cariri, and for 56 events recorded over Cachoeira Paulista from 1998 to 2000. It was found that EPB zonal drift velocities are smaller (&asymp, 60 ms&minus, 1) for events occurring later in the night compared to those occurring earlier (&asymp, 150 ms&minus, 1). The decreasing rate of the zonal drift velocity is &asymp, 10 ms&minus, 1/h. We have also found that, in general, bubble events appearing first in the west-most region of the keograms are faster than those appearing first in the east-most region. Larger zonal drift velocities occur from 19 to 23 LT in a longitude range from &minus, 37&deg, to &minus, 33&deg, which shows that the keogram method can be used to describe vertical gradients in the thermospheric wind, assuming that the EPBs drift eastward with the zonal wind. The method of velocity estimation using keograms compares favorably against the mosaic method developed by Arruda, D.C.S, 2005, but the standard deviation of the residuals for the zonal drift velocities from the two methods is not small (&asymp, 15 ms&minus, 1).

Os ventos neutros termosféricos (VNT) desempenham um papel fundamental na dinâmica da ionosfera. Atuam diretamente na deriva do plasma, sendo o principal mecanismo de manutenção da ionosfera noturna, além de influenciar o comportamento da anomalia de Appleton. Frequentemente, medidas das componentes de VNT são obtidas por equipamentos como interferômetro de FabryPérot (FPI, sigla para Fabry-Pérot interferometer), radar de espalhamento incoerente (ISR sigla para Incoherent Scatter Radar), e equipamentos a bordo de foguetes de sondagem. No entanto, são medidas localizadas e de baixa cobertura espacial. Com o advento de observações realizadas a partir de satélites foi possível obter medidas das componentes de VNT com maior cobertura espacial e temporal. Os modelos de VNT têm se tornado uma ferramenta importante para a compreensão do comportamento da dinâmica da atmosfera neutra e ionizada acima da mesopausa. Contudo, alguns modelos apresentam discordâncias relacionadas ao comportamento na termosfera, especialmente no hemisfério Sul devido a pouca disponibilidade de medidas in situ para calibração. Neste trabalho é apresentado o modelo empírico de VNT denominado Empirical Averaged Thermospheric Wind Model (EArTh Wind), baseado em um estudo estatístico dos registros obtidos pelo satélite Upper Atmosphere Research Satellite (UARS) usando o equipamento embarcado Wind Imaging Interferometer (WINDII) entre 1992 e 1997. O EArTh Wind representa a média longitudinal das componentes do VNT em 250 km de altitude entre ±50o de latitude geográfica, para condições de atividade solar e geomagnética de Φ10,7m = 87,83 SFU e kpm ~ 2- (1,58), respectivamente, e descreve suas variações sazonais (dia do ano) e hora local, moduladas por séries de Fourier. O comportamento das simulações produzidas pelo modelo EArTh Wind mostram boa concordância com a climatologia das componentes de VNT observadas pelo satélite UARS em distintos períodos do ano. Os parâmetros estatísticos utilizados para avaliar o modelo em relação aos dados observados exibiram bons resultados, especialmente no equinócio em ambas as componentes do VNT. Particularmente, melhores resultados foram obtidos para a componente zonal, em todos os períodos do ano. Os testes estatísticos também indicaram que o EArTh Wind se assemelha à versão 2014 do Horizontal Wind Model (HWM14), principalmente para a componente meridional. Uma comparação localizada entre o EArTh Wind e dados obtidos utilizando FPI em Arecibo (18,35o N e 66,75o O), mostrou uma boa concordância da componente meridional, também confirmada pelos parâmetros estatísticos comparativos obtidos. Thermospheric Neutral Winds (TNW) play a crucial role in the dynamics of the ionosphere by acting directly on the plasma drift. The TNW are the main maintenance mechanism of the nocturnal ionosphere. In addition, the TNW influence the behavior of Appleton Anomaly. The componentes of the TNW are usually measured by equipments such as Fabry-Pérot interferometer (FPI), Incoherent Scatter Radar (ISR), and science payloads onboard in rockets. However, these measurements are localized and offer low spatial coverage. With the advance of satellite observations, it was possible to obtain better spatial and temporal data coverage of the TNW’s components. On the other hand, TNW models have become an important tool for understanding the behavior of the dynamics of the neutral and ionized atmosphere above the mesopause. However, some models disagree about the behavior of the TNW at the altitudes of the thermosphere, especially in the South American Sector, mostly due to the lack of in situ measures for calibration. This work presents the TNW model “Empirical Averaged Thermospheric Wind Model (EArTh Wind)” that is based on a statistical study of the records obtained by the UARS satellite, using the onboard Wind Imaging Interferometer (WINDII) equipment from 1992 to 1997. The EArTh Wind represents the longitudinal average of TNW at the altitude of 250 km, within ±50o of geographic latitude for solar and geomagnetic conditions of Φ10,7m = 87,83 SFU and kpm = 2- (1,58), respectively. The EArTh Wind describe the seasonal (day of the year) and local time variability of these mean TNW evaluated by Fourier series. The behavior of the simulations obtained by the EArTh Wind show a good agreement with the climatology of the TNW components observed by the UARS satellite at different periods of the year. The statistical parameters used to evaluate the EArTh Wind presented good agreement whith the dataset for both TNW’s components, especially during the equinoxes. Particullary, a better agreement between the dataset and the zonal component was observed for all periods of the year. The statistical tests indicated that the latitudinal model EArTh Wind resembles the 2014 version of the Horizontal Wind Model, (HWM14), especially for the meridional component. In the localized comparison between the EArTh Wind FPI data from in Arecibo (18.35o N and 66.75o W), the meridional component showed good agreement, also comfirmed by the comparative statistical parameters obtained.