Aspects regarding the influence of High-Intensity Long-Duration Continuous Auroral Electrojet Activity (HILDCAA) intervals on ionospheric dynamics have been objecting to increasing interest in the last years. Notwithstanding, some key interconnections between the HILDCAA intervals impacts on the ionosphere over distinct latitudes, according to the solar cycle phase, remain to require further investigation. In this work, the F2 layer peak height and its critical frequency (hmF2 and foF2, respectively) from Digisonde data obtained over São Luís (2.60° S; 44.21° W), Cachoeira Paulista (22.70° S; 44.98° W), and Port Stanley (51.60° S, 57.9° W), were evaluated to unravel more details of the ionospheric responses to four HILDCAA intervals as case studies. Those are equatorial, low, and mid-latitude stations, respectively, and the main results over them presented a similar trend in terms of solar cycle dependence, with the greater impact on the ionospheric density along with solar maximum conditions, despite the higher frequency of HILDCAA occurrences in the descending and minimum phases. The variation of hmF2 due to HILDCAA effects in comparison to quiet time is about 20% in equatorial and mid-latitudes, while over the low latitude station the hmF2 ranges positively up to 40%. These results enhance our understanding of the HILDCAAs magnitude degree both regarding its solar cycle occurrence, and its effects in different ionospheric latitudinal sections.

The High-Intensity Long-Duration and Continuous AE Activities (HILDCAA) intervals are capable of causing a global disturbance in the terrestrial ionosphere. However, the ionospheric storms' behavior due to these intervals is still not widely understood. In the current study, we seek to comprise the HILDCAA disturbance time effects in the total electron content (TEC) values with respect to the quiet days' pattern by analyzing local time and seasonal dependences, and the influences of the solar wind velocity on a sample of 10 intervals that occurred in the years 2015 and 2016. The main results showed that the hourly distribution of the disturbance TEC may vary substantially between one HILDCAA interval and another. An equinoctial anomaly was found since the equinoxes represent more ionospheric TEC responses than the solstices. Regarding the solar wind velocities, although HILDCAA intervals are associated with highspeed streams, this association does not present a direct relation to TEC disturbance magnitudes at low and equatorial latitudes.

A tropopausa equatorial terrestre é, em geral, tratada como uma região de modestas variações de temperatura e vista apenas como uma interface entre a troposfera e a estratosfera. No entanto, trabalhos recentes têm sugerido que a tropopausa pode ser fonte de perturbações capazes de afetar localmente o clima troposférico. Neste contexto, o presente trabalho descreve uma investigação detalhada das características da tropopausa equatorial sobre a região de Natal-RN, utilizando dados de radiossondagens de balões meteorológicos lançados pelo Centro de Lançamento da Barreira do Inferno (CLBI), entre os anos de 2010 a 2014. Além disso, comparações com modelos computacionais semi-empíricos como o MSIS-90 mostram divergências com os dados experimentais. Foram analisados um total de 1849 casos, sendo 949 sondagens diurnas e 900 noturnas. Foram comparadas as temperaturas mínimas da tropopausa com relação às estações do ano, e se constatou que o mínimo de temperatura ocorre no outono e o máximo durante o inverno, cujos valores médios são, respectivamente, 189,6 K e 194,5 K. A explicação proposta para estes resultados, relaciona a precipitação durantes estas estações com a liberação de energia para alta troposfera.

Equatorial plasma bubbles consist of field‐aligned large‐scale depletions, or irregularities, characterized by drastic ion density rarefactions of the nocturnal low latitude/equatorial ionosphere. Understanding their behavior is important because of their degrading effects on radio wave signals and, consequently, their respective technological applications such as, for example, Global Positioning System applications. In this sense, a methodology of pattern recognition was developed and implemented here using the Long‐Term Ionospheric Anomaly Monitoring in order to infer the plasma bubbles zonal drift velocities, using two receiving stations of global navigation satellite systems data from the Brazilian Continuous Monitoring Network, located near to each other, in Salvador (BA) during geomagnetically quiet periods. The study covered the years of 2012, 2013, and 2014 for the months from September to January of the following year, choosing 10 representative days for each month. The average results for the plasma bubble zonal velocities provided by the model calculations were in agreement with the well‐known values. However, monthly individual analysis showed a behavior anticorrelated with that expected for high solar flux. Probably, the unexpected behavior is due to atypical configuration of the solar activity ascending phase.

Os Distúrbios Ionosféricos Propagantes (TID’s - Travelling Ionospheric Disturbances) são irregularidades no plasma ionosférico que se propagam com velocidades da ordem de dezenas a poucas centenas de quilômetros por hora. Nesse trabalho, foram detectadas e caracterizadas perturbações do tipo LSTID’s (Large scale Travelling Ionospheric Disturbances), em baixas latitudes, durante intensas tempestades geomagnéticas e também a forma como se propagação. Utilizou-se registros ionosféricos obtidos a partir de digissondas do tipo CADI (Canadian Advanced Digital Ionosonde) localizada na cidade de Natal e do tipo DSP (Digisonde Portable Souder) localizadas nas cidades de Cachoeira Paulista, Ramey e Eglin. Os dados de sondagem de Ramey e Eglin foram disponibilizados pela Global Ionosphere Radio Observatory (GIRO). Para observar os efeitos de tempestades sobre a ionosfera polar, foram utilizadas imagens aurorais do polo Norte, obtidas pelo satélite POLAR, que mostraram a intensificação do eletrojato auroral pela injeção de partículas nas cúspides. O período analisado compreendeu os dias 06 e 07 de abril de 2000 e os índices utilizados para caracterizar a atividade magnética nesse período foram Dst, Kp, e AE, além da componente Bz do campo magnético interplanetário. A tempestade ocorrida no dia 6 de abril apresentou um Dstmin = - 288 nT. A partir de gráficos de isolinhas foram verificados comportamentos anômalos da ionosfera sobre as quatro cidades, caracterizando a propagação como sendo do tipo LSTID’s, gerados pela expansão do oval auroral nos polos.

During our research we detected and characterized LSTID (Large Scale Ionospheric Disturbances), in low latitudes, during intense geomagnetic storms and also the way they propagated. It was used ionospheric records obtained from digisondes of CADI type (Canadian Advanced Digital lonosonde) located in the city of Natal and DSP type (Digisonde Portable Souder) located in the cities of Cachoeira Paulista, Ramey and Eglin. The survey data from Ramey and Eglin were provided by Global Ionosphere Radio Observatory (GIRO). To observe the effects of storms on the polar ionosphere, auroral images of the North pole, obtained by the POLAR satellite, were used, which showed the intensification of auroral electrojet by the injection of particles in the cusps. The analyzed period included the days 6th and 7th, April 2000, and the indices used to characterize the magnetic activity in this period were Dst, Kp, and AE, in addition to the Bz component of the interplanetary magnetic field. The storm on April 6th had a Dstmin = -288 nT. geomagnetic storm are capable of affecting the behavior of all ionospheric plasma, thus affecting the operation of signal transmission stations in the telecommunications band and the altitude of satellites in that region. Anomalous behavior of the ionosphere was verified on the four cities, characterizing the propagation as being of type LSTID's, generated by the expansion of the auroral oval at the poles.

Perturbações atmosféricas geradas por ondas de gravidade e com características quase periódicas têm sido intensamente estudadas nas últimas décadas. No entanto, poucos desses estudos se referem a atmosfera equatorial sobre o setor sul americano de latitudes. No presente trabalho se discute resultados relativos a detecção de assinaturas de ondas de gravidade no perfil de temperatura da estratosfera equatorial, em uma faixa de altura compreendida entre 16 – 25 km, a partir de dados de radiossondas instaladas em balões meteorológicos lançados, rotineiramente, do Centro de Lançamentos da Barreira do Inferno (CLBI), localizado em Natal/RN (5,8°S; 35,5°O), durante o ano de 2000. Neste ano foram realizadas 185 sondagens diurnas, sendo que em 29 casos foram observadas perturbações com períodos aproximados compreendidos entre 6 – 28 min, ou seja, compatíveis com ondas de gravidade. Além disso, foi calculado o perfil da densidade de energia potencial, para o caso do dia 23/05/2000, e se constatou que a densidade de energia potencial, associada à esta perturbação, foi da ordem de 0,5 – 4 J/kg.

Atmospheric disturbances generated by gravity waves exhibiting quasi-periodic characteristics have been intensively studied in recent decades. However, only a few of these studies refers to equatorial atmosphere above the South American sector latitudes. In this work we discuss results concerning the detection of gravity waves signatures in the temperature profile of the equatorial stratosphere, in a height range of 16 - 25 km from radiosonde data installed in weather balloons routinely launched by the Launching Center of Barreira do Inferno (CLBI), located in Natal/RN, (5.8 degrees S; 35.5 degrees W), during the year 2000. During this year there were made 185 diurnal surveys, and in 29 of these cases, disturbances were observed with approximate periods between 6 - 28 min, i.e. compatibles with of gravity waves. In addition, the density profile of potential energy was calculated considering the day 05/23/2000, and it was found that the potential energy density, associated with this disorder, was in the range 0.5 - 4 J/kg.

The motion of Medium Scale Traveling Ionospheric Disturbances (MSTIDs) was measured for 1 year from the eastern tip of Brazil, about 10 degrees degrees south of the magnetic and geographic equators using spaced fixed frequency radio transmitters. The motion was very similar during all of the year. The daytime average direction was towards 150 degrees azimuth (clockwise from north) and speed was typically in the range 150-300 m/s. The azimuth varied only slightly during the day being slightly more easterly during evening-morning hours. During winter months there were also some TIDs whose motion was northward. None of the known sources for MSTIDs fits well with MSTIDs having these velocity patterns. A possible unconfirmed source is the Inter-Tropical Convergence Zone (ITCZ). Citation: MacDougall, J., M. A. Abdu, I. Batista, R. Buriti, A. F. Medeiros, P. T. Jayachandran, and G. Borba (2011), Spaced transmitter measurements of medium scale traveling ionospheric disturbances near the equator, Geophys. Res. Lett., 38, L16806, doi: 10.1029/2011GL048598.

Database from CADI (Canadian Digital Ionosonde) recorded at Natal (5.2° S, 36° W) near solar maximum are used to compare with the International Reference Ionosphere (IRI) predictions. Such comparison is done using vertical profiles of electron density and F region peak parameters, the maximum electron density (NmF2) and its corresponding height (HmF2), for geomagnetically quiet and disturbed conditions. The mean behavior of the observed vertical electron density profiles at 0300, 0900, 1500 and 2100 UT (UT = LT + 2.4 hr) for quiet and disturbed periods was compared with IRI profiles. Generally, good agreement between the two sets is noted, but IRI underestimates the heights of the bottomside F region at 0900 and 2100 UT. Also, discrepancies are found between the observed values of NmF2 and HmF2 and those obtained from IRI using URSI coefficients during evening-nighttime period.

Gravity wave effects in the nocturnal thermospheric F-region domain are seldom detected in the intertropical region by optical (airglow) techniques, especially during geomagnetically quiet times, in part because the low inclination of the magnetic field, as opposed to the case of the mid-latitude region, does not favor significant vertical excursions of ionospheric plasma in response to meridional winds. Such difficulty in detecting gravity wave signatures in the F-region by means of optical techniques tends to increase in the absence of geomagnetic storms because of the lack of strong forcing mechanisms necessary to generate high intensity gravity waves. The purpose of this work is to show that during the quiet day of 9 August 1999, the Terminator may have been a source region of wave-like disturbances in the nocturnal F-region at the low-latitude station Cachoeira Paulista (22°41'S; 45°00W, dip 30°). A digital all-sky OI 630nm imager system located at that station has shown propagating wave-like spatial structures in the airglow intensity near the Terminator. This observation supports a previous study on the evidence of the presence of gravity waves during the post-sunset period at the same location by means of a scanning photometer system (1997, Sobral, J. Atmos. Terr. Phys. 59, 1611–1623). The absence of range-type spread-F as monitored by a local digisonde and the absence of radio wave scintillation as monitored by a local GPS receiver, excludes the hypothesis that the wave-like airglow structures are associated with the occurrence of the ionospheric plasma bubbles. Downwards motion of the iso-density real height contours at 22.0 ms−1 and 33.1 ms−1 are observed. The wave detection by the imager system is reported and discussed here.

The understanding of post-sunset zonal drifts of ionospheric plasma depletions in the equatorial and subequatorial regions are of importance to the knowledge of the electrodynamics of the nocturnal ionosphere. Drifts occuring over the low latitude station Cachoeira Paulista — CP (Geogr. 22° 41' S, 45° 00', dip 29° for the epoch of 1985) during the October and March time frames are analyzed for the period of 1980 –1992. That analysis is based upon about 650 days of zonal scanning photometer measurements of the nocturnal OI 630 nm airglow. The zonal motions of valleys of the OI630 nm intensity are used to infer the eastward plasma velocity variations with local time. In this way, the velocity variations with solar activity and magnetic activity are studied. The mean trend in the velocity local time variation is a decrease from early evening to post-midnight hours, as expected in view of the F-region vertical electric fields, naturally decreasing magnitudes after sunset due to recombination. The zonal velocity decay between 21 LT and 02 LT faster during the period of maximum solar activity than during the solar minimum period.

We report photometric southern hemisphere wintertime perturbations of the nocturnal F-region atomic oxygen 630 nm red line intensity which are observed to occur concurrently with apparent ionogram signatures of F-region gravity waves. Such airglow events were detected on a total of 40 days of experiments. The airglow experiments were run at Cachoeira Paulista (CP, geographic 22 ° 41′ S, 45 ° 00′ W, dip 28 ° S). The events are characterized by south-to-north travelling airglow valleys, or depletion events (SNE). They were obtained from a set of 299 experiments performed during the period of 10 August 1977 to 4 July 1984. Their equatorwards velocities, wavelengths and periods vary within the ranges of 150–300 m s−1, 100–200 km and 15 min — 3 h, respectively. They appear during the post-sunset period and remain within the field of view of the meridional scanning photometer from about ten minutes to a few hours. The SNE were seen to occur more frequently in July and were absent from September to March. The photometer scanned ± 75 ° around zenith in the magnetic meridional and zonal planes. Ionogram spread-F and VHF polarimeter data that showed no phase or amplitude scintillations during the SNE indicated no concurrent existence of equatorial plasma depletions. It is shown that the SNE are not necessarily related to geomagnetic disturbed conditions. The present results are, to the authors' knowledge, the first showing gravity wave effects, near the sunset side of the solar terminator, on the low-latitude F-region atomic oxygen red nightglow under undisturbed geomagnetic conditions. The characteristics of these waves point to the solar terminator as their source of generation. A series of physical and morphological features of the phenomena are presented.

O estudo do Conteúdo Eletrônico Total através do método de rotaçăo de Faraday sempre foi de grande importância para o estudo da ionosfera, mas a comparaçăo de dados experimentais com modelos, principalmente modelos que tivessem boa resposta na regiăo equatorial, como é o caso do modelo Bonelli-90, raramente é feita. Esse trabalho consiste em comparar os dados de rotaçăo de Faraday obtidos pôr um polarimetro em Natal-RN com os resultados gerados pelo modelo Bonelli-90.

We report observations of airglow (OI 630 nm) intensity perturbations which are possibly caused by thermospheric gravity waves. Those perturbations are not very frequently observed during the year, as discussed below. Two photometers scanned approximately 75 degrees around zenith in the magnetic meridional and zonal p1lanes at Caçhoeira Paulista (CP, Geogr. 22 41 S, 45000 W, dip 28 S).

The contribution of the excited state species O(S-1) to the production of O(D-1) in the nocturnal F-region is investigated here utilizing rocketborne electron density and photometric (557.7 nm and 630 nm) airglow data obtained over Natal (geogr. 5.8 degrees S, 35.2 degrees W), in Brazil, on October 31, 1986. Even though this contribution is rather small it is observed to remarkably vary with height. In the bottomside ionosphere it varies from 1.15% at 190 km to 6.85% at 265 km. It is suggested here that such rapid height variation in the contribution at the bottomside ionosphere is associated with a positive height gradient of the O-2(+) population at higher vibrational levels (v = 1 and 2). Such hypothesis is consistent with the fact that in the individual neutral dissociative state of the (1) Sigma(u)(+) symmetry, which is the only source channel for the O(S-1), the rate of production of O(D-1) increases with v. The contribution of the cascading process to the OI 630 nm airglow, which is generally assumed to be negligible, is found here to be about 5.1% of the total OI 630 nm airglow intensity.

We measured, as a function of position along the stripe, the intensity of luminescence emitted normally to the junction plane in GaAs/GaAlAs and InGaAsP/InP LED's. We set an upper bound p=0.1 for the depth of modulation in the carrier density under highly excited conditions such that the non-equilibrium carrier density and effective temperature exceed the threshold and enter the domain where formation of CDW's is possible.