Nighttime airglow images observed at the low-latitude site of Sao Joao do Cariri (7.4 degrees S, 36.5 degrees W) showed the presence of a medium-scale atmospheric gravity wave (AGW) associated with the 21 August 2017 total solar eclipse. The AGW had a horizontal wavelength of similar to 1,618 km, observed period of similar to 152 min, and propagation direction of similar to 200 degrees clockwise from the north. The spectral characteristics of this wave are in good agreement with theoretical predictions for waves generated by eclipses. Additionally, the wave was reverse ray-traced, and the results show its path crossing the Moon's shadow of the total solar eclipse in the tropical North Atlantic ocean at stratospheric altitudes. Investigation about potential driving sources for this wave indicates the total solar eclipse as the most likely candidate. The optical measurements were part of an observational campaign carried out to detect the impact of the August 21 eclipse in the atmosphere at low latitudes.

Using airglow data from an all-sky imager deployed at São João do Cariri (7.4∘ S, 36.5∘ W), the start times of equatorial plasma bubbles was studied in order to investigate the day-to-day variability of this phenomenon. Data from a period over 10 years were analyzed from 2000 to 2010. Semimonthly oscillations were clearly observed in the start times of plasma bubbles from OI6300 airglow images during this period of observation, and four case studies (September 2003, September–October 2005, November 2005 and January 2008) were chosen to show in detail this kind of modulation. Since the airglow measurements are not continuous in time, more than one cycle of oscillation in the start times of plasma bubbles cannot be observed from these data. Thus, data from a digisonde at São Luís (2.6∘ S, 44.2∘ W) in November 2005 were used to corroborate the results. Technical/climate issues did not allow one to observe the semimonthly oscillations simultaneously by the two instruments, but from October to November 2005 there was a predominance of this oscillation in the start times of the irregularities over Brazil. Besides, statistical analysis for the data in the whole period of observation has shown that the lunar tide, which has semimonthly variability, is likely the main forcing for the semimonthly oscillation in the start times of equatorial plasma bubbles. The presence of this oscillation can contribute to the day-to-day variability of equatorial plasma bubbles.

In this study, OI 630.0 nm nightglow image data obtained from an all-sky imaging station located at Sao Joao do Cariri (7.4 degrees S, 36.5 degrees W), have been used to study the occurrence of equatorial plasma bubbles (EPBs) over the Brazilian equatorial region. The observations, which took place from September 2000 to December 2010 (almost eleven years), covered a significant part of solar cycle 23 (descending phase of SC23) and the very beginning of solar cycle 24 (ascending phase of SC24). There were 1337 nights of observations with 666 nights with EPB events, which translates to an occurrence rate of similar to 49.8%. Of these nights, 1290 were considered quiet (Dst >= -50 nT) with similar to 50% plasma bubbles occurrence rate. The occurrence of EPBs was studied under three solar activity phases - high solar activity phase (HSA, September 2000 - March 2004), moderate solar activity phase (MSA or descending phase, March 2004 - October 2006) and low solar activity phase (LSA, October 2006 - December 2010). The low solar activity phase is part of the peculiar solar cycle 24, considered the weakest in over a century with most sunspotless days (2008-2009). The maximum occurrence of bubbles, equal to 54.2%, was found during the HSA phase, with percentages characterizing MSA and LSA being respectively 52.4% and 45.8%. The analysis also showed clear seasonal variation in the EPB occurrence with maximum rates in summer, spring, autumn, and the minimum rates in winter for all solar activity phases. Overall, there was observed solar cycle variation in each season with maximum occurrence in HSA followed by MSA and then LSA except in autumn where higher occurrence rate was observed in LSA phase than in MSA phase. (C) 2019 COSPAR. Published by Elsevier Ltd. All rights reserved.

Abstract. Using data from airglow an all sky imager and a coherent backscatter radar deployed at São João do Cariri (7.4° S, 36.5° W) and São Luís (2.6° S, 44.2° W), respectively, the start time of equatorial Spread-F were studied. Data from a period of over 10 years was investigated from 2000 to 2010. The semimonthly oscillations were clearly revealed in the start time of plasma bubbles from Oi6300 airglow images during three periods (September 2003, September–October 2005, November 2005 and January 2008). Since the airglow measurements are not continuous in time, more than one cycle of oscillation in the start time of plasma bubbles cannot be observed from these data. Thus, coherent backscatter radar data appeared as an alternative to investigate the start time of the ionospheric irregularities. Semimonthly oscillation were observed in the start time of plumes (November 2005) and bottom type Spread-F (November 2008) with at least one complete cycle. Technical/climate issues did not allowed to observe the semimonthly oscillations simultaneously by the two instruments, but from September to December 2005 there was a predominance of this spread-F start time oscillation over Brazil. The presence of this oscillation certainly contribute to the day-to-day variability of spread-F.

On 3 October 2005 a mesospheric front was observed over Sao Joao do Cariri (7.4 degrees S, 36.5 degrees W). This front propagated to the northeast and appeared in the airglow images on the west side of the observatory. By about 1.5 h later, it dissipated completely when the front crossed the local zenith. Ahead of the front, several ripple structures appeared during the dissipative process of the front. Using coincident temperature profile from the TIMED/SABER satellite and wind profiles from a meteor radar at Sao Joao do Cariri, the background of the atmosphere was investigated in detail. On the one hand, it was noted that a strong vertical wind shear in the propagation direction of the front produced by a semidiunal thermal tide was mainly responsible for the formation of duct (Doppler duct), in which the front propagated up to the zenith of the images. On the other hand, the evolution of the Richardson number as well as the appearance of ripples ahead of the main front suggested that a presence of instability in the airglow layer that did not allow the propagation of the front to the other side of the local zenith.

Airglow and wind measurements from the Brazilian equatorial region were used to investigate the presence and the effects of the 3-4-day ultrafast Kelvin waves in the MLT. The airglow integrated intensities of the OI557.7 nm, O2b(0-1) and OH(6-2) emissions, as well as the OH rotational temperature, were measured by a multichannel photometer, and the zonal and meridional wind components between 80 and 100 km were obtained from a meteor radar. Both instruments are installed in the Brazilian equatorial region at Sao Joao do Cariri (7.4 degrees S, 36.5 degrees W). Data from 2005 were used in this study. The 3-4-day oscillations appear intermittently throughout the year in the airglow. They were identified in January, March, July, August and October-November observations. The amplitudes induced by the waves in the airglow range from 26 to 40% in the OI557.7 nm, 17 to 43% in the O2b(0-1) and 15 to 20% in the OH(6-2) emissions. In the OH rotational temperature, the amplitudes were from 4 to 6 K. Common 3-4-day oscillations between airglow and neutral wind compatible with ultrafast Kelvin waves were observed in March, August and October-November. In these cases, the amplitudes in the zonal wind were found to be between 22 and 28ms(-1) and the vertical wavelength ranges from 44 to 62 km. Evidence of the nonlinear interaction between the ultrafast Kelvin wave and diurnal tide was observed.

An intense activity of ripples during the nighttime was observed in airglow images over São João do Cariri (36.5°W, 7.4°S) on 10 October 2004 which lasted for two hours. Those ripples appeared simultaneously with the crossing of a mesospheric front and medium scale gravity waves. The ripples occurred ahead of the mesospheric front and their phase front were almost parallel to the phase of the mesospheric front and were almost perpendicular to the phase front of the gravity wave. Using wind measurements from a meteor radar located at São João do Cariri and simultaneous vertical temperature profiles from the TIMED/SABER satellite, on the night of the events and within the imager field of view, the atmospheric background environment in the mesosphere and lower thermosphere (MLT) was investigated in order to understand the instability process that caused the appearance of the ripples. Dynamic and convective instabilities have been pointed out as responsible for creation of ripples in the MLT. The observed ripples were advected by the neutral wind, they occurred into a region with negative lapse rate of the potential temperature and the Richardson number was negative as well. According to these characteristics, the ripple structures could be generated in the MLT region due to the predominance of convective instability.

PreviousNext No Access15th International Congress of the Brazilian Geophysical Society & EXPOGEF, Rio de Janeiro, Brazil, 31 July-3 August 2017The 3-4 day Ultra-Fast Kelvin wave (UFKW) induced airglow and MLT wind variability and its possible interaction with diurnal tide over the Brazilian equatorial regionAuthors: Fábio EgitoRicardo A. BuritiAmauri Fragoso de MedeirosHisao TakahashiFábio EgitoUniversidade Federal do Oeste da Bahia-UFOBUniversidade Federal da Campina Grande-UFCGSearch for more papers by this author, Ricardo A. BuritiUniversidade Federal do Oeste da Bahia-UFOBUniversidade Federal da Campina Grande-UFCGSearch for more papers by this author, Amauri Fragoso de MedeirosUniversidade Federal do Oeste da Bahia-UFOBUniversidade Federal da Campina Grande-UFCGSearch for more papers by this author, and Hisao TakahashiInstituto Nacional de Pesquisas Espaciais.Search for more papers by this authorhttps://doi.org/10.1190/sbgf2017-328 SectionsAboutPDF/ePub ToolsAdd to favoritesDownload CitationsTrack CitationsPermissions ShareFacebookTwitterLinked InRedditEmail Abstract Airglow and wind measurements from the Brazilian equatorial region have been used to investigate the presence and the effects of the 3-4 day Ultra-Fast Kelvin Wave in the MLT. Airglow data came from a multichannel photometer, which measures the OI5577, O2b(0-1) and OH(6-2) airglow integrated intensities and the OH rotational temperature. Wind measurements were performed by a meteor radar, which provides zonal and meridional wind between 80 and 100 km altitude. Both instruments are installed at São João do Cariri (7.4°S, 36.5°W) and provided quasi-simultaneous data in 2005. The results show that the 3-4 day oscillations appear intermittently along the year in both airglow and wind. The 3-4 day oscillations compatible with Ultra-fast Kelvin wave were observed simultaneously in both airglow and wind in March, August and October/November. Ultra-fast Kelvin wave induced amplitudes in the airglow overcome 40% in OI5577 and O2b(0-1) emissions, while in OH(6-2) emission the amplitudes range from 15 to 20%. In the temperature, amplitudes were near 3 K. The presence of the 3-4 day oscillation in the airglow seems to be affected by the local time of the measurements, which occurred particularly in OI5577 emission. It was observed that taking pre-midnight airglow data could hide the presence of 3-4 day oscillation. Such feature is related to the interaction between the Ultra-Fast Kelvin Wave and the diurnal tide, which is indicated by a modulation of the diurnal tide amplitude in the zonal wind at the period of the Ultra-Fast Kelvin Wave. Keywords: wind, airflow, equatorialPermalink: https://doi.org/10.1190/sbgf2017-328FiguresReferencesRelatedDetails 15th International Congress of the Brazilian Geophysical Society & EXPOGEF, Rio de Janeiro, Brazil, 31 July-3 August 2017ISSN (online):2159-6832Copyright: 2017 Pages: 1876 publication data© 2017 Published in electronic format with permission by the Brazilian Geophysical SocietyPublisher:Society of Exploration Geophysicists HistoryPublished Online: 03 Aug 2017 CITATION INFORMATION Fábio Egito, Ricardo A. Buriti, Amauri Fragoso de Medeiros, and Hisao Takahashi, (2017), "The 3-4 day Ultra-Fast Kelvin wave (UFKW) induced airglow and MLT wind variability and its possible interaction with diurnal tide over the Brazilian equatorial region," SEG Global Meeting Abstracts : 1679-1684. https://doi.org/10.1190/sbgf2017-328 Plain-Language Summary KeywordswindairflowequatorialPDF DownloadLoading ...

Using images collected by an all sky imager deployed in São João do Cariri (7.4o S, 36.5o W) from September 2000 to November 2010, the nighttime incidence of clouds has been observed and studied. Most of the nighttime cloudy occurred from February to July, which is related to the rainy season in the area of the observatory. The best period to run optical observations over São João do Cariri starts in the early night up to 22:00 LT (Local Time) throughout the period between August and December. An anti-correlation between the F10.7 cm solar flux index and the number of cloudy nights was observed, which is an evidence of the cosmic rays activity in the lower earth’s atmosphere. The location of the all-sky imager provides reliable optical observations all year through.

ABSTRACT. Using airglow images collected at São João do Cariri (7.4â—¦S; 36.5â—¦W) from 2009 to 2010, the spectral characteristics and seasonality in the propagation direction of small-scale gravity waves were studied. There was a preferential propagation direction of the gravity waves to the east during the summer and spring. However, in the autumn and winter, the waves preferred propagate to the north. These observations can be related to the sources of the gravity waves or due to the filtering process of the wind on the vertical propagation of them. When gravity waves propagate in the same direction of the wind, they can reach critical levels and the vertical propagation of the waves are not allowed. Using wind profiles obtained from the Horizontal Wind Model - 14 (HWM-14), it was constructed blocking diagram in each level of the atmosphere to such areas where the vertical propagation of gravity waves was not permitted. These blocking regions change substantially along the seasons and can be used to explain the observed patterns in the propagation direction of the gravity waves.Keywords: airglow, neutral wind, gravity waves, blocking diagram.RESUMO. Utilizando imagens de aeroluminecência coletadas por um imageador instalado em São João do Cariri (7,4â—¦S; 36,5â—¦W) no período de 2009 a 2010, foram estudadas as características espectrais bem como a sazonalidade na direção de propagação de ondas de gravidade de pequena escala. Foi verificada uma preferência de propagação para leste no verão e na primavera, já no outono e inverno foi observada uma direção preferencial de propagação para norte. Estes resultados podem estar relacionados tanto às fontes que geram estas ondas de gravidade, quanto ao efeito de filtragem dos ventos sobre a região de estudo. As ondas de gravidade que se propagam no mesmo sentido do vento encontram níveis críticos e são filtradas. Com a utilização de perfis de vento obtidos pelo modelo "Horizontal Wind Model" - 14 (HWM-14) foi possível construir, em cada nível da atmosfera, as regiões de bloqueio para as quais a propagação vertical de ondas de gravidade não é permitida. Essas regiões de bloqueio sofreram mudanças sazonais substanciais e explicam satisfatoriamente os padrões observados na direção de propagação das ondas de gravidade.Palavras-chave: aeroluminescência, vento neutro, ondas de gravidade, diagrama de bloqueio.

Two consecutive mesospheric bores were observed simultaneously by two all-sky cameras on 19 December 2006. The observations were carried out in the northeast of Brazil at two different stations: São João do Cariri (36.5° W, 7.4° S) and Monteiro (37.1° W, 7.9° S), which are by about 85 km apart. The mesospheric bores were observed within an interval of ∼ 3 h in the NIR OH and OI557.7 nm airglow emissions. Both bores propagated to the east and showed similar characteristics. However, the first one exhibited a dark leading front with several trailing waves behind and progressed into a brighter airglow region, while the second bore, observed in the OH layer, was comprised of several bright waves propagating into a darker airglow region. This is the first paper to report events like these, called twin mesospheric bores. The background of the atmosphere during the occurrence of these events was studied by considering the temperature profiles from the TIMED/SABER satellite and wind from a meteor radar.

Periodic wave structures in the thermosphere have been observed at Sao Joao do Cariri (geographic coordinates: 36.5 degrees W, 7.4 degrees S; geomagnetic coordinates based on IGRF model to 2015: 35.8 degrees E, 0.48 degrees N) from September 2000 to November 2010 using OI630.0 nm airglow images. During this period, which corresponds to almost one solar cycle, characteristics of 98 waves were studied. Similarities between the characteristics of these events and observations at other places around the world were noted, primarily the spectral parameters. The observed periods were mostly found between 10 and 35 min; horizontal wavelengths ranged from 100 to 200 km, and phase speed from 30 to 180ms(-1). These parameters indicated that some of the waves, presented here, are slightly faster than those observed previously at low and middle latitudes (Indonesia, Carib and Japan), indicating that the characteristics of these waves may change at different places. Most of observed waves have appeared during magnetically quiet nights, and the occurrence of those waves followed the solar activity. Another important characteristic is the quasi-monochromatic periodicity that distinguish them from the single-front medium-scale traveling ionospheric disturbances (MSTIDs) that have been observed previously over the Brazilian region. Moreover, most of the observed waves did not present a phase front parallel to the northeast-southwest direction, which is predicted by the Perkins instability process. It strongly suggests that most of these waves must have had different generation mechanisms from the Perkins instability, which have been pointed out as being a very important mechanism for the generation of MSTIDs in the lower thermosphere.

Equatorial ionosphere plasma bubbles over the South American continent were successfully observed by mapping the total electron content (TECMAP) using data provided by ground-based GNSS receiver networks. The TECMAP could cover almost all of the continent within ~4000km distance in longitude and latitude, monitoring TEC variability continuously with a time resolution of 10min. Simultaneous observations of OI 630nm all-sky image at Cachoeira Paulista (22.7°S, 45.0°W) and Cariri (7.4°S, 36.5°W) were used to compare the bubble structures. The spatial resolution of the TECMAP varied from 50km to 1000km, depending on the density of the observation sites. On the other hand, optical imaging has a spatial resolution better than 15km, depicting the fine structure of the bubbles but covering a limited area (~1600km diameter). TECMAP has an advantage in its spatial coverage and the continuous monitoring (day and night) form. The initial phase of plasma depletion in the post-sunset equatorial ionization anomaly (PS-EIA) trough region, followed by development of plasma bubbles in the crest region, could be monitored in a progressive way over the magnetic equator. In December 2013 to January 2014, periodically spaced bubble structures were frequently observed. The longitudinal spacing between the bubbles was around 600–800km depending on the day. The periodic form of plasma bubbles may suggest a seeding process related to the solar terminator passage in the ionosphere.

This paper performs a study on the application of the triangulation method to infer the height of the atmospheric airglow emission layer. This method determines the maximum correlation for regions of interest between two consecutives images of the same structure in the airglow, obtained by an all-sky imager. The method sets the linearization height of the first image taking with reference the nominal altitude of the studied airglow layer and varies the reference height of the second image to another various altitudes. Then, it is applied the cross correlation in a given area of the image where there is a gravity wave structure. The height/correlation profiles show a convergence of the maximum correlation around the nominal altitude fixed at the first image.

The results from the Whole Atmosphere Model (WAM) at 240km are compared with measurements of equatorial thermospheric winds and temperatures acquired by nearly continual nighttime Fabry–Perot interferometer (FPI) measurements made in northeastern Brazil from September 2009 to August 2012. These comparisons show generally good agreement for the zonal winds with only slight differences seen in regard to the early morning period. For the evening period of 21–23 LT the observed meridional winds differed from the WAM predictions in two respects. First, while the flow direction was generally correct, the speeds of observed cross-hemispheric flow from the summer to the winter hemisphere were generally somewhat greater by 25 to 35ms−1 than the predicted speeds from WAM. In contrast, the observed meridional winds are found to be weaker than the WAM results for winter months for all three years. Second, although the observations and predictions both show similar timing and amplitude for a 3-h period of northward flow in September and October, the observations indicate a shift in the timing of this flow of about 1h, from ∼22 LT in September and October to ∼21 LT in December. The WAM predictions show a systematic shift in phase from 21–00 LT in September to 18–21 LT in December. Regarding temperature, the WAM predictions show a midnight temperature maximum (MTM) with a peak amplitude of 50–65K, in agreement with the observations. However, the WAM results also show a systematic shift in timing of the MTM occurrence, with the MTM peak seen at ∼22 LT in summer and at 00 LT in winter. In contrast, the FPI monthly climatology data show the timing of the MTM peak to be 00±0.5 LT for all months except winter, when the MTM peak is not clearly evident.

ABSTRACT. Simultaneous measurements of meteor winds obtained in SËœao JoËœao do Cariri-PB and Cachoeira Paulista-SP, Brazil, during June-July 2008 were used to investigate the occurrence of nonlinear coupling between atmospheric wave modes. The wind spectrum showed the quasi simultaneous presence of spectral energy peaks in the periods near 16, 24 and 48 hours, consistent with the occurrence of interaction between 48-h and 24-h waves, and the generation of 16-h waves. From the bispectral analysis, it was possible to confirm the occurrence of a 16-hour secondary wave generated by non-linear coupling between the 2-day and diurnal tide primary waves.Keywords: atmospheric tide, bispectral analysis, meteor radar.RESUMO. Medidas simultâneas de ventos meteóricos obtidos em São João do Cariri-PB e Cachoeira Paulista-SP, Brasil, durante os meses de junho e julho de 2008, foram usadas para investigar a ocorrência de acoplamento não linear entre modos de ondas atmosféricas. Os espectros dos ventos evidenciaram a presença quase simultânea de picos de energia espectral nos períodos de ∼ 16, ∼ 24 e ∼ 48 horas, compatíveis com a ocorrência de interação entre as ondas de 48 e 24 horas, e a geraçao da onda de 16 horas. Através de análise biespectral foi possível confirmar que a onda secundária de 16 horas foi gerada pelo acoplamento não linear entre as ondas primárias de 2 dias e a maré diurna.Palavras-chave: maré atmosférica, análise biespectral, radar meteórico.

Medium-scale gravity waves (MSGWs) observed during the Conjugate Point Experiment (COPEX) at Boa Vista (2.8°N; 60.7°S, dip angle 21.7°) have been ray-traced and studied based on zero wind and model wind conditions. Wind profiles have been used from the TIE-GCM and HWM-07 models. Temperature profiles were used from the NRLMSISE-00 and TIE-GCM models, and TIMED/SABER satellite data. Doppler up-shifted MSGWs, at ∼87km of altitude, propagated to higher altitudes into the thermosphere–ionosphere domain than waves that were un-shifted. Most MSGWs propagated upwards up to ∼140km of altitude and were seen to be unlikely candidates to trigger equatorial plasma bubbles (EPBs) at the F layer bottom side. However, three of them propagated up to heights close to the F layer bottom side, where it could act in the EPB seeding directly. Moreover, three MSGWs, which propagated equatorward, could act on EPB seeding by field-line-integrated effects.