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.

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.

On 16–17 July 2007 during an observational campaign at Comandante Ferraz Antarctic Station (62° S, 58° W), a mesospheric wall was observed with an airglow all-sky imager. The wave appeared like an extensive dark region in the all-sky airglow images, with a large depletion in the OH emission. Simultaneous mesospheric winds measured with a MF radar at Rothera station and temperature profiles from SABER instrument, on board of TIMED satellite, were used to obtain the propagation condition of the wave. Wind measurements during four days, around the time of observation of the wave, are presented in order to discuss the type and consistence of the duct in which this wave was propagating. By using wavelet analysis and tidal amplitude components we found that 12 and 8 h components were the most important periodicities around the time interval of the wave observation. A collocated imaging spectrometer, for mesospheric temperature measurements, has been operated simultaneously with the all-sky imager. Direct effects of the mesospheric front have been seen in the spectrometric measurements, showing an abrupt decrease in both OH intensity and rotational temperature when the wave front passes overhead. The main contribution of the present work is the investigation of the type of duct in which the wall event was propagating. We found evidences for a thermal duct structure to support the mesospheric wall propagation. This result was obtained by two types of analysis: (a) the tidal components analysis and winds filtering (harmonic analysis), and (b) comparison between the terms of the m2 dispersion relation.

As part of the SpreadFEx campaign, coordi- nated optical and radio measurements were made from Brazil to investigate the occurrence and properties of equatorial Spread F, and to characterize the regional mesospheric grav- ity wave field. All-sky image measurements were made from two sites: Brasilia and Cariri located 10 S of the mag- netic equator and separated by 1500 km. In particular, the observations from Brasilia provided key data in relatively close proximity to expected convective sources of the grav- ity waves. High-quality image measurements of the meso- spheric OH emission and the thermospheric OI (630 nm) emission were made during two consecutive new moon pe- riods (22 September to 9 November 2005) providing exten- sive data on the occurrence and properties of F-region de- pletions and regional measurements of the dominant gravity wave characteristics at each site. A total of 120 wave displays were observed, comprising 94 short-period events and 26 medium-scale gravity waves. The characteristics of the small-scale waves agreed well with previous gravity wave studies from Brazil and other sites. However, significant differences in the wave propagation headings indicate dissimilar source regions for the Brasilia and Cariri datasets. The observed medium-scale gravity wave events constitute an important new dataset to study their mesospheric properties at equatorial latitudes. These data exhibited similar propagation headings to the short- period events, suggesting they originated from the same source regions. Medium-scale waves are generally less sus- ceptible to wind filtering effects and modeling studies utiliz- ing these data have successfully identified localized regions

On 1 October 2005, during the SpreadFEx campaign, a distinct mesospheric bore was observed over São João do Cariri (7.4° S, 36.5° W), Brazil by using airglow all-sky imagers. The event appeared both in the OI5577 and OH emissions, forming a well extended wave front which was followed by short waves from behind. Simultaneous wind and temperature data obtained by the meteor radar and the TIMED/SABER satellite instrument revealed that the bore event occurred during the Doppler ducting condition in the emission layers.

During the Spread F Experiment campaign, under NASA Living with a Star (LWS) program, carried out in the South American Magnetic Equator region from 22 September to 8 November 2005, two airglow CCD imagers, located at Cariri (7.4° S, 36.5° W, geomag. 11° S) and near Brasilia (14.8° S, 47.6° W, geomag. 10° S) were operated simultaneously and measured the equatorial ionospheric bubbles and their time evolution by monitoring the airglow OI 6300 intensity depletions. Simultaneous observation of the mesospheric OH wave structures made it possible to investigate the relationship between the bubble formation in the ionosphere and the gravity wave activity at around 90 km. On the evening of 30 September 2005, comb-like OI 6300 depletions with a distance of ~130 km between the adjacent ones were observed. During the same period, a mesospheric gravity wave with a horizontal wavelength of ~130 km was observed. From the 17 nights of observation during the campaign period, there was a good correlation between the OI 6300 depletion distances and the gravity wave horizontal wavelengths in the mesosphere with a statistically significant level, suggesting a direct contribution of the mesospheric gravity wave to plasma bubble seeding in the equatorial ionosphere.

Equatorial 3.5-day ultra-fast Kelvin wave was observed in the MLT zonal wind measured by meteor radar at Cariri (7.4°S, 36.5°W, geomag. 8°S) and in the stratosphere-mesosphere temperature structures from the TIMED/SABER data. The ionospheric F-layer bottom-side virtual height hT’F and the critical frequency foF2 observed at Fortaleza (3.9°S, 38.4°W, geomag. 5°S) also showed similar oscillation structures, indicating an influence of the Kelvin wave in the F region height and modulation of E × B uplifting during the evening period. Consequently the ionospheric spread F onset time was also modulated in the same period, around 4 days.

Global Positioning System (GPS) receiver on the CHAllenging Mini-satellite Payload (CHAMP) and the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument, one of four on board the TIMED satellite, provide middle atmosphere temperature profiles by Radio Occultation (RO) and limb viewing infrared emission measurements, respectively. These temperature profiles retrieved by two different techniques in the stratosphere are compared with each other using more than 1300 correlative profiles in March, September and December 2005. The over-all mean differences averaged over 15 and 35km are approximately −2K and standard deviation is less than 3K. Below 20km of altitude, relatively small mean temperature differences ∼1K are observed in wide latitudinal range except for June (during the SABER nighttime observation). In the middle to low latitudes, between 30°S and 30°N, the temperature difference increases with height from ∼0–1K at 15km, to ∼−4K at 35km of altitude. Large temperature differences about −4 to −6K are observed between 60°S and 30°N and 31–35km of altitude for all months and between 0° and 30°N below 16km during June (nighttime).

Lower-mesospheric inversion layers (MILs) were studied using the temperature profiles observed by TIMED/SABER over Cariri (7.5°S, 36.5°W), Brazil, in 2005. A total 175 MILs were identified with the maximum occurrence in April and October and the minimum in January and July. The lower MIL is located in a height region from 70 to 90km, with the peak at around 83±4km with the temperature of 205±5K, and the thickness of 4–10km. The results show large amplitudes of MILs during equinoxes and minimum in solstices, with a clear semiannual variation. A general feature of lower MIL in monthly mean profile was observed twice a year, one from February to May, and the other from August to October with a downward shift of the top level. These results suggest that formation and long persistence of MIL is an important factor to investigate propagation of atmospheric gravity waves in the mesosphere-lower thermosphere (MLT) region.

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.

The noctilucent clouds (NLCs) are high-altitude bright cloud formations visible under certain conditions from high-latitude places during the summer months. If the exact nature of these clouds still remains a mystery, they are an efficient tracer of the dynamic processes at that level, particularly the gravity waves propagating from the stratosphere through the mesopause layer. In this paper, we will describe a technique developed to analyze the structures visible in NLC images. Pictures taken from Sweden during July 2005 will be processed in order to determine the characteristics of the observed waves.

Stratospheric gravity wave activities were deduced from GPS radio occultation temperature profiles obtained by CHAMP satellite between 2001 and 2005. Potential energy profiles are used to analyze the gravity wave activity over South America. The results showed an inter-annual variation of the potential energy integrated between 24 and 34 km of altitude. The gravity wave activity is more concentrated around the equatorial region. In order to evaluate the seasonal variation of the gravity wave activity, a mean potential energy was determined over (10oN-10oS) and (100oW-20oW). The results showed a lower gravity wave activity during winter time, while during spring time the mean potential energy showed an increase in the wave activity. The results of the mean potential energy also showed that the gravity wave activity in the lower stratosphere exhibits a higher wave activity during 2002 and 2004 and a lower wave activity during 2003 and 2005.

PreviousNext No Access10th International Congress of the Brazilian Geophysical Society & EXPOGEF 2007, Rio de Janeiro, Brazil, 19-23 November 2007Observations of the 16-day wave in the equatorial meteor winds and TIMED/SABER temperaturesAuthors: Lourivaldo Mota LimaJoaquim FechineHisao TakahashiP. P. BatistaCristiano Max WrasseG. MlynczakJ. M. Russell HamptonLourivaldo Mota LimaDF/UEPB, BrazilSearch for more papers by this author, Joaquim FechineINPE, BrazilSearch for more papers by this author, Hisao TakahashiINPE, BrazilSearch for more papers by this author, P. P. BatistaINPE, BrazilSearch for more papers by this author, Cristiano Max WrasseIP&D/UNIVAP, BrazilSearch for more papers by this author, G. MlynczakNASA Langley Research Center, Hampton, VA, USASearch for more papers by this author, and J. M. Russell HamptonUniversity, Hampton, VA, USASearch for more papers by this authorhttps://doi.org/10.1190/sbgf2007-430 SectionsAboutPDF/ePub ToolsAdd to favoritesDownload CitationsTrack CitationsPermissions ShareFacebookTwitterLinked InRedditEmail Abstract Horizontal wind measurements obtained from São João do Cariri-PB (7.4° S, 36.5° W), Brazil, associated with equatorial MLT temperature data acquired by the TIMED/SABER satellite, have been used to investigate the presence of planetary-scale oscillations. The data were obtained from January to December, 2005, which were subjected to the spectral analysis and the results revealed the quasi-simultaneous presence of distinct power spectrum with peaks associated with low-frequency oscillations. In this time, our focus is the range period from 12 to 20 days, whose activities were revealed mainly during time-intervals from day 120 to day 250. The characteristics observed suggest that the perturbations were due to presence of 16-day planetary waves. From satellite data, was possible identified a westward propagating 16-day wave with zonal wave number 1. Keywords: winds, atmosphere, oscillationsPermalink: https://doi.org/10.1190/sbgf2007-430FiguresReferencesRelatedDetails 10th International Congress of the Brazilian Geophysical Society & EXPOGEF 2007, Rio de Janeiro, Brazil, 19-23 November 2007ISSN (online):2159-6832Copyright: 2007 Pages: 2431 publication data© 2007 Published in electronic format with permission by the Brazilian Geophysical SocietyPublisher:Society of Exploration Geophysicists HistoryPublished Online: 23 Nov 2007 CITATION INFORMATION Lourivaldo Mota Lima, Joaquim Fechine, Hisao Takahashi, P. P. Batista, Cristiano Max Wrasse, G. Mlynczak, and J. M. Russell Hampton, (2007), "Observations of the 16-day wave in the equatorial meteor winds and TIMED/SABER temperatures," SEG Global Meeting Abstracts : 2185-2188. https://doi.org/10.1190/sbgf2007-430 Plain-Language Summary KeywordswindsatmosphereoscillationsPDF DownloadLoading ...

Meteor radar wind measurement at Cariri (7.4°S, 36.5°W) and Ionosonde measurements at Fortaleza(3.9°S, 38.4°W) have been carried out in 2005. 3 to 5 days period oscillations in the mesospheric zonal wind and ionospheric F-layer bottom height (h’F) and the maximum frequency (foF2) were observed during a period from March 01 to 11, 2005. Atmospheric temperatures observed by the SABER/TIMED satellite also showed a similar periodic oscillations. From the characteristics of the downward phase propagation, longitudinal and latitudinal extension, we conclude that this oscillation must be a 3.5–day Ultra Fast Kelvin (UFK) wave. The observed amplitude of oscillation of the F-layer height caused by the UFK waves, 20–30 km, are significant, and worthwhile to investigate in terms of the day to day variability of the Spread F occurrence.