Amauri Fragoso de Medeiros

Bio: Amauri Fragoso de Medeiros is an academic researcher from Federal University of Campina Grande. The author has contributed to research in topics: Airglow & Gravity wave. The author has an hindex of 25, co-authored 83 publications receiving 1641 citations. Previous affiliations of Amauri Fragoso de Medeiros include National Institute for Space Research & Federal University of Paraíba.

Simultaneous observation of ionospheric plasma bubbles and mesospheric gravity waves during the SpreadFEx Campaign

Abstract: . 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.

Gravity wave and tidal influences on equatorial spread F based on observations during the Spread F Experiment (SpreadFEx)

Abstract: The Spread F Experiment, or SpreadFEx, was per- formed from September to November 2005 to define the po- tential role of neutral atmosphere dynamics, primarily grav- ity waves propagating upward from the lower atmosphere, in seeding equatorial spread F (ESF) and plasma bubbles ex- tending to higher altitudes. A description of the SpreadFEx campaign motivations, goals, instrumentation, and structure, and an overview of the results presented in this special issue, are provided by Fritts et al. (2008a). The various analyses of neutral atmosphere and ionosphere dynamics and structure described in this special issue provide enticing evidence of gravity waves arising from deep convection in plasma bub- ble seeding at the bottomside F layer. Our purpose here is to employ these results to estimate gravity wave characteristics at the bottomside F layer, and to assess their possible con- tributions to optimal seeding conditions for ESF and plasma instability growth rates. We also assess expected tidal influ- ences on the environment in which plasma bubble seeding occurs, given their apparent large wind and temperature am- plitudes at these altitudes. We conclude 1) that gravity waves can achieve large amplitudes at the bottomside F layer, 2) that tidal winds likely control the orientations of the gravity waves that attain the highest altitudes and have the greatest effects, 3) that the favored gravity wave orientations enhance most or all of the parameters influencing plasma instability growth rates, and 4) that gravity wave and tidal structures act- ing together have an even greater potential impact on plasma instability growth rates and plasma bubble seeding.

Conjugate Point Equatorial Experiment (COPEX) Campaign in Brazil: Electrodynamics highlights on spread F development conditions and day-to-day variability

Abstract: [1] A Conjugate Point Equatorial Experiment (COPEX) campaign was conducted during the October–December 2002 period in Brazil, with the objective to investigate the equatorial spread F/plasma bubble irregularity (ESF) development conditions in terms of the electrodynamical state of the ionosphere along the magnetic flux tubes in which they occur. A network of instruments, including Digisondes, optical imagers, and GPS receivers, was deployed at magnetic conjugate and dip equatorial locations in a geometry that permitted field line mapping of the conjugate E layers to dip equatorial F layer bottomside. We analyze in this paper the extensive Digisonde data from the COPEX stations, complemented by limited all-sky imager conjugate point observations. The Sheffield University Plasmasphere-Ionosphere Model (SUPIM) is used to assess the transequatorial winds (TEW) as inferred from the observed difference of hmF2 at the conjugate sites. New results and evidence on the ESF development conditions and the related ambient electrodynamic processes from this study can be highlighted as follows: (1) large-scale bottomside wave structures/satellite traces at the equator followed by their simultaneous appearance at conjugate sites are shown to be indicative of the ESF instability initiation; (2) the evening prereversal electric field enhancement (PRE)/vertical drift presents systematic control on the time delay in SF onset at off-equatorial sites indicative of the vertical bubble growth, under weak transequatorial wind; (3) the PRE presents a large latitude/height gradient in the Brazilian sector; (4) conjugate point symmetry/asymmetry of large-scale plasma depletions versus smaller-scale structures is revealed; and (5) while transequatorial winds seem to suppress ESF development in a case study, the medium-term trend in the ESF seems to be controlled more by the variation in the PRE than in the TEW during the COPEX period. Competing influences of the evening vertical plasma drift in favoring the ESF development and that of the TEW in suppressing its growth are discussed, presenting a perspective on the ESF day-to-day and medium-term variabilities.

An investigation of gravity wave activity in the low-latitude upper mesosphere: Propagation direction and wind filtering

Abstract: horizontal phase speeds of up to � 80 m s � 1 . The large-scale ‘‘band’’ wave patterns (horizontal wavelength between 10 and 60 km) exhibited a clear seasonal dependence on the horizontal propagation direction, propagating toward the southeast during the summer months and toward the northwest during the winter. The direction of propagation was observed to change abruptly around the equinox period in mid March and at the end of September. Using a numerical simulation of gravity wave propagation in a seasonally variable climatological wind field, we have determined that the observed anisotropy in the wave propagation directions can be attributed to a strong filtering of the waves in the middle atmosphere by stratospheric winds. INDEX TERMS: 0310 Atmospheric Composition and Structure: Airglow and aurora; 3332 Meteorology and Atmospheric Dynamics: Mesospheric dynamics; 3360 Meteorology and Atmospheric Dynamics: Remote sensing; KEYWORDS: airglow, winds, gravity waves, wind filtering, imager

Characteristics of mesospheric gravity waves near the magnetic equator, Brazil, during the SpreadFEx campaign

Abstract: 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

Simulation of the seeding of equatorial spread F by circular gravity waves

Abstract: [1] The Naval Research Laboratory three-dimensional simulation code SAMI3/ESF is used to study the response of the postsunset ionosphere to circular gravity waves. We model the coupling of both circular (local) and plane wave (nonlocal) gravity waves to the bottomside F layer as a mechanism for triggering equatorial plasma bubbles. Results support the hypothesis that nonplane gravity waves can more strongly couple to the F layer than plane gravity waves. Results also show that the coupling of the seed wave to the F layer depends on the (nonlocal) growth rate and the local electron density at the position of the seed wave.

An update to the Horizontal Wind Model (HWM): The quiet time thermosphere

Abstract: The Horizontal Wind Model (HWM) has been updated in the thermosphere with new observations and formulation changes. These new data are ground-based 630 nm Fabry-Perot Interferometer (FPI) measurements in the equatorial and polar regions, as well as cross-track winds from the Gravity Field and Steady State Ocean Circulation Explorer (GOCE) satellite. The GOCE wind observations provide valuable wind data in the twilight regions. The ground-based FPI measurements fill latitudinal data gaps in the prior observational database. Construction of this reference model also provides the opportunity to compare these new measurements. The resulting update (HWM14) provides an improved time-dependent, observationally based, global empirical specification of the upper atmospheric general circulation patterns and migrating tides. In basic agreement with existing accepted theoretical knowledge of the thermosphere general circulation, additional calculations indicate that the empirical wind specifications are self-consistent with climatological ionosphere plasma distribution and electric field patterns.

Global Atmospheric Circulation Statistics, 1958-1989

Abstract: Twenty-two monthly statistical quantities make up this dataset of grids which describes the atmospheric general circulation at eleven vertical levels across the troposphere and stratosphere over a 32-year period. These gridded analyses, created from upper air soundings across the globe, span the period from May 1958 to December 1989. The statistical parameters, which are useful for comparing climate model simulations to actual observations, include monthly means and variances of horizontal and vertical wind, temperature, geopotential height, moisture, and horizontal wind divergence. There are also covariance terms describing the relationship between wind, temperature, moisture, and geopotential height. In general, the analyses near the surface of the earth (900mb and below) tend to be less reliable than those of the higher levels because the individual rawinsonde reports are often incomplete due to missing 1000mb reports.

Fast and ultrafast Kelvin wave modulations of the equatorial evening F region vertical drift and spread F development

Abstract: In this paper, we investigate the role of eastward and upward propagating fast (FK) and ultrafast Kelvin (UFK) waves in the day-to-day variability of equatorial evening prereversal vertical drift and post sunset generation of spread F/plasma bubble irregularities. Meteor wind data from Cariri and Cachoeira Paulista (Brazil) and medium frequency (MF) radar wind data from Tirunelveli (India) are analyzed together with Thermosphere-Ionosphere-Mesosphere Energetics and Dynamics/Sounding of the Atmosphere using Broadband Emission Radiometry (TIMED/SABER) temperature in the 40- to 100-km region to characterize the zonal and vertical propagations of these waves. Also analyzed are the F region evening vertical drift and spread F (ESF) development features as diagnosed by Digisonde (Lowell Digisonde International, LLC, Lowell, MA, USA) operated at Fortaleza and Sao Luis in Brazil. The SABER temperature data permitted determination of the upward propagation characteristics of the FK (E1) waves with propagation speed in the range of 4 km/day. The radar mesosphere and lower thermosphere (MLT) winds in the widely separated longitude sectors have yielded the eastward phase velocity of both the FK and UFK waves. The vertical propagation of these waves cause strong oscillation in the F region evening prereversal vertical drift, observed for the first time at both FK and UFK periodicities. A delay of a few (approximately 10) days is observed in the F region vertical drift perturbation with respect to the corresponding FK/UFK zonal wind oscillations, or temperature oscillations in the MLT region, which has permitted a direct identification of the sunset electrodynamic coupling process as being responsible for the generation of the FK/UFK-induced vertical drift oscillation. The vertical drift oscillations are found to cause significant modulation in the spread F/plasma bubble irregularity development. The overall results highlight the role of FK/UFK waves in the day-to-day variability of the ESF in its occurrence season.

Living at the Extremes: Extremophiles and the Limits of Life in a Planetary Context.

Abstract: Prokaryotic life has dominated most of the evolutionary history of our planet, evolving to occupy virtually all available environmental niches. Extremophiles, especially those thriving under multiple extremes, represent a key area of research for multiple disciplines, spanning from the study of adaptations to harsh conditions, to the biogeochemical cycling of elements. Extremophile research also has implications for origin of life studies and the search for life on other planetary and celestial bodies. In this article, we will review the current state of knowledge for the biospace in which life operates on Earth and will discuss it in a planetary context, highlighting knowledge gaps and areas of opportunity.