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Found 11 entries in the Bibliography.
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2009 |
The data from ground based experiments conducted during the 2005 SpreadFEx campaign in Brazil are used, with the help of theoretical model calculations, to investigate the precursor conditions, and especially, the role of gravity waves, in the instability initiation leading to equatorial spread F development. Data from a digisonde and a 30 MHz coherent back-scatter radar operated at an equatorial site, Sao Luis (dip angle: 2.7\textdegree) and from a digisonde operated at another equatorial site (dip angle: -11.5\textdegree) are analyzed during selected days representative of differing precursor conditions of the evening prereversal vertical drift, F layer bottom-side density gradients and density perturbations due to gravity waves. It is found that radar irregularity plumes indicative of topside bubbles, can be generated for precursor vertical drift velocities exceeding 30 m/s even when the precursor GW induced density oscillations are marginally detectable by the digisonde. For drift velocities <=20 m/s the presence of precursor gravity waves of detectable intensity is found to be a necessary condition for spread F instability initiation. Theoretical model calculations show that the zonal polarization electric field in an instability development, even as judged from its linear growth phase, can be significantly enhanced under the action of perturbation winds from gravity waves. Comparison of the observational results with the theoretical model calculations provides evidence for gravity wave seeding of equatorial spread F. Abdu, M.; Kherani, Alam; Batista, I.; de Paula, E.; Fritts, D.; Sobral, J.; Published by: Annales Geophysicae Published on: Jan-01-2009 YEAR: 2009   DOI: 10.5194/angeo-27-2607-2009 |
Overview and summary of the Spread F Experiment (SpreadFEx) We provide here an overview of, and a summary of results arising from, an extensive experimental campaign (the Spread F Experiment, or SpreadFEx) performed from September to November 2005, with primary measurements in Brazil. The motivation was to define the potential role of neutral atmosphere dynamics, specifically gravity wave motions propagating upward from the lower atmosphere, in seeding Rayleigh-Taylor instability (RTI) and plasma bubbles extending to higher altitudes. Campaign measurements focused on the Brazilian sector and included ground-based optical, radar, digisonde, and GPS measurements at a number of fixed and temporary sites. Related data on convection and plasma bubble structures were also collected by GOES 12, and the GUVI instrument aboard the TIMED satellite.\ Fritts, D.; Abdu, M.; Batista, B.; Batista, I.; Batista, P.; Buriti, R.; Clemesha, B.; Dautermann, T.; de Paula, E.; Fechine, B.; Fejer, B.; Gobbi, D.; Haase, J.; Kamalabadi, F.; Kherani, E.; Laughman, B.; Lima, P.; Liu, H.-L.; Medeiros, A.; Pautet, P.-D.; Riggin, D.; Rodrigues, F.; Sabbas, F.; Sobral, J.; Stamus, P.; Takahashi, H.; Taylor, M.; Vadas, S.; Vargas, F.; Wrasse, C.; Published by: Annales Geophysicae Published on: Jan-01-2009 YEAR: 2009   DOI: 10.5194/angeo-27-2141-2009 |
Reconstruction of the gravity wave field from convective plumes via ray tracing We implement gravity wave (GW) phases into our convective plume and anelastic ray trace models. This allows us to successfully reconstruct the GW velocity, temperature, and density perturbation amplitudes and phases in the Mesosphere-Lower-Thermosphere (MLT) via ray tracing (in real space) those GWs that are excited from a deep convective plume. We find that the ray trace solutions agree very well with the exact, isothermal, zero-wind, Fourier-Laplace solutions in the Boussinesq limit. This comparison also allows us to determine the normalization factor which converts the GW spectral amplitudes to real-space amplitudes in the ray trace model. This normalization factor can then be used for ray tracing GWs through varying temperature and wind profiles. We show that by adding GW reflection off the Earth\textquoterights surface, the resulting GW spectrum has more power at larger vertical and horizontal wavelengths. We determine the form of the momentum flux and velocity spectra which allows for easy calculation of GW amplitudes in the MLT and thermosphere. Finally, we find that the reconstructed (ray traced) solution for a deep, convective plume with a duration much shorter than the buoyancy period does not equal the Fourier-Laplace Boussinesq solution; this is likely due to errors in the Boussinesq dispersion relation for very high frequency GWs. Published by: Annales Geophysicae Published on: Jan-01-2009 YEAR: 2009   DOI: 10.5194/angeo-27-147-2009 |
Takahashi, H.; Taylor, M.; Pautet, P.-D.; Medeiros, A.; Gobbi, D.; Wrasse, C.; Fechine, J.; Abdu, M.; Batista, I.; Paula, E.; Sobral, J.; Arruda, D.; Vadas, S.; Sabbas, F.; Fritts, D.; Published by: Annales Geophysicae Published on: Jan-01-2009 YEAR: 2009   DOI: 10.5194/angeo-27-1477-2009 |
Pautet, P.-D.; Taylor, M.; Chapagain, N.; Takahashi, H.; Medeiros, A.; Sabbas, F.; Fritts, D.; Published by: Annales Geophysicae Published on: Jan-01-2009 YEAR: 2009   DOI: 10.5194/angeo-27-2371-2009 |
The Spread F Experiment (SpreadFEx): Program overview and first results Fritts, D.; Abdu, M.; Batista, B.; Batista, I.; Batista, P.; Buriti, R.; Clemesha, B.; Dautermann, T.; de Paula, E.; Fechine, B.; Fejer, B.; Gobbi, D.; Haase, J.; Kamalabadi, F.; Kherani, E.; Laughman, B.; Lima, J.; Liu, H.-L.; Medeiros, A.; Pautet, P.-D.; Riggin, D.; Rodrigues, F.; Sabbas, Sao; Sobral, J.; Stamus, P.; Takahasi, H.; Taylor, M.; Vadas, S.; Vargas, F.; Wrasse, C.; Published by: Earth Planets Space Published on: |
2008 |
The Spread F Experiment, or SpreadFEx, was performed from September to November 2005 to define the potential role of neutral atmosphere dynamics, primarily gravity waves propagating upward from the lower atmosphere, in seeding equatorial spread F (ESF) and plasma bubbles extending 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 bubble 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 contributions to optimal seeding conditions for ESF and plasma instability growth rates. We also assess expected tidal influences on the environment in which plasma bubble seeding occurs, given their apparent large wind and temperature amplitudes 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 acting together have an even greater potential impact on plasma instability growth rates and plasma bubble seeding. Fritts, D.; Vadas, S.; Riggin, D.; Abdu, M.; Batista, I.; Takahashi, H.; Medeiros, A.; Kamalabadi, F.; Liu, H.-L.; Fejer, B.; Taylor, M.; Published by: Annales Geophysicae Published on: 10/2008 YEAR: 2008   DOI: 10.5194/angeo-26-3235-2008 |
2007 |
Published by: Published on: |
During the SpreadFEx campaign from September 22 to November 8, 2005, two airglow CCD imagers, located at near Brasilia (14.8S, 47.6W, Mag. 10S) and at Cariri (7.4S, 36.5W, Mag. 9S) were operated simultaneously and measured the equatorial ionospheric bubble structures and their time evolution by monitoring the OI 6300 emission. From the 10 nights of coincident data, we observed that on some nights the bubbles was formed at the west of Cariri, but not seen from the Brasilia site. This suggests that the bubble formation and development started near the Cariri observation site. Identification of a longitudinal zone where the SpF is seeding is very important in order to find the mechanism of formation. The present paper will discuss SpF seeding mechanisms and possible contribution of the mesospheric gravity wave activity. Takahashi*, H.; Pautet, P.-D.; Fechine, J.; Abdu, M.; Batista, I.; Paula, E.; Sobral, J.H.A.; Gobbi, D.; Arruda, D.; Batista, P.; Sabba, F.; Taylor, M.; Medeiros, A.; Buriti, R.; Wrasse, C.; Fritts, D.; Published by: Published on: YEAR: 2007   DOI: 10.1190/sbgf2007-404 |
2005 |
Yee, J; Christensen, A; Russell, J; Killeen, T; Woods, T; Kozyra, J; Smith, A; Fritts, D; Forbes, J; Mayr, H; , others; Published by: Published on: |
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"Gravity Wave Influences in the Thermosphere and Ionosphere: Observations and Recent Modeling" "Observational and theoretical studies have suggested gravity wave propagation and influences in the thermosphere and ionosphere for half a century. Gravity waves contribute, or are believed to contribute, to a variety of neutral and electrodynamic phenomena ranging from vertical coupling, energy and momentum transport and deposition, neutral perturbations and accelerations, traveling ionospheric disturbances, ionospheric irregularities, and plasma instabilities under quiet conditions to strong coupling from high to low latitudes and accompanying electrodynamics under storm-time conditions. Our goals here are to briefly review what has been learned to date, to illustrate some of the more recent results indicative of gravity wave effects, and to identify some aspects of neutral dynamics not previously considered that we expect may also have significant influences on neutral dynamics and electrodynamics in the thermosphere and ionosphere." Fritts, David; Abdu, Mangalathayil; Pancheva, Dora"; Published by: Published on: YEAR: 0   DOI: "10.1007/978-94-007-0326-1_8" |
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