The impact of gravity waves rising from convection in the lower atmosphere on the generation and nonlinear evolution of equatorial bubble
TL;DR: In this article, a nonlinear evolution of equatorial F-region plasma bubbles under varying ambient ionospheric conditions and gravity wave seeding perturbations in the bottom-side F-layer is studied.
Abstract: . The nonlinear evolution of equatorial F-region plasma bubbles under varying ambient ionospheric conditions and gravity wave seeding perturbations in the bottomside F-layer is studied. To do so, the gravity wave propagation from the convective source region in the lower atmosphere to the thermosphere is simulated using a model of gravity wave propagation in a compressible atmosphere. The wind perturbation associated with this gravity wave is taken as a seeding perturbation in the bottomside F-region to excite collisional-interchange instability. A nonlinear model of collisional-interchange instability (CII) is implemented to study the influences of gravity wave seeding on plasma bubble formation and development. Based on observations during the SpreadFEx campaign, two events are selected for detailed studies. Results of these simulations suggest that gravity waves can play a key role in plasma bubble seeding, but that they are also neither necessary nor certain to do so. Large gravity wave perturbations can result in deep plasma bubbles when ionospheric conditions are not conducive by themselves; conversely weaker gravity wave perturbations can trigger significant bubble events when ionospheric conditions are more favorable. But weak gravity wave perturbations in less favorable environments cannot, by themselves, lead to strong plasma bubble responses.
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TL;DR: In this paper, the role of seed perturbations in the day-to-day variability of occurrence of Equatorial Spread F (ESF) is studied using Ionosonde data for years 2005-2007 at magnetic equatorial location Trivandrum (8.5°N, 77°E, and dip 1.3°N).
22 citations
TL;DR: In this paper, large-scale secondary gravity waves and circulation cells are created by the body forces generated by the dissipation of convectively generated gravity waves over Brazil on 1 October 2005.
Abstract: [1] In a companion paper, we show that large-scale secondary gravity waves and circulation cells are created by the body forces generated by the dissipation of convectively generated gravity waves over Brazil on 01 October 2005. In this paper, we show that these fluid perturbations cause large-scale perturbations of the plasma drift and plasma density in the ionosphere by changing the wind dynamo and transport. These fluid perturbations modify both the amplitude and direction of the plasma drifts. Near the geomagnetic equator, the magnitude of the pre-reversal enhancement can be increased or weakened, depending on the location and local time. Because the circulation cells persist from late afternoon through midnight, the modulation of the vertical drift near the geomagnetic equator persists until midnight. The largest changes of the wind-driven currents can occur either in the E or F region and are determined by the magnitudes of the wind perturbations, conductivities, and conductivity perturbations. The contributions to the plasma transport changes are from advection by the neutral winds along field lines, plasma drifts, and ambipolar diffusion, in the order of their relative significance in the numerical results.
21 citations
TL;DR: In this paper, the authors analyzed pre-midnight equatorial F region observations made by the 30 MHz coherent backscatter radar of Sao Luis, Brazil between August 2010 and February 2012.
Abstract: . We analyzed pre-midnight equatorial F region observations made by the 30 MHz coherent backscatter radar of Sao Luis, Brazil between August 2010 and February 2012. These measurements were processed, and used to create monthly maps of the echo occurrence as a function of local time and height. The maps show the inter-annual variability associated with equatorial spread F (ESF) occurrence in the Brazilian longitude sector. We also constructed monthly curves of the evening vertical drifts, for the Brazilian sector, using measurements by the ion velocity meter (IVM) onboard the C/NOFS satellite. The IVM evening drifts show a good overall agreement with the Scherliess and Fejer (1999) empirical model. Measured and model drifts show the development of the pre-reversal enhancement (PRE) of the vertical plasma drifts during ESF season. Using joint radar and satellite measurements, we found that evening (18:00–18:30 LT) mean non-negative drifts provide a necessary but not sufficient condition for the occurrence of topside ESF echoes. Evening downward (negative) drifts preceded the absence of topside ESF irregularities.
16 citations
Cites background from "The impact of gravity waves rising ..."
...Finally, the occurrence of topside ESF structures despite weak PRE peaks could also be associated with strong initial perturbations provided by atmospheric gravity waves as suggested by theoretical studies (e.g. Kherani et al., 2009)....
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...Previous studies have also suggested that initial density perturbations (seed waves) could play a significant role in the development of ESF (e.g. Abdu et al., 2009; Kherani et al., 2009; Tsunoda, 2010)....
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TL;DR: In this paper, the satellite trace (S-trace) in the ionograms, a precursor to the postsunset ESF occurrence, as observed by Digisondes operated at an equatorial and two magnetic conjugate sites in Brazil during a 66-day observational campaign (Conjugate Point Equatorial Experiment 2002).
Abstract: [1] A better understanding of the precursor conditions for the instability growth is very important for identifying the causes of day-to-day variability in the equatorial spread F (ESF)/plasma bubble irregularity development. We investigate here the satellite trace (S-trace) in the ionograms, a precursor to the postsunset ESF occurrence, as observed by Digisondes operated at an equatorial and two magnetic conjugate sites in Brazil during a 66 day observational campaign (Conjugate Point Equatorial Experiment 2002). The satellite traces first occur at the equatorial site, and sequentially, after a variable delay of approximately 20 to 50 min, they are observed nearly simultaneously over the two conjugate sites. The evening prereversal enhancement in the zonal electric field/vertical drift is found to control its development. Using a three-dimensional simulation code based on collisional interchange instability mechanism, it is shown that the observed S-trace occurrence sequence is fully consistent with the instability initiation over the equator with the field-aligned plasma depletion vertical growth marked by latitudinal expansion of its extremities to conjugate locations. The delay in the S-trace occurrence at the conjugate sites (a measure of the nonlinear growth of the instability for plasma depletion) is controlled also by field line parallel (meridional) neutral wind. The relationship between the S-trace and the large-scale wave structure in the F layer, another widely known characterization of the precursor condition for the ESF development, is also clarified.
16 citations
TL;DR: A three-part review on space weather in Latin America is presented in this paper, which comprises the evolution of several Latin American institutions investing in space science since the 1960s, focusing on the solar-terrestrial interactions, which today is commonly called space weather.
15 citations
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TL;DR: In this paper, the critical flux limiting stage is implemented in multidimensions without resort to time splitting, which allows the use of flux-corrected transport (FCT) techniques in multi-dimensional fluid problems for which time splitting would produce unacceptable numerical results.
2,454 citations
"The impact of gravity waves rising ..." refers background in this paper
...Numerous theoretical and numerical studies have been performed to assess the linear and nonlinear aspects of these complex dynamics (Scannepieco and Ossakow, 1976; Zalesak, 1979; Zargham and Seyler, 1987; Raghavarao et al., 1992; Huang et al., 1993; Keskinen et al., 2003)....
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TL;DR: In this paper, a test of the generally accepted Rayleigh-Taylor (R-T) instability mechanism for equatorial spread F (ESF) is derived following the formalism of Haerendel (preprint, 1973) which takes into account the variations of physical parameters along geomagnetic flux tubes.
Abstract: In a test of the generally accepted Rayleigh-Taylor (R-T) instability mechanism for equatorial spread F (ESF) a linear instability growth rate γ RT is derived following the formalism of Haerendel (preprint, 1973) which takes into account the variations of physical parameters along geomagnetic flux tubes. The resulting form of γ RT extends the results of previous work by including direct dependencies on transequatorial neutral winds, zonal electric fields, vertical and horizontal ionospheric density gradients, the presence of an E region, and chemical recombination. Realistic atmospheric and ionospheric density model inputs are used for the first time to make quantitative calculations of R-T growth rates for a range of geophysical conditions. The key result of this study is that time/altitude domains having positive calculated instability growth rates are found to coincide with observed time/altitude patterns of ESF occurrence over both a monthly and a yearly time frame. This success in being able to model the climatological occurrence of ESF lends support to the physical model adopted for the instability mechanism and opens up new avenues of research into ESF predictability on a night-to-night and even an hour-to-hour basis.
490 citations
"The impact of gravity waves rising ..." refers background in this paper
...These plumes are identified as large-scale depletions or plasma bubbles and are believed to be generated by CII and Rayleigh-Taylor instability mechanism (Sultan, 1996)....
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TL;DR: In this article, the authors show that although initiation by a gravity wave seems likely, the gravity wave interaction cannot yield the large displacements observed without further amplification by the Rayleigh-Taylor instability.
Abstract: Jicamarca radar backscatter maps were made during four consecutive nights in March 1979. Two of these maps displayed single towering plumes extending to nearly 1000-km altitude. On a third night, discussed in detail here, six plumes were generated in clear association with a nearly sinusoidal oscillation of the height of the bottomside of the F layer. The vertical amplitude of the oscillation was several hundred kilometers, and the period about 100 minutes. The plumes were generated either when the bottomside of the F layer was at the highest altitude or in the descending phase of the motion. Families of curves are presented which correspond to the solution of the dispersion relation for gravity waves capable of initiating the observed bottomside oscillations via the spatial resonance mechanism. We conclude that the solutions thus derived are reasonable and present a criterion for how well matched the gravity wave phase velocity and plasma drift have to be to produce a given perturbation in the ionization density. This criterion indicates that although initiation by a gravity wave seems likely, the gravity wave interaction cannot yield the large displacements observed without further amplification by the Rayleigh-Taylor instability. Finally, we show that the preferential generation of plumes during the descending phase of the F layer height oscillation can be explained by a generalized Rayleigh-Taylor instability operating on the distorted ionosphere with the destabilizing effects of gravity, a zonal electric field, and a zonal neutral wind included.
357 citations
"The impact of gravity waves rising ..." refers background in this paper
...Radar Correspondence to:E. Alam Kherani (alam@dae.inpe.br) observations of ESF reveal the existence of plumes that may penetrate to the topside F-layer and attain very high altitudes (Kelley et al., 1981)....
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...br) observations of ESF reveal the existence of plumes that may penetrate to the topside F-layer and attain very high altitudes (Kelley et al., 1981)....
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...Rottger (1981) and Kelley et al. (1981) were the first to note the potential importance of gravity waves (GWs) as a seeding perturbation for the spread F....
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TL;DR: In this paper, an anelastic dispersion relation was derived which includes the damping effects of kinematic viscosity and thermal diffusivity in the thermosphere and which is valid before and during dissipation.
Abstract: [1] The dissipation of high-frequency gravity waves (GWs) in the thermosphere is primarily due to kinematic viscosity and thermal diffusivity. Recently, an anelastic GW dispersion relation was derived which includes the damping effects of kinematic viscosity and thermal diffusivity in the thermosphere and which is valid before and during dissipation. Using a ray trace model which incorporates this new dispersion relation, we explore many GW properties that result from this dispersion relation for a wide range of thermospheric temperatures. We calculate the dissipation altitudes, horizontal distances traveled, times taken, and maximum vertical wavelengths prior to dissipation in the thermosphere for a wide range of upward-propagating GWs that originate in the lower atmosphere and at several altitudes in the thermosphere. We show that the vertical wavelengths of dissipating GWs, λz(zdiss), increases exponentially with altitude, although with a smaller slope for z > 200 km. We also show how the horizontal wavelength, λH, and wave period spectra change with altitude for dissipating GWs. We find that a new dissipation condition can predict our results for λz(zdiss) very well up to altitudes of ∼500 km. We also find that a GW spectrum excited from convection shifts to increasingly larger λz and λH with altitude in the thermosphere that are not characteristic of the initial convective scales. Additionally, a lower thermospheric shear shifts this spectrum to even larger λz, consistent with observations. Finally, we show that our results agree well with observations.
321 citations
TL;DR: In this article, a numerical simulation of the non-linear evolution of the collisional Rayleigh-Taylor instability using a set of equations appropriate for the equatorial F region ionosphere has been performed.
Abstract: A numerical simulation of the non-linear evolution of the collisional Rayleigh-Taylor instability using a set of equations appropriate for the equatorial F region ionosphere has been performed. Our results show that the irregularities produced by the instability grow on the bottomside of the F region peak, as predicted by linear theory, and then the irregularities nonlinearly bubble through to the topside, where linear theory predicts no irregularities. Fourier analysis of the irregularities show one dimensional power law power spectrum for both the vertical and horizontal directions.
255 citations