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 authors analyzed the geophysical conditions for the generation of the irregularities by comparing the nights with and without the equatorial spread F (ESF) and showed that the instability can grow at the F layer bottomside by the Rayleigh-Taylor mechanism only when the Vp Vp < 30 m/s.
7 citations
TL;DR: In this article, a numerical simulation is carried out to estimate the rate of convergence of ionization required to produce a F0.5 layer with peak plasma frequency of 3.2 MHz from three different background layer densities.
6 citations
01 Jan 2011
TL;DR: In this article, a review of the current understanding of the Equatorial Spread F development processes and its day-to-day variability originating from the different coupling processes mentioned above is presented. But, the authors do not consider the effect of the magnetic field on the dynamics of the equatorial ionosphere.
Abstract: The plasma convection pattern of the evening sector equatorial ionosphere sets the condition for the plasma structuring through instability processes leading to the Equatorial Spread F (ESF)/plasma bubble irregularity development and evolution. Vertical coupling through upward propagating atmospheric waves controls/modifies the ionosphere-thermosphere interactive processes that eventually lead to the irregularity development. Instabilities grow by the Rayleigh-Taylor mechanism at the bottom side gradient region of a “rapidly” rising post sunset F layer in the presence of precursor conditions in terms of perturbations in plasma density, convection velocity and polarization electric fields. Field line integrated conductivity controlled by thermospheric meridional/trans-equatorial winds regulates the instability growth. The day-to-day and short term variabilities in the ESF are of major concern for space application and operational systems. Our efforts to understand such variabilities and to predict the ESF occurrence pose important scientific challenges especially because of the complexity of the diverse coupling processes that control them. There is convincing new evidences that during magnetically quiet conditions, the coupling processes due to upward propagating planetary waves and/or modulated tides, and gravity waves, with their highly variable propagation conditions, energy fluxes and periodicities control the ESF variability. Penetrating electric fields and disturbance dynamo electric fields from magnetosphere-ionosphere coupling processes also cause large degree of variability. This chapter provides a review of our current understanding of the ESF development processes and its day-to-day variability originating from the different coupling processes mentioned above.
6 citations
TL;DR: In this article, the authors used spread-F data recorded by ten ionosondes located between 25°N and 45°N from 1997 to 2016, to investigate the longitudinal differences in the statistical characteristics of spread-f occurrence and the probable mechanism for its occurrence at midlatitudes in Eastern Asia.
Abstract: Spread-F is known as the electron density inhomogeneous structures in F layer of ionosphere and can usually be classified as frequency spread-F (FSF) and range spread-F (RSF). Few studies have reported on the statistical characteristics of spread-F occurrences at midlatitudes in Eastern Asia, particularly the comparison of spread-F occurrences between China and Japan. In this paper, we used spread-F data recorded by ten ionosondes located between 25°N and 45°N from 1997 to 2016, to investigate the longitudinal differences in the statistical characteristics of spread-F occurrence and the probable mechanism for its occurrence at midlatitudes in Eastern Asia. Variations in the spread-F occurrences with the solar and geomagnetic activities, season and local time are presented. The main conclusions are as follows: (a) the occurrence percentage of FSF is higher than that of RSF, of which the former is anti-correlated with the solar or geomagnetic activities; (b) higher FSF occurrence percentages mostly appeared during summer, while RSF occurred more frequently in winter near 45°N latitude such as Urumqi, Changchun and Wakkanai; (c) the maximum of the FSF occurrence percentages mostly appeared between 01:00 and 02:00 LT approximately, whereas that of RSF appeared near 00:00 LT; (d) the spread-F occurrence percentages in the coastal or marine areas are higher than those in the inland region between 35°N and 45°N latitudes; however, this phenomenon is not obvious at lower latitudes; and (e) both the mean occurrences of FSF and RSF reach the minimum around 31°N latitude. These above results are helpful for understanding variations in spread-F occurrence at midlatitudes in Eastern Asia.
6 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