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: The spread F Experiment (or SpreadFEx) as discussed by the authors performed an extensive experimental campaign from September to November 2005 to define the role of neutral atmosphere dynamics, specifically wave motions propagating upward from the lower atmosphere, in seeding equatorial spread F and plasma bubbles extending to higher altitudes.
Abstract: We performed an extensive experimental campaign (the spread F Experiment, or SpreadFEx) from September to November 2005 to attempt to define the role of neutral atmosphere dynamics, specifically wave motions propagating upward from the lower atmosphere, in seeding equatorial spread F 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. Initial results of our analyses of SpreadFEx and related data indicate 1) extensive gravity wave (GW) activity apparently linked to deep convection predominantly to the west of our measurement sites, 2) the presence of small-scale GWactivity confined to lower altitudes, 3) larger-scaleGWactivity apparently penetrating to much higher altitudes suggested by electron density and TEC fluctuations in the E and F regions, 4) substantial GW amplitudes implied by digisonde electron densities, and 5) apparent direct links of these perturbations in the lower F region to spread F and plasma bubbles extending to much higher altitudes. Related efforts with correlative data are defining 6) the occurrence and locations of deep convection, 7) the spatial and temporal evolutions of plasma bubbles, the 8) 2D (height-resolved) structures of plasma bubbles, and 9) the expected propagation of GWs and tides from the lower atmosphere into the thermosphere and ionosphere.
15 citations
Cites background from "The impact of gravity waves rising ..."
...These results will be elaborated further by Abdu et al. (2008), Fritts et al. (2008b), and Kherani et al. (2008) in the SpreadFEx special issue of Annales Geophysicae....
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...For more complete discussions of related SpreadFEx analyses, we refer the interested reader to Fritts et al. (2008a, b), Abdu et al. (2008), Kherani et al. (2008), and other papers in the SpreadFEx special issue....
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...More detailed assessments of GW influences on plasma dynamics and instabilities will be provided in our SpreadFEx special issue (see, in particular, Fritts et al., 2008a, b; Abdu et al., 2008; Kherani et al., 2008)....
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TL;DR: Wang et al. as mentioned in this paper used a data set with a time coverage of one solar cycle from two Chinese stations located at exactly the same latitude and a 38 degrees separation in longitude, and having sharp contrasts of ground meteorological conditions, to make comparisons of spread F occurrence rates.
Abstract: Spread F is a widely studied subject, and the occurrence of spread F is affected by many factors. One of these factors is acoustic gravity waves (AGWs) which are very important in seeding spread F. Since most of the AGWs in the ionosphere originate from the lower atmosphere, there should be some regional features of spread F due to the different meteorological or ground conditions immediately beneath the local ionosphere. In this paper, a data set with a time coverage of one solar cycle from two Chinese stations located at exactly the same latitude and a 38 degrees separation in longitude, and having sharp contrasts of ground meteorological conditions, are used to make comparisons of spread F occurrence rates. The results showed that the total number of occurrence or occurrence percentage at Changchun station (very near the coast) is always much higher than that at Urumqi station (in the very center of the Europe-Asia continent). The annual maxima of spread F occurrence are in summer and winter. Other features of spread F occurrence at these two stations are in agreement with known properties of spread F. However, the great difference of occurrence frequency between the two stations is striking and worth further studying.
15 citations
01 Jan 2011
TL;DR: In this article, the role of acoustic gravity waves (AGW) to excite atmospheric and ionospheric disturbances is examined, and the possible role of the AGW to act as a seeding perturbation for equatorial plasma bubbles under varying nature of mean zonal wind and tropospheric thermal source is investigated.
Abstract: The role of acoustic gravity waves (AGWs) to excite atmospheric and ionospheric disturbances is examined in this work. These waves are launched in the atmosphere by tropospheric thermal sources and convective activity. An alternative fully time-spatial dependent nonlinear wave equation of acoustic gravity wave is derived and solved numerically using implicit finite-difference scheme. Their propagation in the atmosphere through mesopause thermal duct and lower thermosphere density duct, the role of nonlinear viscous effect to limit the amplitude of these waves in the density duct and to allow them to escape to higher altitude where they attain large amplitude in the bottomside F region Ionosphere, and the role of the mean zonal wind to reduce their amplitude are investigated in present study. To study AGW induced disturbances in the equatorial Ionosphere, the AGW model is coupled with hydromagnetic equations in Ionosphere. This coupling is explored in the context of the collisional interchange instability (CII) in the F region leading to the formation of equatorial F region plasma bubbles. To do so, AGW model is coupled with the CII model and simultaneously solved numerically. The possible role of the AGW to act as a seeding perturbation for equatorial plasma bubbles under varying nature of mean zonal wind and tropospheric thermal source are also investigated.
13 citations
TL;DR: In this paper, medium-scale gravity waves (MSGWs) observed during the Conjugate Point Experiment (COPEX) at Boa Vista (2.8°N; 60.7°S, dip angle 21.6°S) have been ray-traced and studied based on zero wind and model wind conditions.
13 citations
Cites background from "The impact of gravity waves rising ..."
...…Richmond, 1978; Anderson et al., 1982; Huang et al., 1993; Huang and Kelley, 1996; Sultan, 1996; Tsunoda, 2007, 2010; Keskinen and Vadas, 2009; Kherani et al., 2009) and observational (e.g., Kelley et al., 1981; Sobral et al., 1981, 2001; Rottger, 1982; Hysell et al., 1990; McClure et al.,…...
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...Indeed, theoretical (e.g., Richmond, 1978; Anderson et al., 1982; Huang et al., 1993; Huang and Kelley, 1996; Sultan, 1996; Tsunoda, 2007, 2010; Keskinen and Vadas, 2009; Kherani et al., 2009) and observational (e....
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...Kherani et al. (2009) simulated two gravity waves occurring during the SpreadFEx, and examined propagations of them from a convective source region....
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TL;DR: In this paper, the authors examined the efficiency of the longitudinal variation of the PRVD to act as a seeding for the collisional interchange instability and to give rise to the equatorial plasma bubble.
Abstract: [1] The collisional interchange instability (CII) is known to lead to the equatorial plasma bubble (EPB) development when the ionosphere is raised to higher altitudes by the prereversal electric field or vertical drift (PRVD). The PRVD presents considerable longitudinal variation (with scale size ∼15°) across the sunset terminator and this variation may act as a seeding perturbation as proposed by Woodman (1994) and Huang and Kelley (1996b). In the present work, we examine the efficiency of this longitudinal variation of the PRVD to act as a seeding for the CII and to give rise to EPB in the absence of any other kind of initial perturbation. To do so, we carried out the CII simulation at the equator in a plane perpendicular to the magnetic field. We consider a few simplified cases choosing a Gaussian-shaped longitudinal variation of PRVD with various possible minimum and peak values and finally consider a realistic case with a spatial-temporal configuration of PRVD obtained using SAMI2 model. Simulations with simplified cases show that the EPB develops only for minimum value greater than 20 m/s and amplitude (difference between the peak-to-minimum value) greater than 40 m/s. Simulation with a realistic case shows that the PRVD during high solar flux summer satisfies these threshold conditions and with the seeding scale ∼15°, the EPB of longitudinal size ≈2° is developed toward east of the PRVD peak.
13 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