Equatorial spread-F initiation: Post-sunset vortex, thermospheric winds, gravity waves

Kudeki, Erhan; Akgiray, Ahmed; Milla, Marco; Chau, Jorge L.; Hysell, D. L.

doi:10.1016/j.jastp.2007.04.012

Cited by 135 publications

(155 citation statements)

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“…More recently Kudeki et al (2007) obtained comparable growth times using a linear non-local approach to the problem including altitude dependent gradients, collision frequencies and sheared plasma drifts, and emphasized that it is the counter streaming rather than the shear that is mainly responsible for the instability. It is effectively a wind driven interchange instability, but this alternative name is already being used to describe the instability responsible for the bottom-type Spread F discussed below.…”

Section: Recent Theoretical Effortsmentioning

confidence: 98%

“…The current understanding comes mainly from the efforts of Hysell, Kudeki and colleagues Hysell and Kudeki, 2004;Hysell et al, 2005aHysell et al, , b, 2000aHysell et al, , 2006bKudeki et al, 2007). Hysell and Kudeki (2004) identified a collisional shear instability at the shear region of the F-region that could compete with the GRT in this region and performed numerical simulations to illustrate their growth (see Fig.…”

Section: Recent Theoretical Effortsmentioning

confidence: 99%

“…The mechanism is as follows: The wind, U, produces a vertical current, J, the current polarizes the wave fronts, the polarization field, δE, produces drifts, δv, along the fronts, increasing the original amplitude of the wave perturbation, increasing, in turn, its polarization and consequently the amplitude of the wave perturbation. (After Kudeki et al, 2007). Cartoon showing the physical processes responsible for the "collisional shear instability" which has been proposed to seed a later GRT instability.…”

Section: Recent Theoretical Effortsmentioning

confidence: 99%

“…Cartoon showing the physical processes responsible for the "collisional shear instability" which has been proposed to seed a later GRT instability. The mechanism is as follows: The wind, U , produces a vertical current, J , the current polarizes the wave fronts, the polarization field, δE, produces drifts, δv, along the fronts, increasing the original amplitude of the wave perturbation, increasing, in turn, its polarization and consequently the amplitude of the wave perturbation (after Kudeki et al, 2007). GRT instability. They propose that this instability would undulate the bottom of the F-region and seed later a GRT growth.…”

Section: Recent Theoretical Effortsmentioning

confidence: 99%

“…It is effectively a wind driven interchange instability, but this alternative name is already being used to describe the instability responsible for the bottom-type Spread F discussed below. It is in this regard that the Kudeki et al (2007) emphasis becomes important since the name, collisional shear instability, is confusing.…”

Section: Recent Theoretical Effortsmentioning

confidence: 99%

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Spread F – an old equatorial aeronomy problem finally resolved?

2009

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Abstract. One of the oldest scientific topics in EquatorialAeronomy is related to Spread-F. It includes all our efforts to understand the physical mechanisms responsible for the existence of ionospheric F-region irregularities, the spread of the traces in a night-time equatorial ionogram -hence its name -and all other manifestations of the same. It was observed for the first time as an abnormal ionogram in Huancayo, about 70 years ago. But only recently are we coming to understand the physical mechanisms responsible for its occurrence and its capricious day to day variability. Several additional techniques have been used to reveal the spatial and temporal characteristics of the F-region irregularities responsible for the phenomenon. Among them we have, in chronological order, radio star scintillations, trans-equatorial radio propagation, satellite scintillations, radar backscatter, satellite and rocket in situ measurements, airglow, total electron content techniques using the propagation of satellite radio signals and, recently, radar imaging techniques. Theoretical efforts are as old as the observations. Nevertheless, 32 years after their discovery, Jicamarca radar observations showed that none of the theories that had been put forward could explain them completely. The observations showed that irregularities were detected at altitudes that were stable according to the mechanisms proposed. A breakthrough came a few years later, again from Jicamarca, by showing that some of the "stable" regions had become unstable by the non-linear propagation of the irregularities from the unstable to the stable region of the ionosphere in the form of bubbles of low density plasma. A problem remained, however; the primary instability mechanism proposed, an extended (generalized) Rayleigh-Taylor instability, was too slow to explain the rapid development seen by the observations. Gravity waves in the neutral background have been proposed as a seeding mechaCorrespondence to: R. F. Woodman (ronw@geo.igp.gob.pe) nism to form irregularities from which the instability would grow, but the former are difficult to observe as a controlling parameter. Their actual role still needs to be determined. More recently, radar observations again have shown the existence of horizontal plasma drift velocities counter streaming the neutral wind at the steep bottom of the F-region which produces a fast growing instability from which a generalized Rayleigh-Taylor instability can grow. The mechanisms proposed would explain the rapid development of the large and medium scale irregularities that have been observed, including some seen only by radars. Nevertheless, a proper quantitative theoretical mechanism that would explain how these irregularities break into the very important meter scale ones, responsible for the radar echoes, needs to be developed. This paper makes a selective historical review of the observations and proposed theories since the phenomenon was discovered to our current understanding.

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Section: Recent Theoretical Effortsmentioning

confidence: 98%

Section: Recent Theoretical Effortsmentioning

confidence: 99%

Section: Recent Theoretical Effortsmentioning

confidence: 99%

Section: Recent Theoretical Effortsmentioning

confidence: 99%

Section: Recent Theoretical Effortsmentioning

confidence: 99%

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Spread F – an old equatorial aeronomy problem finally resolved?

2009

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A numerical simulation study of the collisional‐interchange instability seeded by the pre‐reversal vertical drift

2013

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[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 ı ) 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 ı , the EPB of longitudinal size 2 ı is developed toward east of the PRVD peak.Citation: Sousasantos, J., E. A. Kherani, and J. H. A. Sobral (2013), A numerical simulation study of the collisional-interchange instability seeded by the pre-reversal vertical drift,

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Morphology of the postsunset vortex in the equatorial ionospheric plasma drift

Lee

Kil

Kwak

et al. 2015

Geophys. Res. Lett.

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The postsunset vortex in the equatorial ionosphere exhibits clockwise plasma motions after sunset in longitude (time) and altitude coordinates when the equatorial ionosphere is viewed looking northward. We describe the typical morphology of the postsunset vortex using incoherent scatter radar observations at Jicamarca in Peru during the previous solar maximum (2000)(2001)(2002). A pronounced vortical plasma motion appears around 1700 LT along with the onset of the prereversal enhancement (PRE). The center of this vortex is located near an altitude of 270 km. A smaller-scale vortex also appears about 0.5~1 h later at higher altitudes. However, the morphology and occurrence time of this small vortex depend on the characteristics of the coherent backscatter region. We find that the earlier vortex is the major feature of the postsunset vortices because it is repeatable, associated with the PRE, and independent to the occurrence of the coherent backscatter region.

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Equatorial spread-F initiation: Post-sunset vortex, thermospheric winds, gravity waves

Cited by 135 publications

References 13 publications

Spread F – an old equatorial aeronomy problem finally resolved?

Spread F – an old equatorial aeronomy problem finally resolved?

A numerical simulation study of the collisional‐interchange instability seeded by the pre‐reversal vertical drift

Morphology of the postsunset vortex in the equatorial ionospheric plasma drift

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