Onset conditions for equatorial spread <i>F</i> determined during EQUIS II

Hysell, D. L.; Larsen, M. F.; Swenson, C.; Barjatya, Aroh; Wheeler, Timothy F.; Sarango, M.; Woodman, Ron F.; Chau, Jorge L.

doi:10.1029/2005gl024743

Cited by 53 publications

(86 citation statements)

References 11 publications

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“…See for instance Fig. 14 from Hysell et al (2005b). The existence of a seed before Spread F break up is then an experimental fact as shown by this measurement and those of Singh et al (1997), mentioned before.…”

Section: Satellites Rockets and Other Radars And Radar Techniquessupporting

confidence: 78%

“…An additional advantage compared with Jicamarca RTI maps is its capability to cover, almost simultaneously, a two-dimensional crosscut of close to 1000 km in the EW direction at the bottom of the F-region and all altitudes of interest (e.g. Tsunoda, 1980;Hysell et al, 2005bHysell et al, , 2006a. One of their first contributions was to show that the enhanced back scatter was related to plasma bubbles, either using only radar data (Tsunoda, 1980) or with simultaneous plasma density satellite in situ measurements (Tsunoda et al, 1982) as shown in Fig.…”

Section: Satellites Rockets and Other Radars And Radar Techniquesmentioning

confidence: 99%

“…Figure 14 also shows other interesting results. The figure shows a result from an experiment carried out at Kwajalein to study bottom type irregularities using ALTAIR and instrumented rockets (Hysell et al, 2005b(Hysell et al, , 2006a). An important feature that can be seen in Fig.…”

Section: Satellites Rockets and Other Radars And Radar Techniquesmentioning

confidence: 99%

“…Notice the location of the bottom-type irregularities coincident with the altitudes having a westward drift. Notice also the anisotropic electric fields (and drifts) (after Hysell et al, 2005b). …”

Section: Satellites Rockets and Other Radars And Radar Techniquesmentioning

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: Satellites Rockets and Other Radars And Radar Techniquessupporting

confidence: 78%

Section: Satellites Rockets and Other Radars And Radar Techniquesmentioning

confidence: 99%

Section: Satellites Rockets and Other Radars And Radar Techniquesmentioning

confidence: 99%

Section: Satellites Rockets and Other Radars And Radar Techniquesmentioning

confidence: 99%

See 2 more Smart Citations

Spread F – an old equatorial aeronomy problem finally resolved?

2009

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“…The multi-instrument programs of "Guara" campaign in Brasil (Pfaff et al, 1997) completed the spectral analysis and dynamics. The Jicamarca Julia-campaign results (Hysell and Burcham, 1998) and the Central Pacific Altair results prepared the XXIst Century experiments in the Western Pacific (Fukao et al, 2006;Hysell et al, 2005).…”

Section: Introductionmentioning

confidence: 99%

Equinox transition at the magnetic equator in Africa: analysis of ESF ionograms

et al. 2008

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Abstract. We study equatorial night-time F layer behaviour from quarter-hourly ionograms at Korhogo/Ivory Coast (9.2 • N, 5 • W, dip lat. −2.4 • ) during local Spring March-April 1995, declining solar flux period, according to the magnetic activity. The height and thickness of the F-layer are found to vary intensely with time and from one day to the next. At time of the equinox transition, by the end of March, a net change of the nightly height-time variation is observed. The regime of a single height peak phase before 22 March changes to up to three main F-layer height phases after 30 March, each associated to a dominant mechanism. The first phase is identified to the post-sunset E×B pulse, the second phase associated to a change in the wind circulation phenomenon and the third one attributed to pre-sunrise phenomena. The influence of the magnetic activity is identified by the increase in the second peak amplitude. After the 21 April magnetic-equinox period, the height-time morphology becomes more irregular suggesting meridional wind abatement. The initiation, the growth and the maintenance of ESF are explored in relation to these nightly variations. The Rayleigh-Taylor instability is clearly identified as main precursor phenomenon. This is followed by the P-type (F-layer peak spread) structures, the whole with no specific dependence on the magnetic activity and on the F-layer phases, in contrast to further I and F-type (Inside and Frequency spread) ESFs. We discuss our results in the light of recent advanced experiments in Peru and the pacific.

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Elevated electron temperatures around twin sporadic E layers at low latitude: Observations and the case for a plausible link to currents parallel to the geomagnetic field

2013

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[1] We present data from nighttime sounding rocket flights in the low latitude E region. The payloads carried a sweeping Langmuir probe, a plasma impedance probe, and electric field probes. A detailed examination of the plasma density, temperature, and electric field measurements show two strong sporadic E (E s ) layers with very high electron temperatures ( 1000 K) on each side of the upper layer. The lower layer was consistent with the presence of a strong zonal neutral wind shear. The upper layer was strongly influenced by the presence of a strongly negative vertical electric field, with zonal winds and their shears also contributing. A strong downward motion of the plasma from the combined action of the downward electric field and negative zonal wind advected the upper layer far below the region of maximum growth. We have attributed the more puzzling high electron temperatures to frictional heating from parallel currents and shown that the F region nighttime dynamo could easily generate the necessary parallel current densities (1 A m -2 ) near the electron density troughs. The electron temperature was also elevated in the E s layers themselves, implying parallel current densities of the order of 15 A m -2 around the E s peaks. Those parallel currents were attributed to strong Hall current divergences driven by the zonal electric field around the E s peaks.Citation: Barjatya, A., J.-P. St-Maurice, and C. M. Swenson (2013), Elevated electron temperatures around twin sporadic E layers at low latitude: Observations and the case for a plausible link to currents parallel to the geomagnetic field,

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Onset conditions for equatorial spread F determined during EQUIS II

Cited by 53 publications

References 11 publications

Spread F – an old equatorial aeronomy problem finally resolved?

Spread F – an old equatorial aeronomy problem finally resolved?

Equinox transition at the magnetic equator in Africa: analysis of ESF ionograms

Elevated electron temperatures around twin sporadic E layers at low latitude: Observations and the case for a plausible link to currents parallel to the geomagnetic field

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