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  • Shalimov, S.  (5)
  • 1
    Online Resource
    Online Resource
    A model of mid-latitude E-region plasma convergence inside a planetary wave cyclonic vortex
    Copernicus GmbH ; 2002
    In:  Annales Geophysicae Vol. 20, No. 8 ( 2002-08-31), p. 1193-1201
    Details
    In: Annales Geophysicae, Copernicus GmbH, Vol. 20, No. 8 ( 2002-08-31), p. 1193-1201
    Abstract: Abstract. Recently, Shalimov et al. (1999) proposed a new mechanism for large-scale accumulation of long-lived metallic ions in the mid-latitude ionosphere driven by planetary waves in the lower thermosphere. In this mechanism, the combined action of frictional and horizontal magnetic field forces at E-region altitudes causes the plasma to converge and accumulate in large areas of positive neutral wind vorticity within a propagating planetary wave. The present paper provides a theoretical formulation for this mechanism by modelling both horizontal and vertical plasma transport effects within a planetary wave vortex, of cyclonic neutral wind. Non-steady-state numerical solutions of the ion continuity equation show that the proposed accumulation process can enhance the ionization significantly inside the planetary wave vortex but its efficiency depends strongly on altitude, whereas on the other hand, it can be complicated by vertical plasma motions. The latter, which are driven by the same planetary wave wind field under the action of the vertical Lorentz force and meridional wind forcing along the magnetic field lines, can lead to either plasma compressions or depletions, depending on the prevailing wind direction. We conclude that, for shorter times, vertical plasma transport may act constructively to the horizontal gathering process to produce considerable E-region plasma accumulation over large sectors of a planetary wave vortex of cyclonic winds.Key words. Ionosphere (ionosphere-atmosphere interactions; mid-latitude ionosphere; sporadic E-layers) – Meteorology and atmospheric dynamics (waves and tides)
    Type of Medium: Online Resource
    ISSN: 1432-0576
    URL: Article
    DOI: 10.5194/angeo-20-1193-2002
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2002
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  • 2
    Online Resource
    Online Resource
    “Early/slow” events: A new category of VLF perturbations observed in relation with sprites
    American Geophysical Union (AGU) ; 2006
    In:  Journal of Geophysical Research Vol. 111, No. A11 ( 2006-11-23)
    Details
    In: Journal of Geophysical Research, American Geophysical Union (AGU), Vol. 111, No. A11 ( 2006-11-23)
    Type of Medium: Online Resource
    ISSN: 0148-0227
    URL: Article
    DOI: 10.1029/2006JA011960
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 2006
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    SSG: 16,13
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  • 3
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    More evidence for a planetary wave link with midlatitude 〈i〉E〈/i〉 region coherent backscatter and sporadic 〈i〉E〈/i〉 layers
    Copernicus GmbH ; 2000
    In:  Annales Geophysicae Vol. 18, No. 9 ( 2000-09-30), p. 1182-1196
    Details
    In: Annales Geophysicae, Copernicus GmbH, Vol. 18, No. 9 ( 2000-09-30), p. 1182-1196
    Abstract: Abstract. Measurements of midlatitude E region coherent backscatter obtained during four summers with SESCAT, a 50 MHz Doppler system operating in Crete, Greece, and concurrent ionosonde recordings from the same ionospheric volume obtained with a CADI for one of these summers, are used to analyse the long-term variability in echo and Es occurrence. Echo and Es layer occurrences, computed in percent of time over a 12-h nighttime interval, take the form of time sequences. Linear power spectrum analysis shows that there are dominant spectral peaks in the range of 2–9 days, the most commonly observed periods appearing in two preferential bands, of 2–3 days and 4–7 days. No connection with geomagnetic activity was found. The characteristics of these periodicities compare well with similar properties of planetary waves, which suggests the possibility that planetary waves are responsible for the observed long-term periodicities. These findings indicate also a likely close relation between planetary wave (PW) activity and the well known but not well understood seasonal Es dependence. To test the PW postulation, we used simultaneous neutral wind data from the mesopause region around 95 km, measured from Collm, Germany. Direct comparison of the long-term periodicities in echo and Es layer occurrence with those in the neutral wind show some reasonable agreement. This new evidence, although not fully conclusive, is the first direct indication in favour of a planetary wave role on the unstable midlatitude E region ionosphere. Our results suggest that planetary waves observation is a viable option and a new element into the physics of midlatitude Es layers that needs to be considered and investigated.Key words: Ionosphere (ionosphere irregularities; mid-latitude ionosphere) – Meteorology and atmospheric dynamics (waves and tides)
    Type of Medium: Online Resource
    ISSN: 1432-0576
    URL: Article
    DOI: 10.1007/s00585-000-1182-8
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2000
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  • 4
    Online Resource
    Online Resource
    〈i〉E〈/i〉-region wind-driven electrical coupling of patchy sporadic-〈i〉E〈/i〉 and spread-〈i〉F〈/i〉 at midlatitude
    Copernicus GmbH ; 2005
    In:  Annales Geophysicae Vol. 23, No. 6 ( 2005-09-15), p. 2095-2105
    Details
    In: Annales Geophysicae, Copernicus GmbH, Vol. 23, No. 6 ( 2005-09-15), p. 2095-2105
    Abstract: Abstract. This paper investigates the role of neutral winds in the generation of relatively large polarization electric fields across patchy sporadic-E layers, which then map upward to the F region, to create conditions for medium-scale spread-F. The calculations are based on an analytical model that uses the current continuity equation and field-aligned current closures to the F region in order to describe quantitatively a Hall polarization process inside sporadic-E plasma patches during nighttime. In applying this model we use experimentally known values for E and F region, conductances, the ambient electric fields and prevailing neutral winds, in order to estimate the polarization fields that build up inside sporadic-E. It is found that the relatively strong west-southwest neutral winds during summer nighttime can provide the free energy for the generation of sizable polarization electric fields, which have comparable eastward and north-upward components and reach values of several mV/m. Given that the sporadic-E patches have sizes from a few to several tens of kilometers, the polarization fields can map easily to the F region bottomside where they impact ExB plasma uplifts and westward bulk motions, in line with key observational properties of medium-scale spread-F. However, the present simple model needs further development to also include wind forcing of the F region plasma and possible polarization processes inside spread-F. Keywords. Ionosphere (Electric fields and currents; Ionospheric irregularities; Mid-latitude ionosphere)
    Type of Medium: Online Resource
    ISSN: 1432-0576
    URL: Article
    DOI: 10.5194/angeo-23-2095-2005
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2005
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  • 5
    Online Resource
    Online Resource
    Large polarization electric fields associated with midlatitude sporadic E
    American Geophysical Union (AGU) ; 1998
    In:  Journal of Geophysical Research: Space Physics Vol. 103, No. A6 ( 1998-06), p. 11617-11625
    Details
    In: Journal of Geophysical Research: Space Physics, American Geophysical Union (AGU), Vol. 103, No. A6 ( 1998-06), p. 11617-11625
    Abstract: Recent 50 MHz E region coherent backscatter observations and in situ rocket measurements established the existence of enhanced electric fields in the midlatitude ionosphere that can become at times sufficiently large to excite the Farley‐Buneman instability. To understand the origin of these fields, we present a simple quantitative model that relates to a local polarization process acting inside spatially confined, nighttime sporadic E layers of dense ionization. By including the effects of field‐aligned currents in the current continuity equation we estimate the necessary conditions on the relative horizontal E layer extent and the ratio of integrated Pedersen conductivities above and inside the layer for the generation of both zonal and meridional polarization fields. We show that the polarization process can account for the elevated electric fields of several millivolts per meter, which are implied often from backscatter Doppler measurements during unstable E region conditions at midlatitude. The polarization process can become much more effective for dense and strongly elongated E s layers under the action of an enhanced ambient electric field. In this case, large polarization fields that may be capable of exciting Farley‐Buneman plasma waves can be sustained. The stringent requirements for strongly elongated sporadic E layers with sharp boundaries, low ionospheric Pedersen conductivities above the layer in relation to those inside, and relatively large ambient electric fields would explain why type 1 echoes are so rare in midlatitude E region backscatter.
    Type of Medium: Online Resource
    ISSN: 0148-0227
    URL: Article
    DOI: 10.1029/97JA03666
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 1998
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    SSG: 16,13
    Location Call Number Limitation Availability
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    Online Resource
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