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Barabash V.,Lulea University of Technology | Osepian A.,Polar Geophysical Institute | Dalin P.,Swedish Institute of Space Physics
Annales Geophysicae | Year: 2014

Mesospheric water vapour concentration effects on the ion composition and electron density in the lower ionosphere under quiet geophysical conditions were examined. Water vapour is an important compound in the mesosphere and the lower thermosphere that affects ion composition due to hydrogen radical production and consequently modifies the electron number density. Recent lower-ionosphere investigations have primarily concentrated on the geomagnetic disturbance periods. Meanwhile, studies on the electron density under quiet conditions are quite rare. The goal of this study is to contribute to a better understanding of the ionospheric parameter responses to water vapour variability in the quiet lower ionosphere. By applying a numerical D region ion chemistry model, we evaluated efficiencies for the channels forming hydrated cluster ions from the NO+ and O2+ primary ions (i.e. NO+.H2O and O2+.H2O, respectively), and the channel forming H+(H2O)nproton hydrates from water clusters at different altitudes using profiles with low and high water vapour concentrations. Profiles for positive ions, effective recombination coefficients and electrons were modelled for three particular cases using electron density measurements obtained during rocket campaigns. It was found that the water vapour concentration variations in the mesosphere affect the position of both the Cl2+ proton hydrate layer upper border, comprising the NO+(H2O)nand O2+(H2O)nhydrated cluster ions, and the Cl1+ hydrate cluster layer lower border, comprising the H+(H2O)npure proton hydrates, as well as the numerical cluster densities. The water variations caused large changes in the effective recombination coefficient and electron density between altitudes of 75 and 87 km. However, the effective recombination coefficient, αeff, and electron number density did not respond even to large water vapour concentration variations occurring at other altitudes in the mesosphere. We determined the water vapour concentration upper limit at altitudes between 75 and 87 km, beyond which the water vapour concentration ceases to influence the numerical densities of Cl2+ and Cl1+, the effective recombination coefficient and the electron number density in the summer ionosphere. This water vapour concentration limit corresponds to values found in the H2O-1 profile that was observed in the summer mesosphere by the Upper Atmosphere Research Satellite (UARS). The electron density modelled using the H2O-1 profile agreed well with the electron density measured in the summer ionosphere when the measured profiles did not have sharp gradients. For sharp gradients in electron and positive ion number densities, a water profile that can reproduce the characteristic behaviour of the ionospheric parameters should have an inhomogeneous height distribution of water vapour.©Author(s) 2014. Source

Yahnin A.G.,Polar Geophysical Institute | Yahnina T.A.,Polar Geophysical Institute | Frey H.,University of California at Berkeley | Pierrard V.,Belgian Institute for Space Aeronomy
Journal of Atmospheric and Solar-Terrestrial Physics | Year: 2013

Sub-oval proton auroras discovered by the IMAGE spacecraft correlate with EMIC waves (geomagnetic pulsations of the Pc1 range). This means that a common source of the waves and proton precipitation is the ion-cyclotron (IC) instability developing in the vicinity of the equatorial plane. Different forms of the proton auroras reflect different regimes of the IC instability and different conditions in the near-Earth equatorial magnetosphere. To understand what are the conditions for the generation of the sub-oval proton aurora one may map the aurora onto the equatorial plane and compare the projection with some important magnetospheric boundaries. In this report we compare the projection of so-called "proton aurora spots" with the location of the plasmapause. The latter is determined by the plasmapause formation model based on the quasi-interchange instability mechanism. The comparison shows that often the proton aurora spot source is located in the vicinity of the plasmapause or in the cold plasma gradient inside the plasmapause. In some events, the proton aurora spots map well outside the plasmapause. We assume that in the latter case the IC instability develops when westward drifting energetic protons interact with the cold plasma that was earlier detached from the plasmasphere. © 2012 Elsevier Ltd. Source

Kozelov B.V.,Polar Geophysical Institute | Golovchanskaya I.V.,Polar Geophysical Institute
Journal of Geophysical Research: Space Physics | Year: 2010

In the study of scaling properties of auroral luminosity variations by ground-based imaging observations, a problem arises that the actual scaling characteristics are distorted because of contributions to images from extension of auroral structures along the geomagnetic field. The field-aligned trends come into play for whatever small deviations from the magnetic zenith, making questionable the appropriateness of ground imaging data for investigation of turbulence signatures in aurora. In order to clear up how to correct for this effect, we have modeled the distortions, stemming from aspect angle broadening, for synthesized self-similar fluctuations with known scaling characteristics in the plane perpendicular to the magnetic field. Both narrow and wide field-aligned profiles of luminosity were considered. Three estimators for deriving scaling parameters were applied, including the wavelet estimator, dyadic filter estimator, and standard deviation statistical estimator, of which the wavelet estimator is shown to be most robust. The formulas are presented that relate the observed scaling characteristics with the true ones for the case of aurora being observed near magnetic zenith. Copyright 2010 by the American Geophysical Union. Source

Golovchanskaya I.V.,Polar Geophysical Institute | Kozelov B.V.,Polar Geophysical Institute
Journal of Geophysical Research: Space Physics | Year: 2010

We compare scaling properties of electric fields measured by the low-altitude polar-orbiting Dynamics Explorer 2 satellite in the auroral zone and the polar cap under interplanetary magnetic field (IMF) southward conditions. The techniques of logscale diagrams (LDs) and probability density function (PDF) are applied to demonstrate the scale-free structure of electric fluctuations on scales from 0.5 km to 256 km in both regions. It is shown that while the amplitudes of electric field fluctuations are much smaller in the polar cap than in the auroral zone, the scaling characteristics of the fluctuations in the two domains are basically the same. To examine the possibility that electric turbulence in the polar cap may be driven directly by turbulent solar wind variations, we searched for the relationship between the RMS values of the electric fluctuations in the polar cap and solar wind variability and did not find a clear relationship. We also demonstrate that the Poynting flux associated with electric and magnetic fluctuations in the polar cap tends to subside from the flanks toward the center of the polar cap. These findings are more consistent with plasma shear flow on open field lines being the driver of turbulence in the polar cap ionosphere. Copyright 2010 by the American Geophysical Union. Source

Barabash V.,Lulea University of Technology | Osepian A.,Polar Geophysical Institute | Dalin P.,Swedish Institute of Space Physics | Kirkwood S.,Swedish Institute of Space Physics
Annales Geophysicae | Year: 2012

The theoretical PGI (Polar Geophysical Institute) model for the quiet lower ionosphere has been applied for computing the ionization rate and electron density profiles in the summer and winter D-region at solar zenith angles less than 80° and larger than 99° under steady state conditions. In order to minimize possible errors in estimation of ionization rates provided by solar electromagnetic radiation and to obtain the most exact values of electron density, each wavelength range of the solar spectrum has been divided into several intervals and the relations between the solar radiation intensity at these wavelengths and the solar activity index F10.7 have been incorporated into the model. Influence of minor neutral species (NO, H2O, O, O3) concentrations on the electron number density at different altitudes of the sunlit quiet D-region has been examined. The results demonstrate that at altitudes above 70 km, the modeled electron density is most sensitive to variations of nitric oxide concentration. Changes of water vapor concentration in the whole altitude range of the mesosphere influence the electron density only in the narrow height interval 73-85 km. The effect of the change of atomic oxygen and ozone concentration is the least significant and takes place only below 70 km.

Model responses to changes of the solar zenith angle, solar activity (low-high) and season (summer-winter) have been considered. Modeled electron density profiles have been evaluated by comparison with experimental profiles available from the rocket measurements for the same conditions. It is demonstrated that the theoretical model for the quiet lower ionosphere is quite effective in describing variations in ionization rate, electron number density and effective recombination coefficient as functions of solar zenith angle, solar activity and season. The model may be used for solving inverse tasks, in particular, for estimations of nitric oxide concentration in the mesosphere. © Author(s) 2012. CC Attribution 3.0 License. Source

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