Abstract
Abstract. We present a comparison of the electron density and temperature behaviour in the ionosphere and plasmasphere measured by the Millstone Hill incoherent-scatter radar and the instruments on board of the EXOS-D satellite with numerical model calculations from a time-dependent mathematical model of the Earth's ionosphere and plasmasphere during the geomagnetically quiet and storm period on 20–30 January, 1993. We have evaluated the value of the additional heating rate that should be added to the normal photoelectron heating in the electron energy equation in the daytime plasmasphere region above 5000 km along the magnetic field line to explain the high electron temperature measured by the instruments on board of the EXOS-D satellite within the Millstone Hill magnetic field flux tube in the Northern Hemisphere. The additional heating brings the measured and modelled electron temperatures into agreement in the plasmasphere and into very large disagreement in the ionosphere if the classical electron heat flux along magnetic field line is used in the model. A new approach, based on a new effective electron thermal conductivity coefficient along the magnetic field line, is presented to model the electron temperature in the ionosphere and plasmasphere. This new approach leads to a heat flux which is less than that given by the classical Spitzer-Harm theory. The evaluated additional heating of electrons in the plasmasphere and the decrease of the thermal conductivity in the topside ionosphere and the greater part of the plasmasphere found for the first time here allow the model to accurately reproduce the electron temperatures observed by the instruments on board the EXOS-D satellite in the plasmasphere and the Millstone Hill incoherent-scatter radar in the ionosphere. The effects of the daytime additional plasmaspheric heating of electrons on the electron temperature and density are small at the F-region altitudes if the modified electron heat flux is used. The deviations from the Boltzmann distribution for the first five vibrational levels of N2(v) and O2(v) were calculated. The present study suggests that these deviations are not significant at the first vibrational levels of N2 and O2 and the second level of O2, and the calculated distributions of N2(v) and O2(v) are highly non-Boltzmann at vibrational levels v > 2. The resulting effect of N2(v > 0) and O2(v > 0) on NmF2 is the decrease of the calculated daytime NmF2 up to a factor of 1.5. The modelled electron temperature is very sensitive to the electron density, and this decrease in electron density results in the increase of the calculated daytime electron temperature up to about 580 K at the F2 peak altitude giving closer agreement between the measured and modelled electron temperatures. Both the daytime and night-time densities are not reproduced by the model without N2(v > 0) and O2(v > 0), and inclusion of vibrationally excited N2 and O2 brings the model and data into better agreement.Key words: Ionosphere (ionospheric disturbances; ionosphere-magnetosphere interactions; plasma temperature and density)
Highlights
A particular solstice period between 20±30 January, 1993, represents a global`10 day campaign'' period wherein many ionospheric, and thermospheric instruments collected data, and collaborative studies of the structure, dynamics and electron energy balance of the ionosphere were performed using the Millstone Hill and Arecibo incoherent scatter radar data and other groundbased data (Buonsanto et al, 1997; Fesen et al, 1997; Forbes et al, 1997; Richards and Khazanov, 1997; Scali et al, 1997)
An instrument on board the EXOS-D satellite for measuring the temperature distribution of thermal electrons with respect to the geomagnetic ®eld was installed on the tip of the satellite's solar cell paddles perpendicular to the satellite spin axis
The model used is an enhanced and updated version of the IZMIRAN model that we have steadily developed over the years
Summary
A particular solstice period between 20±30 January, 1993, represents a global`10 day campaign'' period wherein many ionospheric, and thermospheric instruments collected data, and collaborative studies of the structure, dynamics and electron energy balance of the ionosphere were performed using the Millstone Hill and Arecibo incoherent scatter radar data and other groundbased data (Buonsanto et al, 1997; Fesen et al, 1997; Forbes et al, 1997; Richards and Khazanov, 1997; Scali et al, 1997). Hierl et al (1997) found a big dierence between the high-temperatureowing afterglow and drift tube measurements (McFarland et al, 1973; Albritton et al.1977) of b as a result of the input of the reactions between the vibrationally excited O2 and O+(4S), and determined the dependence of b on the O2 vibrational temperature, TO2v, over the temperature range 300±1800 for TO2v Tn Ti. Theowing afterglow measurements of b given by Hierl et al (1997) were used by Pavlov (1998b) to invert the data to give the rate coecients bv for the various vibrational levels of O2(v > 0) for the model of the Boltzmann distribution of vibrationally excited molecular oxygen. Pavlov and Berrington (1999) found that the role of the cooling rate of thermal electrons by electron impact excitation of ®ne structure levels of atomic oxygen is not signi®cant at the F2-peak altitudes of the ionosphere for the geomagnetically quiet and disturbed period on 6±12 April, 1990, above Millstone Hill, and the energy exchange between. The new analytical expressions for cooling rates given by Pavlov (1998a, c) and Pavlov and Berrington (1999) are applied to study the thermal balance of the ionosphere and plasmasphere and to perform an examination of the role of these electron cooling rates in the thermal balance of the ionosphere during 20±30 January, 1993
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