Abstract
Abstract. Accurate measurements of electron density in the lower D-region (below 70 km altitude) are rarely made. This applies both with regard to measurements by ground-based facilities and by sounding rockets, and during both quiet conditions and conditions of energetic electron precipitation. Deep penetration into the atmosphere of high-energy solar proton fluxes (during solar proton events, SPE) produces extra ionisation in the whole D-region, including the lower altitudes, which gives favourable conditions for accurate measurements using ground-based facilities. In this study we show that electron densities measured with two ground-based facilities at almost the same latitude but slightly different longitudes, provide a valuable tool for validation of model computations. The two techniques used are incoherent scatter of radio waves (by the EISCAT 224 MHz radar in Tromsø, Norway, 69.6° N, 19.3° E), and partial reflection of radio-waves (by the 2.8 MHz radar near Murmansk, Russia, 69.0° N, 35.7° E). Both radars give accurate electron density values during SPE, from heights 57–60 km and upward with the EISCAT radar and between 55–70 km with the partial reflection technique. Near noon, there is little difference in the solar zenith angle between the two locations and both methods give approximately the same values of electron density at the overlapping heights. During twilight, when the difference in solar zenith angles increases, electron density values diverge. When both radars are in night conditions (solar zenith angle >99°) electron densities at the overlapping altitudes again become equal. We use the joint measurements to validate model computations of the ionospheric parameters f+, λ, αeff and their variations during solar proton events. These parameters are important characteristics of the lower ionosphere structure which cannot be determined by other methods.
Highlights
The high-latitude ionosphere has been intensively studied using various ground-based facilities as well as rocket and satellite-borne instruments
On the basis of model computations we investigate variations of ion composition, electron density and effective coefficient recombination at different altitudes in the D-region produced by the solar proton fluxes
2.4 Electron density and effective recombination coefficient profiles at different solar zenith angles In Figs. 5 and 9–11 we show electron density profiles obtained with the EISCAT radar and the partial reflection method during the solar proton fluxes (SPE) on 17 January 2005 at the same universal times (UT), but different local times (LT)
Summary
The high-latitude ionosphere has been intensively studied using various ground-based facilities as well as rocket and satellite-borne instruments. The strong and irregular spatial and temporal variations in the ionised components and in dynamical processes have a significant influence on the formation of in-homogeneous structures These affect operation of various ground-based and satellite-borne radio engineering facilities, which are used for radio communication over a broad frequency range. To improve propagation prediction methods and to ensure the practicability of radio communication requires knowledge of the spatial and temporal distribution of the electron density profiles in various conditions (quiet and disturbed situations, different seasons and solar zenith angles). We use experimental data from both radars during the solar proton event on 17 January 2005, when the ionisation rate in the D-region is large and measurements of electron density in the lower ionosphere (h
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