Experimental estimation of effective recombination coefficients in the D-region ionosphere at high latitudes during solar eclipses by the method of partial reflections

The photochemical theory of processes in the lower ionosphere is very complicated and up to now it is not completely developed. Therefore introduction of the effective coefficients determining the total speed of several important reactions has been widely adopted when modeling the D -region of the ionosphere. Experimental opportunities for obtaining effective recombination coefficients are rather limited. One of the methods to estimate effective recombination coefficients uses the phenomenon of a solar eclipse. The basis of this method is the idea of Appleton about similarity of the behavior of the linear inductive circuit and variations of the electron concentration in the ionosphere on a fixed height in the absence of the transport processes, the change in the rate of formation of electrons in time and the disappearance of free electrons due to recombination. By analogy with the time constant of the electric circuit Appleton called the reaction of the ionosphere on the process of ionization in the ionosphere as "sluggishness" with a characteristic time constant τ, which is also called the "relaxation time" or "time constant of the ionosphere". During 11 August 1999, 1 August 2008, 11 June 2011, 20 March 2015 solar eclipses at the partial reflection facility of the observatory "Tumanny" (69.0N, 35.7E) observations of the amplitudes of reflections of ordinary and extraordinary waves have been carried out. Using the obtained data the two-dimensional (time, height) distribution of the electron density n e at altitudes of the D -region ionosphere has been calculated. This has made it possible to obtain the behavior of the electron concentration in time at selected altitudes (temporal profiles of electron density at selected altitudes). Using the obtained experimental profiles, the effective recombination coefficients on the heights of the D -region ionosphere have been evaluated. Transport processes of plasma (for example, propagation of acoustic-gravity waves, vertical motion) during eclipses have influenced on the behavior of the temporal profiles of the electron concentration at altitudes of the D -region ionosphere. This has led to the fact that on some heights of the D -region ionosphere determination of effective recombination coefficient became impossible.