Physics of auroral phenomena : proceedings of the 39th annual seminar, Apatity, 29 February-4 March, 2016 / [ed. board: N. V. Semenova, A. G. Yahnin]. - Апатиты : Издательство Кольского научного центра РАН, 2016. - 167 с. : ил., табл.

“P hysics o f Auroral Phenom ena”. Proc. XXXIX Annual Sem inar, Apatity, pp. 87-91, 2 0 1 6 © Polar Geophysical Institute, 2016 Polar Geophysical Institute EXPERIMENTAL DETERMINATION OF THE D-REGION IONOSPHERE EFFECTIVE RECOMBINATION COEFFICIENTS FROM SOLAR ECLIPSE OBSERVATIONS S.M. Cherniakov P o la r Geophysical Institute, 15, Khalturina Str., Murmansk, 183010, Russia, e-mail: sergeich@ pgi.ru Abstract. The photochemistry of processes in the D-region of the ionosphere is difficult and up to the end is not developed. Therefore introduction of the effective coefficients determining the total speed of several reactions was widely adopted when modeling the D-region. Experimental opportunities of obtaining of effective recombination coefficients are rather limited. One of the methods which gives an opportunity to determine effective recombination coefficients is based on the phenomenon of a solar eclipse. During several solar eclipses at the partial reflection facility of the observatory "Tumanny" (69.0N. 35.7E) observations of the lower ionosphere were made and profiles of the electron concentration at heights of the lower ionosphere were received. Using the data effective recombination coefficients at some heights of the D-region of the high-latitude ionosphere were defined. Transport processes in the atmosphere during the solar eclipses did not give the possibility to definite effective recombination coefficient values at many heights. 1. Introduction The D-region of the ionosphere represents the most difficult area of the ionosphere for experimental study. The photochemistry of processes in the D-region is rather difficult and up to the end is not developed. Photochemical schemes demand specification, exist uncertainty in coefficients of separate reactions and concentration of small neutral components. Therefore introduction of the effective coefficients determining the total speed of several reactions was widely adopted when modeling the lower ionosphere, especially the D-region. Possibilities of obtaining of the effective recombination coefficients (ERC) are limited therefore all experimental methods which can define them are of great importance. One of such methods is based on observations of changes of the electron concentration (EC) in the ionosphere during a solar eclipse [Ratcliffe, Weekes, 1963]. Intensity of solar ionizing radiation during a solar eclipse has short-term and known behavior that allows investigating photochemical processes at the known input parameters. The temporary delay between the eclipse maximum (the sunlight minimum) and the minimum of the EC during an eclipse allows calculating ERC at the considered ionosphere heights at the known values of the electron concentration. This method with good approach can be used in the absence of transfer of electrons but the condition carried out not always. Appearance of acoustic-gravity waves at the region of observation, vertical movements etc. break an ideal picture of the EC behavior during "a short night". It considerably complicates obtaining ERC from the used data. 2. Determination of effective recombination coefficients during an eclipse The EC values in the place of observation can be changed depending on the speed of ionization, transfer processes in the region of observation, and also as a result of disappearance of free electrons in the recombination processes or adhesion. The recombination represents a process, the opposite one to ionization, i.e. the process of neutralization. In view of complexity of recombination processes in each separate reaction of disappearance of electrons for the description of the recombination process enter an effective recombination coefficient ot^f which is defined as the total speed of disappearance of electrons in several reactions in unit of time and in unit of volume. In this way the effective speed (coefficient) of electron formation q is entered which is determined as the quantity of the electrons which have appeared in the unit of volume and in the unit of time. At the same time it is necessary to remember that ionization makes the main contribution to free electrons formation and therefore the speed (coefficient) of electron formation is actually the speed (coefficient) of ionization which depends, with other things being equal, first of all on the flux of solar ionizing radiation. But as in the D-region of the ionosphere electron formation is possible not only due to ionization, it will be more general to speak about the speed (coefficient) of electron formation. Therefore use of these two concepts in our case will mean almost same, except cases when their distinction has to be marked out especially. In the D-region of the ionosphere the EC behavior at the fixed height in the absence of processes of electron transfer during changing of electron formation speed in time and disappearance of free electrons in recombination processes conform to the equation [ Ratcliffe , Weekes, 1963]: an, 2 ^ ~ Я~ ^эфф^е • ( 1 ) 87