THE ROLE OF THE ATOMIC OXYGEN CONCENTRATION IN THE IONIZATION BALANCE OF THE LOWER IONOSPHERE DURING SOLAR PROTON EVENTS

It is shown that during a Solar Proton Event (SPE), when the ionization of the mesosphere is of a high degree, experimental data on the electron density obtained with the incoherent scatter technique as well as with partial reflection technique may be used as a criterion for choosing the atomic oxygen profile. The influence of the atomic oxygen concentration on the ionization balance at mesospheric altitudes during SPE on 17 January 2005 is investigated.


Introduction
For construction of the fullest and detailed models of the lower ionosphere it is necessary to determine a role of small components of the top atmosphere of the Earth: oxide of nitrogen, vapor of waters, atoms of oxygen, etc. at formation of structure and composition of the ionosphere at heights of the D region in various geophysical conditions.As concentration of small components are poorly known; there are difficulties of theoretical simulation of electron density and ionic structure of the D region [Danilov, 1989;Zadorozgnyi, 1982].In this paper the influence of variations of atomic oxygen concentration on altitudinal distribution of the charged particles concentration of ionospheric plasma of various grades and an effective factor of recombination are considered during the event of the penetration of solar protons (SPE) to mesospheric heights.

Results of observations and model calculations
Experimental data on the atomic oxygen concentration at heights lower than 80 km are absent.Therefore one uses the high-altitude profiles of atomic oxygen N O (h) received in diffuse-photochemical models for quiet geophysical conditions (Fig. 1 profiles 1-3) [Zadorozgnyi, 1982].It is seen, that the disorder in theoretical estimations of atomic oxygen concentration is very great.For calculation of theoretical N e -profiles of the electron concentration of D-region the model of ionic chemistry has been used [Smirnova et al., 1988;Kirkwood and Osepian, 1995;Osepian and Smirnova, 1996].On the basis of the results of the theoretical simulation, we shall estimate the influence of variations of atomic oxygen concentration on the ionic profile and an effective factor of recombination at different heights of the region of the mesosphere.Fig. 3 presents the profiles of the parameter f + describing ratio at the given height in the ionosphere between total amount of ions-bundles and amount of usual ions.O (α eff ≈ 2.2×10 -7 cm 3 s -1 ).At heights less than 67 km α eff is determined by factors of dissociative recombination of complex proton-hydrated bundles + 1 Cl and mutual neutralization of positive and negative ions.

Conclusions
On the basis of the model calculations and measurements of electron concentration by methods of partial reflections and incoherent scattering influence of variations of concentration of atomic oxygen on ionic profile, altitudinal distribution of electrons and an effective factor of recombination at heights of the D region of the polar ionosphere is investigated.It is shown, that the choice of a profile of atomic oxygen N O (h) in the mesosphere is the basic factor influencing on accuracy of model of the specified parameters.The profile of atomic oxygen during period of SPE in the daytime winter mesosphere is constructed.Calculation of an effective factor of recombination for these conditions is made.

Figure 1 .
Figure 1.Profiles of atomic oxygen According to model calculations, during SPE the concentration of the atomic oxygen at heights of 40-75 km is 2 -8

Figure 2 .
Figure 2. Profiles of the electron concentration at 09:50 UT of 17.01.2005It is seen that the electron density calculated on the basis of N O (h) profiles 1-3 with high concentration of atomic oxygen in all cases exceeds for 2-6 times the measured values N e in the lower part of the D region at h < 70 km.N e (h) profiles calculated on the basis of the profiles 4 and 5 practically coincide and reproduce the size and the form of the experimental N O (h) profile in all the considered intervals of height.On the basis of the results of the theoretical simulation, we shall estimate the influence of variations of atomic oxygen concentration on the ionic profile and an effective factor of recombination at different heights of the region of the mesosphere.Fig.3presents the profiles of the parameter f + describing ratio at the given height in the ionosphere between total amount of ions-bundles and amount of usual ions.

Figure 3 .
Figure 3. Profiles of the parameter f + for five models N O (h)It is seen that with reduction of the atomic oxygen concentration the share of bundles in total amount of positive ions and the interval of heights in which they prevail increases.Fig.4shows the profiles of the parameter − λ determining the ratio of the negative ions concentration to the electron concentration.Reduction N O (h) under conditions of SPE leads to changing of total density of negative ions in all the considered intervals of height.

Figure 4 .
Figure 4. Profiles of the parameter − λ for five models N O (h)

Figure 5 .
Figure 5.A profile of an effective factor of recombination under conditions of SPE at 09:50 UT of 17 January 2005 At heights more than 80 km where ion + 2 O is the prevailing ion for any model of atomic oxygen, the effective factor of recombination is determined by the factor of dissociative recombination of ions + 2