G. M. Kuznetsova

Possibility of estimating the abundance of oxygen atoms and molecules based on electron density measurements in the middle atmosphere

It has been tried to develop the method for estimating the ratio of the densities of oxygen atoms (n1) and nitrogen molecules (n3) as well as n1/n2 and n2/n3 (where n2 is the density of oxygen molecules) at the reference level of the upper thermosphere (120 km), using the data on electron density at altitudes of 120–200 km. This approach is based on an analysis of the semiempirical model (SEM) equation describing the dependence of electron density (N) on the characteristics of the thermospheric neutral gas. The series of the SEM versions [Shchepkin et al., 1997, 2004] was previously developed by the authors of this work. The estimates were performed based on the regular N measurements with the help of a digital ionosonde at ISZF SO RAN, Irkutsk, in 2003–2005.

Calculations of the ionization drift velocity by the Titheridge method, based on the data obtained at the Irkutsk Digisonde

The applicability of the method proposed by Titheridge [1995] to the estimations of the ionization vertical drift velocity V is studied. The values of the F2-layer maximum height, hmF2, obtained from the measurements using the DPS-4 digital ionosonde at Irkutsk (Institute of Solar-Terrestrial Physics) in 2003–2006, are the initial data. The neutral gas parameters were calculated from the [Hedin, 1987] thermospheric model. The obtained calculations of the vertical ionization drift velocity are estimated by comparing with the [Hedin et al., 1991] empirical model. In some cases, good agreement with this model has been obtained. However, such agreement is registered not always, and the cause of such discrepancies is still unclear. The diurnal variations in the vertical ionization drift velocity in different seasons are also discussed.

Response of some ionospheric parameters to geomagnetic disturbances at heights below the F2-layer maximum in September and April 2005

An analysis of ionospheric data obtained during geomagnetic disturbances in April and September 2005 is performed in order to obtain information on the behavior of some ionospheric parameters at heights of the F1 layer. The results of measurements by an Irkutsk digisonde at hourly and 5- and 15-min time intervals were used. It is shown that in September all parameters very actively responded to geomagnetic disturbances in short measurement time intervals. It is also shown that the electron concentration behaves more stable at lower heights of the F1 layer both during strong and moderate disturbances.

Relationship between the daytime critical frequencies of the F2 layer and thermospheric characteristics

The relationship between the critical frequency of the F2 layer and the atmospheric characteristics has been obtained in a general form. It has been shown that this relation makes it possible to sufficiently accurately describe the daytime values of foF2 while comparing them with the observed monthly median values. Such comparisons were performed, first, for the data of measurements in Irkutsk using the DPS-4 digital ionosonde in 2003–2006 and, second, based on the annual variations in the noon foF2 values at 24 stations of the Northern Hemisphere in 1984. The calculations were performed using the MSIS-86 thermospheric model [Hedin, 1987].

Relative concentration of oxygen atoms and molecules at a height of 120 km according to the data of ionospheric measurements

It is convenient to use the semi-empirical model (SEM), developed by the authors earlier and describing the relation of the electron density at heights of the middle ionosphere (120–200 km) to the parameters of the thermosphere and the integral flux of the ionizing solar radiation, to estimate the gas composition characteristics using the data of ionospheric measurements [Shchepkin et al., 2008]. The ratios of the concentrations of oxygen atoms and nitrogen molecules to those of oxygen molecules and atoms at a height of 120 km are compared using two SEM versions. The first version is based on the usage of the coefficients obtained from the measurements of N(h) profiles at Moscow observatory. The electron densities at heights of 120–200 km, obtained at the Institute of Solar-Terrestrial Physics in 2003–2006 using the digisonde, were the experimental data for the second version.

Geomagnetic Storm Effects at F1 Layer Altitudes in Various Periods of Solar Activity (Irkutsk Station)

The influence of geomagnetic disturbances on electron density Ne at F1 layer altitudes in different conditions of solar activity during the autumnal and vernal seasons of 2003–2015, according to the data from the Irkutsk digital ionospheric station (52° N, 104° Е) is examined. Variations of Ne at heights of 150–190 km during the periods of twenty medium-scale and strong geomagnetic storms have been analyzed. At these specified heights, a vernal–autumn asymmetry of geomagnetic storm effects is discovered in all periods of solar activity of 2003–2015: a considerable Ne decrease at a height of 190 km and a weaker effect at lower levels during the autumnal storms. During vernal storms, no significant Ne decrease as compared with quiet conditions was registered over the entire analyzed interval of 150−190 km.

Electron concentration variations in the F1-region during magnetic storms in a low solar activity period

Vertical sensing data obtained with the help of DPS-4 digisondes in Irkutsk and Yakutsk are used to analyze the response of the F1-layer to magnetic disturbances in May 2005. It is found that the electron concentration is decreased at heights of 150–200 km during magnetic storms, and the amplitude of this negative disturbance increases with height. This effect is more distinct in Yakutsk than Irkutsk. The main gas constituents of the thermosphere during disturbed periods are estimated.

Reaction of the ionospheric F1 region to disturbances in October and November 2003 (analysis from Irkutsk digisonde measurements)

We consider the ionospheric response at heights of 120–220 km to geomagnetic disturbances in October and November 2003, which caused a strongly pronounced decrease in the electron content in the noted height range. For this disturbance period, using a technique of the authors, midday variations of the relative content of atomic and molecular oxygen at a height of 120 km were estimated. This estimation was performed with the help of ionospheric measurements (by a digital ionosonde) conducted at the Institute of Solar-Terrestrial Physics of the Russian Academy of Sciences from 2003 to 2006. Comparison of these values with similar values from the mass spectrometer-incoherent scatter (MSIS)-86 model showed that our estimates during disturbance days were two times less. This study continues research into the field of using ionospheric measurements to estimate the relative gas composition of the thermosphere at heights below the maximum of the F2 layer.

Model description of electron concentration in the middle ionosphere

The results of comparison of model calculations of the electron concentration N at ionospheric heights of 120–200 km to the experimental data obtained at a series of geographic points at various levels of solar activity in various seasons of the year in quiet and disturbed conditions are presented and discussed. The calculations are performed using the semiempirical model (SEM) developed by the authors and giving in a general form the relation of N to characteristics of the thermospheric neutral gas and the solar activity index. The data presented in the paper show that the calculations with the SEM in question in the majority of cases agree well with experiment (the difference between them is 10–20%). The authors believe that the results of the comparative analysis presented in the paper manifest a high degree of universality of the discussed SEM.

Disturbances in the F1 ionospheric layer in April 2005

Manifestations of ionospheric disturbances at heights from 120 km to the height hm of the F2-layer maximum are analyzed. The geomagnetic disturbances on April 5, 12, and 13, 2005, are considered. These disturbances are characterized by a pronounced synchronous decrease in the electron concentration over the entire indicated height range. Using the method proposed by the authors, the noontime changes in the relative content of atomic and molecular oxygen at a height of 120 km are estimated. There are a distinct decrease in the ratio of atomic oxygen and molecular nitrogen concentrations and an increase in the ratio of oxygen molecule and atom concentrations.