Vibrational nitrogen concentration in the ionosphere and its dependence on season and solar cycle

A fully time-dependent mathematical model, SUPIM, of the Earth’s plasmasphere is used in this investigation. The model solves coupled time-dependent equations of continuity, momentum and energy balance for the O⁺, H⁺, He⁺, N⁺₂, O⁺₂, NO⁺ ions and electrons; in the present study, the geomagnetic field is represented by an axial-centred dipole. Calculation of vibrationally excited nitrogen molecules, which has been incorporated into the model, is presented here. The enhanced model is then used to investigate the behaviour of vibrationally excited nitrogen molecules with F10.7 and solar EUV flux, during summer, winter and equinox conditions. The presence of vibrational nitrogen causes a reduction in the electron content. The diurnal peak in electron content increases linearly up to a certain value of F10.7, and above this value increases at a lesser rate, in agreement with previous observations and modelling work. The value of F10.7 at which this change in gradient occurs is reduced by the presence of vibrational nitrogen. Vibrational nitrogen is most effective at F-region altitudes during summer daytime conditions when a reduction in the electron density is seen. A lesser effect is seen at equinox, and in winter the effect is negligible. The summer reduction in electron density due to vibrational nitrogen therefore reinforces the seasonal anomaly.     

Dissociative velocity rates of oxygen and ozone in the ionosphere

Summary On the basis of the exponential approximation for the distribution of the concentration of molecular oxygen and ozone in given parts of the ionosphere, expressions have been derived for the changes of the dissociative velocity rates of the oxygen components in the ionosphere. The numerical calculations made reveal negligible changes of these rates for heights above 100 km and sufficiently strong variations in the low ionosphere.     

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.     

The role of vibrationally excited oxygen and nitrogen in the D and E regions of the ionosphere

In this paper we present the results of a study of the effect of vibrationally excited oxygen, O^* ₂, and nitrogen, N^* ₂, on the electron density, N _e, and the electron temperature, T _e, in the D and E regions. The sources of O^* ₂ are O-atom recombination, the photodissociation of O₃, and the reaction of O₃ with O at D region altitudes. The first calculations of O^* ₂(j) number densities, N _j , are obtained by solving continuity equations for the models of harmonic and anharmonic oscillator energy levels, j=1-22. It is found that day time values of N _j are less than nighttime values. We also show that the photoionization of O^* ₂ (j\geq11) by L_<alpha>-radiation has no influence on the D region N _e . In the nighttime D region the photoionization O^* ₂ (j\geq11) by scattered L _<alpha>-radiation can be a new source of O⁺ ₂. We show that the N^* ₂ and O^* ₂ de-excitation effect on the electron temperature is small in the E region of the ionosphere and cannot explain experimentally observed higher electron temperatures.     

A numerical model of ion concentration profiles in the lower ionosphere

Summary A one-dimensional numerical model has been developed which gives the vertical profiles of the electron and ion concentrations at altitudes between 50 and 100 km. The model has been constructed for day-time ionization conditions in midlatitudes and yields a slightly abbreviated scheme of ion-molecular reactions. Neutral species concentrations have been compiled from various authors. Seasonal variations of temperature and the most important neutral species have been taken into account. For the purpose of this paper moderate solar fluxes in all required radiation bands have been considered.     

Day-time variations of the equivalent electron concentration in the non-sounded lower ionosphere

Summary Based on data on the lowest reflected frequencyf _min and on information on the lower and upper boundaries of the non-sounded lower ionosphere, an equivalent electron concentration for all concentrations below the correspondingf _min was determined. Day-time variations of the equivalent concentration are investigated, confirming that there is a cosine relation to the solar zenith angle. The power index of that relation has an outlined seasonal course with a maximum in April and October, while the absolute seasonal minimum is during the winter (the summer minimum is slightly outlined). The mean yearly values of the index are almost constant:n _N 0.5 for solaractivity,I ₁₅₀₀ to 115.10^–22 W Hz^–1 m². During higher activityn _N changes correspondingly toI ₁₅₀₀ according to relation (12). The variations ofn _N during high solar activity show that the altitude gradient and temperature gradient in the low ionosphere are becoming proportional toI ₁₅₀₀ when the solar x-ray radiation exceeds a certain level. The results obtained confirm the reliability of the method developed for employingf _min in aeronomic investigations.     

Modification of electron concentration in the ionosphere in the pump-wave plasma resonance region

We discuss the propagation of sounding radio waves in the inhomogeneous ionosphere, in the reflection area of which there are small-scale artificial magnetically-positioned irregularities. The propagation of radio waves in such an area, where the lateral dimensions of strongly elongated artificial irregularities are smaller than the wavelength, has a diffraction nature. It is shown that the calculation of diffraction parameters makes it possible to derive the amplitude of density irregularities and their relative area perpendicular to the magnetic field direction. Comparison of theoretical calculations with experimental studies on modification of the electron density altitude profile by heating of the ionosphere with midlatitude stand Sura showed that the relative area of the negative density perturbations can reach several percent.     

Approximation of the electron concentration measurements in the middle ionosphere at low solar activity

Geomagnetism and Aeronomy - The set of the electron concentration (N) measurements at heights of 120–200 km have been generalized using the regression equation from the semi-empirical model...     

Factors contributing to the oxygen concentration over the Qinghai-Tibetan Plateau and its contribution rate calculation

A decline in atmospheric oxygen concentration is projected in the 21st century given the background of global warming. The Qinghai-Tibetan Plateau is located at a high altitude, and thus, it faces a hypoxia challenge; however, knowledge of the factors contributing to its atmospheric oxygen concentration is still lacking. Here, we conducted joint observations of ecosystem oxygen production and carbon sinks and near-surface atmospheric oxygen concentrations on the Qinghai-Tibetan Plateau and meteo...     

The ionosphere and solar activity

Summary The correlation between monthly median critical frequencies and solar activity was determined for Washington, D.C. Results were compared with those from a similar study made for six Arctic stations. For noon data (E, F1 andF2 layers), a greater value off _c (at zero sunspot number) and a slightly greater slope were obtained for Washington than for the Arctic locations. The influence of increased solar activity on the behavior of the midnight ionosphere is discussed.     

The role of vibrationally excited nitrogen and oxygen in the ionosphere over Millstone Hill during 16-23 March, 1990

We present a comparison of the observed behavior of the F region ionosphere over Millstone Hill during the geomagnetically quiet and storm period on 16/23 March, 1990, with numerical model calculations from the time-dependent mathematical model of the Earths ionosphere and plasmasphere. The effects of vibrationally excited N₂(v) and O₂(v) on the electron density and temperature are studied using the N₂(v) and O₂(v) Boltzmann and non-Boltzmann distribution assumptions. The deviations from the Boltzmann distribution for the first five vibrational levels of N₂(v) and O₂(v) were calculated. The present study suggests that these deviations are not significant at vibrational levels v = 1 and 2, and the calculated distributions of N₂(v) and O₂(v) are highly non-Boltzmann at vibrational levels v > 2. The N₂(v) and O₂(v) non-Boltzmann distribution assumption leads to the decrease of the calculated daytime NmF2 up to a factor of 1.44 (maximum value) in comparison with the N₂(v) and O₂(v) Boltzmann distribution assumption. The resulting effects of N₂(v > 0) and O₂(v) > 0) on the NmF2 is the decrease of the calculated daytime NmF2 up to a factor of 2.8 (maximum value) for Boltzmann populations of N₂(v) and O₂(v) and up to a factor of 3.5 (maximum value) for non-Boltzmann populations of N₂(v) and O₂(v). This decrease in electron density results in the increase of the calculated daytime electron temperature up to about 1040/1410 K (maximum value) at the F2 peak altitude giving closer agreement between the measured and modeled electron temperatures. Both the daytime and nighttime densities are not reproduced by the model without N₂(v > 0) and O₂(v > 0), and inclusion of vibrationally excited N2 and O2 brings the model and data into better agreement. The effects of vibrationally excited O2 and N2 on the electron density and temperature are most pronounced during daytime.     

The effects of nitric oxide cooling and the photodissociation of molecular oxygen on the thermosphere/ionosphere system over the Argentine Islands

In the past the global, fully coupled, time-dependent mathematical model of the Earths thermo-sphere/ionosphere/plasmasphere (CTIP) has been unable to reproduce accurately observed values of the maximum plasma frequency, foF2, at extreme geophysical locations such as the Argentine Islands during the summer solstice where the ionosphere remains in sunlight throughout the day. This is probably because the seasonal dependence of thermospheric cooling by 5.3 m nitric oxide has been neglected and the photodissociation of O₂ and heating rate calculations have been over-simplified. Now we have included an up-to-date calculation of the solar EUV and UV thermospheric heating rate, coupled with a new calculation of a diurnally varying O₂ photodissociation rate, in the model. Seasonally dependent 5.3 m nitric oxide cooling is also included. With these important improvements, it is found that model values of foF2 are in substantially better agreement with observation. The height of the F2-peak is reduced throughout the day, but remains within acceptable limits of values derived from observation, except at around 0600 h LT. We also carry out two studies of the sensitivity of the upper atmosphere to changes in the magnitude of nitric oxide cooling and photodissociation rates. We find that hmF2 increases with increased heating, whilst foF2 falls. The converse is true for an increase in the cooling rate. Similarly increasing the photodissociation rate increases both hmF2 and foF2. These changes are explained in terms of changes in the neutral temperature, composition and neutral wind.     

The role of vibrationally excited nitrogen in the ionosphere

Theoretical and experimental aspects of the production, transformation, diffusion and loss of N₂ in the upper atmosphere are considered. The N₂-CO₂ near-resonant system in theD andE regions is taken into account. We describe our understanding of the methods necessary to find the vibrational populations of N₂ and CO₂ (asymmetric mode of CO₂). The calculations of the vibrational temperatures in theD, E, andF regions for the mid-latitude ionosphere and an aurora are presented. The connection between the excited species and the 4.26-m radiation intensities is considered. The models for the rate coefficient of the reaction of O⁺ with N₂ and the electron density decrease resulting from N₂ in the F region are discussed.     

Some features of nighttime enhancements in the electron concentration in the F2-layer maximum of the midlatitude ionosphere

Using the data of vertical sounding of the ionosphere in Alma-Ata (76°55′ E, 43°15′ N) conducted in 2002–2012, the reaction of parameters of the ionospheric F2 layer to various types of nighttime enhancements in the electron concentration in the maximum of the layer (NmF2) was studied, including the height of the maximum and bottom of the layer, its semithickness, and electron concentration at some fixed heights. Examples of recordings of a combination of the enhancements caused by different mechanisms are presented. The similarity of the reaction of the F2-layer parameters to the nighttime enhancements caused by the rise of the layer and plasma flux from the protonosphere and passage of large-scale travelling ionospheric disturbances was found. Difficulties in identifying these two events in the case of their equal duration are noted. The difference in the reaction of the F2-layer parameters to the enhancements caused by the rise of the layer and plasma fluxes from the protonosphere and occurrence of the summer midlatitude ionospheric anomaly is shown.     

The mobility spectrum and the ion concentration of large ions in air mixed with N2O gas

Summary Using the divided electrode condenser it was possible to detect the large ion groups formed when small amounts of N₂O gas were mixed with atmospheric air. Eight groups appeared with mobilities ranging from 12.50×10^–4 to 0.60×10^–4 cm/sec: volt/cm. When using the whole electrode condenser the results showed an increase in the total ion concentration of these large ions when small amounts of N₂O gas were mixed with air. The results obtained in this work confirm that N₂O gas acts as a nucleus for condensation which is changed into a large ion by appropriating an electrical charge.     

Some factors controlling the concentration of small ions near the ground

Summary During continuous measurements of the concentration of small ions near the ground made over the period of many months, several causes of variation were identified. During rain in large electric fields, ions of sign opposite to that of the potential gradient were produced in sufficiently large numbers to give rise to very high concentrations over short periods. Sometimes, after rain, a considerable increase in the density of small ions was found, suggesting a reduction in the numbers of nuclei and large ions. In moderate electric fields, a reduction was observed in the concentration of ions of sign opposite to that of the potential gradient in a way corresponding to the electrode effect. A simplified theory of the effect predicts results similar to those found in practice.The paper will appear elsewhere.     

Dynamics of lidar reflections of the Kamchatka upper atmosphere and its connection with phenomena in the ionosphere

The results of Rayleigh lidar sounding of the upper atmosphere over Kamchatka are analyzed in comparison with ionosonde data. A correlation between light backscattering signals at a wavelength of 532 nm and parameters determining the content of plasma in the nocturnal F2 layer of the ionosphere is found. Based on the performed analysis of lidar data and the geophysical situation, a hypothesis about the possible role of Rydberg atoms in the formation of lidar reflections at ionospheric heights is discussed.     

Plasma vortices in the ionosphere and atmosphere

Vortices observed in ionized clouds of thunderstorm fronts have the nature of plasma vortices. In this work, the need to account for the electrostatic instability of plasma in the origination, intensification, and decay of plasma vortices in the atmosphere is shown. Moisture condensation results in mass-energy transfer under the inhomogeneous spatial distribution of aerosols. If a phase volume of natural oscillations is transformed in the frequency-wave vector space in inhomogeneous plasma, the damping of plasma oscillations promotes an increase in the pressure gradients normal to the geomagnetic field. Excitation of the gradient instabilities is probable in atmospheric plasma formations.     

Variability of the ionosphere

Hourly foF2 data from over 100 ionosonde stations during 1967–89 are examined to quantify F-region ionospheric variability, and to assess to what degree the observed variability may be attributed to various sources, i.e., solar ionizing flux, meteorological influences, and changing solar wind conditions. Our findings are as follows. Under quiet geomagnetic conditions (K_p<1), the 1-σ (σ is the standard deviation) variability of N_max about the mean is approx. ±25–35% at ‘high frequencies’ (periods of a few hours to 1–2 days) and approx. ±15–20% at ‘low frequencies’ (periods approx. 2–30 days), at all latitudes. These values provide a reasonable average estimate of ionospheric variability mainly due to “meteorological influences” at these frequencies. Changes in N_max due to variations in solar photon flux, are, on the average, small in comparison at these frequencies. Under quiet conditions for high-frequency oscillations, N_max is most variable at anomaly peak latitudes. This may reflect the sensitivity of anomaly peak densities to day-to-day variations in F-region winds and electric fields driven by the E-region wind dynamo. Ionospheric variability increases with magnetic activity at all latitudes and for both low and high frequency ranges, and the slopes of all curves increase with latitude. Thus, the responsiveness of the ionosphere to increased magnetic activity increases as one progresses from lower to higher latitudes. For the 25% most disturbed conditions (K_p>4), the average 1-σ variability of N_max about the mean ranges from approx. ±35% (equator) to approx. ±45% (anomaly peak) to approx. ±55% (high-latitudes) for high frequencies, and from approx. ±25% (equator) to approx. ±45% (high-latitudes) at low frequencies. Some estimates are also provided on N_max variability connected with annual, semiannual and 11-year solar cycle variations.