A.A. Kuznetsov and V.G. Vlasov (Irkutsk State Technical University, Irkutsk)

The flight of the interplanetary stations Voyager have revealed that auroral regions of strong-magnetized planets are the sources of intensive radio emission. The maser cyclotron resonance of electromagnetic waves and electrons, moving along magnetic force lines, is accepted now as the most likely mechanism for generation of this radiation. The theory points out that inhomogeneities of magnetic field and plasma density also have influence on the generation process. The knowledge about radiation mechanism allows us to determine the parameters of the ionosphere in generation region using the remote measurements data. The process of generation of auroral kilometer radiation of Saturn, Uranus and Neptune have been studied. It is pointed out that the plasma density should depend on the height according to exponent law to obtain the observed energy spectrum of radiation. The limits of parameters of electron beams, which are able to cause the generation, have been found. The electron beams, as it turned out, are stabilized by inhomogeneities of plasma and magnetic field almost during all their track, with the exception of quite narrow altitude intervals (where inhomogeneities of plasma and magnetic field compensate each other). This leads to the discreteness of the radiation spectrum. So, we can estimate the scale of the plasma turbulence (about tens km) and the width of separated spectrum line (up to 1000 Hz).

E.Timofeev ( Polar Geophysical Institute, Murmansk, Russia)

M. Vallinkoski, J. Kangas, P. Pollari and E. Nielsen

Statistically average behavior of the flow angle diagram (FAD) of the 1-m auroral irregularities in the plane perpendicular to the geomagnetic field is analyzed from the combined STARE-EISCAT data selected from 19 individual case studies. Permanently existing upward directed ionization density gradient is found at the ionospheric altitudes of a radar echo layer (100-115 km). It is shown that: 1) on the contrast to theoretical predictions the FAD is asymmetric beginning from the smallest E-fields (0-10 mV/m). A character of the asymmetry is in at least qualitative agreement with the gradient-drift nature of the irregularities generated by the projection of the density gradient to the plane perpendicular to the GMF; 2) for 20-25 mV/m E-fields the FAD is more or less symmetrical relatively to the direction of the primary Hall current, so that minimum of the electron density fluctuations is observed about along the current but the maximum - in the directions deviated by ± 60 degrees; 3) for intermediate 10-15 mV/m E-fields a typical narrow angle cone erosions of the FAD are found those can be interpreted as an effect of the ion drag attributed to the neutral winds.

The found properties of the evolution of the FAD in course of the E-field strength increase are compared with results of the recent computer simulations of the non-linear flow angle scattering of the Farley-Buneman waves responsible for radar aurora. From the comparison it is concluded that such scattering processes seem to be real for E-fields larger that about 15 mV/m (above the FB-threshold).

On the nature of the polar cap flat-type Es-ionisation

A.V.Shirochkov and L.N.Makarova (Arctic and Antarctic Research Institute, Saint-Petersburg, 199397, Russia)

The unsolved problem of the polar cap flat-type Es-ionization nature is considered by means of revaluation of the previous studies of its main morphological features together with the results of the most recent investigations concerning the formation mechanisms of the thin auroral Es-layers. Such approach to the problem allowed the authors to make several reasonable conclusions on the issue. The most probable mechanism of the polar cap Es-layers formation is a vertical ion drift caused by the electric fields of magnetospheric origin. The gravity and tidal waves can be a decisive factor in the Es-layers formation at invariant latitudes greater than 83,5.

A.A. Bogolubov, V.A.Vlaskov ( Polar Geophysical Institute, 15 Halturina Street, Murmansk, Russia)

E.Turunen (Sodankyla Geophysical Observatory, Sodankyla, Finland)

The partial reflection equipment of the Polar Geophysical Institute (PGI-PRE radar) was in operation during summer 1994 (ECHO-94 campaign). During PMSE events, the PGI-PRE radar occasionally detected thin layers (1-2 km) of PMSE kind. The main features of the observed layers are summarized as follows:

- the electron densities calculated by the standard method (from ratio of amplitudes of ordinary and extraordinary components) have maximum at the heights of these layers;

- the altitude of maximum electron density descends approximately 1 km per hour (0.3 m/s), the descent of the layer with time is a common feature of PSME;

- sometimes two layers are present, with similar features at different heights;

- the amplitude of scattered signals has a very strong gradient at the heights of these layers;

- the amplitude variations at the adjacent range gates, separated by 1 km, have more lower level of correlation then at the heights upper and below;

- the evolution of the level of correlation has a periodical (13-15min) structure;

- in the patches, where the level of correlation is below 0.5, the power spectrum of amplitude fluctuations becomes more sloping (by 1);

- the coefficient of turbulence diffusion is high during all period (large than 2´ 10² m²/s )

- the coefficient of turbulence diffusion falls after beginning PMSE;

- these layers are observed between altitudes 80-90 km, with preferred range 84-87 km,this similar to PMSE observations by EISCAT and MST radars (CUPRY, SOUSY);

All these features of partial reflection signals could be regarded as evidence for events of the PMSE kind. In this report we represent only experimental results and do not consider the mechanisms of this layers appearing. We conclude that partial reflection equipment may be used for investigations of features related to PMSE

V.G.Vlasov and G.O.Zhizhko (Irkutsk State Technical University, Irkutsk)

An important link in a chain of energy transfer from the Sun to the Earth is a collision-free transmission channel of the energy from auroral electron beams causing the aurora to the ionosphere. We are dealing with registration of electron temperatures and their gradients higher than usual by several hundred (!) percent and a high level of the high-frequency electrostatic waves in discrete auroral arcs at the F2-region heights; as well as decametric radiation with a rapid decrease in frequency, leaving from that region. There is reason to believe that the set of the above-described facts is reflection of such a phenomenon as an auroral thermal wave, caused by collective dissipation of energy of the auroral electron beams in the inhomogeneous ionospheric plasma. The development of a computer model for the auroral thermal wave was continued in this paper. The system of hydrodynamical equations involving the collective heating source was solved in view of the inertia member. As the computations have shown, taking account of the inertia of ions brings about appreciable slowing down of lift rate of the auroral thermal wave. The calculated rate of decrease of the radiation frequency coincided with the measured one, with a steeper density profile of ionospheric plasma above the maximum of the F2-region, while electron temperature did not exceed 9000 K. A conclusion is drawn that from the velocity profile of the radiation frequency drift it is possible quite definitly to deduce the density profile in the F2-region.

A.A.Namgaladze, A.N.Namgaladze, M.A.Volkov (Polar Geophysical Institute, Murmansk)

The thermospheric and ionospheric effects of the field-aligned current variations at the cusp corresponding to the IMF BY variation from 0 to about -9 nT and back to 0 during an hour have been modelled by the use of the global numerical time-dependent three-dimensional model of the Earth's upper atmosphere. The responses of the electric field potential, electron concentration, ion, electron and neutral temperature, meridional and zonal thermospheric wind velocity to the variations of the field-aligned current density at the cusp have been calculated by solving the corresponding continuity, momentum and heat balance equations.

It has been found that the ionospheric disturbances have appreciable magnitudes at the geomagnetic latitudes 70o-85o. Whereas the electron concentration and temperature disturbances are caused mainly by the ionization and heating processes due to the precipitation, the ion temperature disturbances are influenced strongly by Joule heating of the ion gas due to the electric field disturbances caused by the field-aligned current variations at the cusp. The last strongly influence the zonal and meridional wind disturbances as well via the ion dragging at the cusp region.

The most significant changes are in the zonal thermospheric wind variations due to the ion dragging. The eastward wind disturbances of about 140-200 m/s appear at the geomagnetic latitudes 75o-80o in the midday sector and of about 200-300 m/s in the afternoon sector. The meridional wind disturbances are of about 90 m/s at the geomagnetic latitudes 80o-85o in the midday sector and of about 180 m/s in the afternoon sector . They are also caused by the ion dragging which acts in an opposite direction in comparison with the pressure gradient forcing in the midday sector.

V.A.Ivanov, N.V.Ryabova, V.V.Shumaev (Mari State Technical University, Yoshkar-Ola)

V.P.Uryadov (Radiophysical Research Institute, Nizhny Novgorod)

The wideband oblique sounding of ionosphere on long-distance paths allows to solve both problems connected with prognostic aspects of HF propagation in interest of communication reliability increase and with opportinuty to diagnose of ionospheric disturbances of the global scale. The number of processes caused by different sources of disturbances divided over altitude and along of path are better diagnosed by oblique sounding method as compared with vertical sounding. So, experimental data indicate to the possibility of the fluctuation waveguide formation in the vicinity of F-layer maximum during ionospheric disturbances. For diagnostic of these disturbances it is conveniently to use in the capacity of the probing wave the Pedersen mode (the high-angle ray) which slides along of layer maximum and its highly sensitive to different kind of disturbances.

In report the results of researches of Pedersen mode propagation in quiet and disturbed ionosphere at mid-latitude (spreading to subpolar region) Khabarovsk-Nizhny Novgorod, Khabarovsk-Yoshkar-Ola paths and transpolar Khabarovsk-Murmansk path are presented. For sounding of the ionosphere a chirp sounder in frequency range 3...29 MHz with sweep frequency 350 kHz/s was used. Measurements testify about an essential influence of the irregular structure to Pedersen mode characteristics. It is established that during magnetic/ionospheric disturbances the Pedersen mode frequence range D f_p exceeds in 1.5-3 times its value in a quiet days. The boundary frequency f_b < f_c (where f_c is the connection frequency of Pedersen mode with low-angle ray) dividing the frequency range of Pedersen mode propagation to the parts with different mechanisms of field signal forming in disturbed ionosphere is discovered. It is shown that at frequencies f < f_b (when a considerable part of path the wave slides along of layer) the fluctuation waveguide is formed and it takes place the guiding of Pedersen mode at the expence of interference multiple scattered waves on electron density fluctuation. At frequencies f_b < f < f_c (when distance spreading by wave along of layer is decreased) the influence of irregularities on Pedersen mode propagation leads up to the additional attenuation by means of scattering and it prevails the sliding (anti-ducting) mechanism of propagation.

The horizontal speed of ionospheric disturbances propagation at the altitudes of F-layer on time of shift of cross-correlation function for D f_p and K_p index at Khabarovsk-Murmansk and Khabarovsk-Yoshkar-Ola paths is determined. It makes up value 60-100 m/s.

This work was supported by RFFR under grant 95-02-03582-a.

L.M.Kagan (Radiophysical Research Institute, Nizhny Novgorod)

Analyzing morfology of natural and heater-induced irregularities in ionospheric plasma we have revealed a strong tendecy for their preferable occurrence inside large-scale formations (patches). It is agreed that small-scale irregularities should be spacially coincident with the dominant irregularity-source region since they dissipated in seconds through cross-field diffusion and hence could exist only in the regions where strong irregularity growth counteracted rapid decay. In the gradient-drift theory such source of irregularity growth is represented by large-scale plasma density gradients. In this work as an alternative source of small-scale turbulence we consider intense local field-aligned currents (electric fields), generated due to Lorentz forces inside regions of a large-scale change of plasma pressure under some specific conditions, i.e. increased auroral activity or heater modified ionosphere.

Appearance of the harmonics in the spectrum of artificial emissions generated during heating experiments has been reported earlier. Usually it relates with square modulation of HF powerful wave and distortion of this time dependence due to characteristic time of electron heating/cooling. In EISCAT-HEATING experiment on November 1993 sine-wave modulation regime has been used. Observations show the clear harmonic structure in artificial emissions in this case too. We are discussing a generation of harmonics of a modulation frequency due to non-linear dependence of value of the ionosphere conductivity disturbance from Effective Radiated Power (ERP). A numerical model is used for calculations of the spectrum of the integral conductivity disturbance variations as a function of electron density profile and ERP. For the modulation frequency in the range of 1 - 100 Hz characteristic time of the electron heating/cooling was neglected and intensity ratio of the second harmonic and the third one to those of the fundamental frequency reach up 0.4 and 0.15 respectively. For the modulation frequency 1375 Hz time integration of the electron energy balance equation was used. Characteristic time constants of the electron heating/cooling being different at the different altitudes make more complicated the behavior of the intensity ratio and phase shift of the harmonics of the integral conductivity disturbance variations. The values of the harmonic amplitude ratio in this case decrease to 0.25 and 0.1.

A.B.Pashin and E.G.Belova (Polar Geophysical Institute, Apatity)

The generation of artificial emissions via ionosphere electron heating by amplitude modulated HF radio wave is essential part of the heating experiments. One could find an extensive discussion of the problem of the generation efficiency in the papers on this topic. Generally believed that most effective modulation of the ionospheric conductivity takes place in the region where strong Hall currents flow. Numerical calculations show, however, that two factors producing the ionospheric conductivity variations, namely, disturbances of the electron-neutral collisions frequency and temperature dependent recombination are essential at different altitudes. The first term is significant in the altitude range 80 - 90 km. The second one strongly increases electron density in the region where it's initial value and electron temperature disturbances are large enough. Most effective heating in this case is at the height where Hall current maximum is located. As a numerical modelling is a case study we try to give additional arguments for such behavior of the conductivity disturbances. Consideration of normalized values of the ionospheric conductivity disturbances proves a general rule: for short period modulation < 1 s a rather developed D-region is needed for effective generation of the artificial emissions; high-altitude heating should give a great amplitude of the magnetic pulsations for the modulation period more than 100 s. The discrepancies with the previous theoretical works are discussed.

E.Belova, E.Pchelkina, W.Lyatsky and A.Pashin (Polar Geophysical Institute, Apatity, Russia.)

The problem of magnetic disturbance polarization on the ground for a dipole source in the inhomogeneous ionosphere is solved for two kinds of an horizontal inhomogeneity. There are two cases: a case of large-scale strip when the ionosphere is separated on two parts with different conductivities and a case of meso-scale strip when in the ionosphere a strip with enhanced conductivity is situated. The latter one may be associated with an auroral arc. By using the ''method of reflection'' an electric potential of the polarization field and a current function of the equivalent ionospheric currents are found for these cases. The distributions of the magnetic disturbance polarization ellipses on the ground have been obtained. It is found that under the certain ionospheric conditions the inhomogeneity can get a significant (up to 40%) contribution into the magnetic disturbance amplitude on the ground and change essensially its'polalization. For the case of large strip width the contribution of the inhomogeneity into magnetic variations on the ground is symmetrical relatively to the strip boundary. This boundary separates the regions with different rotation sense of the magnetic disturbance vector. For the case of meso-scale strip it is found that on the ground the magnetic polarization ellipse distribution becomes asymmetrical and complicated. The line separating the regions with different rotation sense becomes curved.

E.Belova, E.Pchelkina, W.Lyatsky and A.Pashin (Polar Geophysical Institute, Apatity, Russia.)

The dependance of amplitude and polarization of the magnetic disturbances on the ground generated by a dipole source with circular polarization which is situated near to the ionospheric inhomogeneity with enhanced conductivity, on its conductivity value was studied in this paper. Two cases of inhomogeneity was taken into consideration: large-scale (wide) strip and meso-scale (narrow) strip. For wide strip the magnetic variations on the ground due to the inhomogeneity are symmetrical relatively to the strip border and to the line being perpendicular to this border and crossing the projection of source point on the ground. The polarization characteristics at any point don't depend on inhomogeneity conductivity value. For narrow strip the polarization ellipses distribution on the ground becomes asymmetrical, complicated and varies for different values of strip conductivity value. For sufficiently large values the major half-axis of polarization ellipses is orientated approximately along direction being perpendicular to the strip border. As an application the polarization on the ground for the case of artificial ionospheric heating near a strip of enhanced conductivity under the conditions of experiment on October 26, 1984 was calculated and compares with experimental results.

M.A.Volkov, O.V.Martynenko, A.A.Namgaladze (Polar Geophysical Institute, Murmansk)

The global numerical model of the Earth's upper atmosphere has been supplemented with a new magnetospheric block containing the magneto-hydrodynamic continuity, momentum and energy balance equations for the magnetospheric plasma. These equations have been added to the modelling equation system for the ion, electron and neutral gases of the ionosphere, protonosphere and thermosphere including the equation for the electric field potential to be solved jointly.

The geomagnetic field is considered as a dipole one at latitudes equatorward from the polar cap boundary and having the field lines opened inside the polar cap. The magnetosphere is empty at closed field lines at the initial time moment when the potential drop across the polar cap appears suddenly together with the plasma source at the polar cap boundary. The plasma sheet and zone 2 field-aligned current formation has been calculated as well as the corresponding ionospheric and thermospheric effects for moderate disturbed conditions.

A.S.Kirillov (Polar Geophysical Institute, Apatity)

A scaled approach according to perturbation theory of first order was applied to obtain the rate coefficients of vibrational energy transfers in molecular adiabatic collisions. The factors on molecular attraction, oscillator frequency change and quasiclassical motion were taken into account in analysis of experimental data on VT-relaxation times in N₂ and O₂. The rate coefficients for VV and VV'-processes in collisions of main atmospheric components obtained according to the approach are compared with the calculations based on Schrodinger and Feynman methods and available experimental data. It is shown that there is good agreement of our calculations with experimental estimations of the rate coefficients for the collisions N₂-N₂, O₂-O₂ and N₂-O₂.

Atomic oxygen is a very importent component of Earth's upper atmosphere. Excited atoms of oxygen are sources of a number of auroral emissions in ultraviolet (130.4 nm and 135.6 nm), visible (557.7 nm and 630.0 nm) and near infrared (732.0 nm and 844.6 nm) wavelength regions. Atomic oxygen and its ion in both grate and excited states are very importent chemical components determining the main chemical cycles in the lower polar ionosphere and thermosphere. The scarce in situ measurements of the atomic oxygen concentration in the auroral thermosphere showed its significant variations in dependence on geophysical conditions and demonstrated a contradiction with the theoretical models. These reasons make very important the development of methods for remote sensing of the atomic oxygen concentration. This work presents the method to derive the concentration of the auroral atomic oxygen from the ratio of the volume emission rates of the two bands of molecular nitrogen. One of these emissions is the band of Vegard-Kaplan system arisen from state of N₂. Another emission is one of molecular nitrogen bands excited predominantly by electron impact, for examples the Second Positive or the First Negative systems. Because of the state is metastable with lifetime of about 1.5 sec this suggests that the state is exposed to sufficient quenching by main atmospheric gases. The aironomic and the laboratory measurements demonstrated that the main quencher of the A3 states in auroral conditions is the atomic oxygen. Therefor, the atomic oxygen concentration may be derived from simultaneous measurements of the altitude profiles of the volume emission rates of the two auroral emissions. Our algorithm was tested in results of some rocket experiments. The comparison of the deduced and given by MSIS model atomic oxygen concentrations demonstrates that the two values are equal at the altitudes higher than 160 km and differ at the lower altitudes.

A.S. Kirillov and G.A. Aladjev (Polar Geophysical Institute, Apatity)

The experimental data of rocket measurements of 5.3-mcm intensities [Rawlins et al.,1981] are analyzed according to one-dimensional non-steady model of polar upper atmosphere. The theoretic-informational approach based on the supposition of entropy maximum for product state distribution is used to determine nitric oxide vibrational excitation in the reaction N(²D)+O₂->NO(v)+O. It is shown that the agreement of calculated NO(v) distributions with experimental data can be obtained in the case of surprisal parameter l~-4 for O(1D)-branch, many-quantum transfers in the vibrational relaxation NO(v)+O and enhanced atomic oxygen concentrations in lower thermosphere. Also the calculated energy efficiency of 5.3-mcm emission agrees the experimental estimation.