N.Gazey (EISCAT group, Rutherford Appleton Laboratory, Chilton, Oxfordshire, OX11 0QX, UK);

P.Smith (Space Physics Group, University of Sussex, Brighton, E Sussex BN1 9QH UK);

H.Koskinen, K.Kauristie (Finnish Meteorological Institute, FIN-00101, Helsinki, Finland).

J.Manninen, T.Turunen (Geophysical Observatory, FIN-99600 Sodankyla, Finland);

The observations of the temporal variations of azimuthal component of ionospheric electric field in the vicinity of an auroral arc before substorm onsets on January 18 and February 18, 1993 are presented. The electric field measurements were supplied by tri-static UHF facility (Tromso, Sodankyla and Kiruna), the auroras were registered by TV cameras in Tromso and Kilpisjarvi and all-sky cameras in Kevo, Muonio and Loparskaya. There were two short-lived arc activations few minutes before the substorm onsets (pseudobreakups). The examined arcs were oriented almost along the geographic meridian. It was found that the both activations were accompanied by the decrease of the azimuthal component of the ionospheric electric field (E). A strong decrease of E was detected also few minutes later and connected evidently with the strong enhancement of auroras to the South from the EISCAT zenith as well as with negative deviation of the H-component of the local magnetic field and Pi2 burst in Lovozero and Sodankyla (actual breakup). We think that the observed response of the ionospheric electric field on the auroral arc brightening may be interpreted as a result of "shorting-out" of the tangential component of the field by a strip of the enhanced conductivity in the ionosphere. The possible consequences of the shorting-out of the large-scale convective electric field by the auroral arc are discussed.

More twenty-years experience of interpretation of high-latitude oblique reflections from meridional chain of ionozondes (Yakutsk-Zhigansk-Tixie Bay) is summarized. In different daily periods, at ionogrammes are exist the additional oblique reflection tracks from ionospheric structures, which typical for this times (polar edge of main ionospheric trough, dayside cusp/cleft, auroras and SAR-arc, polarization jet et al.). In this paper the methodics of definition of structure kind on parameters of oblique tracks at ionogrammes is proposed. It is shown the possibility of systematic monitoring of global ionospheric structures by ground-based data.

M.C.Kelley (School of Electric Engineering, Cornell University, Ithaca, NY, USA)

R.A.Doe (Geoscience and Engineering Center, SRI International, Menlo Park, CA, USA)

We present a consistent physical picture of auroral activity involving coupling between the magnetosphere and the ionosphere via electrostatic and wave- or turbulence-induced field-aligned currents. Both can be generated by the region surrounding the electron acceleration zone. Applying our model to the observations gathered with incoherent scatter radar and optics in Greenland (66.99N, 50.95W) allows us to separate electron heating due to structured fields (with a pronounced maximum in the F layer), static field-aligned currents (with the electron temperature smoothly increasing with altitude from the F layer up to the magnetosphere), and electron impact in the E region. In turn, the temperature observations give us information on the Alfven wave impinging on the auroral F layer and/or the turbulent electrostatic fields which map to the ionosphere.

S.Kirkwood (Swedish Institute of Space Physics, S-981 28, Kiruna, Sweden)

Measurements made by the EISCAT radar in the night-time ionosphere during the polar cap absorption event of October 1989 produced higher electron densities than those calculated from the detailed ion chemistry model. In order to find out possible causes of this discrepancy the electron production and loss rates for various processes have been calculated in the height range 50 through 90 km for the conditions approximating the conditions of measurements. The analysis of the calculated rates has shown that a a onsiderable difference between the real and model number densities of atomic oxygen and ozone can be one of the causes of the discrepancy between the theoretical and measured height profiles of electron density.

In the present work the effects of atomic oxygen and ozone variations on the electron density Ne in the night-time winter lower ionosphere have been studied. It was found that the increase of ozone number density causes the decrease of Ne at the heights 66 through 76 km. The increase of atomic oxygen produces the increase of Ne only at the heights between 74-84 km with a maximum effect at 80 km. The higher measured electron density values than the calculated ones at the heights above 84 km can not be explained, however, by the difference in the atomic oxygen number density. Additional ionization, produced by energetic electrons providing charge neutrality of the precipitating protons and not included in the model, can be a cause of this disagreement.

The dual-frequency L-band signals of GPS and GLONASS satellites are very effective instruments for making measurements of ionospheric TEC in world-wide scale. GPS satellites have the inclination about 55 degrees and GLONASS do 64, so the last is more useful to monitore the ionosphere on the high latitudes. The joint use of its is extremely opportuned to monitore the ionosphere in multiple directions simultaneously and on a large scale with high space resolution. An excellent resource of GPS data is International GPS Servise for Geodynamics (IGS). The IGS is based on about 4O globally distributed permanent GPS stations. A few of them are planed to place in Russia.

In the report we present the some results of using of GPS for the studies the middle-latitudenal and subauroral ionosphere over a region 2O E. The observations were provided with the dual-frequency GPS receivers on the stations of IGS network.

The relations of rate coefficients k(v)/k(v=0) for the reaction of collisional deactivation of metastable nitrogen N₂(A3,v) on atomic oxygen have been calculated according to Landau-Zener approximation. The calculation shows the increase of the relations with the rise of v for ³P and ¹D -channels and sharp decrease below unity for v>0 in the case of ¹S -channel. The dependence of the rate coefficient relations for the three channels on the change of the equilibrium distance between N₂ nuclei in the transfer A3,v -> X1,v' is shown. The influence of every reaction channels on vibrational kinetics of molecular nitrogen in auroral atmosphere is investigated. It is shown that vibrational excitation of N₂ is invariant in the cases of the production of atomic oxygen in ³P or ¹D states and significantly differs in the case of ¹S production.

We consider the increase of nitric oxide concentration in thin layers of enhanced luminosity intensities during artificial and natural electron precipitation in upper atmosphere. Collective relaxation of electron beam, strong Langmuir turbulence, the collapse of formated caverns and Landau damping are considered as the reason of ionospheric electron heating. It is shown that the heating of ambient ionospheric electrons and the production of suprathermal tails in electron energy distribution lead to the vibrational excitation of molecular atmospheric components N₂ and O₂. The role of long and short lived states of negative ions N₂^- and O₂^- in the excitation is investigated. The calculations of nitric oxide concentration in the thin layers have been made taking into account the reactions N₂(v>11)+O->NO+O (1) and N(⁴S)+O₂(v)->NO+O (2). Special attention is paid to the study of the influence of the efficiency of O₂ vibrational excitation in the decrease of activation barrier of reaction (2) and increase of nitric oxide production.

A.V.Volosevich (State Pedagogical University, Mogilev, Belarus)

The estimation of the frequency of electron-ion collisions is made on the basis of the kinetic equation. In an undisturbed ionosphere this frequency is more less than the frequency of electron collisions with neutral corpuscles. However, it depends linearly from an electron density, so in the auroral conditions it may exceed the electron-neutral collision frequency in E-region, and caused by it the short radiowave absorption becomes comparable with the absorption caused by electron-neutral collisions. This thesis is illustrated by numerical calculations with the usage of EISCAT data.

S.Kirkwood

The advanced program for the quantitative estimation of the flux-energy spectra of the auroral electrons on the base of electron density profiles is proposed. The electron density is transformed into the ionisation rate with the assumption of the quasistationarity using a recombination coefficient model. 10-30 electron energies are set in conformity with the range of the profile heights, and the profiles of the ionisation rates per unit incident flux are calculated for each energy on well-known Rees' formula. The determination of electron fluxes is implemented not by least-squares fitting, but by simplex-method. This method suppose that all unknowns are positive, and a linear form from the unknowns must be minimal for the solution. The minimizing form in the program is taken as a difference between the total ionisation rate and the sum of the ionisation rates generated by the searched fluxes. The quality of the solution can be appraised on the portion of unused ionisation rate (or of the ionisation). It varies from 1% to 50% depending on quality of the ionisation profile, feasibility of stationary condition, accuracy of the recombination coefficient model, etc. The spectra received by such simple variant of the simplex method are not monotonous very often. The additional condition that a flux for an energy must not exceed a share of the flux for the preceding energy, can be introduced into the system of equations easily. It does not enlarge the ionisation rate residuals too much, but permit to get more reliable shape of a spectrum. The received by simplex-method spectra are compared with the spectra given by the least-square method. The main advantages of simplex spectra are a) the absence of negative fluxes, and b) the satisfactory values for low energies where the least-square method is not available.

It has been proposed by Lyons (1995) that the expansion phase of substorms results from a reduction in the large-scale electric field imparted to the magnetosphere from the solar wind, following a growth phase due to an enhancement in this electric field. To test this new theory for magnetospheric substorms we performed numerical calculations of the magnetosphere-ionosphere response to a reduction in the large-scale electric field using the global numerical model of the Earth's upper atmosphere (Namgaladze et al., 1995, 1996). The new magnetospheric block for this model (Volkov et al.,1996) containing the magnetohydrodynamic continuity, momentum and energy balance equations for the magnetospheric plasma has been used in the calculations. The electric field potential drop across the polar cap was reduced suddenly from 70 to 10 kV after keeping it constant at 70 kV. The results of the calculations reveal some effects in the plasma sheet behaviour similar to those predicted by Lyons' theory but their magnitudes are small. Further investigations are needful to solve this problem.

Lyons L.R., A new theory for magnetospheric substorms, J.Geophys.Res., 100, No.A10, 19,069-19,081, 1995.

Namgaladze A.A., O.V.Martynenko, A.N.Namgaladze, Global model of the upper atmosphere with variable latitudinal steps of numerical integration, IUGG XXI General Assembly, Boulder, 1995, Abstracts, GAB41F-6, B150, 1995, and (in Russian) Geomagn.Aeronomy, 36, No.2, 89-95, 1996.

Volkov M.A., O.V.Martynenko, and A.A.Namgaladze, MHD-magnetospheric block for the global numerical model of the Earth's upper atmosphere // Physics of Auroral Phenomena. Proceedings of XIX Apatity Seminar, 101-103, 1996.

The seasonal effects in the thermosphere and ionosphere responses to the precipitating electron flux and field-aligned current variations, of the order of an hour in duration, in the summer and winter cusp regions have been investigated for the events of 28-29 January 1992 using the global numerical model of the Earth's upper atmosphere (Namgaladze et al., 1995, 1996). Input data for the precipitating fluxes and field-aligned currents have been taken from the patterns derived by Lu et al. (1995) by combining data obtained from the satellite, radar and ground magnetometer observations for these events when By-component of the IMF was negative. Calculated patterns of the ionospheric convection and thermospheric circulation for both Northern (winter) and Southern (summer) Hemispheres have been compared with observations (Lu et al., 1995; Thayer et al., 1987) and a good agreement with them has been found. It has been established that both ionospheric and thermospheric disturbances are more intensive in the winter cusp region due to the lower conductivity of the winter polar ionosphere and correspondingly larger electric field variations leading to the larger Joule heating effects in the ion and neutral gas temperature, ion drag effects in the thermospheric winds and ion drift effects in the F2-region electron concentration.

Namgaladze A.A., O.V.Martynenko, A.N.Namgaladze, Global model of the upper atmosphere with variable latitudinal steps of numerical integration, IUGG XXI General Assembly, Boulder, 1995, Abstracts, GAB41F-6, B150, 1995, and (in Russian) Geomagn.Aeronomy, 36, No.2, 89-95, 1996.

Lu G., L.R.Lyons, et al., Characteristics of ionospheric convection and field-aligned current in the dayside cusp region, J.Geophys.Res.,100, No.A7, 11,845-11,861, 1995.

Thayer J.P., T.L.Killeen, et al., Thermospheric neutral wind signatures dependent on the east-west component of the interplanetary magnetic field for Northern and Southern Hemispheres as measured from Dynamics Explorer-2, Ann.Geophys., 5A, (6), 363-368, 1987.

The auroral green line, which source is the metastable ¹S state of atomic oxygen, is one of the strongest optical emission features of the aurora. Now in sufficient degree the certain opinion has been developed concerning main channels of the ¹S term excitation. These are the excitation of the oxygen atoms by the auroral electrons, the dissociative recombination of an ion of the oxygen molecule, and the chemical reaction of the oxygen atom with the N₂ molecule exited in the A³ state. However, no the satisfactory quantitative model of an excitation of this emission in aurora has been developed yet. To create the auroral green line model following is required: to solve the problem of auroral electron transport in the Earth's atmosphere, to develop a model describing the ion composition of the disturbed auroral ionosphere and model of excitation of the N₂(A³) term in aurora. The main singularity of our model is the non-standard approach to calculate the excitation of atmospheric gases by auroral electron impact. This approach is based on solution of the auroral electron transport problem by the Monte-Carlo method. The accurate solution of a transport problem was used for construction of simple functional dependence connecting the excitation rates of the atmosphere species at an arbitrary height with an arbitrary auroral electron flux. Our researches have shown that non of the above channels is preferable in excitation of the ¹S term. Their relative contribution to the integral intensity of radiation of a green line depends on both the spectra of auroral electrons, and the duration of their precipitation. Our model has been tasted on the results of the complex rocket satellite experiment. In this experiment a spectrum of auroral electrons, concentrations of the ionized and neutral components of the atmosphere, intensities of the lines of 557.7 nm, 630.0 nm O, the bands 391.4 nm, 337.1 nm, 320.0 nm N₂ were measured simultaneously. The best agreement between the theoretical calculations and the results of measurements is demonstrated.