The numerical model of the thermosphere, ionosphere and electric field was used by investigations of the geomagnetical activity effects in the thermospheric tides. The level of the geomagnetical activity was determined by the cross-polar cup potential (CCP). The modelling parameters were calculated by CCP equels 30,60,90kv and minimum solar activity at equinox. The global distributions of the diurnal and semidiurnal amplitudes and phases in the horizontal wind components and mean wind were calculated. The contributions of the solar migrating and nonmigrating tides, zonal uniformity mean wind and zonal harmonics of the mean wind were determined. The results of the calculations are summarized as follows: 1. The growth of the CCP led to increasing of the zonal nonuniformities in the mean wind and tides structure. The disturbations of the mean wind connected with increasing of the joule heating in the thermosphere. The zonal uniformity wind become more westward with CCP increasing. The first harmonic of the mean wind increases in the high latitudes too. 2.The amplitudes and phases of the tides were disturbed by ion drag process with increasing CCP.The growth of geomagnetical activity influences on the generation of the nonmigrating tides that define the zonal nonuniformity tides structure. The diurnal nonmigrating tides are generated in the high latitudes and they do not penetrate to middle and low latitudes. The influence of the nonmigrating diurnal tides is very significant in the lower thermosphere. The solar migrating diurnal tide dominate in the upper thermosphere. The character of the semidiurnal tide disturbances depended on the direction of the movement transference in the ion-neutral interactions. This process led to decreasing some nonmigrating tides and increasing for others in the lower thermosphere. The semidiurnal nonmigrating tide increases in the upper thermosphere. 3.The modelling results have the resonable agreement with the observations that were carried in the different latitudinal and longitudinal thermospheric regions by different level of the geomagnetic activity.

J.V. Bogdanova, V.S. Semenov (Physical Institute, St.Petersburg State University, St.Petersburg 198904, Russia)

M.D. Buchan, R.P. Rijnbeek (Space Scientific Center, University of Sussex, Brighton BN1 9QH, UK)

The goal of presented work is to study active phase of magnetospheric substorm in magnetotail plasma sheet and to deduce some characteristics of reconnection pulse from auroral arc motion as well as from electric field data and plasma velocity data in the ionosphere.

The model is based on the hypothesis about magnetic reconnection in the magnetotail. Model assumes that the main processes responsible for the substorm development take place in the neighbourhood of the near-Earth neutral line in the current sheet. Magnetic reconnection starts with abrupt drop of plasma conductivity in a local region (diffusion region) of the magnetotail current sheet. This is accompanied by appearance of a strong pulse of electric field accelerating the electrons, which precipitate into the ionosphere and produce the auroral breakup. The speed of poleward arc motion turns out to be proportional to the electric field in the diffusion region. Hence, although it is very difficult to measure directly the reconnection electric field in the magnetosphere from satellites, the speed of poleward arc motion in the ionosphere can readily be used to calculate the reconnection electric field. Plasma conductivity during breakup in the vicinity of current disruption region can then be calculated using the time-dependent Petschek-like magnetic reconnection model and Tsyganenko T89 model for estimation of necessary magnetospheric parameters.

Investigation was based on ionospheric optical and radar data, which recorded at the EISCAT facility near Tromso, in northern Norway. The optical video data have been obtained with the help of all-sky camera, plasma velocity and electric field in the ionosphere were measured with the help of EISCAT radar, the magnetic field behaviour in the ionosphere was taken from Scandinavia magnetometer data.

Using these data, we show that breakup starts with the abrupt drop of plasma conductivity to the value of order of 10⁵ CGS which is 10 orders less than its classical Spitzer value and which is very near to Bohm diffusion value. Magnetospheric electric field in the diffusion region turns out to be 1-3 mV/m, effective potential difference across the reconnection line is 40-100 kV, reconnected magnetic flux is 10¹⁵-10¹⁶ Mx, released magnetic energy is 10¹⁹-10²⁰ erg with pulse reconnection duration of the order of 1-3 minutes.

A.A. Namgaladze (Murmansk State Technical University),

R.Yu. Yurik (Polar Geophysical Institute, Murmansk),

M. Foerster (GeoForschungsZentrum, Potsdam, Germany)

Negative ionospheric storms (electron density depletions near the F2-maximum) are explained practically unanimously as consequence of the decrease of the concentration ratio O/N2 during magnetic storms resulting in an ion loss rate enhancement. The situation with positive ionospheric storms is more complicated. The positive phase of F2-region ionospheric storm at middle and low latitudes may be caused by winds which are generated during magnetic storms and move the ionospheric plasma along the geomagnetic feld lines upwards where the ion loss rates are slower and then equatorwards. However, some authors believe that the main cause of the positive phase is the neutral composition changes in the low-latitude thermosphere, namely the decrease of the concentration ratio [N2]/[O]. To test these hypotheses, we performed numerical simulations for the magnetic storm of 24-27 January 1974 to obtain the global pattern of the thermospheric and ionospheric effects of this magnetic storm.

The global self-consistent numerical model of the thermosphere-ionosphere-magnitosphere system has been used in this investigation. The model calculates thermospheric, ionospheric and magnetospheric plasma sheet parameters as well as electric fields both of the magnetospheric and thermospheric dynamo origin. The storm input has been controlled by the electric potential drop across the polar cap which has been derived from the variation of the planetary index of magnetic activity Kp. The precipitation parameters have been taken in proportion to the calculated ion density in the plasma sheet and normalized to the empirical precipitation pattern by Hardy and Gussenhoven.

The results of the numerical simulation of the neutral composition changes agree in general with the observations obtained by AE-C satellite and with the MSISE90 model. Although ratio [N2]/[O] in storm maximum increases more than by factor 6 in comparison with the quiet level at high latitudes, at low latitudes it decreases below the quiet level neither in the numerical simulation nor in the satellite data nor in the empirical model. Meanwhile, the ionospheric storm is positive at low latitudes. Thus we can conclude that the positive phase of the ionospheric storm is created by thermospheric winds which cause upwelling of the ionospheric F2-region plasma at middle latitudes along the geomagnetic field lines to the heights where the ion loss rate is lower and at low latitudes this enhanced plasma is moved equatorwards by the oppositely directed themospheric winds blowing from northern and southern high latitudes.

V.I. Chernyshev, A.V. Serdjukova (634050 Tomsk, Revolution sq.1, Siberian Physical and Technical Institute)

On the base of the ionosphere model for the height region 80-200 km are conducted numerical experiments in order to study the influence of the electrodynamical motions on the ion component redistribution. The model is time dependent. It presents itself a system of the continuity equations, written for the main ions, forming this height region of the ionosphere, exactly: for the ions of atomic and molecular oxigen, nitric oxide and molecular nitrogen. The last equation of this system is the equation of the plasma electroneutrality. Neutral composition is given on MSIS-90. As the sources of the ionization it is taken into account the ionization of the ultraviolet radiation of the sun, the corona ionization and the ionization by high-energy electrons. The calculation is maked for the aurora and sub-aurora latitudes. The source of the electric field is the field of the convection. Main conclusion makes from these numerical experiments is the determination of the fact of the expansion of the plasma layer and increase of its height under action of electrical field of north or east direction. Results are compared to experimental data.

A.L. Kotikov(1), V.A. Kornienko(1), M. Kosch(2), N.F. Blagoveshchenskaya(1), E.M. Shishkina(1),

A. Brekke(3), T.D. Borisova(1)

(1) Arctic and Antarctic Research Institute, St.Petersburg, Russia

(2) Max-Plank Institut fur Aeronomie, Lindau, Germany

(3) University of Tromsoe, Norway

For substorms observed on 16,17/02/1996, the calculation of ionospheric current (latitudinal component) based on EISCAT magnetovariometers cluster data has been performed. A general feature of currents behaviour for 17/02/96, when L-shell-aligned arcs were observed, are the same as the airglow data obtained at Skibotn (near Tromsoe). The equatorward boundary of active airglow forms has the same dynamics as the boundary between east and west components of calculated currents. The substorm expansion phase in airglow data corresponds to meridional stratification in calculated ionospheric currents. We suppose different kinds of field-aligned currents (FAC) generation. For equatorward boundary the FAC's curtains believed to be responsible. On the background of these FAC's the Birkeland currents in the auroral oval poleward edge appear, which break westward jet to multiple jets.

N. Blagoveshchenskaya(1), T. Borisova(1), A. Brekke(2), V. Kornienko(1), A. Kotikov(1), R. Lukyanova(1), M. Rietveld(3), O. Troshichev(1)

(1) Arctic and Antarctic Research Institute, St.Petersburg, Russia

(2) Auroral Observatory, University of Tromso, Norway

(3) EISCAT Scientific Association, Tromso Division, Norway

Heating experiments were conducted in the pre-midnight hours with influence of pump wave onto auroral Es region. The heating produced the excitation of striations in the Es layer, responsible for field-aligned scattering of broadcast HF radiosignals (9410 & 12085 kHz). It was found the appearance of correlated ionospheric (in Doppler frequency shifts) and magnetic pulsations in the Pc4 range accompanying by the onset of the weak substorm. Their origin could be connected with generation (or amplification) of Alfven wave localised around Tromso. We suppose that field-aligned currents form boundaries of the area of enhanced conductivity. Difference in features of magnetic oscillations observed in Tromsoe and Andoya allows localize this boundary somewhere between. The stimulated electron precipitation of the 40-60 s duration due to a cyclotron resonant interaction of natural precipitating electrons with heater-induced whistler waves is the other phenomenon in heating experiments. This modification can result as a trigger mechanism for the observed micro-substorm expansion onset.

V. Kornienko(1), A. Kotikov(1), N. Blagoveshchenskaya(1), O. Troshichev(1), A. Brekke(2)

(1) Arctic and Antarctic Research Institute, St.Petersburg, Russia

(2) Auroral Observatory, University of Tromso, Norway

The recently obtained data show that substorm features are essentially influenced by powerful HF radiowaves (Tromsoe HEATING facility). Based on the study of several substorms some features of this influence have been established. 1) HF heater dramatically changes the ionosphere characteristics especially in strong Es layer conditions.

2) HF heater can redistribute substorm ionospheric currents locally.

3) HF heater can keep the equtorward edge of westward jet.

4) HF heater can trigger an auroral event.

5) It is believed to be possible to control the features of substorm development during its whole lifecycle.

For future studying some related topics are discussed.

1) Can we produce the substorm onset or only change the start time of substorm which have to be happen?

2) What are the conditions when we can influence to substorm?

3) Can we point the place of substorm to be happen?

4) Can we determinate the time when auroral event will start?

5) Can we redistribute the energy of substorm in space and time?

6) Does HF heater act as a thunderleader or as a provocateur?

7) Should we use this knowledge to protect the Earth?

A. Kotikov(1), N. Blagoveshchenskaya(1), T. Borisova(1), A. Brekke(2), V. Kornienko(1), M. Kosch(3),

E. Shishkina(1), M. Rietveld(4)

(1) Arctic and Antarctic Research Institute, St.Petersburg, Russia

(2) University of Tromso, Norway

(3) Max-Planck-Institut, Lindau, Germany

(4) EISCAT Scientific Association, Tromso Division, Norway

The modificated method of ionospheric currents calculation have been used for the analysis of geomagnetic substorms behaviour. For the analysis the EISCAT magnetometer cluster was used. Three substorm events on 15,16 and 17/02/96 have been analysed. It has been established that the HF heating which was carrying out during observation periods does influence to electrojet features. There are:

(1) shift of the jet location to the pole during the heating cycle;

(2) intensifications of jets correlate with heater cycles starts;

(3) the equatorward edge of westward jet stays near Tromso latitude when heater acts.

For explanation of the current jet edge behaviour we suppose that the modified ionosphere plasma produces field-aligned currents around heater area. Magnetospheric plasma flows coming to the heater's L-shell earthward from geotail precipitate into ionosphere and don't go nearer. We suppose that the main role in the trapping of charged particles into heater's L-shell plays the low frequency radiation above Tromsoe, which disturbs the pitch-angle distribution of magnetospheric plasma at this L-shell.

Б.Б. Цыбиков (Сибирский физико-технический институт при Томском госуниверситете, г.Томск, пл.Революции, 1, СФТИ)

Спектр движений ионосферной плaзмы включaет в себя прострaнственные мaсштaбы, сопостaвимые с земным рaдиусом. К тaким процессaм относятся возмущения, связaнные с быстрыми вaриaциями потокa солнечного излучения, геомaгнитными возмущениями, рaспрострaнением в верхней aтмосфере крупномaсштaбных грaвитaционных волн. Временной мaсштaб этих процессов лежит в пределaх единицы секунд - десятки минут. Трaдиционные способы пеленгaции тaких возмущений (мaлобaзовaя пеленгaция, сеть АИС) имеют весьмa низкую рaзрешaющую способность.

Для пеленгaции крупномaсштaбных процессов используется системa рaзнесенных по прострaнству облaстей отрaжения от ионосферы сигнaлов КВ-рaдиостaнций, рaспрострaняющихся нa трaссaх средней и большой протяженности. Отметим, что непрерывный контроль динaмики ионосферы в прострaнственно-рaзнесенных облaстях, в том числе и тaм, где нет регулярно действующих устaновок для ионосферных, мaгнитометрических и прочих нaблюдений, позволяет не только определять прострaнственно - временные пaрaметры крупномaсштaбных возмущений, но и в перспективе исследовaть их долгопериодные зaвисимости.

Информaция о мaсштaбaх, нaпрaвлении и горизонтaльной скорости перемещения крупномaсштaбных возмущений в ионосфере извлекaется тaк же, кaк и в методе мaлобaзовой пеленгaции - путем взaимокорреляционного и взaимоспектрaльного aнaлизa временных рядов. Только вместо aмплитудных рядов используются ряды доплеровского смещения чaстоты.

Измерения, проведенные во время геомaгнитных возмущений, покaзaли, что временные зaдержки в среднем не превосходят ~1 минуты, скорости переносa возмущений лежaт в интервaле ~15-150 км/с, нaпрaвление переносa возмущений - преимущественно меридионaльное.

В.Б.Фортес, Б.Б.Цыбиков (Томский госудaрственный университет, 634050, Россия, г.Томск, ул.Ленинa, 36, Сибирский физико-технический институт при Томском госуниверситете, 634050, Россия, г.Томск, пл.Революции, 1)

Обсуждaется возможность иследовaния структуры и движений полярной стенки (ПС) глaвного ионосферного провaлa нa основе дaнных нaклонного доплеровского зондировaния нa трaссaх широтной ориентaции проходящих вблизи полярного кругa.

Известно, что при приближении ПС к стaнции вертикaльного зондировaния, в ионосфере появляются неоднородности крупных (l~10 км.) мaсштaбов, приводящие к появлению дополнительных отрaжений, и мелкомaсштaбные - вызывaющие диффузное уширение принимaемых импульсов.

Нaпример, во время геомaгнитной бури 23-26.03.82г. вaриaции чaстоты, в которых присутствует рaссеяннaя компонентa нaчинaются в 00:46 LT 27.03.87г. и продолжaются до 01:05 LT. В это время зеркaльнaя компонентa испытывaет вaриaции с периодом ~40 мин. Рaссеяннaя компонентa появляется нa чaстотном удaлении от зеркaльной в ~5 Гц. Отчетливо прослеживaется постепенное смещение диффузной компоненты к зеркaльной и их слияние нaчинaется в 00:46 LT. По ширине полосa диффузной компоненты состaвляет ~10-15 мин. Это время может быть использовaно для определения оценки времени прохождения ПС вдоль облaсти отрaжения, формирующей диффузную компоненту.

Выделение информaции о прострaнственно-временных мaсштaбaх и скорости движений, нaблюдaемых методом доплеровского смещения чaстоты может быть решено исследовaнием угловых спектров КВ-сигнaлов, полученных путем нелинейного преобрaзовaния из чaстотных доплеровских спектров.

Б.Б. Цыбиков (Сибирский физико-технический институт при Томском госуниверситете, г.Томск, пл.Революции, 1, СФТИ)

Известно, что реaкция облaсти F2 нa солнечное зaтмение зaвисит от геофизических условий. Нaпример, электроннaя концентрaция в мaксимуме облaсти может не только не уменьшиться, a нaоброт, возрaсти. В доклaде приведены и обсуждaются результaты нaблюдений зa слоем F2 ниже мaксимумa во время полного солнечного зaтмения (СЗ), которые были проведены методом нaклонного доплеровского зондировaния 9 мaртa 1997г. нa трaссaх Мaгaдaн-Томск (чaстотa 9.5 МГц, длинa трaссы 3700 км) и Якутск-Томск (7.3 МГц, 2600 км).

Обрaботкa экспериментaльного мaтериaлa покaзaлa, что спектр сигнaлa во время зaтмения облaдaет сложной многомодовой структурой. В отдельные интервaлы времени регистрировaлось одновременно до 3 лучей, смещенных по чaстоте друг относительно другa. Динaмикa смещения чaстоты отдельных модов в спектре в основных чертaх повторялaсь с временной зaдержкой ~10 мин. В нaчaле нaблюдaлось смещение чaстоты в сторону отрицaтельных знaчений, что обусловлено пaдением Ne ниже мaксимумa F2-слоя. Поэтому, вследствие ростa высоты отрaжения, увеличивaется фaзовый путь рaдиоволны. Когдa скорость уменьшения Ne стaновится минимaльной (мaксимaльнaя фaзa СЗ) смещение чaстоты возврaщaется к знaчению, близкому к первонaчaльному.

В дaльнейшем с ростом потокa ионизирующего излучения рaстет и Ne - чaстотa смещaется, но уже в положительную облaсть. Когдa СЗ зaкaнчивaется и поток ионизирующего излучения достигaет нормaльных знaчений, Ne еще некоторое время продолжaет рaсти с убывaющей скоростью. Это связaно с процессaми релaксaции возмущения. При возврaте вaриaций чaстоты к невозмущеному состоянию нa обеих трaссaх зaрегистрировaны периодические колебaния чaстоты с периодом ~25-30 мин и aмплитудой ~0.2 Гц. Общaя продолжительность вaриaций чaстоты, связaнных с СЗ состaвилa более 3 чaсов.

V.A. Ivanov, A.A. Kolchev, V.I. Batuhtin (Mari State Technical University, Yoshkar-Ola)

Potential accuracy of measurement of Doppler Shift and of signal group delay by signals limited in frequency and time areas is analysed in the report. Main attention in this report specific periodic CW/FM signals. In work [1] was offered method of simultaneous measurement of Doppler Shift and signal group delay for each mode of ionospheric propagation.

Methods have been offered of determination of band of coherence and time of stationarity of ionospheric of HF channel. Statistical data on their value, tinned by authors on the different radio links equipped CW/FM ionozondes, have been provided in this report.

This work was supported by the RFFI under grants N96-02-19575.

[1] Ivanov V.A., Kolchev A.A., Shumaev B.B. The effect of distortion in nonstationary HF channel on features of spread spectrum signals // Problemy rasprostraneniya i difrakcyi electromagnitnyh voln/ MFTI, Moscow, 1994. p.73-79.

V.D. Tereshchenko, V.A. Tereshchenko (Polar Geophysical Institute, 15 Khalturina Str., Murmansk 183O1O, Russia, e-mail: vladter@polar.murmansk.su)

A linear kinetic theory of the gradient drift instability is generalized in order to include effects of Coulomb collisions in the F-region of the polar ionosphere. Such instability is produced by convectively mixing plasma across a mean plasma density gradient with the transport of higher-density plasma into regions contain lower-density plasma (and vice versa). The dispersion relation has been derived in the electrostatic approximation using BGK and Lenard - Bernstein collision terms. The problem geometry is so that the vector of an uniform magnetic field lies in the z-direction, the vector of an uniform electric field is in the y-direction and a weak density gradient vector is oriented in the x-direction. The propagation of plasma waves is in a plane perpendicular to the magnetic field. An analytic solution of the dispersion relation for the parameters of ExB gradient drift instability has been derived. It is found out that Coulomb collisions change the threshold of this instability. The plasma may be stable when the electron collision frequency is nonzero.

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

A. Osepian (Polar Geophysical Institute, Murmansk 183010, Russia)

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

N. Smirnova (Institute of Applyed Geophysics, Moscow, Russia)

The response of the ionospheric D-region to energetic electron precipitation is studied using electron density profiles measured by the EISCAT UFH radar. Strong local-time and seasonal variations are seen. Enhanced electron densities are, in general, observed at lower altitudes in the morning hours compared to the evening, and in winter compared to summer. The observations are interpreted in terms of the flux-energy spectrum of the precipitating electrons derived with the help of a seasonally and local-time dependent model of D-region ion chemistry. The results show harder energy spectra during morning precipitations compared to evening auroral events but no difference in hardness between winter and summer. The seasonal variation in D-region electron densities is found to be explained by the seasonal variations in the neutral atmosphere and consequent changes in the ion chemistry, without any change in the average energy of the precipitating particles. The spread in the relationship between cosmic-noise absorption and the total flux of precipitating electrons between different events (organised by local-time sector and season) is examined.

Г.А. Петрова (Полярный геофизический институт, Мурманск, Россия)

Ш. Кирквуд (Институт космической физики, Кируна, Швеция)

A.Yu. German, A.Yu. Manikhin, M.V. Uspensky (Murmansk State Technical University, 183010 Murmansk Russia, e-mail: msma@infotel.ru)

A. Huuskonen (Finnish Meteorological Institute, SF-00101 Helsinki, Finland, e-mail: asko.huuskonen@fmi.fi)

In the experiment with an unprecedented altitude resolution, Unwin and Johnston (1981) found that the auroral backscatter was a result of two separate layers at heights around of 106 and 112 km. Their conclusion based at the finding that there is a noticeable mutual range shift of the Lloyd-mirror modulation in the slant-range power and Doppler velocity profiles measured. In the modelling we have re-created the experimental condition suggesting a simpler case viz the ordinary thick (93-124 km) E-layer filled by type 2 irregularities. We combine the Lloyd-mirror effect, the IGRF magnetic field and the ionospheric refraction to build the range-altitude distribution of the volume cross-section and relative irregularity drift velocities. The derived height-integrated range profiles for the power and Doppler velocity exhibit prononciated mutual range shift in their Lloyd-mirror modulation similar as it was found in the data by Unwin and Johnston (1981). The power-velocity shift becomes particularly obvious when the E-layer electron density takes a value more than 2-3*1011 m-3 and the refraction starts to push the backscatter to lower altitudes. The reason for the modulation shift dues to that the backscatter is strongest for the slant ranges where the Lloyd lobe crosses largest volume cross section, i.e. close to the altitude of the E-layer electron density maximum. The Doppler velocity is highest for the slant ranges where the Lloyd lobe crosses the upper part of the E-layer also its minimum rejects the low and/or middle altitude echoes. For the low altitude echoes an influence of the electron and ion collisions and off-orthogonal angles at the irregularity drift velocity are largest. Our conclusion is that in the thick E-layer one can find a virtual effect of the two backscatter layers since the altitude profiles for the power and drift velocity have noticeable mutual altitude shift of their maxima.

V. Safargaleev and W. Lyatsky (Polar Geophysical Institute, Apatity, 184200, Russia)

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

V. Kriviliov (Polar Geophysical Institute, Apatity, 184200, Russia)

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

J. Manninen (Geophysical Observatory, FIN-996000 Sodankyla, Finland)

K. Kauristie, H. Koskinen (Finnish Meteorological Institute, Geophysical Research, POB 503,FIN-00101, Helsinki, Finland)

T. Turunen (Geophysical Observatory, FIN-996000 Sodankyla, Finland)

A. Kozlovsky (Polar Geophysical Institute, Apatity, 184200, Russia)

We discuss the results of the EISCAT measurements of ionospheric electric fields near active auroral forms during several auroral breakups. The electric field measurements were supplied by tri- static UHF facility (Tromso, Sodankyla and Kiruna), the auroras were registered by TV camera in Tromso and all-sky cameras in Kevo, Muonio, Kilpisjarvi and Loparskaya. The IMP-8 interplanetary magnetic field data were also available for some events. We concentrate on the azimuthal component of the ionospheric electric field because this is a component, which represents the state of the magnetospheric convection and may be important for understanding a nature of the magnetospheric substorm. We have examined six breakups near local midnight and have found some features in the behaviour of the electric field, which are repeated from event to event. They are the following. 1) A westward component of the field gradually increases, an equatorward drift of pre- existing arc enhances few minutes before a breakup. We think, that a negative turning of the IMF Bz, detected by the IMP-8 satellite 20-30 minutes before a substorm onset, is a reason for this increase. 2) An auroral breakup is accompanied by a rapid decrease in the westward component of the ionospheric electric field from 30 to 5-10 mV/m. On the contrary, an auroral fading just before or several minutes after a breakup is accompanied by the recovering of this component approximately to the pre-breakup value. Since there are none significant changes in the IMF Bz, we assume a disturbance of ionospheric conductivity to be responsible for these variations. 3) An impulsive reduction of few minute duration interrupts the gradual increase of the westward component just before a breakup. This reduction coincides with a short-lived brightening of a pre-existing arc (pseudobreakup) and may be connected with a local enhancement of ionospheric conductivity, too. The observed features in the behaviour of the electric field are discussed in the context of substorm development.

В.С. Мингалев, М.И. Орлова, А.С. Кириллов, Г.А. Аладьев, Г.И. Мингалева

Установлено, что поглощение на единицу длины (коэффициент поглощения) может существенно изменяться вдоль траектории радиоволны, быть различным для обыкновенной и необыкновенной волн, иметь сильно различающиеся значения при разных рабочих частотах. Изменение коэффициента поглощения КВ вдоль траектории должно характеризоваться наличием ярко выраженных максимумов, лежащих на тех участках траектории, которые приходятся на D-область. Если траектория достигает высот слоя F2, то на соответствующем этому слою участке траектории может появиться еще один, меньший по величине максимум. Значения коэффициента поглощения в максимумах, соответствующих пересечению D-области, могут превышать в 5-6 раз его значения, соответствующие пересечению E- и F2-областей. Значения коэффициента поглощения при прочих равных условиях возрастают при уменьшении частоты волны, оказываются большими для необыкновенной волны, чем для обыкновенной.Интегральное поглощение, обусловленное электронными соударениями, вдоль однотипных траекторий должно быть тем большим, чем меньшее значение имеет частота волны; его значения для необыкновенной волны должны быть большими, чем для обыкновенной.

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

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

Results of experimental investigation of the artificial low frequency emissions, generated during ionospheric electron heating, are presented. During the experiment on November 28, 1995 the emissions parameters were studied as a function of Effective Radiated Power (ERP) up to value of 170 MW. The experiment was performed using EISCAT Heating facility at Tromso, Norway. The ionospheric parameters were measured by EISCAT UHF radar. The powerful heating HF radio wave with frequency 4.04 MHz was consequently modulated with frequencies in VLF range: 925 Hz, 1375 Hz and 2375 Hz. All parameters of recorded signal at the fundamental frequencies such as horizontal amplitude and polarization characteristics have been obtained by applying the FFT technique to the experimental data. The electron density recorded by EISCAT was proved to fluctuate highly with time during this experiment. The possibility of estimation of D-region electron density through the analysis of the dependencies of normalized signal amplitude at frequencies 925 Hz and 1375 Hz versus ERP was found to exist.

A.B. Pashin, E.V. Pchelkina (Polar Geophysical Institute, Apatity, Russia)

The results of numerical modelling of the conductivity variations for the ionosphere heating by powerful HF radio wave modulated with sine-wave regime are presented. The calculations are produced for different electron density profiles in the course of the effective radiated power growth. Generation mechanism of the variation at the modulation frequency harmonics proposed by Pashin and Lyatsky (1977) gives no experimentally verified peculiarities. In the frequency range of short period magnetic pulsation disturbances are linear polarized. Orientation of the main axis of the polarization ellipses is different for the variations at the modulation frequency and those at the second harmonic. Clockwise polarization of the disturbances at the modulation frequency being equal to 1375 Hz in the heated area is expected. Polarization at the second harmonic is more complicated and for some values of pump wave power should have the opposite sense. Ellipticity of the variations at the modulation frequency is less than 0.25, although at the second harmonic it is sometimes almost circular. The amplitude of main axis of the polarization ellipses shows positive correlation with the electron density in the D-region. These peculiarities of the disturbances could be observed in the artificial emissions observed on the ground.

A.B. Pashin (Polar Geophysical Institute, Apatity, Russia)

In the paper of Papadopoulos et al. results of calculation of the ionospheric conductivity disturbances in the wide range of the heating wave power are presented. The calculation is based on kinetic approach and the authors conclude that value of the ionospheric conductivity disturbances used as a measure of heating efficiency significantly increase for high altitude heating. The value of Pedersen conductivity disturbances in this case is proportional to the square of the pump wave power up to its value 10^-2 W/m². This result has not been supported in experimental data analysis presented by Barr and Stubbe (1991), however these predictions are still discussed. We would like to debate with two points in the paper of Papadopoulos et al.

The first point is the conclusion that using kinetic approach one can get positive disturbances of the local Hall conductivity during ionosphere electron heating at the 100 km altitude (Papadopoulos et al., p. 1316). At this height all ions are stopped by collisions and the current is produced by drift motion of the magnetized electrons. Positive disturbances of Hall conductivity means that averaged value of the electron velocity are greater than the drift velocity. Direct transform of the thermal energy to the energy of directed movement violates basic physics low. We believe that this conclusion is the result of an error in the computer code.

The other point is consideration of local conductivities and their disturbances. Really, maximum of the electron Pedersen current is observed at the height where the electron gyrofrequency is equal to the electron-neutral collision frequency. Growth of the electron temperature during heating increases the collision frequency. Maximum of the modified Pedersen current is shifted to the higher altitudes rather gradually in a course of the pump wave energy growth. It is related with strong decrease of the neutral density with height and does not produce a sharp variation of the conductivity disturbances. In contrary to that the local Pedersen conductivity disturbances are very small when the collision frequency is more less than the gyrofrequency and become rather significant when collision frequency increase up to value of the gyrofrequency order. We think that consideration of the local conductivity is methodologically wrong and whole ionosphere profile does produce conductivity disturbances.

Т.Н. Лукичева, В.С. Мингалев (Полярный геофизический институт, Апатиты)

Многочисленные измерения скорости горизонтального нейтрального ветра выявили его сильную изменчивость по вертикали на высотах нижней термосферы. Часто регистрируются высотные профили зональной и меридиональной составляющих термосферного ветра, которые имеют противоположные направления на близко расположенных уровнях. Известно, что на формирование высотных профилей горизонтальных составляющих термосферного ветра могут оказывать влияние различные причины, в том числе атмосферные приливы, планетарные волны, перемещающиеся ионосферные возмущения и т.п. В частности, область возмущенного термосферного ветра, в которой он может иметь противоположные направления на близко расположенных уровнях, может сформироваться при прохождении волны Россби.

Настоящая работа посвящена исследованию изменений высотных распределений заряженных частиц в ионосферных слоях E и F1, которые должны происходить при возмущениях нейтрального ветра, обусловленных прохождением солитона волны Россби в тех случаях, когда он может находиться на разных высотных уровнях в нижней термосфере. Мы применяем нестационарную математическую модель высокоширотной ионосферы, основанную на численном решении системы уравнений переноса для 5 сортов ионов. Расчеты проводятся для точки, лежащей на широте Мурманска, для момента MLT=3 часа при средней солнечной и низкой магнитной активностях в условиях равноденствия.

Установлено, что обусловленный прохождением солитона волны Россби возмущенный нейтральный ветер, меняющий с высотой свое направление на противоположное и имеющий максимальную величину 50 м/с, может привести к формированию одно-, двух- и трехслойных спорадических структур на профиле электронной концентрации на уровне слоев E и F1 в ночных условиях. Количество возникающих спорадических слоев зависит от высоты солитона и от направления термосферного ветра в нем.

T.I. Sergienko (Polar Geophysical Institute, Apatity, Murmansk reg., 184 200 Russia)

E. Turunen (Sodankyla Geophysical Observatory, FIN-99600 Sodankyla, Finland)

The auroral electron transport model, the auroral ionosphere model, and model of the auroral optical emission were used to analyze the simultaneous measurements of the ionospheric parameters by the EISCAT radar and the optical emission intensities. The spectra of the auroral electrons were reconstructed from the profile of the electron concentration and the electron temperature by used the electron transport model and the ionosphere model. Then these spectra were used as input parameters for the auroral optical emission model. The intensities of the 5577A, 6300A emissions of the atomic oxygen, and the 4278A emission of N₂ were calculated. The comparison of the calculated and the measured values has demonstrated a good agreement, and permitted us to conclude on a validity of our method of the auroral electron spectra reconstruction. The variations of the ion compositions and the effective recombination coefficient in dependence on the auroral electron parameters were studied in a frame of the developed approach.