Polar Geophysical Institute Research Articles

Detection of infrasound from the Vitim bolide on September 24, 2002

An infrasonic signal from an atmospheric bolide explosion was detected on September 24, 2002 near the Vitim river, Irkutsk region (57.9 N, 112.9 E). The signal was detected by three spatially separated microbarographs of the Polar Geophysical Institute (PGI), Kola Science Center, Russian Academy of Sciences, Apatity (67.6 N, 33 E) at a distance of 4000 km from the source. The acoustic gravity signal from a falling meteorite at high latitudes was detected at such a distance for the first time in Russia.

Interpretation of ionospheric F-region structures in the vicinity of ionisation troughs observed by satellite radio tomography

Abstract. Tomographic images of the spatial distribution of electron density in the ionospheric F-region are presented from the Russian-American Tomography Experiment (RATE) in November 1993 as well as from campaigns carried out in northern Scandinavia in November 1995 and in Russia in April 1990. The reconstructions selected display the ionisation troughs above the tomographic chains of receivers during geomagnetically quiet and disturbed periods. Two mathematical models of the high-latitude ionosphere developed in the Polar Geophysical Institute have been applied for interpretation of the observed tomographic images.Key words. Ionosphere (electric fields and currents; ion chemistry and composition; plasma convection)

Modelling turbulent energy dissipation in the high-latitude mesosphere

Abstract The global numerical model of the Earth's thermosphere, ionosphere and protonosphere constructed at the Kaliningrad Observatory of IZMIRAN and Polar Geophysical Institute in Murmansk (Namgaladze et al., 1991), hereafter referred to as PGI97, is being extended to encompass modelling of the mesosphere. Here we report the first predictions of turbulent intensities in the height regime 80 to 90 km. Recently, Hall (1997) reported estimates of the turbulent energy dissipation rate, e, using the EISCAT VHF radar located in Northern Norway (69°N, 19°E), which has, in turn, been compared to in situ measurements. Thus initial testing of PGI97 has concentrated on the same region. The agreements between PGI97 and EISCAT results for summer and winter solstice mesospheres are good. The general seasonal variation has been investigated, again showing good agreement with the EISCAT results. However, when examining the average energy dissipation in the 80–90 km height regime, the model shows less variability than the observations.

The effect of radar sensitivity on auroral backscatter threshold parameters

Radar auroral backscatter observed by the Scandinavian Twin Auroral Radar Experiment (STARE) radars is compared with the current density in an eastward electrojet as seen by the Scandinavian Magnetometer Array (SMA) for about half an hour on March 27, 1977. The value of the height‐integrated Hall conductivity, obtained from the ionospheric electric field measured by the STARE radars and from the SMA estimates of the ionospheric current density, is considered as a measure of the mean electron density at the height of the diffuse auroral backscatter. The dependence of the volume cross section for auroral backscatter on the ionospheric electric field and electron density is analyzed, and the following points are shown. (1) For a STARE radar directed approximately perpendicular to the Hall current in the backscatter region and ionospheric electric fields between 15 and 35 mV/m, the turbulence level of 1‐m plasma waves associated with diffuse radar echoes has a linear dependence on the field. For larger values of the electric field, the turbulence level seems to saturate to a constant value. (2) A minimum height‐integrated Hall current density of 82 A/km was required to observe diffuse backscatter by either of the STARE radars. The threshold Hall current density is constant to within 20% for all electric field strenghs. For threshold backscatter the height‐integrated conductivity is inversely proportional to the ionospheric electric field. (3) The threshold current values are determined by the sensitivity of the radar used. The squared threshold Hall current is proportional to the minimum detectable value of the backscatter cross section. The radar sensitivity concept is verified quantitatively for the 144‐MHz STARE radar in Finland and for the 90‐MHz radar of the Polar Geophysical Institute.

Numerical modelling of the thermosphere-ionosphere coupling during substorm

The numerical calculation results of the thermospheric parameters ( [O] [N 2] ratio and Tn) and critical frequencies of F2-region of ionosphere, foF2, in the global scale for the recovery phase of the substorm are presented. The calculations were executed with the use of the Global Self-consistent Model of the Thermosphere, Ionosphere and Protonosphere (GSM TIP) was constructed in the Kaliningrad Observatory of the IZMIRAN and modified in the Polar Geophysical Institute. The influences of the global distribution of Joule dissipation on the neutral atmosphere and ionosphere parameters are discussed. It is emphasised that the Joule dissipation in the neutral atmosphere is a main cause of the negative disturbance in the F2 region of the ionosphere.

Russian‐American tomography experiment

AbstractTo intercompare various techniques used in reconstructing tomographic images, and to benchmark those results with direct observations obtained by the incoherent scatter technique, an experimental campaign and subsequent analysis program‐the Russian‐American Tomography experiment (RATE)‐were implemented in late 1993. Russian experiment teams from the Polar Geophysical Institute in Murmansk and Moscow State University joined with American investigators from the Phillips Laboratory and the Massachusetts Institute of Technology, and an array of four receiving stations was set up in the northeastern United States and in eastern Canada to obtain data for the tomographic reconstructions. Phase‐difference and total‐phase tomographic reconstruction techniques have been employed and are intercompared. The spatial/altitude distribution of ionospheric electron content was observed by the MIT Millstone Hill incoherent scatter radar that scanned the ionosphere in a plane parallel to the satellite overflights. We present preliminary reconstructions of the ionospheric structure observed during a severe midlatitude ionospheric storm that took place during the campaign. The drastic large‐scale changes in the ionospheric structure that accompanied the November 1993 storm were well observed by the two diagnostic techniques.©1994 John Wiley & Sons Inc

Electric field and electron density thresholds for coherent auroral echo onset

Simultaneous observations of the Polar Geophysical Institute 83‐MHz auroral radar and the European Incoherent Scatter facility were used to study the coherent echo threshold phenomenon. It is shown that, for electric fields not far from the Farley‐Buneman instability threshold of ∼20 mV/m, the onset of echo occurrence was due to an electron density increase above some threshold value. This value was estimated to be ∼2.5 × 1011 m−3. For smaller electric fields of 5‐10 mV/m, echoes were not observed even for electron densities double the above threshold value. The importance of both factors, electric field and electron density, and some other effects are discussed in light of recent studies of coherent echo intensities and their dependence on plasma conditions at electrojet altitudes.

A VHF incoherent scatter receiving station at the Russian Polar Geophysical Institute: the current status and a brief description

This paper describes the first stage of a Russian VHF-incoherent scatter receiving station near Murmansk. The facility is planned to operate in connection with the EISCAT VHF-radar. Basic technical features of the design are described and some performance tests are presented, obtained using the completed single module of the antenna system.

A comparison of satellite measurements of electric and magnetic fields and particle fluxes with ground-based geophysical data

Data from one pass (orbit 1547) of the Intercosmos-Bulgaria-1300 satellite near the Kolsky peninsula are analyzed along with data from ground-based magnetometers of the Polar Geophysical Institute chain and measurements of radio-aurora and optical emissions. Consideration is given to: (1) the relationship between the field-aligned currents and the electric field; (2) the relationship between the field-aligned currents and the characteristics of precipitating particles; and (3) the relationship between auroral structures (e.g., the electrojet, and optical and radio auroras) and field-aligned currents and the electric field. Attention is restricted to the qualitative interrelationship of the phenomena in the morning sector. 25 references.