P. Bencze

Further results referring to the neutral density depletions attributed to plasma bubbles

Abstract The interaction between the ionized and neutral components of the upper atmosphere (ion drag, air drag) is not limited to the large-scale motions, but it works also among the small-scale motions. This is demonstrated by neutral density depletions (NDD) revealed by us in the neutral density measurements of great time resolution of the San Marco V satellite. The morphological and statistical investigations indicate that NDDs and plasma bubbles have similar characteristics. On the other hand, according to modelling, depletions of the total neutral density discovered by us below a height of about 350 km (collision-dominated case) in the vicinity of the equator might be really due to equatorial plasma bubbles. The relation of the NDDs to plasma bubbles (ion density depletions) is studied partly by direct comparison and modelling, partly indirectly by the distribution of the occurrence of NDDs according to local solar time, to season, to height and to longitude. All of them are arguing in favour of the plasma bubble origin of the NDDs.

Whistler ducts and geomagnetic pulsation resonant field line shells near L = 2—are they identical?

Abstract Data from the processing of about 1700 whistlers recorded in Tihany ( L -value of propagation, equatorial electron density and tube content) are compared with geomagnetic pulsation characteristics (mainly of periods) as recorded at the nearby Nagycenk Observatory ( L ∼2). In addition, the number of whistlers recorded at Panska Ves (Czech Republic) for more than ten years (1971–1979, 1987, 1990) are compared with the Nagycenk pulsation activity. Both results can be reconciled with the supposition that whistler ducts and geomagnetic field line shells are closely connected with each other as they appear simultaneously with enhanced probability, and the position of these structures is similar within the magnetosphere.

Ring current heating of the low latitude thermosphere connected with geomagnetic disturbances

Abstract The excess thermospheric density at low latitudes during the recovery phase of geomagnetic disturbances found in earlier studies has been related to the ring current belt. This would mean that the geomagnetic effect is due not only to an auroral but also to an equatorial source. The low latitude excess density could be separated into a storm time dependent and a local time dependent component. Thus, the morphology of this effect is similar to that of the geomagnetic disturbance field. The heating can be attributed mainly to the precipitation of energetic neutral particles produced by charge exchange, as well as to the dumping of energetic charged particles due to wave-particle interaction. The local time dependent component could be connected also with the asymmetry of the composition of the ring current and with the irregular shape of the plasmasphere.

On a possible ring current effect in the density of the neutral upper atmosphere

Abstract The neutral post-storm effect is reconsidered by means of accelerometric data. Since Δρ has proved to be different function of Kp during and outside recovery phases, but a unique function of Dst, the latter is considered as a better index for correcting the effect of geomagnetic activity in models, i.e. it seems that the ring current plays an important role in the geomagnetic effect of the equatorial thermosphere.

Investigation of the thermosphere-ionosphere interaction by means of the neutral post-storm effect

Abstract Previous investigations of the authors based on the decay rates of many satellites have demonstrated the existence of a post-storm effect in the neutral atmosphere after geomagnetic storms. Its maximum appears 4–6 days after the storm onset. It generally lasts 8–10 days, but if there is also an ionospheric post-storm effect, then it is about twice as long at mid-latitudes and in the evening hours. The observed characteristics of the post-storm effect seem to indicate that it is related to the precipitation of ring current particles due to charge exchange and wave-particle interactions.

Investigation of the variation of the neutral density wave pattern on the basis of San Marco V data

Abstract Neutral density measurements by the Drag Balance Instrument (DBI) on board the Italian San Marco V satellite are made with high time resolution. These measurements permit the direct investigation of the thermospheric wave pattern variation in the equatorial zone. The investigation has been carried out not only statistically, but also through case studies. One of the interesting results is that, although the wave amplitude generally increases continuously with altitude, there are some cases when it changes abruptly. These abrupt changes can occur at different altitudes. The coupling processes such as ion drag and spatial resonance have also been studied as a function of altitude (h), local solar time (LST) and other parameters.

Observational results hinting at the coupling of the thermosphere with the ionosphere/magnetosphere system and with the middle atmosphere

Abstract Total density data based on CACTUS microaccelerometer measurements have been analysed between 220 and 700 km altitudes at low latitudes in the time interval 1975–79. Instantaneous residual density values with respect to atmospheric models for quiet as well as for disturbed days have been investigated as a function of local solar time (LST). It has been found that the density residuals present conspicuous increases of the variance in several LST intervals as well as a general broadening which can be in connection with various coupling mechanisms between the thermosphere and the ionosphere/magnetosphere on the one hand, and the middle atmosphere on the other. An attempt is made to select those mechanisms responsible for the observed features.

Surplus of negative charge flow in point-discharge current as shown by variations on different time scales at Nagycenk station

Abstract Data of point-discharge current measurements at the Nagycenk station covering more than three decades have been used for demonstrating the variations of this atmospheric electric parameter on different time scales. The diurnal variation of the point-discharge current shows an early morning minimum and an afternoon maximum as represented by charges brought down to ground by a metal point (elevated to a height of about 8 m), and this is valid for charges of both signs. On the diurnal time scale, there is a surplus of negative charge flow which peaks in the afternoon. A predominance of negative charge flow was also found on the annual time scale as indicated by the monthly mean values of transported charges of both signs. The monthly mean ratio of negative to positive charge is well above 1.0 from April to October and it is below 1.0 merely in the first three months of the year. Determining an average ratio of negative to positive charge for each individual year between 1961 and 1996, it was shown that the yearly average ratio is usually above 1.0 (except for 4 years). Some comparisons between results of Nagycenk and those obtained simultaneously at other stations showed a certain agreement; however, they also revealed discrepancies between individual values of the transported charges. Notwithstanding, a surplus of negative charge flow was detected even by these comparisons. The results derived on different time scales do confirm that point-discharge current plays an important role in the transfer of charges to the Earth; at the same time a predominance of negative charge flow could be proved.

Similar behaviour of the thermosphere and the ionosphere in the recovery phase of geomagnetic disturbances

Abstract The neutral density excess as compared to the MSIS 86 model indicates a double valued dependence on the Kp geomagnetic activity index; a very similar dependence was found in some ionospheric parameters. The similarity hints at coupling between the ionosphere and the neutral upper-atmosphere during geomagnetic disturbances. Relations between the changes of these parameters and the neutral density are considered.

Modelling of the Propagation of Radio Waves Transmitted by GPS Satellites in an Ionosphere with Irregularities

The results concerning the modelling of the propagation of radio waves transmitted by GPS satellites in the presence of sporadic E layers are described. The greatest deviations of the difference between the true path and the geometrical path found for the higher frequency from the difference true path-geometrical path obtained for the lower frequency attain values of the order of 26 cm at the zenith angle 75° of the satellite in the N-S direction (summer, night and low solar activity conditions) and about 7 cm in the W-E direction (summer and winter night, as well as low solar activity conditions).