I. Almár

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.

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.

Comparison of the surface grooves on gaspra and phobos

Abstract A morphological analysis of the linear features on asteroids 951 Gaspra and 243 Ida as well as on the Martian moon Phobos is presented. On all of these small bodies there are different groove systems. In every case the most numerous grooves constitute a system with a characteristic direction almost perpendicular to the long axis of the body, and a coverage of the visible surface. It is supposed that these are indications of their layered inner structure. Together with some kind of magnetism discovered at Gaspra and Ida they suggests that these small bodies of the Solar System may originate from the near surface of some ancient, already differentiated planetary bodies of larger dimension.

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.