Two distinct sources of magnetospheric heating in the atmosphere: the aura and the ring current

In this paper, we demonstrate that, besides the well-known corpuscular heating of auroral origin, there is another heat source in the equatorial region of the neutral upper atmosphere acting during and after geomagnetic storms as a consequence of the precipitation of ring current ions. The effect of the two sources has been separated on the basis of their induced diurnal variations using measurements from the CACTUS micro-accelerometer. In Almár and Illés-Almár [Adv. Space Res., this issue, 2004, doi:10.1016/j.asr.2003.04.060], the observational facts and our suggestion for the improvement of the CIRA'86 model are summarized to draw the attention of the constructors of the new CIRA model on two effects that are not yet built into the earlier CIRA models. In the present paper, we try to outline the possible physics behind the observational facts necessitating the improvement of the model

Weather reacting to geomagnetic storms

In the first 15 years of the Space Age satellite position measurements derived from visual and photographic observations helped to determine the decay rate of satellites, by means of which the first models of the upper-atmosphere have been calculated. Our group concentrated on the study of the geomagnetic effect and collected several ten thousand observations from Europe and from Asia before and after geomagnetic storms. It was already conspicuous during data gathering that there are considerably less satellite observations in the time periods following almost every geomagnetic storm than in the preceding ones – indicating that the cloudiness might increase considerably after geomagnetic storms. The paper presents the statistical treatment of this phenomenon

Neutral density depletions attributed to plasma bubbles

Neutral density measurements in the equatorial thermosphere by the accelerometer of the San Marco V satellite in 1988 indicate from time to time sudden density depletions of 10-20 s. As the occurrence of such events maximizes between 1700 and 0300 hours local solar time, we interpret them as manifestations of the crossings of plasma bubbles by the satellite

New results concerning the geomagnetic effect in the upper atmosphere

89 equivalent duration values based on more than 30000 satellite observations were used to derive relations between different geomagnetic parameters and the correlated changes in upper atmospheric density during magnetospheric storms. The results demonstrate how the storm-time relative density increase depends on the intensity of the magnetospheric storm, on the altitude of the perigee and on its geocentric distance from the center of the diurnal bulge

Investigation of the density wave activity in the thermosphere above 220 km

Based on CACTUS (Capteur Accélérométrique Capacitif Triaxial Ultra Sensible) microaccelerometer measurements it has been demonstrated that — after taking into account all effects included in the MSIS'86=CIRA'86 (COSPAR, 1988) model - there are residual fluctuations in the density of the upper atmosphere much larger than that the accuracy of the measurements can account for. These fluctuations are attributed to some kind of wave activity (Illés-Almár, 1993, Illés-Almár et al. 1996a). The average deviations from a model are considered as a measure of the amplitude of the waves in the atmosphere and are analysed as a function of geomagnetic coordinates, altitude and local solar time, in order to identify possible wave sources either in the lower lying atmosphere or in the thermosphere/ionosphere system. As a first step, the present investigation intends to make a map of the wave pattern by this method

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

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

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

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 interaction

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

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

Wave-Like Variations and Sudden Density Decreases in the Lower Thermosphere as Measured by the San Marco V Satellite

Neutral density measurements were carried out by the microaccelerometer on board the Italian San Marco V satellite in 1988. During the final week of its existence the satellite's perigee decreased to as low as 130 km. Measured density values were compared to the corresponding CIRA '86 (MSIS '86) or to our dMSIS model values. The residuals reveal a wavy structure of different time scales. Characterising the wave amplitude by the average deviation of the residuals, its dependence on different parameters was studied. These investigations demonstrated that the wave-amplitude varies with height, local solar time and geomagnetic disturbance level. There is a particularly developed wave pattern in the average deviations below 200 km. Case studies indicated that there are sudden density decreases of 20–30 sec duration that might be in connection with plasma bubble crossings by the satellite. Altogether 261 such cases were identified and their distribution as a function of height, LST and longitude have been investigated