SAMBO-GEOS: On three-dimensional substorm dynamics — A case study for 4 March 1979

For investigations of the isolated magnetospheric substorm the ground-based and satellite geophysical data are discussed. The active phase of the substorm has two parts: an active-convective phase and a classical active phase. The analysed data show that the breakup of the substorm takes place at closed and not very much stretched magnetic field lines.     

Magnetospheric and ionospheric manifestations of interplanetary foreshocks

The geometry of a typical interplanetary shock front in the vicinity of the Earth’s orbit predicts that the leading edge of the foreshock region comes into contact with the magnetosphere a few hours ahead of geomagnetic sudden impulses (SI). There is reason to believe that the interaction of the magnetosphere with the foreshock leads to magnetic and ionospheric disturbances, which can be detected by ground-based instruments. We searched for specific precursors of SIs in data from the Scandinavian riometer network and in the short period geomagnetic pulsation data from mid-latitude magnetometers. We found that SIs were preceded by the following three features: (1) an increase in riometric absorption, (2) excitation of Pcl magnetic pulsations and (3) a spectral broadening of the Pc3 magnetic pulsations. Our observations may be useful for the study of acceleration processes in the solar wind. These observations are also of potential forecasting interest.     

Solar wind dependence of the Pc1 wave activity

There are a host of factors influencing the excitation of Pc1 geomagnetic pulsations, which are ULF waves in the frequency range between 0.2 and 5 Hz. We have studied carefully the dependence of the pearl-type Pc1 activity at Sodankylä, Finland (L = 5.1) on the plasma density N in front of the magnetosphere, the bulk velocity V of the solar wind, and the intensity B of the IMF. The result is as follows: high values of N and reduced values of V are favorable to appearance of Pc1, whereas the dependence of Pc1 activity on B is practically absent. We also show that the probability of Pc1 occurrence decreases with the interplanetary electric field, and increases with solar wind impact pressure and with the plasma to magnetic pressure ratio “beta”.     

Morphology and physics of short-period magnetic pulsations

This review is devoted to the main problems of experimental and theoretical investigations of geoelectromagnetic waves in the frequency range from 0.1 to 5 Hz. These waves constitute the short-period subclass of so-called geomagnetic pulsations. The short-period pulsations are represented by Pc1, Pc2, Pi1, Ipdp types and some subclassifications. The understanding of the pulsation mechanisms provides an insight into the structure and dynamics of the Earth's magnetosphere. We focus our attention on Pc1 pearl pulsations and on the classical (evening) Ipdp, for which basic physical concepts have been established. Other types and varieties are outlined also, but in less detail. In these cases, the physical mechanism is not always clear (as, for example, in the case of morning Ipdp), and/or the morphology is still to be determined carefully (Pc2 and discrete signals in polar cusps as typical examples).Short-period pulsations are a spontaneous, sporadic phenomenon which undergo a certain evolution in the course of a magnetic storm. We consider the storm-time variation as a natural background, and we use this background to collect the information about the pulsations in an orderly manner. At the same time, together with the transient storm-time variation of pulsation activity, quasi-periodic variations take place, which are connected with the Earth's and Sun's rotation, Earth's orbital motion and solar cycle activity. The study of these regular variations allows us to have a new approach to the mechanisms of excitation and propagation of short-period geomagnetic pulsations.     

Localized Enhancements of Energetic Proton Fluxes at Low Altitudes in the Subauroral Region and Their Relation to the Pc1 Pulsations

A special kind of variation of energetic proton fluxes inside the anisotropic precipitation zone is considered using the data from the low-altitude satellites NOAA/TIROS. The variation is characterized by a localized (within 1° of latitude) enhancement of >30 keV protons, both trapped at the spacecraft altitude and precipitating. A close correlation is shown between the morphological characteristics of the proton precipitation and the Pc1 pulsations observed by the ground-based geophysical observatory Sodankylä. The probability of observation of the Pc1 pulsation by a ground-based station decreases with increasing MLT distance between this station and the projection of the satellite detecting the precipitating protons. The Pc1 pulsation frequency decreases as the proton burst latitude increases. These findings support the ion-cyclotron mechanism of the Pc1 production suggesting that both wave generation and particle scattering occur in the source region.