Institution: | aInstitute of Physics of the Earth, 10 B. Gruzinskaya, Moscow 123995, Russia bSodankylä Geophysical Observatory, Tähteläntie 112, FIN-99600 Sodankylä, Finland cInstitute of Solar-Terrestrial Physics, P.O. Box 4026, Irkutsk 664033, Russia |
Abstract: | 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”. |