Long-period irregular pulsations under the conditions of a quiet magnetosphere

Abstract

Simultaneous observations of high latitude long period irregular pulsations at frequencies of 2.0-6.0 mHz (ipcl) and magnetic field disturbances in the solar wind plasma at low geomagnetic activity (Kp ~ 0) have been studied. The 1 s data on the magnetic field registration at Godhavn (GDH) high latitude observa tory and the 1 min data on the solar wind plasma and IMF parameters for 2011-2013 were used in an anal ysis. Ipcl (irregular pulsations continuous, long), which were observed against a background of the IMF Bz reorientation from northward to southward, have been analyzed. In this case other solar wind plasma and IMF parameters, such as velocity V, density n, solar wind dynamic pressure P = ρV 2 (ρ is plasma density), and strength magnitude B, were relatively stable. The effect of the IMF Bz variation rate on the ipcl spectral composition and intensity has been studied. It was established that the ipcl spectral density reaches its maxi mum (~10-20 min) after IMF Bz sign reversal in a predominant number of cases. It was detected that the ipcl average frequency (f) is linearly related to the IMF Bz variation rate (ΔBz/Δt). It was shown that the depen dence of f on ΔBz/Δt is controlled by the α = arctan(By/Bx) angle value responsible for the MHD disconti nuity type at the front boundary of magnetosphere. The results made it possible to assume that the formation of the observed ipcl spectrum, which is related to the IMF Bz reorientation, is caused by solar wind plasma turbulence, which promotes the development of current sheet instability and surface wave amplification at the magnetopause.