Reorientation of the IMF Bz Component as a Trigger of Isolated Bursts of Long-Period Pulsations in the Region of the Dayside Polar Cusp

The study of simultaneous observations of isolated bursts of ipcl pulsations (irregular pulsations continuous long period) in a frequency range of 1.3–6.3 mHz in the region of the dayside polar cusp and the dynamics of the Bz component of the interplanetary magnetic field (IMF) is carried out. It is found that, isolated ipcl bursts are observed in the cusp region in 61% of cases (first group) after a change in the direction of the IMF Bz component from north to south and in 39% of cases (second group) with a change in the Bz direction from south to north. The bursts of the two groups had approximately the same spectral composition but differed in the intensity, duration of wave packets, and excitation conditions. Depending on the change in the sign of the Bz component (from positive to negative or from negative to positive), the spectral density of ipcl pulsations reached the maximum value in 10–20 min or 5–10 min, respectively, after the instant of Bz reorientation. It is shown that the dynamics of other geoeffective parameters of the solar wind and IMF was relatively stable before the reorientation of the Bz component and after, i.e., during the excitation of wave packets of ipcl pulsations. The totality of experimental facts suggests that the only trigger of isolated ipcl bursts under conditions of a moderately disturbed magnetosphere may be a change in the direction of the IMF Bz component, not only from north to south but also from south to north. A hypothesis is put forward about the excitation of isolated ipcl bursts observed in the dayside cusp region as a result of stationary reconnection both in the forenoon sector of the magnetosphere and near polar cusps.