Geomagnetic pulsations in 1–4 mHz frequency range (Pc5/Pi3) in the magnetotail at different levels of disturbances in the interplanetary medium

Abstract

In this paper, we study parameters of geomagnetic pulsations in the 1–4 mHz frequency range (Pc5/Pi3) in the magnetotail, utilizing data obtained by Cluster satellites at different levels of fluctuations in the interplanetary magnetic field (IMF) and the solar wind dynamic pressure in 2016. Particular attention is given to the conditions of “zero” disturbance when amplitudes of fluctuations in the interplanetary medium are smaller compared to their typical values. Both under quiet and disturbed conditions, waves of different spatial scales are recorded, with the occurrence rate of large-scale waves increasing under undisturbed conditions. Amplitudes of the large-scale waves occurring in the magnetotail under low intensity of fluctuations outside the magnetosphere are from few tenths to a few nanoteslas (nT), and their power is approximately equal in longitudinal and transverse components. Presumably, these waves are magnetotail eigen-modes.

Geomagnetic pulsations in 1–4 mHz frequency range (Pc5/Pi3) in the magnetotail at different levels of disturbances in the interplanetary medium

“…An example of pulsations in the tail observed at a low amplitude of IMF fluctuations on July 18, 2016 (day 200) is given in Figure 2. This finding is similar to that described in [Nosikova et al, 2022] for the August 8, 2007 event when largescale pulsations in the magnetotail also occurred against the background of almost complete switch-off of external disturbances. To understand whether such a coincidence is accidental or not, we analyze the distributions of Pc5/Pi3 pulsation parameters in the magnetotail at different fluctuation amplitudes in front of the bowshock.…”

“…Changes in the pulsation parameters are observed 2-4 hrs before the substorm without an obvious external trigger. Nosikova et al [2022] for one case have shown a high coherence of pulsations in both polar caps and large-scale pulsations in the magnetotail observable at the "zero" level of external disturbance. The question about the statistical relationship of non-triggered substorms and other transient processes in the magnetosphere with the parameters of geomagnetic pulsations in the range of a few millihertz in the magnetotail calls for a separate study.…”

“…Using magnetometric measurements made at a ground-based low-latitude station and in the magnetotail, the authors examine fluctuations directly related to pulse and quasi-periodic SW dynamic pressure fluctuations. Apparent periods of these fluctuations range from 2 to 6 min; in the time domain, they practically coincide with fluctuations in SW, and the maximum coincidence between pulsations on Earth and in the tail is observed with a shift of 120 s. Yagova et al [2017] and Nosikova et al [2022] have shown that specific high-quality oscillations in the tail lobes occur with almost complete switch-off of fluctuations of the same frequency range in the interplanetary medium. A detailed analysis of pulsations in the range of a few millihertz in both polar caps and the magnetotail before a non-triggered isolated substorm allowed an assumption to be made that these pulsations can act as a precursor of a weak non-triggered substorm.…”