Abstract
Abstract. In this work a study of the effects of the high-intensity long-duration continuous AE activity (HILDCAAs) events in the magnetotail was conducted. The aim of this study was to search the main frequencies during HILDCAAs in the Bx component of the geomagnetic field in the magnetotail, as well as the main frequencies, at which the magnetotail responds to the solar wind during these events. In order to conduct this analysis the wavelet transform was employed during nine HILDCAA events that coincided with Cluster spacecraft mission crossing through the tail of the magnetosphere from 2003 to 2007. The most energetic periods for each event were identified. It was found that 76 % of them have periods ≤4 h. With the aim to search the periods that have the highest correlation between the IMF Bz (OMNI) component and the Cluster Bx geomagnetic field component, the cross wavelet analysis technique was also used in this study. The majority of correlation periods between the Bz (IMF) and Bx component of the geomagnetic field observed also were ≤4 h, with 62.9 % of the periods. Thus the magnetotail responds stronger to IMF fluctuations during HILDCCAS at 2–4 h scales, which are typical substorm periods. The results obtained in this work show that these scales are the ones on which the coupling of energy is stronger, as well as the modulation of the magnetotail by the solar wind during HILDCAA events.
Highlights
Geomagnetic activity occurs when there are disturbances in the Earth’s magnetosphere caused by an enhanced solarwind–magnetosphere energy transfer
All periods here noted in the geomagnetic Bx component were found in the same range observed by Souza et al (2016) for the most energetic periods found in the interplanetary magnetic field (IMF) Bz component, using 52 HILDCAAs that occurred between 1995 and 2011
The main goal of this paper was to identify the main periods of HILDCAA events in the magnetotail, as well as to find the major periods of energy transfer from solar wind to the magnetotail and from the magnetotail to the auroral region
Summary
Geomagnetic activity occurs when there are disturbances in the Earth’s magnetosphere caused by an enhanced solarwind–magnetosphere energy transfer. HILDCAA event is a kind of auroral activity and its cause is associated with the southward interplanetary magnetic field (IMF) Bz component of Alfvén waves (Tsurutani and Gonzalez, 1987; Tsurutani et al, 2004). These events are defined by four criteria: (i) the AE index has to attain at least one peak value ≥ 1000 nT, (ii) the event must last for a minimum of 2 d, (iii) the AE index cannot drop below 200 nT for more than 2 h at a time, and (iv) the event cannot occur during the main phase of a geomagnetic storm (Dst < −50 nT). During HILDCAA events the auroras are weak or moderate, distributed in the whole auroral zone and can last several days, while during substorms, auroras are confined in small regions and last only 15 min (Guarnieri, 2006)
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