Spatio‐temporal entropy analysis of the magnetic field to help magnetic cloud characterization

Abstract

[1] The aim of this work is to create a methodology to characterize the dynamics of magnetic clouds (MCs) from signals measured by satellites in the interplanetary medium. We have tested spatio-temporal entropy (STE) technique to study 41 MCs identified by other authors, where the plasma sheath region has been identified. The STE was implemented in Visual Recurrence Analysis software to quantify the order in the recurrence plot. Some tests using synthetic time series were performed to validate the method. In particular, we worked with interplanetary magnetic field (IMF) components B x , B y , B z of 16 s. Time windows from March 1998 to December 2003 for some MCs were selected. We found higher STE values in the sheaths and 0 STE values in some of the three components in most of the MCs (30 among 41 events). The trend is the principal cause of the lower STE values in the MCs. Also, MCs have magnetic field more structured than sheath and quiet solar wind. We have done a test considering the magnetic components of a cylindrically symmetric force-free field constructed analytically, with the result of 0 STE value. It agrees with the physical assumption of finding 0 STE values when studying experimental data in MC periods. The new feature just examined here adds to the usual features, as described in Burlaga et al. (1981), for the characterization of MCs. The STE calculation can be an auxiliary objective tool to identify flux ropes associated with MCs, mainly during events with no available plasma data but only with IMF.

Nonlinear fluctuation analysis for a set of 41 magnetic clouds measured by the Advanced Composition Explorer (ACE) spacecraft

“…However, in the previous figures, there is a pattern in the persistence values between all MC events. We believe that these results are valid, because we know that MCs are organized structures in the plasma (Ojeda et al, 2005(Ojeda et al, , 2013) that have an increase of "memory" in the time series.…”

“…It is possible to see anisotropy of magnetic field fluctuations in an average interplanetary MC at 1 AU (Narock and Lepping, 2007;Ojeda et al, 2013Ojeda et al, , 2014. We do not expect to find the same behavior in all three components by the existence of anisotropy.…”

“…The four techniques explained previously are used in this work. Some models were tested to successfully reconstruct the magnetic structure of MCs (Dasso et al, 2005;Ojeda et al, 2013), which implies that a memory exists in the time series of IMF. We hypothesize that the magnetic field inside these structures has greater persistence than ambient solar wind.…”

“…We work with 41 of 80 events (73 MCs and 7 cloud candidates) identified by Huttunen et al (2005). These events in chronological order are shown in Table 1 ((see more details in Ojeda et al, 2013Ojeda et al, , 2014, where the same data set was studied with other techniques: the spatio-temporal entropy and discrete wavelet transform). The columns from the left to the right give a numeration of the events, year, shock time (UT), MC start time (UT), MC end time (UT), and the end time (UT) of the third region, respectively.…”

“…The important subset of ICMEs, known as interplanetary magnetic clouds (MCs), a term introduced by Burlaga et al (1981), is characterized fundamentally by enhanced magnetic field strengths with respect to solar wind ambient values (Klein and Burlaga, 1982;Burlaga, 1991). A comprehensive study about the properties of MCs at 1 astronomical unit (AU) was approached by Ojeda et al (2013Ojeda et al ( , 2014 and Klausner et al (2014).…”