Interpretation of non-conventional coherent structures in magnetospheric plasma system

Abstract

One of the natural laboratory for the study of solitary waves is the Earth’s magnetosphere. The large gradient in particle properites at the magnetospheric boundary layers initiate the perturbation which leads to the generation of solitary waves. These structures propagate either parallel or perpendicular to the local magnetic field. The E-field bipolar structures moving parallel to the background magnetic field (Electrostatic Solitary Waves (ESWs)) are observed ubiquitously in different magnetospheric boundary regions. The satellite electric borne instruments recorded the signatures of ESWs as bipolar (two half sinusoids of opposite polarity), monopolar (one half sinusoid) and tripolar (two half sinusoids of one polarity with an intervening half sinusoid of opposite polarity) pulses in the Electric Field (E-field) data. High resolution satellite borne instruments, however, identified more kinds of composite and complex organized structures such as offset bipolar pulse (ofbp) (Fig. 1 (a)) [1, 2, 3], paired monopolar pulse (mpp) (Fig. 1 (b)) [1] and wiggled bipolar (Fig. 1 (c)) [4] E-field structures. For both an ofbp and an mpp, the distance between the two peaks are relatively large compared to the characteristic width of the each peak. The fine difference between an ofbp and mpp lies in the finite slope of the E-field connecting the two lobes for the former. An mpp, on the other hand, is a pair of two simple monopoles with opposite polarities while the slope of the electric field connecting the two poles goes ideally to zero. In case of wiggled bipolar pulses, it is characterized in having subsidiary peak in both positive and negative lobes of a smooth bipolar pulse.