On the Existence of Subsonic Solitary Waves Associated with Reconnection Jets in Earth’s Magnetotail

Abstract

The Magnetospheric Multiscale Spacecraft (MMS) has detected the signature of electrostatic solitary waves (ESWs) occurring in the reconnection jet site of the Earth’s magnetotail (Liu et al.). These observations have motivated us to explore the mechanism underlying the formation of fast- and slow-mode ion-acoustic solitary waves in the magnetotail region. To this end, we have formulated a three-component magnetized plasma model consisting of nonthermal electrons and two cold ion beams streaming parallel and antiparallel to the magnetic field, respectively. In this work, we have examined the existence conditions for ion-acoustic subsonic waves in a suprathermal space plasma comprising two counterstreaming (drifting) ion beams interacting with a suprathermal electron background. An exact (nonperturbative) nonlinear technique has been adopted to examine the role of the beam velocity and the spectral index on the evolution of subsonic waves. Linear analysis reveals that subsonic waves are unstable when the beam velocity is lower than a threshold value; hence in this regime, only conventional supersonic (fast) waves are formed. On the other hand, when the beam velocity exceeds the threshold, either supersonic or subsonic waves may exist. The combined impact of the beam velocity and electron superthermality on the characteristics of subsonic solitary waves has been analyzed. Our results are shown to be in good agreement with observations of slow ESWs by the MMS spacecraft. Our findings will help to unfold the so-far unexplored dynamical characteristics of subsonic waves that may occur in the reconnection site of Earth’s magnetotail.

Evolution of Subsonic Shock Waves Associated with Reconnection Jets in Earth’s Magnetotail

“…The findings of this investigation should help elucidate themostly unexplored-characteristics of subsonic shock waves observed in the magnetosphere. Our investigation establishes the possible occurrence of subsonic shocks inside reconnection jets of Earth's magnetosphere (Liu et al 2019;Lakhina et al 2021;Singh et al 2023), based on observations by Liu et al (2019).…”

“…A short algebraic calculation reveals that there is a threshold value in the beam velocity above which subsonic IA waves exist, while the interval below is an unstable region. This was discussed in recent work by Singh et al (2023; see Figures 1-3 therein).…”

“…Notice that coefficients A and B are both negative in this case (while C > 0), which prescribes positive values of Φ m , but negative Δ and negative  (see the definitions above). Note that slow IA shocks only occur for values of the beam velocity exceeding a certain threshold value, as discussed in Singh et al (2023). The phase speed increases for higher beam speed (value), and also for larger electron spectral index (kappa).…”

“…The kappa distribution was initially introduced by Vasyliunas (1968) as a heuristic model to interpret data from OGO 1 and OGO 3 spacecraft within Earth's magnetosphere. Subsequently, kappa-type (non-Maxwellian) distribution functions have been applied to characterize suprathermal particle populations in the solar wind (Armstrong et al 1983) and in planetary magnetospheres, e.g., Earth's, Saturn's, and Jupiter's (Leubner 1982;Singh et al , 2022Singh et al , 2023Varghese et al 2023).…”

Oblique Electrostatic Solitary and Supersolitary Waves in Earth’s Magnetosheath

“…These observations have motivated plasma physicists to explore the occurrence of ESWs in various space and planetary settings through theoretical models, predominantly relying on the analytical methodology established independently by Sagdeev (1966) and Washimi & Taniuti (1966), corroborated by computer simulations (Kakad et al 2016;Singh et al 2020Singh et al , 2021Singh et al , 2022Singh et al , 2023. ESWs have garnered significant attention in recent years, primarily due to the advent of plasma wave receivers capable of capturing high time resolution waveform data (Huang et al 2016;Wang et al 2023).…”