Solar Wind Penetration into Dusty Magnetospheres creates Electrostatic Waves and Structures

TL;DR

This study addresses how solar wind penetration into dusty, multi-ion magnetospheric plasmas drives very-low-frequency electrostatic waves and nonlinear structures. By formulating a bi-ion dusty plasma with field-aligned ion shear and stationary dust, the authors derive a nonlinear mKdV/KdV framework and analyze the formation of double layers and solitons via Sagdeev potentials and solitary-pulse solutions. Applying the model to Jupiter’s positively charged-dust magnetosphere and Saturn’s negatively charged-dust environment with O$^{+}$ and H$^{+}$ ions, they predict extremely low wave frequencies in the mHz range, growth rates on minute timescales, and DL widths of several kilometers, with solitons spanning around a kilometer, consistent with scale differences between Earth’s ionosphere and these giant-planet systems. The results illuminate dust-modified drift–ion-acoustic dynamics in large magnetospheres and provide a framework for interpreting spacecraft data and guiding future numerical simulations.

Abstract

The low frequency electrostatic perturbations have been investigated in a bi ion plasma in the background of static dust. It is shown that the field aligned shear flow of both the ions produce low frequency electrostatic instabilities and create nonlinear structures, the double layers and the solitons. The general theoretical model is applied to the magnetospheres of Jupiter (with positively charged dust) and Saturn (with negatively charged dust) which have oxygen ions in addition to protons. This model predicts the existence of extremely low frequency electrostatic waves with real frequencies of the order of a milli Hertz (mHz) to several mHz and this range of frequencies have been reported in literature for these plasma environments. The estimated width of the nonlinear structures vary from a few hundred meters to a few kilometers. These structures are similar to that observed in the oxygen and oxygen hydrogen plasmas in Earth's upper ionosphere which is free from dust.

Figures (12)

• Figure 1: (a) Real part of frequency $\omega_r$ vs $k_z$ is plotted using Eq.\ref{['LDR stat dust']} with varying $n_{d0}$ (b) Imaginary part of frequency $\omega_i$ vs $k_z$ is plotted using Eq.\ref{['LDR stat dust']} with varying $n_{d0}$ where the observed value of $n_{d0}$ corresponds to solid black curve. Other plasma parameters are $z_d=10$, $B_0=0.029259$ G, $T_e=5$ eV, $k_y=9.63982\times 10^{-6}\ \text{cm}^{-1}$, $L_n=2.07473\times 10^6\ \text{cm}$, $S_a=0.001$ and $S_b=0.004$.
• Figure 2: (a) Real part of frequency $\omega_r$ vs $k_z$ is plotted using Eq.\ref{['LDR stat dust']} with varying $z_d$ (b) Imaginary part of frequency $\omega_i$ vs $k_z$ is plotted using Eq.\ref{['LDR stat dust']} with varying $z_d$ where the observed value is $z_d=10$ (represented by the solid black curve).Other plasma parameters are $B_0=0.029259$ G, $n_{d0}=147.87\ \text{cm}^{-3}$, $T_e=5$ eV, $k_y=9.63982\times 10^{-6}\ \text{cm}^{-1}$, $L_n=2.07473\times 10^6\ \text{cm}$, $S_a=0.001$ and $S_b=0.004$.
• Figure 3: (a) Compressive DL normalized potential $\Phi$ vs $\xi$ is plotted by varying Mach number $M$ (b) DL Sagdeev potential profile $\mathcal{S}(\Phi)$ vs $\xi$ is plotted using Eq.\ref{['Sagdeev Pot']} by varying $M$. Other parameters are $B_0=0.029259$ G, $T_e=5$ eV, $n_{d0}=147.87\ \text{cm}^{-3}$, $S_a=0.1$ and $S_b=0.4$.
• Figure 4: (a) Compressive DL normalized potential $\Phi$ is plotted vs $\xi$ using Eq.\ref{['DL +ive dust']} by varying $n_{d0}$ (b) Sagdeev potential $\mathcal{S}(\Phi)$ vs $\Phi$ is plotted using Eq.\ref{['Sagdeev Pot']} for compressive DL by varying $n_{d0}$. Other parameters are $z_d=10$, $B_0=0.029259$ G, $T_e=5$ eV, $S_a=0.1$, $S_b=0.4$ and $M=0.283$.
• Figure 5: Normalized potential $\Phi$ vs $\xi$ is plotted for a compressive soliton with varying Mach number $M$ using Eq. \ref{['KdV soliton']}. Other parameters are $B_0=0.029259$, $T_e=5$ eV, $n_{d0}=147.87\ \text{cm}^{-3}$, $S_a=0.051$ and $S_b=0.204$.