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تسجيل مستخدم جديدElectrostatic solitary waves in the Earths bow shock: nature, properties, lifetimes and origin
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We present a statistical analysis of more than two thousand bipolar electrostatic solitary waves (ESW) collected from ten quasi-perpendicular Earths bow shock crossings by Magnetospheric Multiscale spacecraft. We developed and implemented a correction procedure for reconstruction of actual electric fields, velocities, and other properties of ESW from measurements, whose spatial scales are typically comparable with or smaller than spatial distance between voltage-sensitive probes. We determined the optimal ratio between frequency response factors of axial and spin plane antennas to be around 1.65/1.8. We found that more than 95% of the ESW in the Earths bow shock are of negative polarity and present an in depth analysis of properties of these ESW. They have spatial scales of about 10--100 m that is within a range of $lambda_{D}$ to $10lambda_{D}$, amplitudes typically below a few Volts that is below 0.1 of local electron temperature, and velocities below a few hundreds km/s in spacecraft and plasma rest frames that is on the order of local ion-acoustic speed. The spatial scales of ESW are distinctly correlated with local Debye length $lambda_{D}$. ESW with amplitudes of 5--30 V or 0.1--0.3 Te have the occurrence rate of a few percent. The ESW have electric fields generally oblique to local magnetic field and propagate highly oblique to shock normal ${bf N}$; more than 80% of ESW propagate within 30$^{circ}$ of the shock plane. In the shock plane, ESW typically propagate within a few tens of degrees of local magnetic field projection ${bf B}_{rm LM}$ onto the shock plane and preferentially opposite to ${bf N}times {bf B}_{rm LM}$. We argue that the ESW of negative polarity are ion phase space holes produced in a nonlinear stage of ion-ion ion-streaming instabilities. We estimated lifetimes of the ion holes to be 10--100 ms, or 1--10 km in terms of spatial distance.
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