Variations of solar electron and proton flux in magnetic cloud boundary layers and comparisons with those across the shocks and in the reconnection exhausts

TL;DR

This study investigates how solar electron and proton fluxes vary in magnetic cloud boundary layers, reconnection exhausts, and shocks, revealing energy-dependent signatures that suggest magnetic reconnection is common in boundary layers.

Contribution

It provides the first comparative analysis of particle flux variations in boundary layers, reconnection exhausts, and shocks, highlighting reconnection signatures in boundary layers.

Findings

Proton flux increases more at lower energies in boundary layers.

Electron flux shows energy-dependent anisotropy and correlation changes.

Flux variations suggest reconnection occurs frequently in boundary layers.

Abstract

The Magnetic cloud boundary layer (BL) is a dynamic region formed by the interaction of the magnetic cloud (MC) and the ambient solar wind. In the present study, we comparatively investigate the proton and electron mean flux variations in the BL, in the interplanetary reconnection exhaust (RE) and across the MC-driven shock by using the Wind 3DP and MFI data from 1995 to 2006. In general, the proton flux has higher increments at lower energy bands compared with the ambient solar wind. Inside the BL, the core electron flux increases quasi-isotropically and the increments decrease monotonously with energy from ~30% (at 18 eV) to ~10% (at 70 eV); the suprathermal electron flux usually increases in either parallel or antiparallel direction; the correlation coefficient of electron flux variations in parallel and antiparallel directions changes sharply from ~0.8 below 70 eV to ~0 above 70 eV. Similar results are also found for RE. However, different phenomena are found across the shock where the electron flux variations first increase and then decrease with a peak increment (>200%) near 100 eV. The correlation coefficient of electron flux variations in parallel and antiparallel directions is always around 0.8. The similar behavior of flux variations in BL and RE suggests that reconnection may commonly occur in BL. Our work also implies that the strong energy dependence and direction selectivity of electron flux variations, which are previously thought to have no enough relevance to magnetic reconnection, could be considered as an important signature of solar wind reconnection in the statistical point of view.