Abstract
Magnetotail reconnection plays a crucial role in explosive energy conversion in geospace. Because of the lack of in-situ spacecraft observations, the onset mechanism of magnetotail reconnection, however, has been controversial for decades. The key question is whether magnetotail reconnection is externally driven to occur first on electron scales or spontaneously arising from an unstable configuration on ion scales. Here, we show, using spacecraft observations and particle-in-cell (PIC) simulations, that magnetotail reconnection starts from electron reconnection in the presence of a strong external driver. Our PIC simulations show that this electron reconnection then develops into ion reconnection. These results provide direct evidence for magnetotail reconnection onset caused by electron kinetics with a strong external driver.
Highlights
Magnetotail reconnection plays a crucial role in explosive energy conversion in geospace
The magnetotail current sheet is usually in the equatorial (x–y) plane, and its normal is in the z direction in the geocentric solar ecliptic (GSE) coordinate systems
The current sheet observed in the Magnetospheric Multiscale (MMS) event, is unusual—it is almost in the x–z plane (its normal N = (−0.3076, 0.9506, −0.0408) is almost in the y direction in the GSE coordinate system, see “Local coordinate system for the MMS event” in “Methods”)
Summary
Magnetotail reconnection plays a crucial role in explosive energy conversion in geospace. We show, using spacecraft observations and particle-in-cell (PIC) simulations, that magnetotail reconnection starts from electron reconnection in the presence of a strong external driver. Our PIC simulations show that this electron reconnection develops into ion reconnection These results provide direct evidence for magnetotail reconnection onset caused by electron kinetics with a strong external driver. We report detection of electron reconnection in the magnetotail using high-resolution measurements by the Magnetospheric Multiscale (MMS) spacecraft[29], and further analysis shows that the electron reconnection does occur within a strongly externally driven environment, which provides experimental evidence for the onset of magnetotail reconnection caused by electron kinetics with a strong external driver
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