Global structure of magnetotail reconnection revealed by mining space
magnetometer data
Abstract
Reconnection in the magnetotail occurs along so-called X-lines, where
magnetic field lines tear and detach from plasma on microscopic spatial
scales (comparable to particle gyroradii). In 2017–2020 the
Magnetospheric MultiScale (MMS) mission detected X-lines in the
magnetotail enabling their investigation on local scales. However, the
global structure and evolution of these X-lines, critical for
understanding their formation and total energy conversion mechanisms,
remained virtually unknown because of the intrinsically local nature of
observations and the extreme sparsity of concurrent data. Here we show
that mining a multi-mission archive of space magnetometer data collected
over the last 25+ years and then fitting a magnetic field representation
modeled using flexible basis-functions, faithfully reconstructs the
global pattern of X-lines; 24 of the 26 modeled X-lines match
($B_z=0$ isocontours are within $\sim2$ Earth radii
or $R_E$) or nearly match ($B_z=2$ nT isocontours are within
$\sim2 R_E$) the locations of the MMS encountered
reconnection sites.