Magnetic reconnection is a fundamental physical process in plasmas whereby stored 40 magnetic energy is converted into heat and kinetic energy of charged particles. 41Reconnection occurs in many astrophysical plasma environments and in laboratory 42 plasmas. Using very high time resolution measurements, NASA's Magnetospheric 43 2 Multiscale Mission (MMS) has found direct evidence for electron demagnetization and 44 acceleration at sites along the sunward boundary of Earth's magnetosphere where the 45 interplanetary magnetic field reconnects with the terrestrial magnetic field. We have (i) 46 observed the conversion of magnetic energy to particle energy, (ii) measured the electric 47 field and current, which together cause the dissipation of magnetic energy, and (iii) 48identified the electron population that carries the current as a result of demagnetization 49 and acceleration within the reconnection diffusion/dissipation region. 50 51 Introduction 52

The success of the Magnetospheric Multiscale mission depends on the accurate measurement of the magnetic field on all four spacecraft. To ensure this success, two independently designed and built fluxgate magnetometers were developed, avoiding single-point failures. The magnetometers were dubbed the digital fluxgate (DFG), which uses an ASIC implementation and was supplied by the Space Research Institute of the Austrian Academy of Sciences and the analogue magnetometer (AFG) with a more traditional circuit board design supplied by the

Data acquired by the Fast Auroral Snapshot (FAST) Small Explorer during the 24–25 September 1998 geomagnetic storm have been used to determine the controlling parameters for ionospheric outflows. The data were restricted to dayside magnetic local times. Two primary sources of ion outflows are considered: ion heating through dissipation of downward Poynting flux and electron heating through soft electron precipitation. Ion outflows are shown to be correlated with both, although ion outflows have a higher correlation with soft electrons, measured by the density of precipitating electrons. At 4000 km altitude it is found that fi = 1.022 × 109±0.341nep2.200±0.489, where fi is the ion flux in cm−2 s−1 and nep is precipitating electron density, with a correlation coefficient r = 0.855, based on log‐log regression. This scaling law can be mapped to other altitudes by scaling the flux and density with the magnetic field magnitude. The ion flux is also correlated with the Poynting flux, fi = 2.142 × 107±0.242S1.265±0.445, where S is the Poynting flux at 4000 km altitude in mW m−2 and r = 0.721. Either of these two scaling laws can be used specify ion outflow fluxes, since there is a strong intercorrelation between the various parameters. In particular the present study cannot completely eliminate either of the two candidate processes (ion versus electron heating in the ionosphere, corresponding to Poynting flux versus soft electron precipitation). Soft electron precipitation does have a higher correlation coefficient, however, and if possible the precipitating electron density scaling law should be used. Since Poynting flux may be more easily specified in global simulations, for example, this scaling law is a useful alternate. For the interval under study the ion outflows were dominated by oxygen ions, predominantly in the form of ion conics, with a characteristic energy of order 10–30 eV.

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