Energy Flux Densities at Dipolarization Fronts.

Dipolarization fronts (DFs) have been suggested as crucial energy conversion sites contributing significantly to global energy transfer in the magnetosphere. However, energy partitioning of DF‐driven energy transfer remains hitherto elusive. Using high‐cadence data from MMS spacecraft, we present a detailed investigation of energy flux densities at two DFs with/without surface ripples. We find that during both DF intervals, electron enthalpy flux increases dramatically, carries the greatest energy, and well correlates with local energy conversion. Poynting flux also increases but contributes to a relatively smaller portion. Ion enthalpy flux which in magnitude is slightly smaller than electron enthalpy flux barely changes. Particle kinetic energy and heat fluxes are negligible. Strong difference in energy fluxes observed by different spacecraft is found at the rippled DF, indicating three‐dimensional energy transport. These results indicate that energy budgets at the DFs are dominated by electron physics, rather than ion dynamics suggested by previous studies. Plain Language Summary: Dipolarization fronts, earthward‐propagating transient magnetic structures, have been well documented to be crucial energy conversion sites contributing significantly to global energy transfer in the magnetosphere. However, owing to the limited capacity of previous spacecraft measurements, energy partition of energy transfer driven by the fronts remains not well understood so far. In this study, taking advantage of high‐resolution measurements from MMS which measure particle velocity distributions orders of magnitude faster than previous spacecraft, we present the first in‐situ investigation of energy flux densities at the fronts in the magnetotail. We reveal that energy budgets at the fronts are dominated by electron enthalpy flux and redistributed by electron flow moving along front ripples. Key Points: Electron enthalpy and Poynting fluxes carry the greatest energy and well correlate with local energy conversionIon energy flux which in magnitude is slightly smaller than electron energy flux barely changes across the frontsEnergy transport becomes three‐dimensional due to rippling effect induced by front surface waves [ABSTRACT FROM AUTHOR]