Data from the NASA Magnetospheric Multiscale (MMS) mission are used to
investigate asymmetric magnetic reconnection at the dayside boundary between
the Earth's magnetosphere and the solar wind (the magnetopause).
High-resolution measurements of plasmas, electric and magnetic fields, and
waves are used to identify highly localized (~15 electron Debye lengths)
standing wave structures with large electric-field amplitudes (up to 100 mV/m).
These wave structures are associated with spatially oscillatory dissipation,
which appears as alternatingly positive and negative values of J dot E
(dissipation). For small guide magnetic fields the wave structures occur in the
electron stagnation region at the magnetosphere edge of the EDR. For larger
guide fields the structures also occur near the reconnection x-line. This
difference is explained in terms of channels for the out-of-plane current
(agyrotropic electrons at the stagnation point and guide-field-aligned
electrons at the x-line).