Evidence of Diffusion Regions at a Subsolar Magnetopause Crossing

On 1 April 2001, the Polar satellite crossed a subsolar magnetopause associated with antiparallel magnetic fields. Over a width ∼6 magnetosheath ion skin depths ( ∼3 magnetospheric ion skin depths), perpendicular ion flows different from E×B/B² as well as Hall magnetic and electric field signatures were observed. At a smaller scale, the electron flow decoupled from the magnetic field near a deep minimum in the magnetic field strength. Separatrices were identified as boundaries of low frequency electric field turbulence associated with density minima and parallel electric fields. The reconnection rate was less than 2% of the asymptotic Alfvén speed.