Observations and simulations of asymmetric magneticfield reconnection

摘要

[1] Comparisons of asymmetric magnetic field reconnection at the subsolarmagnetopause are made between satellite data and computer simulations for the ratio ofthe antiparallel components of the magnetic fields at the boundaries being about threeand the density ratio being 10 to 30. The bipolar electric field and quadrupolarmagnetic field of symmetric reconnection are not found in either the simulations or theexperimental data because the Hall term in the generalized Ohm's Law (the leadingterm on its right side on the ion scale) is a factor up to 100 smaller on the magnetosheathside of the current layer than on the magnetospheric side. Average plasma densitiesand fields at six THEMIS magnetopause crossings agree with open simulations providedthat the experimental data is in the joint variance, not minimum variance, frame. Thisis because the magnetic field component normal to the assumed planar current sheet is notconstant for asymmetric reconnection while it is forced to be approximately constantby the mathematics of minimum variance analyses. A north-south asymmetry of the fieldsand flows in asymmetric reconnection is found in both the simulations and the spacemeasurements. The simulations and the satellite data both have regions the order of theelectron skin depth in size that contain significant electric fields. In such structures,parallel electric fields exist in the simulation throughout the current layer. Such parallelfields are similar to those reported earlier from Polar satellite data.