Analysis of the step response function relating the interplanetary electric field to the dayside magnetospheric reconnection potential

We present a statistical analysis of the response of the magnetic reconnection rate between the interplanetary magnetic field and the magnetosphere to southward turnings of the interplanetary magnetic field. The magnetic reconnection rate is calculated from Super Dual Auroral Radar Network (SuperDARN) measurements. The polar cap boundary is identified as the offset circle (3° toward midnight from the magnetic pole) that best separates high spectral width backscatter, indicative of open magnetic field lines, from low spectral width backscatter. The electric potential on the boundary is determined from the best fit of the line‐of‐sight F region plasma velocity to an eighth‐order spherical harmonic function of ionospheric electrical potential. The reconnection rate is determined from the electric potential on the boundary and the expansion rate of the polar cap. Solar wind data (velocity and magnetic field) are obtained from Wind spacecraft measurements and propagated to the magnetopause. The relationship between interplanetary electric field and the magnetic reconnection rate is analyzed by calculating linear response functions. We determine that the convection term in the reconnection rate measurement exhibits a unimodal response to the interplanetary electric field, whereas the boundary motion term in the reconnection rate measurement exhibits a bimodal response, with a positive mode (increase in polar cap expansion rate) followed by a negative mode. The response of the dayside reconnection rate to a step change in the interplanetary electric field exhibits a transient response of one hour duration followed by a steady state response at a level that is half of the peak response.