Articles | Volume 35, issue 3
Regular paper
28 Mar 2017
Regular paper |  | 28 Mar 2017

Magnetic reconnection during steady magnetospheric convection and other magnetospheric modes

Benoit Hubert, Jean-Claude Gérard, Steve E. Milan, and Stanley W. H. Cowley

Abstract. We use remote sensing of the proton aurora with the IMAGE-FUV SI12 (Imager for Magnetopause to Aurora Global Exploration–Far Ultraviolet–Spectrographic Imaging at 121.8 nm) instrument and radar measurements of the ionospheric convection from the SuperDARN (Super Dual Aurora Radar Network) facility to estimate the open magnetic flux in the Earth's magnetosphere and the reconnection rates at the dayside magnetopause and in the magnetotail during intervals of steady magnetospheric convection (SMC). We find that SMC intervals occur with relatively high open magnetic flux (average  ∼  0.745 GWb, standard deviation  ∼  0.16 GWb), which is often found to be nearly steady, when the magnetic flux opening and closure rates approximately balance around 55 kV on average, with a standard deviation of 21 kV. We find that the residence timescale of open magnetic flux, defined as the ratio between the open magnetospheric flux and the flux closure rate, is roughly 4 h during SMCs. Interestingly, this number is approximately what can be deduced from the discussion of the length of the tail published by Dungey (1965), assuming a solar wind speed of  ∼  450 km s−1. We also infer an enhanced convection velocity in the tail, driving open magnetic flux to the nightside reconnection site. We compare our results with previously published studies in order to identify different magnetospheric modes. These are ordered by increasing open magnetic flux and reconnection rate as quiet conditions, SMCs, substorms (with an important overlap between these last two) and sawtooth intervals.

Short summary
Remote sensing of the polar aurora and ionospheric convection is used to characterize the interaction between the solar wind and the Earth magnetosphere during steady magnetospheric convection (SMC) intervals and compare them with other previously studied geomagnetic conditions. It is found that the Earth magnetosphere may exhibit four different coupling modes ordered by increasing open magnetic flux and magnetic reconnection rate: quiet times, SMC, substorm and sawtooth events.