Dynamics of the substorm growth phase as observed using CANOPUS and SuperDARN instruments

Abstract

The substorm growth phase in four substorm events was studied using ground‐based observations from the Canadian Open Unified Study (CANOPUS) array of meridian scanning photometers and magnetometers, the Gillam all‐sky camera, and two Canadian Super Dual Auroral Radar Network (SuperDARN) radars. The following common features were revealed: A proton aurora that has a latitudinal width of ∼2° moves equatorward remaining near the equatorward boundary of the intense electron precipitation zone. The proton aurora intensifies during the growth phase toward the onset of the substorm intensification. The latitudinal width of the electron precipitation region narrows during the growth phase reaching 2°–5° of latitudinal width just before the substorm intensification, which indicates significant stretching of magnetic field lines and thinning of the plasma sheet. At the beginning of the growth phase, convection is intensified near the proton aurora band, forming a flow with a large‐amplitude westward component. This enhanced westward component of the convection is in agreement with magnetometer observations of the increased eastward electrojet in this region. The maximum of the flow moves equatorward following the proton aurora band. Prior to substorm intensification, the convective flow develops significant latitudinal gradients. All‐sky images available for one event indicate that just before a substorm intensification, a large auroral vortex develops from an auroral arc imbedded in the proton aurora region and then intensifies. These observational constraints are discussed with respect to a possible mechanism which can lead to a large scale auroral vortex at substorm intensification.