Reconstructing Substorms via Historical Data Mining: Is It Really Feasible?

The evolution of the low-latitude magnetosphere over the substorm cycle is reconstructed based on a new high-resolution 3D representation of the magnetic field and nearest-neighbor data mining. The study covers radial distances 2.5-25RE and employs a record-large pool of spacecraft data taken during 1995-2019. The magnetospheric state is quantified by four indices, representing the ground geomagnetic activity and its temporal trends in the entire +/- 90 degrees range of geomagnetic latitude: the SuperMAG SMR, the midlatitude positive bay MPB, the auroral SML, and the polar cap PC index. The developed technique has been tested on specific substorm events, with the results presented in the form of 5-min cadence diagrams and animations of the magnetic field line configurations and electric current distributions. In all the analyzed events, the initial intensification and radial expansion of the inner tail current is accompanied by a gradual stretching of the magnetic field, followed by its sudden collapse, dramatic depletion of the current beyond R similar to 12RE, and a large-scale dipolarization of the field around the time of MPB peak, after which the system recovers and tends to its pre-substorm state.