Towards a Full Understanding of Magnetic Storms and Substorms

For the discipline of Space Physics, there are two outstanding topics that evade resolution in spite of decades/centuries of dedicated research: magnetic storms and substorms. The space phenomenon called magnetic storm, alternatively known as a geomagnetic storm, was first reported in the 19th century by Alexander von Humboldt. He made recordings on the bearing of a magnetic compass in Berlin from May 1806 to June 1807. With this effort, he revealed a notable erratic deflection of the compass bearing on 21 December 1806. Later scientific investigation using the magnetic disturbances on the ground led to the introduction of three phases of a geomagnetic storm: initial, main, and recovery phase. The three phases are generally marked by worldwide systematic variations of the horizontal component of the Earth's magnetic field. However, deviations from this systematic variation can occur for some geomagnetic storms with apparent absence of the initial phase. Geomagnetic storms generally last for 2 to 3 days. Embedded within a geomagnetic storm, the shorter-duration geomagnetic disturbances are most evident at the high-latitude region. Nature reveals this association even with the first awareness of geomagnetic storm as Alexander von Humbolt noted bright auroral displays accompanying the erratic deflection of a compass bearing.

Through the establishment of global networks of all-sky-cameras to monitor the worldwide distribution of auroras, Syun-Ichi Akasofu in 1984 recognized a unique and identifiable sequence of auroral displays called auroral substorms. The latter indicates that each one of these disturbances constitute an elementary building block of a geomagnetic storm. Subsequent research revealed that auroral substorms are merely one of the facets of disturbances that span over a vast volume of space.

The rather simplistic view of activities in space is now challenged in many ways. Progress in space research equipped with highly-sophisticated instrumentations on the ground and in space has blossomed into a discipline that has close ties with daily human activities as witnessed by space weather development and significant implications on the physical processes responsible for implosive phenomena in our Universe. Although there are many theories proposed for both geomagnetic storms and substorms, there is yet no consensus on their underlying physical processes. This Research Topic aims to reflect on the present status of space research and contemplate how to achieve a full understanding of these natural phenomena.