What I learned from auroral substorms

Abstract:

Since the CCMD is a Chapman Conference, I will a few remarks about Chapman’s research life which is closely related my study of auroral substorms. Chapman asked me to find a way by which the solar wind energy

enters the magnetosphere to cause geomagnetic storms. Since I did not know much about geomagnetic storms at that time, I wanted to examine, to begin with, a large number of magnetic and auroral records. I soon found that there must be something else in the solar wind other than protons and electrons. This “unknown quantity” was found to be the Bz component (Fairfield). This study eventually led me to the power ε of the solar wind-magnetosphere dynamo; the magnetosphere responds to ε when it exceeds 10¹⁸ erg/s. Then, I studied the storm of February 11, the greatest geomagnetic storm and aurora in the last century and found that an explosive auroral activity repeated five times during the storm. Each activity is the auroral substorm which I had been studying in parallel with geomagnetic storm in 1964. The year 1964 was an interesting year because the magnetotail was discovered by Ness, and Petschek proposed a theory of magnetic reconnection. In 1967, I met Alfven for the first time during a conference in Norway. He greatly emphasized to me that I should take the “current lines” approach as “the second approach to cosmical electrodynamics”, instead of “magnetic field lines” approach. For this purpose, with a collaboration of a number of colleagues, we set up a excellent magnetometer network. From this long-time effect (1970-2013), we learned that the magnetosphere cannot hold energy of more than 10²³ ergs and tries to stabilize itself by unloading it with a rate 5x10¹⁸ erg/s (which is manifested as the expansion phase of auroral substorms), so that the explosive auroral activity lasts only for about one hour as observed.