Study Of The Energy Budget During Isolated Auroral Substorms

The solar atmosphere permanently releases ionized material forming the solar wind, which carries the frozen-in interplanetary magnetic field (IMF). When the solar wind reaches the space environment of the Earth, the IMF and the geomagnetic field can reconfigure their topology in the process of magnetic reconnection. Geomagnetic field lines are therefore opened by the interplanetary medium and dragged anti-sunward by the solar wind flow, which gives the Earth magnetosphere an elongated shape. This process results in the accumulation of open magnetic flux and energy in the geomagnetic tail. Eventually, when a significant amount of open magnetic flux has been accumulated and convected downtail, intense magnetic reconnection also occurs inside of the magnetotail, in the central plasma sheet, and the magnetic field lines return to a closed configuration, which reduces the amount of open magnetic flux. This flux closure process releases a significant amount of energy often estimated to be of the order 10^15 - 10^16 J stored in the tail, which can trigger auroral substorms, as a result of the solar wind - magnetosphere interaction. The released energy is distributed between the ionosphere, the ring current, the plasma sheet, and the formation of a plasmoid. In this work, we combine data from the ESA Cluster and the NASA IMAGE spacecraft to investigate three reconnection events occurring in 2001. We compare in-situ measurement from Cluster and auroral FUV imaging from IMAGE complemented by SuperDARN radar measurement of the ionospheric convection. The auroral hemispheric power is computed using the IMAGE-FUV images of the electron and proton aurora. The amount of open geomagnetic flux is estimated using the imaging of the proton aurora and the magnetic reconnection rates are derived from both missions and the SuperDARN data. We analyze the energy circulation by assessing the energy conversion and dissipation for each individual process during different substorm periods. We compare the hemispheric power, open magnetic flux and reconnection rates and search for a possible relation between them.