Joint Control of Substorm Onset by Titan and Saturn

RUSSELL, C. T.; JACKMAN, C. M.; WEI, H. Y.; MA, Y. J.; GE, Y. S.; BERTUCCI, C.; DOUGHERTY, M. K.

Congreso; AGU Fall Meeting 2007; 2007

Terrestrial substorms occur with a sudden release of energy into the night magnetosphere and aurora zone. This energy is ultimately derived from the bulk flow of the solar wind coupled to the magnetosphere via dayside reconnection. Substorms at Jupiter and Saturn are in many respects similar to their terrestrial counterparts except that the energy is supplied from the rotational energy of the planet that is transferred from the ionosphere by field- aligned currents to the ions added to the magnetosphere by ionization of the E-ring and the Titan atmospheres. When the magnetospheric field is no longer able to contain the build up of rotational energy, tail reconnection occurs releasing the "excess" plasma down the tail and returning the magnetosphere to a lower stress state. Menietti and coworkers have reported that SKR is modulated by the phase of Titan in its orbit about Saturn. We examine the phase of Titan during substorms observed by their north-south field changes in the tail and find a strong association with Titan being very close to local midnight. In fact, Titan is usually within one Saturn rotation of midnight when the substorm occurs. This suggests that the periodic stretching of the magnetic field in synchronism with Saturn's rotation is the final factor leading to instability and release of the plasmoid. Thus both Titan and Saturn play a role in controlling the onset of saturnian substorms.