Waves and Instabilities in Saturn's Magnetosheath: 1 Mirror Mode Waves and Their Impact on Magnetopause Reconnection

Abstract

A comprehensive catalog of 1,589 Saturn magnetosheath traversals by Cassini between 2004and 2012 was used to perform a statistical study of mirror mode (MM) waves and assess their role ininfluencing magnetic reconnection at the magnetopause (MP). MM waves have been observed in manyplanetary magnetospheres and magnetosheaths, comets and the solar wind. Understanding the conditionsunder which they grow and dominate can reveal their role in influencing plasma dynamics. Using athresholding method on both magnetic field and plasma data, MM wave candidates can be identified. Themagnetic field characteristics and occurrence distributions of these waves against different locations andconditions were found. MM waves were found from 4 to 19 hr local time (partly due to data coverage), anddistances of 0–12 RS from the magnetopause (MP). The occurrence of MM dips was more frequent near theMP and magnetosheath flanks, analogous to the Jovian system. MM dips exhibited a minimum field strengthsaturation ∼0.5 nT, with the largest dip inferred to be in mirror‐stable plasma. Notably, larger amplitude MMdips were typically found nearer the MP boundary which increases Δβ across the boundary thus increasing themagnetic shear necessary for the onset of MP reconnection. Thus, MM waves may be important in plasmadynamics near Saturn's magnetopause.