Modelled MHD Instabilities and Magnetic Reconnection at the Mercury's Magnetopause in Preparation for BepiColombo/SERENA Experiment

The ESA/JAXA BepiColombo mission waslaunched successfullyin October 2018 and among its scientific objectives is the investigation of the physical conditions in which magnetic reconnection occurs. Kelvin-Helmholtz waves and magnetic reconnection are believed to be the key drivers of plasma transport and planetary magnetospheres are excellent laboratories to investigate them.In preparation of the scientific phase of BepiColombo, we usedata from MESSENGER crossings of Mercury's dayside magnetopausefor investigating the development of MHD instabilities and connect the intensity of these instabilities with the estimated magnetic reconnection phenomena at Mercury's magnetopause [1,2].Based on a flexible numerical incompressible magnetohydrodynamic (MHD) approach utilised for studying a coupled Kelvin-Helmholtz (KH) and tearing mode (TM) instabilities [3], we investigate the magnetic reconnection rates under the identified high-shear and low-shear IMF conditions in the MESSENGER data [1,2]. We determine a threshold value of the magnetic reconnection rate when the MHD instabilities are present based on the reconnection rates derived from MESSENGER data [1] in case of high-shear (24 November 2011) and low-shear (21 November 2011) magnetopause reconnection. Furthermore, we study in which of the eight Highly Compressed Magnetospheric Events at Mercury analysed in [2], KHTM instabilities could possibly develop. Then we are able to address questions whether MHD instabilities are triggered for low reconnection rate cases, when the size of the magnetosphere is largely controlled by induction effects [2] or this is only valid in case of high reconnection rates when the induction-driven shielding and reconnection-driven erosion seems balance each other. We will also discuss the scientific applicability of this approach to support the scientific objectives and operations of SERENA experiment [4] onboard BepiColombo, providing information on the coupling processes that occur in the Mercury complex system surface-exosphere-magnetosphere.

References [1] DiBraccio et al. 2013, JGR, 118, 997-1008 [2] Jia et al. 2019, JGR Space Physics, https://doi.org/10.1029/2018JA026166 [3] Ivanovski et al.2011, JTAM, vol. 41, No. 3, pp. 31-42 [4] Milillo et al. 2005, SSR.