Magnetic reconnection is a universal plasma process that converts magnetic energy into plasma jetting and plasma (thermal and suprathermal) heating. The process is important in many space and laboratory contexts. While plasma jetting is well established, both theoretically and observationally, the mechanisms whereby bulk (thermal) plasma heating occurs in a collisionless plasma remain poorly understood. Since such heating is an important aspect of the overall reconnection process, there is a need to explore its sources and manifestations in detail. The proposed ISSI Team will use a combination of plasma simulations and in-situ spacecraft observations over a range of plasma conditions to systematically study bulk ion and electron heating. Specifically, we will focus on the following key unanswered questions:
(1) What plasma parameter regimes or inflow boundary conditions determine the degree of ion and electron thermal heating in reconnection exhausts?
(2) What are the characteristics (e.g., anisotropy and spatial profiles) of the ion and electron thermal heating and how do they change with inflow conditions?
(3) Where are the key heating sites for ions and electrons? What is the nature of the exhaust boundaries for different inflow boundary conditions?
These science squestions will be addressed using already established Wind, ACE, STEREO, THEMIS/ARTEMIS, Geotail, and Cluster data sets of reconnection exhausts detected in different regions of near-Earth space (the solar wind, magnetosheath, magnetopause and magnetotail), which offer a large range of parameter regimes and boundary conditions, together with a series of kinetic plasma simulations covering a wide range of plasma parameters in the inflow regions. We have assembled a team of theoreticians, plasma simulators, experimentalists and data analysts from 5 countries, with complementary expertise to tackle the proposed focused science questions. The systematic nature of the study should ultimately lead to the determination of the key physics controlling bulk ion and electron heating in reconnection. The findings from the proposed investigations should be general and will be relevant to all space and astrophysical plasmas where reconnection occurs.