Distributions of Cool/Dense and Hot/Tenuous Plasma Regions in the Magnetotail Plasma Sheet Depending on Substorm Phases and Solar Wind as Follows From Global Magnetospheric Simulations

Abstract The major driver that controls the dayside merging process and magnetospheric convection is approximated best by combinations like F = VB sin 2 ( θ / 2 ). Under fixed solar wind flow pressure Pd , which controls plasma sheet pressure, the ratio of temperature T and density N (e.g., rTN = T 1/2 / N , which influences the precipitation and auroral currents) can vary by a few orders of magnitude in the plasma sheet, being spatially inhomogeneous and dependent on both solar wind and substorms. To explore these dependences further, we ran two simulations using the global MAGE‐0.75 model available in Community Coordinated Modeling Center, whose inputs have similar alternating interplanetary magnetic field Bz variations, similar magnitudes of F and Pd drivers, and constant but different solar winds. We confirm that slow/cold/dense (or fast/hot/tenuous) solar wind forms cold/dense (or hot/tenuous) plasma sheet, respectively, in the near‐flank regions. Although these solar wind‐induced rTN values differ in two simulations by a factor of ∼12, their substorm sequences as well as peak values of global magnetotail variables (polar cap potential, open magnetic flux, and lobe magnetic field) are very similar. Substorms strongly modify the rTN distribution in the mid‐ and near‐tail. During substorm expansion and recovery phases, the reconnection‐related fast flows produce a high‐ rTN region in the central tail sector, which supplies the inner magnetosphere with tenuous and heated plasma. Different from that, during the growth phase, enhanced 3D sunward convection in the inner tail caused by dayside merging intensifies the replacement of previously heated plasma by the cold dense plasma from surrounding regions, tending to smear out large rTN differences across the mid‐tail. This often occurs in association with strong Bz depletion and severe current sheet thinning in the near‐tail, which both can be a consequence of magnetic flux removal toward the dayside as described by Hsieh and Otto's (2014, https://doi.org/10.1002/2013ja019459 ) scenario.