Science Questions What is responsible for the "near" prompt onset of convection in the inner magnetosphere? Fast mode rarefraction wave?. How is the dayside electric field in the inner magnetosphere related to solar wind drivers? Why is the electric field in the inner magnetosphere in the inner magnetosphere often a significant fraction of the Solar Wind dawn dusk field? How do pressure gradients in the inner magetopshere controll the flow of plasma towards the days side? How do perturbations in the solar wind electric field, pressure, and other "controll" dayside convection on rapid time scales (>1 minutes)? These question require "precision"a timiing only possible using measurements from relatively stationary spacecraft on the days side magnetosphere and and also at the magnetopause, magnetosheath, solar wind. Van Allen Probes and MMS provide this unique capablitity

After the spike associated with the shock ramp there is 'prompt" on set of net sunward convection – toward the magnetopause. This onset is more rapid than expected from the "Dungey Cycle". IMF was negative. This is consistent with a scenario of how the change in the\ reconnection rate at the frontside magnetopause is transmitted through out the magnetosphere. MMS at and upsteam of the magnetosphere is a necessary component of a precision study of the changes in reconnecion driving and the response of dayside convection. RBSP B

Reconnection Geometry

Coronitti and Kennel, JGR 1973

E- field (neg) Azimuthal perp to B (Shock Compressional plus Poloidal) E-Field ( neg) Radial perp to B Ttoroidal) B-Field ( neg) Radial perp to B (Poloidal) B- field (neg) Azimuthal perp to B B-Field Parallel to average B Shock Compression) Shock Impact: Compression; Toroidal, Compressional plus MOre Three wave modes are excited by shock impact. Relative Strength governed by where the shock hit and how it propagates to Probe. Plus there is the issue of Fast rarefraction waves inducing sunward convection

Extrapolation orientation of shock fronts from the L1 point or even from the Moon is not accurate Where the shock "piston' hit the magnetopause (east/west/north/south of subsolar point influences which modes compressional, toroidal, poloidal) are excited

First panel is the EFW spin fit (10.5 s) electric field in ~ dawn-dusk direction. This measurement is dominated by waves with amplitudes >32 mV/m ptp during during every storm as indicated by SYM H (third panel). The second panel is the dawn-dusk electric field averaged over 10 minutes from both spacecraft (superposed). This is nomally the convection electric field- but it also includes contributions fromm injection events. Notice the convection electric field is directed preferentially in the positive dawn-dusk direction- the direction of sunward convection. Notice also the convection electric field is often peaks at ~4 mV/m which is very comparable to the magnitude of the "solar wind electric field" (Vx sw x Bz sw). The solar wind electric field and the measured RBSP electric fields are largest during the main phase of geomagnetic storms and smaller during the recovery phase. The bottom panel shows the solar wind flow pressure and Bmag. These typically are enhanced at the beginning of the storm and models indicate thesubsolar magnetopause can move within ~8-9 Re durng the intial phases of the storm when ULF are strong. This may lead to effective radial transport outward and loss of particles throug magnetopause shadowing. Towards the end of the storms, during periods of lower flow pressure, when the estimated position of the magnetopause is outward many storm have large wave electric fields. These are times when relativistic fluxes increase to and often above the pre-storm levels. includes only EFW above 3.2 Re