Dayside Science: Solar Wind Plasma Entry into the Magnetosphere

During the first year of the mission, IMAGE will spend roughly 2 months exploring the dayside magnetosphere, with spacecraft apogee shifting steadily from low to middle latitudes.* The main focus of the science investigation during this phase of the mission will be on the entry of solar wind/magnetosheath plasma into the magnetosphere.

It is generally accepted that the principal mechanism for the bulk entry of solar wind plasma is the interconnection of the Earth's magnetic field with the interplanetary magnetic field (IMF), a process known as magnetic merging or reconnection. According to the "open model" of the magnetosphere, the primary sites of entry are the polar cusps, bundles of recently merged or "opened" field lines that enter the polar ionosphere in each hemisphere in a narrow region centered on local noon and located an average of 15 degrees equatorward of the magnetic pole. Through radio sounding of density enhancements in the northern hemisphere cusp, RPI will map the precipitation of magnetosheath plasma from the magnetopause down to the ionospheric footprint of the cusp, as imaged with FUV. If the density of the cusp plasma population is high enough, MENA will provide complementary imaging of cusp ions with energies above 1 keV.

The nature of the density enhancements (whether continuous or discrete) observed in the cusp and of the auroral emissions associated with the cusp footprint will reveal whether merging and the injection of magnetosheath plasma into the cusp are occurring in a quasi-steady or pulsed fashion. It will then be possible to study the conditions under which the two forms of merging occur and assess their relative importance in the transport of solar wind/magnetosheath plasma into the magnetosphere.

Other phenomena that IMAGE will investigate during the dayside science phase of the mission include

  • "erosion" of the magnetopause and the resulting equatorward motion of the cusp as a result of magnetic reconnection (RPI, MENA, FUV)

  • the structure of the low-latitude boundary layer (LLBL) and magnetopause: RPI measurements of the density profile of the LLBL and magnetopause will provide information about the role of diffusive processes--as opposed to merging--in plasma entry.

  • magnetopause and LLBL dynamics: the role of waves and instabilities in the generation and maintenance of magnetopause/boundary layer structure (RPI)

*During this phase of the mission, the spacecraft will make its closest approach to the magnetopause, and, if the magnetopause is strongly compressed because of an increase in solar wind dynamic pressure, may even pass through it into the magnetosheath. Such encounters with the magnetopause would provide an opportunity for ground-truth testing of RPI radio sounding measurements--for example, by making it possible to compare RPI local density measurements within the magnetopause and the LLBL with density profiles determined remotely from radio sounding.

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