Electric and Magnetic Field and Plasma Density Measurements During Multiple Dayside Boundary Layer Crossings On Cluster

Cluster observed multiple crossings of the dayside boundary layer on 26.January 2001 when the four spacecraft orbited out between 12 and 13 Earth radii near 15 h local time. The magnetic latitude of Cluster varied between 50 and 44 degrees, which meant that the spacecraft were conjugated with the frontside cusp or cleft at ionospheric al- titudes. The solar wind magnetic field was initially southward and then turned to a steady value in the -Y direction during the boundary layer crossings. Electric and magnetic field measurements and calculated E x B velocities, together with high time resolution plasma density information from spacecraft potential measurements, will be used to describe the boundary layer crossings. Data from near Earth polar orbiting spacecraft and from ground networks will be used to provide complementary infor- mation of the polar and cusp conditions during the Cluster boundary layer crossings.