Simultaneous remote sensing and in situ observations of plasmaspheric drainage plumes

Plasmaspheric drainage plumes are regions of dense plasma that extend outward from the plasmasphere into the outer magnetosphere. We present observations of plumes for two events, 2 June 2001 and 26–27 June 2000. Our observations come from two sources. A global perspective is provided by the IMAGE extreme ultraviolet (EUV) imager, which routinely obtains images of the helium portion of the plasmasphere above total densities of 30–50 e− cm−3. Simultaneous in situ observations of plasmaspheric plumes are obtained by the Magnetospheric Plasma Analyzer (MPA) instruments onboard the Los Alamos National Laboratory (LANL) geosynchronous satellites. The in situ measurements of LANL MPA and the remote sensing images of IMAGE EUV are complementary data sets that together provide a more complete picture than either alone. The MPA instruments measure density far below the EUV effective density threshold with greater spatial resolution and often see plasma outside the EUV field of view. Flow speeds are also measurable by MPA. EUV images place the single‐point measurements in a global dynamical context and allow separation of spatial and temporal effects. For the 2 June 2001 and 26–27 June 2000 events, both local and global measurements showed the same location, shape and temporal development of the plume(s), and a density distribution obtained from the EUV image at 0305 UT on 2 June agrees with the LANL MPA density recorded at that time. Analysis of MPA flow data verifies that plume plasma moves sunward, as expected. Sunward flow speeds weaken with decreasing disturbance level, and duskside flow speeds may be increased by the subauroral polarization stream. The fine‐scale density variations within plumes may be caused by a highly structured inner magnetospheric E‐field and/or may be existing plasma structure that is carried sunward. The good agreement between the local and global measurements also validates the EUV image mapping method and promises to help quantify EUV images in terms of number density.