| Summary: | [1] For the large geomagnetic disturbance on April 11, 2001, we combine data from the Millstone Hill radar, a network of GPS TEC receivers, and the DMSP F‐12 and IMAGE satellites, to estimate the sunward flux of thermal plasma associated with erosion of the outer plasmasphere/ionosphere in the dusk sector. Direct radar observations of the E×B advection of SED plasma determine a flux of >10E26 ions/s to the noontime cusp at F‐region heights. DMSP in situ observations provide a similar estimate. Assuming a dipolar magnetic field, we project our low‐altitude observations into the outer plasmasphere, obtaining a total sunward flux of >10E27 ions/s. High‐altitude IMAGE EUV observations of the plasmasphere drainage plume provides an estimate of 1.5 × 10E27 ions/s for the sunward flux. Such rates of sunward plasma transport are sufficient to deplete a 1‐Re shell of the outer plasmasphere in ∼1 hour.
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