Cold dense plasma in the outer magnetosphere

Cold dense plasma (CDP) with energies less than 32 eV in the outer magnetosphere, L ∼ 10, is reported using data obtained by Geotail. We have found unexpectedly recurrent CDP in afternoon magnetic local times. CDP is often accompanied by westward flows, indicating that the regions with CDP are located outside the corotation region and the plasma is presumably convected toward the magnetopause. CDP is observed in the cases of both small and moderate geomagnetic activity. We have calculated the location of the stagnation point as a function of cross‐tail potential by using a Volland‐Stern‐type Volland , 1973; Stern , 1975 convection model. Stagnation point locations are variable even if the cross‐tail potential or geomagnetic activity is small, which could lead to a high rate of the observation of plasmaspheric material at the Geotail orbit. However, part of the cold plasma is directly supplied by the ionosphere without passing through the plasmasphere. The number of supplied particles could be larger on the drift orbits close to the stagnation points. Finally, an average quantity of cold plasma flowing through the Geotail orbit with quasi‐stable westward convection is estimated to be 3.6 × 10 25 ions/s with a standard deviation of 3.7 × 10 25 ions/s, as compared to 9.4 − 14 × 10 25 ions/s for the polar wind toward the plasma sheet.