Investigation of the source region of ionospheric oxygen outflow in the cleft/cusp using multi-spacecraft observations by CIS onboard Cluster - Bogdanova, Y.V.; Klecker, B.; Paschmann, G.; Kistler, L.M.; Mouikis, C.; Moebius, E.; Rème, H.; Bosqued, J.M.; Dandouras, I.; Sauvaud, J.A.; Cornilleau-Wehrlin, N.; Laakso, H.; et al. (Advances in Space Research, 2004)