ALBERT

Description: [1]  Although distant-tail plasmoids are perceived to extend across most of the magnetotail (~40 R E ), recent studies in the near-Earth region (X 〉 -30 R E ) have revealed that near-Earth reconnection (where plasmoids originate) is likely localized and takes place preferentially on the dusk side. This discrepancy in plasmoid azimuthal extent suggests that a plasmoid may grow as it moves from near Earth to the distant tail. Comprehensive multi-point, mid-tail plasmoid observations can be used to test this hypothesis. Between October 2010 and July 2011 the ARTEMIS spacecraft (P1 and P2) at the Earth-Moon Lagrange points (mid-tail, X ~ -45 to -65R E ) provided simultaneous two-point observations across the magnetotail for 4 days every lunar month, with a large range of spacecraft separations (0.1 to 25R E ). We find that plasmoids near lunar orbit, like other near-Earth reconnection-related phenomena, occur preferentially on the dusk side of the magnetotail. Two-point ARTEMIS observations reveal that the typical plasmoid azimuthal size in our dataset is about 5 to 10 R E , much smaller than expected from previous distant-tail observations. Plasmoids with an azimuthal size greater than 9 R E also exist, but only at geomagnetic activity levels higher (AE peak  〉 400nT) than typically found in our dataset (median AE peak  ~ 230 nT for our plasmoid dataset, median AE ~ 100 nT during the entire period of ARTEMIS magnetotail observations). We conclude that plasmoids during small to moderate substorms (AE peak  〈 400nT) do not grow beyond ~10 R E until they have moved tailward of ~ -45 to -65 R E . Plasmoids during large substorms (AE peak  〉 400nT), however, either grow beyond ~10 R E before they reach lunar distance or initially extend across a large portion of the magnetotail.