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Ann. Geophys., 22, 2507-2514, 2004
www.ann-geophys.net/22/2507/2004/
© European Geosciences Union 2004
Multipoint analysis of the spatio-temporal coherence of dayside O+ outflows with Cluster
M. Bouhram1, B. Klecker1, G. Paschmann1, H. Rème2, A. Blăgău1,3, L. Kistler4, P. Puhl-Quinn1,*, and J.-A. Sauvaud2
1Max-Planck-Institut für extraterrestrische Physik, D-85741 Garching, Germany
2CESR-CNRS, BP-4346, F-31028 Toulouse, France
3Space Science Institute, R-76911 Bucharest, Romania
4Space Science Center, University of New Hampshire, Durham, NH-03824, USA
*now at Space Science Center, University of New Hampshire, Durham, NH-03824, USA
Abstract. The spatial distribution of ionospheric ion outflow from
the dayside cusp/cleft has previously been studied in great detail with
numerous satellite missions, but only statistically. Between July and
November 2001, the orbit configuration of the Cluster multi-satellite system
close to its perigee (4 Earth radii) allows for delay times between
spacecraft of about 4 and 35min in crossing the cusp/cleft. This
enables for the first time to assess the spatial and temporal coherence of
O+ ion outflow on time scales of the order of the satellite time lag.
After presenting two contrasting events in detail, O+ velocities and
outflow intensities from three spacecraft, available on 18 events, all with
a similar orbit, have been cross-correlated to quantify the degree of
coherence in the outflow. The main result from the analysis is that, although
dayside outflows are a permanent feature, steady-state conditions are
surprisingly never achieved. In particular, a significant variability is
found for convection drift and local outflow intensities on small time
scales. This variability of local intensities is not found to depend on the
total strenghth of the outflow, which is much more stable and increases with
the dynamic solar wind pressure.
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