Spatio-Temporal Features in the Mid-Altitude Cusp: Cluster-IMAGE-SuperDarn
Correlated Observations

J. M. Bosqued, H. U. Frey, and C. P. Escoubet


The very elongated tetrahedron configuration of the ESA Cluster quartet near
the perigee is ideally suited for exciting studies of the mid-altitude (5-8
RE) cusp dynamics and possible relationships with dayside reconnection. Since
two years different inter-spacecraft separations, from ~600 km to ~5000 km
(summer 2002), provide new opportunities to study the large-scale spatial
stability and temporal evolution of the cusp key structures observed under a
variety of interplanetary conditions. We will review a number of cusp
encounters occurring for different interplanetary conditions, by combining
the Cluster multi-point ion data with global dayside imaging data provided by
the IMAGE-FUV-SI12 instrument, and/or ground-based data provided by the
SuperDarn radars. The Cluster Ion Spectrometry (CIS) data reveal that
discontinuous, step-like, "saw tooth", V-shaped, or multiple dispersed cusp
features are frequently observed by the Cluster fleet. First, an example of
one-to-one correlation between pulsating ion injections seen by Cluster/CIS
and their ionospheric counterpart, in the form transient flow bursts observed
by SuperDarn, will be presented. The correlated data analysis at both
altitudes allows to evaluate consistent FTE properties when IMF-Bz<0 and
unambiguously demonstrate that patchy reconnection is operating on the
dayside magnetopause. Global IMAGE-FUV images are unique to identify
ionospheric ion precipitation cusp signatures, to study the global dynamics
of the cusp ion precipitation, and to try to separate temporal and spatial
inter-related effects. For one cusp crossing, during a sudden increase of the
solar wind pressure, IMAGE and-CLUSTER data will be combined to reveal that
multiple ion dispersions observed in the northern post-noon sector (13-14H
MLT, IMF-By>0) by 2 or 3 Cluster spacecraft, with a repetition period of the
order of a few minutes, are clearly associated with a series of localized
spots in the IMAGE data. These transient brightenings created by the >1 keV
proton precipitation are presumably related with repeated solar wind dynamic
pressure pulses. A number of studies have recently suggested that under
favorable conditions, e.g., IMF-By>>Bz, a double cusp could appear related
with separated reconnection sites and, thus, explained as separated spatial
structures. Search of evidence of such examples has been carried out in the
Cluster-CIS database. Although ion signatures of "double" cusp encounters are
often observed as a consequence of IMF changes, probable signatures of
separated reconnection sites are rarer. An example of such event will be
finally presented.

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Presented at the Magnetospheric Imaging Workshop, 
Yosemite National Park, California, U.S.A., Feb. 9 - 13, 2003.