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Ann. Geophys., 25, 1691-1707, 2007
www.ann-geophys.net/25/1691/2007/
© European Geosciences Union 2007
High-latitude plasma convection from Cluster EDI: variances and solar wind correlations
M. Förster1, G. Paschmann2, S. E. Haaland2,3, J. M. Quinn4, R. B. Torbert5, H. Vaith2, and C. A. Kletzing6
1GeoForschungsZentrum Potsdam, Potsdam, Germany
2Max-Planck-Institut für extraterrestrische Physik, 85748 Garching, Germany
3Department of Physics, University of Bergen, Norway
4Boston University, Boston, MA 02215, USA
5University of New Hampshire, Durham, NH 03824, USA
6University of Iowa, Iowa City, IA 52242, USA
Abstract. Based on drift velocity measurements of the EDI instruments on Cluster during
the years 2001–2006, we have constructed a database of high-latitude
ionospheric convection velocities and associated solar wind and magnetospheric
activity parameters.
In an earlier paper (Haaland et al., 2007), we have described the method, consisting
of an improved technique for calculating the propagation delay between the
chosen solar wind monitor (ACE) and Earth's magnetosphere, filtering the data
for periods of sufficiently stable IMF orientations, and mapping the EDI
measurements from their high-altitude positions to ionospheric altitudes.
The present paper extends this study, by looking at the spatial pattern of the
variances of the convection velocities as a function of IMF orientation, and
by performing sortings of the data according to the IMF magnitude in the
GSM y-z plane, |ByzIMF|, the estimated reconnection electric field, Er,sw,
the
solar wind dynamic pressure, Pdyn, the season, and indices characterizing
the ring current (Dst) and tail activity (ASYM-H).
The variability of the high-latitude convection shows characteristic spatial
patterns, which are mirror symmetric between the Northern and Southern
Hemispheres with respect to the IMF By component.
The latitude range of the highest variability zone varies with
IMF Bz similar to the auroral oval extent.
The magnitude of convection standard deviations is of the same order as,
or even larger than, the convection magnitude itself.
Positive correlations of polar cap activity are found with |ByzIMF|
and with Er,sw,
in particular.
The strict linear increase for small magnitudes of Er,sw starts to deviate
toward a flattened increase above about 2 mV/m.
There is also a weak positive correlation with Pdyn.
At very small values of Pdyn, a secondary maximum appears, which is even
more pronounced for the correlation with solar wind proton density.
Evidence for enhanced nightside convection during high nightside activity
is presented.
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