|
|
 |
|
|
Ann. Geophys., 22, 585-602, 2004
www.ann-geophys.net/22/585/2004/
© European Geosciences Union 2004
Occurrence statistics of magnetic impulsive events
T. Moretto1, D. G. Sibeck1, and J. F. Watermann2
1Laboratory for Extraterrestrial Physics, NASA Goddard Space Flight Center, Greenbelt, Maryland, USA
2Danish Meteorological Institute, Copenhagen, Denmark
Abstract. In this study, we perform a statistical investigation of magnetic
impulse events identified in the Greenland magnetometer stations
through the years 1995–2001. We focus on occurrence statistics
that can be determined reliably with an automatic event
identification procedure. Durin the first two years we observed almost
40% more events than in the following years. Season is not a
significant factor in event occurrence. Event occurrence peaks
near 12:00 UT, corresponding to approximately 10:00 magnetic local
time (MLT) at the west coast of Greenland. More events occur prior
to local noon than after. Event days are not distributed evenly.
Large amplitude events, particularly, tend to appear on
consecutive days. Events are observed at lower latitudes at
earlier local times in a way consistent with the projection of the
outer magnetospheric boundary into the ionosphere. Event latitude
depends on dipole tilt angle in a manner similar to that reported
for the cusp. Events occur during intervals of enhanced Kp. The
main reason for this is that the events themselves contribute to
the Kp index. Events exhibit a preference for high solar wind
velocity. In particular, the large amplitude events occur during
high-speed streams. A slight preference for lower density and more
radial interplanetary magnetic fields, as compared to the nominal
solar wind distribution, is also observed. However, both the
nominal solar wind and event distribution exhibit large
differences from year to year, indicating that events occur under
a broad range of conditions.
Key words. Ionosphere (ionospheric disturbances) Magnetospheric
physics (magnetosphere-ionosphere interactions;
solar wind-magnetosphere interactions)
Full Article in PDF (466 KB) |
|
|
