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Ann. Geophys., 19, 649-653, 2001
www.ann-geophys.net/19/649/2001/
© European Geosciences Union 2001
Magnetospheric response to the solar wind as indicated by the cross-polar potential drop and the low-latitude asymmetric disturbance field
S. Eriksson, L. G. Blomberg, N. Ivchenko, T. Karlsson, and G. T. Marklund
Alfvén Laboratory, Royal Institute of Technology, SE-10044 Stockholm, Sweden
Abstract. The cross-polar potential
drop Φpc and the low-latitude asymmetric geomagnetic
disturbance field, as indicated by the mid-latitude ASY-H magnetic
index, are used to study the average magnetospheric response to the solar wind
forcing for southward interplanetary magnetic field conditions. The state of
the solar wind is monitored by the ACE spacecraft and the ionospheric
convection is measured by the double probe electric field instrument on the
Astrid-2 satellite. The solar wind-magnetosphere coupling is examined for 77
cases in February and from mid-May to mid-June 1999 by using the interplanetary
magnetic field Bz component and the reconnection electric field. Our
results show that the maximum correlation between Φpc
and the reconnection electric field is obtained approximately 25 min after the
solar wind has reached a distance of 11 RE from the Earth, which is
the assumed average position of the magnetopause. The corresponding correlation
for ASY-H shows two separate responses to the reconnection electric
field, delayed by about 35 and 65 min, respectively. We suggest that the
combination of the occurrence of a large magnetic storm on 18 February 1999 and
the enhanced level of geomagnetic activity which peaks at Kp = 7- may
explain the fast direct response of ASY-H to the solar wind at 35 min,
as well as the lack of any clear secondary responses of Φpc
to the driving solar wind at time delays longer than 25 min.
Key words. Magnetospheric physics
(solar wind-magnetosphere interactions; plasma convection) – Ionosphere
(electric fields and currents)
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