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Ann. Geophys., 24, 2611-2617, 2006
www.ann-geophys.net/24/2611/2006/
© European Geosciences Union 2006
Magnetoconjugate phenomena in Alaska and Macquarie Is., Australia in 2003: position of the global maximum iso-aurorae
L. A. Hajkowicz
Dept. of Physics, University of Queensland, Qld. 4072, Australia
Abstract. An extensive magnetometer network in Alaska and Canada
(consisting of 6 auroral and sub-auroral stations) and at Macquarie Is. (Australia)
was used to study magnetoconjugate phenomena in 2003, using the
H-component magnetograms. Altogether 193 magnetically disturbed days (with
ΣKp≥10) were used in the analysis. The maximum negative swing
in the H-component (ΔH) was assigned for each day from the auroral
conjugate station's data. Two types of magnetoconjugate data were found:
Type-1 when the daily (00:00–24:00 h UT) substorm activity was faithfully
reproduced in the H-component variations in the northern and southern
auroral zones, and Type-2 when a major peak in disturbance was largely
missing in one conjugate location. A distinct maximum in the occurrence of
the Type-1 events was in the southern summer (northern winter), reaching
almost 70 per cent of cases. A minimum in this type of events was in the
southern autumn and winter (around 40%). The correlation between
ΣKp and ΔH for auroral stations faithfully reproduced the
percentage occurrence of the Type-1 events for various seasons, with the
maximum correlation coefficient r≈0.8 in summer.
The time conjugacy of the events (i.e. the events occurring with a small
time displacement in the southern and northern auroral zones) was highest
for the auroral stations located close to the theoretical conjugate point
location at L-value ≈ 5 (i.e. College and Macquarie Is.). The
substorm onsets started earlier at the stations positioned east of the
conjugate point of Macquarie Is. in spring and winter, indicating a westward
drift of auroral disturbance with velocities of 1.4–1.6 km/s.
The magnitude of average ΔH increased rapidly past the invariant
latitude of Macquarie Is. towards the latitude of its nearest northern
conjugate station College , particularly in spring. The average level of
disturbance was consistently lower by about 30% at Macquarie Is. than at College.
Since Macquarie Is. is the only available auroral station
in the southern auroral zone the maximum southern auroral activity level
(maximum iso-aurorae) should be inferred from magnetic data obtained at a
northern conjugate station positioned at a slightly higher L-value, such as
College (L-value = 5.73). It is concluded from the above considerations that
the maximum iso-aurorae is located at a shell with L-value ≥ 5.73 in
both hemispheres.
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