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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 24, issue 10
Ann. Geophys., 24, 2611–2617, 2006
https://doi.org/10.5194/angeo-24-2611-2006
© Author(s) 2006. This work is distributed under
the Creative Commons Attribution 3.0 License.
Ann. Geophys., 24, 2611–2617, 2006
https://doi.org/10.5194/angeo-24-2611-2006
© Author(s) 2006. This work is distributed under
the Creative Commons Attribution 3.0 License.

  20 Oct 2006

20 Oct 2006

Magnetoconjugate phenomena in Alaska and Macquarie Is., Australia in 2003: position of the global maximum iso-aurorae

L. A. Hajkowicz 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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