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Study of the geoelectric fields at Vostok, Antarctica

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Corney, Rita(Rita C-Lin) (2002) Study of the geoelectric fields at Vostok, Antarctica. Research Master thesis, University of Tasmania.

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Abstract

In fair weather regions, a downward directed geoelectric field of ~ 100 —
200 Vm-1 can be measured at the surface of the Earth. At high latitudes, the
interaction of the solar wind and interplanetary magnetic field with the Earth's
magnetosphere and ionosphere imposes a variable dawn-to-dusk potential drop
of 20 — 150 kV on the geoelectric field. Large scale horizontal electric fields
in the ionosphere map into the vertical component of the near surface electric
field. A total of 133 fair weather days of vertical geoelectric field data from Vostok,
Antarctica (78.5°S, 107°E; corrected geomagnetic latitude, 83.5°S), obtained
during 1998, were selected to investigate the suitability of the Vostok site for
studies of the global electric circuit and confirm the linkage between the solar
wind imposed potential patterns and the near surface electric field.
Seasonal variations in the diurnal electric field at Vostok are compared with
the Carnegie diurnal curves, after appropriate allowance is made for the influence
of the solar wind. Consistent features include the shift to later UT hours of the
maximum between Southern Hemisphere (SH) summer and winter months, the
seasonal constancy of the timing of the diurnal minimum and the diurnal range
of the total dataset. The range of the diurnal curves, expressed as a percentage of
the mean, increases by 7 to 9% when the imposed polar cap potential contribution
is subtracted. The range of the total diurnal curve increases from 28% to 37%
of the mean value, comparable with the Carnegie value of 37%. However, the
diurnal range of the Vostok SH summer diurnal curve, 51% of the mean value,
is excessive compared to the Carnegie value of 40%. The average magnitude
of the electric field at Vostok peaks in the SH winter and is a minimum in the
SH summer, consistent with global thunderstorm activity and monthly averages
of recently re-analysed Carnegie data [Adlerman and Williams, 1996]. However,
the Vostok equinoctal mean is similar to the Vostok SH winter mean while the
Carnegie equinoctal mean is similar to the Carnegie SH summer mean. Broad
similarity of the Vostok and Carnegie diurnal-seasonal variations confirms Vostok
as a suitable site for global circuit studies but the possibility that the comparisons
are influenced by seasonal and diurnal variations in the average conductivity at
ground level or possible inaccuracies in the ionospheric potential model used to
subtract the influence of the solar wind on the Vostok data cannot be excluded.
Variations of the vertical electric field measurements are compared with both
Weimer [1996] and IZMEM [Papitashvili et al., 1994] model calculations of the
imposed polar cap potential above Vostok station. Variations of the electric
field measurements are calculated using two previously published procedures,
a monthly method as used by Frank-Kamenetsky et al. [2001], and a yearly
method as per Frank-Kamenetsky et al. [1999]. By investigating the correlations
between these parameters for individual UT hours, we confirm and extend
the diurnal range over which sigificant correlations have been obtained. Using
the yearly method, nineteen individual UT hours are significantly correlated with
the Weimer model predictions and ten with the IZMEM model predictions. The
linkage between ionospheric potential differences above Vostok and ground-level
vertical electric field is clearly demonstrated. The ratio between the two variables
is expected to be contant. Diurnal variations in the magnitude of the ratio for
individual UT hours allows both models to be tested against the measured Vostok
data, demonstrating that Antarctic polar plateau geoelectric field measurements
can be used to investigate polar convection.

Item Type: Thesis (Research Master)
Keywords: Electric fields, Geophysics, Geomagnetism
Copyright Holders: The Author
Copyright Information:

Copyright 2002 the Author - The University is continuing to endeavour to trace the copyright
owner(s) and in the meantime this item has been reproduced here in good faith. We
would be pleased to hear from the copyright owner(s).

Additional Information:

Thesis (M.Sc.)--University of Tasmania, 2002. Includes bibliographical references

Date Deposited: 25 Nov 2014 00:51
Last Modified: 19 Jul 2016 02:42
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