Geofizika, Vol. 25 No. 1, 2008.
Izvorni znanstveni članak
On minimizing the external field contributions in annual means of the European geomagnetic observatories
Giuliana Verbanac
; Department of Geophysics, Faculty of Science, University of Zagreb, Zagreb, Croatia
Monika Korte
Sažetak
The aim of this study is to provide a method for minimizing the external
field contributions in the observatory annual means and try to separate, interpret
and explain all the different external field signals present in these
data. Investigating the European geomagnetic observatory biases over 42
years, considered as contributions of the crustal field, and generally assumed
to be constant in time, we noticed the link to the solar cycle, with short period
variations in the order of ±10 nT. Developing an empirical method for minimizing
the external fields presented in the observatory annual means, we
were able to reduce them better than the used of the external field description
included in the global Comprehensive Model, CM4 (Sabaka et al., 2004) was.
The external field module provided by the POtsdam Magnetic model of the
Earth, POMME-2.5, (Maus et al., 2005) was considered for investigating the
sources and characteristics of various external field contributions. We have
been able to separate magnetospheric and ionospheric fields, as well as to remove
a still significant variation with a function properly scaled by Ap and
Dst indices. With this procedure the external field contributions in the annual
means are minimized to an uncertainty level of ±2 nT. Our study shows a way
to obtain corrected observatory annual means, in order to be used for different
studies of the internal geomagnetic field.
Ključne riječi
observatory annual means; external field; ring current; magnetospheric field; ionospheric currents; magnetic field models
Hrčak ID:
25448
URI
Datum izdavanja:
1.7.2008.
Posjeta: 884 *