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Comparison studies of the long-term
magnetic and auroral data sets of FMI have increased our knowledge about
the statistical behaviour of auroras. Especially, the probability to
see auroras is known to increase in Southern Finland if the magnetometer
at
Nurmijärvi records changes larger than 3 nT per ten seconds. The
corresponding threshold for Sodankylä latitudes is about 5 nT per
ten seconds.
The bar plots show the hourly maxima changes in the horizontal magnetic
field components (in units 0.01 nT/s) recorded at the Nurmijärvi
and Sodankylä observatories during yesterday and today. The magnetically
quiet hours are marked with blue bars and the disturbed hours with
red bars. An hour is considered as disturbed if the value in scale
of the plot exceeds 30 in Nurmijärvi or 50 in Sodankylä.
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