Forecasting auroras from regional and global magnetic field measurements
We use the connection between auroral sightings and rapid geomagnetic field variations in a concept for a Regional Auroral Forecast (RAF) service. The service is based on statistical relationships between near-real-time alerts issued by the NOAA Space Weather Prediction Center and magnetic time deri...
Main Authors: | , , , , , , , , , , , , , |
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Format: | Article |
Language: | English |
Published: |
Copernicus Publications
2016-06-01
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Series: | Geoscientific Instrumentation, Methods and Data Systems |
Online Access: | http://www.geosci-instrum-method-data-syst.net/5/253/2016/gi-5-253-2016.pdf |
Summary: | We use the connection between auroral sightings and rapid geomagnetic field
variations in a concept for a Regional Auroral Forecast (RAF) service. The
service is based on statistical relationships between near-real-time alerts
issued by the NOAA Space Weather Prediction Center and magnetic time
derivative (d<i>B</i>∕d<i>t</i>) values measured by five MIRACLE magnetometer
stations located in Finland at auroral and sub-auroral latitudes. Our database
contains NOAA alerts and d<i>B</i>∕d<i>t</i> observations from the years
2002–2012. These data are used to create a set of conditional probabilities,
which tell the service user when the probability of seeing auroras exceeds the
average conditions in Fennoscandia during the coming 0–12 h. Favourable
conditions for auroral displays are associated with ground magnetic field
time derivative values (d<i>B</i>∕d<i>t</i>) exceeding certain latitude-dependent
threshold values. Our statistical analyses reveal that the probabilities of
recording d<i>B</i>∕d<i>t</i> exceeding the thresholds stay below 50 % after NOAA
alerts on X-ray bursts or on energetic particle flux enhancements.
Therefore, those alerts are not very useful for auroral forecasts if we
want to keep the number of false alarms low. However, NOAA alerts on global
geomagnetic storms (characterized with <i>K</i><sub><i>p</i></sub> values > 4) enable
probability estimates of > 50 % with lead times of 3–12 h.
RAF forecasts thus rely heavily on the well-known fact that bright auroras
appear during geomagnetic storms. The additional new piece of information
which RAF brings to the previous picture is the knowledge on typical storm
durations at different latitudes. For example, the service users south of
the Arctic Circle will learn that after a NOAA ALTK06 issuance in night,
auroral spotting should be done within 12 h after the alert, while at
higher latitudes conditions can remain favourable during the next night. |
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ISSN: | 2193-0856 2193-0864 |