Magnetic Observatory Viby
Sollentuna, Sweden · geographic coordinates: 59°27' N
17°54' E · geomagnetic coordinates (2017): 57°51' N, 106°13' E
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Local weather conditions in Viby cloudy/overcast temperature: 16.4 oC dewpoint: 3.1 oC
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 (plots last generated: 21.04.2018 17:05)
Explain these plots!
A magnetic field is characterized by a vector in three-dimensional
space. Upon international agreement, the horizontal component towards North is termed X and the horizontal component towards
East is called Y.
The vertical component (towards Earth's center) is called Z.
The absolute intensity (magnetic flux) of the geomagnetic field is just under 50000 nT on the Earth's surface. This magnetometer
can measure variations on the order of a few nT during quiet geomagnetic conditions. During extreme solar storms, variations of
up to 1500 nT can occur. Depending on the disturbance level, the magnetogram uses different scales identified by the background color
(white/yellow/amber/red), allowing for a quick recognition of disturbed conditions.
The scale on the vertical axis shows the intensity variation in nT, the horizontal axis shows UTC time.
This magnetometer is located in Viby, about 15 km north of Stockholm, Sweden.
It measures the horizontal components of the Earth's magnetic field.
The above magnetogram shows the
evolution of the local magnetic field. It allows to draw conclusions
particularly on the probability of observing northern lights (aurora borealis)
at the location of the magnetometer.
Earth rotates below the auroral oval. Directly opposite the dayside, the
auroral oval is elongated towards south. As the Swedish east coast is
substantially more eastern than central and western Europe, the area around
Stockholm will rotate below the auroral oval about 30 minutes before central European
longitudes. Therefore, this Stockholm-based magnetometer can provide a first idea
of geomagnetic activity at northern-central latitudes before the peak of the
oval reaches locations further west.
The magnetogram shows intensity variations
with time of the geomagnetic field in Viby. The rather small variations are primarily caused by the solar
wind, which continuously moves onto the Earth's magnetic field. Changes in its velocity, density and
magnetic orientation influence orientation and intensity of the geomagnetic field.
The disturbance of the magntic field can have a considerable effect on the distribution of
electrically charged molecules in the ionosphere (upper atmosphere) which gives rise to northern lights. The
magnetometer is able to measure effects much smaller than causing aurora, which makes it a well-suited tool for
forecasting northern lights.
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The magnetogram A magnetogram shows the temporal evolution of the magnetic flux density of the Earth's magnetic field at its location:
Bx:
change of the North-South component of the magnetic flux density:
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By:
change of the East-West component of the magnetic flux density:
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Bz:
change of the vertical component of the magnetic flux density:
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the smaller Bx, the higher the probability for polar lights
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evening hours: the higher By,
the higher the probability for polar lights
morning hours: the smaller By,
the higher the probability for polar lights
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the higher Bz, the higher the probability for polar lights
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Often, instead of Bx und By the
horizontal intensity BH (quadratic sum of
Bx and By) as well as the
magnetic declination D = arctan (By/Bx) is used.
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WMM 2015 model, Chulliat et al., doi: 10.7289/V5TH8JNW. Picture credit: NOAA/NGDC/CIRES |
Strong disturbances caused by solar activity are usually seen in the
horizontal components of the magnetic field. The vertical component can
be used to infer the location of the electrojets. These electric currents
run along the auroral
ovals and are, give and take, responsible for all magnetic disturbances resulting from
magnetic substorms close to the surface. Hence changes in the vertical component represent
a good measure for the strength of local substorms.
More about K values and the auroral oval
The K index
is a measure of the maximum fluctuation of the horizontal magnetic
field component ΔBH in fixed three-hour intervals. It is a historically grown,
quasi-logarithmic measure of the occurrence probability for polar lights.
It is calculated as the difference of maximal and minimal magnetic field strength in
eight predefined 3-hour intervals per day.
The association of K values with amount of disturbance is
chosen depending on the latitude of the magnetic observatory in a way
so that the statistical distribution of worldwide K values
is reached. This means that K is an universal measure for polar light probabilities, and also that
stations at higher (geomagnetic) latitudes require larger fluctuations to reach a given K level.
For a given disturbance of the geomagnetic field, K values remain comparable globally. This also
allows for computing a global, so-called planetary Kp Index (Kp Indices from 1868 on).
Disturbances on the K scale can roughly be translated in how
far south the auroral oval will reach according to this map. Basically, for disturbances
equivalent to K5 or greater (G1-level storms) there is a fair chance for northern lights in Stockholm.
For a fair chance of observing northern lights in northern central Europe, a level of
K6 should be reached.
Only from K8
the chances for visible aurorae in central Europe are high. It is a good idea to also consider local circumstances at other
magnetometers, like SAM Haimhausen or by looking at a Magnetometer Stack covering your region.
SAM Viby measures the evolution of the x and y components
of the Earth's magnetic fields. As only the relative changes with respect to the values at 00:00 UTC are
regarded, an absolute calibration against long-term drifts of the instrument is not required.
To determine the K value, SAM Viby uses this conversion, appropriate for latitudes on the transition between mid and high latitudes:
K value |
magnetic field disturbance
ΔBx |
color code |
magnetic field |
G value |
0 |
below 10 nT |
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quiet
| G0
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1 |
below 20 nT |
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2 |
below 40 nT |
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unsettled
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3 |
below 60 nT |
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disturbed
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4 |
below 105 nT |
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active
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5 |
below 180 nT |
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minor storm
| G1
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6 |
below 300 nT |
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moderate storm
| G2
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7 |
below 495 nT |
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strong storm
| G3
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8 |
below 750 nT |
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severe storm
| G4
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9 |
exceeding 750 nT |
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extreme storm
| G5
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Developed and maintained by Robert Wagner. This service is based on Simple Aurora Monitor, designed by the SAM project by Karsten Hansky and Dirk Langenbach.
Parts of the hardware have been generously donated by Ralf Pitscheneder and had been previously used at polarlichtinfo.de.
Running SAM_linux & SAManpy software by Robert Wagner, powered by python on Raspberry Pi
If you enjoy this service and find it helpful, please consider donating. Any small amout is
thankfully acknowledged and used towards running costs of the magnetometer. Donations are handled through paypal
(you do not need to have a paypal account to donate) and initiated by clicking this button:
Alternatively, use this address to donate bitcoins:
1BLDRNRVfLhVrKHra9aXBy3wiweFxMT9FG
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Copyright & Impressum
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