P. Schmoldt, PhD - MTNet - DIAS

2.2. Electric currents in the magnetosphere
Storm strength Decrease of surface magnetic field
weak 50 nT
moderate 100 nT
strong 150 nT
great 500 nT
Tab. 2.2.: Decrease of the Earth’s surface magnetic field during the main phase of a magnetic storm depending on the storm strength;
values from McPherron [2005].
Fig. 2.13.: Equivalent current model representing DP1 by the use of polar electrojets (PEJ) on the night-side as thick black arrows
along the 67 degree latitude towards the Harang discontinuity at local midnight; from Schmucker [1985].
sectors (Fig. 2.14). The main phase of the storm is followed by the recovery phase,
the source of smoothed storm-time variations D, where Dst variations are caused by the
equatorial ring current (ERC), i.e. the stream of trapped particles encircling the Earth.
DS variations on the other hand describe the effect due to ERC that is not completely
closed, indicating the local disturbances of the universal-time-dependent Dst variations
[Schmucker, 1985; McPherron, 2005].
Polar substorms can also emerge without prior ssc events, generating geomagnetic bays
which appear as smooth temporary departures of the undisturbed level from early evening
to early morning at mid-latitudes with equivalent current systems similar to the ones of
DP1 [Schmucker, 1985] (Fig. 2.13).
2.2.4. Solar flare effect
The solar flare effect (sfe) originates from ionisation of the Earth’s ionospheric D and E
layers (Fig. 2.4) due to intense solar wave emission, causing an increase of the ionospheric
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