Geomagnetic storms and substorms are a natural hazard similar to hurricanes,
floods etc. Severe storms cause communications problems, abruptly increase
drag on spacecraft, and can even cause electric utility blackouts over a
wide area. Severe substorms strongly affect communications and electrical
systems in high-latitude and polar regions. Solar and geomagnetic activity
also probably influences the Earth's climate and human health.
North-South (Bz) component of the Interplanetary Magnetic Field
(IMF) in the GSM frame of reference is the main factor controlling
geomagnetic activity. Under southward directed IMF the Earth's magnetosphere
is open to input from the solar wind flow. This energy is accumulated
in the magnetosphere and is subsequently released and dissipated during
geomagnetic storms and substorms. Other characteristics of the solar wind are
Since practical importance of solar wind measurements was recognized,
a number of approaches was developed for prediction of the geomagnetic
activity basing on the solar wind data.
Usually geomagnetic indices Kp, Dst, AE are estimated
with the use of linear filters or neural networks.
In our technique simple and a bit different approach is used:
As geomagnetic activity is clearly controlled by the solar wind,
we assume that an appropriate function of the solar wind
parameters describing input to the magnetosphere, can characterize
also the geomagnetic activity. Predicted level of the geomagnetic
activity is formulated qualitatively (e.g., quiet, weak, strong ...)
Such qualitative characteristics appear to be less accurate compared
with results of other methods in which concrete values of Dst and
Kp indices are obtained.
However, at present time interpretation of these indices in terms of their
practical consequencies is anyway qualitative, especially during
the real-time forecast. Difference between actual and predicted
indices (that is error of prediction) is also often high.
Therefore, we consider that qualitative prediction of the level
of geomagnetic activity is adequate, at least at the current
level of our knowledge.
We have chosen epsilon parameter (ε) as such integral characteristic
of the solar wind influence on the magnetosphere. It was first introduced
by Perreault and Akasofu [Geophys. J. R. Astr. Soc., 54, 547, 1978]
as the measure of the solar wind energy input due to the process of the
magnetic field merging at the front-side magnetopause.
Here we use it in the form ε = 2•107•Vi•B2•sin(θ/2)4 Watt,
where B is in nT, Vi is in km/s, θ is IMF angle in YZ plane.
We integrate ε to obtain total energy input during some specific
interval of time.
Typical geomagnetic storm starts after 3 hours of Bz=-10 nT [Gonsalez et al,
JGR, 99, 5771-5792, 1994].
The corresponding energy input is about 1016 Joules.
Typical energy accumulated during substorm growth phase is about 1015 J.
[Pulkkinen et al., JGR, 103, 15-28, 1998].
Contracted-oval (small) substorms are often associated with
only 1014 J input [Petrukovich et al, subm. to JGR].
Three parameters are calculated: integral of energy input during
preceeding 90 min (E90),
integral of energy input during preceeding 180 min (E180)
and integral of energy input during
interval with ε > 1010 W (Eac). The reset to Eac = 0 occurs after 30 minutes
of input smaller than this threshold.
E90 parameter better describes substorms-level activity, while
E180 and Eac
are more adequate for storm-level activity.
More information can be found in Petrukovich et al., [subm. to GRL].
Geomagnetic activity predictions calculated by our method
are presented in the plots of ACE data as color-coded bars.
Substorm activity is predicted basing on E90:
Quiet: E90 < 1014 J. No activity or very small activations observed mainly
by optical tools. IMF is probably northward (at least on average).
Weak substorms: E90 = 1014 - 1015 J.
Contracted oval substorms and/or
normal substorms of low amplitude are likely. Geomagnetic activity
in the auroral zone is probably less than 500 nT.
Strong substorms: E90 = 1015 - 5•1015 J.
Strong global substorms, all night-side
magnetosphere is involved. Auroral geomagnetic disturbances are probably
less than 1000 nT.
Storm-time substorms: E90 > 5•1015 J.
Ground activity more than 1000 nT is anticipated.
Most probable during geomagnetic storm intervals.
Storm activity is predicted using E180, Eac and E90:
Quiet: No storm. All what doesn't fit into other categories below.
Weak activity: E180 < 1016 J, but
Eac > 1016 and E90 > 2•1015 J.
Dst is probably within -50 nT.
Typical during large recurrent substorms and HILDCAA type events (prolonged
intervals with moderate southward IMF > -10nT ).
Intense Storm: E180 = 1016 - 1017 J.
Dst is probably between -50 nT and -200 nT.
Major storm: E180 > 1017 J.
Dst is probably < -200 nT.
We also supply Dst geomagnetic index prediction calculated with the use of
Burton et al. [JGR, 80, 4204-4214, 1975] approach with modifications of
Murayama [Rev. Geophys. Space Phys., 20, 623-629, 1982] and Feldstein et al.
[Space Sci. Rev., 59, 83, 1992, Planet. Space Sci., 32, 975-984, 1984].
We cannot guarantee the quality and reliability of these predictions
and do not encourage their use for other than illustrative purposes.
Author: Anatoli Petrukovich
Questions and comments are welcomed at firstname.lastname@example.org