solar wind. These are also our motivations. â Here we show our prediction and modeling results, including the 2003 `Halloween' storm and the 1859 Carrington ...
Modeling and Predicting the Dst Index Xinlin Li, Alexa Halford (CU/LASP), and Michael Temerin (U. of California at Berkeley) Introduction/Motivation
Model Description
The Dst index is based on 4 magnetometers, which are widely spaced in longitude and also located away from the equator to avoid the magnetic perturbations from the equatorial electrojet, see Figure below. They are adjusted to remove the quiet time Sq ionospheric current perturbations and the secular variation of the magnetic field due to changes in the internal currents of the Earth. The Dst index is widely used to determine the onset and strength of magnetic storms It has been known since the work of Burton et al.[1975] that the Dst can be well modeled and predicted using the solar wind as input. Since then, many scientists have tested and improved the prediction. The motivation for attempting such improvements is usually a combination of a practical desire to make a better prediction, a desire to understand which features of the interaction between the solar wind the magnetosphere are most important in producing magnetospheric activity, and to learn to what extent the activity is directly controlled by the solar wind. These are also our motivations. Here we show our prediction and modeling results, including the 2003 `Halloween’ storm and the 1859 Carrington Event.
Dst=dst1+dst2+dst3+(pressure) + (direct IMF b Z) + offset
dstx(t+dt)=dstx(t) + (driver term) +
(decay term), the driver term is similar for all three, which are a strong function of VX, BZ, NP , the clock angle and the angle between VX and the dipole axis. The decay terms are quite different.
(pressure)=[p1b2 +n(p2v2/sin2.52(Φ) +
p3)]1/2 , includes IMF pressure and a term proportional to the solar wind density in additional to the dynamic pressure.
(direct IMF bZ)=0.478bZsin11(Φ), is a
small term with an average magnitude of 0.7 nT and sometimes over 10 nT (it cannot be eliminated).
offset=s1 + s2 sin(2πt/yr + s3) + s4t + s5t, may compensate for a portion of the secular variation that may not have been removed in Dst.
Results
Rrelevant solar wind parameters and the components of the predicted Dst and the Dst index from Kyoto WDC for 60 days in 1998 [Temerin and Li, 2002].
Scatter plot of predicted Dst vs Kyoto Dst for each year, 1995-2002, from the same run (fixed model parameters).
The 2003 `Halloween’ storm
Relevant solar wind parameters and comparison of predicted Dst (under two different v X ) with provisional Dst and AMIE Dst, from the same run (fixed modeling parameters).
Comparison of predicted Dst with Kyoto Dst for the largest magnetic storms with good solar wind measurements during 1995-2002, from the same run (fixed model parameters)
The 1859 Carrington Storm
Assumed solar wind parameters [Siscoe and Crooker, 2005] and modeled Dst in comparison with the magnetometer measurements in Bombay, India [Li et al., 2005].
References: Burton, R. K., R. L. McPherron, and C. T. Russell, An empirical relationship between interplanetary conditions and Dst, \jgr {\sl 80}, 4204, 1975. Temerin, M. and X. Li, A new model for the prediction of Dst on the basis of the solar wind JGR, vol. 107, 1472, 2002. Li. X., M. Temerin, B. T. Tsurutani, S. Alex, Modeling of 1-2 September 1859 super magnetic storm, Adv. Space Res., in press, 2005. Siscoe, G., and N. Crooker, Dst of the Carrington Storm of 1859, Adv. Space Res., in press, 2005.
(From Kyoto University, WDC for Geomagnetism Website)
Acknowledgements: WIND: 3-D Plasma and Energetic Particle (R. P. Lin) and Magnetometer (R. Lepping); ACE: SWEPAM (R. Skoug, D. J. McComas) and Magnetometer (C. W. Smith, N. F. Ness); WDC for Geomagnetism, Kyoto University, Japan
Summary Given solar wind conditions, large-scale magnetospheric activities are predictable; the magnetosphere has an organized way to respond. For reliable and accurate forecast of magnetospheric activities, reliable and accurate solar wind measurements are absolutely necessary. Based on our model, a very fast solar wind with a very large negative IMF Bz can produce a super magnetic storm with minimum Dst less than -1600 nT
Future Work • Using the Dst prediction model as a tool, study the detailed physical processes governing the large scale responses of the magnetosphere to solar wind variations.
