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Forecast of Geomagnetic Storm based on CME and IP condition

IHY WB 2-3 Sep. 23, 2009. Forecast of Geomagnetic Storm based on CME and IP condition. R.-S. Kim 1 , K.-S. Cho 2 , Y.-J. Moon 3 , Yu Yi 1 , K.-H. Kim 3 1 Chungnam National University 2 Korea Astronomy and Space Science Institute 3 Kyunghee University. Geomagnetic storm.

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Forecast of Geomagnetic Storm based on CME and IP condition

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  1. IHY WB 2-3 Sep. 23, 2009 Forecast of Geomagnetic Storm based on CME and IP condition R.-S. Kim1, K.-S. Cho2, Y.-J. Moon3, Yu Yi1, K.-H. Kim3 1Chungnam National University 2Korea Astronomy and Space Science Institute 3Kyunghee University

  2. Geomagnetic storm • What is a geomagnetic storm? • Disturbances in the geomagneticfield caused by gusts in the solarwind that blows by Earth. • Large negative perturbations of Dst index are indicative of a geomagnetic storm. • Causes of a geomagnetic storm • Main origin: Coronal Mass ejection (CME) • Circumstance: Interplanetary condition

  3. Forecast of geomagnetic storm • Forecasts of a geomagnetic storm based on, • IP condition for urgent warning • CME parameters for 2~3 days early warning  We use a two-step prediction for the storm forecast capability.

  4. CME and geomagnetic storm • What parameters of CMEs control their geoeffectiveness? • Only a small portion of the CMEs result in the geomagnetic storms. • For front-side and large angular width events (1997~2003), Source location (L) Earthward direction (D) Initial speed (V) Magnetic field orientation of CME source region (M)

  5. Geoeffectiveness of CME parameters • Location • The source locations of geoeffective CMEs are asymmetrical in longitude. • The offset 15° to the west gives the best results. • Dst vs. distance from the offset • Speed • The CME speeds are roughly correlated with the strength of geomagnetic storms, but even slow CMEs can trigger geomagnetic storms.

  6. Geoeffectiveness of CME parameters • Magnetic field orientation • |Θ| ≤ 90°  southward |Θ| > 90°  northward • All CMEs associated with the super storms (Dst ≤ -200 nT) have southward magnetic field orientations. • Direction parameter • The ratio of distance between the shorter CME front and the solar center to that of the longer CME front. • The direction parameter has better correlation than the other parameters.

  7. Geomagnetic storm prediction model • Comparison of their correlations with the Dst index • Direction parameter has the best correlation, but magnetic field orientation has the worst correlation. • We divide the CMEs into two groups according to their magnetic field orientation. • Empirical geomagnetic storm prediction model • Formula to predict the geomagnetic storm strength (Dst index) • For southward events, • For northward events,

  8. Evaluation of the storm prediction model • Forecast based on the storm prediction model • The relationship between observed Dst index and predicted Dst index for northward events (cc=0.81) is better than for southward events (cc=0.67).

  9. Evaluation of the storm prediction model • Forecast based on the storm prediction model • For 64 halo or partial halo CMEs associated with M and X class solar flares, • ‘yes’ prediction: predicted Dst ≤ -50 nT • ‘yes’ observation: the occurrence of a geomagnetic storm • The mean probability of geomagnetic storm is about 63% (40/64) and 44 events are correctly forecasted (69%).  To improve the forecast capability of our model, we examine IP condition.

  10. IP Condition of geomagnetic storm • Interplanetary parameters (Echer et al., 2008) • What IP parameter has the strongest relation with storm strength among the IP condition such as the magnetic field, electric field, solar wind speed and dynamic pressure. • Most strong storms (Dst ≤ -100 nT) have peak Bs between 10–20 nT, and peak Ey between 5–10 mV/m.

  11. IP Condition of geomagnetic storm Gonzalez -Tsurutani empirical criteria (1987) Bs ≥ 10 nT or Ey ≥ 5 mV/m for t ≥ 3 h For the storms with Dst > -150 nT, 50% of the storms are satisfied. For the storms with Dst ≤ -150 nT, 93% of the stronger storms are satisfied. Our storm criteria is Dst ≤ -50 nT  We need to modify these criteria.

  12. IP Condition of the 64 CME • Data • Interplanetary Bz and Ey • ACE Magnetic Field 1-Hour Level 2 Data (B) • ACE/SWEPAM Solar Wind Experiment 1-Hour Level 2 Data (V) • E=-V×B  Ey=-BxVz+BzVx

  13. Bz minimum and Ey maximum Bz ≤ -5 nT, Ey ≥ 3 mV/m IP Condition for 64 CME • Duration time of Bz, Ey criteria • t ≥ 2h

  14. Forecast using IP criteria IP criteria We select the criteria for moderate storms (Dst ≤ -50 nT)  Bz ≤ -5 nT or Ey ≥ 3 mV/m for t ≥ 2 h For 64 events, 90% of the storms are in the IP criteria. 80% are correctly forecasted (51/64) (cf. CME parameter: 69%)

  15. Forecast using CME and IP condition For 64 events CME criteria: storm prediction formulae IP criteria: Bz ≤ -5 nT or Ey ≥ 3 mV/m for t ≥ 2 hour

  16. Conclusions • Empirical geomagnetic storm prediction model • Formulae to predict the geomagnetic storm strength (Dst index) based on CME parameters • For southward events, • For northward events, • Empirical IP criteria • For more better forecasts, we consider the IP conditions, since the CME characteristics can change during its propagation. • Our empirical IP criteria: Bz ≤ -5 nT or Ey ≥ 3 mV/m for t ≥ 2 h • 90% of the storms satisfy the IP criteria. • For 20 exceptional events, 15 cases can be explained by the IP conditions. • Forecast using CME and IP conditions • We found that all geomagnetic storms occur when the CME conditions or IP conditions are satisfied.

  17. CME parameters • Earthward direction parameter (D) • Advantages • The direction parameter can be directly estimated from the coronagraph observation  it can reduce the ambiguity of location caused by occulting disk. • It includes both of the CME propagation and angular effect of cone model.

  18. CME parameters • Magnetic field orientation angle θ (Song et al., 2006) • Magnetic reconnections between southward interplanetary magnetic field and the northward directed geomagnetic field occur at the day side of magnetopause and then transport energy from the solar wind into the magnetosphere. • If we assume that the magnetic field orientation of a CME is preserved during its interplanetary transit to Earth, we can expect that a CME with southward field orientation will cause a geomagnetic storm.

  19. Forecast using IP condition Limitation of the forecast using CME parameter We assumed that, The effective acceleration ceases at some distance less than 1 AU and then CME travels with a constant speed to Earth (Gopalswamy et al, 2001). The direction of the CME propagation (at C2 or C3 region) does not change through its travel to the Earth. The magnetic field orientation of ICME has the same direction as in the CME source region. The changes of CME characteristics increase the ambiguity in the storm forecast. We used the plane-of-the-sky speed  Error in predicted storm occurrence time. We use the IP condition to increase the storm forecast capability.

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