Response of geomagnetic activity indices to the solar wind parameters

1. Response of geomagnetic activity indices to the solar wind parameters Byung-Ho Ahn Kyungpook National University Daegu, Korea 2009 UN BSS & IHY Workshop Daejeon, Korea September 21-25, 2009

2. The goal of this study The response of Dst index to the variation of the interplanetary magnetic field (IMF), more specifically, interplanetary electric field, Ey(VBs). The relationship between AL and Dst during geomagnetic storm. Storm – substorm relationship

3. Data Dst index : 1998 - 2006 (dynamic pressure of the solar wind has been removed.) IMF parameters : 1998 - 2006 (from Ace Satellite) AL index : 1998 - 2006 (Quick Look Preliminary hourly-mean indices)

4. Dst – Ey relationship

5. For a given VBs, there seems to be an upper limit of the Dst index. Dst (nT) ≈ -15 VBs (mV/m) + 50 For example, whenever the VBs reaches 10 mV/m, the Dst becomes less than -100 nT.

6. Dst-Ey relation (main phase)

7. Dst –Ey relation (recovery phase)

8. Scatter of Dst for a given Ey

9. The significant scatter of the Dst index during a given level of the VBs suggests that there is another factor(s) contributing to development of magnetic storms other than magnetospheric convection.

10. dDst* dt Dst* τ = Q(t) - Are we successful in predicting Dst based on IMF parameters? • Burton et al.(1975) • Q(t) : injection term • τ : decay time

11. Improvement of Burton et al. (1975)' s algorithm has been proposed. • Fenrich and Luhmann(1998) • O’Brein and McPherron(2000) • Wang et al.(2003) • Park and Ahn(2009) etc.

12. Q(t) and τ of several models

13. Injection Term by Park and Ahn(2009) • Q(t) = ΔDst* = function of Ey • Main phase : Q(t) = -3.16 VBs – 4.00 • Recovery phase : Q(t) = 0

14. ΔDst – Ey relationship (main phase)

15. ΔDst – Ey relationship (recovery phase)

16. Dst predictions by IMF parameters

17. Burton et al. (1975) and O’Brein and McPherron(2000) c.c = 0.85 c.c = 0.85

18. Park and Ahn(2009) c.c = 0.84

19. Most important Interplanetary structures that caused intense geomagnetic storms (Dst≤-100nT) during solar cycle 23 • Sheath field(SH) : 24% • Magnetic cloud proceeded by a fast shock(sMC) : 24% • Sheath field followed by a magnetic cloud(SH+MC) : 16% • Corotating interaction region(CIR) : 13% Echer et al., 2008

20. Sheath field(SH)

21. Magnetic cloud proceeded by a fast shock(sMC)

22. Sheath field followed by a magnetic cloud(SH+MC)

23. Corotating interaction region(CIR)

24. All types of IMF structures

25. No clear signature reflecting the type of interplanetary structure in the Dst-Ey relationship is noted. • Dst depends primarily upon Bs/Ey.

26. Gonzalez and Tsurutani(1987) • Ey>5 mV/m with T(duration)>3 hours lead to intense (Dst < -100nT) magnetic storms. Kamide et al.(1998) • Dst variance during magnetic storm can be solely reproduced by Ey. • Needed to identify the role of substorm during magnetic storm.

27. Substorm contribution • Daglis(1997) : enhanced O+ (ionospheric) contribution to the ring current during intense storms • Lui et al.(2001) : Both substorms and enhanced convection contribute to the buildup of the storm-time ring current.

28. Dst-Ey relation (main phase)

29. Dst –Ey relation (recovery phase)

30. ΔDst – Ey relationship (main phase)

31. ΔDst – Ey relationship (recovery phase)

32. November. 20 – 21, 2003

33. August 30 – 31, 2004

34. Summary • For a given level of VBs, there seems to be an lower limit of the Dst index, indicating that Ey determines at least the minimum size of magnetic storms. • 2. No clear signature reflecting the type of interplanetary structures in the Dst-Ey relationship is noted. Dst depends • primarily upon Bs/Ey.

35. 3. The significant scatter of the Dst index during a given level of the VBs suggests that there is another factor contributing to the development of magnetic storms other than the magnetospheric convection, possibly substorms. 4. Substorms seem to contribute more significantly to the ring current intensification during intense storms than moderate ones.

36. Thank You