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Solar Sources of Large Geomagnetic Storms During Solar Cycle 23

Solar Sources of Large Geomagnetic Storms During Solar Cycle 23. Gopalswamy (NASA/GSFC) Michalek, H. Xie, S. Yashiro (CUA) R. A. Howard (NRL). Objective.

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Solar Sources of Large Geomagnetic Storms During Solar Cycle 23

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  1. Solar Sources of Large Geomagnetic Storms During Solar Cycle 23 Gopalswamy (NASA/GSFC) Michalek, H. Xie, S. Yashiro (CUA) R. A. Howard (NRL) GMU March 14-16 2005

  2. Objective • To identify the solar sources of large (Dst < -100 nT) geomagnetic storms of solar cycle 23, as reported by WDC (http://swdcwww.kugi.kyotou.ac.jp/dstdir/index.htm), and document their properties. • To identify CMEs corresponding to the magnetic clouds reported during solar cycle 23 and study the strength of the geomagnetic storms associated with them. • Solar sources examined: • Solar front-side coronal mass ejections (CMEs) from SOHO/LASCO • Low-latitude coronal holes from Yohkoh/SXT; KPNO/He 10830; SOHO/EIT CDAW WG1-WG4 Topic 2: What are the properties of the solar events that give rise to (most) major Geomagnetic storms? GMU March 14-16 2005

  3. Method • Examine all the CMEs that occurred 1-5 days before the time of the storm. • Identify the front-side CMEs. If more than one, pick the fastest and widest (such CMEs are likely to travel large distances from the Sun). Compile CME properties. • For those storms without acceptable CMEs, examine low-latitude coronal holes Dst CMEs (height-time) Flares When CMEs are isolated, it is easy to associate a storm with its CME As in the 2003 11 21 storm GMU March 14-16 2005

  4. A CME-related Storm Largest storm of cycle 23; Dst = -472 nT Gopalswamy et al. 2005 GRL GMU March 14-16 2005

  5. Sometimes it is very difficult! Dst CME height-time Flares The extended main phase of the storm is probably due to many successive CMEs GMU March 14-16 2005

  6. Overview • 80 intervals were identified from Jan 1996 to December 2003. • 12 intervals had possible fluctuation within the same storm (or extended storms due to multiple CMEs) • 9 storms occurred during SOHO data gap • Remaining 64 storms analyzed were analyzed • 55 were CME-associated • 3 were probably CIR-related • 1 is being investigated for source • CIR –associated storms: Dst=-105, -128, -117 nT • CME-related storms: Dst = -100 to -472 nT Fig. 1 Distribution of storm strengths. The dates of top 5 storms are marked GMU March 14-16 2005

  7. Longitudes of Storm-related CMEs N 37/55 = 67% 18/55 = 33% 15W 20001029 2003/6/18 2000/4/7 E W 2003/11/20 S East-West Asymmetry of solar sources is confirmed (Wang et al. 2002; Zhang et al. 2003) Larger storms (Dst < -200 nT) seem to occur Close to the disk center (±15 deg) ODst < - 200 nT O - 300nT < Dst < - 200 nT O Dst < - 300 nT GMU March 14-16 2005

  8. East limb Event -145 nT Only east limb event; small storm; shock running into preceding CME GMU March 14-16 2005

  9. West limb Event - 288 nT CME from W 66; sheath related storm GMU March 14-16 2005

  10. Solar-cycle Variation of Storms & CMEs The annual number of geomagnetic storms roughly tracks the number of front-side halo CMEs. However, there are more Halo CMEs than the storms. When weaker storms are included, the numbers become closer (Michalek et al. 2004). Also, for some asymmetric halos only the shock arrives at Earth because the CMEs are heading almost orthogonal to the Sun-Earth line. Year 1999 is unusual in that there were very few intense storms even though there were many Front-side Halo CMEs. GMU March 14-16 2005

  11. Properties of Storm–related CMEs Gopalswamy, 2004 Storm Storm 030618 001025 000404 The speed distribution of storm-producing CMEs is similar to that of halo CMEs. The three near-limb CMEs appear as halos because of the disturbance above the opposite limb. At earth, the shock and sheath of these asymmetric halos are observed. The sheath contains southward B component causing the storms. The CMEs were full halos (69%) and partial halos (31%). GMU March 14-16 2005

  12. Dst-CME Speed Relationship There is a reasonable correlation between CME speed and the strength of the Dst Index (correlation coefficient = -0.51). The scatter is very large. The single outlier with Dst ~ -100 nT is due to a limb event. The earthward speed is likely to be much smaller Srivastava and Venkatakrishnan (2002) obtained the red line using 5 events, which does not seem to hold for the larger sample Blue line is obtained when storms associated with magnetic clouds are considered (r=-0.55) GMU March 14-16 2005

  13. LWS/CDAW on Geomagnetic Stormshttp://cdaw.gsfc.nasa.gov/ Three Geomagnetic Storms associated with Coronal holes Date of peak Dst 1996/10/23  - 105 nT 2002/11/21  - 128 nT 2003/07/16  - 117 nT GMU March 14-16 2005

  14. CHs Associated with Large (Dst < -100 nT) Geomagnetic Storms GMU March 14-16 2005

  15. Microwave Enhancement 104 K disk AR Filament GMU March 14-16 2005

  16. 2003/07/15 03/07/15 19:06 GMU March 14-16 2005

  17. 1996/10/20 GMU March 14-16 2005

  18. 2002/11/20 GMU March 14-16 2005

  19. Storms Associated with Magnetic Clouds • Relaxing the Dst < -100 nT criterion we considered magnetic cloud events alone and identified the associated front-side CMEs. There were 85 MCs observed by Wind. Only 66 had overlap with SOHO data • The Dst – Vcme correlation similar. • In addition to CME speed, the magnetic field and its orientation are also important. For example, the Dst-VB correlation (r=0.81) is much better than the Dst-V correlation (r = 0.55) • Bz and total B have similar correlation with Dst GMU March 14-16 2005

  20. Storms Associated with Magnetic Clouds • Since CMEs are the near-Sun manifestations of magnetic clouds, the Dst – Vcme relationship should mimic the Dst-Vmc relationship. • The Dst-Vmc correlation cofficient(0.74) is much larger than that for Dst-Vcme (0.55) • However, the Dst-VmcB correlation (r=0.79) is very similar to the Dst-VcmeB correlation (r = 0.81) GMU March 14-16 2005

  21. Summary • Most (95%) of the intense (Dst < -100 nT) geomagnetic storms are associated with front-side fast and wide CMEs; the remaining (5%) are associated with corotating interaction regions. This confirms previous studies (e.g. Gosling, 1993) • The properties of Storm-related CMEs are similar to those of halo CMEs. • Most of the severe storms (Dst < -300 nT) were associated with CMEs originating from close to the disk center (±20 deg). • There are generally more geoeffective CMEs originating from the western hemisphere of the Sun. However, the largest storm of cycle 23 originated from E18 (2003 11 21 storm due to the 2003 11 18 CME). • Asymmetric halos are not very geoeffective because only the shock flanks and/or shock sheaths arrive at Earth. • In addition to the kinematic properties of CMEs, we must consider magnetic properties for a better understanding of their geoeffectiveness. This involves devising ways of estimating B when the CMEs are still near the sun. GMU March 14-16 2005

  22. Topic 2: Answers • Location on the Sun: Center-West • Flares: Bigger on the average • CME properties: Faster & Wider on the average • SEP events: Overlap in longitude; Avg SEP-event longitude more western • Dst-Vcme correlation: 0.55, similar to Vicme-Dst • Dst – VcmeB highest correlation 0.81 • CIR storms: 3/76 ~ 4% GMU March 14-16 2005

  23. References • Gopalswamy, 2004, in ASSL series, ed. G. Poletto & S. Suess, chapter 8, in press. • Gosling, J. T., 1993, JGR, 98, 18937 • Michalek, G. et al. 2004, under preparation • Srivastava, N. & Venkatakrishnan, P. V., 2002, GRL 29, 1287 • Wang, Y.-M. et al., 2002, JGR, 107, 1340 • Zhang, J. et al., 2003, ApJ, 582, 520 GMU March 14-16 2005

  24. Longitudes of Storm-related CMEs N 37/55 = 67% 18/55 = 33% 15W SEP E W S East-West Asymmetry of solar sources is confirmed (Wang et al. 2002; Zhang et al. 2003) Larger storms (Dst < -200 nT) seem to occur Close to the disk center (±15 deg) ODst < - 200 nT O - 300nT < Dst < - 200 nT O Dst < - 300 nT GMU March 14-16 2005

  25. Newton 1943 GMU March 14-16 2005

  26. B and Bz have similar correlation with Dst r = 0.74 for |Bz| GMU March 14-16 2005

  27. Worst-Case Scenario t = a.bv + c • There were only 25 of the 8000 CMEs had speed > 2000 km/s; only 4 with speed > 2500km/s • Inferred speeds of historical events is < 2800 km/s • CMEs probably have a speed limit of ~ 3000 km/s • This limit arises from the maximum energy extractable from an active region (<1034 erg) • The Sun-Earth Travel time of shocks has a limit of ~ half a day a= 151.002, b=0.998625, and c=11.5981 GMU March 14-16 2005

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