1. CME-associated dimming regions Alysha Reinard 12, Doug Biesecker 1, Tim Howard 3 1 NOAA/SEC 2 University of Colorado 3 Montana State University SHINE 2006

2. Data SOHO/EIT 195Å bandpass SOHO/EIT 195Å bandpass Search for dimmings Search for dimmings CME associated dimmings from 1997 to 2005 CME associated dimmings from 1997 to 2005 100+ dimming events 100+ dimming events 55 events with known 55 events with known ICME counterparts 14 include magnetic 14 include magnetic cloud parameters (more are being added!) ICME parameters obtained ICME parameters obtained from the ACE spacecraft

3. A pre-event image is subtracted from each frame A pre-event image is subtracted from each frame Objective: determine the extent of the dimming in area and intensity Objective: determine the extent of the dimming in area and intensity Data reduction

4.  “Dim pixels”: pixels which are at least one standard deviation below the image mean Region of interest selected by hand Region of interest selected by hand area = # dim pixels area = # dim pixels intensity = sum of dim pixels intensity = sum of dim pixels Data reduction

5. CME/dimming time difference range: -0.9-3.1hrs mean=1.1±0.9hrs median=1.1hrs Most CMEs are seen in C2 0-2 hours after associated dimming Most CMEs are seen in C2 0-2 hours after associated dimming Consistent with similar initiation time Consistent with similar initiation time

6. Dimming durations range: 0.6-22 hrs mean=7.4±4.0 median=7.2  Average dimming lasts ~3-12 hours

7. CME widths vs. dimming widths Dimming widths are equal to or smaller than CME widths Dimming widths are equal to or smaller than CME widths CME expansion CME expansion Regions beyond dimming participating in event Regions beyond dimming participating in event

8. Depletion and recovery Depletion time: field lines are open, material escapes Depletion time: field lines are open, material escapes Recovery time: corona replenishes the lost material Recovery time: corona replenishes the lost material depletionrecovery

9. Recovery slopes have a two-part structure ~40% of the time Two mechanisms operating in coronal recovery? Two mechanisms operating in coronal recovery? More study is needed More study is needed

10. In situ magnetic field magnitude vs. distance of dimming from center of solar disk CMEs originating near disk center will directly intersect the ACE spacecraft. CMEs originating near disk center will directly intersect the ACE spacecraft. Central regions of an ICME have stronger magnetic fields Central regions of an ICME have stronger magnetic fields r= -0.38 sig=99.3%

11. r= 0.35 sig=97.1% In-situ magnetic field magnitude vs. dimming area CMES with larger dimmings tend to have stronger magnetic fields CMES with larger dimmings tend to have stronger magnetic fields

12. r= 0.41 sig=98.7% In-situ composition vs. dimming area CMEs with larger dimmings tend to come from hotter source regions with higher elemental abundances? CMEs with larger dimmings tend to come from hotter source regions with higher elemental abundances? r= 0.55 sig=99.9%

13. Total magnetic flux may correlate with dimming area r=0.75 sig=99.8% Relatively strong correlation, but few data points. More magnetic cloud events are being added to the analysis r=0.65 sig=98.4%

14. Magnetic cloud size r=0.65 sig=98.8% r=0.09 correlation driven by Size of magnetic cloud does not correlate with area or length of dimming Size of magnetic cloud at 1AU is expected to correlate with dimming duration if the dimming is a direct effect of the CME

15. Magnetic flux With dimming (36) Without dimming (11) Poloidal flux 37.2±7.7 37.2±7.7 ↑ 20.1±3.6 Toroidal flux 41.2±15.5 41.2±15.5 ↑ 11.7±3.9 Total flux 78.4±22.7 78.4±22.7 ↑ 31.8±7.4

16. ICMEs with associated dimmings are very similar to those without, except Helium which is more enhanced in dimming-related events With dimming (36) No dimming (11) O +7 /O +6 0.53±0.05 0.54±0.11 Q Fe 12.1±0.3 11.9±0.5 He/H0.056±0.0050.039±0.004 Mg/O0.21±0.020.25±0.03 Density8.1±1.07.9±1.0 Temp57000±700053000±7000 VpVpVpVp472±16493±25 B10.7±0.99.2±1.4

17. Summary Dimming time evolution Dimming time evolution Dimming duration averages 7±4 hours Dimming duration averages 7±4 hours Recovery is slower than depletion; has two slopes 40% of the time Recovery is slower than depletion; has two slopes 40% of the time CME/dimming CME/dimming Dimmings usually begin 0-2 hours before CME is visible in C2 Dimmings usually begin 0-2 hours before CME is visible in C2 CME widths are larger, on average than dimming widths CME widths are larger, on average than dimming widths Weak correlation between dimming area and magnetic cloud flux/composition parameters Weak correlation between dimming area and magnetic cloud flux/composition parameters Larger dimmings are associated with larger, more energetic CMEs that have more magnetic energy, are more strongly heated and contain higher heavy ion abundances Larger dimmings are associated with larger, more energetic CMEs that have more magnetic energy, are more strongly heated and contain higher heavy ion abundances Dimming-related events have more magnetic flux and more helium at ACE Dimming-related events have more magnetic flux and more helium at ACE Larger CME events are more likely to produce dimmings Larger CME events are more likely to produce dimmings Helium measurements provide some evidence that dimming material directly enters the body of the CME Helium measurements provide some evidence that dimming material directly enters the body of the CME