CME-associated CME-associated dimming regionsdimming regions

Alysha ReinardAlysha Reinard1212, Doug Biesecker, Doug Biesecker11, , Tim HowardTim Howard33

11NOAA/SEC NOAA/SEC 22University of ColoradoUniversity of Colorado

33Montana State UniversityMontana State University

SHINE 2006SHINE 2006

DataData SOHO/EIT 195Å bandpassSOHO/EIT 195Å bandpass Search for dimmings Search for dimmings

CME associated dimmings from 1997 to CME associated dimmings from 1997 to 20052005

100+ dimming events100+ dimming events 55 events with known 55 events with known ICME counterpartsICME counterparts 14 include magnetic 14 include magnetic cloud parameters (more cloud parameters (more are being added!)are being added!) ICME parameters obtainedICME parameters obtainedfrom the ACE spacecraftfrom the ACE spacecraft

A pre-event A pre-event image is image is subtracted from subtracted from each frameeach frame

Objective: Objective: determine the determine the extent of the extent of the dimming in dimming in areaarea and and intensityintensity

Data reductionData reduction

“ “Dim pixels”: Dim pixels”: pixels which are pixels which are at least one at least one standard standard deviation below deviation below the image meanthe image mean Region of Region of interest selected interest selected by handby hand areaarea = # dim = # dim pixelspixels intensityintensity = sum = sum of dim pixelsof dim pixels

Data reductionData reduction

CME/dimming time CME/dimming time differencedifference

range: -0.9-3.1hrsmean=1.1±0.9hrsmedian=1.1hrs

Most CMEs are Most CMEs are seen in C2 0-seen in C2 0-2 hours after 2 hours after associated associated dimmingdimming

Consistent Consistent with similar with similar initiation initiation timetime

Dimming durationsDimming durations

range: 0.6-22 hrsmean=7.4±4.0 median=7.2

Average Average dimming lasts dimming lasts ~3-12 hours~3-12 hours

CME widths vs. dimming CME widths vs. dimming widthswidths

Dimming widths Dimming widths are equal to are equal to or smaller or smaller than CME than CME widthswidths CME expansion CME expansion Regions beyond Regions beyond dimming dimming participating participating in eventin event

Depletion and recoveryDepletion and recovery

Depletion time: field lines are open, material Depletion time: field lines are open, material escapesescapes

Recovery time: corona replenishes the lost materialRecovery time: corona replenishes the lost material

depletion

recovery

Recovery slopes have a Recovery slopes have a two-part structure ~40% of two-part structure ~40% of

the timethe time

Two mechanisms operating in coronal recovery?Two mechanisms operating in coronal recovery? More study is neededMore study is needed

In situ magnetic field In situ magnetic field magnitude vs. distance of magnitude vs. distance of

dimming from center of solar dimming from center of solar diskdisk

CMEs originating CMEs originating near disk center near disk center will directly will directly intersect the intersect the ACE spacecraft. ACE spacecraft.

Central regions Central regions of an ICME have of an ICME have stronger stronger magnetic fieldsmagnetic fields

r= -0.38sig=99.3%

r= 0.35sig=97.1%

In-situ magnetic field In-situ magnetic field magnitude vs. dimming areamagnitude vs. dimming area

CMES with larger CMES with larger dimmings tend to dimmings tend to have stronger have stronger magnetic fieldsmagnetic fields

r= 0.41sig=98.7%

In-situ composition vs. In-situ composition vs. dimming areadimming area

CMEs with larger dimmings CMEs with larger dimmings tend to come from hotter tend to come from hotter source regions with higher source regions with higher elemental abundances?elemental abundances?

r= 0.55sig=99.9%

Total magnetic flux Total magnetic flux maymay correlate with dimming correlate with dimming

areaarea

r=0.75sig=99.8%

Relatively strong Relatively strong correlation, but few correlation, but few data points. More data points. More magnetic cloud events magnetic cloud events are being added to the are being added to the analysisanalysis

r=0.65sig=98.4%

Magnetic cloud sizeMagnetic cloud sizer=0.65sig=98.8%

r=0.09

correlation driven by

Size of magnetic Size of magnetic cloud does not cloud does not correlate with correlate with area or length area or length of dimmingof dimming

Size of magnetic cloud at Size of magnetic cloud at 1AU is expected to 1AU is expected to correlate with dimming correlate with dimming duration if the dimming is duration if the dimming is a direct effect of the CMEa direct effect of the CME

Magnetic fluxMagnetic flux

With dimming With dimming (36)(36)

Without Without dimming (11)dimming (11)

Poloidal Poloidal fluxflux

37.237.2±±7.7 7.7 ↑ 20.120.1±±3.63.6

Toroidal Toroidal fluxflux

41.241.2±±15.5 15.5 ↑ 11.711.7±±3.93.9

Total fluxTotal flux 78.478.4±±22.7 22.7 ↑ 31.831.8±±7.47.4

ICMEs with associated dimmings are ICMEs with associated dimmings are very similar to those without, very similar to those without,

except Helium which is more enhanced except Helium which is more enhanced in dimming-related eventsin dimming-related events

With dimming With dimming (36)(36)

No dimming No dimming (11)(11)

OO+7+7/O/O+6+6 0.530.53±0.05±0.05 0.540.54±0.11±0.11

QQFeFe 12.112.1±0.3±0.3 11.911.9±0.5±0.5

He/HHe/H 0.056±0.0050.056±0.005 0.039±0.0040.039±0.004

Mg/OMg/O 0.21±0.020.21±0.02 0.25±0.030.25±0.03

DensityDensity 8.1±1.08.1±1.0 7.9±1.07.9±1.0

TempTemp 57000±700057000±7000 53000±700053000±7000

VVpp 472±16472±16 493±25493±25

BB 10.7±0.910.7±0.9 9.2±1.49.2±1.4

SummarySummary Dimming time evolutionDimming time evolution

Dimming duration averages 7Dimming duration averages 7±±4 hours4 hours Recovery is slower than depletion; has two slopes 40% Recovery is slower than depletion; has two slopes 40% of the timeof the time

CME/dimmingCME/dimming Dimmings usually begin 0-2 hours before CME is Dimmings usually begin 0-2 hours before CME is visible in C2visible in C2

CME widths are larger, on average than dimming widthsCME widths are larger, on average than dimming widths Weak correlation between dimming area and Weak correlation between dimming area and magnetic cloud flux/composition parametersmagnetic cloud flux/composition parameters Larger dimmings are associated with larger, more Larger dimmings are associated with larger, more energetic CMEs that have more magnetic energy, are energetic CMEs that have more magnetic energy, are more strongly heated and contain higher heavy ion more strongly heated and contain higher heavy ion abundancesabundances

Dimming-related events have more magnetic flux Dimming-related events have more magnetic flux and more helium at ACEand more helium at ACE Larger CME events are more likely to produce dimmingsLarger CME events are more likely to produce dimmings Helium measurements provide some evidence that Helium measurements provide some evidence that dimming material directly enters the body of the CMEdimming material directly enters the body of the CME