Ion-neutral Coupling in Solar ProminencesHolly Gilbert: NASA GSFC

SDO AIA composite made from three of the AIA wavelength bands, corresponding to temperatures from .7 to 2 million degrees (hotter = red, cooler = blue).

LASCO C2 on January 4, 2002

Extreme ultraviolet Imaging Telescope (EIT) 304Å on February 2, 2001

Prominences

Filaments

o Length ~ 10 - 1000 Mm, Height ~ 1 - 100 Mm, Width ~ 1 - 10 Mm (1 Mm = 1000 km = 108 cm)

o Lifetime ~ hours - monthso T < 104 K, N ~ 1010 cm-3, M ~ 1015 gmo V ~ 5 - 100 km s-1

Some fundamental questions• How are prominences formed?

• Are there fundamental differences between the various types (active region vs. quiescent)?• What drives prominence evolution?• What causes eruption?• Does prominence density, magnetic structure, & pre-eruptive dynamics tell us something fundamental about the magnetic structure and available energy of the CME?

Motivation: • Understanding prominence support• Understanding prominence mass loss

• Observations of vertical flows: do ion-neutral interactions play a role? • By understanding the ion-neutral coupling what can we infer about the magnetic structure?

z

y

x B

g

Mass loss via. Cross field diffusion (Gilbert et al. 2002; 2007)

2i

GD B

BgJ

GD BJ

GDJ

Force Balance in a Multi-Constituent Prominence PlasmaGeneral Momentum Balance Equation ( jth particle species)

2ˆj j j j j j j j j j j r

GMp n eZ

t r

u u u E u B e;

j j k k j R j T j j j k k j jk kF F m u u u uP L

Other assumptions:

o Neglect flows along the magnetic fieldo Constant density and temperature throughout

systemo Collision frequencies appropriate for subsonic flow

speeds (our calculated flow speeds are less than 0.1 km s-1 )

o Local magnetic field is exactly horizontal to the (locally flat) solar surface

EXAMPLE: Proton Force Balance

1p y p p pe e z p z p H H z p zu g u u u u

p He He z p z p zp He He zu u u u

1p z p pe e y p y p H H y p yu u u u u

p He He y p y p yp He He yu u u u

z-component:

y-component:

B = Bêx

g = -êzGM/r2

Ωj = Zj eB/mj

Perpendicular Flow in a H-He Prominence Plasma

z

y

x B

g He yuH yu

He yu

p yu

e yu

H zu

He zu

He zu

p zu

e zu

g B

Primary drifts

Secondary drifts

Tertiary drifts

o Total atom density (1010 cm-3)o Helium abundance by number (0.1)o H and He ionization fractions (0.5

and 0.1)o Temperature (7 x 103 K)o Magnetic field (10 G)

Parameter StudyConsidered dependence of particle velocities on variation of several parameters (reference values in parentheses):

0

1

2

3

4

5

6

8 9 10 11 12

(a) Total Atom Density

log 10 [ n (cm-3) ]

log

10 [

– uz (

cm s

-1) ]

He

H

0

1

2

3

4

5

6

0 .05 .10 .15 .20 .25 .30 .35 .40

He

H

Helium Abundance by Number

(b) Helium Abundance

0

1

2

3

4

5

6

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

log

10 [

– uz (

cm s-

1 ) ]

(c) Hydrogen Ionization

Hydrogen Ionization Fraction

He

H

0

1

2

3

4

5

6

0 .05 .10 .15 .20 .25 .30 .35 .40

(d) Helium Ionization

Helium Ionization Fraction

H

He

0

1

2

3

4

5

6

4 5 6 7 8 9 10

log

10 [

– uz (

cm s-

1 ) ]

Temperature (T in units of 103 K)

(e) TemperatureHe

H

0

1

2

3

4

5

6

2.5 5.0 7.5 10.0 12.5 15.0 17.5 20.0

(f) Magnetic FieldHe

H

Magnetic Induction (B in units of Gauss)

He prom Heh u H prom Hh u

10 -3

2 -1-3

10 cm5 10 cm scmHu

n

-3sun

10 -3sun

cmR24 hours

0.01 R 10 cmprom

He

nh

-3sun

10 -3sun

cmR520 hours

0.01 R 10 cmprom

H

nh

Time Scales for Neutral Atom Loss

( vertical prominence dimension)promh

Loss Times for Helium and Hydrogen

Helium:

Hydrogen:

~ 1 day

~ 22 days

10 -3

4 -1-3

10 cm10 cm scmHeu

n

Ha (l=656 nm)January 30, 2000, 20:11:22

UT

He I (l=1083 nm)January 30, 2000, 20:10:15 UT

Both Images from the HAO Mauna Loa Solar Observatory

Ha (l=656 nm) He I (l=1083 nm) He I (l=1083 nm)

He I (l=1083 nm)

He I (l=1083 nm) He I (l=1083 nm)

Ha (l=656 nm)

Ha (l=656 nm)

Ha (l=656 nm) Ha (l=656 nm)

Initial Comparison of H and He Observations

Quantitative Analysis

Study temporal and spatial Changes in the relative H and He in filaments via the absorption and He I / Hα absorption ratio

Chose large/stable and small/stable filaments that could be followed across the solar disk

Used co-temporal Hα (6563 Å) and He I (10830 Å) images from the Mauna Loa Solar Observatory in 2004

Kilper (Master’s thesis) Developed an IDL code that scales and aligns each pair of images, selects the filament, and calculates the absorption ratio at every pixel

Alignment of images is key to a pixel-by-pixel comparison

Gilbert, Kilper, & Alexander, ApJ 671, 2007

He/H absorptionDarker pixel ↔ Helium

deficitBrighter pixel ↔ Helium

surplus

“Edge effects”

January 2004

“Large & stable”

Top view at disk center

Cylindrical representat

ion of a filament

View along filament

axis

Larger vertical column density

Small vertical column density

Filament axis

What do we expect??Geometrical considerations: the simplest picture

Dark = relative He deficit

Bottom edge with white

bands

Top edge with dark band

Top edge with dark band

Bottom edge with white

bands

Somewhat more realistic geometryDark = relative He deficit

White = relative He surplus

Observed near east limbcenter disk west limb

Interpretation of “Edge effects”

Far from disk center, one edge is at the top, and one at the bottom (where the barbs appear)

In a relatively stable filament, He drains out of the top rapidly (relative He deficit)

He draining out of bottom is replaced by He draining down from above (no relative He deficit)

Diffusion timescales In the context of filament threads…..

Coronal plasma in between threads

-3sun

10 -3sun

cmR24 hours

0.01 R 10 cmprom

He

nh

-3sun

10 -3sun

cmR520 hours

0.01 R 10 cmprom

H

nh

Coronal plasma can readily ionize neutral material draining into it

Expect very short draining

timescales….. However……

For high density filament threads, draining timescale will not be too small– it depends on

vertical column density

LWS TR&T Focused Science Team on Plasma Neutral Gas Coupling

Chromosphere component;My team: prominencesPhil Judge: Thermal & magnetic models for ion-neutral chromospheric studiesJames Leake: Modeling effects of ion-neutral coupling on reconnection & flux ememergence in chromosphere

Ongoing related work

LWS TR&T Focused Science Team on Plasma Neutral Gas Coupling

Ionosphere component;Geoffrey Crowley: Thermosphere-ionosphereJiuhou Lei: Ion-neutral processes in the equatorial F-regionWenbin Wang: Global ionospheric electric field variations

Key questions to be addressed

What physical mechanism(s) set the cross-field scale of prominence threads?

Are ion-neutral interactions responsible for vertical flows and structure in prominences?

Use idealized studies to develop physical insight into core processes:

Cross-field diffusionThermal nonequilibriumRayleigh-Taylor instability

Approach

Advance to full multidimensional modeling

Utilize observations to guide and test new physical insights

Thank you