hinode/sot observations of quiescent prominences

PROM 2007 Workshop Monday 29-October-2007

Hinode/SOT Observations of Quiescent Prominences

Thomas Berger, T. Tarbell, N. Hurlburt, B. Lites, R. Shine, G. Slater, A.Title, S. Tsuneta, J. Okamoto, K. Ichimoto, Y.

Katsukawa, M. Kubo, S. Nagata, T. Shimizuand the rest of the SOT Team


Hinode Overview

SOTSolar Optical Telescope

XRTX-ray Telescope

EISExtreme Ultraviolet Imaging Spectrometer


FPP

OBU

OTA


HDM (Heat Dump Mirror)

CLU (collimator Lens Unit)

PMU (Polarizaiton Modulator Unit)

Tip-tilt mirror

SOT Overview

Optical Telescope Assembly (OTA):• 0.5 m Gregorian Telescope• Built by NAOJ/JAXA/Melco

Focal Plane Package (FPP):• Broadband Filter Imager (BFI)• Narrowband Filter Imager (NFI)• Spectropolarimeter (SP)• Built by Lockheed/HAO• Cameras by E2V/RAL

Introduction

Focal Plane Package (FPP)


Introduction• Hinode/SOT images prominences above the solar limb in two wavelengths:

• Ca II H-line at 396.8 nm 0.054”/pix

• H Balmer Alpha line at 656.3 nm 0.08”/pix

• Spatial resolution determined by 2x2 pixel summing. 2-pixel resolution is:

• Ca H-line ~ 160 km

• H-alpha ~ 230 km

• Typical temporal resolution values are 30--60 sec (15--30 sec cadence).

• SOT telescope is diffraction limited with no seeing distortions.


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Ca II H-line 396.8nm30-Nov-2006NW limb 6 hrs.


Sample RegionsTS1, TS2 = horizontal time slicesBox = averaged vertical time slice


Horizontal Time Slices

TS2

TS1

Oscillations of unknown origin


Vertical Composite Time Slice16 1-pixel slices summed horizontally


Vertical Composite Time Slice16 1-pixel slices summed horizontally

1 2

34

56

78

v1 = 8.9 km/sv7 = 9.3 km/sv8 = 8.9 km/s< v > = 9.0 km/s

v2 = 12.2 km/sv3 = 19.2 km/sv4 = 12.6 km/sv5 = 11.9 km/sv6 = 8.9 km/s< v > = 12.9 km/s

Downflows Upflows


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Example Vortex CloseupGrid = 2”

2.5 RotationsRate = 3.27 x 10-3 rad/sec

~3000 km diameter




Upflow Plumes CloseupGrid = 2”


656 658 660 662 664 666

1

2

3

v1 = 7.1 km/sv2 = 14.2 km/sv3 = 19.9 km/s

Upflow Plume Structure & Velocity Estimates34 sec between frames


668 670 672 674 676 678

3

v3 = 14.4 km/s

Upflow Plume Structure & Velocity Estimates34 sec between frames


680 682 684

7500

km

Upflow Plume Structure Detail34 sec between frames

4

v4 = 26.3 km/s

2250 km


Plume Velocity Measurements

v = 23 km/s v = 21 km/s

v = 18 km/s

v = 23 km/s

a = -0.18 km/s2




Downflow Stream CloseupGrid = 2”


Example Downflow Stream




H- Line center 656.3nm25-April-2007SW limb (rotated) 5 hrs.


Overlay of Ca II H-line on H-alpha




H-alpha 656.3nm8-Aug-2007NE limb 4 hrs.




Ca II H-line 396.8nm16-Aug-2007NW limb 5 hrs.




H-alpha 656.3nm16-Aug-2007NW limb 5 hrs.




Ca II H-line 396.8nm03-Oct-2007NW limb 5 hrs.


H-alpha 656.3nm +408 mA03-Oct-2007NW limb

408 mA ~ 20 km s-1


Examples of non-plume forming prominences:

• Quiescent prominences with little or no discernible vertical motions:• 23 December 2006• 11-12 July 2007• 4-5 August 2007

• Active region prominences• 9 November 2006 (Okamoto prominence)• 18 December 2006• 9 February 2007




Ca II H-line 396.8nm23-Dec-2006NW limb 16 hrs. w/gap




Ca II H-line 396.8 nm12-July-2007NE limb 4 hrs.




Ca II H-line 396.8 nm5-Aug-2007NW limb 6 hrs.


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Active Region 10922Ca II H-line 396.8 nm9-Nov-2006W limb 1 hr.




Active Region 10930Ca II H-line 396.8 nm18-Dec-2006W limb 6 hrs.




Active Region 10940Ca II H-line 396.8 nm18-Dec-2006W limb 10 hrs.


Findings• Two appearances of quiescent prominence structures in Hinode/SOT database:

• “Sheet” or “Hedgerow” prominences with ubiquitous vertical motion.

• “Horizontal” prominences w/ no obvious vertical motion.

• Sheet prominences always show the presence of upflow plumes, downflow streams, and large-scale vortices. There is no such thing as a static sheet prominence.

- Dark upflow “plumes” are intermittent, < V > ~ 20 km/sec, 10 minute characteristic lifetime, 400 - 700 km width.

- Bright downflow “streams”, < V > ~ 10 km/sec, 10 min characteristic lifetime, 250 - 700 km width.

- Vortices, characteristic scale 103 km, 3x10-3 rad/sec

- Rotational endpoint structures

- Bright “support arches” ~5000 km above photosphere

- Arches “break” under the weight of accumulated plasma

• Horizontal prominences always show horizontal flows on “shorter” disjoint fibrils.- Very little or no vertical motions - “vertically static”.- No obvious plume formation.- All AR prominences seen so far appear “horizontal” in structure.


Hypotheses

• What causes the dark buoyant upflows?

• 1. Thermal plume hypothesis: the upflow plumes are caused be localized heatings in the photosphere at the magnetic neutral line. The source of the heating is magnetic reconnection at the cancellation sites of larger magnetic elements.

The heating causes a density deficit relative to the surrounding plasma. This causes the heated volume to rise adiabatically in the form of a thermal plume. Flow character is turbulent and does not appear to follow magnetic field lines.

The constant rise speed of the plumes implies that the bouyancy force is balanced by fluid dynamic and/or magnetohydrodynamic “drag” forces. Assuming only fluid dynamic drag, a characteristic size R = radius of spherical “bubble”, and a unity drag coefficient:

=


• 1. Thermal plume hypothesis: (cont.)

Hypotheses

Assuming a perfect gas in pressure equilibrium

Using g = 274 m s-2, v = 20,000 km s-1, T = 7000 K, and R = density scale height at T(7000) = 300 km,

Temperature in plumes ~60,000K - sufficiently hot to reduce level populations necessary for scattering of Ca II and H-alpha radiation.



Hypotheses

Note: the foregoing assumes plume kinetic energy density >> magnetic field pressure. i.e. this is a high-Beta plasma “in the corona”.

Low & Hundhausen, ApJ, 443, 818, 1995.

Given the density of prominence plasma (ne ~1011 cm-3), this can only happen where B ~ 0.



Hypotheses

A really wild idea: These thermal plumes exist everywhere where there is magnetic reconnection in the lower atmosphere.

I.e., the prominence material simply makes the plumes visible by their inability to scatter chromospheric radiation.

Either you heard it here first...

or I will plausibly deny ever having said this...


• 2. Magnetic Bubble hypothesis: (courtesy B.C. Low) We suppose that magnetic reconnection in the photosphere results in highly evacuated magnetic “bubbles” that rise through the prominence due to the density deficit caused by the magnetic field energy density.

Hypotheses

In this case, both the Lorentz force and fluid dynamic drag resist the bouyancy force of the “bubble”.

The temperature of the bubble remains at ambient temperature. The plumes are dark because the density is so low that chromospheric Ca H-line and H-alpha radiation are no longer efficiently scattered in the plumes.

A really wild idea: These magnetic bubbles exist everywhere where there is magnetic reconnection in the lower atmosphere. They are just made visible by prominences...

Either you heard it here first...

or I will plausibly deny ever having said this...


Coming soon....

• More (better) Doppler velocity measurements in H-alpha.• Many more prominences in Cycle 24 with other instruments!

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STEREOHe II 304Å22-Sep-2007

hinode/sot observations of quiescent prominences

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