The Active Region Monitor (ARM) beauty.nascom.nasa/arm

Royal Observatory of Belgium Peter T Gallagher (NASA/GSFC)

The Active Region Monitor (ARM)http://beauty.nascom.nasa.gov/arm

Peter T GallagherL-3 Communications GSI

NASA Goddard Space Flight Center


o Extremely simple approach based on mature technologieso IDL, Perl, C-shell, HTML

o No advanced image processing … yet

o No distributed computing

What ARM does and does not doWhat ARM does and does not do


Basic Architecture of the Basic Architecture of the Active Region Monitor (ARM)Active Region Monitor (ARM)

Apache Web Serverhttp://beauty.nascom.nasa.gov/arm

Data ProcessingAnd Archiving

SOHOEIT/MDI

GONG+Mags

BBSOH-alpha

NOAASRS

NOAASXI

SOLIS FASR

C-shellIDLPerl

IDL sockets


MagnetogramArchive

Step 1. LocateMost Recent Magnetogram

Step 2. ReadMost Recent Magnetogram

IDLSockets

Step 3. Identify and ExtractActive RegionsActive Regions

IDLObjectMaps

Step 4. Quality Control(Seeing, Position, Saturation)

Step 6. AlgorithmsI. Fractal II. Gradient III. Neutral Line IV. EFR V. Wavelet

Step 5. TransformTo Disk Center

nter

Step 7: TransferTo Active Region Monitor


Physical Motivation - The Magnetic FieldPhysical Motivation - The Magnetic Field

o Line of sight B-field

o Zeeman effect

o ±2000 G

o Corona: < 1

o Photosphere: > 1

π

8/

2~

2B

Tnk

P

P B

B

G=QuickTime™ and aCinepak decompressorare needed to see this picture.


The Induction EquationThe Induction Equation

o The evolution of magnetic fields in solar active regions can be described by the magnetic induction equation

€

∂B

∂t=∇ × (v × B) +

1

Rm

∇ 2B

o Rm is 108 to 1010 in photosphere.

o Field “frozen” into the plasma.

o Field is advected by bulk plasma motions

B

Plasma


ARM ExtensionsARM Extensions

Include measures that are sensitive to the small-scale nature ofenergy storage and release in the solar atmosphere.

o Fractal dimension: relates to the active region complexity.

o Field gradient: indicative of pressure build-up in the photosphere.

o Neutral lines: related to energy release locations.

o Emerging flux regions: can act as energy release triggers.

o Wavelet analysis: diagnostic of small and large scale morphology.


Fractal Dimension - MotivationFractal Dimension - Motivation

o Turbulent plasma motions => Fields follow a random walk.

o Lawrence and co-workers find that line-of-sight fields scale in a self-similar and fractal manner.

o Correlation between Mt. Wilson classification and the fractal dimension (Gallagher, McAteer, & Ireland, 2003).

o Tao et al. (1995) showed that the advection of magnetic flux tubes by random motions results in a spatial distribution of flux which is fractal.

o Percolation theory: geometry of flux concentrations on the solar surface naturally results in fractal dimensions consistent with observational values (Vlahos et al., 2002; Schrijver et al., 1992; Seiden & Wentzel, 1996).

o Measuring the fractal dimension of an active region magnetic field is an essentially global investigation of the scaling properties of the magnetic field.


Fractal Dimension - MethodsFractal Dimension - Methods

o Box-Counting Dimension (Mandelbrot):

o The box-counting dimension can then be then determined from the slope,

o Perimeter-Area Dimension (Hausdorff):

o The perimeter-area dimension can then be obtained from,

€

N(ε) = ε−δ BC

€

δBC =log(N(ε))

log(1/ε)

€

P = Aδ PA / 2

€

δPA = 2log(P)

log(A)


Fractal Fractal Dimension Dimension - Example- Example

~ 1.0 - 1.2 ~ 1.2 - 1.4 ~ 1.4 - 1.6 δ ~ 1.5 - 1.7

o Error ~ ± 0.1


o It is because the field is frozen into the plasma in the photosphere that large transverse gradients are observed across the neutral line of large δ spots (Patty & Hagyard, 1986; Zhang et al., 1994).

o Converging photospheric flows sweep opposite polarity fields towards the neutral line of the δ.

o Over a period of hours, the continued concentration of opposite polarities in a relatively small area leads to strong transverse gradients (Gallagher, Moon, & Wang 2002).

energy_buldup (hrs - days) >> energy_resease (secs - mins)

o An instability in the corona results in the release of stored (Lin & Forbes, 2001; Priest & Forbes, 1990)

Horizontal Gradient - MotivationHorizontal Gradient - Motivation

QuickTime™ and aGIF decompressorare needed to see this picture.


Horizontal Gradient - MethodHorizontal Gradient - Method

o The horizontal gradient of the line-of-sight field, Bz(x,y) can be calculated using,

o The magnitude of the gradient can then be evaluated using,

o While the direction can be found from,

€

∇hBz(x, y) =∂Bz (x, y)

∂x

⎛

⎝ ⎜

⎞

⎠ ⎟̂ i +

∂Bz (x, y)

∂x

⎛

⎝ ⎜

⎞

⎠ ⎟̂ i

€

∇hBz (x, y) =∂Bz (x, y)

∂x

⎛

⎝ ⎜

⎞

⎠ ⎟2

+∂Bz(x, y)

∂x

⎛

⎝ ⎜

⎞

⎠ ⎟2

€

θ =arctan∂Bz(x,y)

∂x,∂Bz(x,y)

∂y

⎛

⎝ ⎜

⎞

⎠ ⎟


Horizontal Horizontal Gradient Gradient - Example- Example

o Gradients are large for large fields in close proximity.


Neutral Line - MotivationNeutral Line - Motivation

o Energy can be stored in the corona when sunspots of opposite polarity are pushed together, thereby forming an extended current sheet above the neutral line in the overlying magnetic field (Parker, 1963; Roumeliotis & Moore, 1993).

o “Break-out” model: gradual shearing motion both across and along the neutral line, can result in the formation of unstable arcades structures in the solar corona, which can then erupt (Antiochos, Devore, & Klimchuk, 1999).

o Observational flare signatures in neutral line morphology (Zharkova et al., this meeting).


Neutral Line - MethodNeutral Line - Method

o The magnetogram is first smoothed using a boxcar filter - this removes much of the statistical noise which would otherwise limit the effectiveness of subsequent steps.

o Contours of constant magnetic flux are then overlayed on the magnetogram at the zero Gauss level.

o Pixels along these contours are then extracted and used to create a binary image, with pixels along the neutral line have a value of 1, and all others being set to 0.

o This binary mask can then be used to extract gradient values along the neutral line by multiplying it with the gradient map.


Neutral LineNeutral Line - Example - Example


Emerging/Submerging Flux Regions (ESFRs) - Emerging/Submerging Flux Regions (ESFRs) - MotivationMotivation

o Filament eruptions can be triggered by ESFRs (Feynman & Martin, 1995).

o Major flares tend to be associated with new flux emergence (Tang & Wang, 1993; Wang et al. 2003; Zharkova).

o CMEs, which may be associated with filament eruptions and/or flares, may also be triggered by ESFRs (Green et al., 2003).

o Emerging flux model (Heyvaerts, Priest, & Rust, 1977).

o Flux-rope destabilization by flux injection (Krall, Chen, & Santoro, 2000).


Emerging/Submerging Flux Regions (ESFRs) - Emerging/Submerging Flux Regions (ESFRs) - MethodMethod

o Automatic monitoring of ESFRs is therefore extremely important to tracking and predicting solar activity.

o ESFRs will be monitored using full-disk MDI and GONG magnetograms in conjunction with a near real-time running-difference algorithm.

o Each newly processed magnetogram can be differentially rotated to the location of the previously processed magnetogram and subtracted.

o ESFRs are then identified as areas in the difference image showing large deviations (say, 3 ) above the mean difference level.

o ESFR frequency and location will then be cataloged and overplotted on images obtained at EUV or X-ray wavelengths, for example.


Emerging Emerging Flux Regions (ESFRs) Flux Regions (ESFRs)

- Example- Example


Emerging Flux Regions (ESFRs) - ExampleEmerging Flux Regions (ESFRs) - Example

QuickTime™ and aGIF decompressorare needed to see this picture.


Wavelets - MotivationWavelets - Motivation

o Measuring the fractal dimension of an active region magnetic field is an essentially global investigation of the scaling properties of the magnetic field.

o Such an approach could easily overlook spatially localized scale features, such as the emergence/submergence of flux tubes. Such locations are of especial interest in flare physics and are also vital in detailing the evolutionary path of active region development.

o A wavelet analysis of magnetograms can discriminate such regions.

o It is this lengthscale content which is crucial for theories of active region development.


o Test the suitability of various wavelet decomposition schemes (Haar, à trous, etc.)

o Find and characterize the local scale content of magnetograms and analyze this in the context of flare occurrence locations, times, rates and flux emergence/submergence.

o Characterize the evolution of spatial distribution of magnetogram scale content via entropy measures.

Wavelets - MethodWavelets - Method


Wavelets - ExampleWavelets - Example


Summary of ModificationsSummary of Modifications

Algorithm Data Product1. Fractal - Fractal dimension

2. Gradient - Gradient magnitude map- Gradient direction map- Maximum gradient- Position of maximum gradient

3. Neutral Line Identification - Location- Orientation

4. Emerging Flux Regions - Location- Frequency- Magnitude

5. Wavelet - Scale content maps- Spatial scale entropy


Potential Field Extrapolations - MotivationPotential Field Extrapolations - Motivation

o Energy release occurs in the corona.

o Coronal field topology is crucial to understanding and predicting activity (Antiochas, 1990; Aulanier et al. 2000).

o Fast and easy to implement - IDL code to be added to SSW.


o In equilibrium, and in the absence of flows, the magnetohydrostatic force balance equation can be written,

where P is the gas pressure, and FG is the force due to gravity. If the pressure gradients and gravity are negligible, we have

so that the current must be parallel to the magnetic field. In other words,

where is a function of position within the force-free magnetic field. The simplest solution to this equation can be obtained when = 0. This extrapolated field is then current-free, or potential.

Potential Field Extrapolations - MethodPotential Field Extrapolations - Method

€

0 = −∇P + J × B + FG

€

0 = J × B

€

∇×B = αB


Potential Field Extrapolations - ExamplePotential Field Extrapolations - Example

- simple bipolar topology δ - complex multipolar topology


ConclusionsConclusions

o Improve stability and reliability of ARM.

o Include advance image processing techniques.

o Incorporate a potential field extrapolation and visualization tool into ARM.

o FITS data products.

o ARM and VSO/EGSO?

The Active Region Monitor (ARM) beauty.nascom.nasa/arm

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