Karen Meyer

University of St Andrews

Scotland

1st year PhD student (3 months in)

Magnetic Carpet• Magnetic Carpet

• Super-granular cells. On small scales they give the dominant flow pattern on the surface of the

Sun.

Diameters: 10-50,000km ( ~ 14,000km).

Flows : Up-flow at cell centre/down-flow at edge. Horizontal radial outflow in cell centres

Velocities ~ 0.5 km/s. Strong downflows where 2 or more cells meet.

• Supergranular cells play an integral part in the evolution of the magnetic carpet

Magnetic Carpet Fluxes• Three main classifications: ephemeral regions, network fields, intra-network

fields.

• Ephemeral Regions (Harvey and Martin 1973). Cluster of newly emerging bipolar pairs. Hagenaar (2001) - 38,000 fragments. - flux ~ 2.6x1018 - 4.1x1020Mx ( 3x1019Mx, Harvey 1993). • Network Fields (Martin 1988): - found at sights of strong down-flows ( edges of 2 or more s/g cells). - produced from residuals of other flux concentrations - Properties : flux: 1x1018 ~ 1x1019 Mx. - 90% ~ephemeral regions, 10% ~ intra-network elements.

• Intra-network fields: smallest of concentrations- originate within s/g cells as emerging bipoles (flux: 1x1016 ~ 1x1018 Mx)

• Dynamics of three flux types important for many small scale solar

phenomena- X-ray Bright Points, Explosive Events.

Evolution of Magnetic Carpet Fields• Four main processes: 1) Flux Emergence: new magnetic features of opposite polarity (equal

flux) appear as pairs.

2) Cancellation : distinct opposite polarity fragments come into contact and mutually loose flux (consider coronal consequences next).

3) Coalescence: joining of same polarity elements on contact.

4) Fragmentation: splitting up of large features into 2 or more elements (mechanism unclear ~ granulation or instability).

Emergence CoalescenceCoalescence Fragmentation Cancellation

Magnetic Carpet Coronal Field.• The magnetic elements in the carpet extend up into the chromosphere and

lower corona where they are connected between one another.

• Emergence and surface motions may built up

significant amounts of energy : coronal heating,

X-ray bright points

• Recycle time for photospheric field ~14hr

(Hagenaar 2001).

• Close (2004) – remap time for the corona.

12hr, 240x240 Mm2, 286 fragments

Coronal remap time 1.4hr ~ quiet sun

corona is highly dynamic.

NLFFF Models• Previous theoretical models have mostly considered only potential fields.

Aim : Construct a nlfff magnetic carpet model.

• Features.

Extended area of the Sun – 10x10 supergranular cells

Include flux emergence, cancellation, etc.

Model a nlfff corona based on surface motions.

• Topics to consider.

Complex non-potential small scale coronal field.

Magnetic Topology and Connectivity.

Location of free magnetic energy and electric current.

The Model

• Two component model (van Ballegooijen, Mackay).

Coronal : magnetofrictional relaxation technique

Photosphere: Evolves Bz at the photosphere through an analytical boundary condition (van Ballegooijen)

- no numerical overshoot

- no numerical diffusion.

Flux transport movies