PERSISTENT STRUCTURES IN NEAR-

SURFACE FLOWS FROM RING DIAGRAMS

RACHEL HOWE, UNIVERSITY OF BIRMINGHAM

D. BAKER, L. HARRA, MSSL

R. KOMM, NSO

R. BOGART, STANFORD

PROBING THE SUN INSIDE AND OUTLeverhulme-funded project at MSSL

1st Workshop June 2011

INTRODUCTION

• The Sun has flows at many scales, from global rotation to flows around active regions and down to granules.

• Many of these show variations with solar cycle.

• Here we are looking for persistent structures in local flow features over an extended period.

DIFFERENTIAL ROTATION

• 2D rotation profile, based on RLS inversions

• Faster near equator, slower at poles

ANALYSIS

• Use synoptic maps of zonal/meridional flows from ring diagrams (GONG and HMI)

• Average over all depths

• At each latitude and rotation, we subtract mean over all times/longitudes to remove differential rotation and first-order temporal variations such as the torsional oscillation (as well as systematic effects)

• Then plot residuals as longitude—time maps

• Differential rotation causes features to drift in longitude from one rotation to the next.

• Features (e.g., flows into active regions/remnants) persisting for more than one rotation will show up as diagonal streaks

GONG ZONAL VELOCITYLONGITUDE—TIME PLOTS

Note diagonal ‘grain’

Paired light-dark streaks suggest flows into or out of feature that drifts with differential rotation.

Slope up == faster than Carrington rate

Slope down == slower than C.R.

Shallower slope means more difference.

GONG MERIDIONAL VELOCITY

Not much to see here – quieter at minimum?

MDI/HMI MAGNETOGRAMS(Timescale of GONG)

Note slope of features differs from that seen in flows

GONG ZONAL VELOCITYOn HMI timescale.

HMI ZONAL VELOCITYNote strong stripes at high latitudes.

For common data, correlation with GONG is > 80%

HMI MERIDIONAL VELOCITYSome grain visible here too.

HMI MAGNETOGRAMS

DIFFERENTIAL ROTATION

Use cross-correlation analysis to translate stripes slope to rotation rate

Green – Magnetograms

Black – Global inversions

Red – HMI ring vx correlation

Blue – GONG ring vx correlation

DIFFERENTIAL ROTATION

Use cross-correlation analysis to translate stripes slope to rotation rate

Green – Magnetograms

Black – Global inversions

Red – HMI ring vx correlation

Blue – GONG ring vx correlation

Cyan – EIT 195 Angstrom correlation

Orange – GONG PFSS coronal hole maps

HIGH-LATITUDE VX REWRAPPED WITH ESTIMATED VELOCITY

HIGH-LATITUDE VX REWRAPPED WITH EST. VELOCITY -5 NHZ

DISCUSSION

• Near-surface flows –especially zonal – show signatures of features persisting from a few to many rotations, migrating as would be expected from differential rotation.

• Low latitudes traceable to active region/plage?

• Rotation rate from magnetic features not quite the same as from flows – anchoring depth?

• High latitudes – Hathaway giant cells? Looks like an l=1 structure, anticorrelated n/s.

• Correlation analysis not good enough to pick up changes in differential rotation.