The Sun as a whole: activity as seen by helioseismology

A.C. Birch(Max Planck Institute for Solar

System Research)

Low degree (ell = 0, 1, 2) mode frequencies change with the solar cycle (BiSON data)

shift 0.01% of mode frequency

Red = Scaled 10.7cm flux

From Anne-Marie Broomhall

Ok. But why?What else can be measured?

• Dependence on mode parameters:– Frequency (upper turning point)– Angular degree (lower turning point)

• Other mode properties:– Damping rates– Amplitudes (energy input rate)

• Flows:– Differential rotation / zonal flows (Global helio.)– Meridional circulation (local helio.)– 3d flows (local helio.)

Outline

• Cycle variations of mode parameters

• Flows associated with the cycle

• Future directions

The cycle in mode parameters

Libbrecht and Woodard (1990, Nature)

BBSO data, angular degree up to 140Reminder: 1986 is cycle min., 1988 cycle beginning

Cycle dependence changes with frequency(Libbrecht & Woodard, 1990)

Latitude inversion of frequency shifts(Libbrecht & Woodard, 1990)

Solid Line = inversion of even splittings (m dependence)Squares = limb brightness Dashed line = limb brightness same resolution as inversion result

(medium-ell) frequency changes come from latitudes of activity

Figure from R. Howe, method of Howe et al. (2002), GONG data

Frequency dependence of low degree modes

Anne-Marie BroomhallBasu et al. (2012)

Black=average frequency shift

Red=10.7cm flux

Blue=ISN

Cycle 22 Cycle 23 Cycle 24

What is going on?

Claim: change in the range of depths where the solar-cycle changes are happening

High-ell mode frequencies vary with the solar cycle also (MDI dynamics)

1996 (min.) Spring-2001 (near max)

Fall-2001(near max)

Rhodes et al. (2014)

More complicated than a simple surface termMPSI = ``magnetic plage strength index”Physics?

Interpretation• An extensive and rich literature

• Physical origin of frequency changes:– Changes in (MHD) turbulence near the surface (e.g., Goldreich et al.

1991, Dziembowski et al., 2001)– Changes in magnetic field in chromosphere (e.g. Jain & Roberts, 1993)– Changes in subsurface structure (e.g. Baldner & Basu, 2008)– General agreement (I think) that thermal effects alone are not enough

(Balmforth et al. 1996)

(the above are not mutually exclusive)

A point to remember: energy input doesn’t change!

Dampingrate

Energy input

Mode amplitude

Mode power

Salabert & Jimenéz-Reyes (2006, LOWL data)

Flows associated with the cycle

Zonal flows vary with the cycleGONG data

Ring diagram measurements

Red = fast rotation

Blue = slow rotation

Scale is +/- 25 m/s

Black contours = |B|

Polynomial fit removed at each time

Fast on equatorward side of activity. Appears before (large scale) activity.

Komm et al. (2013)

Meridional circulation varies with the cycle

GONG data

Ring diagram measurements

Red = Northward

Blue = Southward

Scale is +/- 25 m/s

Black contours = |B|

Convergence toward active latitudes

Komm et al. (2013)

Active regions have near-surface inflows

Gizon, Spruit, Birch 2010Cooling drives inflows into AR: Spruit 2003

Flows before and during active region emergence(w/ Schunker, Braun)

• HMI/SDO observations• Identify active regions that emerge into

relatively quiet Sun• Make surface flow maps using

helioseismology• Look at flows after averaging over 60

emergening active regions

Average over AR

B contours at 50,100, 150 G

Zoom in

t = 34 hr

AR

Max. flow 150 m/s

Inner circle: 30 Mm radius

Contours = |B|at 50, 100, 150 G

Future directions

• Connect global and local helioseismic measurements of the cycle:– Global modes: sunspots + plage + ?– Local helio: can potentially sort it out

• A related point:– Geometry matters (even at ell=1). – Models (I think) need to take care of horizontal and vertical

variations to understand cycle differences.

• High ell mode frequencies are now available. This is an opportunity.

The end

Converging flow!

Note offset.

Average over AR

Zoom in

t = -13 hr

AR

Max. flow 100 m/s

Inner circle: 30 Mm radius

Simoniello et al. (2013)