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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). Red = Scaled 10.7cm flux. shift 0.01% of mode frequency. - PowerPoint PPT Presentation
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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)