University:
Boston University
Course:
CAS AS 311 | Planetary Physics
Academic year:

2022
Views:

292

Pages:

22
Author:

alarmesb63z

Solar rotation • If the Sun were spherically symmetric and did not rotate, all modes with the same l and n but different m would have the same frequency. • Rotation lifts this degeneracy, giving rise to “rotational splittings” of the modes: Expected rotation profile Solar Rotation from helioesismology The Tachocline The tachocline Mathematical modeling of solar magneto-dynamics Authors: Spiegel, Edward A.; Zahn, Jean-Paul Final Report, 1 Nov. 1988 - 31 Oct. 1991 Columbia Univ., New York, NY. Astrophysics Lab. …We have isolated the probable seat of the solar cycle in the shear layer recently detected by helioseismology just below the convection zone. We call this layer the solar tachyline because of certain analogies to the oceanic thermocline… Characterizing the tachocline Basu (1997) W(r) = W c + dW d ( ) 1 + exp éë rd - r / w ùû ; W c = value of W deep in the interior w = half width of the transition layer rd = mid-point of transition region. Thus, the rotation rate increases from a factor 1 / (1 + e) of its max. to 1 / (1 + (1 / e)) its max. in the range rd - w to rd + w. (I.e. w is the characteristic thickness between 0.377 to 0.622 of the transition). dW=Wsur - W c Averages Equator 150 300 450 600 MDI GONG MDI GONG MDI GONG MDI GONG MDI GONG Jump 19.38 18.82 15.07 14.41 -1.93 -1.06 -29.39 -30.32 -64.64 -68.92 Position 0.689 0.692 0.693 0.694 0.703 0.697 0.717 0.702 0.731 0.707 Width 0.0022 (0.006) 0.0024 (0.006) 0.0046 (0.011) 0.0040 (0.010) 0.0111 (0.028) 0.0084 (0.021) 0.0201 (0.072) 0.0144 (0.051) 0.0289 (0.089) 0.0204 (0.062) • The tachocline is prolate. • The thickness of the tachocline is higher at higher latitudes. The Solar Cycle and Helioseismology Change in frequencies Change in frequencies as a function of solar activity The solar cycle in frequencies Changes in solar rotation: The zonal flows m/s Solar zonal flows First sign of cycle 24? m/s Rises upwards at about 1 m/s Bifurcation not seen earlier Meridional Flows: these are flows from the solar equator to the poles Solar variability: Changes in solar structure The Future of Helioseismology: The study of active regions We are beginning to be able to probe the structure of active regions Sub-surface flows appear to converge towards active regions And the far-side of the Sun of course!