Can sunspots be produced by equipartition magnetic fields residing at the buttom of the convection zone
Joy's law states that the line joining the two poles of a bipolar magnetic region (BMR) makes an angle with the latitudinal line, called the tilt, which increases with increase in latitude. If the solar dynamo operates at the bottom of the convection zone and the BMRs on the surface are produced by the fields generated there, then they should obey Joy's law. We give a theoretical model for these tilts, and show that the observations severely constrain the field strength at the bottom of the convection zone between 60 and 160 kG. For fields stronger than 160 kG, magnetic bouyancy dominates over Coriolis force and the tilts produced are very small compared to the observed. Whereas, for fields weaker than 60 kG, Coriolis force dominates over buoyancy and makes them emerge at very high latitudes, well above the typical sunspot latitudes. Fields above 60 kG are an order of magnitude stronger than the fields that can be in energy equipartition with the velocity fields at the bottom of the convection zone. Such strong fields will severely inhibit dynamo action. In addition, we do not know how a dynamo could produce such a strong field. We propose a couple of mechanisms by which equipartition fields could possibly produce BMRs with the observed tilts: (a) Giant cells, if they exist, can dominate over Coriolis force and drag these equipartition fields in their updraughts, (b) Small scale turbulence can itneract with the flux tube and exchange momentum with it, thus suppressing Coriolis force and making them emerge at the sunspot latitudes. We show that these two mechanisms can make equipartition fields emerge at the sunspot latitudes with the proper tilts, provided their sizes are smaller than a couple of hundred kilometers. We also show that special anchoring mechanisms have to be invoked in order to make equipartition fields of any size produce BMRs with the observed tilts.
- OSTI ID:
- 6614483
- Report Number(s):
- CONF-930189-; CODEN: AASBAR
- Journal Information:
- American Astronomical Society, Bulletin; (United States), Vol. 24:4; Conference: 181. meeting of the American Astronomical Society (AAS), Phoenix, AZ (United States), 3-7 Jan 1993; ISSN 0002-7537
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
GENERAL PHYSICS
CONVECTION
FUNCTIONAL MODELS
SUNSPOTS
MAGNETIC FIELDS
CORIOLIS FORCE
DRAG
SIMULATION
TURBULENCE
ENERGY TRANSFER
HEAT TRANSFER
MASS TRANSFER
SOLAR ACTIVITY
STARSPOTS
STELLAR ACTIVITY
661320* - Auroral
Ionospheric
& Magnetospheric Phenomena- (1992-)