Mark Miesch (High Altitude Observatory)

Cycle Variability and Surface Flux Transport in a 3D Babcock-Leighton Solar Dynamo Model
When Jul 27, 2017 from 02:30 PM to 03:30 PM
What
  • Colloquium
Where SH Lecture Hall
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Over the last two decades, Babcock-Leighton (BL) dynamo models have arguably emerged as the leading paradigm for explaining the origin of the 11-year solar activity cycle (22-year magnetic cycle). The defining characteristic of BL models is the critical role of magnetic flux emergence and dispersal in the operation of the dynamo. Emerging flux structures are manifested in the solar photosphere as bipolar magnetic regions (BMRs) with systematic orientations (known as Hale’s and Joy’s laws) that, upon further evolution due to differential rotation, meridional circulation, and convection, generate mean poloidal fields. We have recently developed an innovative solar dynamo model that captures this BL process explicitly in three dimensions. It’s called the Surface flux Transport And Babcock-LEighton (STABLE) solar dynamo model and it can be regarded as a unification of previous BL dynamo models (2.5D in latitude and radius) and surface flux transport (SFT) models (2D in latitude and longitude), building on the proven successes of each. Joy’s Law is the tendency for sunspot pairs (BMRs) to be tilted relative to the east-west direction with a tilt angle that systematically increases with latitude. All BL dynamo models rely on it, but few before STABLE have been able to explicitly capture departures from Joy’s law due to random scatter of BMR tilt angles, which is observed to be substantial. STABLE simulations suggest that the this tilt angle scatter may be sufficient to account for the observed variability in the amplitude of solar cycles. We find that tilt angle scatter can also induce extended periods of low activity known as Grand Minima. Furthermore, our model can usually recover from Grand Minima on its own, a feat that has eluded some previous BL models. I will also discuss the SFT aspects of STABLE, including convective flux transport, 3D poloidal field generation and the role of magnetic pumping.