41 research outputs found
Polar Field Puzzle: Solutions from Flux-Transport Dynamo and Surface Transport Models
Polar fields in solar cycle 23 were about 50% weaker than those in cycle 22.
The only theoretical models which have addressed this puzzle are surface
transport models and flux-transport dynamo models. Comparing polar fields
obtained from numerical simulations using surface flux transport models and
flux-transport dynamo models, we show that both classes of models can explain
the polar field features within the scope of the physics included in the
respective models. In both models, how polar fields change as a result of
changes in meridional circulation depends on the details of meridional
circulation profile used. Using physical reasoning and schematics as well as
numerical solutions from a flux-transport dynamo model, we demonstrate that
polar fields are determined mostly by the strength of surface poloidal source
provided by the decay of tilted, bipolar active regions. Profile of meridional
flow with latitude and its changes with time have much less effect in
flux-transport dynamo models than in surface transport models.Comment: ApJ (accepted
Observations, Modeling, and Predictions of Solar Activity From the Deep Interior to the Corona
Solar activity is a manifestation of magnetic self-organization processes that involve complex dynamical coupling of various layers of the Sun acting over a broad range of spatial and temporal scales. Synergy of observational, theoretical, and modeling efforts is key to understanding solar activity variation, dynamics, and evolution and to developing reliable physics-based forecasts of long-term solar cycles and short-term activity manifestations, seasons of solar activity, such as periods of enhanced flaring and CME activity. The session welcomes observers, modelers, and theoreticians to share their results and ideas and to discuss current challenges, development of emerging fields (such as data assimilation), and the analysis of historical and modern observational data using theoretical modeling, interpretations, and predictions
Theory of Solar Meridional Circulation at High Latitudes
We build a hydrodynamical model for computing and understanding the Sun's
large-scale high latitude flows, including Coriolis forces, turbulent diffusion
of momentum and gyroscopic pumping. Side boundaries of the spherical 'polar
cap', our computational domain, are located at latitudes .
Implementing observed low latitude flows as side boundary conditions, we solve
the flow equations for a cartesian analog of the polar cap. The key parameter
that determines whether there are nodes in the high latitude meridional flow is
, in which is the interior rotation
rate, n the radial wavenumber of the meridional flow, the depth of the
convection zone and the turbulent viscosity. The smaller the
(larger turbulent viscosity), the fewer the number of nodes in high latitudes.
For all latitudes within the polar cap, we find three nodes for
, two for , and one or none for
or higher. For near our model exhibits 'node
merging': as the meridional flow speed is increased, two nodes cancel each
other, leaving no nodes. On the other hand, for fixed flow speed at the
boundary, as is increased the poleward most node migrates to the pole and
disappears, ultimately for high enough leaving no nodes. These results
suggest that primary poleward surface meridional flow can extend from
to the pole either by node-merging or by node migration and
disappearance.Comment: Accepted in Ap