# Dynamo, Dynamical Systems and Topology

July 25, 2011 to August 19, 2011
Nordita
Europe/Stockholm timezone

## Tentative program

Week 1: 25-29 July
Monday, 25 July
9:00-12:00 Registration, computer set-up
14:00-16:00 Discussion of the program agenda
and presentation plan
16:00-17:00 Welcome reception

Tuesday, 26-29 July
Program Topic: "Numerical simulations and mean-field theory"
- Recent results of numerical dynamo simulations
- Effects of magnetic helicity and cross-helicity
- Models of turbulent diffusivity and magnetic pumping
- Progress in mean-field dynamo models
- Links between numerical simulations and mean-fields models

Tuesday, July 26, 9:30 - 12:00 (coffee break 10:30-11:00)

- Effects of magnetic helicity and cross-helicity
A. Brandenburg, V. Pipin, D. Sokoloff, K. Kuzanyan, N. Yokoi

Wednesday, July 27, 9:30 - 12:00 (coffee break 10:30-11:00)

- Cross-helicity, models of turbulent diffusivity and magnetic pumping

N.Yokoi, Cross-helicity modeling (cont.)
I. Rogachevskii, Models of turbulent pumping
N. Kleeorin, Compressibility effects in turbulent pumping and diffusivity

Thursday, July 28, 9:30 - 12:00 (coffee break 10:30-11:00)
- Mean-field dynamo models
V. Pipin,  Surface-shear dynamo model
G. Guerrero, Flux-transport solar dynamo models, advantages and issues

Friday, July 29, 9:30 - 12:00 (coffee break 10:30-11:00)

- Mean-field dynamo theory and observations

K. Kuzanyan, Review of observations of cross-helicity
A. Bonanno, Dynamo model with meridional flow with deep stagnation point

Week 2: 1-5 August

Monday, August 1
- Turbulence models in dynamo theory

A. Brandenburg, Introduction to tau-approximation
K.-H. Raedler, Comments on tau- and smoothing approximations
I. Rogachevskii, Comparison of tau approximation with others analytical approaches

Tuesday, August 2

- Dynamical models and dynamo
M.Reshetnyak, Break of symmetry in Parker's dynamo
N. Kleeorin, How to calculate the integral of motion, and Kolmogorov theory in the contents of dynamo theory

Wednesday, August 3

- Recent results of numerical dynamo simulations
R. Simitev, Convective-driven dynamo and applications to the Sun
F. Busse, Applications of thin-shell models to the Sun
P. Kapyla, Stratified convective dynamos in a spherical shell
A. Brandenburg, Low Prandtl number simulations

Thursday, August 4
- Oscillatory and chaotic regimes
D. Mitra, Kinematic dynamos with shear and fluctuating alpha effect
Xing Wei, Kinematic dynamo action in spherical Couette flow

Friday, August 5
- Subgrid scale models
N. Mansour, SGS MHD LES models
N.Yokoi, Incorporation of helicity effects in sub-grid scale models

Week 3: 8-12 August
Program Topic: "Astrophysical Dynamos"

Monday, August 8

Individual project and collaborations

Tuesday, August 9
A. Bobrick, Mass transfer in white dwarf-compact object binaries
R. Arlt, Angular-momentum removal through stellar radiation zones

Wednesday, August 10
D. Sokoloff, Simple model for geodynamo reversals
M.Reshetnyak,  Compressibility and Kinetic Helicity Generation in Geodynamo

Thursday, August 11
K. Kuzanyan, Observable statistical properties of current helicity distribution in
solar active regions as manifestation of multi-scale nature of solar
turbulence
D. Sokoloff, Cluster analysis of the butterfly diagram

Friday, August 12
A. Bonanno, Stellar dynamo
D. Sokoloff, Polar branches of stellar activity waves: dynamo models
Sharanya Sur,  Galactic dynamo

Week 4: 15-18 August
Program Topic: "Dynamo, Magnetic Self-Organization and Links to Observations"

Monday, 15 August
Joern Warnecke, Coronal mass ejections driven by dynamo action underneath the solar surface
Fabio Del Sordo, The generation of vorticity through irrotational forcing

Tuesday, 16 August
Elisabete M. de Gouveia Dal Pino,  Magnetic Flux Transport in turbulent Astrophysical environments: the role of Magnetic Reconnection
Phil Goode, Strange solar cycles

11:00 Nordita seminar: Irina Kitiashvili, Multi-scale dynamics of the Sun

Wednesday, 17 August
Jan Stenflo, Bipolar magnetic regions on the Sun: Global analysis of the SOHO/MDI data set
Alexander Kosovichev, Helioseismology and magnetic field observations from SDO
Maarit Mantere, New interpretation of starspots

1:30pm Seminar: Irina Kitiashvili, Realistic simulations of solar magnetoconvection

3:30pm Göran Scharmer, Observations of the Evershed effects

Thursday, 18 August
Phil Goode, New solar observational results that support local dynamos
Jan Stenflo, Collapsed, uncollapsed, and hidden magnetic flux on the quiet Sun
Vincent Duez, Relaxation in rotating stellar radiation zones
Simon Candelaresi, Magnetic helicity, topological interpretation, relaxation and transport

3:30pm  - Jan Snellman, 1D models of Boussinesq convection

Afternoon tea topics:
Nobumitsu Yokoi, Comments on solar wind turbulence
Nobumitsu Yokoi, Magnetic reconnection
Axel Brandenburg, Solar winds results

19 August
9:00 - 12:00 Final reports by participants
- Concluding remarks, future plans

Understanding the origin of solar and stellar magnetic field is one of the central problems of physics and astrophysics, and a key to understanding the cosmic magnetism, in general. There are two main difficulties in studying this problem: 1) magnetic fields are generated by turbulent dynamos in convection zones below the visible surface, not accessible by direct observations; 2) solar and stellar magnetic activity is a multi-scale phenomenon, involving physical processes on very small scales, probably, below the current observational limit, and at the same time showing remarkable large-scale spatial and temporal organizations over a whole star. The prime target of our investigation is the Sun, which serves as the Rosetta Stone in this field and holds the key to unlocking the secrets of magnetic field generation in the Universe. The most detailed observational data and theoretical models have been obtained for the Sun, but also a very significant progress has been in observations and theories of magnetism on other stars.

Observationally, most efforts for solving the problem of solar and stellar magnetism are focused on developing helio- and asteroseismology for probing the structure and dynamics inside the Sun and stars and detecting changes associated with magnetic fields, on high-resolution observations for probing small-scale and even unresolved magnetic structures and their organization and evolution, and on studying large-scale patterns of sunspots and starspots and magnetic activity cycles.

Theoretically, this problem is addressed by developing physical models at three different levels of the spatial and temporal domain: 1) direct 3D MHD simulations of small volumes of the convection zone with the highest possible resolution (local dynamo); 2) 2D and, more recently, 3D mean-field theories of the global dynamo on the scale of the activity cycle, based on turbulent sources and transport models; 3) simple 1D non-linear dynamical models to investigate long-term evolution of the dynamo. These approaches have been developed independently and quite successfully by different groups.