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Small-scale Dynamo Action in the Quiet Sun : Observational
Aspects
Big Bear Solar Observatory
Valentina Abramenko
Big Bear Solar Observatory, CAEmail: [email protected]
XXV IUGG/IAGA, Melbourne, Australia
7/05/2011
Turbulence is ubiquitous in the photosphere. A question is: are velocities capable to ensure the increasing, or, al least, non-decreasing magnetic flux?
Kinetic and Magnetic Energy Spectra
Kinetic dissipation scales , λ ν
Spatial scale
Kinetic Spectrum
wavenumber
Pow
er S
pec
tru
m
Magnetic dissipation scales, λ η
Magnetic Spectrum
Case of High Prandtl number, Pr= λ ν / λ η >> 1 Small-scale dynamo action is ensured
Batchelor 1959Nakagawa & Priest 1973Schekochinin+ 2003
XXV IUGG/IAGA, Melbourne, Australia
7/05/2011
Kinetic and Magnetic Energy Spectra
Kinetic dissipation scales , λ ν
Spatial scale
Kinetic Spectrum
wavenumber
Pow
er S
pec
tru
m
Case of Low Prandtl number, Pr= λ ν / λ η <<1 Small-scale dynamo action is questionable
Magnetic dissipation scales, λ η
Magnetic Spectrum
Boldyrev and Cattaneo 2003Iskavov +2007Pietarila Graham + 2010
XXV IUGG/IAGA, Melbourne, Australia
7/05/2011
Kinetic and Magnetic Energy SpectraObserved Velocity Spectra
XXV IUGG/IAGA, Melbourne, Australia
7/05/2011
Kinetic and Magnetic Energy SpectraObserved Magnetic Spectra
-1/3
XXV IUGG/IAGA, Melbourne, Australia
7/05/2011
Kinetic and Magnetic Energy SpectraComparison
λη ?λη ~ η3/4 = K3/4
XXV IUGG/IAGA, Melbourne, Australia
7/05/2011
Bright points detection
Detection criteria: lifetime longer than 20 s; area larger than 2 pixels; brightness above the mean image brightness.
Total: 13597 tracked BBs for th=85 DN 7148 tracked BPs for th=120 DN
7/05/2011XXV IUGG/IAGA, Melbourne,
Australia
Trajectory coordinates measurements (black) vs residual jittering of the telescope (red)
XXV IUGG/IAGA, Melbourne, Australia
7/05/2011
Max jittering: 0.2 pixel = 0.2 x 0.0375” = 5.4 km on the solar surface
This is placeholder copy This is also placeholder copy
Big Bear Solar Observatory
Trajectories of BPs
Typical examples of BPs trajectories. Time intervals between adjacent circles is 10 s. The blue large circles mark the start points of the trajectories.For each tracked BP, the average diameter was calculated.
7/05/2011XXV IUGG/IAGA, Melbourne,
Australia
Big Bear Solar Observatory
Diffusivity in the Photosphere
(x0,y0)
(x10,y10)
(xN,yN)
For each BP, we compute a set of displacements from the start point:
(Δ l)2i = (xi-xo)2+(yi-y0)2
and a set of corresponding time delays:
Then for each we average
displacements from all tracked BPs.
We thus obtain Displacement Spectrum:
7/05/2011XXV IUGG/IAGA, Melbourne,
Australia
Slide Title Here
Big Bear Solar Observatory7/05/2011
XXV IUGG/IAGA, Melbourne, Australia
Manso Sainz+2011 Hinode SOT/SP