Hurlburt Matthews Proctor 1996 paper: SIMULATIONS
In magnetic regions of strong convection, mean flows arise along tilted fields (with
respect to gravity)
Flows speed up as fields tilt toward horizontal, then vanish AT horizontal
Traveling waves also arise and speed up similarly; wave speeds are slower than flow
speeds, and can be reversed.
Neal’s poster: The Proctor Effect:
As the mean inclination of the magnetic field through a layer of compressible fluid
increases, 1) the pattern of cells formed
by magnetoconvection travel at an increasing horizontal rate, vp and 2) increasing,
mean shear flows produce surface flows
that can be comparable to the convective flow velocities, u. (from Hurlburt, Mathews
and Proctor (1996)).
Solar plasma flows and convection with oblique magnetic fields (Nina, 2010)
(Observational tests of simulations:
Moving charges in the Sun’s plasma create a complex network of magnetic fields. This
is at the heart of dynamic solar events, such as active regions, sunspots,
and coronal mass ejections. We study magnetoconvection, the motion of magnetized
ionized fluids (plasmas), to better understand the Sun.
Models of solar magnetoconvection often assume simplified magnetic fields that are
either completely vertical or horizontal. Realistic fields, however, are often inclined at
oblique angles. We analyze high resolution data from the Solar Optical Telescope on
the Hinode spacecraft, and compare velocities with magnetic field inclinations. We then
compare results with predictions from a numerical model of nonlinear compressible
Hurlburt, N.E., Matthews, P.C., Proctor, M.R.E. Nonlinear Compressible Convection in
Oblique Magnetic Fields. 1996, ApJ 457:933-938
Berger, T., et al. Hinode Solar Optical Telescope Data Analysis Guide. Version 3.3. 09
Mar 2009.
This work was supported by NSF grant 0807651. We thank colleagues R. Shine, M.
DeRosa, M. Cheung, T. Berger, A. Sainz-Dalda, G. Slater, Z. Frank and R. Seguin at
Lockheed Martin Solar and Astrophysics Laboratory for generously providing guidance
and facilities for this research.
Hinode is a Japanese mission developed and launched by ISAS/JAXA, collaborating
with NAOJ, NASA and STFC (UK), ESA, and NSC (Norway).
Hurlburt, Neal E.; Matthews, Paul C.; Proctor, Michael R. E., Nonlinear Compressible Convection in
Oblique Magnetic Fields,
1996ApJ...457..933H
Searching for the Proctor Effect using Hinode (Neal, Nina, Zita, 2010)
Matthews, et al. (JFM,1992) proved that there are no stationary modes when linearized
compressible magnetoconvection is in the presence of magnetic field with an
inclination from the vertical. Instead all convective modes take the form of traveling
waves, with the convection pattern moving horizontally with a speed that is a function
of angle and field strength. Hurlburt, Matthews and Proctor (ApJ 1996) confirmed that
this behavior extends into the fully nonlinear regime and conjectured that this may play
a role in the dynamics of sunspot penumbra.
We discuss the possible behavior, search for its signature in Hinode data and discuss
it’s relevance to solar observations. In particular we begin to explore the impact of this
“Proctor Effect” in current investigations that compare surface observations and
helioseismic inversions.
Preliminary Results: Active Region
Simple scatter plots of the local field inclination and flow speed shows a high degree of
scatter. The patterns visible in the active region map successfully reproduce previous
results of an inflow pattern in
the penumbra and outflow in the moat. Simple scatter plots of the local field inclination
and flow speed shows a high degree of scatter, but there is a suggestion of a angle
dependence matching that is compatible with the expectation of the Proctor Effect, and
with an amplitude of ~2 m/s/degree. A similar plot of flow speed against field strength
shows a decrease, as would be expected as the field dampens the convection. Sorting
the points by field strength (not shown) suggests that this contributes to the scatter in
the angle plot.
CONCLUSIONS
While the results are tenuous, it appears that the Proctor Effect may be detectable in
the data from Hinode/SOT. A more thorough study is underway to refine the results. If
these flows are confirmed, then it may well be the case that the small, large scale flow
patterns seen in correlation tracking may is influenced by the field configuration. We
have not considered the second consequence of the Proctor Effect, the angular
dependence of the mean surface flow, in this study. These flows need not align with the
pattern motion we studied. We have conjectured that they are seen as the Evershed
flow in sunspot penumbra, and suspect they may have more subtle effects in weaker
fields regions.
We thank R. Shine, M. De Rosa, and Z. Frank for their assistance and guidance. This
work was supported by NASA through grants NAS5-38099,
NNM07AA01C, NNG04EA00C and Lockheed Martin Internal Research Funds.
FLUX PUMPING AND MAGNETIC FIELDS IN THE OUTER PENUMBRA OF A
SUNSPOT
Nicholas H. Brummell, Steven M. Tobias, John H. Thomas, and Nigel O. Weiss
The Astrophysical Journal, 686:1454Y1465, 2008 October 20
We interpret the transverse motions as corresponding to roll-like convective flows, while the
inward radial velocity is more likely to be a traveling pattern than bodily motion, as suggested by
studies of traveling waves in magnetoconvection when the imposed field is inclined (Matthews
et al. 1992; Hurlburt et al. 1996, 2000; Thompson 2005).