Detalles de publicación

PP 06053

The origin of the reversed granulation in the solar photosphere

M. C. M. Cheung, M. Schüssler, and F. Moreno-Insertis
Max-Planck Institut for solar system research, Lindau, Germany Instituto de Astrofisica de Canarias, Tenerife, Spain
We study the structure and reveal the physical
nature of the reversed granulation pattern in the solar
photosphere by means of 3-dimensional radiative hydrodynamics
simulations. We used the MURaM code to obtain a realistic model
of the near-surface layers of the convection zone and the
photosphere. The pattern of horizontal temperature fluctuations
at the base of the photosphere consists of relatively hot granular
cells bounded the cooler intergranular downflow network. With
increasing height in the photosphere, the amplitude of the
temperature fluctuations diminishes. At a height of $z=130-140$ km
in the photosphere, the pattern of horizontal temperature
fluctuations reverses so that granular regions become relatively
cool compared to the intergranular network. Detailed analysis of
the trajectories of fluid elements through the photosphere reveal
that the motion of the fluid is non-adiabatic, owing to strong
radiative cooling when approaching the surface of optical depth
unity followed by reheating by the radiation field from below. The
temperature structure of the photosphere results from the
competition between expansion of rising fluid elements and
radiative heating. The former acts to decrease the temperature of
the fluid whereas the latter acts to drive it upwards towards the
radiative equilibrium temperature. After the fluid overturns and
descends towards the convection zone, radiative energy loss again
decreases the entropy of the fluid. Radiative heating and cooling
of fluid elements that penetrate into the photosphere and overturn
do not occur in equal amounts. The imbalance in the cumulative
heating and cooling of these fluid elements is responsible for the
reversal of temperature fluctuations with respect to height in the
photosphere.

 
Aceptado para publicación en A&A | Enviado el 2006-11-03 | Proyecto 3I1303