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Session 2 - The Solar Photosphere and Magnetic Field.
Display session, Monday, June 10
Tripp Commons,

[2.02] On the Turbulence of the Solar Photosphere

A. Nesis, R. Hammer, H. Schleicher (Kiepenheuer-Institut fuer Sonnenphysik)

Velocity fields of convective origin and unresolved velocity fluctuations ("turbulence spots") are distributed on the solar surface in characteristic ways. The velocity field fluctuations (measured as Doppler shifts) show a pattern similar to that of the granulation, while the turbulence spots are concentrated in the intergranular space near the granular borders and are apparently connected with shear flows. Doppler velocity fields as well as turbulence spots are tightly connected with the dynamics of the granular layers but seem to influence the overlying layers. Emerging ordered laminar convective flows produce shear flows which subsequently generate turbulence, apparently a major controller of the atmospheric dynamics of the sun.

A central issue is the extension of the granular dynamics into the overlying photospheric layers.

In this investigation we address mainly the turbulence spots: the change of their distribution with height in the photosphere, their generation, and their relationship to the granular velocity. We are also interested in the granular velocity patterns and their extension into the photospheric layers. Our observational material consists of spectrograms of excellent spectral and spatial quality. Doppler velocity field and turbulence are measured simultaneously at various heights in the photosphere by means of absorption lines of different strength. To investigate the extension of the influence of the granular dynamics into the photospheric layers we use the coherence analysis, which makes use of the characteristic dynamical patterns of the turbulence and Doppler velocity.

We find that the small scale turbulence pattern changes rapidly with height over a scale of one pressure scale height. This result can be seen as a manifestation of lateral diffusion of turbulence in the intergranular space after its generation by the shear flow at granular borders. This explains the turbulent state of the intergranular space.

Program listing for Monday