Micro- and macroturbulent motions and the velocity spectrum of the solar photosphere

✍ Scribed by C. Jager

• Publisher: Springer
• Year: 1972
• Tongue: English
• Weight: 508 KB
• Volume: 25
• Category: Article
• ISSN: 0038-0938
• DOI: 10.1007/bf00155744

✦ Synopsis

A given motion field in a stellar atmosphere is usually observed through 'filters' defined by line shifts and -broadenings and conventionally called macroturbulence and microturbulence.

These 'filters' can be defined and computed exactly, as a function of the wave number of the velocity field (Figure I).

We apply the results to several cases of an assumed motion field spectrum, and to observations of broadenings and displacements of solar Fraunhofer lines formed at a depth ~ = 0.1 (Figure 2),

The results show that virtually all energy of the photospheric motions at that level is contained in a small range of wavenumbers, corresponding to the observed distribution of granular cell diameters. In other words: a well-developed spectrum of hydrodynamical turbulence extending over a large range of wavelengths does not exist at that level of the photosphere.

* By z5 we mean the monochromatic optical depth in the continuous spectrum at 5000 ,~.