3 Granulation

With the previous Section providing the physical background, we now have the tools (and the language) to discuss the various manifestations of convection at the surface of the Sun, treating in this Section the energetically most significant pattern; the solar granulation.

The solar granulation pattern was first observed and described by Herschel (1801), who interpreted the pattern as being due to “hot clouds” floating over a cooler solar surface. Nasmyth (1865Jump To The Next Citation Point) later referred to the pattern as one similar to “willow leaves”. Dawes (1864Jump To The Next Citation Point) was the one who coined the term “granules”, contesting the description of NasmythJump To The Next Citation Point with respect to the shapes – this illustrates that already then spatial resolution of observation was a factor of great importance. The first good photographs, published by Janssen (1896) ended the controversy.

The granulation pattern is in fact, as we now know, associated with heat transport by convection, on horizontal scales of the order of a thousand kilometers, or one megameter (Mm). So, Nasmyth was on the right track concerning the temperature, and must have seen essentially the pattern we know today, but the prolific Dawes (who published 5 – 6 MNRAS papers per year in that period of time) managed to establish the name for it.

 3.1 Observational constraints
 3.2 Convective driving
 3.3 Scale selection
 3.4 Horizontal patterns and evolution
 3.5 Exploding granules
 3.6 Surface entropy jump
 3.7 Temperature fluctuations
 3.8 Average structure
 3.9 Vorticity
 3.10 Shocks
 3.11 Energy fluxes
 3.12 Connections with mixing length recipes

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