Long-Term Solar Variability (LSV) Section
Sunspots and Photospheric Dynamics
Sunspots are the most prominent manifestations of magnetic field in the visible layers of the solar atmosphere. Their origin is a dynamo process operating in the solar convection zone. Magnetic field generated there over timescales typical for the solar cycle (~11 years) is transported toward the solar surface through a rapid flux emergence process leading to the formation of active regions. The typical size of sunspots is somewhat larger than the Earth's diameter, their magnetic field is with ~3,000 Gauss strength about 10,000 times stronger than the Earth's magnetic field. Such strong fields modify the convective energy transport leading to a central region (umbra) with predominantly vertical field and a brightness reduced to about 10-20% of that of the undisturbed solar surface. Even though the umbra appears dark compared to the solar surface, the temperature is still 4,000 to 4,500 K. The umbra is surrounded by a filamentary region (penumbra) with a brightness of about 75% (Figure 1). The latter region has strongly inclined field and exhibits large scale outflows of several km/s, the Evershed flow, named after its discoverer (Evershed 1909). At higher resolution the umbra of a sunspot shows fine structure on spacial scales similar to those observed in penumbral filaments. The umbra is not uniformly dark, but shows bright "umbral dots" with a diameter of a few 100 km. At highest possible resolution umbral dots show similar to penumbral filaments a central dark lane (Scharmer et al 2002), Figure 1.
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Figure 1: [enlarge], Sunspot observed with the Swedish Solar Telescope (SST). This image shows the transition from the dark umbra (bottom) toward solar granulation (top). The penumbra in-between shows filaments with central dark lanes. Credit: The SST is operated by the Royal Swedish Academy of Sciences, observation taken 2002 by G. Scharmer. |
HAO scientists undertake state-of-the-art computer simulations of sunspots. Read More »
Currently, HAO scientists are working to further enhance sunspot modeling capability by extending the computational domain of a typically observed active region both horizontally and vertically to more realistically simulate flux emergence into the chromospheres. Read More »
See Profiles in Science page for Matthias Rempel.