Properties of Umbral Dots as Measured from the New Solar Telescope Data and MHD Simulations
Abstract
We studied bright umbral dots (UDs) detected in the main sunspot of AR NOAA 11108 and compare their statistical properties to a state-of-the-art MHD model of a sunspot. The study is based on high resolution data recorded on September 20, 2010 by the New Solar Telescope (NST) at Big Bear Solar Observatory and 3D MHD simulations of sunspots. The 46 min data set included photospheric (0.3nm TiO filter centered at 705.7 nm) and chromospheric (0.025nm Hα Lyot filter) adaptive optics corrected and speckle reconstructed images. Bright UDs, living longer than 150 s, were detected and tracked using an automatic UD detection code. Total 1553 (620) UDs were detected in the photospheric (chromospheric) data. Our main findings are: i) none of the analyzed UDs is of an exact circular shape, ii) the diameter-intensity relationship only works for bright umbral areas, and iii) UD velocities inversely related to their life time. Comparison of photospheric and chromospheric data showed that nearly all photospheric UDs can be identified in the chromospheric images. However, it appears that some small closely spaced UDs appear in the chromospheric images as a single cluster, which may lead to the underestimation of the total number of detected chromospheric UDs. Also, while slow moving and long living UDs seem to exist in both chromosphere and photosphere, fast moving and short living ones are detected mainly in the photospheric images. Comparison of model and observed data shows that both types of UDs display very similar statistical characteristics. The main difference between parameters of model and observed UDs is that i) the average number of observed UDs per unit area is smaller than that of the model UDs, and ii) on average, the diameter of model UDs is slightly larger than that of observed ones.
- Publication:
-
SDO-3: Solar Dynamics and Magnetism from the Interior to the Atmosphere
- Pub Date:
- October 2011
- Bibcode:
- 2011sdmi.confE..86Y
- Keywords:
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- SDO;
- SDO-3;
- SDO 3;
- SDO Workshop;
- LWS/SDO-3/SOHO-26/GONG-2011 Workshop;
- Solar Dynamic Observatory