Areas of Polar Coronal Holes from 1996 Through 2010
| Autor: | Nishu Karna, William Dean Pesnell, Michael S. Kirk, S. A. Hess Webber |
|---|---|
| Rok vydání: | 2014 |
| Předmět: |
Physics
Astronomy Coronal hole Astronomy and Astrophysics Coronal loop Solar cycle 24 Corona Solar cycle Space and Planetary Science Observatory Physics::Space Physics Extreme ultraviolet Imaging Telescope Astrophysics::Solar and Stellar Astrophysics Polar Astrophysics::Earth and Planetary Astrophysics |
| Zdroj: | Solar Physics. 289:4047-4067 |
| ISSN: | 1573-093X 0038-0938 |
| Popis: | Polar coronal holes (PCHs) trace the magnetic variability of the Sun throughout the solar cycle. Their size and evolution have been studied as proxies for the global magnetic field. We present measurements of the PCH areas from 1996 through 2010, derived from an updated perimeter-tracing method and two synoptic-map methods. The perimeter tracing method detects PCH boundaries along the solar limb, using full-disk images from the SOlar and Heliospheric Observatory/Extreme ultraviolet Imaging Telescope (SOHO/EIT). One synoptic-map method uses the line-of-sight magnetic field from the SOHO/Michelson Doppler Imager (MDI) to determine the unipolarity boundaries near the poles. The other method applies thresholding techniques to synoptic maps created from EUV image data from EIT. The results from all three methods suggest that the solar maxima and minima of the two hemispheres are out of phase. The maximum PCH area, averaged over the methods in each hemisphere, is approximately 6 % during both solar minima spanned by the data (between Solar Cycles 22/23 and 23/24). The northern PCH area began a declining trend in 2010, suggesting a downturn toward the maximum of Solar Cycle 24 in that hemisphere, while the southern hole remained large throughout 2010. |
| Databáze: | OpenAIRE |
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