Areas of Polar Coronal Holes from 1996 Through 2010
Areas of Polar Coronal Holes from 1996 Through 2010
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DOI：
10.1007/s11207-014-0564-0
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发表时间：
2014-11-01
期刊：
影响因子：
2.8
通讯作者：
Kirk, M. S.
中科院分区：
文献类型：
--
作者：
Webber, S. A. Hess;Karna, N.;Kirk, M. S.
极地日冕洞（PCHs）追踪整个太阳周期的太阳磁场变化。它们的大小和演化已被研究作为全球磁场的代用物。本文介绍了1996年至2010年对PCH区域的测量结果，这些测量结果来自于一种更新的周界追踪方法和两种天气图方法。周长追踪方法利用太阳和日光层天文台/极紫外成像望远镜（SOHO/EIT）的全盘图像，沿太阳边缘探测PCH边界。一种天气图方法利用SOHO/迈克尔逊多普勒成像仪（MDI）的视距磁场来确定两极附近的单极边界。另一种方法将阈值技术应用于由EIT的EUV图像数据创建的天气图。三种方法的结果都表明，两个半球的太阳极大值和极小值是相异的。在数据所跨越的两个太阳极小期（在太阳周期22/23和23/24之间），每个半球的方法平均得到的最大PCH面积约为6%。北半球PCH区域在2010年开始下降，表明该半球向第24太阳周期的最大值下降，而南半球的洞在2010年仍然很大。
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.