arXiv 0901.11582009-01-09astro-ph.SR

第23太阳活动周期间EUV极冕洞的自动探测

Automated Detection of EUV Polar Coronal Holes During Solar Cycle 23

Michael S. Kirk, W. Dean Pesnell, C. Alex Young, Shea A. Hess Webber

备注：: 18 pagers, 7 figures, accepted to Solar Physics
DOI：: 10.1007/s11207-009-9369-y

摘要：

提出了一种新的极冕洞自动检测方法。这种方法被称为周长跟踪，使用SOHO上的极紫外成像望远镜（EIT）在太阳活动周期23期间拍摄的一系列171，195和304张完整的磁盘图像来测量极冕洞的周长，因为它们出现在四肢上。周长跟踪通过在太阳边缘进行测量，最大限度地减少了由各种波长的发射等离子体造成的视线遮蔽。周长追踪还允许从数据中有机地得出极地自转周期为33天。我们称之为哈维轮换率，并从1900年1月4日开始计算哈维轮换。根据测量的周长，我们可以将曲线拟合到数据中，并在最佳拟合线内导出面积。1996年，在第23个太阳活动周开始时，我们观测到北极洞的面积约为太阳总表面积的4.2%，2007年约为3.6%。南极洞的面积在1996年约为4.0%，在2007年约为3.4%。因此，北极和南极的空洞面积现在比第23个周期开始时小了不超过15%。这与极性磁场相比，测量到现在比一个周期前少了大约40%。

英文摘要：

A new method for automated detection of polar coronal holes is presented. This method, called perimeter tracing, uses a series of 171, 195, and 304 Å full disk images from the Extreme ultraviolet Imaging Telescope (EIT) on SOHO over solar cycle 23 to measure the perimeter of polar coronal holes as they appear on the limbs. Perimeter tracing minimizes line-of-sight obscurations caused by the emitting plasma of the various wavelengths by taking measurements at the solar limb. Perimeter tracing also allows for the polar rotation period to emerge organically from the data as 33 days. We have called this the Harvey rotation rate and count Harvey rotations starting 4 January 1900. From the measured perimeter, we are then able to fit a curve to the data and derive an area within the line of best fit. We observe the area of the northern polar hole area in 1996, at the beginning of solar cycle 23, to be about 4.2% of the total solar surface area and about 3.6% in 2007. The area of the southern polar hole is observed to be about 4.0% in 1996 and about 3.4% in 2007. Thus, both the north and south polar hole areas are no more than 15% smaller now than they were at the beginning of cycle 23. This compares to the polar magnetic field measured to be about 40% less now than it was a cycle ago.

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