Variation in sunspot properties between 1999 and 2011 as observed with the Tenerife Infrared Polarimeter
Variation in sunspot properties between 1999 and 2011 as observed with the Tenerife Infrared Polarimeter
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DOI：
10.1051/0004-6361/201118635
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发表时间：
2012-03
影响因子：
6.5
通讯作者：
R. Rezaei;C. Beck;C. Beck;W. Schmidt
中科院分区：
文献类型：
--
作者：
R. Rezaei;C. Beck;C. Beck;W. Schmidt
目标。本文研究了第23太阳活动周下降阶段和第24太阳活动周开始阶段的磁场强度和太阳黑子本影强度的变化。方法.我们分析了从1999年到2011年用德国真空塔望远镜（VTT）的特内里费红外偏振仪（TIP）观测到的183个太阳黑子的样本。磁场强度由一条近红外光谱线中的斯托克斯-V信号的塞曼分裂导出，Fe i 1564.8 nm、Fe i 1089.6 nm或Si i 1082.7 nm。这避免了来自无场安静的太阳环境的非偏振杂散光的影响，这些杂散光会影响斯托克斯-I在本影中看到的分裂。测量了最小阴影连续强度和最小阴影面积。结果发现第23太阳周后期太阳黑子有系统的减弱趋势，具有比循环开始时更小的最大磁场强度。磁场强度随时间下降约94 Gyr −1，这远远超出了预期的统计波动，因为接近周期最大值（14 Gyr −1）的太阳黑子数量较多。在相同的时间间隔内，本影的连续强度以Ic yr −1的1.3（±0.4）%的速率增加，而本影面积没有显示出任何高于统计方差的趋势。在新的第24周，太阳黑子比第23周末的太阳黑子表现出更高的场强和更低的连续强度，从而中断了这一趋势。结论.与初始阶段相比，太阳黑子在太阳周期的后期阶段具有本质上较弱的场强和较亮的本影，其面积没有任何显着变化。在新的周期中，太阳黑子的场强突然增加，这表明周期变化在任何跨周期的长期趋势中占主导地位。我们发现，在整个周期中，场强略有下降，强度增加，这是一个长期趋势。
Aims. We study the variation in the magnetic field strength and the umbral intensity of sunspots during the declining phase of the solar cycle No. 23 and in the beginning of cycle No. 24. Methods. We analyze a sample of 183 sunspots observed from 1999 until 2011 with the Tenerife Infrared Polarimeter (TIP) at the German Vacuum Tower Telescope (VTT). The magnetic field strength is derived from the Zeeman splitting of the Stokes-V signal in one near-infrared spectral line, either Fe i 1564.8 nm, Fe i 1089.6 nm, or Si i 1082.7 nm. This avoids the effects of the unpolarized stray light from the field-free quiet Sun surroundings that can affect the splitting seen in Stokes-I in the umbra. The minimum umbral continuum intensity and umbral area are also measured. Results. We find that there is a systematic trend for sunspots in the late stage of the solar cycle No. 23 to be weaker, i.e., to have a smaller maximum magnetic field strength than those at the start of the cycle. The decrease in the field strength with time of about 94 Gyr −1 is well beyond the statistical fluctuations that would be expected because of the larger number of sunspots close to cycle maximum (14 Gyr −1 ). In the same time interval, the continuum intensity of the umbra increases with a rate of 1.3 (±0.4)% of Ic yr −1 , while the umbral area does not show any trend above the statistical variance. Sunspots in the new cycle No. 24 show higher field strengths and lower continuum intensities than those at the end of cycle No. 23, interrupting the trend. Conclusions. Sunspots have an intrinsically weaker field strength and brighter umbrae at the late stages of solar cycles compared to their initial stages, without any significant change in their area. The abrupt increase in field strength in sunspots of the new cycle suggests that the cyclic variations are dominating over any long-term trend that continues across cycles. We find a slight decrease in field strength and an increase in intensity as a long-term trend across the cycles.