對太陽黑子說再見？

對太陽黑子說再見？
Say Goodbye to Sunspots?
by Phil Berardelli
on 14 September 2010, 2:41 PM
Weaklings. Without penumbrae, which can be seen in the yellow image, today's sunspots are weakening magnetically.
虛弱的，沒有半影，它可以在黃色圖片看到，今天的太陽黑子正在磁性地減弱
Credit: William Livingston/NSO

Scientists studying sunspots for the past 2 decades have concluded that the magnetic field that triggers their formation has been steadily declining. If the current trend continues, by 2016 the sun's face may become spotless and remain that way for decades—a phenomenon that in the 17th century coincided with a prolonged period of cooling on Earth.

Sunspots appear when upwellings of the sun's magnetic field trap ionized plasma—or electrically charged, superheated gas—on the surface. Normally, the gas would release its heat and sink back below the surface, but the magnetic field inhibits this process. From Earth, the relatively cool surface gas looks like a dark blemish on the sun.

Astronomers have been observing and counting sunspots since Galileo began the practice in the early 17th century. From those studies, scientists have long known that the sun goes through an 11-year cycle, in which the number of sunspots spikes during a period called the solar maximum and drops—sometimes to zero—during a time of inactivity called the solar minimum.

The last solar minimum should have ended last year, but something peculiar has been happening. Although solar minimums normally last about 16 months, the current one has stretched over 26 months—the longest in a century. One reason, according to a paper submitted to the International Astronomical Union Symposium No. 273, an online colloquium, is that the magnetic field strength of sunspots appears to be waning.

Since 1990, solar astronomers Matthew Penn and William Livingston of the National Solar Observatory in Tucson, Arizona, have been studying the magnetic strength of sunspots using a measurement called Zeeman splitting. Named after the Dutch physicist who discovered it, the splitting is the distance that appears between a pair of lines in a spectrograph of the light given off by iron atoms in the sun’s atmosphere. The wider the splitting, the greater the intensity of the magnetic field that created it. After examining the Zeeman splitting of 1500 sunspots, Penn and Livingston conclude that the average magnetic field strength of sunspots has declined from about 2700 gauss—the average strength of Earth's field is less than 1 gauss—to about 2000 gauss. The reasons for the decrease are not clearly understood, but if the trend continues, sunspot field strength will drop to 1500 gauss by as early as 2016. Because 1500 gauss is the minimum required to produce sunspots, Livingston says, at that level they would no longer be possible.

The phenomenon has happened before. Sunspots disappeared almost entirely between 1645 and 1715 during a period called the Maunder Minimum, which coincided with decades of lower-than-normal temperatures in Europe nicknamed the Little Ice Age. But Livingston cautions that the zero-sunspot prediction could be premature. "It may not happen," he says. "Only the passage of time will tell whether the solar cycle will pick up." Still, he adds, there's no doubt that sunspots "are not very healthy right now." Instead of the robust spots surrounded by halolike zones called penumbrae, as seen during the last solar maximum (photo), most of the current crop looks "rather peaked," with few or no penumbrae.

"It is a very interesting sequence of observations," says solar physicist Scott McIntosh of the National Center for Atmospheric Research in Boulder, Colorado. The researchers "have carefully analyzed their data and the trend appears to be real," he says.

Solar physicist David Hathaway of NASA's Marshall Space Flight Center in Huntsville, Alabama, agrees but with a caveat. "It's an important paper," he says. But the sunspot magnetic field calculations don't take into account a lot of small sunspots that appeared during the last solar maximum. Those sunspots have weaker magnetic fields, which, if not included, could make the average sunspot magnetic field strength seem higher than it really was.
http://news.sciencemag.org/sciencenow/2010/09/say-goodbye-to-sunspots.html

太陽黑子"不健康" 2016年或對人類"說再見"
2010年09月16日09:45
來源：《科技日報》

　本報訊 （記者張夢然）據美國《科學》雜志網站9月15日（北京時間）報道，科學家研究發現，太陽黑子的磁場在過去20年內呈穩步下降趨勢。按目前的趨勢發展下去，到2016年，太陽表面的黑子將變得了無蹤跡，並將維持至少數十年。此一現象上次發生時，正是17世紀地球的長時間低溫期。

　　黑子看上去就像太陽光球中的一些深暗色斑點，其磁場比周圍強，溫度比周圍低，是主要的太陽活動現象。太陽黑子活動存在著明顯的周期性，平均為11.2年。其中，在開始的4年左右的時間裡，黑子會越來越多，活動劇烈，其數值達到極大的那一年，稱為太陽活動峰年﹔而隨后的7年時間裡，黑子活動逐漸減弱，數目也越來越少，在達到“極小值”（甚至可為零）的那一年，稱為太陽活動谷年。

　　太陽活動谷年可看做是一個新周期的開始年。在天文學家對黑子活動從1755年開始標號統計至今，應是迎來第24個太陽活動周期的時候。而最近的一個太陽黑子極小值，截至去年也應徹底結束。但奇怪的是，科學家們發現，本次太陽極小值居然延續了超過26個月，而其通常隻會延長約16個月，26個月無疑破了本世紀內延長時間的紀錄。據提交給國際天文聯合會的一份報告稱，太陽黑子的磁場強度出現減弱這一現象，正是太陽黑子極小值時期被“拖長”的原因。

　　在位於美國亞利桑那州的國家太陽天文台，馬修·佩恩與威廉·利文斯頓自1990年起便利用“塞曼分離”測量法對太陽黑子的磁場強度進行研究。在探測了1500個太陽黑子后，兩人得出結論：黑子的磁場從約2700高斯降至2000高斯。《科學》雜志指出，切勿認為700高斯的降值不多，要知道，地球的平均磁場還不到1高斯。

　　盡管磁場降低的原因至今未明，但據利文斯頓推測，按目前的趨勢一路發展下去，不用到2016年，太陽黑子磁場就會跌至1500高斯。因為1500高斯已是產生黑子的最小極值，屆時，黑子們恐怕將不復存在。

　　在人類的歷史上，這種現象並非首次發生。在1645年至1715年間，太陽黑子一直呈“失蹤”狀態，這一時期被稱為“蒙德極小值”。而該現象發生時，整個歐洲正在經歷持續了數十年的低溫“小冰河期”。但利文斯頓警告說，目前就預言會出現“零太陽黑子”的狀態還為時過早，還要觀察太陽周期是否能隨時間推移而回升，但無疑，太陽黑子們現在“很不健康”。

　　美國國家大氣研究中心太陽物理學家斯科特·麥金托什表示，該分析十分仔細且研究數據確鑿無疑。

　　

　　《漢書·五行志》關於公元前28年5月10日“日出黃有黑氣，大如錢，居日中央”的描述,是現今世界上公認最早的太陽黑子記錄。然而，其后兩千年裡沒有誰真正在乎它。只是近幾十年來，科學家才逐漸認識到，太陽黑子活動與地球上的地質、天氣現象等密切相關，並會干擾甚至損害各種電子產品。尤其在此災難頻發之年，很多人相信都是太陽惹的禍，往輕裡說也是推波助瀾。所以，佩恩等人的發現甭管確實與否，至少能讓我們鬆口氣。(科技日報)
http://scitech.people.com.cn/BIG5/12741533.html

科學家稱太陽活動會引起地球降溫