太陽黑子周期揭密神奇蝴蝶圖英語美文

Sunspot Cycles: Deciphering the Butterfly Pattern

150多年以前，科學家證實，太陽黑子的活動是週期性的，它的平均週期約為11年;大約90年以前，科學家在這一研究領域又有了新的突破，他們繪製出太陽黑子週期性變化示意圖後，發現赫然呈現在紙上的竟是一隻只翩翩起舞的“蝴蝶”;而現在科學家又有了新的任務，他們正試圖揭開這幅太陽黑子“蝴蝶圖”的祕密……

A little more than 150 years ago, scientists learned that the number of sunspots (temporarily cool, dark areas) on our sun waxes and wanes over a period of about 11 years. About 90 years ago, scientists learned that there"s a butterfly-shaped pattern to this cycle. Now they are trying to learn what drives that pattern.

國際在線消息：150多年以前，科學家證實，太陽黑子的活動是週期性的，它的平均週期約為11年;大約90年以前，科學家在這一研究領域又有了新的突破，他們繪製出太陽黑子週期性變化示意圖後，發現赫然呈現在紙上的竟是一隻只翩翩起舞的“蝴蝶”;而現在科學家又有了新的任務，他們正試圖揭開這幅太陽黑子“蝴蝶圖”的祕密……

據美國“每日科學”網站2月4日報道，有關研究者表示，揭開“蝴蝶圖”的祕密可以讓科學工作者更好地預測太陽風暴(solar storms)何時來臨。太陽風暴爆發時，將會影響通訊、威脅衞星、破壞臭氧層，這與人們的生活息息相關，所以這項研究具有十分重要的意義。

太陽黑子和太陽黑子周期

想揭開問題的謎底，我們必須要對下面一些基本概念有所瞭解。首先我們要知道什麼是太陽黑子(sunspots)和太陽黑子周期(sunspot cycle)。

太陽黑子是人們最早發現也是人們最熟悉的一種太陽表面活動。明亮的太陽光球表面經常出現一些小黑點，這就是太陽黑子。美國國家大氣研究中心高地天文台的`太陽天文學家埃米·諾頓解釋説，太陽黑子之所以產生是因為太陽內部磁場發生變化的結果。

太陽黑子的數量並不是固定的，它會隨着時間的變化而上下波動，每11年會達到一個最高點，這11年的時間就被稱之為一個太陽黑子周期。太陽黑子周期是1843年由一名德國天文學家發現的。

諾頓表示，不僅是太陽黑子的數量會在這11年中發生變化，同時它們所處的位置也會隨之改變。每當一個太陽黑子周期開始的時候，最先出現的黑子總是在離赤道較遠處(平均緯度為35度)，然後由高緯度向低緯度方向移動，最終黑子出現的位置漸漸靠近太陽赤道。

翩翩起舞的“蝴蝶圖”

1904年，英國天文學家愛德華·蒙德發現了一幅奇異的景象，記錄太陽黑子周期變化的圖表竟然呈現出一幅展翅欲飛的蝴蝶圖案。

蒙德以緯度為縱座標，以時間(年份)為橫座標，繪出太陽黑子的分佈圖後，發現漸漸靠近赤道的太陽黑子就像蝴蝶的兩隻翅膀。如果把幾個太陽黑子周期的圖案繪製在一起，就組成了一連串翩翩起舞的“蝴蝶”。

神祕的太陽發電機效應

目前，科學家們正致力於研究這個神奇的太陽黑子“蝴蝶圖”。太陽天文學家諾頓説，要想揭開謎底，首先要從所謂的太陽發電機效應(Solar Dynamo)説起。她説：“太陽發電機效應是太陽物理學中最為神祕的事物之一，它指的是在太陽內部和太陽表面的機械運動轉化成磁能的過程。”

因為太陽黑子活動區域被認為是強磁場區，同時太陽黑子會在11年的週期內發生增多和減少的現象，所以科學家認為太陽磁場也會在這一時期內增強或減弱。諾頓説：“太陽黑子周期的循環性是證明太陽內部磁場在這個週期裏發生變化有力的證據。”

諾頓和她的同事建立了太陽表面和內部的不同種類的熱氣流電腦模型，他們認為這有助於更好地瞭解太陽發電機效應，同時也有助於解釋太陽黑子移動產生“蝴蝶圖”的原因。

最佳理論

諾頓的同事吉爾曼説，對於太陽黑子活動圖為什麼會呈現蝴蝶圖案這個問題，目前還沒有一個統一的科學結論。其中，最主要的理論是以吉爾曼同事迪科派蒂的電腦模擬為基礎的。

迪科派蒂的電腦模擬將太陽黑子的移動和被稱為經向流的等離子流聯繫了起來。經向流在太陽赤道和兩極之間流動，它的全部過程被稱之為太陽活動週期。

經向流就像擁有兩個傳送帶的系統。這兩條“傳送帶”一個位於北半球，一個位於南半球，每個“傳送帶”都沿着太陽表面，從赤道運動到北極或是南極。到達極地時，每條“傳送帶”會轉個彎，進入太陽內部。經向流經過太陽內部的最外層即環流區返回到赤道。當“傳送帶”到達太陽赤道時，它又會轉頭沿着來的路徑，重新回到太陽表面，開始新一輪的循環。

一個太陽活動週期的時間為22年，或者説是兩個太陽黑子周期。這個理論認為，“傳送帶”的兩半都擁有相似的太陽黑子圖案，這就是為什麼太陽黑子活動遵循着11年的週期——等於太陽活動週期的一半。

根據迪科派蒂的的理論，太陽黑子在太陽表面流動會留下痕跡，這種痕跡還被帶到太陽內部，科學家們相信，太陽黑子的磁場在這裏形成，而新的太陽黑子則是在最近週期內的痕跡上形成的。

通過了解經向流速度的變化以及過去的太陽黑子周期，迪科派蒂和同事相信他們也許能夠預測太陽黑子活動的時間和強度，從而也能對太陽風暴有所瞭解。他説：“事實上，在最近的工作中，我們預測因為經向流在目前週期內的速度放慢，所以下一個週期，即週期24的開始將會被推遲。”A little more than 150 years ago, scientists learned that the number of sunspots (temporarily cool, dark areas) on our sun waxes and wanes over a period of about 11 years. About 90 years ago, scientists learned that there"s a butterfly-shaped pattern to this cycle. Now they are trying to learn what drives that pattern.

Understanding what generates the sunspot pattern may allow scientists to provide better forecasts of solar storms, which can cause power outages and disrupt satellite communications on Earth.

But first, what are sunspots? What"s the sunspot cycle? And what"s this pattern?

Sunspots are thought to result from a shifting magnetic field inside the sun, explains Aimee Norton, a solar astronomer with the High Altitude Observatory at the National Center for Atmospheric Research in Boulder, Colorado.

The number of sunspots fluctuates over time, reaching a peak every 11 years. This 11-year pattern is known as the sunspot cycle and was discovered in 1843 by German astronomer Samuel Heinrich.

Not only does the number of sunspots fluctuate over the 11-year period, but so too do their locations, Norton said. Over the period, the sunspots migrate from about 35 degrees north and south latitude toward the sun"s equator.

In 1904 English astronomer Edward Maunder noticed an artful pattern to the cycle.

When the latitude and time of sunspots from an entire cycle are plotted on a map, the migration of sunspots toward the equator looks like two wings of a butterfly. Several cycles plotted together look like a trail of butterflies.

Solar Dynamo

Scientists are now trying to understand why the sunspot belt moves toward the equator over the course of the 11-year cycle. To understand this, Norton said, requires understanding the so-called solar dynamo.

"This is one of the major mysteries in solar physics," she said. "The dynamo is a process by which the mechanical motions on and in the sun are converted into magnetic energy."

Since sunspots are believed to be regions of intense magnetic field and since they increase and decrease over an 11-year cycle, scientists believe that the sun"s magnetic field must also increase and decrease in time.

"The cyclical nature of the sunspot cycle is strong evidence that the magnetic field within the sun is being regenerated during this cycle," Norton said.

Generated by the flow of hot gases, the sun"s electric currents in turn generate magnetic fields.

Norton and her colleagues are building computer models of the various flows on and in the sun to help them understand the solar dynamo. This should, in turn, explain the reason for the sunspot migration pattern.

"Some details of the migration pattern as observed in spot behavior is beyond the current capability of dynamo models to produce, but it may be possible with more elaborate models now under development," said Peter Gilman, a colleague of Norton"s at the High Altitude Observatory.

Best Theory

Gilman said there is no scientific consensus on why sunspot-migration diagrams take the shapes of butterflies. A leading theory is based on computer modeling by colleague Gilman"s colleague Mausumi Dikpati.

Dikpati"s models link the migration to a current of plasma called the meridional flow, which circulates between the sun"s equator and its poles. It"s all part of a process called the Hale cycle.

The flow is like a system of two conveyor belts, one in the northern hemisphere and one in the southern hemisphere. Each belt travels along the surface of the sun, from the equator to the pole (north or south, depending on the hemisphere). At its pole, each belt turns the corner, diving into the sun"s interior.

The flow makes its return trip to the equator through the convection zone, the outermost layer of the sun"s interior. As the belt approaches the equator, it turns and follows a path toward the sun"s surface, and the cycle begins again.

A single Hale cycle takes about 22 years, or two sunspot cycles. The thinking is that the two halves of the "conveyor belt" have similar sunspot patterns on them, which is why sunspot activity follows an 11-year cycle—half a Hale cycle.

According to Dikpati"s theory, sunspots leave an imprint on the surface flow. This imprint is carried into the interior, where scientists believe the sunspot-producing magnetic fields are generated. New sunspots form based on the imprints created during the most recent cycle.

By understanding the variation of the meridional flow"s speed and the sun"s past sunspot cycles, Dikpati and colleagues believe they may be able to forecast the timing and intensity of sunspot activity—and therefore of solar storms.

"In fact, in a very recent work, we are predicting the onset of the next cycle—cycle 24—will be late, because the meridional flow slowed down in the current cycle," Dikpati said.

According to the forecast, the next solar cycle will begin in 2007 to 2008. That means that cycle 24 would begin about a half year late, or about 11 years and six months after the beginning of cycle 23.