Another way to light a fire.
Another way to light a fire.
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另一种生火的方法。
DOI：
10.1126/science.263.5148.757
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发表时间：
1994
期刊：
影响因子：
56.9
通讯作者：
J. Glanz
中科院分区：
文献类型：
--
作者：
J. Glanz
大多数太阳物理学家试图解释太阳日冕是如何被加热到其可见表面温度的200倍的--这显然是对太阳物理学的蔑视--寻找将太阳表面的搅动转化为热对流的方法（见正文）。但是爱荷华州大学的杰克·斯卡德认为，没有必要寻找复杂的方法来将这种能量向上输送并将其倾倒到日冕粒子中。他认为这些粒子在到达日冕之前就已经拥有了所需的全部能量。斯卡德指出，像任何气体一样，日冕底部的等离子体由许多不同能量的粒子组成。他说，太阳强大的引力将运动较慢、能量较低的粒子限制在靠近太阳表面的一层;只有能量较高、温度较高的粒子才能升到太阳表面以上。他说，这种“过滤”可能会导致温度随着高度而迅速升高。尽管很简单，但这种机制并没有赢得斯卡德的同行。这是因为他必须对靠近太阳表面的粒子速度分布做出一个主要假设：在分布的高能端有一个不寻常的粒子丰度。如果没有这些高能量的“尾巴”，过滤产生的热粒子就太少，无法提高温度。斯卡德尔认为，太阳表面层的热驱动搅动很容易产生等离子体，其中含有大量的极高能量粒子。但是国家太阳天文台的杰克·齐克却不这么认为。“他有很多工作要做，以显示如何[尾巴]可以生产。芝加哥大学的尤金帕克是日冕研究的先驱，他补充说，”没有人知道什么会在太阳附近产生热粒子”。如果等离子体没有尾巴，Zirker说，这种机制就像“说如果猪有翅膀，它们就能飞。”斯卡德反驳说，卫星观测显示太阳风中有热尾，它起源于日冕。没有人会立刻否定他的理论，特别是因为它已经显示出一种不可思议的能力来预测其他理论所质疑的加热方面-例如，观察到从太阳黑子附近的明亮区域向上看到的等离子体环在顶部最热。在斯卡德尔的图片中，最高的温度自然会出现在最高的海拔，那里有最多的慢粒子被过滤掉。但是，在斯卡德尔能够找到一种令人信服的方法来钉在他的等离子体上之前，他的大多数寻找日冕热源的同事都选择了可扩展性而不是优雅。JG
Most solar physicists trying to explain how the sun's corona is heated to 200 times the temperature of its visible surface-in apparent defiance of thermodynamicslook for ways to tum the churning of the solar surface into a heat ource (see main text). But Jack Scudder of the University of Iowa thinks there's no need to search for elaborate ways to funnel this energy upward and dump it into the coronal particles. He thinks the particles have all the energy they need before they ever get to the corona. Like any gas, the plasma at the base of the corona consists of particles of many different energies, Scudder notes. The sun's intense gravity, he says, confines sIowermoving, lower-energy particles to a layer near the surface; only the higher-energyhotter-particles can rise far above the solar surface. This" filtering," he says, could produce a rapid increase in temperature with height. For all its simplicity, this mechanism isn't winning over Scudder's peers. That's because he has to make one major assumption about the particles' velocity distribution close to the solar surface: an unusual abundance of particles at the high-energy end of the distribution. Without these high-energy" tails," the filtering would yield too few hot particles to boost the temperature. Scudder believes that the heat-driven churning in the sun's surface layers could readily produce a plasma that has an unusually large fraction of very-high-energy particles. But Jack Zirker of the National Solar Observatory doesn't see it that way." He's got a good deal of work to show how [the tails] could be produced." Adds the University ofChicago's Eugene Parker, a pioneer in the study of the corona," Nobody knows what would produce the hot particles" near the sun. And if the plasma has no tails, says Zirker, the mechanism is" like saying if pigs had wings they could fly." Scudder counters that satellite observations have revealed hot tails in the solar wind, which originates in the corona. And no one is rejecting his theory out of hand, especially since it has shown an uncanny ability to predict aspects of the heating with which other theories have struggled-for example, the observation that the loops of plasma seen arching upward from the bright regions near sunspots are hottest at the top. In Scudder's picture, the highest temperatures would naturally occur at the highest altitudes, where the greatest number of slow particles have been filtered out. But until Scudder can find a convincing way to pin tails on his plasma, most of his colleagues looking for a coronal heat source are opting for plausibility over elegance.-JG