英语听力文摘 English Digest 489、船尾那条温柔的尾流带（在线收听）

A Smooth Wake

平静的尾流

（A smooth wake on today's moments of science）

Female: Donne and I are on a fantacy cruise. The sun has set and were standing on the rear deck. Look at the reflection of the moon.

Male: You might expect a ship's wake to be more agitated than the surrounding water. Instead, it's a smooth path through the waves that can extend for miles behind the ship. How come?

F: The wake starts out smooth because the passage of the ship destroys whatever wave patterns were there before the ship came through. The reason it stays smooth has to do with tiny organic molecules–such as decomposed plankton–on the surface of the water.

There are always some organic molecules on the ocean's surface, but as the ship pushes along, it plows these molecules to the sides. This leaves the wake something like a winter road that has just been snow-plowed, with piles of snow on both sides of the road.

The center of the wake is relatively free of organic molecules, but the two sides each have an accumulated pile-up. These stretch behind the ship on either side of the wake like ribbons.

M: Well, that's interesting. But how does this keeps wake smooth?

F: It turns out that a thin ribbon of organic molecules on the surface of water is really good at suppressing small waves. These two ribbons, on either side of the wake, act like guardrails, preventing small waves from entering and crossing the wake.

M: So that's why the wake stay so smooth

女：多恩和我正在进行着一场不可思议的巡游。太阳下山了，照耀在（船的）后舱。看，月亮的影子。

男：你或许还期望（船的）尾流要比四周的水更汹涌吧？相反，它却是一条穿梭于海浪间的、可以在船尾延伸至几公里的平静轨迹。如何形成的呢？

女：尾流一开始就是平静的，因为在船经过之后，它的路径变改变了之前波浪的路径。尾流保持平静的原因还与水面上微小的有机分子有关，比如说已分解的浮游生物。

海面上总是会有一些有机分子。但是随着船只前行，它会把这写分子推到一两边。这就让尾流有点像在冬天里刚刚开通的雪路一样，路两旁是成堆的雪。

相对来说，尾流的中间就没有了有机分子，而两边就堆积了很多。在船后面，两边倒偶像这样延伸，就像两条带子一样。

男：嗯，有意思！但是它是怎样保持水流平静的？

女：水面上薄薄的有机分子带真的很能“镇压”周围的小波浪。尾流两边的两条带状物就像护栏一样，阻止小波浪进入甚至横穿过尾流。

男：这就是尾流如此平静的原因啊！

【words & expressions】

rear deck：n. 后舱

decomposed：adj. 已腐烂的，已分解的

plow：vt. 犁；耕；开路

start out：启程

push along：离开

guardrail：n. 护栏；栏杆