ACT科学推理背景知识系列-演替与大气层

 

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ACT科学推理背景知识系列
演替


某一地段上群落由一种类型自然演变为另一类型的有顺序的更替过程,称为演替。主要标志为群落在无中国组成上发生了变化;或者是在一定区域内一个群落被另一个群落逐步替代的过程。它是植物群落动态的最重要特征。 演替一般分为原生演替和次生演替。

原生演替(primary successsion)

在从未有过生物生长或虽有过生物生长但已经被彻底消灭了的原生裸地上发生的生物演替,称为原生演替,又称初生演替。例如:在由海底火山喷发形成的一个新岛上,由覆盖的冰层融化而暴露的某一地区上开始的演替就属于原生演替。在原生演替中生长的第一批物种,成为先驱物种。原生演替在完全没有植物的基础上,因植物移居发生的演替,由此逐渐发生的演替叫做原生演替系列(prisere)

In primary succession pioneer species like lichen, algae and fungi as well as other abiotic factors like wind and water start to "normalize" the habitat. Primary succession begins on rock formations, such as volcanoes or mountains, or in a place with no organisms or soil. This creates conditions nearer optimum for vascular plant growth; pedogenesis or the formation of soil is the most momentous process.

Primary succession on Rangitoto Island



次生演替(secondary succession)

原来的植物群落由于火灾,洪水,涯崩,火山爆发,风灾,人类活动 等因素,大部分消失后所发生的演替。由其他部分进入,或者残存根系,种子重新生长而发生的。这种演替又叫做次生演替系列(subsere)

Secondary succession is one of the two types of ecological succession of plant life. As opposed to the first, primary succession, secondary succession is a process started by an event (e.g. forest fire, harvesting, hurricane) that reduces an already established ecosystem (e.g. a forest or a wheat field) to a smaller population of species, and as such secondary succession occurs on preexisting soil whereas primary succession usually occurs in a place lacking soil.



 
大气层
 


大气层(atmosphere)又叫大气圈,地球被这一层很厚的大气层包围着。大气层的主要成分主要有,氮气,占78.1%;氧气20.9% 氩气0.93%;少量二氧化碳,稀有气体和水蒸气。大气层的空气密度随高度而减小,越高空气越稀薄,大气层厚度约为1000千米以上,无明显界限,分为对流层,平流层,中间层,暖层。

对流层(Troposphere

接近地球表面的一层大气层,空气的移动式以上升气流和下降气流为主的对流运动。它的厚度不一,两极上空为8000米,赤道上空为17千米,是大气层最稠密的一次,总质量的3/4,刮风,下雨,降雪等天气现象都在对流层,有强对流运动。

The troposphere is the lowest portion of Earth's atmosphere, and is also where all weather takes place. It contains approximately 75% of the atmosphere's mass and 99% of its water vapour and aerosols.[2] The average depths of the troposphere are 20 km (12 mi) in the tropics, 17 km (11 mi) in the mid latitudes, and 7 km (4.3 mi) in thepolar regions in winter.

A view of Earth's troposphere from an airplane



平流层(Stratosphere)

对流层上面,知道高于海平面50千米这一层,气流主要表现为水平方向运动,对流现象减弱,这一大气层叫做平流层,又称同温层。这里基本上没有水汽,晴朗无云,很少发生天气变化,适于飞机飞行,在20-30千米高处,氧分子在紫外线作用下,形成臭氧层,保护地球上生物受太阳紫外线及高能粒子袭击。

The stratosphere is stratified in temperature, with warmer layers higher and cooler layers farther down. This is in contrast to the troposphere, near the Earth's surface, which is cooler higher and warmer farther down.

中间层(Mesosphere)

平流层以上,到离地球表白85千米,叫做中间层。该层内因臭氧含量低,同时,能被氮,氧等直接吸收的太阳短波辐射已经大部分被上层大气所吸收,所以温度垂直递减率很大,对流运动强盛。中间层顶附近的温度约为190℃;空气分子吸收太阳紫外线辐射后可发生电离,习惯上称为电离层,有时在高纬度地区夏季黄昏时有夜光云出现。

In the mesosphere temperature decreases as the altitude increases. The upper boundary of the mesosphere is the mesopause, which can be the coldest naturally occurring place on Earth with temperatures below 130 K (−226 °F; −143 °C).

暖层(Thermosphere)

又名电离层,中间层以上是暖层,距地表80-800千米,特点是太阳光中的紫外线被该层中的氧原子大量吸收,因此温度升高,故称为暖层。在300千米高度时,气温可高达1000℃,但这里空气稀薄,并不会真正感到热,暖层中的 氮N2O 氧O2 和氧原子O,在强烈的紫外线和宇宙射线作用下,已经处于高度电离状态。

Thermospheric temperatures increase with altitude due to absorption of highly energetic solar radiation. Temperatures are highly dependent on solar activity, and can rise to 2,000 °C (3,630 °F). Radiation causes the atmosphere particles in this layer to become electrically charged (ionosphere), enabling radio waves to bounce off and be received beyond the horizon. In the exosphere, beginning at 500 to 1,000 kilometres (310 to 620 mi) above the Earth's surface, the atmosphere turns into space.

 Nomenclature of atmospheric regions based on the profiles of electric conductivity (left), temperature (middle), and electron density (right)




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