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本帖最后由 无敌浩克One 于 2015-3-31 17:01 编辑
2015.3.31 comprehension note!
The recent, apparently successful, prediction by mathematical models of an appearance of El Nino—the warm ocean current that periodically develops along the Pacific coast of South America—has excited researchers. Jacob Bjerknes pointed out over 20 years ago how winds might create either abnormally warm or abnormally cold water in the eastern equatorial Pacific. Nonetheless, until the development of the models no one could explain why conditions should regularly shift from one to the other, as happens in the periodic oscillations between appearances of the warm El Nino and the cold so-called anti-El Nino. The answer, at least if the current model that links the behavior of the ocean to that of the atmosphere is correct, is to be found in the ocean.
It has long been known that during an El Nino, two conditions exist: (1) unusually warm water extends along the eastern Pacific, principally along the coasts of Ecuador and Peru, and (2) winds blow from the west into the warmer air rising over the warm water in the east. These winds tend to create a feedback mechanism by driving the warmer surface water into a “pile” that blocks the normal upwelling of deeper, cold water in the east and further warms the eastern water, thus strengthening the wind still more. The contribution of the model is to show that the winds of an El Nino, which raise sea level in the east, simultaneously send a signal to the west lowering sea level. According to the model, that signal is generated as a negative Rossby wave, a wave of depressed, or negative, sea level, that moves westward parallel to the equator at 25 to 85 kilometers per day. Taking months to traverse the Pacific, Rossby waves march to the western boundary of the Pacific basin, which is modeled as a smooth wall but in reality consists of quite irregular island chains, such as the Philippines and Indonesia.
When the waves meet the western boundary, they are reflected, and the model predicts that Rossby waves will be broken into numerous coastal Kelvin waves carrying the same negative sea-level signal. These eventually shoot toward the equator, and then head eastward along the equator propelled by the rotation of the Earth at a speed of about 250 kilometers per day. When enough Kelvin waves of sufficient amplitude arrive from the western Pacific, their negative sea-level signal overcomes the feedback mechanism tending to raise the sea level, and they begin to drive the system into the opposite cold mode. This produces a gradual shift in winds, one that will eventually send positive sea-level Rossby waves westward, waves that will eventually return as cold cycle-ending positive Kelvin waves, beginning another warming cycle.
five-step training Practice:
A recent mathmatical model help scientists to figure out why the E1-NINO goes through a circle of warm-cold mode.
The answer should be found in the sea. Then the author talked about two conditions happened in the sea.
Then the author explained the movement a negative R wave specifictly including: how this wave generating a negative signal that would not only raise the sea level of eastern side of Pacific where the warm water trend flowed but also tending to raise the sea level of western side; how the R wave moving westard till the west coach where it is broken into a K wave that will travel at the opposing direction against R wave to reach the east side of Pacific. With the promotion of earth rotation, the speed of K wave is much faster than it of R wave.
When this K wave finally reaches the east side, it generates a positive signal which makes the water temperature turn cold and thus start a new circle of water getting warm.
I am suprised that I can rememer so much details about this passage!
The function of the first paragraph is to state the TOPIC. To display the author's support for this new model by mentiong that the past method failed to explain the conditions ...
Then the second paragraph starting with continuingly talking about the answer in the sea mentioned at the end of the first paragraph: two elements: the wind and the water. Then he talked about how these two elements interacting each other. In the middle of second paragraph, the author presented one contribution of the model.
The third paragraph kept explaining the condition of wave travelling generated by the model till finally the reason of the circulation is explained.
The attitude of the writer is supporting the fundation of that math model!
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It can be inferred from the passage that which of the following would result fairly immediately from the cessation of the winds of an El Nino?
At first, I looked for the word cessation for several seconds. When I finally 100% sure that there was no cessation in the passage did I realize this is a question of 取非。 After all, I realized the type of the question before seeing the answer which is better than the last time. Maybe next time I could do better. Good Signal!!
I. Negative Rossby waves would cease to be generated in the eastern Pacific.
II. The sea level in the eastern Pacific would fall.
III. The surface water in the eastern Pacific would again be cooled by being mixed with deep water.
I did this wrong only because I misunderstood the meaning " is generated as".
This phrase does not express a passive tense, on the contrary, it means the form of sth is, or sth is showing as the form of ...
the wind send the signal, and the signal changed into a form of R wave. so if without the wind, there would be no signal and thus no R wave at all.
Which of the following, if true, would most seriously undermine the validity of the model of El Nino that is presented in the passage?
(A) During some years El Nino extends significantly farther along the coasts of Ecuador and Peru than during other years.
not mentioned, out of scope
(B) During periods of unusually cool temperatures along the eastern Pacific, an El Nino is much colder than normal.
not mentioned, out of scope
(C) The normal upwelling of cold water in the eastern Pacific depends much more on the local characteristics of the ocean than on atmospheric conditions.
not relevant: I mistook this choice the right one because there is evidence in the passage shows that the winds block the upwelling. however, this sentence is talking about what helps to lift the water not block, thus has no relation with the question.
(D) The variations in the time it takes Rossby waves to cross the Pacific depend on the power of the winds that the waves encounter.
direct contradiction: then head eastward along the equator propelled by the rotation of the Earth at a speed of about 250 kilometers per day
(E) The western boundary of the Pacific basin is so irregular that it impedes most coastal Kelvin waves from heading eastward.
relative sentence: which is modeled as a smooth wall but in reality consists of quite irregular island chains, such as the Philippines and Indonesia.
as we all know, smooth plain strengthen reflection while irregular plain lessen the reflection. So if the western boundary of pacific basin is too irregular to allow reflection, then the model will be invalid.
PS, "is modeled" is the key which means this condition is an assumtion and could be false.
I did it wrong because I failed to catch the meaning beneath which is expressed by "is modeled". |
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