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发表于 2018-1-6 08:52:00
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As a physicist in training, L. Alvarez was thinking the atmospheric motion in terms of conservation of mass, energy and angular momentum. If the hot air rises at the equator and the cold air sinks at the high latitude regions, one would expect an eastward jet stream at the high altitude, as one often sees it from the weather maps on TV weather analysis shows. This eastward jet stream can be easily understood by the conservation of the angular momentum as the high altitude air parcels move from equator to mid- and high latitudes. This is similar to the situation of a figure skater rotating faster as she concentrates her body weight toward her body center. However, it appeared that nobody paid any attention to the air flow direction near the surface as the air parcels move from high latitudes toward the equator to fill the gaps left from the hot rising air parcels. Furthermore, Alvarez realized that the majority of the areas in the low latitude regions were covered by oceans where the topographic and frictional effects were minimal. Therefore, based on the conservation of angular momentum, L. Alvarez hypothesized that there should exist a steady and systematic air flow near the oceanic surface in the low latitude region that always moves westward and toward the equator. This time, he submitted a science proposal to National Science Foundation (NSF) and proposed to lead an expedition team to actually measure the equatorial surface air flow to confirm his hypothesis.
L. Alvarez's proposal to NSF was declined and he was advised that the air flow he described in the proposal was called "trade winds" and was part of the so-called "Hadley cell" explained based on the conservation of angular momentum more than 250 years ago by George Hadley, which was already well known in the atmospheric science community:
Hadley, G., 1735: Concerning the cause of the general trade winds. Phil. Trans., 29, 58-62.
The observational characters and physical mechanism of the "Hadley cell" were discussed in almost every monograph or textbook in the field of atmospheric dynamics, for example,
Lorenz, E. N., 1967: The Nature and Theory of the General Circulation of the Atmosphere. World Meteo. Org., Geneva, 161 pp.
Lindzen, R. S., 1990: Dynamics in Atmospheric Physics. Cambridge Univ. Press, Cambridge, UK, 310 pp.
An easy and interesting location to observe the steady trade winds is at the Big Island of Hawaii where the steady northeast trade winds coupled with the mountain on the island form two distinctively different regional climates on the two sides of the mountain. On the windward side of the mountain, it is tropical rain-forest whereas on the leeward side, it has a desert climate.
When I heard Alvarez's story on his proposal to NSF, I first laughed at the occurrence of such an event (of a Nobel Prize recipient submitting a proposal to verify the Hadley cell). While trying to understand how he arrived at this idea, I learned and understood his contribution to solving the dinosaur extinction puzzle and realized the importance of bringing fresh ideas from outside to the field. [他山之石 可以攻玉。] Later, much later, one of my own science works happened to be closely related to Alvarez's work on dinosaur extinction. The close connection was immediately realized and firmly established as a result of my awareness of Alvarez's work on dinosaur extinction. My efforts in understanding how Alvarez might develop the idea of Hadley cell in his NSF proposal got paid off.
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