Detailed knowledge of each of the jet streams of the earth’s hemisph

游客2025-02-21 32

问题          Detailed knowledge of each of the jet streams of the earth’s hemispheres-
   its location, altitude and strength-is critical to modern-day weather
   forecasting, as well as to more specific applications such as the routing of
Line aircraft. By way of definition, a jet in fluid dynamics is simply a core of fluid
(5)    moving at a higher velocity than the surrounding fluid,  and although
   complicated to describe mathematically, the jet streams in the atmosphere are a
   straightforward, natural result of the meridional (equator-to-pole) temperature
   gradient in the earth’ s atmosphere. Analogous flows exist on other planets with
   substantial atmospheres having similar temperature gradients.
(10)       The temperature gradient derives from the differential solar heating of the
   spherical surface of a planet: the surface is generally warmest at the equator
   and grows progressively cooler as one moves poleward. The centrifugal effects
   of the earth’s rotation, often called the Coriolis force, deflect the north-south
   transport of heat from the equator to the poles into the predominantly east-west
(15)    motion of the jet stream. The relative strength, or velocity, of the jet stream is
   proportional to the intensity of this thermal gradient.  During the winter
   months, when the equator-to-pole temperature disparity is at its greatest, the
   jet stream reaches its maximum velocity, while during the summer months,
   when the temperature gradient between the equator and the pole is considerably
(20)    less, the jet stream reaches its minimum velocity.
         The jet stream does not maintain a straight, zonal flow from west to east
   but rather takes on a more serpentine look, often with dramatic dips to the
   south or rises to the north. There are two major reasons for these nonzonal
   motions: the temperature gradient between the equator and the poles and the
(25)    presence of land masses on the earth’s surface. The meridional temperature
   gradient between the equator and poles that gives rise to the jet stream also
   produces secondary atmospheric circulations, or eddies which, referred to by
   meteorologists as baroclinic waves, have a complex interaction with the jet
   stream, one that is intriguingly two-sided. The eddies modify the distribution of
(30)    temperature and kinetic energy within the atmosphere, a process that has a
   pronounced effect on the location and movement of the jet stream, which itself
   interacts with these waves,  acting not only as a transport or steering
   mechanism but transferring momentum and energy back to the waves.
         The presence of land masses on the earth’s otherwise watery surface also
(35)    modifies the distribution of temperature, because continents heat and cool at a
   dramatically slower rate than do the oceans. The topography of the land also
   influences the jet stream’s location-mountain ranges and plains on large
   continents, for example, significantly imbalance the distribution of atmospheric
   temperature, narrowing the jet stream. And since the jet stream is a thermally
(40)    driven phenomenon, the more complicated the three-dimensional temperature
   structure of the earth’s atmosphere, the more "wandering" will take place in
   the course of the jet stream. [br] The passage suggests that when jet streams interact with continents with few mountain ranges and plains, which of the following also happens?

选项 A、More "wandering" occurs in the jet stream than would probably occur over the ocean.
B、The continent in question heats and cools at a faster rate than it would without the jet stream.
C、The jet stream becomes more narrow and focused than it would be over the ocean.
D、The temperature of the jet stream is distributed more evenly than if the continent had more mountains.
E、The jet stream evinces more signs of being a thermally driven phenomenon than it does in other situations.

答案 D

解析

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Detailed knowledge of each of the jet streams of the earth’s hemisph

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