. Compendium of meteorology. Meteorology. EXTRATROPICAL CYCLONES 581 gap. The lifting of a tongue of warm air relative to a colder environment, illustrated in Fig. 2, can be as- sumed to furnish a great part of the increase in kinetic energjr during the cyclonic development from wave to vortex. The tropopause is also shown in the profiles. It has a crest over the warm-front surface and a trough over the cold-front surface, and the amplitude of the tropo- pause oscillation increases with the growth of the cy- clone. In Fig. 2d the tropopause has a deep depression almost coinciding with the cycl
. Compendium of meteorology. Meteorology. EXTRATROPICAL CYCLONES 581 gap. The lifting of a tongue of warm air relative to a colder environment, illustrated in Fig. 2, can be as- sumed to furnish a great part of the increase in kinetic energjr during the cyclonic development from wave to vortex. The tropopause is also shown in the profiles. It has a crest over the warm-front surface and a trough over the cold-front surface, and the amplitude of the tropo- pause oscillation increases with the growth of the cy- clone. In Fig. 2d the tropopause has a deep depression almost coinciding with the cyclone center, which is at that stage surrounded by air of cold origin up through the whole troposphere. Details of tropopause structure, such as the frequent subdivision into multiple tropo- pauses, have been left out in Fig. 2. Hatched areas in Fig. 2 indicate the location of the main precipitation areas of the cyclone. The largest area is covered by the warm-front rain, where the air from the warm tongue climbs the receding wedge of cold air and condenses much of its moisture. A more narrow zone of precipitation accompanies the cold front where some air from the lower part of the warm tongue is lifted by the advancing cold wedge. Higher portions of the warm tongue move faster than the cold-front wedge and are not lifted by it. The described upward motion of the warm air next to the frontal surfaces should be visualized as being superimposed on the general pattern of vertical motion, upward in the front half and downward in the rear half of the cy- clone (Fig. 1). This general, upward motion is some- times sufficient to cause rain where it is not called for as a consequence of upgliding on frontal surfaces. Some extensive warm-sector rains and also the rain in the front half of a cold trough or a cold vortex are prob- ably to be explained by the general upward motion shown in Fig. 1. To complete the precipitation picture of the cyclone the air-mass precipitation should also be a
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