专业英语2-new.ppt

A different process occurs when there is interaction between a polar trough and the main polar front, giving rise to an instance occlusion. A warm conveyor belt on the polar front ascends an upper tropospheric jet forming a stratiform cloud band, while a low-level polar trough conveyor belt at right angles to it produces a convective cloud band and precipitation area poleward of the main polar front on the leading edge of the cold pool. 当极地槽和主要的极锋相互作用，会产生不同的过程，会引起瞬间锢囚。 极锋的暖传送带上升到对流层上部的急流区形成层状云带，然而与低空极地槽垂直的传送带会在冷空气前边缘形成主要极锋向极的（向北的）对流云带和降水区。? The occurrence of the frontolysis(frontal decay) is not necessarily linked with occlusion, although it represents the final phase of a front’s existence. Decay occurs when differences no longer exist between adjacent air masses. This may arise in four ways: through their mutual stagnation over a similar surface, as a result of both air masses moving on parallel tracks at the same speed, as a result of their movement in succession along the same track at the same speed, or by the system incorporating into itself air of the same temperature. 尽管锋消代表锋面存在的最后阶段，但锋消并不一定与锢囚联系在一起。 当临近的气团之间的差异不再存在时，消亡就发生了。 这可能是由4个方面引起的：一是在同一地面上停滞；二是两气团以相同速度平行运动；三是因为先后以相同的速度沿着相同的轨迹运动；四是由于系统并入到与它本身具有同样温度的空气中。 Frontal characteristics The activity of a front in terms of weather depends upon the vertical motion in the air masses. If the air in the warm sector is rising relative to the frontal zone, the fronts are usually very active and are termed ana-fronts. Whereas sinking of the warm air relative to the cold air masses gives rise to less inactive kata-fronts. 以垂直运动分 Ana front Kata front （1）至（5）為上滑鋒。其中（3）為標準情形。雲系在鋒後。 （6）至（10）為下滑鋒。其中（10）為標準情形。雲系在鋒前。 The warm front The warm front represents the leading edge of the warm sector in the wave. The frontal zone here has a very gentle slope, of the order 1/2°-1°, so that the cloud systems associated with the upper portion of the front herald its approach some 12 hours or more before the arrival of the s