Question

Explain Air masses and fronts. Also, write a note on various types of fronts?

Answer 1

Approach:
Write about Air masses and fronts Write in detail types of fronts

Air masses:
Air masses are the large bodies of air with fairly uniform temperature and moisture characteristics. An air mass can be several thousand kilometres (or miles) across and can extend upward to the top of the troposphere. We characterize each air mass by its surface temperature, environmental lapse rate, and surface specific humidity.

Air masses acquire their characteristics in source regions. In a source region, air moves slowly or not at all, which allows the air to acquire temperature and moisture characteristics from the region ’s land or ocean surface.

Fronts:
A given air mass usually has a sharply defined boundary between itself and a neighbouring air mass. This boundary is termed a front.

Types of fronts:

Cold fronts:
When cold air invades warmer air, the boundary is a cold front. Because the cold air mass is colder and therefore denser than the warmer air mass, it remains in contact with the ground. As it moves forward, it forces the warmer air mass to rise above it. As the warm air mass rises, it cools adiabatically, water condenses, and clouds form. If the warm, moist air is unstable, severe convection may develop.


Warm fronts:
In contrast to a cold front, a warm front is one in which warm air moves into a region of colder air, as the cold air retreats (Figure 6.6). Again, the cold air mass remains in contact with the ground because it is denser. As before, the warm-air mass is forced aloft, but this time it rises up on a long ramp over the cold air below. This rising motion, called overrunning, creates stratus— large, dense, blanket-like clouds—that often produce precipitation ahead of the warm front. If the warm air is stable, the precipitation will be steady. If the warm air is unstable, convection cells can develop, producing cumulonimbus clouds that provide heavy showers or thunderstorms.


Occluded fronts:
In an occluded front, a cold front overtakes a warm front. The warm air is pushed aloft, so that it no longer touches the ground. This abrupt lifting by the denser cold air produces precipitation.