4 July 2024 : Daily Answer Writing

Q1) Describe the various types of fronts and their role in formation of extra-tropical cyclones.

(250 Words/15 Marks

ANS

Front can be described as a sloping boundary which separates two opposing air masses having contrasting characteristics in terms of air temperature, humidity, density, pressure, and wind direction.

The process of creation of new fronts or regeneration of old and decaying fronts already in existence is called frontogenesis. Various types of fronts can be studied as:

1. Warm Front:
2. Warm air mass moves towards the cold air mass, creating a warm front.
3. Warm and light air becomes active and aggressive and rises slowly over cold and dense air.
4. Cold Front:
5. Cold air mass moves towards the warm air mass, its contact zone is called the cold front.
6. Here, cold air becomes active and aggressive and invades the warm air territory, forcibly uplifting the warm and light air.
7. Stationary front: Stationary front is formed when two contrasting air masses converge in such a way that they become parallel to each other and there is no ascent of air.
8. Occluded front: Occluded front is formed when cold front overtakes warm front and warm air is completely displaced from the ground surface.

Figure: Extra tropical cyclone

The role of fronts in formation of extra-tropical cyclones can be as studied:

1. As per the polar front theory (aka wave theory, Bergen theory), the polar fronts created due to convergence of two contrasting air masses viz. warm, moist and light tropical airmasses (westerly winds) and cold, and dense polar air masses are responsible for the origin and development of temperate cyclones.
2. Initially, when the process begins, the front is stationary. In the northern hemisphere, warm air and cold air blows from south and north respectively.
3. In second stage, unstable fronts are formed. Warm and cold air masses penetrate the territories of each other, forming a wave like front.
4. At third stage, a well-developed extra tropical cyclone, with a warm and a cold front is developed. It consists of pockets of warm air sandwiched between the forward and rear cold sector of the cold air. The warm air being light glides over the cold air and condensation occur. It creates a sequence of clouds ahead of the warm front, causing precipitation.
5. Next, the warm sector is narrowed in extent due to the advancement of cold front at faster rate than warm front, and cold front comes nearer to warm front.

6. Lastly, advancing cold overtakes the warm front and occluded front is formed.

Finally, warm sector completely disappears, occluded front is eliminated and ultimately cyclone dies out. The temperate cyclones produced along polar front travel from west to east (as opposed to tropical cyclones) under the influence of the westerlies and yield widespread precipitation over large area. The effect is less pronounced in the summer seasons due to the weakening of the temperature contrast.