Frontogenesis and Frontolysis, Classification of Fronts

Frontogenesis and Frontolysis

Frontogenesis is a Latin-derived word means 'the creation of altogether new fronts' or 'the regeneration of the decaying fronts already in the existence'. Frontolysis, on the contrary, means the destruction or dying of a front. It would not be out of the place to mention that fronts do not come into the existence all of a sudden; rather than they appear only after the processes of the frontogenesis have been in the operation for sometimes. In the same way, the act of weakening or the vanishing of the existing fronts is not accomplished suddenly. The process of the frontolysis must be continuous for some time in order to destroy and existing front.

Frontogenesis is likely to occur when the winds blow in such a way that the isotherm becomes packed along the leading edge of the intruding air mass. Convergence of the wind toward a point or the contraction toward a line augments the process of frontogenesis.

On the contrary, the divergence of the wind from the point or the dilation from a line is helpful to the process of the frontolysis. Frontolysis, therefore, is likely to occur when the fronts move into the regions of the divergent air flow. This is the region why on crossing the subtropical high-pressure regions, the fronts generally disappear.

To summarize all the things when the contrasting air masses have the convergent movement the frontogenesis occurs. The temperature contrast in the converging air masses is another most important prerequisite for the process of the frontogenesis to occurred. The fronts come to the existence only when the above two conditions are fulfilled simultaneously. On the contrary, when the air masses move away from each other or when the temperature contrast between the adjacent air masses diminishes due to one reason or the other reason i.e the fronts are started for decaying.

Classification of fronts

As a result of the observation of the atmospheric conditions at the surface and aloft, the following types of the fronts are identified to the earth surface:

1: Cold front

2: Warm front

3: Occluded front

4: Stationary front

The detail description of the fronts are as follow:

1: Cold front:

A cold front is defined as the front along which the cold air is invading the warm air zone. Since the colder air mass is denser, it remains at the ground and forcibly uplifts the warmer and the lighter air mass. Actually, when the pressure distribution is such as to force the cold air to advanced and the warm air to retreat the zone of the transition is known as the cold front. The vertical structure of the warm air that is forced upward by an advancing wedge of the cold air determines the type of the weather produced along the cold front. The cold front, in general, is associated with the narrow band of the cloudiness and the precipitation. The sky also becomes clear soon after the passage of the fronts. However, the weather produced along the cold front is more violent. Cold front leads to the heavy precipitation of the short duration.

2: Warm front:

A warm front is defined as a gently sloping frontal surface in which there is an active movement of the warm air over the cold air. As the surface position of a warm fronts moves, the warm air gradually ascends the gently sloping surface of the wedge of the cold air lying ahead, it cools adiabatically. This cooling leads to the cloudy condensation and the precipitation. Unlike the cold front, the changes in the temperature and the wind direction are gradual. Warm front leads to the light precipitation of the long duration. During the winter, an inversion of the temperature is produced along the warm front which is situated near the surface. This lead to the freezing rain or the sleet in the very cold air ahead of a warm front.

3: Occluded front:

An occluded front is defined as a front formed when the front overtakes a warm front. The cold front moves more rapidly than the warm front with the result that the warm sector is progressively reduced in the size. Ultimately the cold front overtakes the warm front and completely displaces the warm air at the ground and the cold and the warm fronts combine into one. Thus, along and the backward swinging occluded front comes into the existence. There are two types of occlusion.

A: cold front occlusion: this cold front occlusion occurs when the cold air which overtakes the warm air colder than the retreating cold air. This type of the occlusion is common.

B: warm front occlusion: this type of warm front occlusion occurs when the retreating cold air mass is colder than the advancing cold air mass.

4: Stationary front

These types of fronts are situated in which the surface position of a front does not moves. Therefore, such front is called the stationary front. The wind motion on either side of such boundary is nearly parallel to the position of the fronts. Whenever some over-running of the warm air occurs along a stationary front warm front type precipitation is likely to be produced.

Concepts of climate change

Since the creation of the earth, a great change in the climate has been reported over much of the globe. The Siberian desert which is once thickly populated and the Rajasthan nearly two million years ago were much greenery with the rivers wider than that of the Indus and the Ganga. Similarly, the desert area of the southwestern USA central Asia and the southern Europe enjoyed a humid climate only two or three thousands years ago.

The climate is thus the most variable aspect of the natural environment. It varies all the timescale and in the different amplitude. The extreme climatic events that are responsible for this variability pose the great risk of different dimensions to the successful functioning both the severe flood and the drought problem frequently.

The main factors which are changing the world climate are as follows:

1: Greenhouse effect

2: Global warming

3: Ozone layer depletion

4: Sea level rise

References:

.S.C., Santee. Environmental Science. India, New Center: New Center Book Agency (P) Ltd, 2004.

Lal, D.S. Climatology, Sharda Pustak Bhawan, Allahabad.(2010)