Archive | Articles

Tropical disturbances are classified into four categories: (1) easterly waves, (2) tropical depressions, (3) tropical storms, and (4) hurricanes or typhoons.

The tropical atmosphere should be considered as a heat sink of the radiant energy obtained through short-wave solar radiation and terrestrial radiation. Vast expanse of the tropical oceans plays a significant role in the supply of atmospheric heat.

Geographically, the tropical atmosphere lies between the Tropic of Cancer and the Tropic of Capricorn. But from meteorological point of view, the boundaries of the tropical atmosphere are determined by the high pressure cells of the subtropics in both the hemispheres.

On the basis of structure, storm tracks, and general characteristics, anticyclones are divided into the following four distinct types:

Anticyclones are high pressure systems around which the wind blows clockwise in the northern hemisphere, and counterclockwise in the southern hemisphere. There are various types of anticyclones such as the cold-core anticyclones of the high latitudes and the warm-core anticyclones of lower latitudes.

Anticyclones play much less important a role in the weather-drama at the surface of the earth in comparison with cyclones. Since anticyclones produce clear conditions and are almost weather-less, no serious study has been conducted on their development.

When the cold front overtakes the slow moving warm front, the warm air is forced upward. The meeting of the two fronts creates an occluded front. Under normal conditions, in the later stages of occlusion the cyclone weakens and ultimately dissipates.

In case the cyclone passes the observer along the line cd, he is to the south of the centre of storm. If the change of weather is followed along this line, the appearance of high cirrus clouds on the western horizon heralds the approach of a wave cyclone.

Changes in weather will depend on the position of the observer in relation to the cyclone passing overhead. If the cyclone passes the observer along the line ab, the weather observed will be somewhat different from that experienced along the line cd.

Bjerknes’ model of an extratropical cyclone was produced in 1918 after investigating the structure of a large number of cyclones in north-western Europe.

Schematic represen­tation of the development of a wave cyclone along a frontal zone. It depicts all the four stages of the development of a travelling wave cyclone (extratropical cyclone).

This theory, as stated earlier, is also called the frontal theory or the wave theory of the origin of extratropical cyclones.

The fickleness and variability of weather characteristics caused by atmospheric disturbances that move from west to east in the belt of prevailing westerlies gave an incentive to the weather scientists to make investigations and researches.

Much of the highly variable and cloudy weather we come across in the temperate zone is the direct result of travelling cyclones. The terms extra tropical cyclones, temperate cyclones, or depressions are interchangeably used to denote these moving cyclones in the mid-latitude zone.

When the distribution of temperature is such that at every level the environmental lapse rate is greater than the dry adiabatic lapse rate, the displaced parcel of air has a tendency to continuously move upward till its temperature is equal to that of the surrounding air.

The general global distribution of the cyclone tracks. A glance at the map shows that the general direction of movement of temperate cyclones is from west to east with frequent trends towards the southeast to northeast.