When the two opposite – natured air masses meet, they try to continuously retain their identities of temperature and humidity. In this process, a sloping boundary develops between them, which is called Front. Blair states that, “The surface of the air – masses that are separated by a line are called front”.
The basic conditions essential for the origin of front:
The following conditions are considered necessary for the origin of the front:
1. Air – masses of different nature: When two differently heated air – masses, or a cold and a hot air – mass meet face – to – face to each other, they attempt to enter each other’s area, due to which a wave – type front is formed.
2. The difference in humidity: When atmospheric humidity is respectively found to be more or less due to more or less temperature, more humid wind invades upon the lesser humid wind, due to which fronts are formed.
3. Atmospheric circulation: Horizontal and vertical movements of the winds, and the conditions of divergence and convergence in them are also responsible for the origin of fronts.
Types of front:
The scholar Patterson has divided fronts into the following types:
1. Warm Front: This is a sloping frontal surface, along which active movement of warm air over cold air takes place.
2. Cold Front: Such a front is formed when a cold air mass replaces a warm air mass by advancing into it and lifting it up.
3. Stationary Front: In the parallel movement of two opposing air – masses, separation and absence of peripheral motion of the air masses characterize a Stationary Front.
4. Occluded Front: Such a front is formed when a cold air – mass overtakes a warm air – mass and goes underneath it. The warm sector diminishes and the cold air – mass completely replaces the warm sector on the ground.
