II. The Atmosphere

4. Front

When a cold air mass and a warm air mass with different characteristics meet, the boundary will be a non-continuous surface called a front. The air on the two sides of the front is different in characteristics such as temperature, humidity, wind, and weather. In fact, a front is a transition zone; its width can vary from several kilometers to dozens of kilometers. The region in which the front intersects the land surface is called the frontal surface.

When cold air moves forward, it will displace the warm air and force the warm air to recede; this kind of front is called a cold front (Fig. 4). In the reverse situation, it is called a warm front. When the strength of the cold and warm fronts are not significantly different the front will linger and it will be called a stationary front.

The cold front

Fig. 4: The cold front.