- Life Cycle of a frontal depression. Warm air moves faster than cold and every now and again, it forces its way into the cold air, making a bulge in the polar front. This is the commencement of a frontal depression, since as the warm, less dense air pushes into the cold denser air, the pressure falls. The following sketch shows the life cycle of a depression:
Life cycle of a frontal depression.
When the depression is fully developed, the air behind the cold front moves faster than the air in the warm sector. As a result the warm sector is undercut and lifted off the ground. The front is then said to be occluded.The air ahead of and behind the occlusion was originally the same but with the movement of the warm sector and the passage of time, the temperature changes. If the air behind the occluded front is colder than that in front, the occlusion is called a cold one. If it is the other way around, it is referred to as a warm occlusion.
- Weather changes with a frontal depression. The characteristics and changes of weather an observer would experience when a frontal depression passes over his position is indicated in the table.
The example refers to a frontal depression in the southern hemisphere (the arms of the depression always point towards the equator). The line A_ _ _B in the sketch represents the relative movement of the observer.
Frontal depression (southern hemisphere).
- Table of weather changes.
