Advections, It Tells Us Whats Going and Whats Coming

With a cold front playing games with us across the Brazos Valley today, most of us were feeling the tropical air, but areas just to the north and west of Bryan expereinced a much cooler air mass in place. Once the front passed, much cooler air filtered in and Cold Air Advection took place.

Advection is a meteorological term used to describe the movement of an air mass. Such terms that are used with advection are cold air advection and warm air advection. For example, if cold air advection occurs at a certain location, then that specific area will experience colder air. This is  because colder air is moving/advancing into that area, which in turn would drop the temperature.

When talking about a mature mid-latitude cyclone (or area of low pressure), there are usually 2 or more different air masses that the cyclone divides. Usually north or west of a cyclone, there is a continental polar (dry, cold air) or a maritime polar (moist, cold) air mass, while to the south and east of the cyclone is a continental tropical (dry, warm), or maritime tropical (moist, dry) air mass. All of these possible air masses have different densities or weight in a given volume), where a moist and warm has a low density, while a dry and cold air mass is more dense.

In other words, its like water and oil. Since oil has a lower density then water, the oil will float on top while the water stays on the bottom. Or you can think of it like a rubber duck floating in a bath tub on top of the water. Since the duck is hollow and made of rubber, its density is low, so it will float.

When talking about advection, moisture is important, but not as important as temperature. Colder air is more dense then warmer air. Therefore, when cold air advection occurs, the cold air will slip under the warm air and replace the warm air. In the meantime, depending on how much cold air there is, the older warm air mass, would "float" above the newer colder air mass.

From all of this information, when talking about a cold front, it is a surface which divides air masses. Behind a cold front is typically a more dense air mass, whether it is maritime polar or continental polar. Additionally, since the air mass behind a cold front is very dense, it tends to hug close to the surface. When this colder/denser air mass advances, cold air advection is taking place.

Note: Cold air is the most dense and cold air acts like a bully. When cold air advances, its not because warm air is retreating, its because the cold air wants to move in that particular direction. The same goes for a retreating cold air mass, warm air is not advancing, it is only replacing a cold air mass that has moved away. Remember, the air mass which has the most mass will have the most control.