Thermal advection causes height changes. That is what this writing is about. The reason for the height change is because the density of the air can change. Cold air is denser since the air molecules move at a slower speed and can thus be closer together. Warm air is less dense and takes up a larger volume. As air warms, the molecules bump into each other more rapidly and thus the air expands as a result. Warm air advection is the horizontal movement of warmer air into a location. For this writing we will look at low level warm air advection. The top diagram below shows warm air advection. Notice going left to right on the diagram that the 850 mb level is closer to the surface. Where it is closer to the surface the air is colder and where it is higher aloft the air is warmer. The warm air advection process contributes to height rises. This is the reason that low level warm air advection contributes to rising air and increased precipitation chances. Over time the 850-mb level on the top right side of the diagram will increase due to warmer air moving in. Cold air advection is the horizontal movement of colder air into a location. For this writing we will look at low level cold air advection. The bottom diagram below shows cold air advection. Notice going left to right on the diagram that the 850 mb level is higher above the surface. Where it is closer to the surface the air is colder and where it is higher aloft the air is warmer. The cold air advection process contributes to height falls. This is the reason that low level cold air advection contributes to sinking air and decreased precipitation chances. Over time the 850-mb level on the bottom left side of the diagram will decrease due to colder air moving in.  |