Temperature Convergence


This series of Haby Hints looks at 10 mechanisms that can create a burst point for convection. The burst point is the location where a thunderstorm first forms and climbs vertically throughout the troposphere. Convection is air rising due to positive buoyancy. The topic in this writing is temperature convergence.

Temperature is important since it influences the density of the air. Warmer air is less dense and it is easier for less dense air to lift in the vertical. This is a reason why storms often form first in the afternoon. In the afternoon, solar heating tends to be at a maximum. Also, different regions of air with different temperatures have trouble mixing. When warmer air moves toward colder air, instead of completely mixing, much of the warmer air will deflect over the colder air. Since colder air is denser and warmer air is less dense, it is the warmer air that will tend to rise over the colder air. Thus when air streams interact that have different temperatures it can help initiate vertical motions. Convergence is air piling into a region. For temperature convergence to increase instability what is needed is a piling of warm air. This can create a relatively larger bubble of warm air that when interacting with surrounding air will tend to help it rise. An analogy is to think of a developing bubble of air in a pot of water that is warming toward boiling. Bubbles will collect and build and then break away to rise to the top of the water surface. In the case of temperature convergence, warm air is being pooled together by the surrounding wind flow. This can create a location that is the burst point for thunderstorm development.