A thermal column is a column of rising air in lower altitudes of the atmosphere. Thermal columns are created by uneven heating patterns of the Earth’s surface from solar radiation. The sun warms the ground, and the air directly above the ground begins to warm. As the warm air expands, it becomes less dense than the air around it and rises. As the warmer air rises, it cools due to its expansion in lower high-altitude pressures. When it cools to the same temperature as the surrounding air, it stops rising. Downward flow surrounds a thermal column. The downward flow is caused by colder air being displaced at the top of the thermal column. Thermal columns are also known simply as thermals.
The size and strength of a thermal column is influenced by the properties of lower atmosphere. When the air is cold, warm air bubbles form near the ground and rise like hot air balloons. The air is thought to become unstable as it rises. If there is a warm layer of air above the thermal column, it can prevent the thermal from rising high and then causes the air to be stable. Thermal columns are often indicated by the presence of visible cumulus clouds. A steady wind causes thermals and the respective cumulus clouds to align in rows oriented with wind direction. As the cumulus clouds form by the riding thermal air, water vapor begins to condense into water droplets. The droplets release latent heat energy which allows the air to rise higher. As the air mass becomes unstable and condenses even more water vapor, showers or even thunderstorms can form.
Thermal columns are one of many sources of lift that soaring birds use to climb higher into the air.