As a meteorologist with extensive experience in atmospheric dynamics, I can provide a comprehensive explanation of what causes a downdraft. A downdraft is a column of sinking air that moves downward relative to the surrounding air. It is the opposite of an updraft, which is an upward-moving air current. Downdrafts are an essential part of the atmospheric circulation and play a critical role in weather phenomena such as thunderstorms and tornadoes.

There are several mechanisms that can lead to the formation of downdrafts:


1. Thermal Downdrafts: The most common type of downdraft occurs in thunderstorms. During the day, the sun heats the ground, causing the air near the surface to become warmer and less dense. This warm air rises in what is known as an updraft. As the air rises, it cools due to the decrease in atmospheric pressure at higher altitudes. The cooling air can no longer support the upward motion and begins to sink, forming a downdraft. This process is a fundamental part of the convective cycle in thunderstorm development.


2. Orographic Downdrafts: When air is forced to rise over a mountain range due to orographic lifting, it cools and condenses, forming clouds and precipitation. Once the air has lost its moisture, it becomes heavier and can sink on the leeward side of the mountains, creating a downdraft.


3. Mesoscale Downdrafts: In larger weather systems, such as mesoscale convective systems (MCS), downdrafts can form as a result of the dynamics within the system. These downdrafts are often associated with the collapse of the updrafts and can lead to severe weather conditions like heavy rain and hail.


4. Dowdrafts in Tornadoes: In the case of tornadoes, downdrafts play a crucial role in the formation and maintenance of the storm. The rotation of the storm can cause some of the air to be ejected from the updraft and descend to the ground, creating a downdraft. This downdraft can then interact with the ground, enhancing the rotation and leading to the development of a tornado.


5. Radiative Cooling Downdrafts: At night, the ground cools more rapidly than the air above it. This can lead to the formation of a temperature inversion where the air near the surface is cooler than the air above. If the air near the surface is disturbed, it can sink and spread out, creating a downdraft.


6. Dynamic Downdrafts: These occur when the horizontal wind flow is disrupted by obstacles such as buildings or other structures. The wind is forced to rise over the obstacle, and as it does so, it cools and can become heavier, leading to a downdraft on the leeward side.

7.
Frontal Downdrafts: When a cold front moves through an area, it can force warm air to rise ahead of the front. As this warm air cools, it can sink and create a downdraft.

Downdrafts can have significant impacts on weather and aviation. They can lead to sudden changes in wind direction and speed, which can be hazardous for flying. Additionally, downdrafts can bring heavy rain, hail, and even dust storms, affecting visibility and causing damage on the ground.

Understanding the causes and dynamics of downdrafts is crucial for weather forecasting and for the safety of those who rely on accurate weather information.

read more >>

Updraft and downdraft, in meteorology, upward-moving and downward-moving air currents, respectively, that are due to several causes. Local daytime heating of the ground causes surface air to become much warmer than the air above, and, because warmer air is less dense, it rises and is replaced by descending cooler air.read more >>