Updraft Definition
There are two terms commonly and widely used in meteorology with respect to air currents. They are updraft/vertical draft and downdraft. An updraft is a small-scale rising air current usually within a cloud. Similarly, a downdraft is a downward moving current of air within a cloud. Both these phenomena can be caused due to several factors. A very simple example of the updraft is the upward movement of the warm air from the surface towards the sky. Similarly, the example of downdraft is the downward movement of the cool air from the skies to the surface of the earth.
Causes of an Updraft
During the daytime because of the radiation being reflected by the ground, the air above the surface gets heated. Local daytime heating makes the surface warmer and since the air gets warmer it gets less dense than the cool air above it. Because of this relative difference in the density, the warmer air begins to ascend upwards from the surface and is replaced by the cooler air which descends towards the surface. This movement of the warm air is known as thermal updraft because there is an updraft of warm air. The updraft is also created because of the turbulence that occurs when an air current passes over the barriers of topography such as the mountains. There are also common cases of updrafts occurring in thunderstorms as well. Such a type of updraft is known as thunderstorm updraft.
The updrafts are especially important as they play a significant role in the development of a storm. Especially during the early stages of a storm the warm air rising because of thermal updraft reaches the level when the condensation starts which supports the starting of the precipitation. With the cooling and falling of the precipitation in a mature storm, both the updrafts and downdrafts are caused. These drafts are also caused by the low pressure and high-pressure regions. Low-pressure regions attract large volumes of air which as it rises upward causes an updraft. Sometimes there is a rotation of the air current while moving upwards towards a low-pressure region or until the warm air of a thermal updraft encounters an air current with lower density, which comes to be known as rotating updraft.
Effects of Updrafts
Whenever there is a huge amount of moist and wet air that forms an updraft, it can lead to phenomena such as cyclones or tornadoes. For example, a supercell updraft is a thunderstorm that is caused by the presence of a deep and persistent rotating updraft. Whenever a thermal updraft which consists of warm air goes up away from the surface it cools down and later precipitates which mostly leads to rainfall because of a phenomenon known as convection. Thus, a convective updraft is a phenomenon causing rainfall in most cases. Not only, updrafts but such natural phenomena are also caused because of the downdrafts as well. Whenever there is a downdraft in huge amounts and vigorous speed it is known as downburst or microburst which has the capability to cause a tornado.
Many times there are plenty of accidents as well caused because of thermal updraft/convective updraft, thunderstorm updraft, or a rotating updraft. These updrafts and downdrafts are a huge problem for flight travel and are major contributors to airplane crashes even during take-offs and landing. An example of such an incident is the crash of Delta Airlines Flight 191 during its final landing at the Dallas International Airport in 1985.
Conclusion
As is clear from the article, an updraft or a downdraft is a natural phenomenon occurring because of the movement of air currents upward or downward respectively. These phenomena are responsible for a lot of natural activities such as rainfall, thunderstorms, tornadoes, or a supercell. Because of the turbulence that is created in the atmosphere because of such phenomena they are known for bad weather conditions and are grave risks to flight travels and also can cause severe natural calamities as well. An image of an updraft is shown below:
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FAQs on Updraft
1. What is an updraft in geography, and how is it formed?
An updraft is the upward movement of an air parcel in the atmosphere. The most common cause is convection. The process begins when solar radiation heats the Earth's surface. This heat is transferred to the air directly above the ground, causing it to warm up, expand, and become less dense than the surrounding cooler air. Due to this lower density, the warm air begins to rise, creating an upward current known as an updraft.
2. What is the main difference between an updraft and a downdraft?
The primary difference lies in the direction of air movement and their causes. An updraft is rising air, typically caused by surface heating (convection), while a downdraft is sinking air, often caused by evaporative cooling or the drag from falling precipitation within a storm. Updrafts are responsible for cloud formation, whereas strong downdrafts can cause hazardous weather phenomena like microbursts near the ground.
3. How do updrafts lead to the formation of clouds and thunderstorms?
Updrafts are crucial for cloud formation. As a parcel of warm, moist air rises, it moves into regions of lower pressure and expands, causing it to cool (a process called adiabatic cooling). When the air cools to its dew point temperature, the water vapour within it condenses into tiny liquid water droplets or ice crystals, forming a visible cloud. If the updraft is very strong and persistent, it can build the cloud vertically into a towering cumulonimbus cloud, which is the type that produces thunderstorms, heavy rain, and lightning.
4. What are some common real-world examples of updrafts?
Updrafts occur in several forms in nature. Key examples include:
- Thermals: These are columns of rising warm air that glider pilots and birds like eagles use to gain altitude without flapping their wings.
- Orographic Lift: This occurs when wind encounters a mountain or hill, forcing the air to rise up and over the terrain.
- Frontal Wedging: At a weather front, less dense warm air is forced to rise over a colder, denser air mass.
- Convective Updrafts: These are the powerful, localised updrafts that act as the engine for thunderstorms and tornadoes.
5. Why are updrafts a significant factor in the study of meteorology and aviation?
Updrafts are fundamentally important for two main reasons. In meteorology, they are the primary mechanism for transporting heat and moisture vertically through the atmosphere, driving the formation of clouds and most weather systems. In aviation, while gentle updrafts can provide lift for aircraft like gliders, the violent updrafts within a thunderstorm can cause severe turbulence. This turbulence can pose a serious structural risk to aircraft and is a major safety concern that pilots are trained to avoid.
6. What causes an updraft to start rotating and form a mesocyclone?
An updraft itself is just vertical air motion. For it to rotate, another atmospheric ingredient is needed: wind shear. Wind shear is a change in wind speed or direction with increasing altitude. This difference creates a horizontal rolling motion in the air near the surface. A powerful, sustained thunderstorm updraft can then act like a vacuum, drawing this horizontally spinning tube of air upwards and tilting it into a vertical position. This vertically rotating column of air within the updraft is called a mesocyclone, which is the precursor for the formation of most powerful tornadoes.
