Chapter 10 Adiabatic processes, lapse rates and rising air

Summary

This video script explains the two main processes by which air temperature changes: diabatic and adiabatic processes. Diabatic processes involve direct energy exchanges, like heating or cooling over hot or cold surfaces, while adiabatic processes are driven by compression or expansion without energy exchange. The script also discusses the environmental lapse rate, which varies with altitude and atmospheric conditions. Different mechanisms, such as orographic lifting, frontal lifting, convergence, and convection, lead to air rising or sinking. Additionally, buoyancy and gravitational forces play a role in air movement, influenced by temperature differences that determine air density and vertical motion.

Takeaways

• 😀 Diabatic processes involve direct energy exchanges, like heating or cooling due to contact with hot or cold surfaces.
• 😀 Adiabatic processes, on the other hand, do not involve energy exchange but instead rely on compression or expansion of air.
• 😀 Air temperature changes due to adiabatic processes are governed by the air's pressure and volume changes, with warmer air expanding and cooler air contracting.
• 😀 The dry adiabatic lapse rate is 10°C per 1,000 meters, meaning a rising air parcel will cool by 10°C for every 1,000 meters it ascends.
• 😀 When air is lifted high enough, it eventually reaches the lifting condensation level (LCL) where condensation starts to occur, releasing latent heat.
• 😀 After reaching the LCL, the air cools more slowly, at the moist adiabatic lapse rate of about 5°C per 1,000 meters, due to the release of energy during condensation.
• 😀 The environmental lapse rate (ELR) describes the actual temperature decrease with altitude in the atmosphere, and it varies with surface temperature and weather conditions.
• 😀 The ELR is influenced by solar and terrestrial radiation, with the near-surface air cooling at night and warming during the day.
• 😀 Adiabatic cooling occurs when air rises and expands, and there are four main mechanisms for air lifting: orographic lifting, frontal lifting, convergence, and convection.
• 😀 Orographic lifting occurs when mountains force air to rise, causing cooling and potential cloud formation, while leeward slopes tend to be warmer and drier due to descending air.
• 😀 Frontal lifting happens when warm and cold air masses collide, forcing warm air to rise, while convection is caused by surface heating, leading to localized thunderstorms.

Q & A

What are the two main types of temperature changes in air parcels?

The two main types of temperature changes in air parcels are diabetic and adiabatic processes. Diabetic processes involve direct energy exchanges, like heating or cooling due to contact with hot or cold surfaces, while adiabatic processes involve no net energy exchange and are driven by the compression or expansion of air.

How does an adiabatic process cause temperature changes in air?

In an adiabatic process, when air is compressed, the molecules move faster, causing the air to warm up. When air expands, the molecules move slower, which cools the air down. This process occurs without any energy exchange with the surroundings.

What happens to air temperature as it rises in the atmosphere?

As air rises in the atmosphere, it enters a region of lower pressure, causing it to expand and cool. This cooling occurs at a rate known as the dry adiabatic lapse rate, which is 10°C per 1,000 meters of altitude.

What is the dry adiabatic lapse rate?

The dry adiabatic lapse rate refers to the rate at which the temperature of a rising air parcel decreases in the absence of moisture. This rate is approximately 10°C per 1,000 meters of altitude.

What is the lifting condensation level (LCL) and why is it important?

The lifting condensation level (LCL) is the height at which air rises to the point where it cools enough to reach saturation, causing condensation. It marks the point where clouds begin to form and is important in understanding cloud formation and weather patterns.

What happens after an air parcel reaches the lifting condensation level?

After an air parcel reaches the lifting condensation level, further lifting causes condensation, which releases energy. As a result, the rate of cooling decreases, and the air parcel cools at the moist adiabatic lapse rate (approximately 5°C per 1,000 meters), rather than the dry adiabatic rate.

How does the environmental lapse rate (ELR) differ from the dry and moist adiabatic lapse rates?

The environmental lapse rate (ELR) refers to the actual rate at which temperature decreases with altitude in the atmosphere, which can vary depending on local conditions. Unlike the dry and moist adiabatic lapse rates, which are constant under specific conditions, the ELR depends on factors like surface heating, cooling, and air movement.

What are the primary mechanisms that cause air parcels to rise?

The primary mechanisms that cause air parcels to rise include orographic lifting (air forced upward by mountains), frontal lifting (when warm and cold air masses collide), convergence (horizontal convergence forcing air to rise), and convection (local surface heating causing air to rise).

What is orographic lifting and how does it affect weather?

Orographic lifting occurs when mountains act as barriers to air flow, forcing air to rise over the mountains. As the air rises, it cools and can form clouds, often leading to precipitation on the windward side of the mountains. On the leeward side, the air warms and dries, often creating a rain shadow effect.

How does the temperature of an air parcel affect its buoyancy and movement?

The temperature of an air parcel affects its buoyancy. Warm air is less dense and tends to rise, while cooler air is denser and tends to sink. This difference in density is driven by temperature, with warmer air having lower density than the surrounding cooler air.