Stability Quiz For CPL

DALR: Dry Air’s Cooling Rate

Dry air: Think of air that hasn’t reached its “dew point” yet. It’s like a balloon that hasn’t been filled with enough water vapor.
DALR: When dry air rises, it cools down at a steady rate. This rate is the DALR.
Imagine a balloon: If you let go of a helium-filled balloon, it rises because it’s lighter than the air around it. As it goes higher, the air pressure is lower, so the balloon expands. This expansion makes the balloon’s gas cool down. The DALR is similar, but with air instead of a balloon.

An inversion occurs when temperature increases with altitude. Inversions prevent mixing between lower-level and upper-level winds, making the atmosphere stable.

At higher altitudes where temperatures are low, with very little water vapor present, the Saturated Adiabatic Lapse Rate (SALR) can approach the Dry Adiabatic Lapse Rate (DALR) around -40 degrees Celsius.

Stable: SALR < ELR (Dry air parcel sinks)
Unstable: ELR < SALR (Dry air parcel rises)
Conditionally unstable: DALR > ELR > SALR (Dry air parcel sinks, saturated air parcel rises)

The Environmental Lapse Rate (ELR) in the actual atmosphere can vary widely.

The Dry Adiabatic Lapse Rate (DALR) is the rate at which dry (unsaturated) air cools or warms as it rises or descends in the atmosphere. It’s a constant rate of 1°C per 100 meters.

An inversion occurs when temperature increases with altitude, resulting in a negative lapse rate.

An isothermal atmosphere has no lapse rate, making it stable due to the lack of change in kinetic energy.

An inversion occurs when temperature increases with altitude, resulting in a negative lapse rate.

Adiabatic processes in the atmosphere occur when air is compressed or expanded due to natural forces. For example, when a parcel of air is forced to rise in the atmosphere, decreasing pressure causes it to expand. This expansion cools the air adiabatically, as the air rises and expands. Rising air is common in low-pressure systems, and the resulting cooling can lead to condensation and cloud formation.

Conversely, when air is forced to descend, increasing pressure causes it to compress and warm adiabatically. This warming process is often associated with high-pressure systems and prevents cloud formation.

DALR: A Quick Guide

Dry air: Think of air that hasn’t reached its “dew point” yet.
DALR: When dry air rises or falls, its temperature changes at a steady rate.
Rate: It cools or warms by 10°C for every 1 kilometer it rises or falls.
Example:

Starting temperature: 30°C
Rising 2 kilometers: 30°C – (2 km * 10°C/km) = 10°C
So, after rising 2 kilometers, the temperature of the dry air will be 10°C.

Stable: SALR < ELR (Dry air parcel sinks)
Unstable: ELR < SALR (Dry air parcel rises)
Conditionally unstable: DALR > ELR > SALR (Dry air parcel sinks, saturated air parcel rises)

An inversion occurs when temperature increases with altitude. High-pressure systems often occur in winter, and in these systems, air descends at the center. As the air descends, it warms adiabatically, becoming warmer than the air at lower levels. This is known as a subsidence inversion.

The Saturated Adiabatic Lapse Rate (SALR) is the rate at which saturated air cools or warms as it rises or descends in the atmosphere. It’s approximately 0.6°C per 100 meters (1.8°C per 1000 feet) or 6°C per kilometer.