Atmospheric stability and instability are determined by examining the vertical profile of temperature (known as the lapse rate) and wind speed in the atmosphere. The lapse rate describes how the temperature changes with height. There are three main types of lapse rates:
Stable Atmosphere: In a stable atmosphere, the temperature decreases with height at a rate greater than the dry adiabatic lapse rate (about 5.5°C per 1000 meters). This means that colder, denser air is situated beneath warmer, less dense air. Stable conditions inhibit vertical air movement because the cold air resists rising through the warmer air above it. Stable conditions are often associated with calm winds and limited vertical mixing of pollutants.
Unstable Atmosphere: In an unstable atmosphere, the temperature decreases with height at a rate less than the dry adiabatic lapse rate. This means that the air near the surface is warmer and less dense than the air aloft. As a result, the warmer air rises and displaces the cooler air above, creating vertical motion. Unstable conditions can lead to the development of convective clouds, thunderstorms, and enhanced vertical mixing of pollutants.
Neutral Atmosphere: In a neutral atmosphere, the temperature changes with height at a rate close to the dry adiabatic lapse rate. There is little resistance for vertical air movement, and air parcels can move freely without significant buoyancy forces.
To determine atmospheric stability and instability using wind speed and environmental temperature, meteorologists and atmospheric scientists use weather balloons equipped with instruments that measure temperature, humidity, and wind speed at various altitudes. These measurements are used to construct a vertical profile of the atmosphere.
Based on the lapse rate and wind profile, meteorologists can identify stable, unstable, or neutral atmospheric conditions. Stable conditions are typically associated with a decrease in wind speed with height, while unstable conditions may result in increasing wind speeds with height due to vertical mixing.
It's important to note that atmospheric stability and instability are crucial factors in weather forecasting, air quality assessments, and understanding the behavior of pollutants in the atmosphere.