Dry Adiabatic Lapse Rate Calculator
Results
The estimated final temperature is:
Understanding the Dry Adiabatic Lapse Rate (DALR)
In meteorology, the Dry Adiabatic Lapse Rate (DALR) is the rate at which the temperature of an unsaturated (dry) parcel of air decreases as it rises or increases as it descends. This cooling or warming occurs solely due to changes in atmospheric pressure, without any heat exchange with the surrounding environment.
The Physics Behind DALR
When a parcel of air rises, it encounters lower pressure. To equalize this pressure, the air parcel expands. This expansion requires work, and that work comes from the internal energy of the air, causing the temperature to drop. Conversely, when air sinks, it is compressed by higher pressure, which increases its internal energy and temperature.
The Constant Values
The DALR is a relatively constant value because it depends on the gravity of the Earth and the specific heat of dry air at constant pressure:
- Metric: Approximately 9.8°C per 1,000 meters (or 0.98°C per 100 meters).
- Imperial: Approximately 5.4°F per 1,000 feet.
How to Calculate Dry Adiabatic Lapse Rate Manually
To calculate the temperature of an air parcel at a new altitude, use the following formula:
Where:
- Tinitial: Starting temperature of the air parcel.
- Altitudechange: The difference between the final altitude and starting altitude.
- LapseRate: 9.8 (for Celsius/meters) or 5.4 (for Fahrenheit/feet).
Real-World Example
Imagine a parcel of dry air at sea level (0 meters) with a temperature of 20°C. If a wind pushes this air parcel up a mountain to an elevation of 3,000 meters, what will its temperature be?
- Identify the altitude change: 3,000 – 0 = 3,000 meters.
- Calculate how many 1,000-meter units it rose: 3,000 / 1,000 = 3 units.
- Multiply by the DALR: 3 units × 9.8°C = 29.4°C decrease.
- Subtract from initial temp: 20°C – 29.4°C = -9.4°C.
Important Note: Dry vs. Saturated
This calculator uses the "Dry" lapse rate. If the air cools to its dew point, water vapor begins to condense into liquid water. This process releases latent heat, which slows the cooling process. At that point, you would switch from using the DALR to the Saturated Adiabatic Lapse Rate (SALR), which is typically around 5°C to 6°C per 1,000 meters.