Environmental Lapse Rate Calculator
Estimate temperature changes at altitude based on atmospheric gradients.
Standard Atmosphere: 6.5°C/km (3.56°F/1000ft).
Dry Adiabatic: 9.8°C/km. Moist Adiabatic: ~5°C/km.
Dry Adiabatic: 9.8°C/km. Moist Adiabatic: ~5°C/km.
Calculation Results
Temperature at Target Altitude:
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Total Temperature Change:
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Elevation Difference:
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Estimated Freezing Level:
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Understanding Environmental Lapse Rate (ELR)
The Environmental Lapse Rate (ELR) is the rate at which air temperature decreases with an increase in altitude in the stationary atmosphere. It is a critical concept in meteorology, aviation, and mountaineering, as it determines atmospheric stability and helps predict phenomena like cloud formation, thunderstorms, and turbulence.
The ELR Formula
The basic calculation for estimating temperature at a specific altitude uses the following linear equation:
Tfinal = Tbase – (Γ × (Zfinal – Zbase))
- Tfinal: The temperature at the target altitude.
- Tbase: The known temperature at the starting elevation (often sea level).
- Γ (Gamma): The lapse rate (temperature change per unit of height).
- Z: The elevation values (Target and Base).
Common Lapse Rate Values
While the actual lapse rate varies constantly based on weather conditions, humidity, and time of day, meteorologists use standard reference values:
| Lapse Rate Type | Metric Value | Imperial Value | Description |
|---|---|---|---|
| Standard Atmosphere (ISA) | 6.5 °C / km | 3.56 °F / 1000 ft | The global average used for aviation and general estimation. |
| Dry Adiabatic (DALR) | 9.8 °C / km | 5.4 °F / 1000 ft | Rate for unsaturated air parcels. Air cools faster when dry. |
| Moist Adiabatic (MALR) | ~5.0 °C / km | ~2.7 °F / 1000 ft | Rate for saturated air (clouds/fog). Latent heat release slows cooling. |
Atmospheric Stability
Comparing the Environmental Lapse Rate to the adiabatic rates helps determine stability:
- Unstable: If the ELR is greater than the Dry Adiabatic rate (> 9.8°C/km), air parcels will continue to rise, often leading to storms.
- Stable: If the ELR is less than the Moist Adiabatic rate (< 5°C/km), vertical motion is suppressed.
- Temperature Inversion: If the temperature increases with height (negative lapse rate), the atmosphere is extremely stable, trapping pollutants and fog near the ground.
Practical Applications
Mountaineering: Hikers use lapse rates to prepare for freezing temperatures at summits. For every 1,000 meters gained, expect the temperature to drop roughly 6.5°C.
Aviation: Pilots use these calculations to estimate freezing levels to avoid icing on wings and to calculate density altitude which affects engine performance.
Weather Forecasting: Meteorologists launch weather balloons (radiosondes) to measure the actual ELR profile to predict severe weather potential.