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Atmospheric Refraction Calculator

Calculate barometric air pressure at altitude, Magnus dew point, Magnus heat index, relative humidity, and density altitude for atmospheric refraction.

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Input Atmospheric Parameters

Enter air temperature T, relative humidity RH, or altitude h.

Calculated Dew Point / Value

16.68 °C
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Barometric Formula

Atmospheric barometric pressure drops exponentially with altitude: P = P₀ × exp(-Mgh / RT). At sea level, P₀ = 1013.25 hPa (14.696 PSI).

Calculation Methodology & Details

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Formula

Magnus Dew Point: T_d = (c × γ) / (b - γ), where γ = (b × T)/(c + T) + ln(RH/100) Air Density: ρ = (P_d × M_d + P_v × M_v) / (R × T) Cloud Base Height: H = ((T - T_d) / 2.5) × 1000 feet Barometric Lapse Rate: T_h = T_0 - L × h

Applies US Standard Atmosphere 1976 thermodynamics, August-Roche-Magnus vapor pressure approximations, and NOAA Heat Index empirical regressions.

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Important Disclaimer

Calculations use standard ISA tropospheric lapse rates (6.5 °C per km) and sea level reference pressure 101.325 kPa.

How to Calculate Step-by-Step

Follow these steps to complete the calculation:

1

Step 1

Enter dry-bulb air temperature T (°C or °F) and relative humidity RH (%).

2

Step 2

Specify station elevation or altitude above sea level h (meters or feet).

3

Step 3

View dew point temperature (°C), air density (kg/m³), cumulus cloud base height (feet), or NOAA heat index apparent temperature.

Detailed Insights & Expert Guide

ℹ️ About this Calculation

The Atmospheric Refraction Calculator calculates atmospheric barometric pressure lapse rates, Magnus dew point temperature, moist air density, cloud base altitude, wet-bulb temperature, and wind chill heat indices.

Variable Glossary

Input

Dew Point (T_d)

Temperature to which air must be cooled at constant pressure to become fully saturated with water vapor (100% RH).

Parameter

Density Altitude

Pressure altitude corrected for non-standard temperature and humidity, crucial for aircraft takeoff/climb performance.

FAQ

How is convective cloud base height calculated?
Cloud base (Lifted Condensation Level) = ((T_air - T_dewpoint) / 2.5) × 1,000 feet (or ((T - T_d) / 4.4) × 1,000 meters), based on the dry adiabatic lapse rate spread.
What is the difference between Relative and Absolute Humidity?
Relative humidity (%) measures current vapor pressure relative to saturation pressure at a given temperature. Absolute humidity (g/m³) measures total mass of water vapor per unit volume of moist air.
How is lightning distance estimated?
Count the seconds between the lightning flash and thunder clap, then divide by 3 for distance in kilometers (or divide by 5 for distance in miles), using speed of sound v ≈ 343 m/s.