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Atmospheric Science

Atmosphere Layers Simulator

Compute pressure, temperature, density and speed of sound at any altitude using the International Standard Atmosphere (ISA) model. Compare troposphere, stratosphere, mesosphere and thermosphere on interactive charts.

Altitude setting

Troposphere (0-11 km)
Pressure
—
hPa
Temperature
— °C
Density ρ
— kg/m³
Speed of Sound a
— m/s
Surface Ratio (Pressure)
— %
Kinematic Viscosity ν
— m²/s
Mean Free Path
— nm
Temp
Theory & Key Formulas
Troposphere (0-11 km)：
$T = 288.15 - 6.5h$ [K]
$p = 101325 \left(\frac{T}{288.15}\right)^{5.256}$ [Pa]

Lower stratosphere isothermal layer (11-20 km)：
$T = 216.65$ K, $p = p_{11}e^{-g(h-h_{11})/(RT)}$

$\rho = p/(RT)$, $a = \sqrt{\gamma RT}$

🎓 Learn the Structure of the Atmosphere Through Conversation

🙋
It gets colder when you climb a mountain. If higher altitude is closer to the Sun, why does it get colder instead of warmer?
🎓
Good question. The distance from Earth to the Sun is about 150 million km, while even the highest mountains are only about 8.8 km tall. That height difference is negligible relative to the Sun. The atmosphere is warmed mainly because it absorbs infrared radiation emitted from the ground. At higher altitude, you are farther from that heated surface and the air is less dense, so less radiation is absorbed. That is why the lower troposphere is warmer.
🙋
But you said temperature increases with altitude in the stratosphere. Is that because of the ozone layer? What is the mechanism?
🎓
Yes. Ozone (O3) directly absorbs high-energy ultraviolet radiation (UV-B: 280-315 nm and UV-C: 100-280 nm) and converts it to heat. This absorption layer is concentrated around 15-35 km, so temperature rises there. Near the stratopause around 50 km, temperature recovers to roughly -3°C. Because the ozone layer acts as a heat source, the stratosphere becomes a warm cap that limits upward transport of tropospheric water vapor and clouds.
🙋
Passenger aircraft often fly at 10-12 km, near the lower stratosphere. Why do they fly that high?
🎓
Mainly for fuel efficiency. Lower air density reduces drag; at 10 km, density is about 25% of the surface value. Drag scales strongly with density, so resistance falls greatly. Lift also decreases, so aircraft must fly faster, but the overall fuel economy is still better. The lower stratosphere also has less turbulence and more stable flight. Jet engines also benefit thermally from low ambient temperatures near -50°C.
🙋
How is this atmosphere model used in CAE?
🎓
It is essential in aerospace CFD. For aircraft aerodynamic analysis, ISA pressure, temperature, and density at the target altitude are used as CFD boundary conditions. It is also used for engine performance calculations, wing Reynolds-number estimates, and reentry capsule heating analysis where upper-atmosphere density matters. Because the speed of sound in air ($a=\sqrt{\gamma RT}$) changes with temperature, the model is especially important for transonic and supersonic simulations.

Frequently Asked Questions

What is the International Standard Atmosphere (ISA)?
It is a standard model of altitude, temperature, pressure, and density defined by ICAO (International Civil Aviation Organization). Reference values at sea level: pressure 101325 Pa, temperature 288.15 K (15°C), density 1.225 kg/m³. It is defined in multiple layers: the troposphere (0–11 km) where temperature decreases at 6.5 K/km, the lower stratosphere (11–20 km) is isothermal at 216.65 K, and the upper stratosphere (20–32 km) where temperature increases at 1 K/km, etc.
What is the atmospheric pressure at 8848 m (Mount Everest)?
According to the ISA model, it is about 314 hPa (about 31% of sea level pressure), and the temperature is about −42°C. The partial pressure of oxygen is also about 31% of sea level, making it extremely difficult to summit without supplemental oxygen. Hillary and Tenzing used oxygen cylinders when they first climbed in 1953. ISA is an average for a standard year, so actual values vary with season and latitude.
How does the speed of sound change with altitude?
The speed of sound is given by $a = \sqrt{\gamma RT}$ and depends only on temperature (γ=1.4, R=287 J/kgK), not directly on pressure or density. In the troposphere, as altitude increases, temperature decreases and the speed of sound also decreases. Sea level: 340 m/s → lower stratosphere (T=216.65 K): about 295 m/s. The Mach number of a high-speed aircraft is the ratio of its speed to this local speed of sound, so at the same flight speed, the Mach number is higher at higher altitudes.
What are the characteristics of the mesosphere and thermosphere?
The mesosphere (50–80 km) sees temperature drop again, reaching the lowest atmospheric temperature (about −90°C) near 80 km. It is also the layer where meteors burn up. The thermosphere (above 80 km) absorbs extreme ultraviolet (EUV) from the sun and can reach over 1000°C, but the air is so thin that the heat content is low. The ISS flies in the thermosphere (around 400 km altitude).
How to use the ISA model for aircraft CFD analysis?
In aircraft CFD, ISA values at the flight altitude (pressure p, temperature T, density ρ, dynamic viscosity μ) are set as far-field boundary conditions. Dynamic viscosity is calculated using Sutherland's formula: $\mu = \mu_0(T/T_0)^{3/2}(T_0+S)/(T+S)$. The boundary conditions for compressible flow, determined by Mach number M = V/a, also change with altitude. In OpenFOAM, this can be set with the freestream boundary condition; in Ansys Fluent, pressure correction for altitude can be done under 'Operating Conditions'.

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How to Use

  1. Set altitude using the h-slider (0–100 km range) or enter exact value in h-the field
  2. The simulator applies ISA (International Standard Atmosphere) model equations to compute pressure, temperature, density, and sound speed at your selected altitude
  3. Review output table showing layer classification (troposphere, stratosphere, mesosphere, thermosphere) and corresponding atmospheric parameters

Worked Example

At h=10,000 m (cruise altitude for regional aircraft): Temperature = 223.25 K (−49.9°C), Pressure = 26,436 Pa (0.261 atm), Density = 0.413 kg/m³, Sound speed = 299.5 m/s. Compare to sea level (h=0 m): T=288.15 K, P=101,325 Pa, ρ=1.225 kg/m³, a=340.3 m/s. The lapse rate in troposphere is −6.5 K/km; above 11 km (stratosphere), temperature stabilizes then increases due to ozone absorption.

Practical Notes

  1. Troposphere (0–11 km): primary weather layer; use for aircraft performance, wind load analysis, and meteorological input to CFD models
  2. Stratosphere (11–47 km): temperature inversion; critical for high-altitude aerospace design, satellite drag estimation, and upper-atmosphere acoustics
  3. Mesosphere (47–85 km): coldest layer (min 186 K); used in meteor ablation studies and near-space vehicle trajectories
  4. Thermosphere (>85 km): exponential density decay; required for satellite orbital decay calculations and ionospheric coupling analysis