Meteorology is one of the central subjects in the theoretical training for Instrument Rating (IR). It provides the necessary knowledge to analyse and evaluate weather conditions and anticipate their effects on the flight. This knowledge is crucial for the safety and efficiency of flights, especially in instrument flight operations.
The atmosphere
1. structure of the atmosphere
- Layers:
- Troposphere: The lowest layer in which almost all meteorological processes take place. It extends from the earth's surface to a height of around 8 km at the poles and up to 18 km at the equator. The temperature decreases with altitude, which promotes the vertical circulation of air.
- Stratosphere: Extends from the tropopause to an altitude of around 50 km. Here, the temperature increases with altitude, which increases the stability of this layer. It contains the ozone layer, which absorbs ultraviolet radiation.
- Further layers: Mesosphere, thermosphere and exosphere, which are less relevant for aviation.
- Importance for aviation:
- The troposphere is particularly important as weather phenomena such as clouds, precipitation and turbulence occur here. The height of the tropopause influences the range of jet streams and turbulence.
2. Temperature, air pressure and density
- Temperature:
- It decreases in the troposphere by an average of 2 °C per 1,000 ft. Temperature inversions, in which the temperature increases with altitude, can have stabilising effects and hinder air circulation.
- Air pressure:
- The standard pressure at sea level is 1013.25 hPa. With increasing altitude, the pressure decreases exponentially, which influences the performance of aircraft engines and the efficiency of aerodynamic surfaces.
- Density:
- Depends on temperature, pressure and humidity. Less dense air at high altitudes leads to lower engine performance and reduced lift.
3. standard ISA atmosphere
- Definition: The International Standard Atmosphere (ISA) serves as a reference for the calibration of instruments and the calculation of performance data.
- Standard values: Temperature +15 °C, pressure 1013.25 hPa, temperature decrease of 6.5 °C per 1,000 m.
4. barometric altitude calculation
- Altimeter: Uses the ambient pressure to display the altitude. Correct settings are crucial:
- QNH: Local air pressure reduced to sea level.
- QFE: Pressure on the ground at the airport.
- Standard pressure (1013.25 hPa): Used above the transition level.
Wind
1. definition and types of wind
- Definition: Wind is the horizontal movement of air masses due to pressure differences between high and low pressure areas.
- Species:
- Ground wind: Influenced by friction with the earth's surface.
- High wind: More constant and stronger, as the friction is low. Jet streams are a prominent example.
2. turbulence
- Mechanical turbulence: Formed by obstacles such as mountains or buildings.
- Thermal turbulence: Caused by upward movement of warm air, often in sunny regions.
3. wind systems and lee waves
- Global wind systems:
- Trade winds, westerly winds and polar easterly winds.
- The Coriolis force influences the deflection of air masses.
- Lee waves:
- Form behind mountains in strong winds and can lead to severe turbulence.
Thermodynamics
1. humidity and aggregate states
- Humidity:
- Absolute humidity: Actual amount of water vapour.
- Relative humidity: Ratio to the maximum possible humidity.
- States of aggregation:
- Transitions between liquid, gaseous and solid. Evaporation, condensation, sublimation and freezing are crucial for cloud formation.
2. adiabatic processes
- Dry adiabatic: Temperature change without phase transition (approx. 1 °C per 100 m).
- Wet adiabatic: Slower cooling (approx. 0.5 °C per 100 m) due to latent heat.
Clouds and fog
1. cloud formation and types
- Education: Cooling of moist air masses below the dew point.
- Species:
- Cumulus: Vertically extended clouds, often associated with thermal activity.
- Stratus: Horizontal stratus clouds, which often lead to visual obstructions.
- Cirrus: High clouds of ice crystals that indicate changes in the weather.
2. fog and haze
- Fog:
- Types: radiation nebulae, advection nebulae, mixed nebulae.
- Vapour: Obstruction of visibility due to suspended particles.
Flight hazards
1. icing
- Species: Clear ice, rough ice, mixed icing.
- Dangers: Reduced aerodynamics, blocked sensors.
2. turbulence and wind shear
- Turbulence due to jet streams or mountains.
- Wind shear: Sudden change in wind force or direction.
3. thunderstorms and tornadoes
- Thunderstorm: Electrical discharges, strong updraft.
- Tornadoes: Rotating winch with extremely high destructive power.
Meteorological information
1. weather observations
- METAR, TAF and SIGMET.
2. weather maps
- Analysing fronts, printing systems.
3. meteorological flight planning
- Assessment of conditions at destination and alternative airports.
Conclusion
Meteorology provides essential knowledge for analysing and evaluating weather conditions and correctly assessing their impact on flight. This knowledge enables pilots to make informed decisions, increase safety and minimise risks. The intensive study of the topics presented here is essential, as weather phenomena represent one of the greatest challenges in aviation. The subject of meteorology therefore forms an indispensable basis for safe and efficient flight guidance, especially in instrument flight.
Source references:
EASA FCL