Meteorology
Meteorology
Meteorology tests the atmosphere, pressure, wind, clouds, precipitation, icing, thunderstorms, visibility and METAR/TAF interpretation. For Iran, the exam also expects awareness of hot summer thermal lows, dust, mountain waves over the Zagros and rapid weather changes near frontal systems.
Core rules
- Pressure decreases with height; QNH is the altimeter setting that gives elevation at an aerodrome, QFE gives height above the aerodrome, and 1013 hPa is used for flight levels.
- Wind is named by the direction from which it blows. METAR wind direction is true; take-off and landing wind is reported magnetic. Wind shear and gust fronts are hazardous near thunderstorms.
- Cloud forms when air is cooled to its dew point. A small temperature/dew-point spread indicates high humidity and a risk of mist or fog.
- Icing occurs in supercooled cloud or freezing rain; it increases weight and drag and reduces lift. Carburettor icing can occur at temperatures well above freezing.
- Thunderstorms require moisture, instability and a lifting trigger; avoid them by at least 20 nm and do not attempt to fly under a storm.
Worked example
A METAR reports temperature 18°C and dew point 15°C. The spread is 3°C, so the air is close to saturation. With overnight cooling or moist advection, mist or fog is likely. The pilot should check the trend and be prepared for reduced visibility, especially at a low-lying aerodrome.
Traps
- Using METAR wind as magnetic.
- Reading QNH as QFE.
- Assuming clear skies mean no turbulence near mountains.
- Underestimating carburettor icing on a warm, humid day.