Meteorology
What this domain tests
Meteorology tests the ISA, pressure and wind systems, cloud and icing, thunderstorms, tropical cyclones, METAR/TAF decoding and SIGMET use. Mauritius lies in the trade-wind belt and is exposed to tropical cyclones from November to April.
Core rules
- ISA: sea-level temperature 15 degrees C, lapse rate 1.98 degrees C per 1,000 ft, tropopause at 36,090 ft and minus 56.5 degrees C.
- Pressure: QNH is the altimeter setting that gives elevation on the ground; QFE gives height above a datum. Low pressure and high temperature increase density altitude.
- Icing: most likely between 0 degrees C and minus 20 degrees C in visible moisture; clear ice forms from large supercooled droplets, rime from small droplets.
- Thunderstorms require moisture, instability and a lifting trigger; avoid the mature stage, hail and microbursts. Use weather radar and do not penetrate a cell.
- Tropical cyclones: a SIGMET and the Mauritius cyclone bulletin govern; expect strong low-level wind shear and heavy rain.
Worked example
ISA temperature at FL 300: 15 minus (1.98 x 30) = 15 minus 59.4 = minus 44.4 degrees C. If the actual temperature is minus 54 degrees C, the air is colder than ISA, so true altitude is lower than indicated altitude, which is a safety issue over high terrain.
Traps
Reading a METAR trend as a forecast rather than a two-hour observation; confusing QNH and QFE; forgetting that a TAF is valid for a specific period and may be amended; treating a SIGMET as advisory when it warns of hazardous weather.
Key habit
Decode METAR/TAF in a fixed order: wind, visibility, weather, cloud, temperature, pressure, trend. Then ask what it means for your takeoff or alternate.