Meteorological Instruments, Observations, and Networks
Core concepts
Know surface instruments: barometers, thermometers, hygrometers, anemometers, rain gauges, and ceilometers. Understand upper-air observations by radiosonde, including pressure, temperature, humidity, and wind measurement, and the sources of error. Study automatic weather stations, synoptic and climatological networks, and the WMO Global Observing System, including GTS and AMDAR. Learn about instrument exposure, calibration, and representativeness.
Traps
Questions often test the difference between a Stevenson screen and aspirated shields. Know that radiosonde humidity sensors degrade at low temperatures. Do not confuse station pressure with sea-level pressure. Be careful with units and with the distinction between accuracy and precision.
Worked example
A station at 900 hPa reports a station pressure of 900 hPa; to obtain QNH, apply the hypsometric correction for the station elevation. If the station is 1000 m above sea level, the correction is roughly 100 hPa, giving a QNH near 1000 hPa, which is consistent with typical surface pressures.