FAAM CORE Measures the total water (i.e. liquid plus vapour) in the atmosphere at 64Hz using a Lyman-Alpha absorption hygrometer developed by the Met Office.

Instrument

Total Water Content ProbeA Lyman-alpha absorption instrument, normally operating in the 0-13 g.kg-1 range, with nominal uncertainties of ±0.15 g.kg-1and a sensitivity of nominally 0.01g.kg- 1 (around 16µmol/mol). This instrument derives its calibration by comparing measurements in clear air during profiles with the General Eastern Instrument, on every flight. The sensor is situated outside the aircraft and the housing has been designed to minimise aerodynamic effects on the sample, so allows air to be drawn through the forward end of the sensor at speeds approaching that of the aircraft (100m/s). It incorporates two powerful heaters that instantaneously vaporise all non-gaseous water to permit a ‘total water content’ measurement, and thus only measures ‘humidity’ out of cloud. A rapid-response instrument, the absolute calibration of the TWC is entirely dependent on flight-by-flight calibration against other measurements (normally the General Eastern).

Data

Range 0 to 20 g.kg-1, Accuracy ±0.15g.kg-1. Can be used as a fast response hygrometer.

Further Details

Contact Joss Kent at the MetOffice