Upper Air Humidity from Automatic Aircraft Surveillance Data

Abstract. Upper air humidity information is under sampled in the current operational meteorological observing network. Radiosondes observations form the backbone, but radiosondes balloons are typically launched only once or twice per day to limit the costs. The number of aircraft humidity observations are low in Europe, because in Europe only a few aircraft are equipped with water vapour sensors.

In this paper a novel technique is presented to derive humidity information from aircraft Automatic Dependent Surveillance Broadcast (ADS-B) data, whenever an aircraft is descending or ascending. The retrieved virtual temperatures observations, averaged over a vertical layer of 500 m, have an accuracy between 0.5 K and 0.75 K when compared to European Centre for Medium Range Forecast (ECMWF). Using additional external temperature information, estimates of the specific humidity can be calculated with an accuracy of 3–4 g kg^-1 and in some cases between 2–3 g kg^-1 (that is, when more than 20 estimates are available at the same reference height within 20 minutes). Applying the method to measurements from the Falcon F20 French research aircraft SAFIRE shows that even a single aircraft can be used to derive high-quality virtual temperature information (observation error ≈ 0.5 K). Comparison with Aircraft Meteorological Data Relay (AMDAR) and radiosonde humidity showed similar statistics.

Since ADS-B data is received from all ascending or descending aircraft in the vicinity of an airport, a vast amount of upper air virtual temperatures could be made available, when ADS-B information is gathered by ADS-B receivers installed at, or nearby airports.