. The distribution of commercial aircraft weather observations and their use in numerical weather prediction

Abstract
Weather observations from commercial aircraft constitute a critical component of the global observing system, and have been shown to be the most valuable observation source for frequently updated numerical weather prediction (NWP) systems over North America. However, the distribution of aircraft observations is highly irregular in space and time. Coverage is most dense over the contiguous United States and Europe, with secondary maxima in East Asia and Australia / New Zealand. High-altitude observations are generally available only in frequently used flight routes, particularly over the North Pacific and North Atlantic Oceans, with diurnal patterns that are relatable to normal flight schedules. Ascent and descent observations, which provide vertical profiles of the atmosphere for numerical weather prediction initialization, cover a much smaller area globally, as do observations of water vapor mixing ratio. Trends in the number of observations available are evident in various parts of the globe, with a notable increase in observation frequency in South America over the past year. Networks of regional carriers, such as TAMDAR, and new reporting protocols such as MODE-S or ADS-B (as already implemented in Europe) provide opportunities to widely expand coverage of aircraft observations and to improve short-term NWP.