Abstract
Abstract. This paper revisits the knowledge on the residence time of water in the atmosphere. Based on state-of-the-art data of the hydrological cycle we derive a global average residence time of 8.9 ± 0.4 days (uncertainty given as 1 standard deviation). We use two different atmospheric moisture tracking models (WAM-2layers and 3D-T) to obtain atmospheric residence time characteristics in time and space. The tracking models estimate the global average residence time to be around 8.5 days based on ERA-Interim data. We conclude that the statement of a recent study that the global average residence time of water in the atmosphere is 4–5 days, is not correct. We derive spatial maps of residence time, attributed to evaporation and precipitation, and age of atmospheric water, showing that there are different ways of looking at temporal characteristics of atmospheric water. Longer evaporation residence times often indicate larger distances towards areas of high precipitation. From our analysis we find that the residence time over the ocean is about 2 days less than over land. It can be seen that in winter, the age of atmospheric moisture tends to be much lower than in summer. In the Northern Hemisphere, due to the contrast in ocean-to-land temperature and associated evaporation rates, the age of atmospheric moisture increases following atmospheric moisture flow inland in winter, and decreases in summer. Looking at the probability density functions of atmospheric residence time for precipitation and evaporation, we find long-tailed distributions with the median around 5 days. Overall, our research confirms the 8–10-day traditional estimate for the global mean residence time of atmospheric water, and our research contributes to a more complete view of the characteristics of the turnover of water in the atmosphere in time and space.
Highlights
The time it takes before evaporated water from land and oceans is returned to the land surface as precipitation is a fundamental characteristic of the Earth’s hydrological cycle
Trenberth (1998) found a global average residence time of atmospheric moisture of 8.9 days based on evaporation and 9.1 days based on precipitation, and attributed this difference to the input data having a non-closure of the Published by Copernicus Publications on behalf of the European Geosciences Union
Applying Eq (2) to estimates of the global hydrological cycle (Fig. 1) yields a global mean residence time of atmospheric water of 8.9 ± 0.4 days
Summary
The time it takes before evaporated water from land and oceans is returned to the land surface as precipitation is a fundamental characteristic of the Earth’s hydrological cycle This atmospheric residence time of moisture is not often discussed in the scientific research literature. The global average residence time of atmospheric moisture is mostly seen as non-controversial knowledge in textbooks (e.g., Chow et al, 1988; Hendriks, 2010; Jones, 1997; Ward and Robinson, 2000), general water literature (e.g., Bodnar et al, 2013; Savenije, 2000) and educational web pages (e.g., UCAR, 2011). It is safer to interpret them as local timescales of atmospheric moisture recycling (van der Ent and Savenije, 2011). Trenberth (1998) found a global average residence time of atmospheric moisture of 8.9 days based on evaporation and 9.1 days based on precipitation, and attributed this difference to the input data having a non-closure of the Published by Copernicus Publications on behalf of the European Geosciences Union
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