Water in the Earth's atmosphere

Abstract

Abstract. Water is the key to our existence on this planet and it is involved in nearly all biological, geological, and chemical processes. Life on Earth depends very much on the remarkable properties of water. The availability of freshwater is for many regions one of the key concerns in connection with global climate change. The atmosphere contains only about 0.001% of the water available on our planet. Despite this small amount its horizontal and vertical distribution plays a key role in the global water cycle and the Earth's climate. The atmosphere has direct connections to most of the other reservoirs and steers the redistribution of water between them with an average turnover time of about 10 days. Evaporation over the oceans exceeds precipitation and over land evapotranspiration amounts only to 2/3 of the precipitation reaching the ground. Consequently, there is a net flux of water from the oceans towards the continents, of course via the atmosphere, which has the largest overall volume of fluxes. Water is present in the atmosphere as solid, liquid, or gas. Water vapour is the most important greenhouse gas in the atmosphere and, in addition, changes of water phase and cloud-radiation interaction contribute strongly to the global energy cycle. Water is also a physically and chemically integral part of other biogeochemical cycles. Although there have been large efforts and improvements in recent years, uncertainties in quantifying the components of the atmospheric water cycle still exist. Observational capabilities on the global scale are not satisfactory at present, but the advent of new satellites devoted to the global observation of precipitation and cloud systems along with dedicated modelling projects certainly will improve the situation. Progress is urgently needed to adequately contribute to the answer of one of the central questions in the context of global warming: Is the hydrological cycle accelerating?

Where Does the Iberian Peninsula Moisture Come From? An Answer Based on a Lagrangian Approach

“…About 90% of the water in the atmosphere emanates from the oceans, lakes, and other open water bodies (Quante and Matthias 2006). Through atmospheric transport and associated transfer processes, some of the water that evaporates over the oceans reaches the land and may precipitate.…”

“…Therefore, the greatest variations in water vapor in space occur with increasing height above the surface; specifically, water vapor concentrations decrease markedly with increasing height. Important variations also occur close to the surface, where concentrations vary by more than three orders of magnitude from 10 ppm by volume (ppmv) in the coldest regions of the earth's atmosphere to as much as 5% by volume in the warmest regions (Quante and Matthias 2006). Most of the water vapor is concentrated in the tropical atmosphere, which contains more than 3 times as much water as the extratropical atmosphere.…”

A close look at oceanic sources of continental precipitation

“…For example, near the surface, where most water vapor resides, concentrations vary by more than 3 orders of magnitude, from 10 parts per million by volume in the coldest regions to as much as 5% in the warmest [Quante and Matthias, 2006]. The tropical atmosphere contains more than 3 times as much water vapor as the extratropical.…”

“…Globally, the hydrological cycle is characterized by the evaporation of about 500,000 cubic kilometers of water per year, of which 86% is from the oceans and 14% is from the continents [Quante and Matthias, 2006]. Most of the water that evaporates from the oceans (90%) is precipitated back into them, while the remaining 10% is transported to the continents, where the water precipitates.…”

Estimates of land and sea moisture contributions to the monsoonal rain over Kolkata, deduced based on isotopic analysis of rainwater

“…Satellite-based observations and pan evaporation data indicate that the quantity of moisture returned to the atmosphere by the process of evaporation is substantial and plays a significant role in governing the regional water budget. According to global estimates, the hydrological cycle involves an annual rate of evaporation of about 500 000 km 3 of water, around 86 % of which come from the oceans, with the remainder originating from the continents (Quante and Matthias, 2006). Using the Eulerian moisture tracking method in a global study, Van der Ent et al (2010) showed that about 40 % of terrestrial precipitation originates from land evaporation.…”