Earth global water cycle

The presence of water as solid, liquid, and gas is a feature that makes Earth unique in the solar system and that makes life possible as we know it. The transport of water and the energy exchanged as it is converted from one state to another are important drivers in our weather and climate. One of the key missions is to develop a better understanding of the global water cycle at a variety of scales so that we can improve model forecasts of climate trends,... 

Within the MBWB, small corrections for the water exchange between the Earth and space are not taken into account. A model of the global water cycle can be based on describing the hydrology of comparatively large territories. In this case the basic unit of such a territory is compartment Qy of the Earth surface of size Aby latitude and AXj by longitude. 

Franck, S. and Bounamam, C., 2001. Global water cycle and Earth s thermal evolution. /. Geodynam., 32, 231-46. 

The ocean contains the bulk of the Earth s water (1.37 X 10 g) and moderates the global water cycle. The distribution of the mass of water is about 80% in the ocean and about 20% as pore water in sediments and sedimentary rocks. The reservoir of water in rivers, lakes, and the atmosphere is trivial (0.003%). Disregarding the pore water because it is not in free circulation, we find that 97% of the world s cycling water is in the ocean (Table 9-3). The unit of 10 g is so common in geochemical cycles that it is sometimes called a geogram. The average residence time of water in the atmosphere with respect to net transfer (evaporation minus precipitation over oceans) from the oceans to the continents is about one-third of a year [0.13 X 10 g/(3.83 — 3.47 x 10 g/year) =... 

EARTH S WATER We examine the global water cycle, which describes how water moves from the ground to surface to the atmosphere and back into the ground. We compare the chemical compositions of seawater, freshwater, and groundwater. 

All the water on Earth is connected in a global water cycle ( Figure 18.15). Most of the processes depicted here rely on the phase changes of water. For instance, warmed by the Sun, liquid water in the oceans evaporates into the atmosphere as water vapor and condenses into liquid water droplets that we see as clouds. Water droplets in the clouds can crystallize to ice, which can precipitate as hail or snow. Once on the ground, the hail or snow melts to liquid water, which soaks into the ground. If conditions are right, it is also possible for ice on the ground to sublime to water vapor in the atmosphere. 

EARTH S WATER (SECTION 18.3) Earth s water is largely in the oceans and seas only a small fraction is freshwater. Seawater contains about 3.5% by mass of dissolved salts and is described as having a salinity (grams of dry salts per 1 kg seawater) of 35. Seawater s density and salinity vary with depth. Because most of the world s water is in the oceans, humans may eventually need to recover freshwater from seawater. The global water cycle involves continuous phase changes of water. 

The high concentration of solute particles in the oceans can be traced to the global water cycle in which water from the atmosphere falls to the earth as rain or... 

As shown in Figure 2.1, the free water on Earth s surface is now transported between the land, atmosphere, ocean, and mantle through a global hydrological cycle. From... 

The global heat cycle drives the hydrological cycle, which in turn controls the salinity of seawater. The most important contributor of heat to the crustal-ocean-fectory is solar radiation. The flux of solar radiation that reaches Earth is termed insolation. Only a fraction of the incoming solar radiation reaches Earth s surfece, because a large portion is either reflected or absorbed by the atmosphere. That which reaches Earth s surface is also either reflected or absorbed. In the end, about half of the incoming radiation is absorbed by the rocks and water on Earth s surfece. (A detailed heat budget is provided... 

An important block of the MBWB is the methods of determination of various parameters of the water cycle. Such methods are based on the use of surface, satellite, and airborne measurements. The MBWB used as a global model makes it easier to understand the role of the oceans and land in the hydrological cycle, to identify the main factors that control it, as well as to trace the dynamics of its interaction with plants, soil, and topographic characteristics of the Earth surface. It is based on the interaction between the elements of the water cycle, and takes natural and anthropogenic factors into account by means of information interfaces with other units of the global model (Krapivin and Kondratyev, 2002). 

Rainwater is the consequence of several steps in the water cycle brought about by evaporation, condensation, and precipitation. The water in the atmosphere has a residence time of approximately 8-9.6 days before precipitating as rainfall. As mentioned above, in this cycling the global volume of precipitation that falls onto the Earth each year is of the order of 5.8 x 105 km3, from which approximately 21% falls onto the land and about 79% onto the sea (see Figure 6.2). 

The hydrologic cycle refers to the fluxes of water, in all its states and forms, over the Earth. Table 21.1 gives the estimated volume and percentage of total water in all the major global reservoirs, and Table 21.2 shows the estimated annual fluxes between major reservoirs. We note that 97% of the Earth s water resides in the oceans. Of the remainder, about is sequestered in the ice caps of Greenland and Antarctica, and is in underground aquifers and lakes and rivers. Only a fraction of 10-5 is in the atmosphere, almost all of which is in the form of water vapor. If the total water vapor content of the atmosphere were suddenly precipitated, it would cover the Earth with a rainfall of only 3 cm (see Problem 21.1). 

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