Explain why residence time in the atmosphere for water is short but the flux in and out of the atmosphere is huge.
The residence time in the atmosphere refers to the average amount of time a water molecule spends in the atmosphere before it is removed through various processes. On the other hand, the flux in and out of the atmosphere refers to the amount of water entering and leaving the atmosphere over a given period.
The residence time for water in the atmosphere is relatively short because there are several processes that efficiently remove water molecules, such as precipitation, condensation, and evaporation. These processes constantly cycle water in and out of the atmosphere.
To understand why the residence time is short, consider the following explanations:
1. Precipitation: When water vapor condenses into liquid or solid form, it falls as precipitation. This process removes water from the atmosphere and brings it back to the Earth's surface in the form of rain, snow, or hail. The condensed water quickly returns to the surface, thereby decreasing the residence time in the atmosphere.
2. Condensation: As water vapor cools, it can condense into tiny droplets, forming clouds. Eventually, these droplets grow larger and become raindrops or snowflakes, leading to precipitation. Condensation is a significant process that removes water vapor from the atmosphere and reduces the residence time.
3. Evaporation: While evaporation occurs primarily at the Earth's surface, it also takes place in the atmosphere. However, since the amount of water vapor in the atmosphere is limited compared to the Earth's surface bodies of water, the rate of evaporation from the atmosphere is relatively small. This results in a shorter residence time for water in the atmosphere.
While the residence time in the atmosphere is short, the flux of water into and out of the atmosphere is substantial. This is primarily due to the global water cycle, which involves the movement of water between the atmosphere, land, and oceans. The flux is significant because of the following processes:
1. Evaporation: Water from the Earth's surface continually evaporates into the atmosphere. This includes evaporation from bodies of water, soil, and vegetation. The combined evaporation from these sources leads to a large flux of water vapor into the atmosphere.
2. Transpiration: Plants absorb water from the soil through their roots and release it into the atmosphere through small openings in their leaves, a process known as transpiration. This contributes to the flux of water from the surface to the atmosphere.
3. Precipitation: The water vapor present in the atmosphere condenses and falls back to the surface as precipitation. Precipitation can occur in the form of rain, snow, sleet, or hail, and it can yield large amounts of water returning to the ground, rivers, lakes, or oceans.
In summary, the residence time for water in the atmosphere is short due to precipitation, condensation, and evaporation. However, the flux in and out of the atmosphere is significant as it involves processes such as evaporation, transpiration, and precipitation, which constantly cycle water between the atmosphere and the Earth's surface.