# § 34. Water in the atmosphere (textbook)

§ 34. Water in atmosphere

1. Remember where the three states can be Water?

2. How does the global water cycle?

Concept of humidity. Some amount of water in a transparent invisible vapor in the air is always there. Prove in air and water, quite easily. Just think of the freezer refrigerator. Where it took snow and ice, since there is no water poured? They were formed from water that "has gone" back to the air. In an atmosphere of water vapor comes as a result of evaporation from the surface of oceans, rivers, lakes, Soil et al. The content of water vapor in the air called humidity.

But evaporative air can not hold vapor infinite. This limit depends on its temperature. From Fig.  shows that the higher the temperature the more pair may be contained in 1 m3 air. For example, 1 m3 air at 200 С  may contain any number of couples, but not more than 17 grams of water. If the air is absorbed maximum for a given temperature of the steam, it's called saturated. Often air is unsaturatedIe it contains water pair less than they might have. For example, over the steppes and deserts are always dry air, unsaturated, because there is little evaporation.

Fig. Dependence of water vapor in saturated air temperature from its

Absolute and relative humidity. Absolute humidity - The number of water vapor (in grams) that contained in 1 m3 air. For example, say: absolute humidity is 15 g / m3This means that 1 m3 air contained 15 g of steam. World's most absolute humidity in Antarctica - One hundredth of fate g / m3, The largest at the equator - 23 g / m3. Lowest in Ukraine in January - about 3 g / m3.

For unsaturated air show relative humidity. It - ratio (percentage) of water vapor contained in air to that its quantity can be in the air at this temperature. Thus, if in air containing 3 g / m3 couples, but for most of this temperature its possible content of 5 g / m3, The relative humidity be 3: 5 x 100% = 60%. This means that air contains only 60% of the more water vapor that it could accommodate at this temperature.

Relative humidity is always high (85%) in equatorial latitudes. This is because there all year round high temperatures and large evaporation from the surface. Similarly, high relative humidity and polar areas, but due to low temperature (for cold saturation air does not need much moisture). In temperate latitudes the relative humidity winter is higher than in summer. For example, in Ukraine in winter is higher than 80%, and summer decreases to 60-70%. Especially low relative humidity in the desert - 50% and below. Air humidity is 30%, considered very dry.

To measure relative humidity using appliance hygrometer.

Formation clouds. As you know, with high temperatures decreases. Evaporating, the water goes into the air. Warm air rises up and reaches a level where it cools and the relative humidity it becomes 100%, that air was saturated.

With further increasing temperature saturated air no longer can keep a provisional amount of water vapor. Some of it is be superfluous. Then go "excess" water vapor into liquid condition - condensation. Sometimes water vapor can pass and in solid state - turn into ice crystals. So, at the cooling air saturated with water vapor allocated kraplynky water. With its cluster at a considerable height above the ground formed clouds. Each kraplynka in the clouds a million times smaller than a pea. Making them fall to the ground very slowly. These mini-kraplynky like fuzz, hang in the air.

Types clouds. Clouds vary in appearance and height, which are formed. In appearance distinguished meteorologists dozens of different types of clouds. The main ones are cirrus, thick, layered.

Cirrus clouds highest. They are formed at an altitude of 10.6 km and consist of very small ice crystals because these altitudes Temperature below zero. This thin veil. Sometimes they remind white stretch yarn, feathers or beams.

Thick clouds appear at 2-5 km altitude. They look like huge dazzling white domes, towers, mountains. If cumulus darken then drops of water are merging, becoming larger. Then, cumulus converted to Cumulonimbus, bringing rain with thunderstorms.

Layered clouds formed low - at an altitude of 2 km. They are similar A gray mist that rose above the ground. Layered clouds cover the sky thick veil. Among them may fall very fine rain (mist) or weak snow.

Level of clouds covering the sky are called Clouds. It determined "by eye". When the clouds closed all the sky, clouds is 10 scores if pivneba - 5 points, when the sky is clear - 0 points. Average annual cloudiness for the whole planet is 5 points. Most precipitation observed in the equatorial and temperate latitudes, is dominated by ascending air movements. The clouds carry heat and moisture from the bottom up and from the equator to poles, adjusting the temperature on Earth.

ТHorticulture. Condensation of water vapor can occur not only at different altitudes and and near the surface. Then formed fog- Accumulation of large numbers of extremely small, suspended in the air drops. Heavy fogs deteriorating visibility, so dangerous for traffic transport.