Unit 2. Surface Runoff and Ground Water
Unit 1. Atmospheric moisture Exercises (A) 1. Learn new words: evaporation – испарение to exist – существовать amount of moisture – количество latent heat – скрытое тепло влаги heat loss – тепловые потреи saturation limit – предел to maintain evaporation – насыщения влаги поддерживать испарение precipitation – атмомферные to achieve – достигать осадки tiny particles – крошечная частица cold air – холодный воздух condensation nuclei –ядра warm air – теплый воздух конденсации absolute humidity – абсолютная влажность relative humidity – относительная влажность constant – постоянный . 2. Translate the following word combinations: as part of the global hydrological cycle; by evaporation and transpiration; in the form of precipitation; any part of the atmosphere; to depend on temperature; very little moisture; can be evaporated into warm air; several expressions; to be used for; the amount of moisture in the air; the mass or weight of water vapour; in grams per cubic centimeter; the ratio of the weight of water vapour; to the weight of the air; to remain constant; the ratio of the actual amount of water in the air; to the maximum amount; in all three states of matter in the atmosphere; to change from one to other; to be known as phase changes; significant amounts of energy; in the process of evaporation; one gram of water; from a liquid to a vapour state; to be quickly compensated by conduction and radiation; in the reverse process of condensation; the initial humidity of the air; the greater the potential evaporation from water surfaces; in turbulent conditions; to reach saturation point or alternatively; some tiny particles or nucleus. Text (A) Read the text «Atmospheric moisture»: As part of the global hydrologica1 cycle, moisture is continually entering the atmosphere by evaporation and transpiration, and leaving it in the form of precipitation. The amount of moisture that any part of the atmosphere can hold at any one time (saturation limit) depends on temperature: cold air can hold very little moisture, and much more moisture can Ъе evaporated into warm air before it becomes saturated. Several expressions are used for describing йе amount of moisture in the air. Absolute humidity is the mass or weight of water vapour per unit volume of air, in grams per cubic centimetre; however, as а body of air rises or sinks it undergoes volume changes, and its absolute humidity is thus not а constant figure. Meteorologists make use of the term specific humidity, the ratio of the weight of water vapour to the weight of the air, since this figure remains constant whatever the volume changes, unless water is actually added or lost from the body of air. Another expression пьеМ to the meteorologist is relative humidity, which is the ratio of the actual amount of water in the air to the maximum amount the air could hold at that temperature, stated as а percentage. Moisture exists in all three states of matter in the atmosphere, as vapour, liquid, or solid; changes from one to other are known as phase changes, and significant amounts of energy are involved in accomplishing these changes. In the process of evaporation, 600 calories of latent heat are required to change one- pram of water from a liquid to a vapour state. Normally such a heat loss would be quickly compensated by conduction and radiation. In the reverse process of condensation, latent heat is released into the atmosphere, causing a slight rise in temperature. Three principal factors favor evaporation. First, the initial humidity of the air: the drier the air, the greater the potential evaporation from water surfaces. Second, heat is needed to maintain evaporation, and the rate of evaporation will be proportionally higher depending on the warmth of the water surface and the air immediately above it. Third, wind force can be a significant factor, especially in turbulent conditions, where saturated air is continually replaced by fresh air. In peneral, the preatcr the wind strength, the more effective evaporation is likely to be. Condensation occurs either when enough water is evaporated into the air mass for it to rеach saturation point or alternatively, when the temperature drops sufficiently to achieve the same result. The second method is the more common. However, condensation occurs only with the utmost difficulty in the pure air which exists in the hipher layers of the atmosphere. A basic requirement is some tiny particle or nucleus on which the water vapour can condense. In the lower atmosphere this is normally no problem, since abundant condensation nuclei exist, principally common salt derived from the sea, and dust particles.
Exercises (B) 1. Establish compliance between parts of sentences: 1. moisture is continually entering 1. as vapour, liquid or solid the atmosphere by evaporation 2. the initial humidity of the air, and transpiration wind force and the heat 2. several expressions are used 3. and leaving it in the form of for describing precipitation 3. moisture exists in all three stages 4. phase changes of matter in the atmosphere 5. the amount of moisture in the air: 4. changes from one state to other absolute, specific and relative state are known as humidity 5. three principal factors favor evaporation:
2. Speak about absolute and relative humidity using material of the unit and data of table:
Table 1
Unit 2. Surface Runoff and Ground Water Exercises (A) 1. Learn new words: rate of precipitation – норма porous strata – пористый пласт осадков artesian – артезианский water body – водоем, водная масса well – колодец to exceed – превышать to define – определять to infiltrate – просачиваться to lie – лежать to reach – достигать soil moisture deficit – дефицит bottom – дно почвенной влаги portion – часть stream bad – речное русло to penetrate – проникать, stream channel – русло потока просачиваться loss – потеря
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