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Unit 2. Surface Runoff and Ground Water

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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


relative humidity – относительная


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

Absolute humidity Relative humidity
Absolute humidity is the total mass of water vapor present in a given volume of air. It does not take temperature into consideration. Absolute humidity in the atmosphere ranges from near zero to roughly 30 grams per cubic meter when the air is saturated at 30 °C. Absolute humidity is the mass of the water vapor ( ), divided by the volume of the air and water vapor mixture ( ), which can be expressed as: The absolute humidity changes as air temperature or pressure changes. This makes it unsuitable for chemical engineering calculations, e.g. for clothes dryers, where temperature can vary considerably. As a result, absolute humidity in chemical engineering may refer to mass of water vapor per unit mass of dry air, also known as the mass mixing ratio (see "specific humidity" below), which is better suited for heat and mass balance calculations. Mass of water per unit volume as in the equation above is also defined as volumetric humidity. Because of the potential confusion, British Standard BS 1339 (revised 2002) suggests avoiding the term "absolute humidity". Units should always be carefully checked. Many humidity charts are given in g/kg or kg/kg, but any mass units may be used. The field concerned with the study of physical and thermodynamic properties of gas–vapor mixtures is named psychrometrics.   The relative humidity of an air-water mixture is defined as the ratio of the partial pressure of water vapor (H2O) in the mixture to the saturated vapor pressure of water at a given temperature. Thus the relative humidity of air is a function of both water content and temperature. Relative humidity is normally expressed as a percentage and is calculated by using the following equation: Relative humidity is an important metric used in weather forecasts and reports, as it is an indicator of the likelihood of precipitation, dew, or fog. In hot summerweather, a rise in relative humidity increases the apparent temperature to humans (and other animals) by hindering the evaporation of perspiration from the skin. For example, according to the Heat Index, a relative humidity of 75% at 80.0 °F (26.7 °C) would feel like 83.6 °F ±1.3 °F (28.7 °C ±0.7 °C) at ~44% relative humidity.  



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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