Chapter 6 Flashcards
Hydrologic cycle
The water is on continuous exchange among oceans, the atmosphere and the continents. This unending circulation of earth’s water supply has come to be called the Hydrologic cycle.
The hydrologic cycle is a gigantic system powered by energy from
the sun in which the atmosphere provides the vital link between ocean and continents.
As water evaporates from ocean, wind transports
moisture-laden air, often over great distances.
Complex processes of cloud formation result in
precipitation.
Evaporation process is
the evaporating of water vapor from the ocean (water surfaces).
Transpiration
a process of evaporating from soil, lakes and grass.
evapotranspiration
combination of transpiration and respiration
Water in the atmosphere is only
0.001% of the total air
The process of changing states requires
heat that can be absorbed or released
The process of changing states requires heat that can be absorbed or released. This heat is called
latent heat
The heat energy is often measured in
calories.
One calorie is the amount of heat required to
raise the temperature of one gram of water 1oC.
Heat is added to the sample in processes of
melting and evaporation
Heat is released from the sample in processes of
freezing and condensations
Vapor pressure
The water vapor has its pressure that added to the atmospheric pressure.
This pressure of the water vapor alone is called Vapor pressure
Saturation vapor pressure
When air is saturated the pressure exerted by the water vapor
The saturation vapor pressure rises with
increasing temperature
from solid to gas (calories)
580 cal
from solid to liquid (calories)
80 calories
Absolute humidity is
the mass of water vapor (in kg) in a given volume of air (in m3)
It is difficult to monitor the water vapor content of a
moving mass of air
Also the air volume is affected by
the changing temperature and pressure, so the use of this method is not a good indicator of humidity
Mixing ratio is
the mass of water vapor (in grams) in a unit mass of dry air (in kg)
The mixing ratio is not affected by
changes in pressure and temperature as absolute humidity
Relative humidity is
a ratio of the air’s actual water vapor content compared with amount of water vapor required for saturation at that temperature
The relative humidity changes by:
- adding or subtracting moisture,
- changing temperature.
Adding or subtracting moisture: when water vapor is added to a parcel
of air its relative humidity
increases until reaches saturation (the relative
humidity is 100%)
Adding or subtracting moisture: when water vapor is added to a parcel of air its relative humidity increases until reaches saturation (the relative humidity is 100%). When the relative humidity exceeds 100% the excess of water vapor
condenses to form liquid water
Changing temperature: when the water vapor content remains constant adecrease in temperature results in
an increase in relative humidity
Dew point is
the temperature to which a parcel of air would need to be cooled to reach saturation
Measuring humidity:
- Hygrometers
Hair hygrometer
The electric hygrometer:
Hygrometers:
A variety of instruments called hygrometers can be used to measure
relative humidity
variety of instruments called hygrometers can be used to measure
relative humidity. One of the simplest hygrometers is
the psychrometer,
A variety of instruments called hygrometers can be used to measure
relative humidity. One of the simplest hygrometers is the psychrometer,
which consists of
two identical thermometer mounted side by side. One thermometer is called the wet bulb, h as a thin muslin wick tied around the end
To use the psychrometer the cloth wick is
saturated with water and a
continuous current of air is passed over the wick, either by fanning air past
it. As a result water evaporates from the wick absorbing heat energy from
the thermometer to do so and the temperature of the wet bulb drops.
To use the psychrometer the cloth wick is saturated with water and a
continuous current of air is passed over the wick, either by fanning air past
it. As a result water evaporates from the wick absorbing heat energy from
the thermometer to do so and the temperature of the wet bulb drops. The
amount of cooling that takes place is directly proportional to
the dryness of the air
To use the psychrometer the cloth wick is saturated with water and a
continuous current of air is passed over the wick, either by fanning air past
it. As a result water evaporates from the wick absorbing heat energy from
the thermometer to do so and the temperature of the wet bulb drops. The
amount of cooling that takes place is directly proportional to the dryness of
the air. The drier the air, the
greater the cooling
The larger the differences
between the wet bulb and dry bulb temperatures the
lower the relative
humidity.
………………. the two thermometers will have identical readings
If the air is saturated, no evaporation will occur
Hair hygrometer
The principle of it is that
the hair changes length in proportion to changes in relative humidity
The hair hygrometer uses
bundle of hairs linked mechanically to an indicator that is calibrated between 0 and 100%. The hair hygrometer is less accurate than the psychrometer
The electric hygrometer
It contains an electrical conductor coated with a moisture -absorbing chemical. It works on the principle that electric current flow varies as the relative humidity varies.
