ZIMSEC O Level Geography Notes: Humidity
-a quantity representing the amount of water vapor in the atmosphere.
- It is measured using a hydrometer.
- The wet and dry bulb thermometer is also known as a psychrometer.
- Weather satellites can also measure the amount of humidity in the atmosphere.
- A hygrometer measures the humidity in the atmosphere using two thermometers: dry and wet bulb thermometers.
- The wet bulb thermometer is wrapped in thin muslin and dipped in a container of water to keep the muslin cloth wet.
- If the air is dry water evaporates from the muslin and cools such that the mercury contracts.
- The dry bulb is not affected hence the two show different readings.
- The wet bulb shows a low reading whilst the dry bulb shows a higher reading.
- Depression/Difference=the reading of the dry bulb less the reading of the wet bulb thermometer.
- The humidity is then found by reading humidity tables. For example if there is no difference between the two readings the humidity is 100%
- Electronic hygrometers are also used. These are easier to read.
- Relative humidity is measured in percentage terms.
Types of humidity
There are several ways to measure and express humidity:
- Absolute Humidity-the total mass of water vapor present in a given volume of air.
- Relative Humidity-the amount of water vapor in a given volume of air at a given temperature.
- Specific Humidity-the ration of the mass of water vapor to the mass of the parcel of air.
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