Absolute Humidity

In the simplest of terms, humidity is the amount of water vapor that is present in the air at any point in time. This can be expressed as absolute humidity, relative humidity or specific humidity. By measuring the amount of humidity present in the atmosphere, weather experts can predict the temperature of any day. Almost all weather reports generated anywhere in the world point out the percentage of humidity that is present in the atmosphere.

What is Absolute Humidity?
Absolute humidity is the exact amount of water that is present in a given volume of air. This gives a precise measurement of the amount of water present, and thus lets the experts calculate the percentage of humidity in the atmosphere. Absolute humidity calculators specify the amount of grams of water vapor present in each cubic meter of air.

A higher amount of absolute humidity present in the atmosphere means that people will feel hotter when they are outdoors. This happens because the greater amount of water vapor in the air results in lesser amounts of perspiration, or sweat, being evaporated from a persons body. As a result, the cooling effect of the evaporation of perspiration is negated. Absolute humidity levels also indicate the likelihood of dew, fog or precipitation that may occur.

Absolute Humidity vs Relative Humidity
Relative humidity is another way of measuring the amount of water vapor present in the air. Relative humidity is the amount of moisture present in the atmosphere, at any given point in time, compared with the amount of moisture that would be in the air if the moisture was completely saturated, at the same temperature. So while absolute humidity is an exact measure of the amount of moisture, relative humidity is the comparison of this amount with another amount.

What this means is that if the actual temperature at a point is 27 degrees Celsius, and the relative humidity is 75%, the temperature would feel like 29 degrees Celsius. It is this relative humidity that weather forecasters display on their reports. Absolute humidity is the measurement that they use in order to derive the percentage of relative humidity in the air. Forecasters thus create an absolute humidity table for one entire day, and arrive at an average figure in order to calculate the relative humidity in the form of a percentage.

Measuring Humidity
The task of measuring absolute humidity and relative humidity is carried out by many different devices. The most common of these devices is known as a hygrometer, or a psychrometer. Using remotely placed satellites is also a very popular way of calculating humidity levels on a global scale. These satellites are made use of for the purpose of all major weather forecasts.

Interestingly, some buildings also use a device known as a humidistat. These are used along with a thermostat (which carries out temperature control in the building), in order to regulate the amount of humidity that is present inside that specific building. The humidistat functions by affecting the amount of absolute humidity in the building.

In order to convert relative humidity to absolute humidity, the following formula is used.

H_abs = (H_sat)(RH/100)

Where
H_abs = Absolute humidity,
H_sat = Saturation humidity, and
RH = Relative humidity at the same temperature.

By using this method forecasters can calculate absolute humidity as well as relative humidity for any given day or time. The ideal relative humidity value for human beings is between 30% and 60%. If the humidity is more than this, perspiration of human beings will be ineffective and they will feel hotter. If it is less than this amount, humans will suffer from excessive thirst and dry skin.

Knowing absolute humidity is definitely helpful for forecasters, but for laymen it is the relative humidity value that is far more important. Relative humidity can only be derived with the help of absolute humidity.