Weather Instruments: Thermometer, Hygrometer, Barometer and Others

Weather Instruments

Meteorologists usually make use of a variety of weather instruments to measure elements of weather like temperature, atmospheric pressure, humidity, rainfall, and direction and speed of the wind.

Meteorologists usually make use of a variety of instruments to measure elements of weather like temperature, atmospheric pressure, humidity, rainfall, and direction and speed of the wind. So, let us have a look at some of the weather instruments.

Thermometer

The instrument used for measuring temperature is called the thermometer. A thermometer is a narrow glass tube filled with mercury that expands on heating and contracts on cooling. It has two measuring scales ° the Celsius (°C) and the Fahrenheit (°F) scale. However, for most scientific purposes the Celsius scale is the preferred scale. One scale can be converted into the other scale using the formula: °F=(°C°9/5)+32

To measure the accurate temperature, the thermometer is kept in a box, called the Stevenson Screen. It protects the thermometer from the sun's direct heat and allows free circulation of air.

Nowadays, an automatic thermometer, called thermography, is used at weather stations. It gives a continuous record of temperature over twenty-four hours.

Barometer

The instrument used for measuring atmospheric pressure is called a Barometer. It consists of a long glass tube, sealed at one end and open at the lower end and this tube is immersed into a container of mercury. The atmospheric pressure forces the mercury up into the tube, adjacent to a scale. Reading the scale gives us the record of atmospheric pressure. However, there are certain limitations like altitude, latitude, temperature, etc., which may hamper the readings.

To overcome these difficulties, we use an aneroid barometer. Inside this instrument, there is a small, flexible metal capsule called an aneroid cell.

For keeping a continuous record of pressure changes, an automatic barometer, called a barograph is used. It records the atmospheric pressure on graph paper.

Hygrometer

There are various devices used to measure humidity. One such device is a hygrometer. A simple hygrometer consists of wet and dry bulb thermometers which are fixed on a wooden frame. The hygrometer is placed in the Stevenson screen.

The dry-bulb thermometer measures the temperature of the dry air. In the wet-bulb thermometer, the thermometer bulb is wrapped in a muslin cloth and is kept wet by a wick which is dipped into a reservoir containing distilled water.

The evaporation of water has a cooling effect and the temperature indicated by the wet-bulb thermometer is less than the dry-bulb thermometer. Thus, the difference in the temperatures indicated by the two thermometers gives a measure of Relative Humidity. In case, both the thermometers show the same reading, relative humidity is 100 percent and the air is saturated.

Humidity is measured on a global scale using remotely placed satellites. These satellites can detect the concentration of water in the atmosphere, and send various water vapor images, which play an important role in monitoring climatic conditions like the formation of thunderstorms and in weather forecasts.

There are a few more weather instruments let us have a quick look at them.

Anemometer: Used to measure wind speed.
Beaufort Wind scale: Used to measure wind speed with simple observations.
Rain Gauge: Used to measure rainfall.
Wind Vane or Weather Cock: Used to measure the direction of the wind.

Read More: What is the difference between weather and climate? Science Class 7