Tag: elements of weather and climate :rainfall and air pressure

Diurnal range of temperature is the difference between the maximum and minimum temperatures of the same days. Cloud cover, urban heat, land-use change, aerosols, water vapor, and greenhouse gases are caused due to changes in the diurnal range of temperature. As the distance from the sea increases diurnal range of temperature also increases. In dry tropical climates and on high mountain plateaus where solar radiation is maximum, diurnal range of temperature increases.

Stevenson screen is used for providing shelter for meteorological instruments, particularly wet and dry bulb thermometers. It is kept 1.25 meters above the ground by legs. It is done so to avoid strong temperature gradients at ground level. Stevenson screen has sides to encourage the free passage of air. For reflecting heat radiation, it is painted white. It was invented by the British engineer and meteorologist Sir Thomas Stevenson.

A device which is used to measure atmospheric pressure is known as Barometer. There are two types of barometers:- mercury and aneroid.

Atmospheric pressure is balanced by a column of mercury in case of a mercury barometer.

Aneroid barometer also called non-liquid barometer. Because of its smaller size and convenience, it is widely used in portable instruments and in aircraft altimeters.

Degree Celsius is the standard unit to measure temperature. It was developed by Swedish astronomer Andres Celsius in 1742. In degree Celsius, zero degrees represents the freezing point of water and 100 degrees represents water’s boiling point at the standard atmosphere. The standard atmosphere is the mean barometric pressure at the mean sea level.

Isohyets are imaginery lines joining places of equal rainfall. These lines are generally drawn on a weather map.

Celsius is the scale which measures temperature. It was developed by Swedish astronomer Andres Celsius in 1742. Freezing point of the water is the temperature at which water starts converting into ice. As per the Celsius scale, zero degrees is the freezing point of the water. The boiling point is the temperature at which water starts converting into vapors. As per Celsius scale, 100 degrees is the boiling point of the water.

The mean annual rainfall is calculated for data collected for a long period of time (30 - 35) years because rainfall is highly variable from day today. It adequately characterizes the rainfall regime in an area and its surroundings. World Meteorological Organization (WMO) recommends continuous 30-year records to calculate mean annual rainfall.

In modern thermometer, mercury is used as it is a reflective liquid. It is bright and opaque, so it’s easy to see movement of mercury inside the capillary tube and to read accurately. Even mercury does not wet the glass. So, if temperature is falling then you do not get inaccurate readings. It is also good conductor of heat. So, it reacts quickly to change in temperature.

• Thermogram is an instrument which is used for creating images based on heat radiation emitted from any object. It has many applications ranging from medical settings to weather stations. Hence A is the correct option.
• The thermometer measures the temperature of the human body.
• Isotherms are the lines joining various points on the map having the same temperature during a given period. Hence B and C are incorrect.

Mean daily temperature is the average temperature in each period of 24 hours. It is measured at 1.5 meters above ground level. Mean daily temperature can be determined by finding out the mean of maximum and minimum temperature of a day.