User talk:Gokulss

measurement of tempraure and rainfall

In everyday language weather means such qualities as wet or fine, warm or cold. For most people, such descriptive terms are adequate. However, many industries today require more quantitative assessments of the weather, with the use of standardised terms measured by suitably designed instruments. The science of the study of weather is called meteorology; the meteorologist measures temperature, rainfall, pressure, humidity, sunshine and cloudiness, and makes predictions and forecasts about what the weather will do in the future. Temperature The hotness or coldness of a substance is called its temperature and is measured with a thermometer. The ordinary thermometer consists of a hollow glass bulb attached to a narrow stem with a thread-like bore. The bulb is filled with liquid, usually mercury, but also alcohol when very low temperatures need to be measured, which expands when the temperature rises and contracts when the temperature falls. The amount of expansion and contraction is measured by a calibrated scale. Whilst thermometers are really measuring their own temperature, they are usually needed to measure the temperature of the surrounding air. To ensure that the temperature of the surrounding air is the same as the thermometer, it must be shaded from sunlight and be exposed to adequate ventilation. These conditions are provided by enclosing the thermometer within a wooden box with louvred sides, called a Stevenson screen. Why measure the weather? In everyday language weather means such qualities as wet or fine, warm or cold. For most people, such descriptive terms are adequate. However, many industries today require more quantitative assessments of the weather, with the use of standardised terms measured by suitably designed instruments. The science of the study of weather is called meteorology; the meteorologist measures temperature, rainfall, pressure, humidity, sunshine and cloudiness, and makes predictions and forecasts about what the weather will do in the future. Temperature The hotness or coldness of a substance is called its temperature and is measured with a thermometer. The ordinary thermometer consists of a hollow glass bulb attached to a narrow stem with a thread-like bore. The bulb is filled with liquid, usually mercury, but also alcohol when very low temperatures need to be measured, which expands when the temperature rises and contracts when the temperature falls. The amount of expansion and contraction is measured by a calibrated scale. Whilst thermometers are really measuring their own temperature, they are usually needed to measure the temperature of the surrounding air. To ensure that the temperature of the surrounding air is the same as the thermometer, it must be shaded from sunlight and be exposed to adequate ventilation. These conditions are provided by enclosing the thermometer within a wooden box with louvred sides, called a Stevenson screen. Why measure the weather? In everyday language weather means such qualities as wet or fine, warm or cold. For most people, such descriptive terms are adequate. However, many industries today require more quantitative assessments of the weather, with the use of standardised terms measured by suitably designed instruments. The science of the study of weather is called meteorology; the meteorologist measures temperature, rainfall, pressure, humidity, sunshine and cloudiness, and makes predictions and forecasts about what the weather will do in the future. Temperature The hotness or coldness of a substance is called its temperature and is measured with a thermometer. The ordinary thermometer consists of a hollow glass bulb attached to a narrow stem with a thread-like bore. The bulb is filled with liquid, usually mercury, but also alcohol when very low temperatures need to be measured, which expands when the temperature rises and contracts when the temperature falls. The amount of expansion and contraction is measured by a calibrated scale. Whilst thermometers are really measuring their own temperature, they are usually needed to measure the temperature of the surrounding air. To ensure that the temperature of the surrounding air is the same as the thermometer, it must be shaded from sunlight and be exposed to adequate ventilation. These conditions are provided by enclosing the thermometer within a wooden box with louvred sides, called a Stevenson screen. Why measure the weather? In everyday language weather means such qualities as wet or fine, warm or cold. For most people, such descriptive terms are adequate. However, many industries today require more quantitative assessments of the weather, with the use of standardised terms measured by suitably designed instruments. The science of the study of weather is called meteorology; the meteorologist measures temperature, rainfall, pressure, humidity, sunshine and cloudiness, and makes predictions and forecasts about what the weather will do in the future. Temperature The hotness or coldness of a substance is called its temperature and is measured with a thermometer. The ordinary thermometer consists of a hollow glass bulb attached to a narrow stem with a thread-like bore. The bulb is filled with liquid, usually mercury, but also alcohol when very low temperatures need to be measured, which expands when the temperature rises and contracts when the temperature falls. The amount of expansion and contraction is measured by a calibrated scale. Whilst thermometers are really measuring their own temperature, they are usually needed to measure the temperature of the surrounding air. To ensure that the temperature of the surrounding air is the same as the thermometer, it must be shaded from sunlight and be exposed to adequate ventilation. These conditions are provided by enclosing the thermometer within a wooden box with louvred sides, called a Stevenson screen. Relative humidity is measured by comparing the actual mass of vapour in the air to the mass of vapour in saturated air at the same temperature. For example, air at 10�C contains 9.4 g/m3 of water vapour when saturated. If air at this temperature contains only 4.7 g/m3 of water vapour, then the relative humidity is 50%. When unsaturated air is cooled, relative humidity increases. Eventually it reaches a temperature at which it is saturated. Further cooling leads to condensation of the excess water vapour. The temperature at which condensation sets in is called the dew point. The dew point, and other measures of humidity can be calculated from readings taken by a hygrometer. A hygrometer has two thermometers, one dry bulb or standard air temperature thermometer, and one wet bulb thermometer. The wet bulb thermometer is an ordinary thermometer which has the bulb covered with a muslin bag, kept moist via an absorbent wick dipped into water. Evaporation of water from the muslin lowers the temperature of the thermometer. The difference between wet and dry bulb temperatures is used to calculate the various measures of humidity Why measure the weather? In everyday language weather means such qualities as wet or fine, warm or cold. For most people, such descriptive terms are adequate. However, many industries today require more quantitative assessments of the weather, with the use of standardised terms measured by suitably designed instruments. The science of the study of weather is called meteorology; the meteorologist measures temperature, rainfall, pressure, humidity, sunshine and cloudiness, and makes predictions and forecasts about what the weather will do in the future. Temperature The hotness or coldness of a substance is called its temperature and is measured with a thermometer. The ordinary thermometer consists of a hollow glass bulb attached to a narrow stem with a thread-like bore. The bulb is filled with liquid, usually mercury, but also alcohol when very low temperatures need to be measured, which expands when the temperature rises and contracts when the temperature falls. The amount of expansion and contraction is measured by a calibrated scale. Whilst thermometers are really measuring their own temperature, they are usually needed to measure the temperature of the surrounding air. To ensure that the temperature of the surrounding air is the same as the thermometer, it must be shaded from sunlight and be exposed to adequate ventilation. These conditions are provided by enclosing the thermometer within a wooden box with louvred sides, called a Stevenson screen. The Stevenson Screen Why measure the weather? In everyday language weather means such qualities as wet or fine, warm or cold. For most people, such descriptive terms are adequate. However, many industries today require more quantitative assessments of the weather, with the use of standardised terms measured by suitably designed instruments. The science of the study of weather is called meteorology; the meteorologist measures temperature, rainfall, pressure, humidity, sunshine and cloudiness, and makes predictions and forecasts about what the weather will do in the future. Temperature The hotness or coldness of a substance is called its temperature and is measured with a thermometer. The ordinary thermometer consists of a hollow glass bulb attached to a narrow stem with a thread-like bore. The bulb is filled with liquid, usually mercury, but also alcohol when very low temperatures need to be measured, which expands when the temperature rises and contracts when the temperature falls. The amount of expansion and contraction is measured by a calibrated scale. Whilst thermometers are really measuring their own temperature, they are usually needed to measure the temperature of the surrounding air. To ensure that the temperature of the surrounding air is the same as the thermometer, it must be shaded from sunlight and be exposed to adequate ventilation. These conditions are provided by enclosing the thermometer within a wooden box with louvred sides, called a Stevenson screen. Figure 2.2. The maximum-minimum thermometer Why measure the weather? In everyday language weather means such qualities as wet or fine, warm or cold. For most people, such descriptive terms are adequate. However, many industries today require more quantitative assessments of the weather, with the use of standardised terms measured by suitably designed instruments. The science of the study of weather is called meteorology; the meteorologist measures temperature, rainfall, pressure, humidity, sunshine and cloudiness, and makes predictions and forecasts about what the weather will do in the future. Temperature The hotness or coldness of a substance is called its temperature and is measured with a thermometer. The ordinary thermometer consists of a hollow glass bulb attached to a narrow stem with a thread-like bore. The bulb is filled with liquid, usually mercury, but also alcohol when very low temperatures need to be measured, which expands when the temperature rises and contracts when the temperature falls. The amount of expansion and contraction is measured by a calibrated scale. Whilst thermometers are really measuring their own temperature, they are usually needed to measure the temperature of the surrounding air. To ensure that the temperature of the surrounding air is the same as the thermometer, it must be shaded from sunlight and be exposed to adequate ventilation. These conditions are provided by enclosing the thermometer within a wooden box with louvred sides, called a Stevenson screen. . The mercury barometer Why measure the weather? In everyday language weather means such qualities as wet or fine, warm or cold. For most people, such descriptive terms are adequate. However, many industries today require more quantitative assessments of the weather, with the use of standardised terms measured by suitably designed instruments. The science of the study of weather is called meteorology; the meteorologist measures temperature, rainfall, pressure, humidity, sunshine and cloudiness, and makes predictions and forecasts about what the weather will do in the future. Temperature The hotness or coldness of a substance is called its temperature and is measured with a thermometer. The ordinary thermometer consists of a hollow glass bulb attached to a narrow stem with a thread-like bore. The bulb is filled with liquid, usually mercury, but also alcohol when very low temperatures need to be measured, which expands when the temperature rises and contracts when the temperature falls. The amount of expansion and contraction is measured by a calibrated scale. Whilst thermometers are really measuring their own temperature, they are usually needed to measure the temperature of the surrounding air. To ensure that the temperature of the surrounding air is the same as the thermometer, it must be shaded from sunlight and be exposed to adequate ventilation. These conditions are provided by enclosing the thermometer within a wooden box with louvred sides, called a Stevenson screen. Variation of absolute humidity with temperature Relative humidity is measured by comparing the actual mass of vapour in the air to the mass of vapour in saturated air at the same temperature. For example, air at 10�C contains 9.4 g/m3 of water vapour when saturated. If air at this temperature contains only 4.7 g/m3 of water vapour, then the relative humidity is 50%. When unsaturated air is cooled, relative humidity increases. Eventually it reaches a temperature at which it is saturated. Further cooling leads to condensation of the excess water vapour. The temperature at which condensation sets in is called the dew point. The dew point, and other measures of humidity can be calculated from readings taken by a hygrometer. A hygrometer has two thermometers, one dry bulb or standard air temperature thermometer, and one wet bulb thermometer. The wet bulb thermometer is an ordinary thermometer which has the bulb covered with a muslin bag, kept moist via an absorbent wick dipped into water. Evaporation of water from the muslin lowers the temperature of the thermometer. The difference between wet and dry bulb temperatures is used to calculate the various measures of humidity. The hygrometer Wind The air is nearly always in motion, and this is felt as wind. Two factors are necessary to specify wind, its speed and direction. The direction of wind is expressed as the point of the compass from where the wind is blowing. Air moving from the north-east to the south-west is called a north-east wind. It may also be expressed in degrees from true north. A north-east wind would be 45�. A south-west wind would be 235�. The wind speed can be expressed in miles or kilometres per hour, meters per second, knots or as a force on the Beaufort scale. The Beaufort Scale Force	Description	Conditions	Wind speed (mph) 0	Calm	Smoke rises vertically	0 1	Light air	Smoke drifts	1-3 2	Light breeze	Leaves rustle; vane moved by wind	4-7 3	Gentle breeze	Leaves in constant motion; light flag extend	8-12 4	Moderate breeze	Raises duct and loose paper; small branches move	13-18 5	Fresh breeze	Small trees sway; crested wavelets on inland water	19-24 6	Strong breeze	Large branches in motion; whistling in telegraph	25-31 7	Moderate gale	Whole trees in motion	32-38 8	Fresh gale	Breaks twigs off trees; impedes walking	39-46 9	Strong gale	Slight structural damage to buildings	47-54 10	Whole gale	Large branches broken; some trees uprooted	55-63 11	Storm	Large trees uprooted	64-72 12	Hurricane	Widespread damage occurs	73+

Precipitation The amount of rain, sleet, snow or hail which falls in a specified time is expressed as the depth of water it would produce on a large, level impermeable surface. Usually it is expressed in millimetres although inches may sometimes be used. Rainfall is measured daily (24 hours) by means of a rainguage. Today's rainguages are simple to use with pre-calibrated scales on their sides. When measuring rainfall, certain precautions have to be taken against the effects of obstructions, wind, splashing and evaporation. Sunshine Many weather stations record the amount of bright sunshine during daylight hours. A typical measuring instrument is the Campbell-Stokes sunshine recorder. This consists of a glass ball which focuses the Sun's rays, burning a hole in an index card. As the Sun moves around the sky, so the burnt hole extends along the index, which is marked in hours to record the amount of direct sunshine