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Meteorological Equipment Used to Measure Meteorology Elements

In the previous article we have learned about measurement of various Met elements with the help of conventional equipment. In this section we shall learn briefly about the field Met equipment which are also used to measure these Met elements. Digital Aneroid Barometer (DAB) The Digital Aneroid Barometer uses a silicon resonant pressure transducer for measurement of pressure and altitude. It should be protected from fall, direct sunlight, strong Electromagnetic radiation and heat sources. The instrument can also communicate, through a serial RS232 connector, with a compatible computer system or printer. Operation The instrument is switched on by the OFF/ON…

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Care and Maintenance of Meteorological Instruments

Special care should always be taken to keep the instruments clean. This not only enhances their performance but also lengthens their useful life and improves their appearance. Shifting of Met Instruments Any permanent shift / change of the observatory or any instrument particularly the barometer must be intimated to the C Met O, and JD Met (E) and also to be annotated in the current weather register. Instruments are to be shifted (particularly barometer) only under strict supervision of the met officers. Where Met Officers are not available, the controlling command is to detail a met officer to supervise the…

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Measurement of Wind

Since the wind is motion of air, it exerts a certain force. The speed of the wind can therefore, be measured in terms of the effect it produces on various objects in its path. It can either be measured by devising suitable instruments or it can be measured by using the effect it produces on natural objects in the surroundings and estimate the strength of the wind. The wind velocity is fully described by two quantities; its speed and direction. The speed may be indicated in any one of the following units: (a) Knots (or nautical miles per hour) (b)…

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Measurement of Visibility

The visibility is a decisive factor in aviation. Therefore, an observer has to be very careful while measuring or reporting visibility. It is measured in terms of maximum distance at which an object is visible and recognized, generally measured in units of meters/kilometres. During daytime visibility is estimated using land marks at known distance which are depicted on a polar diagram. At night the method adopted is to estimate the equivalent daytime visibility. This is done by installation of lights of standard candle power (100 CP) at different distances. If such lights are not available, the visibility is estimated by…

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Measurement of Precipitation

Precipitation whether it is rain or snow is expressed as the depth to which it would cover a horizontal projection of the earth’s surface, if there were no loss by evaporation, run-off or infiltration and if any part of the precipitation falling as snow or ice were melted. It is expressed in units of millimetres. Measurement is made of the total precipitation, whether of rain, hail or snow in the form of liquid water. That is any snow or hail is melted and added to any rain that has already fallen. Rain Gauge The amount of rainfall in a station…

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Measurement & Observation of Height of Cloud Base

Observations of clouds fall into four categories namely estimation of the amount of cloud, recognition of the forms of clouds present, measurement or estimation of the height of the cloud base and determination of the direction from which the clouds are moving. Observations in each of these categories are part of the information to be included in routine reports. The height of the cloud base at any land observing station is measured (estimated) from the ground in the vicinity of the observer. When the visibility is poor because of haze or mist, the cloud base is often ill defined and…

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Instruments Used for Measuring Relative Humidity

Humidity is the term used to express the moisture contents of the atmosphere. Humidity is expressed in many terms i.e. Relative Humidity, Absolute Humidity, Specific Humidity, Mixing Ratio etc. The most convenient method of finding the humidity of the air for meteorological purposes is by the use of Wet and Dry bulb thermometers, and it is expressed as Relative humidity in percentage. It is calculated from dry and wet bulb thermometers readings taken at same time by using Hygrometric Tables. Following instruments are used to measure the RH directly. (a) Psychrometer. (b) Hygrometer. Psychrometer Psychrometer is an instrument used to…

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Use of Altimeter

Altitude is the vertical distance of a level, a point or an object considered as a point, measured from  mean sea level. An altimeter is an instrument which measures pressure and causes a needle to move across a dial. The dial is calibrated in feet rather than pressure as we know that pressure decreases as altitude increases. In addition, altimeters have a means of adjusting the needle to take changes in the surface atmospheric pressure into account. In the section A of the the pressure at the airfield, which is at sea level, is 1010 hPa. The altimeter reads zero…

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Calculation of Atmospheric Pressure

Atmospheric pressure is the force per unit area exerted by the atmosphere on any surface in contact with it. If pressure is considered as the weight of a column of air of unit cross sectional area above a surface, the pressure at the upper surface will be lesser than that at the lower surface. Thus, atmospheric pressure will decrease with an increase in height. Reduction of Pressure to Standard Level Reduction to aerodrome level (QFE) The barometer reading with corrections applied gives the atmospheric pressure at the cistern level and to get the pressure at the aerodrome level, this value…

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Measurement of Atmospheric Pressure

The atmospheric pressure at any level is measured by the weight of the column of air standing on the unit area at that level and extending vertically to the upper limits of the atmosphere. Units of Pressure The standard unit of force is the NEWTON (N) and on an average atmospheric pressure at sea level is 1,00,000 Newtons per square metre or 1 Pascal. This pressure is sometimes known as a BAR. To  easure small variations in pressure it is convenient to divide the bar in to 1000 parts and so the standard meteorological unit of pressure is the MILLIBAR…