Meteorological Instruments Presentation 2024

Meteorological Instruments & Methods of Observation for the Students of Meteorology and the Personnel as well. Its detailed informative presentation.

1. Meteorological Instruments & Methods of Observation National Center Of Meteorology (NCM) – Presidential Court Abu Dhabi – United Arab Emirates Instructor : Khalid Masood Syed – Senior Climate Analyst

2. Meteorological Observations are used for : 1. Real time preparation of weather analysis and forecasts. Study of Climate. Local weather (Wx.) – dependent operations, e.g., (a) Local aerodrome flying operations. (b) Construction work on land and sea. 4. Hydrology. 5. Agro-Meteorology. 6. Research in Meteorology and Climate. 7. Exchange of observations through GTS (Global Telecommunication System)

3. General weather elements for surface observation station : 1- Present Wx. 2- Past Wx. 3- Winds ( Direction + Speed ) 4- Visibility 5- Clouds ( Amount + Type + Height ) 6- Temperatures 7- Relative Humidity, Dew point, Vapour pressure etc. 8- Pressure 9- Precipitation 10- Solar Radiation 11- Net Radiation 12- Evaporation 13- Sunshine duration 14- Soil Temperatures

4. Units : Pressure = hPa, (1 hPa = 1 mb) Temperature = °C Wind speed = m/s or knots Wind Direction = Degree ( True North clockwise ) Relative Humidity = Percent ( % ) Rain fall = mm Evaporation = mm Visibility = m and km Sunshine duration = hours ( h ) Clouds height = meter or feet Amount of clouds = oktas.

5. TEMPERATURE: Definition : Temperature is the condition which determines the direction of the net flow of heat between two bodies. OR Air Temperature is a measure of the average speed at which air molecules are moving , high speed correspond to higher temperature

6. TEMPERATURE: Units : °F = Fahrenheit Invented by Germen Physicist “ Gabriel Fahrenheit ” 32°F = Freezing point 212°F = Boiling point °C = Centigrade or Celsius This scale devised by Swedish astronomer “Anders Celsius” 0°C = Freezing point 100°C = Boiling point.

7. TEMPERATURE MEASURING INSTRUMENTS : Glass Thermometer : Generally, to measure the air temperature, including maximum, minimum, dry bulb, wet bulb temperature, liquid–in–glass thermometers are still commonly used.

8. Types of Glass Thermometers : Ordinary Thermometers : This is the most accurate instrument of all meteorological thermometers. Usually it is mercury–in–glass type. The ordinary thermometers are used in a thermometers screen (or Stevenson Screen) to avoid Radiation errors. Should keeps in vertical position with the bulb at the lower end. Ord Max Min

9. Types of Glass Thermometers : 2. Maximum Thermometers : This type of thermometers is mercury-in-glass. This can be reset intentionally by the observer by holding it firmly, bulb end downward and swinging his arm until the mercury column is reunited. Maximum thermometer should be mounted at an angle of about (2°) two degrees from the horizontal with the bulb at the lower end. Ord Max Min

10. Types of Glass Thermometers : 3. Minimum Thermometers : In minimum thermometer various liquid can be used i.e., ethyl alcohol, pentane and toluol. It is important that the liquid should be pure, otherwise tendency will decrease if liquid impure. In case if ethyl alcohol, should be completely free of acetone. Minimum thermometers should be supported in a similar manner to maximum thermometers, in a near-horizontal position. Ord Max Min

11. Types of Glass Thermometers : 4. Soil Thermometers : The standard depths for soil temperature measurement are 5,10,20,30,50 & 100 cm below the surface of the ground. The thermometers are mercury-in-glass with their stem bent at right angle (90°), or any other suitable angle. The thermometer bulb in sink into the ground to the required depth. The thermometers tube assemblies should be suspended or slipped in a thin-walled metal or plastic tube sunk into the ground to the required depth. Installation of Soil Thermometers

12. Types of Glass Thermometers : 5. Measuring Grass Minimum Temperatures : Thermometers to measure grass minimum temperature will be used the same as Minimum thermometers. The grass minimum temperature is the lowest temperature reached overnight by a thermometers freely exposed to the sky just above short grass. The thermometers should be mounted on suitable support. It should be inclined at an angle of about 2° from the horizontal with the bulb lower than the stem. It should be 5 cm above the ground and in contact with the tips of the grass. Normally, the thermometer is exposed at the last observation hour before sunset and the reading is taken next morning. The instrument is kept with in screen or indoor during the day. However, at stations where an observer is not available near at sunset time, it may be necessary to leave the thermometer exposed throughout the day. Grass Minimum Thermometer

13. Types of Glass Thermometers : CORRECTIONS : At the time of initially issued thermometers, a dated calibration certificate giving the corrections which should be applied to the readings to achieve the required accuracy. In general, if the errors at selected points in the range of a thermometers are all within + 0.05 °C, no corrections will be necessary, and the thermometer can be used directly as ordinary thermometer, maximum, minimum, soil or grass minimum thermometers. If the errors are greater than 0.05 °C, then a table of corrections should be available with the observer at the place of reading.

14. Types of Thermometers : 6. Mechanical Thermographs : This type still commonly used, it is relatively inexpensive, reliable and portable. Such thermographs incorporate a rotating chart mechanism common to the classical recording instruments. The movement of recording pen is controlled by the change in curvature of bimetallic strip, which is fixed to an arm attached to the frame. Mechanical Thermograph

15. Types of Thermometers : 7. Digital Temperature Probe: This high-quality probe is using a highly stable and accurate platinum sensing element. Waterproof construction and used materials ensure long-term reliability in extreme environmental conditions. This Type of probe used in AWS too. Features : Waterproof construction. Long-term reliability in extreme environmental conditions. Low power consumption. Digital Temperature Probe Digital Temperature Panel Meter

16. Types of Thermometers : Exposure: Radiation shield serves as a shading for temperature sensing units against solar radiation and rain. The shield is composed of nine gradually overlapping circular diaphragms, which create louvers around the sensing unit. This enables free flow of air between the diaphragms. The body of diaphragms and the base is made from plastic, connecting material is made from stainless material or aluminium alloys. To ensure better screening of luminous or thermal energy, the inside surface of diaphragms are painted in matt black colour, and it is not smooth, but it is indented as well. The shield design enables - with help of a bolt - its quick installation on the mast arm, and with help of the cable bushing with the thread - an easy fastening on the sensing unit inside the shield. Radiation Shield

17. ATMOSPHERIC PRESSURE : Definition : The atmospheric pressure on a given surface in the force per unit area exerted by virtue of the weight of the atmosphere above. The pressure is thus equal to the weight of vertical column of air above a unit area surface, taken horizontally and extending to the outer limit of the atmosphere. Units : The basic unit for atmospheric pressure measurements is the Pascal (Pa) (or Newton per square meter). In practice we add hecto to this unit when reporting pressure for meteorological purposes, as a hecto Pascal (hPa), hPa is equal 100 Pa .One hPa equals one millibar (mb) and 100 Newton per square meter.

18. PRESSURE MEASURING INSTRUMENTS : The Atmospheric Pressure is generally measured with Mercury Barometers, Electronic Barometers and Aneroid Barometers. General Exposure requirements : It is important that the location of barometer at observation station be selected with great care .The main requirements of the place of exposure are uniform temperature, good light, away from draughts (wind current coming into a room), a solid and vertical mounting, and protection against rough handling should be always shielded from direct sunshine and should not be placed near any heating apparatus or when there is a draught.

19. PRESSURE MEASURING INSTRUMENTS : Mercury Barometers : There are several types of Mercury Barometers in use of Meteorological Stations. The most common Barometers are : I - Fixed Cistern. II - Fortin type.

20. PRESSURE MEASURING INSTRUMENTS : Reading of Mercury Barometers : When seeing with a mercury barometer, the attached thermometer should be read first. This reading should be taken as quickly as possible, as the temperature of the thermometer may rise owing to the presence of the observer. The vernier should be set to meniscus and the reading taken. The vernier is correctly adjusted when its horizontal lower edge appears to be touching the highest part of the meniscus. The eye should be in such a position that both front and back lower edges of the vernier are in the line of vision. The barometer is manufactured to read correctly when the air temperature surrounds the barometer is 0°C and installed at MSL (Mean Sea Level) and Latitude of 45°. Accordingly, a thermometer is attached to the barometer and a correction should be made to temperature, elevation and latitude (gravity). A correction table is attached for the temperature and gravity (latitude & elevation).

21. PRESSURE MEASURING INSTRUMENTS : Exposure of Mercury Barometers : It is always preferable to hang the mercury barometers on an inside wall. For very accurate work, the best position would be in an unheated basement room with no windows and with a small electric fan to prevent any stratification of temperature. Care should be taken to guard against heating of the barometer by artificial light during a barometer reading. The barometer should be mounted in a place where it is not subject to vibration, preferably on a solid wall. The instrument must be mounted with the mercury column vertically. To protect the barometer from rough handling, dust and air currents, it is recommended that the instrument be placed in a box.

22. PRESSURE MEASURING INSTRUMENTS : 2. Electronic Barometers : Electronic barometers are used in Automatic Weather Stations (AWS) and are frequently used to display digital outputs or digitalized analogue outputs. Reading of Electronic Barometers : This type of barometers measures the atmospheric pressure of the surrounding space or any space which is connected to it via a tube. In general, the barometer should be set to read the pressure at the level of the instrument. On board a ship or at low level land station, the instrument may be set to indicate the pressure at mean sea level provided the elevation of station.

23. PRESSURE MEASURING INSTRUMENTS : Exposure of Electronic Barometers : Electronic Barometers require a clean, dry atmosphere which is free corrosive (harmful) substances. The barometer should also be kept at a constant temperature. The instrument should be mounted in such a manner as to avoid mechanical shock and vibration. It should also be mounted away from electro-magnetic sources or where this is not possible, the wires and casing should be shielded. Barometers with digital read-out should be mounted so that there is good several lighting but should not face a window or other strong light source.

24. PRESSURE MEASURING INSTRUMENTS : 3. Aneroid Barometers : The greatest advantages of conventional aneroid barometers over mercury barometers are their compactness and portability, which make them particularly convenient for use at sea or in the field. The main components are a closed metal chamber, which prevents collapsing due to the external atmospheric pressure. The aneroid chamber may be made of steel or beryllium copper materials which have elastic properties. Aneroid Barometer

25. PRESSURE MEASURING INSTRUMENTS : Accuracy Requirement : The scale errors at any point should not exceed + 0.3 hPa and should remain within this tolerance over period of at least a year, when in normal use. Reading of Aneroid Barometers : An Aneroid Barometer should always be read in the same orientation (vertical or horizontal). It should be tapped lightly before it is read. As far as possible, it should be read to the nearest 0.1 hPa. Exposure of Aneroid Barometers : The exposure requirements for an Aneroid Barometer are like those for mercury barometers. Aneroid Barometer

26. PRESSURE MEASURING INSTRUMENTS : 4. Barographs : The principle of the Barograph is like that of the Aneroid Barometer, except that a recording pen is used instead of a pointer. The advantage of the Barograph is that it shows the pressure tendency (rising, falling etc.). This is important for synoptic weather observation. Requirements : (a) Should graduate in hPa. (b) Relate to 0.1 hPa. (c) Should have a scale factor of 10 hPa to 1.5 cm on the chart. (d) Scale error should not exceed 1.5 hPa at any point. Barograph

27. PRESSURE MEASURING INSTRUMENTS : Reading of Barographs : The barograph should be read without touching the instrument. The time mark and any inspection of the instrument involving lifting the cover, etc., should always be made after the reading is completed. Accuracy of Reading : The Chart should be read to the nearest 0.1hPa. Barograph

28. PRESSURE MEASURING INSTRUMENTS : Exposure of Barographs : The Barograph should be installed where it is protected from sudden changes in temperature, from vibration and from dust. It should not be exposed to direct sunshine. The barograph should also be placed at a location where it is unlikely to be tempered with by un-authorized persons. Mounting on a sponge rubber cushion in a convenient means of reducing the effects of vibration. The site selected should be dry and clean. It should also be relatively free of substances in the air which would cause corrosion. It is important to mount the instrument so that its face will be at a convenient height for reading of eye level. If a barograph has to be sent by air or if it is transported at a high altitude, the pen arm should be disconnected. Barograph

29. RELATIVE HUMIDITY : Definition : The ratio in percent (%) of the observed vapour pressure to the saturation vapour pressure with respect to water at the same air temperature and pressure. Unit : Relative Humidity = % (percent).

30. RELATIVE HUMIDITY : Meteorological requirements : Humidity measurement at the Earth’s surface is required for meteorological analysis and forecasting, for climate studies, and for many special applications in hydrology, agriculture, aeronautical services and environmental studies, in general. Method of Measurements : The instrument for measuring humidity is known as a Hygrometer or Hygrograph. There are various types of Hygrometers to measure the humidity. General Exposures : The general requirements for the exposure of humidity sensors are like those for temperature sensors.

31. RELATIVE HUMIDITY MEASURING INSTRUMENTS : Indirect Method : 1. The Assmann aspirated psychrometers : Two mercury-in-glass thermometers, mounted vertically side by side in chromium or nickel-plated polished metal frame, are connected by ducts to an aspiration. The aspiration may be driven by a spring or an electric motor. One thermometer bulb has a well-fitted muslin wick which, before use, is moistened with distilled water. Each thermometer is located inside a pair of coaxial metal tubes, highly polished inside and out. The tubes are thermally insulated from each other.

32. RELATIVE HUMIDITY MEASURING INSTRUMENTS : Indirect Method : 2. Psychrometer by August : To measure the Temperature and the extreme Temperatures and to determine relative humidity; electrically driven aspirator with battery (rechargeable by charger unit) to ventilate both thermometers; consisting of: Stand, thermometer support, aspirator, psychrometer thermometers, maximum- and minimum-thermometer. By this method from the dry and wet bulb readings we calculate the actual vapour pressure, dew point temperature and relative humidity.

33. RELATIVE HUMIDITY MEASURING INSTRUMENTS : Indirect Method : 2. Psychrometer by August : Observation Procedure : The wick should be free of grease, moistened with distilled water. Dirty or crusty wicks should be replaced. The mercury columns of the thermometer should be inspected for breaks, which should be closed, or thermometer replaced. Important point for the observations are : Moisture the wet bulb. Wind the clockwork motor (or start the electric motor). Wait two or three minutes until the wet bulb reading has become steady. Read the dry bulb. Read the wet bulb.

34. RELATIVE HUMIDITY MEASURING INSTRUMENTS : Direct Method : 3. (A) - The Hair Hygrometers : The hair Hygrograph or Hygrometer is a satisfactory instrument for use in a situation or during periods where extreme and very low humidities are seldom or never found. The rate of response of the hair Hygrometer is very dependent on-air temperature and amount of water vapour in the atmosphere. Hair Hygrometer

35. RELATIVE HUMIDITY MEASURING INSTRUMENTS : Direct Method : 3. (B) - The Hair Hygrographs : The most used Hair Hygrometer is the Hygrograph. This employs a bundle of hairs held under slight tension by a small spring and connected to a pen arm is such a way as to magnify a charge in the length of the bundle. A pen at the end of the pen arm is in contact with a paper chart fitted around a metal cylinder and registers the angular displacement of the arm. The principle is that the hair contracts or expands according to the amount of moisture in the air. Hair Hygrograph

36. RELATIVE HUMIDITY MEASURING INSTRUMENTS : Direct Method : 3. Hair Hygrometers & Hygrographs : Exposure and Siting : The Hygrographs or Hygrometers should be exposed in a thermometer screen, Ammonia is very destructive to natural hair, and industrial plants using ammonia should be avoided.

37. RELATIVE HUMIDITY MEASURING INSTRUMENTS : Direct Method : 4. Digital Relative Humidity Sensor: This prob offers the relative humidity element in an advanced digital sensor that is ideal for weather networks. The electronics within the sensor provide accurate measurements, and the sensor is easy to use. This digital output allows a simple connection and measurement by many data logging systems. Another benefit is that this digital output avoids the extra errors associated with measuring analog sensors. Digital Relative Humidity Sensor Digital Temp. & R. H Display

38. RELATIVE HUMIDITY MEASURING INSTRUMENTS : Direct Method : 4. Digital Relative Humidity Sensor: Exposure and Siting : it is standard practice to install the sensor within a housing, known as a shield. The shield prevents solar radiation from heating the sensor and creating measurement errors. The radiation shield also provides a degree of protection from adverse weather, such as hail or driving rain. The most common type of shield is a relatively small, naturally ventilated screen that is low maintenance and requires no power. Radiation shield

39. SURFACE WINDS : Measurements and Observations : Surface wind is usually measured by a Wind Vane and Cup or Propeller aerometer . When the instrumentation is temporarily out of operation or when it is not provided, the direction and force of the wind may be estimated as table provides wind speed equivalents in common use for estimation.

40. SURFACE WINDS : Estimation of Winds : In the absence of equipment for measuring the wind, the observation must be made by estimation (Beaufort scale). Errors in observations made in this way be large, but provided the observations are used with caution the method may be justified as providing data that would otherwise not be available at all.

41. SURFACE WINDS : Wind Direction : Direction may be estimated from a Vane, mounted on a pole which has pointers indicating the principal points of the compass. In case of absence of instruments, or when the instrumental equipment is in unserviceable, the direction should be estimated by observing the drift of smoke from an elevated chimney , the movement of leaves , the flag direction , etc. Wind Speed : Cup Anemometers are commonly used to determine the Wind Speed and consist of two sub-assemblies, the rotor and the signal generator.

42. SURFACE WINDS : Beaufort scale number and description Wind speed equivalent at standard height of 10 meters above open flat ground Specifications for estimating speed over land knots m/s 0 Calm < 1 0-0.2 Calm: smoke rises vertically. 1 Light air 1-3 0.3-1.5 Direction of wind shown by smoke-drift but not by wind vanes. 2 Light breeze 4-6 1.6-3.3 Wind felt on face; leaves rustle; ordinary vanes moved by wind. 3 Gentle breeze 7-10 3.4-5.4 Leaves and small twigs in constant motion; wind extends light flag. 4 Moderate breeze 11-16 5.5-7.9 Raises dust and loose paper; small branches are moved. 5 Fresh breeze 17-21 8.0-10.7 Small trees in leaf begin to sway, crested wavelets form on inland waters. 6 Strong breeze 22-27 10.8-13.8 Large branches in motion; whistling heard in telegraph wires; umbrellas used with difficulty. 7 Near gale 28-33 13.9-17.1 Whole trees in motion; inconvenience felt when walking against the wind. 8 Gale 34-40 17.2-20.7 Breaks twigs off trees; generally, impedes progress. 9 Strong gale 41-47 20.8-24.4 Slight structural damage occurs (chimneypots & slates removed). 10 Storm 48-55 24.5-28.4 Seldom experienced inland; trees uprooted; considerable structural damage occurs. 11 Violent storms 56-63 28.5-32.6 Very rarely experienced; accompanied by widespread damage. 12 Hurricane 64 & over 32.7&over - Knot = 1.8 km/hour Knot = nautical mile/hour Wind Speed equivalents ( Beaufort Scale )

43. SURFACE WINDS : Exposure of Winds Instruments : The standard exposure of Wind instruments over level, open terrain 10 meters above the ground. Open terrain is defined as an area where the distance between the Anemometer and any obstruction is at least 10 times height of the obstruction.

44. PRECIPITATION : Definition : Precipitation is defined as liquid or solid droplets falling from clouds. It includes rain, hail, and snow.

45. PRECIPITATION : Unit : The unit of Precipitation is millimeter (mm) for liquid precipitation. Daily measurements of precipitation should be made at fixed times. Less than 0.2 mm is generally referred to as a trace. Snow fall measurements are made in units of centimeters and tenths. Less than 0.2 cm is generally called a trace. The depth in mm of the water collected on any surface from precipitation. Accordingly, if we have an area of 1m 2 and the amount of precipitation is 1mm (depth 1mm), then the volume amount of collected water by this surface of = 1m 2 x 1mm = 100 x 100 x 1 cm 3 /10 = 1000 cm 3 = 1 liter

46. PRECIPITATION MEASURING INSTRUMENTS: Manual Rain Gauges : Precipitation Gauges are often known as Rain Gauges, the most common instruments used to measure Precipitation. Rain Gauge in the form of a right cylinder, and with a funnel to measure rain. The commonly used precipitation gauges consist of a collector placed above a funnel leading into a container where the accumulated water and melted snow are stored between observation times. The container should have a narrow entrance and be sufficiently protected from radiation to minimize the loss of water by evaporation. Rain Gauge

47. PRECIPITATION MEASURING INSTRUMENTS: Automatic recording precipitation Gauges : Automatic recording of precipitation has the advantage that it can provide better time resolution that manual measurements, and it is possible to reduce the evaporation. It provides the intensity of rain which is an important parameter for Hydrological and Agricultural applications. Three types of automatic recorder are generally use : 1. The weighing-recording type. 2. Tipping - bucket type. 3. Float type

48. PRECIPITATION MEASURING INSTRUMENTS : 1. The Weighing-recording type Gauge : This type of recorder is only satisfactory for measuring all kinds of Precipitations. All precipitations, both liquid and solid forms, is recorded as it falls. The capacity ranges from 150-750 mm. The Gauges must be maintained to minimize evaporation losses, which can be accomplished by adding sufficient oil to the Container to form a film over the water surface.

49. PRECIPITATION MEASURING INSTRUMENTS : 2. Tipping - Bucket type Gauge. The Tipping-bucket rain gauge is suitable for measuring the rate of rainfall as well as the accumulated totals, at rates up to 200 mm/ hr or more.

50. PRECIPITATION MEASURING INSTRUMENTS : 3. Float Gauge : In this instrument, the rain passes into a float chamber containing a light float, as the level of the water within the chamber rises, the vertical movement of the float is transmitted by a mechanism, to the movement of a pen on a chart. Recording on clockwork driven drum; nominal recording period 7 days; recording height 80 mm, recording chart width for 10 mm rain divided into 1/10 mm.

51. RADIATION : Solar Radiation is the energy emitted by the sun. Radiation measurements are used for the following purposes. The study of the transformation of energy within the earth – atmospheric system. The analysis of the properties and distribution of the atmosphere regarding its constituents, such as aerosols, water vapour, ozone, etc. The study of the distribution and the variation of incoming, outgoing and Net radiation. The satisfaction of the needs of biological, medical, agricultural, architectural and industrial activities with respect to Radiation. The verification of satellite Radiation measurements and algorithms. Pyranometer

52. RADIATION MEASURING INSTRUMENTS : Pyranometer Instrument Measuring Parameters Main use Absolute pyrheliometer Direct solar radiation Primary standard Pyrheliometer Direct solar radiation a) Secondary standard for calibrations b) Network Spectral Pyrheliometer Direct solar radiation in broad spectral bands (e.g. with OG 530, RG 630, etc. filters) Network Sunphotometer Direct solar radiation in narrow spectral bands (e.g. at 500 + 205 nm, 368 + 2.5 nm) a) Standard b) Network Pyranometer a) Global radiation b) Sky radiation c) Reflected solar radiation a) Working standard b) Network Spectral Pyranometer Global radiation in broadband spectral ranges (e.g. with OG 530, RG 630, etc. filters) Network Net Pyranometer Net global radiation a) Working standard b) Network Pyrgeometer a) Upward long-wave radiation (downward-looking) b) Downward long-wave radiation (upward-looking) Network Pyrradiometer Total radiation Working standard Net Pyrradiometer Net total radiation Network

53. SUNSHINE DURATION : Sunshine Recorder : The term Sunshine is associated with the brightness of the Solar disk exceeding the background of diffuse sky light or better observable by the human eyes with the appearance of shadows behind illuminated objects. According to Commission recommendation 10 (CIMO-VIII), Sunshine duration for a given period is defined as the sum of that subperiod for which the direct solar irradiance exceeds 120 W m -2 . Unit : The units used are seconds or hours. For Climatological purposes used are hours per day or daily sunshine hours. Campbell-Stokes Sunshine Recorder

54. SUNSHINE DURATION– INSTRUMENT AND METHOD OF MEASUREMENTS : Campbell-Stokes Sunshine Recorder (burn method): It’s used for recording the Sunshine duration; black lacquered unit with clear glass dome; dome bracket can be aligned by means of a box level.   The C ampbell-Stokes Sunshine Recorder consists essentially of a glass sphere mounted concentrically in a section of a spherical bowl. The glass sphere has a diameter of approx. 96 mm. The diameter of which is such that the sun’s rays are focused sharply on a card held in grooves in the bowl. The sun burns intensive traces on the card according to its apparent course and owing to the intensity of the radiation. Campbell-Stokes Sunshine Recorder

55. SUNSHINE DURATION– INSTRUMENT AND METHOD OF MEASUREMENTS : Sunshine Cards : Sunshine Cards to be used during the different seasons, as per following duration. Campbell-Stokes Sunshine Recorder Upper Groove: 16 Oct. – 28 Feb Center Groove: 1 Mar. – 15 Apr. & 1 Sep. – 15 Oct. Lower Groove: 15 Apr. – 31Aug.

56. EVAPORATION : Definition : Quantity of water evaporated from an open water surface or from the ground called Evaporation. Unit : The unit of time is normally a day, and the depth may be measured in either millimeters (mm) or centimeters (cm). The usually measuring accuracy is 0.1 to 0.01 mm.

57. EVAPORATION MEASURING INSTRUMENT : There are different types of instruments used to measure Evaporation. Among the various types of instruments in use, the Class A pan. The Class A Pan : The pan designed cylindrically, 25.4 cm deep and 120.7 cm in diameter. The bottom of pan is supported 3 to 5 cm above the ground level on an open-frame wooden platform; air can circulate under the pan. The pan is constructed of galvanized iron 0.8 mm thick, copper or Monel metal, and is normally left unpainted. The pan is filled to 5 cm below the rim; this is known as the reference level. The water level is measured by hook gauge or a fixed-point gauge. The pan is refilled whenever the water level drops by more than 2.5 cm from the reference level. The Class A Pan

58. EVAPORATION MEASURING INSTRUMENT : Exposure of Evaporation Pan : The station should be level and free from obstruction, such as trees, buildings, shrubs, or instrument shelters. The plot should be fenced to protect the instruments and to prevent animals from interfering with the water level. The Fence should not affect the wind structure over the pan. Under no circumstance should the instrument be placed on a concrete slab or asphalt, or on a layer of crushed rock. The Class A Pan

59. AUTOMATIC WEATHER STATION (AWS) : AUTOMATIC WEATHER STATION (AWS) AWS – SENSORS/DEVICES COMMONLY USED

60. AUTOMATIC WEATHER STATION (AWS) : DATA LOGGER-MODEM-BATTERY-PRESSURE BOX BATTERY BAROMETER