1. Meteorology Science of waters of atmosphere Atmosphere: Atmosphere is the gaseous envelope around the earth Weather and Climate Weather- “the state of the atmosphere with respect to heat or cold, wetness or dryness, calm or storm, clearness or cloudiness”.  Climate – “the average course or condition of the weather at a place usually over a period of years as exhibited by temperature, wind velocity, and precipitation”.

2. Meteorology Weather and Climate Weather refers, generally, to day-to-day temperature and precipitation activity, whereas climate is the term for the average atmospheric conditions over longer periods of time. TROPOSPHERE: It is the zone of atmosphere adjacent to earth. It is approximately upto 7 miles above sea level. In this zone almost 100 % of moisture contents are present and there is comparatively high temperature gradient in this region

3. Subject Introduction Atmosphere and Troposphere: (1)Scientific Study of Hydrological Cycle. (2) Branch of Science which deals with the occurrence, distribution, movement and properties of waters on, under & over the earth’s surface with their relations to the environment. Troposhere/Hydrosphere (approx. 15 km) Lithospere (approx. 1 km) Atmosphere (approx. 50 km)

4. Global Water Volumes Atmosphere: 12900 Km 3 (0.001 % of T.W., 0.5% of volume of atmosphere) Troposphere: 12900 Km 3 (100 % of A.W.) Lithosphere: 23.4 x 10 6 Km 3 (0.017 % of T.W.) Rivers: 2120 Km 3 (0.0002 % of T.W.) Oceans: 1338 x 10 6 Km 3 (96.54 % of T.W.) Total Global Water: 1385.98 x 10 6 Km 3 (0.02% of Planet Mass)

5. Watershed & Catchment Watershed: Total area of land draining at a particular section of the stream / river due to surface runoff only. (depends on topography only) Catchment: Total area of land draining at a particular section of the stream / river due to surface runoff and sub-surface runoff. (depends on topography and ground stratifications, both)

6. VAPOUR PRESSURE The pressure exerted by the water vapours present in the atmosphere. It is usually denoted by “e” and expressed in millibars. Millibar SATURATION VAPOUR PRESSURE: The pressure exerted by water vapours, when the air is fully saturated with water vapours is known as the saturation vapour pressure. ISOBARS: These are the lines joining points of same atmospheric pressure.

7. RELATIVE HUMIDITY AND DEW POINT RELATIVE HUMIDITY AND DEW POINT Dew Point: The temperature at which air becomes saturated at a given atmospheric pressure. Relative humidity: The ratio of actual vapour pressure at certain temperature and the saturation vapour pressure.

8. RELATIVE HUMIDITY AND DEW POINT RELATIVE HUMIDITY AND DEW POINT The relation between temperature and saturation vapour pressure is shown in Figure 2 Suppose that a parcel of air has a temperature “T” and vapour pressure “e” indicated by point D in the Fig. If more vapour were added at constant temperature the point “D” would move vertically upward and the air would be saturated and the corresponding saturation vapour pressure would be “e s ”.

9. RELATIVE HUMIDITY AND DEW POINT RELATIVE HUMIDITY AND DEW POINT The difference e s - e = Saturation deficit The relation (e/ e s ) x 100 = Relative Hhumidity. --------------2.1

10. RELATIVE HUMIDITY- MEASUREMENT RELATIVE HUMIDITY- MEASUREMENT The instruments used for measurements of relative humidity are: The instruments used for measurements of relative humidity are: (i) Psychrometer(ii)Hair hygrometer (i) Psychrometer(ii)Hair hygrometer (iii) Hygrograph(iv)Thermo-hygrograph Psychrometer consists of two thermometers. (i)Dry bulb thermometer (i)Dry bulb thermometer (ii) Wet bulb thermometer.

11. RELATIVE HUMIDITY- MEASUREMENT RELATIVE HUMIDITY- MEASUREMENT Psychrometer Psychrometer consists of two thermometers. (i)Dry bulb thermometer (i)Dry bulb thermometer (ii) Wet bulb thermometer.

12. RELATIVE HUMIDITY- MEASUREMENT RELATIVE HUMIDITY- MEASUREMENT Psychrometer The mercury bulb of wet bulb thermometer is covered by a jacket of clean muslin cloth saturated with water. This is done by putting a beaker with distilled water underneath so that the bulb is not submerged in water but only the cloth. Then water rises due to capillary action. The thermometers are ventilated by whirling or by use of a fan. As a result of evaporation cooling take place. Readings are taken on both the thermometers simultaneously. The dry bulb reading is denoted as Td and wet bulb reading as Tw. The difference of these two temperatures is called the wet bulb depression T d -T w = wet bulb depression -------------------2.2

13. MEASUREMENT OF TEMPERATURE MEASUREMENT OF TEMPERATURE The temperature is measured with the help of thermometers. There are two types of thermometers. The temperature is measured with the help of thermometers. There are two types of thermometers. (i)Maximum thermometer (Mercury Type thermometer) (i)Maximum thermometer (Mercury Type thermometer) (ii) Minimum Thermometer (Alcoholic type thermometer) MEAN DAILY TEMPERATURE: It is the average of maximum and minimum temperatures during past 24 hours. It is defined as ‘t 0 9 am to 9 am

14. NORMAL DAILY TEMPERATURE NORMAL DAILY TEMPERATURE Average daily mean temperature for a given data over the past 30 years period. MEAN MONTHLY TEMPERATURE: It is the average of the mean monthly maximum and minimum temperatures. OR It is the mean temperature of the mean daily temperature. MEAN ANNUAL TEMPERATURE:It is the mean temperature of the 12 months. LAPSE RATE: The change in temperature per unit distance in the vertical direction from the Earth Surface.

15. Example 2.1 Given the air temperature as T a = 24 o C and the wet bulb temperature T w = 21 o C. Find relative humidity and dew point. Solution: From Equation 2.1 Wet bulb depression = 24 o - 21 o = 3 o C. From table A-1, Appendix-A, we get, For T a =24 o C, e s = 22.27 mm of Hg For T w =21 o C e w = 18.65 mm of Hg Therefore Equation 2.4 yields e = 18.65-0.485(3) = 17.20 mm of Hg Relative humidity = [17.20/22.27]x100 = 77 % And the dew point is the temperature read from Table A-1 of Appendix-A corresponding to ‘e’ which is 19.7 o C.

17. (i) Dry Adiabatic Lapse Rate: It is the rate of change of temperature when air is not fully saturated with water vapours. The average value of this is 5.4 o F per 1000 ft. (ii)Wet (Saturated) Adiabatic Lapse Rate: When air is fully saturated then rate of change of temperature is called wet adiabatic, lapse rate. Its average value is 3.0 o F per 1000 ft. (iii)Pseudo Adiabatic Lapse Rate: After condensed particles have fallen down fully (i.e. after rain fall) then the rate of change of temperature is called pseudo adiabatic lapse rate. Its average value is also 3.0 o F per 1000 ft.

18. EXAMPLE 2.2 A parcel of air has a temperature of 50 o F on surface of earth. At a height of 609.60 m the air becomes saturated. Rain fall occrues and air again becomes dry on the leeward side of a mountain. Find out temperature of this parcel of air, at an altitude of 1524 m on leeward side of the hill. Solution: Temp. at 609.60 m = 50 - (5.4x609.60/304.80) = 50 - 10.8= 39.2 o F Temp. at 2133.60 m = 39.2 - (3x5) (1524+609.6=2133.6)= 39.2 – 15= 24.2 o F Temp. on leeward side at 1524 m= 24.2+ (5.4 x2) = 24.2 + 10.8= 35 o F

19. Measurement of Wind Measurement of Wind Wind speed is measured with an instrument called Anemometer. This instrument gives continuous record over some graph called Anemograph. A very well known Anemometer is Dynes Apparatus. It gives reading in miles of total wind movement in 24 hours. Wind has both speed and direction. Wind direction is the direction from which wind is blowing. Wind speed is usually given in miles per hours, meters per second or knots. (1m/sec = 2.2 mph and 1 knot = 1-1/7 mph)