1. HUMIDITY AND WATER VAPOUR

2. Role and causes of water vapour in the atmosphere Humidity-amount of water vapour in the atmosphere Sources of water vapour-earth’s surface and transpiration Determines – weather and climate-role in green house effect  Specific humidity  Absolute humidity  Relative humidity

3. Saturation vapour pressure(SVP)-partial pressure of w.v in saturated air SVP-increases rapidly with temperature

4. VARIATIONS IN HUMIDITY Specific humidity –remains relatively constant from day to night Highest humidity-at the time of lowest temp-before sunrise Seasonal humidity variations depend- seasonal changes in temp and atmospheric circulation Av.relative humidity values in summer and winter –not differ much Specific humidity-much greater in summer Monsoon –relative and specific humidity –increase dramatically

5. EVAPORATION AND CONDENSATION In atmosphere-water-3 phases-solid, liquid and gas High wind speed-greater the evaporation Relative humidity-near or exceeds 100%-wv- condense on nuclei to form water droplets or ice crystals Water droplets in the cloud grow larger-fall as rain

7. HUMIDITY MEASURING INSTRUMENTS Hair hygrometer Hygrograph Psychrometer

8. Hair hygrometer

9. Hygrograph

10. Psychrometer