Atmospheric humidity

The presentation shows how relative humidity affects other ecological parameters in meteorology. This also shows the relationship between and among the ecological parameters in meteorology

1. Specific humidity Relative humidity Saturation mixing ratio Vapour pressure Mixing ratio Absolute humidity Atmospheric Humidity Melanie A. Calicdan

2. Outline

3. Introduction

4. Measurements Various ways of e xpressing h umidity Humidity Absolute humidity Saturation mixing ratio Mixing ratio Vapour Pressure Relative humidity Specific humidity

5. Absolute humidity (g of vapour/m3 of air)– expresses the vapour content of the air using the mass of water vapour contained in a given volume of air. Absolute humidity changes when the volume changes, even though the mass of water vapour has not changed. Specific humidity ( g of vapour/kg. of air)– measures the water vapour content of the air using mass of water for a given mass of air. Specific humidity doesn’t change as the air parcel expands or is compressed. Vapour Pressure – measures the water vapour content of the air using partial pressure of the water vapour in the air. Measurements

6. Measurements Mixing Ratio (g of water vapour/kg. of dry air) - refers the ratio of the mass of water vapour to the mass of dry air in the sample. It is not affected by changes in pressure and temperature. Saturation mixing ratio - refers to the mass of water vapour that can held in a kilogram of dry air at saturation. Saturation can be generally defined as the condition of liquid water or the deposition of ice at a given temperature and pressure. Relative humidity – the most commonly used to measure humidity. It is the amount of water in the air relative to the saturation amount the air can hold at a given temperature multiplied by 100. Temperature Degrees Celsius Vapor (g) per Kilogram of Dry Air 50 88.12 40 49.81 30 27.69 20 14.85 10 7.76 3.84

7. Fig. 1 Illustration on how relative humidity changes in a parcel of air with an increase in air temperature Note: T he more water vapour in the air, the higher the relative humidity is at a given temperature. Air with a relative humidity of 50% contains half of water vapour it could hold at a particular temperature. Measurements

8. Factors Change the amount of water vapour available – Example: Lake – relative humidity can be increased by evaporation from the surface of the lake. Water vapour Humidity Change the temperature of the air - Example: No water vapour is added. Air temperature Relative humidity

9. Note: Relative humidity varies considerably, tending to be the highest close to dawn when the air temperature is at its lowest, and decreasing as the air temperature rises. The decrease in the relative humidity towards midday tends to be the largest in summer. In areas with high humidity levels, the transmission of solar radiation is reduced because of atmospheric absorption and scattering. High humidity reduces evaporation of water and sweat. Consequently, high humidity accompanied by high ambient temperature causes a lot of discomfort. ( http://mnre.gov.in )

10. Effects of Humidity Transpiration of water vapour through leaf stomata depends on the gradient of moisture between the leaf interior (which is saturated) and the overlying air, as well as the availability of moisture in the soil. The lower the atmospheric humidity, the greater the transpiration rate. The transpiration rate is determined by a balance between the amount of energy available to convert water from the liquid to vapour phase and the moisture gradient. Transpiration rates also depend on the resistance to water movement between the leaf and the air. A tmospheric humidity affects the organisms by modifying its water content. Some forms are hygroscopic and absorb water from moist air. Different studies showed that specific organisms gains or lose weight depending on the humidity’s in a certain environment. Animals Plants

11. Humans Humans too are very sensitive to humidity because our skin relies on the air to get rid of moisture. So if the air is at 100% relative humidity, sweat will not evaporate into the air. As a result, we feel much hotter than the actual temperature when the relative humidity is high. If the relative humidity is low, we can feel much cooler than the actual temperature because our sweat evaporates easily, cooling ­us off. For example, if the air temperature is 75 degrees Fahrenheit (24 degrees Celsius) and the relative humidity is zero percent, the air temperature feels like 69 degrees Fahrenheit (21 C) to our bodies. If the air temperature is 75 degrees Fahrenheit (24 C) and the relative humidity is 100 percent, we feel like it's 80 degrees (27 C) out. People tend to feel most comfortable at a relative humidity of about 45 percent ( www.science.howstuffworks.com ). High humidity causes health problems such as sunstroke and heatstroke.

12. Instruments

13. Sling p sychrometer - often used to determine relative humidity. Consists of thermometers (wet bulb and dry bulb). The difference between the dry and wet bulb reading will give with the aid of psychometric table, the dew point temperature and the relative humidity. Performed near saturation but under read at lower humidities Hygrothermograph – records both relative humidity and temperature on graph paper in the same manner as the thermograph and barograph do.

14. Hair hygrometers – it works on the fact that hair changes its length when humidity varies. This device usually consists of a number of human or horse hairs connected to the mechanical lever system. When humidity increases the length of the hair becomes longer. This device is less accurate than the psychrometer . Satellites – on a global scale, humidity is being measured using remotely placed satellites. These satellites are able to detect the concentration of water in the troposphere at altitudes between 4 and 12 kilometers . Satellites that can measure water vapour have sensors that are sensitive to infrared radiation.

15. Relationship of humidity to other Meteorological Parameters Weather Parameters Relationship Remarks Air pressure Inversely proportional More humidity in the air, the lighter the air pressure and When less humidity is in the air, there is more air pressure. ( Givoni , 1976). Air temperature Directly related to solar radiation Higher the temperature, the higher is the amount of energy in the air. (Bharat and Sheeba , 2011) Precipitation Directly proportional As precipitation increases , humidity also increases. Temperature Inversely proportional Temperature changes; relative humidity also changes but in opposite direction. Soil temperature Indirect and minimal Air temperature was the factor that influenced most the soil temperature. ( Salamene et. al. 2010) Wind Less affected Air pressure differences between different locations will cause air pressure differences which in turn produce air movement (wind)

16. Climate Variables and their Correlation

17. Humidity – Ocean and Land Earth has become more humid in recent decades.

18. Thank you!