GEOG 111 1st Edition Lecture 18 Outline of Last Lecture I Review from last lecture II Water in the atmosphere a Phase changes of water b Effects examples III Humidity Outline of Current Lecture I Measures of water vapor in the atmosphere II Conclusion of temperature lecture Current Lecture I Measures of water in the atmosphere a Saturation if you add any more water vapor to the atmosphere the excess must be removed by condensation or deposition latent phase change i Amount of water vapor the atmosphere can hold is due to temperature b Relative humidity vapor pressure saturation vapor pressure 100 i Can range from close to 0 to 100 ii Desert environments are very far from being saturated iii In contrast once VP SVP 1 relative humidity 100 and atmosphere is saturated iv Plays into comfort levels 1 If relative humidity is low while temperature is high there is tremendous amounts of cooling through perspiration 2 In contrast in high temperatures with high relative humidity there is a very small cooling effect c Ways to saturate the air i Evaporation ii Moisture advection horizontal transport of water vapor by the wind 1 Ex Bermuda high off the coast of NC brings in clockwise winds from the Atlantic ocean iii Decreasing the temperature of the air 1 Decreasing the SVP the atmosphere s ability to hold water vapor 2 Radiational cooling net radiation is negative at night more radiation leaving than coming in a Inverse relationship between temperature and relative humidity i RH is maximized in early morning and minimized late afternoon ii Evaporational cooling is greatest mid afternoon hours best time to work out These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute 3 Virga rain droplets that evaporate before reaching the ground because bottom layer of ground is so dry very quickly cool down the atmosphere a Cooling always accompanies rain b How much cooling depends on virga which depends on relative humidity d Dew point temperature the temperature to which the air must be cooled in order to reach saturation i Serves as a readily available indicator for atmospheric water vapor content ii Varies between 60 70s iii DPT is much higher in the summer than winter in Eastern U S 1 Pacific ocean is much cooler than Atlantic so there s not nearly as much evaporation and dew point is not nearly as high iv Seasonal patterns of DPT 1 Why is the dew point lower in the winter Air is much colder and can t hold as much water vapor is dry Also there s a high frequency of days in which dry continental wind is coming from the West and Northwest 2 Why is it higher in the summer Much warmer and vegetation is more active acting as a pump through the soil evapotranspiration through stomata Dew point will be higher in a forest than a parking lot Also winds average out of the South and Southwest in the summer and are bringing in marine air a Trees effectively pull tons of water out of the soil and can cause an area to become more prone to droughts v Diurnal day night patterns of DPT in the summer 1 Pattern a Decrease 12 5 am i Formation of dew that takes water vapor out of air b Increase 5 9 am i Evaporation of dew c Decrease 10 am 3 pm i Convection mixing down of more dry air d Increase 3 8 pm i Thundershowers virga II Conclusion of temperature lecture a Horizontal temperature patterns i Specific heat water s is higher which requires more energy to warm up cool down ii Surface mobility water moves around iii Water transparency radiation can reach deeper layers not just the surface iv Evaporation not much energy left to warm water v Which hemisphere has the greatest seasonal temperature change Northern Hemisphere has much more land surfaces than ocean vi Southern Hemisphere has a marine climate b Latitude strongly related to annual solar insolation c Ocean currents i Pacific and Atlantic oceans circulate clockwise ii East coasts of continents have cold currents while West coasts have warm currents
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