Extra Credit #4 - Humidity and Cloud Formation

1. Air becomes saturated when the rate of condensation equals the rate of evaporation.
   
   
2. Air at a temperature of 25 degrees C has a saturation vapor pressure of about 30 millibar.
   
   
3. 60 degrees F is equal to 15.5 degrees C (Appendix D, p. 420). From Figure 5.7, the saturation mixing ratio at 15.5 C is about 11 g/kg. The actual mixing ratio is only 8 g/kg, so the air is unsaturated
   
   
4. 50 degrees F is about 10 degrees C; at 10 degrees F the saturation mixing ratio is 8 g/kg, which is equal to the actual mixing ratio. At this point, the air is saturated.
   
   
5. The air's dew point temperature (i.e. temperature at which air becomes saturated) in this case is 50 degrees F (10 degrees C). You can find this by locating the 8 g/kg line on the vertical axis, and drawing a straight horizontal line over to the saturation curve. At this intersection, drop a vertical line straight down to the temperature axis and read off the temperature value - that's the dew point temperature.
   
   
6. If the temperature continues to fall, you would observe dew (i.e. condensed water vapor) gathering on surfaces around you. Fog may also form close to the ground. As it becomes colder, more water vapor will leave the air and accumulate in liquid form. This will reduce the amount of water vapor in the air - the dew point temerpature will decrease.
   
   
7. A cloud exhibiting vertical development and precipitation is known as cumulonimbus.
   
   
8. High clouds exist in the upper troposphere where temperatures are below freezing. Therefore, all high clouds (i.e. cirrus, cirrostratus, cirrocumulus) consist of ice particles. The tops of these clouds are limited by the height of the tropopause. Either of these properties is sufficient to answer this question.
   
   
9. The term adiabatic means that no heat energy is trasferred between an air parcel and its environment. Any changes in the air parcel's temperature is due to internal expansion/compression, or due to release of latent heat.
   
   
10. A dry adiabatic process means that no liquid water vapor is present in the parcel (parcel is unsaturated); a moist adiabatic process means that liquid water is present in the parcel (parcel is saturated, water vapor condenses, latent heat released by condensing water molecules warms the parcel).