Lecture 16 Outline of Last Lecture I. RemindersII. Weather of the dayIII. Reviewa. Warm Rainb. Cold Rainc. Auto Conversiond. Ice Nucleie. Bergeron ProcessIV. Processes by which Ice GrowsV. Wet process procedureOutline of Current Lecture II. Review for the testa. Study Guide questionsCurrent LectureTest Wednesday! On the test there will be 60 questions taken from readings, homework questions, and PowerPoint’s. 1. Know dry and moist lapse rates and how to estimate surface temperature from 850 mb temperature and surface dew point. Example: well mixed afternoon vs. night time low (dew point)2. Ways that saturation is produced in the atmosphere There are 4 major ways that saturation is produced in the atmosphere. The idea of saturation is that it represents the condition where the amount of vapor is in equilibrium with a plain surface of pure water. The saturation vapor pressure, in order to have equilibrium, means having saturation from the water that is equal to that of the air pushing down on the water. Given that we have a certain amount of water in the atmosphere, the only way to obtain saturation if it isn’t already saturated is to decrease the temperature. Lower temperatures mean that vapor pressure becomes lower. A key point here is that vapor pressure of the air, which is what we have lower to create Atm Ocn 100 1nd Editionsaturation, means also a lower air temperature. Well how do we lower the air temperature? That is an important question it can sometimes be difficult. One way we can lower air temperature is to raise humidity. Raising the amount of water in the air is how you raising humidity. Sometimes this means feeding water into the air. Another way we can lower air temperature is through radiation, or a diabetic process. Parcel will radiate its energy, or radiate its heat away from air parcel, which then causes it to become cooler. The parcel will have a net radiated loss of heat, which causes temperature to fall and that could bring it to radiation. This can also happen through rising motion. If there is no exchange of energy, a parcel can rise adiabatically. Adiabatically means there is no exchange of energy with surroundings. And as we know as the air parcel increases in height the temperature will decrease. Another way lower air temperature is through conduction. This means that an air parcel has to be in contact with another medium like surface, if that surface is colder then the air parcel; the air parcel will take on the temperature of the surface. This will typically only become dew, and only become cold enough at point of contact. This is not though a good way to form clouds. Another way the air can become cooler is through mixing. Air parcels can mix with the air above. If is it mixed with wind, the mixture can become saturated through mixing, and then the mixing of air parcels with different temperatures and humidity can produce saturation. This is actually how you can see breathe on a cold day.This 4th mechanism is mixing. This is key to the atmosphere! In important thing to remember is that even if individual components of the mixture are not saturated, the mixture itself can be saturated. Evaporation only occurs if less than 100% relative humidity but this means that it can’t make it saturated. So then the only way to reach saturation here would be through getting more moisture and then mixing with air above. Mixing goes hand in hand with conduction of temperature and moisture to produce saturation. How clouds are formed.Clouds have to be formed by saturation in the air. How can you create a cloud? There are 4 mechanisms to form a cloud…Conduction, mixing, radiation, and expansional cooling Expansional cooling means that the parcel rises and then cools. In cloud formation expansional cooling is very important. The other ones can produce saturation but barely, so any cloud produced by those mechanisms tends to be more marginal cloud. Sometimes there is not cloud condensation to create big enough droplets to create precipitation or anything more than a fog. Different clouds are produced from each mechanism.Fog becomes in contact with surface…each mechanism creates different types of fogs.The thickest type of fog is upslope fog. This type of fog has contact with the ground and then can produce a strong cloud that can create precipitation. 3. Surface station vs. upper air station model, wind direction and speed conventions, pressure coding on station modelOn the test we will be given models and be asked what temperature and dewpoint of the model is. Know how to do that. Make sure to know that in an upper air station dewpoint is the dewpoint depression. Temperature is in Celsius for the upper air station models, but in the regular station models the temperature is in Fahrenheit. We should also know knots for this test.4. 850 mb map, how high is it compared to local surface height?In a lot of the lectures now we have looked at constant pressure maps which means that pressure was the same at any point on the map. Other maps we have looked at are constant height maps. 850 mb is about 1500 meters above sea level. Or is about 4500 feet. In Denver the height is 5280. If that is its height what is the pressure? The pressure is about 830 mb typically. A typical pressure here in Madison would be 300 meters above sea level. Then we would be 1200 meters above us at 850 mb.How fast temperature changes with height, and dry, mixing in air to the ground in Madison, 850 mb is 1.2 kilometers above us on average. Our temperature compared to 850 mb assuming it is well mixed, compressional warming will warm at about 12 degrees Celsius. This is about 20 degrees Fahrenheit. Often we can look at 850 mb to determine what the temperature will be at some time in the future. The future prediction at 850 mb is better then looking at a temperature upstream. We would look at 850 mb temperature to see what that means for surface temperature in Madison. On an 850 mb map we can see where cold air or warm air is coming from. 5. What is Doppler effect?This has to do with radars. This was in the text. Radars measure the reflection of radiation and for radars the wavelength is chosen as radiation it is going to emit. This is the same wavelength of radiation that’s in microwaves. Waves go out hit the precipitation field and then reflect it back. The amount of reflection and strength of echoes it hears…will then be translated to a reflectivity factor. The reflectivity factor