AOS 100/101 Spring 201t8 HOMEWORK #5 (Due Fri. April 6) Please provide concise,
ID: 291147 • Letter: A
Question
AOS 100/101 Spring 201t8 HOMEWORK #5 (Due Fri. April 6) Please provide concise, grammatically correct, neatly written answers to the following questions. All questions can be answered in, at most, a few sentences. Don't forget to write your name on the paper!!! NAME: 1)This problem involves consideration of two air parcels originally at the surface of the Earth. Parcel A is saturated and has a specific humidity of 10 g kg1. Parcel B has a relative humidity of 97% and a specific humidity of 20 g kg". Which parcel experiences a larger temperature decrease upon being lifted 1 km? Explain your answer (10 pts) 2)This question will involve consideration of conditions observed on two different days. On Day One, the surface temperature is 25°C and the surface dewpoint is 15°C. On Day Two, the surface temperature is 25°C and the surface dewpoint temperature is 20°C. If cumulus clouds form on both days, on which of the two days is the cloudbase (i.e. the height of the bottom of the cloud) higher? Clearly explain the reasoning you used to arrive at your answer (10 pts) 3) Cloud properties are measured on two different days. On Day One, there are fewer cloud condensation nuclei (CCN) in the air than on Day Two. The exact same amount of liquid water is observed in the clouds on the two different days Why is the Day One cloud more likely to precipitate t han the Day Two cloud? (10 pts) 4)On a summer morning you observe that the air near the surface is saturated and has a temperature of 20°C. A pilot friend of yours has taken an early morning flight and reports that the temperature at 2 km elevation is 4°C. Is it reasonable to expect thunderstorms to develop in the afternoon? Clearly explain the reasoning you used to arrive at your answer (10 pts)Explanation / Answer
1) Temperature decrease with height depends on the saturation of the parcel. Parcel A is saturated while Parcel B is close to saturation. Although Parcel B has more water vapor per kilogram of dry air, it is not completely saturated. In other words, Parcel B doesn't have the amount of water vapor at its maximum potential, whereas Parcel A does. Completely saturated parcels cool slowly as the release of more latent heat during the ascent decreases the rate of cooling. This means that Parcel B will cool at a faster rate than Parcel A, thus Parcel B will experience a larger temperature decrease upon being lifted 1 km.
2) Cloud base height is calculated using the equation:
CBH (in feet) = [(Air temperature - Dew point temperature) / 2.5] x 1000
On Day One, the cloud base height is (25 - 15) / 2.5 x 1000 = 4000 ft.
On Day Two, the cloud base height is (25 - 20) / 2.5 x 1000 = 2000 ft.
Larger the spread between air temperature and dew point temperature more will be the height of the cloud base. This is because condensation will be delayed if the surface is drier, but it will speed up if the surface is wetter. Closer the dew point temperature is to the air temperature more will be the level of humidity. Thus, on Day One, the cloud base height will be at a higher elevation as the surface is relatively drier than on Day Two as indicated by the lower temperature at which the surface attains saturation.
3) Fewer Cloud Condensation Nuclei on Day One means lesser amount of water attracted to nuclei and more amount of precipitable water. The cloud on Day Two with more CCN will have less precipitable water as more amount of water will hold on to nuclei.
Suppose the number of liquid water droplets on both days is 100
The number of CCN on Day One is 50
The number of CCN on Day Two is 100
Each droplet will occupy a nucleus, so on Day One, there will be 50 droplets available for precipitation. On Day Two, all the droplets will be attracted to the nuclei and none will be left for precipitation.
So, the cloud on Day One is more likely to precipitate than the cloud on Day Two.
4) The temperature decrease with height is substantial given that it decreases at an average of 8C per km. However, the instability arising due to the temperature difference alone can't be used for forecasting a thunderstorm later in the day. Mechanisms pertaining to air parcel lifting and the presence of a prominent vertical wind shear would also be crucial for a thunderstorm to take place. The absence of vertical wind shears can inhibit the thick and deep vertical motion required for a thunderstorm. So it is not quite reasonable to expect a thunderstorm in the afternoon without looking at other natural conditions.