HUMIDITY, CONDENSATION, & CLOUDS
1. What is condensation and what conditions are nec- essary for condensation to occur?
2. What is evaporation? What conditions make it more likely to occur?
3. When we say that air is saturated what does that mean?
4. What is humidity?
5. What is relative humidity? How do we calculate the relative humidity of the air?
6. What are the two ways that we can increase or de- crease the relative humidity of air?
7. What does the term dew point temperature mean? How is the difference be- tween the dew point and air temperature related to relative humidity?
8. What are the four main cloud groups and their types? Be able to recognize them in the sky.
9. How can you distinguish altostratus clouds from cirrostratus?
10. What happens to the general size of clouds as they increase in altitude?
PUTTING IT INTO PRACTICE PART 1: THE ADIABATIC PROCESS
In this section, you will be calculating the air temperature as a parcel of air lifts up over a mountain range and back down the other side. Assume that the parcel of air starts off with a temperature of 65 F at sea level and a Dew-Point Temperature of 54 F. Dry Adiabatic Rate : 5.5 F for every 1,000 feet of elevation change. The rate at which unsaturated air cools while lifting or warms while descending. Saturted (Wet) Adiabatic Rate: 3.3 F for every 1,000 feet of elevation change. The rate at which saturated air COOLS. Warming air will never maintain 100% relative humidity, so you never use the saturated rate with warming air.
CACLCULATING THE TEMPERATURE OF A RISING PARCEL OF AIR:
1. If the dew point is 54 F and the air temperature is 65 F. At sea level (0ft) on the windward side of the mountain in the diagram below, is the relative humidity of the air starting out at 100%? Why or why not?
2. Assume that this same air is forced upward by a mountain range. When it starts to rise to 1,000ft, will it cool at the DRY or SATURATED adiabatic rate?
3. Using the rate that you chose from question 2, calculate the temperature change on the diagram below up to 2,000 feet. What is the temperature of the parcel of air at 2000 ft?
4. At 2,000 ft., is the relative humidity of the parcel of air 100%? Yes or No?
5. Above 2,000ft, will the rising air begin cooling at the DRY or SATURATED adiabatic rate?
6. On the diagram below, calculate the air temperature changes all the way up to 5,000 feet using the rate you chose in question 5. What is the temperature at 5,000 ft?
0 ft65 F
7. On the diagram to the right, finish calculating the air temperature as it descends from 5,000 feet back down to sea level (0ft). What is the tem- perature at sea level on the leeward side of the mountain?
HINT: If the air is forced to descend it will WARM at the Dry Adiabatic Rate.
TYPES OF CLOUDS
low middle high clouds of vertical development
In the diagram below, draw in and label the major cloud types.
1. The table to the right lists the total amount of water vapor air at specific temperatures can hold (capacity). Looking at the data, what general statement can you make about the relationship between temperature and capacity?
2. What is the formula for calculating the relative humidity of air?
3. Suppose it is 40 degrees F outside and there is 2.88 g/kg of water vapor in the air. Using the formula from question #2, calculate the relative humitidy. (Write out all your calculations)
4. What would happen to the relative humidity of this parcel of air if you warmed the air in the scenario above to 60 degrees? Assume there is no change in the amount of water vapor (2.88g/kg). Calcu- late how the relative humidity changed when the air warms to 60 degrees.
5. What is the dew point temperature of the air in this scenario? In other words, at what temperature would this parcel of air reach 100% relative humidity?
4PUTTING IT INTO PRACTICE PART 2: CALCULATING RELATIVE HUMIDITY
Relative Humidity: a percentage describing how close the air is to reaching saturation. Saturation: when the air is at 100% relative humidity and can no longer hold any more water vapor Dew Point: temperature at which a parcel of air reaches saturation (100%RH) Capacity: the total amount of water vapor that air at a specific temperature can hold.
CALCULATING RELATIVE HUMIDITY
Temperature (F) Capacity (g/kg) -40 0.12 -30 0.21 -20 0.35 -10 0.58 0 0.94 10 1.52 15 1.89 20 2.34 25 2.88 30 3.54 35 4.33 40 5.28 45 6.40 50 7.74 55 9.32 60 11.19 65 13.38 70 15.95 75 18.94 80 22.43 85 26.48 90 31.16
HUMIDITY, CONDENSATION, & CLOUDS