Name: Date: ES: 1 2 3 4 Dew Point and Cloud Formation Part A: Run some water over your hands. After shaking off the excess, wave them back and forth until they are dry. 1. Describe the change in temperature you feel as you wave your hands back and forth. 2. a) What type of phase change is happening that causes the change in temperature that you felt? b) Does this type of phase change require energy or does it release energy? (use ESRT pg 1) 3. If you attached a damp cloth to the bulb of a thermometer and waved it back and forth, what would you expect to happen to the temperature reading on the thermometer? Why? ---------------------------------------------------------------------------------------------------------------------- Part B: How to use a sling psychrometer to find relative humidity and dew point Background: Dry bulb Thermometer Wet bulb Thermometer - Water evaporates from sock = cools bulb - The more evaporation, the lower the temperature The Dry Bulb ALWAYS has a higher temperature than the Wet Bulb. Only time it is equal is if the air is totally saturated and evaporation can t occur
Report Sheet 1 Dry-Bulb Temperature: C Wet-Bulb Temperature: C Dry-Bulb - Wet- Bulb: C Dewpoint Temperature (ESRT 12): C Relative Humidity (ESRT 12): % Report Sheet 2 1. Convert the dry-bulb temperature and dewpoint temperature you found in Report Sheet 1 to F. Record th information and the Relative Humidity on Report Sheet 2. 2. Retrieve the current conditions for your area from weather bug on the smartboard and record this information on Report Sheet 2. Your Measurements Temperature F Dewpoint F Relative Humidity % Current Observations from NWS Temperature F Dewpoint F Relative Humidity % ------------------------------------------------------------------------------------------------------------------------------ Part C: Practice: Fill in all missing columns using the information provided and your ESRT. Location Air Wet Bulb Temp Temp A 19 o C 19 o C B 4 o C -1 o C Dry Bulb & Wet Bulb Difference C 21 o C 4 o C D 18 o C 5 o C Dew Point E 9 o C 2 o C Relative Humidity
1. When air temperature (the dry bulb temperature) is closer to the dewpoint, what happens to relative humidity? Use the chart you just completed and the charts of ESRT page 12 to help answer your question. Give example data points to support your answer. 2. Think about a rainforest and a desert that are both 90 o F. Which one do you think would have a higher relative humidity? Explain your answer. 3. Prediction: How do you think it would feel to be somewhere that has a relative humidity at 100%? What do you think might be happening? 4. For which location is precipitation most likely? Why? ------------------------------------------------------------------------------------------------------------------------------- Part D: Look at the diagram below and answer the questions that follow. 1. Write down at least three observations. 2. What are some questions you have about the diagram and what it means? 3.Explain what the diagram is showing about relative humidity, temperature, dewpoint, and weather. Discuss with your partner and use your textbook to help you.
Part D: Use the following cartoon to respond to the questions that follow about the relationships between air temperature, relative humidity, and dew point temperature. 1. What is doing the talking in the first and second frames? 2. What happened to the difference between the dew point temperature and air temperature as the frames progress? 3. What happens to the relative humidity as the frames progress? 4. What happens when the dew point and air became the same temperature? 5. What is missing from this cartoon in order for condensation to really occur? (HINT: think small!)
Part F: Follow the procedure below to help visualize and relate condensation to relative humidity and dew point. Procedure: 1. Use a thermometer to measure the air temperature of the classroom. 2. Using the chart below to find the capacity of the air to hold water vapor at that temperature. 3. Fill the metal can halfway with water. Add some ice to the water and slowly stir with the thermometer.
4. As soon as condensation appears on the outside of the can, quickly record that temperature as your dew point temperature. 5. Use the chart below to find the capacity of air to hold vapor at the dew point temperature. This is your specific humidity. 6. Find the relative humidity by using the following formula: Relative Humidity = Specific Humidity Capacity Capacity of Air to hold water vapor Temp. C Capacity g/kg Temp. C Capacity g/kg -10 1.8 13 9.5-9 1.9 14 10.1-8 2.1 15 10.8-7 2.3 16 11.6-6 2.5 17 12.3-5 2.6 18 13.2-4 2.9 19 14.0-3 3.1 20 15.0-2 3.3 21 15.9-1 3.6 22 17.0 0 3.8 23 18.1 1 4.1 24 19.2 2 4.4 25 20.4 3 4.8 26 21.7 4 5.1 27 23.1 5 5.5 28 24.6 6 5.9 29 26.1 7 6.3 30 27.7 8 6.8 31 29.4 9 7.3 32 31.2 10 7.8 33 33.1 11 8.3 34 35.1 12 8.9 Questions: 1. Explain how the dew formed on the outside of the can. 2. Why is it important to quickly record the temperature at which dew first appears on the outside of the can? 3. What would happen to relative humidity if the air temperature was warmer at the start?
4. What is the relative humidity when air temperature and dew point temperature are equal?