Chapter 7. Clouds, Precipitation, and Weather Radar
1. A cumulus cloud forms in the updraft of a convective circulation over warm ocean waters. The sea-level temperature is 20 °C (68 °F) and the relative humidity is 40%. The mixing ratio of the air at sea-level is __________ grams per kilogram (Table 6.4of your Weather Studies textbook). The air ascends and cools at the dry adiabatic rate, eventually becomes saturated, and a cloud forms. Use the Stüve diagram (Figure 6.19 of your Weather Studies textbook) to determine the approximate altitude where the relative humidity of the ascending air equals 100%. Answer: __________ km
2. Within a cloud at a temperature of −10 °C (14 °F), the saturation vapor pressure surrounding a supercooled water droplet is 2.86 mb and the relative humidity is 100%. What is the relative humidity of the air surrounding an ice crystal in the same cloud? Answer: __________ %. Hence, the cloud is [(saturated) (supersaturated)] for ice crystals.
3. What is the dewpoint in radiation fog at a temperature of 5 °C (41 °F)? Answer: _____ °C
4. Suppose that a cloud droplet has a terminal velocity of 1 cm per second. If the air is calm (no updrafts or downdrafts), how long would it take for the cloud droplet to descend from the cloud base a vertical distance of 2000 m? Answer: _________ hours. Within that time frame, the cloud droplet is [(likely) (unlikely)] to evaporate in the unsaturated air below cloud base.
5. As a very general rule, 10 cm of fresh snow melts to 1 cm of liquid water. The density of fresh water is 1 gram per cubic cm. Hence, the average density of fresh snow is 0.1 gram per cubic cm. Determine the density of snow if the ratio of snowfall depth to melt-water depth is 3 to 1. Answer: __________ grams per cubic cm; ratio of 30 to 1. Answer: __________ grams per cubic cm


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