ATMO 170A1 1st Edition Lecture 14 Outline of Last Lecture I.Two Ways to Achieve SaturationII.Three Ways to Lower the Temperaturea.Dewb.Fogb.i.Radiation Fogb.ii.Advective Fogc.CloudsOutline of Current Lecture II. Measuring HumidityIII. Forming Cloudsa. Cloud Condensation NucleiIV. Idea Behind Swamp Coolersa. Heat IndexV. Cloud in a Bottle ExperimentCurrent LectureMeasuring Humidity- We measure humidity with a psychrometer. ◦ Swing for a minute.◦ Read the difference between the two temperatures. ◦ Dry Air: The difference in temperature is large.◦ Humid Air: The difference in temperature is small.Forming Clouds- For clouds to form, you need:◦ Air to cool to RH of 100% (or higher). This happens when a parcel rises. ◦ Cloud Condensation Nuclei (CCN)- Water vapor requires a surface to condense on; many aerosols provide this surface or condensation nuclei. ◦ Condensation nuclei generally range from about ~0.1 µm to 1 µm in radius. For comparison, fog and cloud droplets are generally >10 µm radius.◦ This includes: dust, volcanic output, factory smoke, forest fires, salt from ocean spray, and sulfate particles emitted by phytoplankton. ◦ The best condensation nuclei are hygroscopic particles that attract water vapor to them. These include salt, sulfates, nitric acid particles, and silver iodide. Idea Behind Swamp Coolers- Swamp cooler adds water droplets.- Water will evaporate → Energy is taken from the environment → Cooling- This works really well for deserts, but as soon as the monsoon hits, it stops working.- Heat Index◦ Represents what a person feels due to heat and humidity▪ 105°F → 10% RH (Dry) → Feels like 100°F▪ 105°F → 50% RH (Humid) → Feels like 135°F Cloud in a Bottle Experiment- ONLY water in the bottle:◦ Pump air → Pressure increases → Cork pops out → Pressure drops very quickly → RH: 100% → Nothing happens (don't see anything)- Water AND a match in the bottle:2◦ Match provides cloud condensation nuclei → Pump air → Pressure rises → Cork popsout → Pressure drops → Temperature drops → RH = 100% → Get condensation around condensation cloud nuclei → Water droplets scatter light and we can detect it with our