Transcript Weather 3
Topic 7 What is atmospheric moisture? • Atmospheric moisture refers to the amount of water in the air • All 3 phases are included: solid, liquid and gas (water vapor) What is the name of the process in which water vapor enters the atmosphere? How much energy is required for this process? • The process in which water vapor enters the atmosphere is evaporation. The energy required for evaporation is 540 cal/g (front cover of ESRT). What are the factors affecting evaporation? 1) Amount of energy available; more energy, increases temperature and increases evaporation 2) Surface area. More area allows for a greater interface between the air and water 3) Degree of saturation (how much water there is in the air already). If air is saturated, less evaporation. 4) Wind speed. Greater wind speeds allow for air to be replaced, bringing in new air that is less saturated. What is humidity and absolute humidity? • Humidity is the general term that refers to the water vapor content in the atmosphere • Absolute humidity is the amount of water vapor in each unit of air What is relative humidity and how can it be measured? • Relative humidity is the ratio of the amount of water vapor in the air (absolute humidity) to the maximum amount that the air can hold at a specific temperature • Relative humidity is expressed as a percent (in other words how much of the air is actually filled with water vapor. • It can be measured with an instrument called a psychromter or a sling psychrometer. • ESRT pg. 12 How is relative humidity affected if the temperature changes? • If the temperature increases, and absolute humidity remains the same, the relative humidity will decrease because warm air can hold more moisture so the total percent filled with water vapor is less. • If the temperature decreases, while the absolute humidity remains the same, the relative humidity will increase because cold air holds less moisture so the total percent filled with water vapor is more. What is dew point and how can it be determined? • Dew point is the temperature in which the absolute humidity is at its maximum meaning the air is completely saturated with water vapor. • It can be determined by using a psychrometer and the ESRT on pg. 12. • First located the dry bulb temperature (dry air) • Subtract the wet bulb temperature value from the dry bulb temperature • Find on the reference tables where the two values for step one and step two intersect or meet. How are clouds formed? The clouds form when an air mass rises, expands and cools off below its dew point. Condensation will occur (water vapor to a liquid). What is the cloud base altitude and can we determine it? • The cloud base altitude is the elevation at which a cloud begins. • It can be determined by using a chart in the Appendix of your Review Book (pg A-25). • You need to know the air temperature and the dew point temperature. What are the different types of clouds? Names of clouds are based upon the altitude at which they begin, the shape and if there is precipitation associated with it. Meanings of Prefixes (altitude): 1) Cirro = high level clouds 2) Alto = mid level clouds 3) Stratus = low level clouds 4) Nimbus/Nimbo = precipitation clouds Meanings of Suffixes: 1) Cumulus: tend to look like cotton balls 2) Stratus: Layered and uniform 3) Cirrus: Thin and wispy