test 3 - Water Basics(required Reading Unit 12 esp pp...

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Water Basics. (required Reading) Unit 12 esp pp 144-150 Distribution of Water within Earth System - Unequal distribution between ocean water (97%) and fresh water (3%) - Regarding worlds fresh water supply o 75 % glacier ice sheets o nearly 25% groundwater o What about the remaining < 1%? Lakes and rivers 0.33% Soil 0.06% Atmosphere 0.035%* Significance of Atmospheric Moisture - Represents a small fraction of the total fresh water supply (0.035%) but extremely important - Most atmospheric moisture exists as water vapor ; liquid droplets and ice crystals in clouds account for most of the rest - One of the key ingredients in atmospheric instability Hydrologic Cycle - complex system of exchanging involving water as (1) gas/water vapor, 2. liquid and 3 solid ice as it moves through the Earth system. - Simply, water moves: o From oceans to atmosphere via evaporation o From atmosphere to land surface via condensation and precipitation o From land to oceans via run off Humidity: - Refers to water vapor content of atmosphere - Amount of water vapor that can be held in the atmosphere is dependent on air temperature o Warmer air can hold more o Cooler air can hold less - Maximum amount of water vapor that can be held at a given temperature: saturation capacity or CAP. - Increase temp, increase cap or decrease temp, lower cap - Amount of water vapor actually in the atmosphere: specific humidity or SH (from Lab Manual) - Sling psychrometers and hygrometers - Relative humidity (RH) and the dew point temperature used to assess the water vapor content of the atmosphere. - Relative Humidity:
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Refers to a ration (expressed as a %) based on 1. the amount of water vapor actually in the air compared to 2. the maximum amount of water vapor that the air can hold at a given temperature. o SH/ CAP x 100= RH% What does RH% tell us? - How close a parcel of air is to its saturation level o If RH = 20% (far from saturation, dry) o If RH% = 80% (closer to saturation, humid) - Air is saturated or filled to capacity: o When RH% =100% o When SH = cap o When air temperature = dew point (temperature) Dew point refers to the temperature at which a parcel of air is (or will be) fully saturated. How can we use the dew point temp? Its 3 am Air temp is 46F Dew point is 43 F Is the RH high or low Its 2 pm Air temo is 84 Dew point is 43 F Relationship between RH and Temperature over the course of a typical day: - inverse relationship - RH high near dawn when air temp is low o Why? Cap is low - RH low in afternoon when air temp is hugh o Why? Cap is high Heat Index - Combines air temp and relative humidity. - Tells us how uncomfortable that combination “ feels” or how dangerous it might be (heat exhaustion, heat stroke) - On hot days, we perspire. When our sweat evaporates, it provides a cooling mechanism. But high humidity levels slow down evaporation and our ability to cool down. We feel uncomfortable. Atmospheric Instability
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test 3 - Water Basics(required Reading Unit 12 esp pp...

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