Survey
* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project
Download Moisture and Atmospheric Stability
Document related concepts
no text concepts found
Transcript
9/19/2011 Water Vapor — Odorless — Colorless — Changes state easily Moisture and Atmospheric Stability Chapter 4 — Solid, liquid, gas — Movement of water through the atmosphere — — — — — — — Oceans Glaciers Rivers Lakes Air Soil Living tissue Movement of Water Through the Atmosphere Movement of Water Through the Atmosphere — Hydrologic Cycle — Transpiration — The unending circulation of Earth’s water supply — Powered by the Sun — Plants releasing water to the atmosphere — Like evaporation but from plants — Water Balance — Amount of water vapor remains constant — Continents — More precip than evap. — Oceans — More evap. Than precip. — More precip. Is added from runoff Water Change of State Water Change of State — Only substance — Liquid — Solid, liquid, gas (in atmosphere) — H2O (2 hydrogen's and 1 oxygen) — Ice — — — — — Low kinetic energy Atoms vibrate Heat added Atoms move faster Melting occurs — — — — Molecules tightly packed Fast moving Slide past each other Add heat — Enough energy to break surface — Becomes a gas — (Doesn’t have to boil) — Liquid 1 9/19/2011 Water Change of State Water Change of State — Gas — Molecules widely spaced — Energetic Random motion Water Change of State Water Change of State — Heat is absorbed — Solid à Liquid — Liquid à Gas — Latent heat of evaporation — Energy needed to escape the surface — Evaporation = cooling process — Heat from liquid goes to gas — Leaves liquid with less heat Less Energy (heat) in liquid — Heat is released — Liquid à Solid — Gas à Liquid — Latent heat of condensation — Forms clouds — Warms surrounding air — Can produce large dark clouds Energy (heat) Water Change of State Humidity — Sublimation — The amount of water vapor in the air — Conversion of a solid directly to a gas — Doesn’t become a liquid — Dry ice — Amount varies 0-4% — Terms related to humidity — — — — — Absolute humidity Mixing ratio Vapor pressure Relative humidity Dew point — Deposition — Conversion of a gas directly into a solid — Doesn’t become a liquid — Frost 2 9/19/2011 Humidity Humidity — Absolute Humidity — Mixing Ratio — Mass of water vapor in a given volume of air — g/m3 — Mass of water vapor in air compared to the remaining mass of dry air — g/kg Mass of water vapor (grams) Volume of air (cubic meters) Mass of water vapor (grams) Mass of dry air (kilograms) — Changes with pressure and temp. — Not effected by changes with pressure and temp. — Absolute humidity Mass of water vapor (grams) Volume of air (cubic meters) Humidity Humidity — Vapor Pressure — If atmosphere is high in humidity — If atmosphere is low in humidity — Low vapor pressure — More evap. than conden. — Net evaporation — High vapor pressure — More condensation than evap. — Net condensation More Pressure Less evaporation More Condensation Less Pressure More evaporation Less Condensation Relative Humidity — Ratio of the actual water vapor in the air compared with the amount of water vapor required for saturation at that temp (capacity) — Amount of water vapor (grams) Capacity (kilogram) — Capacity – how much water vapor can hold Equal Evaporation and Condensation — Vapor Pressure — Equilibrium — Equal conden. and evap. — Air is saturated — Can’t hold anymore water vapor — 100% humidity — Temp. dependent — Warmer air can hold more — Colder air can’t hold as much Relative Humidity — Amount of water vapor (grams) Capacity (kilogram) — If the amount of water vapor in the air is 3.5g and the temp is 5oC then what is the relative humidity? 3.5 / 5.5 = .64 x 100 = 64% Capacity Capacity Capacity 3 9/19/2011 Relative Humidity Relative Humidity — Amount of water vapor (grams) — How relative humidity changes Capacity (kilogram) — If the amount of water vapor in the air is 19.2g and the temp is 25o C then what is the relative humidity? 19.2 / 20.0 = .96 x 100 = 96% Capacity Capacity — Water vapor — Increase — Relative humidity goes up — Until 100% then — Condensation occurs — Decrease — Relative humidity goes down — Temperature — Increase — Decrease in rel. hum. — Decrease — Increase in rel. hum. Amount of water vapor must remain the same Relative Humidity Relative Humidity — Amount of water vapor (grams) — Amount of water vapor (grams) Capacity (kilogram) Capacity (kilogram) — If the amount of water vapor in the air is 3.5g and the temp is 5oC then what is the relative humidity? How about at 0oC? — If the amount of water vapor in the air is 19.2g and the temp is 25oC then what is the relative humidity? How about at 30oC? 3.5 / 5.5 = .64 x 100 = 64% 19.2 / 20 = .96 x 100 = 96% 3.5 / 4.0 = .87 x 100 = 87% — Decrease in temp. = Increase in rel. hum Capacity Capacity Capacity Capacity Relative Humidity — Natural Changes in Temp. — Daily changes in temp — Nighttime vs. daytime — Horizontal temp. changes — Winds — Vertical temp. changes — Hot air rising — Cold air sinking 19.2 / 28.0 = .69 x 100 = 69% — Increase in temp. = Decrease in rel. hum Dew-Point Temperature — The temp to which air needs to be cooled to reach saturation — At dew point — Condensation occurs — Clouds — Dew — Frost — Example — Temp = 23oC — Dew point = 19oC If the air cools to 19oC then the air will be saturated 4 9/19/2011 Humidity Measurement — Measuring Relative Humidity — Hygrometer — Psychrometer — Wet bulb — Decreases due to evap. — Dry bulb — Difference btwn. wet and dry bulb indicates rel. hum. — Large difference — Low rel. hum. — Small difference — High rel. hum. — No difference — Air is saturated Adiabatic Temperature Changes — When air is allowed to expand, it cools — When air is compressed, it warms — Parcel of air — — — — — Term used to describe a volume of air Moving upwards Pressure becomes lower as it goes up The air expands and cools 10oC per 1000 m — Dry adiabatic rate Processes That Lift Air — Orographic lifting — Air is forced to rise over a mt. Humidity Measurement — Measuring Relative Humidity — Hair hygrometer — Hair changes length with humidity — Increase in rel. hum. — Hair lengthens — Decrease in rel. hum. — Hair shrinks — Not as accurate as psychrometer — Electric hygrometer — Electrical conductor — Electrical current varies with rel. hum. — Used with weather balloons and stations Adiabatic Temperature Changes — 10oC per 1000 m — Dry adiabatic rate — If cools to dew point — Clouds form — Lifted condensation level — Latent heat given off — Rate of cooling reduced — Wet adiabatic rate — Varies 5-9OC per 1000 m Processes That Lift Air — Orographic lifting — Air is forced to rise over a mt. — Cools condenses — Clouds form — Frontal wedging — Warm, less dense air forced over cool dense air — Convergence — Then air descends — Cool air warms — Creates — Rain shadow desert — Converging winds force air upward — Localized convective lifting — Warm air rising 5 9/19/2011 Processes That Lift Air Processes That Lift Air — Frontal wedging — Warm, less dense air forced over cool dense air — Front- 2 different air masses collide — Warm Front — Faster moving warm air meets cold air — Warm air gets forced upward Processes That Lift Air — Localized convective lifting — Warm air rising — Thermals — (Cold air sinking) — Subsidence — Hot sunny afternoon — Convergence — Converging winds force air upward Atmospheric Stability — Stability — Stable Air — Parcel of air — Cooler than surroundings — Resists vertical movement — Doesn’t rise thunderstorms — Unstable Air — Parcel of air — Warmer than surroundings — Continues to rise Atmospheric Stability Atmospheric Stability — Different — Absolute Stability — Environmental Lapse Rate — Environmental lapse rate is less than wet adiabatic rate — Decrease in temp with altitude — 6.5oC per km — Avg. for entire troposphere — Adiabatic Rate When air expands, it cools When air is compressed, it warms Deals with parcels of air Dry adiabatic rate — 10oC per 1000 m — Wet adiabatic rate — Varies 5-9OC per 1000 m — — — — 6 9/19/2011 Atmospheric Stability Atmospheric Stability — Absolute Instability — Conditional Instability — Environmental lapse rate is greater than dry adiabatic rate — Environmental lapse rate is in between then wet and dry adiabatic rate Stability and Daily Weather — Stable Air — Widespread clouds — Horizontal clouds — Little to no precip. — Unstable Air — Towering clouds — Heavy precip. The stability of the air plays a major role in the type of weather we receive 7
