Geography Notes 2.18.16
Geography Notes 2.18.16 Geog 1112
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This 4 page Class Notes was uploaded by Tizhana Turner on Monday February 22, 2016. The Class Notes belongs to Geog 1112 at Georgia State University taught by Zaina Qureshi, Lashonda J. Williams in Fall 2015. Since its upload, it has received 23 views. For similar materials see Intro to weather and climate in Geography at Georgia State University.
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Date Created: 02/22/16
Geography 2.16.16 What’s going on with the weather today? Any clouds? What does it look like? Wispy, lumpy, sheety? Yes, lumpy clouds. Temperature warm or cold? Cool, but warmer than yesterday. Is it humid? no Any precipitation? Yes last night Is it windy? yes Measuring Humidity: Hair Hygrometer Principle: Human hair changes in length with respect to changes in relative humidity. Measuring Humidity: Sling Psychrometer Two thermometers on a swinging device. Wet “sock” – wetbulb temp Dry air temp. Twirl instrument, water evaporates. Use air temp, wetbulb depression to find RH. Measuring Humidity: Satellites Water vapor absorbs Infrared. (IR). Light areas= high amounts of water vapor. Dark areas= low amounts of water vapor Important for weather forecasting! Chapter 7 pt. 2 Stability: When will air rise? Air parcel: Large “bubble” of air with uniform temperature and humidity. Stability: Tendency of an air parcel to rise or sink on its own. (Often depends on air parcels becoming saturated). How to Reach Saturation Depends on moisture in the air and temperature. Increase the water vapor. Lower the temperature How? Add moisture, Mix air masses together, and lift individual air parcels. When air is saturated, T=Td and RH= 100% Add water vapor: Ex: rain evaporating Mix warm and cold air: Changes temperature and water vapor content. Ex: contrails and visible breath. Lifting Air Parcels Air parcel forced to rise. Expands due to lower pressure. Temperature cools Most common method of cloud formation Methods of Lifting Air Convergent Lifting Convectional Lifting Orographic Lifting Frontal Lifting Lapse Rates; Adiabatic and Diabatic Processes Lapse rate: change of temp. with height Adiabatic: no loss or gain of heat (expansion and compression of air) Diabatic: heat exchange involved. Lapse Rates: Adiabatic Cooling When an air parcel rises, it expands and the temperature decreases. A parcel cooler than the surrounding air is denser becomes compressed and warms as it sinks. Lapse Rates: Dry Adiabatic Rate (DAR) Better name: Unsaturated adiabatic rate Rate which the temperature of n unsaturated (RH<100%) air parcel will change as it rises/sinks Average DAR: 10 degrees C/km. Adiabatic Cooling at the DAR Air parcels cools internally as it expands under lower air pressure. Saturation by Lifting Dew point of the unsaturated air parcel does not change Wen rising air parcel cools to the dew point, it becomes saturated. Height of saturation, cloud bases= Lifting Condensation Level (LCL) Lapse Rates: Saturated Air Parcel Saturated air above the LCL cools at a slower rate than the DAR. Due to latent heat release. (condensation releases heat, partially offsets adiabatic cooling) Lapse Rates: Moist Adiabatic Rate (MAR) Better name: Saturated adiabatic rate Variable number More condensation= more latent heat release = smaller MAR Average: 6 degrees C/km 2.18.16 What’s going on with the weather today? Any clouds? What does it look like? Wispy, lumpy, sheety? no Temperature warm or cold? Cool, but warmer than yesterday. Is it humid? no Any precipitation? No Is it windy? No wind Air Forced Up a Mountain (From CH.8) Below LCL: Unsaturated air cools at Dar Dew point doesn’t change Above LCL: Saturated air cools at MAR Dew point cools at MAR Result: clouds and precipitation on windward side. Air Forced Down a Mountain Clouds “rained out” at top of mountain Unsaturated air parcel temperature warms at DAR Dew point doesn’t change. Result: Clear skies; warmer and drier on leeward side. M0untain Recap Windward side (upslope): Cool, cloudy, and wet Leeward side: (downslope): warm, sunny, dry (rain shadow) Deserts often downwind of large mountain ranges. Atmospheric Stability Stability: The tendency of an air parcel to rise or sink on its own Why important? Stability affects clouds and precipitation What determines if air will rise or sink? Density differences between air parcel and environment Air parcel denser than environment: parcel sinks Air parcel less dense than environment: parcel rises Ideal gas law: Density inversely related to temperature. As temp. goes up, density goes down Parcel colder than environment: parcel sinks (stable) Parcel warmer than environment: parcel rises (unstable) Types of Stability: Absolutely Unstable How to determine if an unsaturated air parcel will rise or sink Compare environmental lapse rate (ELR) to DAR and Mar ELR bigger than DAR? Parcel rises (Absolutely Unstable) Clouds of vertical development; tstorms Unstable as the environment lapse rate is greater than the dry adiabatic lapse rate, e.g., the environmental lapse rate = 12 degrees C/1000m Types of Stability: Absolutely Stable ELR smaller than MAR? Parcels sinks (Absolutely Stable) Clear skies; layered or wispy clouds if air s forced to rise. Temperature inversions and trapped pollution in extremely stable conditions. Stable as the environment lapse rate is less than the moist adiabatic lapse rate, e.g., the environmental lapse rate = 5 degrees C/1000m. Types of Stability: conditionally Unstable Unsaturated air parcel stable, becomes unstable when saturated. ELR in between DAR and MAR: Conditionally Unstable Vertical clouds/tstorms (in unstable layer) Georgia in summer Conditionally unstable as the environment lapse rate is greater than the moist adiabatic lapse rate and less than the dry adiabatic lapse rate, e.g., the environmental lapse rate= 7 degrees C/1000m.
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