Physical Geography Week 4 Notes
Physical Geography Week 4 Notes GEOG 101 001
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GEOG 101 001
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This 5 page Class Notes was uploaded by Julia Parenti on Wednesday February 24, 2016. The Class Notes belongs to GEOG 101 001 at Towson University taught by Dr. Ken Barnes in Spring 2016. Since its upload, it has received 30 views. For similar materials see Physical Geography in Geography at Towson University.
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Date Created: 02/24/16
Physical Geography Lecture 6 Solar Energy: Insolation and Flows Insolation The amount of solar radiation striking the earth’s surface determines relative rates of surface heating Energy striking the surface may be: reflected unused back to space (albedo) transformed into sensible heat transformed into latent heat via evaporation evaporation is a cooling process: removes heat from local environments Heat has the capacity to initiate movement or flows heat energy is unevenly distributed on the planet large scale circulations of the atmosphere and the ocean operate to redress global energy imbalances heat energy is transferred poleward via winds and ocean currents Heat Transfer Processes Conduction molecule to molecule transfer Convection energy transferred by vertical movement Advection energy transferred by horizontal movement Radiation energy traveling through air or space as electromagnetic waves Atmospheric Moisture: Relative Humidity, Dew Point, Condensation and Precipitation Relative Humidity One of several humidity measures to describe the amount of water vapor in the air Definition: the amount of water vapor present over the maximum amount of water vapor the air can hold (capacity) at any given temperature RH=(amount/capacity) x100 Dew Point: the temperature at which the air becomes saturated. Air declines in temperature to reach this point. Condensation: condensation of water vapor occurs once the temperature falls below the dew point Precipitation: occurs if water droplets or ice crystals in the atmosphere grow and gain sufficient mass to fall to the surface. occurs when air is forced to rise from the surface and air parcels cool below the dew point Condensation The process by which water vapor in the atmosphere changes phase from gas to tiny liquid droplets or ice crystals The conditions for required for condensation air must be saturated condensation nuclei must be present provides a mechanical surface upon which water vapor can condense centers of condensation and droplet / ice crystal growth dust ice salt pollen aerosols other fine particles Precipitation This is the collective name for moisture in liquid or solid form that is heavy enough to fall from the atmosphere o Drizzle sleet rain snow hail Hail is the product of precipitation that has made several round trips above the freezing level in the vertical currents of a cumulonimbus cloud. Have distinctive concentric growth rings Atmosphere must be unstable for precipitation to occur instability occurs when air is uplifted from the surface Mechanisms of uplift: convergence convection orographic frontal or cyclonic Adiabatic Heating and Cooling The change of temperature within a parcel of vertically moving air is because of expansion and compression When an air parcel expands, it cools When an air parcel compresses, it warms The rate of cooling is influenced by the relative humidity of the air parcel unsaturated air cools more rapidly than saturated air when air becomes saturated and water vapor condenses, liberated latent heat suppresses the rate of temperature decline Lapse Rates: Environment Versus Adiabatic Environmental Lapse Rate average =6.4 ºC/+1000 m apply to stationary air (temp change within the troposphere) varies daily and seasonally Adiabatic lapse rates apply to air parcels that are in vertical motion Dry adiabatic lapse rate: applies to unsaturated air. R.H. is less than 100% 10 º C/+1000m (9.8 ºC/+1000m_ 5.5 ºF/ +1000m sinking air warms by compression at +10 ºC/1000m Saturated (moist or wet) adiabatic lapse rate R.H. is 100% the liberation of latent heat slows the rate of cooling 5 or 6 ºC/+1000m depends on the amount of water vapor and temperature 3.3 ºF/+1000m Greenhouse Effect Make the earth habitable average global temp would be about 28 ºC (50 ºF) colder The atmosphere allows visible light (shortwave) radiation to pass through shortwave is transformed into heat energy (terrestrial radiation) at the earth’s surface The atmosphere slows the flow of long wave energy from the surface to space absorbs heat energy radiated from Earth’s surface delays transfer of heat from Earth into space heat is countradiated back to the surface heat is energy is recycled several times between the surface and the atmosphere before is escapes to space The gases responsible include: water vapor CO2 Methane CFCs Lecture 7 The Global Distribution of Solar Energy Energy in the Earth: Atmosphere System The sun’s radiation on the earth’s surface is unevenly distributed due to the curvature of the earth’s surface (sphericity) produces latitudinal differences of temperatures Reasons for Spatial and Temporal Variations in Insolation Geographical and temporal variations in solar energy received at the surface are a function of sun angles Daily variations in solar energy received at the surface are due to rotation Seasonal variations in solar energy received at the surface are due to: axial tilt: 23.5 degrees parallelism: axis remains pointed in a constant direction in space revolution: annual orbit of the earth around the sun changing length of the daylight period Insolation and Sun Angles Tropics receive more concentrated insolation due to the Earth’s curvature Receive 2.5x more solar energy than the poles o Surface insolation is a function of sun angles high sun angles energy is more concentrated on surface low albedo: low over both land and water surfaces passes through shorter distances in the atmosphere less opportunity for loss of radiation o Low (oblique) sun angles energy is less concentrated on surface temperatures are lower at the surface High albedo (especially over water) pass through greater thickness of the atmosphere less solar energy reaches the surface Subsolar point and declination Subsolar point: the point on the earth’s surface being struck by the vertical (direct) rays of the sun due to surface curvature, only one point at any given time experiences the direct (vertical) rays of the sun no shadows are cast when sun is directly overhead Declination: the latitude of the subsolar point the subsolar point changes position throughout the year shifts a total of 47 degrees of latitude from: 23.5 degrees N (tropic of cancer) to 23.5 degrees S (tropic of Capricorn) never poleward of these two latitudes Solar Noon: Sun at its highest daily position in the sky (above horizon). highest daily sun angle Time of greatest insolation peak temperature lags behind peak insolation Energy Imbalance Surplus energy to redress energy imbalances is transported poleward by: winds transporting sensible and latent heat in water vapor ocean currents transporting sensible heat Significant Seasonal Events: Northern Hemisphere Winter solstice December 21 or 22 subsolar point located on tropic of Capricorn Spring equinox March 20 or 21 subsolar point located on Equator Summer solstice – June 20 or 21 subsolar point located on Tropic of Cancer Fall equinox – September 22 or 23 subsolar point located on equator The events and dates are reversed for the southern hemisphere
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