GEOG203-MaterialNotes-Sep7th&12th

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McGill University *

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Geography

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Oct 30, 2023

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GEOG203: Environmental Systems – Material Notes: Sept 7 th & 12 th Christopherson et al. pp.48-57, 66-72, 92-111 Wavelength: distance between corresponding points on any two successive waves. - According to Wien’s Displacement Law , all objects radiate energy in wavelengths related to their individual surface temperatures; the hotter the object the shorter the mean wavelength of maximum intensity emitted - Surface temperature of the sun: 6000 K (6273 degrees Celsius) Blackbody: a perfect absorber of radiant energy; it absorbs and subsequently emits all the radiant energy that it receives. - The sun, being a hotter object, emits a much GREATER amount of energy per unit area of its surface than does a similar area of a cooler object like earth - The suns radiated energy is shortwave radiation that peaks in the short visible wavelengths whereas earths radiated energy is long wave radiation concentrated in infrared wavelengths - Thermopause ; region at the top of the atmosphere (approx. 480 km above earths surface) o Outer boundary of earths energy system that provides a useful point at which to assess the arriving solar radiation before it is diminished by means of scattering and absorption in passage through the atmosphere Insolation (incoming solar radiation): solar radiation that is intercepted by earth o Applying specifically to radiation arriving at earth’s atmosphere and surface  Measured as the rate of radiation delivery to a horizontal surface; watts per square metre (W m 2 ) o *Watt = 1 joule (unit of energy) per second Solar constant: the average insolation received at thermopause when earth is at its average distance from the sun (value of 1372 W m 2 ) Subsolar point: the only point where insolation arrives perpendicular to the surface (hitting it from directly overhead) Net Radiation: balance between incoming short-wave energy from the sun and all outgoing radiation from earth and the atmosphere (energy inputs minus energy outputs) Seasonality - Seasonal variations are a response to the changes in the sun’s altitude, or the angle between the horizon and the sun - At sunrise or sunset, the sun is at the horizon, so its altitude is 0 degrees - If the sun reaches halfway between the horizon and directly overhead, it is at 45 degrees - If the sun reaches the point directly overhead, it is at 90 degrees altitude

Rotation - A little less than 24 hours in duration - Determines daylength - Creates the apparent deflection of winds and ocean currents - Produces the twice daily-rise and fall of the ocean tides in relation to the gravitational pull of the sun and the moon - Daylength at the equator is always evenly divided (12 hours of day 12 hours of night) o All other latitudes experience uneven daylength – except for two days on the equinoxes Revolution - Earths speed in orbit (107 280 km h) combined with earths distance from the sun, is what determines the time required for one revolution around the sun o Which then determines the length of the year and duration of the seasons Tilt of Earth’s Axis - Plane of the ecliptic : imaginary plane containing the Earth’s orbit around the sun - The tilt angle is said to be 23.5 degrees (23.45 degrees) Axial Parallelism - Earth’s axis maintains the same alignment relative to the plane of ecliptic and to Polaris and to other stars Sphericity - The shape of the earth causes the parallel rays of the sun to fall at uneven angles on earth’s surface - Earths curvature means that insolation angles and net radiation received vary between the equator and the poles Annual March of the Seasons - Extremes of daylength happen in December and June o The 21 st of both months are solstices

- Solstices are specific points in time at which the suns declination is at its position farther north at the tropic of cancer or south at the tropic of Capricorn - Tropic comes from “ tropicus ” meaning a turn or change o Thus, a tropic latitude: where the suns declination appears to briefly stand still and then turn and head toward the other tropic pp. 66-72 Atmospheric Composition Temperature and Function - Principle substance of the atmosphere is air (mixture of gases) - Beyond the limits of the atmosphere is the exosphere, “outer sphere” where the less dense atmosphere is essentially a vacuum (as far as 32000 km from earth) Atmospheric Profile - The pressure of the atmosphere (measured as force per unit area) pushes inward on all of us, and we also exert the same pressure outwards or else we would essentially be crushes by the mass of air around us Atmospheric Composition Criterion Heterosphere : outer atmosphere (begins at 80km altitude and extends outward to the exosphere and interplanetary space) - Gases in the heterosphere occur in distinct layers sorted by gravity according to their atomic weight (they do not mix) Homosphere : underneath the heterosphere; extends from an altitude of 80km to earth’s surface - Blend of gases Atmospheric Temperature Criterion Thermosphere - Also known as the “heat sphere” - Upper limit is the thermopause

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- Temperatures rise drastically to 1200 degrees Celsius or higher - The intense solar radiation in this part of the atmosphere excites individual molecules (mainly nitrogen and oxygen) to high levels of vibration (motion) o Kinetic energy (energy of motion) is the vibrational energy that we measure as temperature - Heat is created when kinetic energy is transferred between molecules, and thus, between bodies or substances – so because the density of molecules is so low, the number of molecules is not great enough to transfer heat to our skin and there is very little heat that is produced, thus we would label the heat in the thermosphere to be “cold” Mesosphere - Area 50km to 80km above earth – is within the homosphere - Mesopause = the outer boundary; coldest portion of the atmosphere averaging -90 degrees Celsius Stratosphere - Area from 18 to 50 km above earth’s surface - Temperatures increase with altitude - Outer bound = stratopause - Location of the o-zone layer - As greenhouse gases increase – a noted stratospheric cooling is the response Troposphere - Encounters incoming solar radiation as it surges through the atmosphere to the surface - Contains 90% of the total mass of the atmosphere and bulk of all water vapour, clouds, and air pollution - The tropopause (upper limit) is defined by an average temp. of -57 degrees

Atmospheric Function Criterion Ionosphere - Extends throughout the thermosphere and into the mesosphere below - Absorbs cosmic rays, gamma rays, x-ryas, and shorter wavelengths of ultraviolet radiation (changing atoms to positively charged ions) - Distinct regions: D, E, F1, F2 layers = important for broadcast and GPS signals - These particular regions reflect certain radio wavelengths including AM radio and other shortwave radio broadcasts Ozonosphere - Portion of the stratosphere that contains an increased level of ozone - Ozone is a highly reactive oxygen molecule made of up of three oxygen atoms (O 3 ) - Absorbs shorter wavelengths of ultraviolet radiation - UV energy is converted to heat energy, helping life on earth by filtering some of the sun’s harmful rays pp. 92-111 Energy-Balance Essentials - Earths energy budget: balance between shortwave solar radiation to earth, and shortwave and longwave radiation to space - Energy income: insolation / Energy Expenditure: radiation to space - Transmission: uninterrupted passage of shortwave and longwave energy through either the atmosphere or water - Earth- Atmosphere energy budget: o Shortwave radiation inputs: ultraviolet light, visible light, near-infrared wavelengths o Longwave radiation outputs: thermal infrared wavelengths - Energy budget is different at every location, as solar energy is unevenly distributed by latitude and fluctuates seasonally Types of Heat (Relating to Earth-Atmosphere Energy Budgets) - Sensible heat: can be sensed by humans as temperature; it comes from kinetic energy of molecular motion - Latent heat (hidden heat): energy loss or gain when a substance changes from one state to another Methods of Heat Transfer - Radiation: transfer of heat in electromagnetic waves (i.e., from sun to earth) o Temperature of the object/substance determines the wavelength of radiation it emits  Hotter the object = shorter the wavelength emitted - Conduction: molecule to molecule transfer of heart energy as it diffuses through a substance - Convection: transfer of heat by mixing or circulation (gases and liquids) In the atmosphere or in bodies of water: o Warmer (less dense) masses tend to rise o Cooler (denser) masses tend to sink This establishes patterns of convection; usually involves a strong vertical motion

Energy Pathways & Principles - Insolation (incoming solar radiation) o Consistent daylength and high sun altitude produce fairly consistent insolation values (approx. 180-220 watts per square metre) throughout the equatorial and tropical latitudes o Decreases towards the poles (25 ° latitude) in both the Northern and Southern hemispheres o Greater insolation at the surface occurs in low latitude deserts worldwide because of frequently cloudless skies Scattering & Diffuse Radiation - Scattering: accounts for a % of the insolation that does not reach earth’s surface (happens as a result of atmospheric gases, dust, etc., interacting with insolation to redirect radiation changing the direction of the lights movement) but is reflected back to space - Diffuse Radiation: energy that still reaches earth’s surface after scattering has occurred o Composed of waves travelling in different directions – therefore, casts shadowless light on the ground - Direct Radiation: energy that travels in a straight line to earths surface; unaffected - Refraction: the bending action that occurs when insolation enters the atmosphere - traveling through different mediums (i.e., empty space to atmospheric gases; air into water) that have an effect on its speed, subsequently shifting its direction Reflection and Albedo - Albedo: reflective quality or intrinsic brightness of a surface o Reported as the percentage of insolation that is reflected:  0% albedo = total absorption / 100% albedo = total reflectance - High Albedo: o Lighter coloured surfaces (i.e., snow) o Lower angles on water surfaces = more reflection o Smooth surfaces - Lower Albedo: o Darker coloured surfaces (i.e., asphalt) o Higher angles on water surfaces = less reflection o Rougher surfaces - Surfaces between the tropics (23.5 ° N to 23.5 ° S) “lower albedos”; about 19-38% - Polar regions tend to have higher albedos; 80% due to ice and snow Absorption: assimilation of radiation from one form of energy to another - Solar energy is absorbed by land and water surfaces (about 45%)

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- Solar energy is also absorbed by atmospheric gases, dust, clouds, and stratospheric ozone (approx. 24% total) Clous, Aerosols, and Atmospheric Albedo - Clouds reflect shortwave insolation so that less reaches earth’s surface, and they absorb long wave radiation leaving earth - Presence or absence of clouds can make about a 75% difference in the amount of energy that reaches the surface - Longwave radiation that gets trapped in an insulating cloud layer can create a warming of earth’s atmosphere; namely greenhouse effect Clouds and Earths Greenhouse - Low-thick stratus clouds reflect about 90% of insolation (high albedo) - Cloud albedo forcing : (cooling) an increase in albedo caused by such clouds, and the resulting cooling of earth’s climate - Cloud-greenhouse forcing : (heating) high-altitude crystal clouds reflect about 50% of incoming insolation, there cirrus clouds act as insulation, trapping longwave radiation and raising temperatures Latitudinal Energy Imbalances - Between the tropics : angle of incoming insolation is high; daylength is consistent; little seasonal variation; more energy is gained ( energy surpluses dominate ) - Polar Regions : sun is low, surfaces are light and reflective; approximately half the year, no insolation is received; more energy is lost ( energy deficits prevail )