EESB04 - Review List.pdf

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University of Toronto Scarborough
Environmental Science
Carl Mitchell

EESB04 Review Lecture 2: Hydrological Concepts and Physical Properties of Water - What is Hydrology? - Delineating a watershed - Water balance: S = In Out - Measuring rainfall - Spatial Variability changes over space - Temporal Variability changes over time - Residence Time (T ) R = (assuming input = output) - Spatial distribution of Water - The Hydrological Cycle 1) The land receives more precipitation than evapotranspiration 2) Oceans evaporate more than it receives precipitation 3) Excess of water on land returns to oceans as runoff, which balances #1 and #2 - Principle driving forces of the Hydrological cycle: Solar energy and gravity - Spatial variability in global precipitation (the middle finger graph) - Spatial variability in global evapotranspiration - Spatial variability in global run off - High precipitation + low evapotranspiration = high runoff - Low precipitation + high evapotranspiration = low runoff - Hydrological Models - Empirical statistical relationships, not robust - Deterministic known physical relationships, more robust - Stochastic - statistics - Typical Hydrological Model Structure - Basic models: inputs model outputs - Complex models: outputs may be used for inputs for another model - Typical inputs and outputs - Sensitivity Analysis - Small change = not sensitive, big change = sensitive - Models are made for relative comparisons, and variables with no sensitivity are insignificant in the model - Physicochemical Properties of Water - Molecular structure of water - 3 States: solid, liquid, gas - Hydrogen bonding, strong covalent bonds between O and H - Without H-bonding, water would be a gas (water vapour) at room temperature - Asymmetric structure - 105 angle between the 2Hs in H-O-H - Surface tension, an electrochemical attraction because of hydrogen bonding - Capillarity the upward movement of water, due to effects of wetting and surface tension - Meniscus - The smaller the diameter, the further water can travel up a tube - Phases of Water (remember the terms and molecular structure) - Liquid (Water) and Solid (Ice) freezing and melting - Liquid (Water) and Gas (Water vapour) vaporization/evaporation and condensation - Gas (Water vapour) and Solid (Ice) sublimation and sublimation - Sublimation solid turning into gas (and vice versa) without becoming a liquid - Why do ice cubes float? - Water density maximum is 1.00g/cm at 4C 3 - When temperature drops below that, water becomes less dense and forms hexagonal crystals of ice (less dense), therefore ice floats - Density of Water - Water contracts as it cools, but only to a point at 4C - Beyond 4C, water expands as more H-bonds form hexagonal structures until -29C - Phase Changes - Heat energy is either absorbed or released to change from one phase to another - Amount of heat energy required to break the h-bonds - 1 calorie = 4.184 J (joules) - Ice Water Water Vapour latent heat is absorbed to break h-bonds - Water Vapour Water Ice latent heat is released to form h-bonds - Latent Heat (2 types) - Latent heat involved in phase changes of water - Sensible heat heat that you feel or sense Lecture 3: The Energy Balance and Water in the Atmosphere - Radiation energy in the form of waves and sub-atomic particles - Plancks Law wavelength of energy emitted by a surface decreases as temp increases - Wiens displacement law calculates wavelength at which max energy radiation occurs - max = T = temperature (in Kelvin) - The electromagnetic spectrum - Shorter = blues, violets - Longer = reds - Energy pathways and principles - Driver of energy on Earth is radiation from the Sun - Drivers of spatial & temporal variation: seasons, latitude, clouds, surface characteristics -6 - 1 m = 1.0 10 m - Insolation = INcoming SOLar radiATION - It is shortwave radiation (inputs are UV, visible light, near-infrared wavelengths) - Energy outputs from Earth - Surface Radiation Balance - Direct vs. Diffuse radiation - Shortwave vs. Longwave radiation - Water vapour the most dominant GHG, absorbs Earths long - GHG increase absorption of energy, not necessarily more reflectivity - Measuring energy depends mostly on the surface temp of the body emitting it - Wiens law = what type of energy - Stefan-Boltzmann law = how much energy moved per area per unit time - Q R T 4 - Blackbodies 100% efficient in emitting energy (Ex. Sun, Earth) - Darker things tend to have higher , lighter things have a lower - Solar constant - Suns energy arrives at edge of atmosphere at an average of 1.74 10 W 17 14 2 - Area of Earth is 1.28 10 m - Isc Suns Energy / Area of Earth = 1367 W m Solar Constant - Energy Balance (Fig. 3.2 slide 17) - About of the energy received at the top of the atmosphere is absorbed by the Earth - Clouds and atmosphere play a role in absorption and reflection - Outgoing energy + Incoming energy = 100 (100 units represents the solar constant) - Albedo determines the ability of a substance to reflect energy - Albedo = reflecting radiation / incoming radiation = K/K - Albedo of water extremely variable because of surface, angle of incoming radiation, etc. - Smooth surfaces increase while rough surfaces decrease - Incoming radiation (energy) is absorbed, moved around (spent) as sensible energy - Radiation balance (Q*) - Short energy balance = incoming short reflective short K* = K - K - Reflective short = albedo incoming short K = K - Long energy balance = incoming long reflective long L* = L - L - Radiation balance Q* = K* + L* (net radiation) - 24 hour Q* graph - Heat Transfer at Earths surface by several processes - Conduction molecular transfer - Convection heat transfer by vertical movement - Advection heat movement of liquid or gas horizontally - Expenditure of Net Radiation (Q*) - 3 ways that net radiation is expended from a surface: LE, H, G - Latent heat of Evaporation (LE) energy stored in water vapour as water evaporates - Sensible Heat (H) back and forth transfer between air and surface via convection and conduction - Ground heating or cooling (G) energy flowing through ground only via conduction - Relationship between Net Radiation (Q*) and Expenditure of Net Radiation - We already know that Q* = K* + L* - Expenditure Q* = LE + H + G - So therefore, K* + L* = LE + H + G - Partitioning of LE and H - Main factor is available moisture - A system that is moist will use more latent energy - A system that is dry uses more sensible energy (less water to evaporate) - Review the example of you being at the shore vs. in the middle of the lake! - Bowen Ratio describes type of heat transfer in a water body - - = > 1 = more H than LE, < 1 = more LE than H - Importance of Precipitation - Latent energy a driving force for evaporation and precipitation - Rain and snow are main hydrological inputs to the surface of the Earth - Precipitation a major control on vegetation and ecology - Understanding precipitation inputs is critical (ex. Planning purposes) Lecture 4: Precipitation and Interception - Forming Precipitation (3 processes must occur) 1) Cooling to the dew point 2) Condensation onto nuclei 3) Droplet growth - For precipitation to occur for any appreciable time, this 4 process must occur 4) Importation of water vapour (ex. hurricanes suck in so much air which leads to more precipitation) - Cooling to the Dew Point - Dew point the temperature at which a given parcel of air becomes saturated - Condensation occurs when air parcel cooled beyond dew point or if moisture is added to an air parcel already at dew point - Vertical uplift the common means of cooling air, results in adiabatic cooling - Adiabatic Cooling - The cooling of an ascending air parcel without heat exchange between the parcel and surrounding air mass - Air parcel expanding as it rises because less pressure - Review the 4 key points of air parcel and adiabatic cooling (slide 31) - Dry (DALR) vs. Saturated (SALR) Adiabatic Cooling - DALR: 1C / 100 m (when parcel of air < saturated vapour pressure) - SALR: 0.5C / 100 m (when parcel of air saturated vapour pressure) - Review the Saturation Vapour Pressure graph - Saturation Vapour Pressure the pressure exerted by water vapour molecules in the air when air is saturated with water vapour
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