Final Exam Notes

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Atmospheric & Oceanic Sciences
ATOC 181
Daniel Kirshbaum

ATOC 181 Final Exam Concepts 1: THE EARTH AND ITS ATMOSPHERE Depth and Structure of Atmosphere  atmosphere: thin film of gases & tiny particles (aerosols) surrounding the earth o 99% of mass confined to layer of 0.25% earth’s radius o shields humans from ultraviolet radiation o essential for lif2 (H O2 C2 , O ) o depth = 30 km; weather contained in lower 10-15 km  spheres: layers  pauses: boundaries between layers Layers of the Atmosphere Layer Characteristics - surface up to 12 km troposphere - temperature decreases with height (~6.5°C/km) - where weather occurs - thunderstorm clouds often reach tropopause - temperature initially isothermal (constant) then increased stratosphere with height up to ~50 km - site of ozone layer - may impact weather over season time-scales mesosphere - temperature decreases with height up to ~80 km thermosphere - temperature increases with height  homosphere: well mixed “lower” atmosphere o 8% N 2 21% O2  heterosphere: poorly mixed “upper” atmosphere  ionsphere: electrically charged region with ions & free electrons o plays major role in radiocommunications since it reflects AM signal, allowing transmission over large distances o D region absorbs radio waves, weakening surface signal; much stronger during daytime due to photo ionization Atmospheric Composition  78% N 2 21% O2  H2O ranges from -4% (0 in poles, 4 in tropics)  trace amounts of CO2, 3 & other gases  aerosol particles: suspended tiny soil, salt, ash particles  pollutants: sulphur, nitrogen oxides & hydrocarbons Importance of Ozone, Carbon Dioxide & Water Vapour  ozone (O ) 3 o 97% in upper atmosphere where it forms naturally o shields earth from ultraviolet radiation o layer being depleted near poles by chlorofluorocarbons (CFCs) from spray cans/refrigerants o at surface, primary ingredient in photochemical smog o irritates eyes/throat, damages vegetation  carbon dioxide (C2 ) o used by plants for photosynthesis to produce oxygen o absorbs portion of earth’s outgoing radiation & radiates it back to earth (greenhouse gas) o concentration increasing rapidly  water vapour (H2O) o produced by evaporation/sublimation; lost by condensation/deposition o condenses to form clouds o stores latent heat (released in thunderstorms/hurricanes) o critical global circulation factor o highly effective greenhouse gas o initially water vapour produced by volcanoes, then evaporation of liquid & sublimation of ice contributes to formation of water vapour Greenhouse Effect & Greenhouse Gases  gases & clouds absorb radiation emitted by earth & reradiate it towards earth  some IR is absorbed by atmosphere & is emitted back to surface since doesn’t escape back to space  greenhouses heat up due to lack of vertical mixing  selective absorbers o greenhouse gases generally poor shortwave absorbers but good long wave absorbers o CO , H O, CH , O 2 2 4 3 o O 3bsorbs best in UV o H2O most important/effective greenhouse gas  role of clouds o selective absorbers with competing effects  absorbs IR even in atmospheric window  reflects solar radiation  warms @ night, cools during daytime o large droplets scatter all light wavelengths so clouds appear white o reflection/transmission/absorption depends on cloud type  cirrus: transmission of shortwave (enhances greenhouse effect)  low clouds: reflection of shortwave (opposes greenhouse effect) Mass, Density, Weight & Pressure  mass: the amount of matter/material in the sample volume (kg)  density: the concentration of mass; mass ÷ volume (kg/m ); how much matter there is in a given space o important for buoyancy  weight: the force exerted by the mass due to gravity; mass x gravitational acceleration (kg – m/s )  pressure: the weight of the overlying air column; force per unit area o not felt because it acts in all directions o body’s internal pressure adjusts to atmosphere, so there is no pressure difference Pressure, Density & Temperature Profiles  pressure & density decrease rapidly with height  density may be uniform in well-mixed layers  density decreases with height because heavier particles of air descend  temperature generally decreases with height but is reliant on the layer of the atmosphere o decreases, increases, decreases, increases 2: ENERGY: WARMING THE EARTH AND ITS ATMOSPHERE Energy  energy: the capacity to do mechanical work on some object or fluid; constantly being transformed  work: the motion of an object or fluid resulting from an applied force Forms of Energy Characteristics - energy that results from objects/fluids in motion kinetic energy - ½ mv2 - energy a body possesses in virtue of its position with respect to other gravitational potential energy bodies in the field of gravity - PE = mgh - the collective microscopic kinetic & potential energy of molecules in a substance internal energy - action controls temperature/air - not that different from kinetic, just microscopic - energy propagated in form of electromagnetic waves - all bodies emit electromagnetic waves (ie/ sun) radiant energy - vibration of charged particles within atoms generative electromagnetic fields - every object with a temperature is emitting electromagnetic radiation Conservation of Energy & Adiabatic Processes  1 law of thermodynamics: energy can’t be created nor destroyed, it merely changes form  heating to system must be balanced by work and/or increase in internal energy  without external heating/cooling, work is balanced by changes in internal energy (adiabatic processes)  adiabatic = no heat exchange with surroundings Temperature & Heat  temperature: measure of the kinetic energy of the atoms/molecules within a substance o closely related to internal energy (kinetic part) o slower atomic motions = cooler temperature o molecules move faster as temperatures increase o units: °C, K, °F o at 0 K = -273°C = -495°F, molecular motion ceases (no movement, coldest temperature possible) o thermometer uses fluids/metals that expand as temperature increases & contract as temperature decreases  heat: energy in transit from a hot body to a cold body o after, transfer energy is stored as internal energy o units: calorie (energy needed to heat 12g of H O by 1°C) Specific Heat  heat capacity: ratio of heat added to a substance to its corresponding temperature rise  specific heat capacity: amount of heat required to raise the temperature of 1g by 1°C  takes 4x more energy to heat water than air o explains why oceans take longer to heat up than the air in the summer o UK has much milder winters than Canada since it is surrounded by water to temperature doesn’t change as fast; Canada gets cold air from Arctic & since there isn’t a lot of water, the process isn’t slowed down Latent Heat  latent heat: the energy required to change a substance from one phase to another at a constant temperature  different phases are associated with different molecular configurations o solid: most orderly, least energetic o gas: least orderly, most energetic  to make shift, heat must be absorbed or released  condensation of liquid (from vapour) and ice (from liquid) releases heat o drives cumulus convection o intensifies mid-latitude cyclones o global circulation control  evaporation from surface & clouds/precipitation provides vapour & colds the air  tropics have highest air & sea surface temperature o air can hold more water vapour which it receives through evaporation from warm ocean Heat Transfer Mechanisms  convection + conduction = sensible heat transfer (direct)  conduction: molecular transfer of heat from warm to cold regions o warmer substances = faster molecular motion o collide with nearby molecules, imparting momentum & energy o heat spreads towards colder regions o conductivity: to ability for a material to conduct electricity/heat; speed depends on the material  convection: transfer of heat by mass movement of a fluid; separated into convection & advection; matters more than conduction o relies on instability of atmosphere o occurs naturally in daytime due to solar heating  air near surface warms & becomes lighter  lighter air is buoyant, causing it to rise  cooler, heavier air sinks to take it places o convection: vertical circulations driven by thermal heterogeneities o advection: transfer of properties from one region to another due to bulk motion of air; for warm & cold advection, wind direction must cross isotherms (lines of constant temperatures)  warm advection: wind blows from warm to cold places, warming it up  cold advection: wind blows from cold to warm places, cooling down o convection & adiabatic heating  adiabatic: no heat exchange between parcel and surroundings  rising branches  moves into lower pressure  expands to equilibrate pressure with surroundings  expansion takes work which cools the air  sinking branches  moves into higher pressure  atmosphere does work on parcel, so temperature increases  radiation: all bodies warmer than absolute zero emit electromagnetic radiation o associated with random vibrations of electronics o propagates waves or photons (discrete packets of energy) o properties of waves  wavelength (λ): distance between wave crests  frequency (ƒ): rate of oscillation; rate at which wave crests pass a fixed point  phase speed (v): phase at which a wave travels o warmer = fast electron vibration, shorter wavelengths, higher frequencies, faster speeds, more energetic o Wien’s Displacement Law: relates wavelength of maximum radiation emission to temperature  λ = C/T  sun emits higher energy radiation at a much shorter wavelength  higher temperature = smaller wavelength  lower temperature = larger wavelength 4 o Stefan-Boltzmann Law: radiant energy is proportional to T  small increase in temperature leads to a large increase in electromagnetic radiation Solar Radiation in the Atmosphere  transmission: passes straight through  scattering: deflection of light in all directions by small particles; produces ‘diffuse’ radiation; more effective at short (blue) wavelengths  reflection: light sent mainly backwards instead of all directions  absorption: light absorbed by molecules in the air; ozone is a molecule that absorbs ultraviolet light Absorption, Emission, Transmission, Reflection  absorption & emission o if body emits more energy than it absorbs, it cools; if body absorbs more energy than it emits, it warms o at any time, only ½ the earth is under sunlight  light half: shortwave absorption > infrared emission  dark half: only infrared emission o shortwave: visible light o longwave: infrared light; emitted by the earth o blackbody: an object that absorbs all incoming radiation & emits the maximum radiation possible; ie/ sun & earth’s surface  reflection: waves bounce against objects & return to space depending on surface cover & angle of sun o snow reflects 95% of radiation o water reflects 98% of radiation o albedo: fraction of incident radiation that is reflected  earth primarily ocean & forest so albedo low  4% earth, 20% clouds, 6% scattered back to space  higher/larger albedo = higher reflection Earth’s Energy Balance  equator-to-pole heat transfer needed for steady climate  if not, poles would cool forever & equator would heat forever  point: understand there is stuff coming down & stuff coming up 3: SEASONAL & DAILY TEMPERATURES The Seasons  annual variability in earth-sun distance  earth has less elliptical (non-circular) orbit o 6.5% less radiation in Northern Hemisphere summer  controlled by 2 things: o intensity of radiation: radiant energy received per unit area o amount of daylight: length of time between sunrise & sunset o both larger in the summer Differences in Day Lengths  solstices: longest/shortest days of the year; either 24 hours of light or 24 hours of darkness at poles; lasts for 1 day at arctic circle, 6 months at poles o Arctic circle = 1 latitude getting full day of sunlight (June 21)& full day of darkness (December 21)  equinoxes: 12 hours light, 12 hours darkness everywhere  equator: 12 hours light, 12 hours darkness year round; gets same amount of sunlight all year round  in Canada we get more sunlight in summer & less in the winter  days longer at poles Diurnal Cycle of Temperature  landscape variations o south facing landscapes receive more insulation/sensible warming/evaporation  differences in North & South lead to difference in snow depth, vegetation type, etc. o vegetation cover moderates temperatures  dry soil: nothing for sunlight to evaporate so temperature warms up  moist soil: sun will evaporate the water & create humidity  daytime heating o ground absorbs shortwave radiation causing it to warm  conduction: heat transferred to lower atmosphere  convection: thermals transfer heat vertically  te1mperature rises until long wave emission exceeds shortwave insulation  heat that is lost is mainly due to long wave radiation; amount depends on temperature  temperature heats up as you receive more radiation keeps warming throughout day o in weak winds, strong temperature gradients may exist near surface  convective eddies transport some heat  in strong winds, wind shear & surface drives eddies that effectively mix heat vertically  decreasing temperature with height because with height, temperature from earth mixes with atmosphere  nighttime cooling o earth & atmosphere are always emitting heat o efficient radiator = surface; cools down faster o convection suppressed by strong stability  cold/heavy air beneath warm/light air o radiation inversion forms on calm/clear nights  no thermals that help to mix air vertically  thermals rely on having light air trying to rise & heavy air sinking, so they mix  at night, heavy air below & light air above Controls of Diurnal Cycle  higher solar angle = more heating; lower solar angle = less heating  vegetation type o controls ratio of sensible heat to latent heat o controls moisture content near surface o forests don’t heat up as much as pavement  water vapour & clouds o reduce heating rate (day), cooling rate (night) o moisture in air means radiation that leaves earth comes back because of water o cloudy night is warmer because warm air trapped  winds o stronger winds diminish extremes due to mixing of winds Controls on Temperature  latitude o controls sun & amount of daily sunlight o temperatures decrease towards poles from tropics in subtropics o greater variation in solar radiation between low & high attitudes in winter than summer (isotherms closer together (tighter gradient) in January than in July  land & water distribution (continentality) o temperatures are lower in middle of continents that near the ocean in January; reverse for July o attributed to unequal heating & cooling properties of land & water o solar energy reaching land is absorbed, reaching water is penetrated o water has a high specific heat capacity o hurricane season is September-October because that is when the water is warmest  ocean currents o eastward: warm ocean currents transport warm water polewards o westward: cold water transport equatorward  elevation  vegetation cover 4: ATMOSPHERIC HUMIDITY The Hydrologic Cycle Phases of Water  gas: molecules far apart, moving about freely (highest energy)  liquid: joined together but still constantly jostle & bump into each other  solid: rigidly locked into place with some vibrational activity (lowest energy)  phase changes: liquid to vapour o sealed beaker with dry air above water surface o initially, fast moving liquid molecules escape (evaporation) o as vapour builds up in air, slower moving vapour molecules begin to enter liquid (condensation) o vapour increases until these two processes come into equilibrium (saturation)  controls on evaporation o solar radiation: excites liquid water molecules allowing them to escape (increases evaporation) o warmer temperatures: faster molecular motion (increases evaporation) o stronger winds: blow/mix near-surface moistened layers away (increases evaporation) o humidity moister air closer to saturation, less capacity for vapour (decreases evaporation) *Quantifying Atmospheric Moisture  absolute humidity: total water vapour mass in a volume of air o depends on density of water vapour & volume o parcel size = parcel volume o doesn’t give a real intuition of how much humidity in air  specific humidity: water vapour mass divided by total air mass o highest in tropics since warm air can absorb more water vapour before reaching saturation  mixing ratio: the amount of water vapour in the air divided by the dry air mass o very similar to specific humidity since total air mass dominated by dry contribution  relative humidity: ratio of the amount of water vapour in the air to the maximum amount of water vapour required for the saturation at that temperature & pressure o RH = vapour pressure ÷ saturation vapour pressure = (mixing ratio ÷ saturation mixing ratio) x 100% o if RH = 100% air is saturated o if RH > 100% air is supersaturated o if RH < 100% air is subsaturated  relative vs. specific humidity o specific humidity follows temperature o relative humidity trends more reflective of climate Vapour Pressure  vapour pressure: total air pressure comprised of many individual components o if water vapour high enough, air reaches saturation (reaches capacity to hold water vapour)  strongly depends on temperature  depends on phase (lower for ice)  boiling occurs when saturation vapour pressure matches environments air pressure Dew Point vs. Wet Bulb  dew point: temperature to which air must be cooled at constant pressure to reach saturation  wet bulb: coolest temperature that can be reached through evaporation of water vapour *Moisture Source Regions  south-central & eastern Canada affected by hot, humid air originating in Gulf of Mexico  other parts of Canada affted by cooler, less humid air from Pacific or cold air from Arctic oceans 5: CONDENSATION, FEW, FOG & CLOUDS Dew & Frost  surface cools as it emits long wave radiation  through conduction, air lays in contact with surface also cools  liquid/ice may condense/deposit onto surfaces that transpires moisture/poor at storing heat at above/below 0°C  controls o clouds: trap heat in atmosphere preventing surface from effectively cooling o water vapour: traps heat limited dew/frost potential, but increases dew point o winds: turbulently mix near surface air with warmer air above limiting dew/frost potential  frozen dew: liquid dew formation followed by freezing; ie/ black ice  dry freeze/black frost: plants freeze due to subfreezing air  hoarfrost/white frost: deposition forms delicate tree-like crystals Condensation Nuclei  provides surfaces for water vapour to condense on  water molecules don’t like to stay together when they collide, so attracted to impurities in the air  have difficulty forming in clean are due to surface tension  largest concentrations of nuclei in lower atmosphere near earth’s surface  light so remain suspended in air for many days  hygroscopic (water-seeking) vs. hydrophobic (water-repelling)  heterogeneous nucleation at RH = 100%  homogeneous nucleation of droplets in clean air require RH > 100%  hygroscopic nuclei attract water vapour, allowing condensation at RH < 100% Sizes & Concentration of CCN & Cloud Droplets Type of Particle Approx. Radius # of Particles Per Cubic small (Aitken) condensation nuclei < 0.1 1000 – 10 000 1000 large condensation nuclei 0.1 – 1.0 1 – 1000 100 giant condensation nuclei > 1.0 < 1 – 10 1 fog & cloud droplets > 10 10 – 1000 300 Haze  haze: a layer of dust or salt particles suspended above a region  dry: particles scatter light reducing visibility  wet: condensation on hygroscopic nuclei @ RH < 100%  caused by pollution & other aerosols  particles make the air not clear since they deflect light Fog  cloud: region of condensed water droplets suspended in the air; scatter full spectrum of light so they look white  clouds based at ground are fog or mist o fog: lower visibility (< 0.8 km) o mist: higher visibility (> 0.8 km and < 10 km)  radiation fog: forms due to radiation cooling at surface; aided by weak winds that mix up low levels of spread cooling over deeper level; forms best on clear nights when shallow layer (doesn’t absorb outgoing infrared radiation) of moist air near ground is overlain by drier air  advection fog: warm air passes over cold; surface must be sufficiently cooler than air above so transfer of heat from air to surface will cool air to dew point & produce fog  upslope fog: air cools as it ascends up a slope; forms as moist air flows up along elevated plain, hill or mountain;  evaporation fog: water content increased by evaporation from water surface or from raindrops o steam fog: above warm body of water; forms over lakes on autumn mornings as cold air settles over water still warm from long summer o frontal fog: rain falls through a cold lower layer; develops in shallow layer of cold air just ahead of approaching warm front of behind cold front  mixing fog: mixing of 2 unsaturated parcels of different temperature can produce a cloud Basic Cloud Types  cumulus: white to light gray, puffy; vary in shape due to vertical development; often have rounded domes/towers at top; on humid days composed of water; when they reach the tropopause they can be composed of water & ice; appear harmless but turn into most severe thunderstorms  stratus: stable layer cloud; sheets of clouds; most general type; generally don’t produce precipitation, but sometimes light drizzle over coastal waters; low, uniform bases; composed of water  cirrus: most common type of high clouds; thin & wispy; made of ice; sun shines through them; if thicker would be stratus; moves west to east; movement indicates prevailing winds at their elevation & point to good weather; formed in lower temperatures Satellite Images  geosynchronous: moves through space at same rate as earth rotates; remains above fixed spot on equator & monitors one area constantly  polar orbiting: see whole earth; goes around & around the earth; scans from north to south; on each successive orbit, satellite scans an area farther to the west  visible  IR  IR enhanced  infrared water vapour images: detects radiation at wavelengths of water vapour emission  water vapour images: shows amount of moisture in mid-to-upper troposphere  TRMM: polar orbiting; visible, infrared scanners, microwave images & radar; 3D  CloudSat: mm wavelength radar on satellite; provides detailed cloud structure 6: STABILITY AND CLOUD DEVELOPMENT Adiabatic Processes  parcel: a small, coherent mass (bubble) or air o when forced to rise/sink, it expands/compresses & changes temperature  if no heat exchanged with environment, process is adiabatic  work done to equilibrate pressure between air parcel & surroundings changes parcel temperature  adiabatic process: parcel that expands & cools, or compresses & warms with no interchange of heat with its surroundings  the dry adiabatic lapse rate o approximately 10°C/km o rising air cools, sinking air warms  specific humidity doesn’t change, but relative humidity does  rising parcel brought closer to saturation o compression will warm up parcel by 10°C, it is a constant o further lifting results in condensation (cloud forms) & latent heat released o since heat added during condensation offsets cooling due to expansion, air now cools at moist adiabatic rate  saturated adiabatic lapse rate o lapse rate decreases for saturated parcels  rising: latent heat release offsets cooling  sinking: evaporative cooling offsets warming o depends on temperature: warm air carries more water so it experiences more latent heat release/evaporation o this is why thunderstorms & hurricanes happen o released latent heat makes them rise through atmosphere o if saturated parcel with water droplets were to sink, it would compress & warm at moist adiabatic rate because evaporation of liquid droplets would offset rate of compressional warming o not constant, varies with temperature & moisture content Density, Buoyancy and Stability  at fixed pressure, warm air is less dense than cold air  buoyancy force related to difference between parcel density & that of surrounding environment o warmer, lighter: positive buoyancy, accelerates up o colder, heavier: negative buoyancy, accelerates down  if parcel displaced upward is colder than environment, it will accelerate back down (stable) Stability  lapse rate: rate at which air temperature changes with elevation  environmental lapse rate: rate at which air temperature surrounding us will be changing if we were to climb upward in atmosphere  an absolutely stable atmosphere o occurs when environmental lapse rate < saturated adiabatic lapse rate o comparing parcel against temperature profile of theoretical parcel o will start with same temperature as surroundings o rising parcel is colder & denser than air surrounding it o if given the chance, will return to its original position  an absolutely unstable environment o occurs when environment lapse rate > dry adiabatic lapse rate o rising air will continue to rise because it is warmer & less dense than surrounding air o layers will immediately overturn (warm air rises, cold air sinks) restoring stability  a conditionally unstable atmosphere o occurs when environmental lapse rate is between saturated adiabatic lapse rate & dry adiabatic lapse rate o atmosphere is stable if rising parcel is unsaturated o atmosphere is unstable if rising parcel is saturated o real atmosphere contains layer of differing stability *Processes Influencing Stability  general considerations o warmer air below & colder air aloft = less stable (larger environment lapse rate) o colder air below & warmer air aloft = more stable (smaller environment lapse rate) o increased moisture: parcel saturates more easily, then follows reduced adiabatic lapse rate (less stable)  advection o cold advection aloft and/or warm advection @ surface = less stable o warm advection aloft and/or cold advection @ surface = more stable  opposite process (stabilizing process) happens after cold front comes through  environmental subsidence o in large scale subsidence, troposphere often extremely stable  warms air aloft, leads to strong inversions atop boundary layer  parcels lifted through this environmental o aversion issue  when weather disturbed, atmosphere is in a rising motion (destabilizing effect)  dry air for awhile, air will drop trapping air at low levels  sinking air = fast rate of warming  layer stretching & compressing o descent & compressing = stabilization  top layer descends & warms more than bottom o ascent & stretching = destabilization  top layer ascends & cools more than bottom o get aversion when take layer down & compress is  convective (potential) instability o when lifted, parts of layer may saturate before others depending on moisture profile o if bottom saturates 1 , will cool less rapidly than upper part  continued lifting destabilizes layer  mixing brings layer closer to dry adiabatic o destabilized with respect to saturated parcel motions o stable inversion forms a top of mixed layer, capping the parcel ascent  deep convection o convective storms often result from upper level lifting o leads to layer stretching: cooling aloft, weakening of stable layers o also moistens mid-level flow by lifting moist air upwards from boundary level Cloud Development  mechanisms for cloud development: o surface heating & free convection o uplift along topography o widespread ascent due to convergence of surface air o uplift along weather fronts  earth doesn’t warm universally  thermals created (pockets of air that are warm & rise) & cool as they rise  as temperature changes, air holds less & less water so eventually a cloud forms  cloud-layer stability o fate of cloud depends on saturated lapse rate of stability of cloud-bearing layer o thunderstorms only develop within deep conditionally unstable layers  moist convection o cumulus congestus, cumulonimbus o when we get warm arm, it blows over shore, so have warm air over cold air (unstable)  orographic lifting o air forced upwards as it impinges over a mountain o precipitation happens so air loses moisture o when air goes over side of mountain it is unsaturated  mountain winds/lenticular clouds generated by stable flow over mountains 7: PRECIPITATION Cloud Precipitation  clouds required for precipitation, but n
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