Atmospheric and Ocean Circulation Lecture Notes PDF

**[ATMOSPHERIC AND OCEAN CIRCULATION]** 1. **ATMOSPHERE** Atmosphere thermal machine. Atmospheric circulation air movement -- winds Ocean engine Winds & Currents redistribute energy Sun energy source Water battery Sun emits electromagnetic radiation (just as all bodies, Stephan--Boltzman la...

**[ATMOSPHERIC AND OCEAN CIRCULATION]** 1. **ATMOSPHERE** Atmosphere thermal machine. Atmospheric circulation air movement -- winds Ocean engine Winds & Currents redistribute energy Sun energy source Water battery Sun emits electromagnetic radiation (just as all bodies, Stephan--Boltzman law) [*M* = *σT*^4^]{.math.inline} Electromagnetic radiation as a function of its frequency (wavelength), electromagnetic bands: - UV (\3μm) - Microwaves (1mm -- 1m) Sun emits more energy in the visible short wavelength, more energy radiation Earth emits more energy in the thermal IR long waves, less energy radiation [Atmosphere.] Emission of the Sun interact with atmosphere before reaching the Earth Gas thin layer 90% mass up to \~30km Protecting "shield" (stratosphere) Air (gas) has several components: - N 78% - O 21% - Ar, Ne, He... - H2O, CO2, CH4, N2O, O3, particles (needed to create clouds) variable gases Tropopause ozone layer, energy release resulting of the chemical reactions with part of the sun radiation (in stratosphere T increases with height) To create clouds (created by liquid or ice water particles) we need: - condensation nuclei (salt from the ocean) - temperature drop - water vapor Electromagnetic radiation in atmosphere: - absorbed - transmitted - reflected Most relevant gases in the atmosphere absorb different bands, very little interaction with the visible band (we can see colours and everything is not dark): - CO2 interacts with IR sensible heat wavelength - H2O interacts with IR - O3 absorbs completely the UV band - CH4 does not interact as much with IR as CO2 Greenhouse effect: 1. Short-wave solar radiation -- absorbed by Earth's surface 2. Earth's surface -- emits longwave radiation -- absorbed by GHGs 3. GHGs -- reradiate some energy Earthward, trapping hear in the lower atmosphere Some radiation goes out as well Earth heated by incoming solar energy Atmosphere heated by IR reradiate by GHGs (CO2 and CH4) Radiation depends on latitude: - Lower latitudes sun is higher (closer to the zenith), amount of energy per unit area at the surface is higher. - Higher latitudes opposite, added by the energy bouncing (away, loss of energy) and higher attenuation (thicker atmosphere that the radiation must penetrate). Polar zones same energy for the double of unit area Scattering when energy interacts with a molecule, part of the energy scattered, is lost (that's why the sky is red in sunset) Meridional surface T gradient 90˚ N and S (cold, lower T, higher density) 0˚ (warm, higher T for cloud formation, lower density). Equator air rises by convection, cloud formation, goes up until tropopause, diverges into N or S. Then due to condensation, release energy, gets colder, moves and goes down because of density gradient WATER, characteristics: 1. polar molecule (electrically charged, covalent bonds) 2. cohesive (specially in liquid form, hydrogen bonds, storage of energy) 3. exists in 3 states at Earth's T 4. high heat capacity a lot of energy needed to heat and evaporate an amount of water (to separate molecules) 5. absorption and release of heat through condensation and evaporation Tilted axis of the Earth seasons: amount of energy per unit area varies over the year ΔT (meridional T difference or regional/local caused by different surfaces, clouds, orography) Δρ ΔP Pressure gradient force (drive winds and ocean currents, perpendicular to isobars, from high to low pressure) Closer isobars represent a bigger pressure gradient (P variation in small distance) than more far away isobars (P variation in larger distance) Pressure ≡ force per unit area GENERAL CIRCULATION OF THE ATMOSPHERE - 1 cell model HADLEY Contraction in higher latitudes, ↓T, ↑ρ high pressure (air sinks) Expansion in lower latitudes, ↑T, ↓ρ low pressure (air rises) \* Missing -- rotation of the Earth Forces driving the wind (atmospheric circulation): 1. Pressure gradient force [\$PGF = \\frac{\\Delta P}{\\Delta X}\$]{.math.inline} 2. Coriolis (apparent) force deflects objects (and fluids) trajectories to the right (left) in the N (S) hemisphere Angular velocity remains constant in latitude, linear velocity is higher in lower latitudes. To conserve the momentum tilt to the right of the direction. 0 in equator, max in polar zones 3. Drag depends on type of surface, changes the flow speed, affects Coriolis force. Not parallel to isobars but inclined - 3 cells model FERREL HADLEY CELL (30˚N to 30˚S) -- convergence in 0˚ (ITCZ, surface), Trade Winds Cloud formation at the equator No seasons wet and dry seasons. convergence zone is wet season, when it moves to the south or the north is dry season FERREL CELL (60 to 30˚N and S) -- divergence in 30˚, Westerlies Polar jet stream POLAR CELL (90 to 60˚N and S) -- convergence in 60˚, Polar easterlies 30˚ dry air. Air contracts when goes down, it heats up, pressure increase becomes drier. Rain not usual Front 2 different air masses collide. warm air from the south and cold air from north. Colder air goes under warmer air biggest storms specially in winter POLAR JET STREAM \~60˚N, not a line. 2 air masses with different T and density. Wiggles (Rossby waves) Extratropical/midlatitudinal storms (weekly) in the polar front (interphase between 2 air masses). Vortexes can detach and have low pressure systems Reality of general circulation very related to continents and water different thermoproperties: - land absorbs energy faster, loses energy faster than the water induces differences in the wind circulations - continents are not monolithic blocks, have different coastal contours, differences between hemispheres. - different mountains, zones with grass, snow, water, asphalt different surfaces with different thermodynamic properties (through albedo, amount of energy reflected vs incident energy) ex: forest and snow different albedo, reflect sun radiation differently, different impact in lower air, wind can be created between these two zones. snow zone has a bigger albedo (R/I \~ 1), in a forest the albedo is smaller. Semi-permanent high-pressure systems, vary from N to S hemisphere, and with the seasons Thermoproperties different in water and land ITCZ moves between the 2 tropics during the year, not straight line. COASTAL JETS regional winds, regional climate, cause semi-desertic conditions. - Strong coastal winds in the left part of the continents, bring cold air to the surface. - Produced by sharp contrast between high T inland and lower T over sea. - Wind features along Eastern Boundary Currents - high pressure systems - cold water (2) no evaporation, air relatively dry even over the ocean and inland - cold air - coast parallel wind (1) no lateral transport from water vapor to inland (zonal component) - winds drive upwelling drive cold water from the deep zones into surface, winds intensify cold - water with a lot of nutrients (from the deep water), highest fishery activity in these areas SEA BREEZE can penetrate inland, low specific heat capacity 2. **OCEAN** Page 54 north Atlantic very salty because the mediterranean sea is a salt factory warm and more dense water goes out of the mediterranean and sinks AMOC (Atlantic meridional overturning current) Page 55 close to equator, a lot of evaporation and a lot of rain. subtropicals higher salinity, a lot of evaporation and less precipitation Page 57 the water column of the lake will cool down until it reaches 4 degrees. when the entire column is 4 degrees, it keeps on cooling and has a smaller density than the water at 4degrees. that's why there are blocks of ice in the surface Page 65 driven by ice formation warranty of planets climate the great ocean conve thermohaline circulation surface water in mid latitudes and the equator zones will never sink, there is always a surface layer Page 69 propagation of the drag force across the depth of the water (across the different layers in the water surface), until becoming 0 Page 71 surface wind driven currents effect on water surface is forming a 45 degrees angle (Ekman spiral) direction of the water is 45 degrees to the right compared to wind direction net effect is 90 degrees offset to the wind direction Ekman transport upwelling caused wind Page 72 azores high water net transport into the center, building a dome of water in the middle (pressure gradient) Page 73 creates a dome, with convergence of water in the center, this water starts to go away, creating currents affected by coriolis in their direction Page 74 full of bumps low pressure areas sea surface rises high pressure areas sea surface lowers