Understanding Density and Stratification in Oceanography
School
University of Victoria**We aren't endorsed by this school
Course
EOS 110
Subject
Geography
Date
Dec 11, 2024
Pages
7
Uploaded by EarlPelican4564
EOS WEEK 2 Slide 3 Density: the mass in a given volume -Units like kg / L or g / cm3 -Lower density than surroundings – fluid = rises -Greater density than surrounding – fluid = sinks Slide 4 -Warmer water = less dense Slide 6 -Hot molecules move more / are farther apart and have space between them -Cold molecules move less / packed tightly Slide 8 -Sun warms upper ocean -Warm water floats over the colder water due to less density Stratification:layering of different density / fluids over each other Stable Stratification: low density on top of high density Unstable Stratification: high density on top of low density Thermocline: range of depth where temperature changes rapidly ( thermo – temp.) ( cline changes fast) Mixed layer: actively mixing layer -When graphing the ocean, water surface is always at top of graph / orographic format/ where the depth in on (y) axis and surface on top of plot Slide 9 Fresh water: less dense than salt water – therefore will float on top of salt water Slide 11 Salinity: grams of salt / over kilograms of ocean water -typical ~ 35g / per kg of sea waterSlide 12 -precipitation – river can input fresher surface water?-Evaporation – can create unstable stratification (high density on top / low on bottom)Halocline: depth range where salinity changes most rapidly (halo – salinity) Pycnocline: depth range where density changes most rapidly (pycno – density) Slide 13
EOS WEEK 2 -If there is warm salt water (dense but warm) and cold dense fresh water, it depends on the temperature vs salinity differences Slide 16 -Different temperature (T) and salinity (S) combinations have the same density -(TS diagram)Slide 17 -The atmosphere is warmest at the bottom-Sun heats oceans top / surface, and also atmospheres bottom-Atmospheric pressure strongly affects density and temperatureSlide 18 -Gravity concentrates molecules near Earth’s surface, and makes them farther apart at high elevations Slide 19 Atmospheric pressure: the weight of the air above -Average at sea level = 1013 hPa ~ 1kg / per cm2 -Pressure exerted in all directions Slide 20 Altitude change: expansion / temp change => temperature change -Rising air expands as it encounters lower pressure = cools -Sinking air compresses = warms Lapse rate: rate of cooling (rising) or warming (sinking) air Dry Lapse rate: (not condensing) = 10 °C / 1000m Slide 22 -Tend to see clouds and precipitation where air is rising / and clear skies where air is sinking Slide 23 Windward (up wind): air rising, cooling, precipitation Down wind: air sinking, warms, dry Slide 25 Saturation = max water vapor air can hold at a given temperature -Warm air can hold more water vapor – higher saturation
EOS WEEK 2 Relative humidity= water vapor in air actually / divided by / water vapor at saturation. Dew point= temperature at saturation for a given amount of water vapor. Slide 26 -If liquid water is present, it will evaporate until saturation is reached. Slide 27 -At start, dew point = 10 °C -Relative humidity increases as air cools -Vapor condenses if air cools past saturation -Relative humidity decreases as air warms Slide 28 -Air rising = cooling (expansion) – relative humidity increases -If cools to dew point vapor condenses => clouds / precipitation -Sinking air warms => relative humidity decreases Slide 29 -Condensation – releases heat Slide 30 -Rising air at saturation is cooling from expansion = -10°C / per / 1000 meters-Heating from condensation + 5°C / per / 1000 meters -“wet” (condensation) lapse rate = 5 °C / 1000m-
EOS WEEK 2 Use wet lapse rate when 1)Air at saturation (100% relative humidity) AND 2)Air rising, wet lapse rate different from dry because condensation adds heat Slide 33 Unstable Fast => Slide 34 UnstableStable Slower => -Horizontal density differences make fluids move Slide 35/36 -Same amount of energy increases temperature at land, twice as fast as water -Over the day, land and air above warms faster -Cool more dense air over the ocean moves under warm / less dense air over land = circulation cell Slide 38 -Land closest to coast cooled by incoming / cooler ocean air Water Air Air Water Warm air Cool air Cool air Warm air warm
EOS WEEK 2 unstable stable => Slide 40 b) clockwise circulation cell Slide 42 Temperature (density) differences at ocean surface South óEquator óNorth Slide 43 Low turbulence Surface water moved away from heat. Return flow is relatively shallow. cold Warm => <= cold warm cold
EOS WEEK 2 Slide 44
EOS WEEK 2 Slide 49 Estuary: transition zone where river meets ocean -Fresh water flows toward ocean at top and sea water flows toward land at bottom oMixing and upwelling between flows -My ans= 60m at base of outflowing waters