Oceanography Notes Midterm Corrections



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Oceanography Notes
Midterm Corrections

    • Lines of latitude measure north-south with respect to the equator

    • Old, cold oceanic lithosphere more dense than:

      • underlying warm aesthenosphere

      • continental lithosphere

      • younger oceanic lithosphere

    • Continental Margin order: Shelf, Slope, Rise

    • Oceanic crust floats lower on mantle because it is denser

    • Free oxygen produced by photosynthesis

    • Evaporation is a warming process


Chapter 6

    • atmosphere and ocean interdependent

    • surface currents correlate with wind belts

    • interchangeable results b/w ocean/atmos

    • radiant energy from sun responsible for motion in atmos and ocean

    • ecliptic: the plane traced by earth’s orbit

    • earth tilts at 23.5%

    • earth axis is always pointing in same direction, toward Polaris [N Star]

      • -causes seasons

    • vernal equinox: occur about 21 March, sun directly overhead along equator.

      • -during this, all placed on earth experience same length night and day

      • -N hemis, this is spring

    • summer solstice: june 21. sun at most northerly point in sky, directly above tropic of cancer

      • -at noon this day, sun seems to pause in sky.

    • Tropic of cancer: 23.5 degrees N lat

    • Autumnal equinox: sept 23. sun directly overhead along eq again.

      • -also known as fall equinox in N hemis.

    • winter solstice: dec 22. directly overhead at tropic of Capricorn

      • -S hemis seasons reversed, this is when S hemis most directly facing sun. This is beginning of S hemis summer.

    • tropic of Capricorn: 23.5 degrees S lat

    • declination: angular distance from equatorial plane

      • -sun’s declination varies b/w 23.5 degrees N and S lats on yearly cycle

    • tropics: region b/w Capricorn and Cancer

      • -receive greater annual radiation that poles

    • N hemis: longest day-summer solstice, shortest day-winter solstice

    • Exceptions to daily cycles of light and dark:

      • Arctic circle: 66.5 degrees N lat

      • Antarctic Circle: 66.5 degrees S lat

      • -during N hemis winter, area N of arctic circle experiences 6 months darkness, area S of Antarctic circle experiences 6 months daylight

      • half a year later, this situation reversed

    • sunlight strikes low lat at high angle; radiation concentrated in small area

    • sunlight strikes high lat at low angle; same amount of radiation spread over larger area

    • atmosphere absorbs radiation, so less radiation at high lat, b/c passes through more atmosphere

    • Albedo: percentage of incident radiation that is reflected back to space.

      • -avg albedo of earth’s surface: 30%

      • -ice has higher albedo than soil or vegetation so more radiation reflected back into space at high lats

    • -angle at which sunlight strikes ocean surface determines how much absorbed and how much reflected

      • -directly: 2% reflected

      • -5 degree above horizon: 40% reflected

      • -so, ocean reflects more radiation at high lats

      • Elevation of sun above atmosphere: 90 60 30 15 5

      • Reflected radiation [%] 2 3 6 20 40

      • absorbed radiation [%] 98 97 94 80 60

    • amount of radiation varies annually due to Earth’s seasons

    • amount of radiation varies daily b/c of day and night due to rotation

    • temperature difference b/w equatorial zone and poles remains the same, b/c excess heat transferred from equatorial zone to poles [circulation atmos and ocean]

    • Composition of dry air:

      • Nitrogen 78.1%

      • Oxygen 20.9%

      • Argon .9%

      • CO2 .037%

      • Other trace

    • troposphere: surface-12km[7m]. all weather produced here. much atmospheric mixing.

      • -temperature is cooler with altitude in troposphere

    • air has density

    • higher temperature, lower density [for air]

    • convection cell: rising and sinking air moving in circular fashion

    • warm air holds more water vapor because it has more contact with water vapor due to quick moving particles.

    • warm air moist, cool air dry

      • -warm breezy air-evaporation

    • more water vapor in air=decreased density

    • atmospheric pressure= 1.o atmosphere [14.7lbs/sq inch] at sea lvl

      • -decreases with increasing altitude [pressure depends on weight of air column above]

    • column of cool dense air: high pressure at surface; leads to sinking air

      • -movement toward surface and compression

    • column of warm, less dense air; low pressure at surface; leads to rising air

      • -movement away from the surface and expansion

    • air always moves from high to low pressure areas

    • principles that drive physical movement of air remain same whether earth is spinning or not

    • Coriolis Effect: changes the intended path of a moving body. Gaspard Hustave de Coriolis [1835].

        • does not influence the body’s speed [not a force]

        • this effect causes moving objects on earth to follow curved paths

        • N hemis; object goes right

        • S hemis; object goes left

      • the directions right and left are the viewer’s perspective looking I the direction in which the object is traveling

        • -ball thrown b/w two people will curve slightly to right in N hemis from the thrower’s point of view

        • -greater effect on objects going long-distance, especially N-S

      • result of earth’s eastward rotation

      • the difference in the speed of Earth’s rotation at difference lats causes this effect

      • maximized at poles and zero at the equator.

      • merry-go-round; fall off tangent to circle

      • Coriolis effect perspective; the one looking in direction object is moving

      • distance that a point must travel in a day shorter with increasing lat

      • 1600 km/hr earth sping rate [0 at poles]

      • this change in velocity w/ lat is true cause of Coriolis effect

      • 1400km/hr at 30 degrees lat N and S

      • missile launched straight at target will curve right [to the eye], but really, that target [point on earth] has a faster or slower velocity that the launch point

        • friction not taken into account; has a great effect

      • rate of change of rotational velocity [per degree of lat] increases as the pole is approached from equator

        • [from 200km/hr b/w eq and 30 deg N lat to 600km/hr b/w 30 deg N lat and 60 deg N lat]

        • 60 deg N lat- N pole -> 800km/hr difference

      • max Coriolis effect at poles, no Coriolis effect at equator

      • Coriolis effect summary:

        • -caused by earth rotation and resulting decrease in velocity with increased latitude

        • -influences all moving objects, esp those moving over large distances

        • -changes only direction, not speed

        • -deflection to the right in N hemis, left in S hemis

        • -O at equator; increases with increasing lat; strongest at poles.

    • Hadley Cells: George Hadley [1658-1768] circulation cells resulting from dry air mass at equatorial zone traveling N or S of equator at 30 deg lat becoming dense enough to sink and complete the loop

    • Ferrel cell: 30deg-60deg lat. William Ferrel [1817-1891]. Invented 3-cell [er hemis model. Cell moves coinciding with adjacent cells.

    • Polar cells: 60deg-90deg lat.

    • subtropical highs: high rpessure cones caused by descending air at 30deg N and S lat.

    • polar highs: high pressure regions caused by descending air at poles

      • -both areas: warm under own weight; dry, clear, fair conditions. Not necessarily warm

    • equatorial low: rising air causing a band of low pressure at the equator

    • subpolar low: rising air causing a band of low pressure at 60 deg lat.

      • -both areas: cloudy with much precipitation, because rising air cools and cannot hold its water vapor

    • trade winds: massed of air moving from subtropical high pressure belts to equatorial low pressure belts

      • -steady winds named from “to blow trade” [to blow in regular course]

      • -if earth did not rotate, trade winds blow NS

      • N hemis; northeast trade winds: curve to right; from NE to SW

      • S hemis; southeast trade winds: curve to left; from SE to NE

        • -the coriolis effect curves these winds

    • prevailing westerly wind belts: some of descdending air in subtrops moves along surface to highest lat

      • -SW to NE in N hemis; NW to SE in S hemis

    • polar easterly wind belts: air moving away from high pressure at poles

      • -Coriolis effect at poles strongly deflects winds

      • -blow from: NE in N hemis, SE in S hemis.

    • When polar easterlies collide with prevailing westerlies at subpolar low pressure belts [60 deg lat], the warmer, less dense air of westerlies rises above.

    • doldrums: boundary between trade belts. Lack of winds here.

    • Intertropical Convergence Zone [ITCZ]: doldrums. Between where trade winds converge.

    • Horse latitudes: boundary between prevailing westerlies and trade winds [30 deg lat]

      • -high pressure, clear, dry, fair conditions

      • -air is sinking and surface winds are light and variable [not much rain]

    • polar front: boundary between westerlies and easterlies [60 deg lat]

      • -cloudy, much precipitation. Battelground for different air masses

    • poles are cold deserts [not much precipitation]

    • Ferrel 3-cell idea is only general. Other factors:

      • 1] tilt of earth’s rotational axis, producing seasons

      • 2] low heat capacity of continental rock: colder winter, hotter summer than over oceans

      • 3] Uneven distribution of land, particularly affecting N hemis patterns

    • during winter on continent: atmospheric high pressure, summer: low pressure.

    • such seasonal atmospheric pressure over Asia causes Monsoon Winds.

    • Christopher Columbus: Italian navigator. Toscanelli: astronomer

      • -reached canary islands Aug 3, 1942

      • -called West Indies inhabitants “Indians” because he thought they were near India

      • -1498; South America 1502; Central America


Chapter 6 Lecture

Solar energy creates winds

Example of interactions: El Nino, Greenhouse Effect

Theory: Earth tilt due to Mar’s affect.

35degN-35degS->heat gained

Other lats, heat lost

Heat gained moves to poles

troposphere: 60degC-50degC at min temp

Topopause-Stratosphere-Ozone layer-Mesosphere

dry air and cool air sink <-more dense

moist air and warm air rise<-less dense

-moist air less dense than dry air because water has less mass than N2+O2

high pressure->air coming down; low pressure->air rising

deserts have cool/dry air coming down



cool dense air, higher surface pressure
Chapter 6 cont…

    • weather: conditions in atmosphere at given time and place

    • climate: long-term average of weather

    • cyclonic flow: CCW flow of air around low pressure cells as a result of Coriolis effect on air moving from high to low pressure curving it to the right [N hemis]

    • anticyclonic flow: air leaving high pressure region and curves right, establishes CW flow of air around high pressure cells [N hemis]

    • low pressure->clouds high pressure->sun

    • winter high pressure cells replaced by summer low pressure over continents, so continental wind patterns often reverse themselves seasonally.

    • land breeze: cool air sinking, blowing over ocean in early morning hours.

      • -due to cool sinking air over continents at night as a results of continents having low heat capacity

    • sea breeze: warm air rising, blowing cool air from ocean over continent in afternoon.

      • -due to warm air rising over/above continents during day as a result of continental low heat capacity.

    • Wind Belts and Boundaries:

      Region

      Name

      Pressure

      Characteristics

      0-5

      Doldrums

      L

      Light variable wind. Cloudy/Precip. Hurricanes breed here

      5-30

      Trade Winds

      -

      Strong, steady winds generally from E

      30-60

      Horse Latitudes

      H

      Light, variable wind. Dry, clear, fair. Little precip. Major deserts here

      60

      Prevailing W

      -

      Winds generally from W. Brings US-influencing storms

      60-90

      Polar Front

      L

      Variable wind. Stormy/cloudy year-round

      Poles

      Polar E

      -

      Cold, dry winds generally form E




      Polar High Pressure

      H

      Variable winds. Clear, dry, fair, cold temp, min precip. Cold deserts here.

    • Very high and very low lats, little daily and minor seasonal change in weather

    • midlatitudes: where storms are common

    • storms: atmosphere disturbances: strong wind, precip, thunder/lightning

    • air masses: large volumes of air: definite area of origin, distinctive characteristics.

      • -polar and tropical air masses influence US

      • -most originate over sea. those from land are drier

      • -US influenced more by: polar air masses in winter/tropical air masses in summer

      • -[c]continental [m]maritime [T]tropical [A]arctic [P]polar

    • warm front: contact between warm air mass moving into area of cold air

      • -as air masses move to midlats, they move E some

    • cold front: contact between cold air mass into warm-air area

    • jet stream: narrow, fast, Eastward-flowing air mass. Causes fronts.

      • -above mid lats just below top of troposphere, 6miles high

      • -follows wavy path; causes unusual weather by steering [P] or [T] too far N or S

    • warm always rises above cold

    • temperature difference across cold front greater than warm front

      • -so, rain of cold front usually heavier, briefer

    • Tropical cyclones: huge, rotating masses of low pressure: strong wind, torrential rain

    • hurricanes: name in N, S America

    • typhoons: W N Pacific ocean

    • cyclones: Indian ocean

    • energy of single hurricane greater than all that created in US in 20 years.

    • tropical cyclone begins as low pressure cells break from equatorial low pressure belt, grows as heat energy from ocean picked up

      • -the surface winds feed moisture [water vapor] into storm

      • -the release of vast amounts of water’s latent-heat of condensation power tropical cyclone.

    • Tropical cyclone classification:

      • tropical depression: winds below 38mph

      • tropical storm: 38

      • tropical cyclone: 74mph

    • Saffir-Simpson Scale: hurricane intensity; further classifies; wind speed, dmg

    • 250mph a high

    • 100 tropical cyclones each year. conditions to create:

      • ocean water temperature > 25C -> for evaporation

      • warm/moist air -> supplies latent heat

      • Coriolis effect; cyclone spin CCW in N hemis, CW in S hemis

        • No cyclone directly on equator, because Coriolis is zero. Happens on equator once every 300-400 years

    • June 1-Nov 30 “hurricane season” [not limited to this time frame]

    • hurricanes typically remain in tropics. Driven by trade winds so they move E to W. Last 5-10 days.

    • If more over land, energy source is lost, so they dissipate

    • diameter avg 124miles but can be 500+

    • eye of the hurricane: low pressure center: air here spirals upward; usually calm

    • spiral rain bands compose hurricanes; several inches of rainfall per hour

    • storm surge: responsible for most of a hurricane’s dmg. [90% deaths]. Hill of water

      • -low pressure center produces hill up to 40ft high.

      • -hill where wind blowing shoreward climbs shallow water onto shore. Very bad at high tide.

      • -dramatic increase in sea lvl at shoer

      • -where onshore winds further pile water hit most severely

    • Galveston Texas, 1900; 7000 dead. Category 4.

    • Category 5 3x; 1935[Keys], 1969[Mississippi], 1992[Andrew FL]

    • Mitch [Central America 11k dead]

    • most of world’s tropical cyclone formed in water N of equator in West pacific ocean.

    • 1970 [Bangladesh 40ft Storm Surge killed 1 million] another in 1972; 500k dead. ’91; 200k

    • ocean climate patterns run E-W, are stable. modified by ocean surface currents.

    • equatorial: region spanning equator. abundance solar radiation. Major air movement upward.

      • -storms form here.

    • tropical: regions N/S to cancer, Capricorn. Strong trade winds. NE in N hemis, SE in S hemis. Rough seas.

      • -storms gain energy here.

    • subtropical: regions beyond tropics. High surface salinity. belts of high pressure. little precipitation, much evaporation. Winds weak, currents sluggish. strong boundary currents N-S, particularly along west margins.

    • temperate: regions [midlats] strong westerly winds; from SW in N hemis, NW in S hemis. severe storms, heavy precip. winter esp

    • subpolar: regions; extensive precip due to subpolar low. sea-iced-covered in winter, melts in summer. icebergs common, surface temp rarely greater than 41F in summer

    • polar: region; temps remain at or near freezing. covered with ice, most of year. No sun in winter, all sun in summer

    • sea ice: masses of frozen ice. low temp/high lat

    • icebergs: break off [calve] from glaciers that originate on land

    • pancake ice: forming slush into thin sheet broken by wind and waves

    • ice floes: layer of ice when further freezing occurs to pancakes

    • rate of ice form slows as it thickens, because top ice insulates water below

    • calm water and low temp aid ice formation

    • most of dissolved substances remain in water, notice. Salinity increases under ice.

      • -decreases the freezing point of water

      • -ice becomes ink below surface-> lower surface salinity water freezes in place

    • 17% decrease in overall ice extent

    • accelerated melting at interior poles

      • -due to shifts in N hemis atmosphere circulation patterns

    • most breaking-up [calving] occurs in summer high temps

    • icebergs from in Greenland narrow valleys to ocean.

      • -E and W Greenland current carry bergs into N Atlantic shipping lanes

      • -may take years to melt

    • shelf ice: thick floating sheets of ice formed at edges of glaciers in Antarctica

      • [B-15 4250 sw mile iceberg from shelf ice breaking off]

      • 90% icebergs mass below sea lvl

      • flat tops up to 650ft high. Most below 530ft high

      • Larsen ice shelf decreased by 40% since 1997

      • rate of warming; .5C per decade

    • Argo located Titanic 1985 Robert Ballard

    • World average temp Earth and troposphere: 15c [59F]

    • greenhouse effect: keeps Earth’s surface and lower atmosphere warm.

    • most of sun energy that reaches earth surface: short wavelength, visible almost

    • longer-wavelength infrared radiation; heat; short-wavelength energy converted to this energy when it strikes the surface.

    • energy trapped in atmosphere by ozone layer

    • heat budget: 100 units shortwave solar radiation reflected, absorbed, scattered by various components of Earth

      • 47% of solar radiation absorbed by oceans and continents

      • 23% absorbed by atmosphere and clouds

      • 20% reflected to space by backscatter, clouds, and Earth’s surface

    • peak of intensity of energy of sun; .0002inch wavelength, within visible spectrum

    • earth materials that absorb energy reradiate it back to space as longer wavelengths: infrared [heat. .004 inch long]

    • rates of absorption and reradiation are equal

    • greenhouse effect produced by heat-trapping gases trapping reradiated heat, and reradiating this heat once more.

    • change of wavelength from visible to infrared is the key to understand how greenhouse effect works


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