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Edit Comment Close Premium member Presentation Transcript General Circulation of the Atmosphere: General Circulation of the Atmosphere Tropical heating drives Hadley cell circulation Warm wet air rises along the equator Transfers water vapor from tropical oceans to higher latitudes Transfers heat from low to high latitudesThe Hadley Cell: The Hadley Cell Along equator, strong solar heating causes air to expand upward and diverge to poles Creates a zone of low pressure at the equator called Equatorial low Intertropical Convergence Zone (ITCZ) The upward motions that dominate the region favor formation of heavy rainfall ITCZ is rainiest latitude zone on Earth Rains 200 days a year – aka. doldrumsGeneral Circulation: General Circulation Air parcels rise creating low pressure Heat and expand Become humid Transfer heat (sensible & latent) to poles Transfer of moisture towards poles In mid latitudes Dry air sinks creating high pressure Air flows away from high pressureGeneral Circulation: General Circulation Hadley cell circulation creates trade winds Dry trade winds move from subtropics to tropics and pick up moisture Trade winds from both hemispheres converge in the ITCZ Trade winds warm and rise Contribute to low pressure and high rainfall in the ITCZMonsoons – Circulation in ITCZ: Monsoons – Circulation in ITCZ ITCZ shifts with seasons Circulation driven by solar heating Circulation affected by seasonal heat transfer between tropical ocean and land Heat capacity and thermal inertia of land < waterSummer Monsoon: Summer Monsoon Air over land heats and rises drawing moist air in from tropical oceansWinter Monsoon: Winter Monsoon Air over land cools and sinks drawing dry air in over the tropical oceansCirculation at Mid & High Latitudes: Circulation at Mid & High Latitudes Sinking air from Hadley circulation creates high pressure in subtropics Circulation modified Coriolis effect Monsoons Flow of cold air from high latitudes Coriolis Effect: Coriolis Effect Air moving from high to low pressure is deflected by Earth’s rotation Clockwise rotation in the northern hemisphere Counterclockwise rotation in the southern hemisphereOcean Circulation?: Ocean Circulation? Circulation in the troposphere is caused by atmospheric pressure gradients Result from vertical or horizontal temperature differences Temperature variations caused by latitudinal differences in solar heating Ocean surfaces are heated by incoming surface radiation Do the oceans circulate for the same reason as the atmosphere?No!: No! 90% of solar radiation that penetrates oceans absorbed in upper 100 m Warm water at surface is less dense than the colder water below Water column is inherently stable Very little vertical mixing Water has a high heat capacity Lots of heat required for a small change in temperature Lateral temperature and salinity differences are small over large areasOcean Circulation: Ocean Circulation Ultimately driven by solar energy Distribution of solar energy drives global winds Latitudinal wind belts produce ocean currents Determine circulation patterns in upper ocean Distribution of surface ocean temperatures strongly influence density structure Density structure of oceans drives deep ocean circulation Negative feedback Surface temperature gradients drive circulation Net effect is to move warm water to poles and cold water towards tropicsHeat Transfer in Oceans: Heat Transfer in Oceans Heating occurs in upper ocean Vertical mixing is minimal Average mixed layer depth ~100 m Heat transfer from equator to pole by ocean currents Oceans redistribute about half as much heat at the atmosphereSurface Currents: Surface Currents Surface circulation driven by winds As a result of friction, winds drag ocean surface Water movement confined to upper ~100 m Although well-developed currents ~1-2 km Examples, Gulf Stream, Kuroshiro Current Coriolis effect influences ocean currents Water deflected to right in N. hemisphere Water deflected to left in S. hemisphereEckman Spiral: Eckman Spiral Eckman theory predicts 1) surface currents will flow at 45° to the surface wind path 2) flow will be reversed at ~100 m below the surface 3) flow at depth will be considerably reduced in speed Few observations of true Eckman Spiral Surface flow <45°, but still to an angleEckman Transport: Eckman Transport Observations confirm net transport of surface water is at a right angle to wind direction Net movement of water referred to as Eckman TransportGyre Circulation: Gyre Circulation Wind driven and large scale Sea level in center 2 m higher than edge Eckman transport producing convergence Circulation extends to 600-1000 m Volume of water moved is 100 x transport of all Earth’s rivers Flow towards equator balanced by flow toward pole on westward margin In Atlantic, by Gulf Stream and North Atlantic DriftDownwelling: Downwelling In areas of convergence Surface water piles up in center of gyre Sea level in the center of gyre increases Surface layer of water thickens Accumulation of water causes it to sink Process known as downwellingEquatorial Divergence: Equatorial Divergence Areas of the ocean where divergence of surface currents occurs Equatorial divergence (e.g., Atlantic) In N. hemisphere, NW trades result in westward flowing N. equatorial current Eckman transport moves water to N In S. hemisphere, SW trades result in westward flowing S. equatorial current Eckman transport moves water to S Divergence occurs along the equatorEquatorial Upwelling: Equatorial Upwelling As surface water diverges, sea level falls, surface layer thins and cold water “upwells”Eckman Transport Along Coasts: Eckman Transport Along Coasts Winds along a coast may result in Eckman transport that moves water towards or away from the coast Divergence from easterly winds and southward moving currents SW coast of N. America W coast of N. Africa Divergence from northward moving currents West coasts of S. America and S. AfricaCoastal Upwelling: Coastal Upwelling Coastal divergence results in upwelling as cold water rises to replace surface waterGeostrophic Currents: Geostrophic Currents Eckman transport from wind-driven currents piles water up in gyre center Gravity pulls water down slope Slope is opposite to Coriolis effect Net effect is flow 90° to slope Result is a geostrophic current Geostrophic currents push water in the same direction as the wind-driven flowBoundary Currents: Boundary Currents Gyre circulation pushes water to the west Flow of water around gyres is asymmetric In the western part of gyre water is confined to a narrow fast-moving flow Western boundary current In the eastern part of gyre flow is diffuse, spread out and slow Eastern boundary current Eastern currents tend to be divergent Eckman transport away from continentGulf Stream: Gulf Stream Western boundary current in Atlantic Narrow, fast-moving from Cuba to Cape Hatteras Decreases speed across N. Atlantic Flow broadens and slows becoming N. Atlantic Drift Movement to the south along the Canary Current is very slow, shallow and broadDeep Ocean Circulation: Deep Ocean Circulation Driven by differences in density Density of seawater is a function of Water temperature Salinity Quantity of dissolved salts Chlorine Sodium Magnesium Calcium PotassiumThermohaline Circulation: Thermohaline Circulation Deep ocean circulation depends on temperature (thermo) & salinity (hals) Controls seawater density Density increases as: Salinity increases Temperature decreases Horizontal density changes small Vertical changes not quite as small Water column is stable Densest water on bottom Flow of water in deep ocean is slow However, still important in shaping Earth’s climateVertical Structure of Ocean: Vertical Structure of Ocean Surface mixed layer Interacts with atmosphere Exchanges kinetic energy (wind, friction) and heat Typically well mixed (20-100 m)Vertical Structure of Ocean: Vertical Structure of Ocean Pychnocline (~1 km) Zone of transition between surface and deep water Characterized by rapid increase in density Some regions density change due to salinity changes – halocline Most regions density change due to temperature change – thermocline Steep density gradient stabilizes layerBottom Water Formation: Bottom Water Formation Deep-ocean circulation begins with production of dense (cold and/or salty) water at high latitudes Ice formation in Polar oceans excludes salt Combination of cold water and high salinity produces very dense water Dense water sinks and flows down the slopes of the basin towards equatorAntarctic Bottom Water (AABW): Antarctic Bottom Water (AABW) Weddell Sea major site of AABW formation AABW circles Antarctica and flow northward as deepest layer in Atlantic, Pacific and Indian Ocean basins AABW flow extensive 45°N in Atlantic 50°N in Pacific 10,000 km at 0.03-0.06 km h-1; 250 yNorth Atlantic Deep Water (NADW): North Atlantic Deep Water (NADW) Coastal Greenland (Labrador Sea) site of NADW formation NADW comprises about 50% of the deep water to worlds oceans NADW in the Labrador Sea sinks directly into the western Atlantic NADW forms in Norwegian Basins Sinks and is dammed behind sills Between Greenland and Iceland and Iceland and the British Isles NADW periodically spills over sills into the North AtlanticDeep Atlantic Water Masses: Deep Atlantic Water Masses Deep Atlantic water comes from high latitude N. Atlantic, Southern Ocean and at shallower depth, the Mediterranean SeaAABW and NADW Interact: AABW and NADW Interact NADW flowing south in the Atlantic joins the Antarctic Circumpolar Current NADW and AABW combine Spin around Antarctica Eventually branch off into the Pacific, Indian and Atlantic ocean basinsOcean Circulation: Ocean Circulation Surface water at high latitudes forms deep water Deep water sinks and flows at depth throughout the major ocean basins Deep water upwells to replace the surface water that sinks in polar regions Surface waters must flow to high latitudes to replace water sinking in polar regions Idealized circulation – Thermohaline Conveyer BeltThermohaline Conveyor Belt: Thermohaline Conveyor Belt NADW sinks, flows south to ACC and branches into Indian and Pacific Basins Upwelling brings cold water to surface where it eventually returns to N. AtlanticOcean Circulation and Climate: Ocean Circulation and Climate Warm surface waters move from equator to poles transferring heat pole-ward and into the deep oceans Oceans vast reservoir of heat Water heats and cools slowly Pools of water warmer than normal heat the atmosphere Pools of water colder than normal cool the atmosphere Timescale of months to years Time needed for heating/cooling of waterOcean Circulation and Climate: Ocean Circulation and Climate On long timescales, average ocean temperature affects climate Most water is in deep ocean Average temperature of ocean is a function of Process of bottom-water formation Transport of water around ocean basins Deep water recycle times is ~1000 y Thermohaline circulation moderates climate over time periods of ~ 1000 yIce on Earth: Ice on Earth Important component of climate system Ice properties are different from water, air and land Two important factors affecting climate High albedo Latent heat stored in ice Sea Ice: Sea Ice Salt rejection during sea ice formation Important for bottom water formation Sea ice stops atmosphere from interacting with surface mixed layerSea Ice Distribution: Sea Ice Distribution Most sea ice in Southern Ocean Enormous amount form and melt each season Average thickness ~1 m Landmasses in Arctic prevent sea ice movement Arctic sea ice persists for 4-5 years Reach thickness of 4 m in central Arctic and 1 m on marginsGlacial Ice: Glacial Ice Mountain glaciers Equatorial high altitude or polar lower altitude Few km long, 100’s m wide and 100’s m thickGlacial Ice: Glacial Ice Continental ice sheets Large ice cube Existing ice sheets Antarctica and Greenland ~3% of Earth’s surface or 11% of land surface 32 million km3 (= 70 m of sea level) You do not have the permission to view this presentation. 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Lecture3 Durante Download Post to : URL : Related Presentations : Share Add to Flag Embed Email Send to Blogs and Networks Add to Channel Uploaded from authorPOINTLite Insert YouTube videos in PowerPont slides with aS Desktop Copy embed code: (To copy code, click on the text box) Embed: URL: Thumbnail: WordPress Embed Customize Embed The presentation is successfully added In Your Favorites. Views: 1086 Category: Education License: All Rights Reserved Like it (2) Dislike it (0) Added: January 25, 2008 This Presentation is Public Favorites: 0 Presentation Description No description available. Comments Posting comment... By: akashakhil (7 month(s) ago) this is very interesting publication................................. Saving..... Post Reply Close Saving..... Edit Comment Close By: shaheryar1981 (14 month(s) ago) its a nice presentation to understand the concept of ITCZ. kindly allow me to download it. Saving..... Post Reply Close Saving..... Edit Comment Close Premium member Presentation Transcript General Circulation of the Atmosphere: General Circulation of the Atmosphere Tropical heating drives Hadley cell circulation Warm wet air rises along the equator Transfers water vapor from tropical oceans to higher latitudes Transfers heat from low to high latitudesThe Hadley Cell: The Hadley Cell Along equator, strong solar heating causes air to expand upward and diverge to poles Creates a zone of low pressure at the equator called Equatorial low Intertropical Convergence Zone (ITCZ) The upward motions that dominate the region favor formation of heavy rainfall ITCZ is rainiest latitude zone on Earth Rains 200 days a year – aka. doldrumsGeneral Circulation: General Circulation Air parcels rise creating low pressure Heat and expand Become humid Transfer heat (sensible & latent) to poles Transfer of moisture towards poles In mid latitudes Dry air sinks creating high pressure Air flows away from high pressureGeneral Circulation: General Circulation Hadley cell circulation creates trade winds Dry trade winds move from subtropics to tropics and pick up moisture Trade winds from both hemispheres converge in the ITCZ Trade winds warm and rise Contribute to low pressure and high rainfall in the ITCZMonsoons – Circulation in ITCZ: Monsoons – Circulation in ITCZ ITCZ shifts with seasons Circulation driven by solar heating Circulation affected by seasonal heat transfer between tropical ocean and land Heat capacity and thermal inertia of land < waterSummer Monsoon: Summer Monsoon Air over land heats and rises drawing moist air in from tropical oceansWinter Monsoon: Winter Monsoon Air over land cools and sinks drawing dry air in over the tropical oceansCirculation at Mid & High Latitudes: Circulation at Mid & High Latitudes Sinking air from Hadley circulation creates high pressure in subtropics Circulation modified Coriolis effect Monsoons Flow of cold air from high latitudes Coriolis Effect: Coriolis Effect Air moving from high to low pressure is deflected by Earth’s rotation Clockwise rotation in the northern hemisphere Counterclockwise rotation in the southern hemisphereOcean Circulation?: Ocean Circulation? Circulation in the troposphere is caused by atmospheric pressure gradients Result from vertical or horizontal temperature differences Temperature variations caused by latitudinal differences in solar heating Ocean surfaces are heated by incoming surface radiation Do the oceans circulate for the same reason as the atmosphere?No!: No! 90% of solar radiation that penetrates oceans absorbed in upper 100 m Warm water at surface is less dense than the colder water below Water column is inherently stable Very little vertical mixing Water has a high heat capacity Lots of heat required for a small change in temperature Lateral temperature and salinity differences are small over large areasOcean Circulation: Ocean Circulation Ultimately driven by solar energy Distribution of solar energy drives global winds Latitudinal wind belts produce ocean currents Determine circulation patterns in upper ocean Distribution of surface ocean temperatures strongly influence density structure Density structure of oceans drives deep ocean circulation Negative feedback Surface temperature gradients drive circulation Net effect is to move warm water to poles and cold water towards tropicsHeat Transfer in Oceans: Heat Transfer in Oceans Heating occurs in upper ocean Vertical mixing is minimal Average mixed layer depth ~100 m Heat transfer from equator to pole by ocean currents Oceans redistribute about half as much heat at the atmosphereSurface Currents: Surface Currents Surface circulation driven by winds As a result of friction, winds drag ocean surface Water movement confined to upper ~100 m Although well-developed currents ~1-2 km Examples, Gulf Stream, Kuroshiro Current Coriolis effect influences ocean currents Water deflected to right in N. hemisphere Water deflected to left in S. hemisphereEckman Spiral: Eckman Spiral Eckman theory predicts 1) surface currents will flow at 45° to the surface wind path 2) flow will be reversed at ~100 m below the surface 3) flow at depth will be considerably reduced in speed Few observations of true Eckman Spiral Surface flow <45°, but still to an angleEckman Transport: Eckman Transport Observations confirm net transport of surface water is at a right angle to wind direction Net movement of water referred to as Eckman TransportGyre Circulation: Gyre Circulation Wind driven and large scale Sea level in center 2 m higher than edge Eckman transport producing convergence Circulation extends to 600-1000 m Volume of water moved is 100 x transport of all Earth’s rivers Flow towards equator balanced by flow toward pole on westward margin In Atlantic, by Gulf Stream and North Atlantic DriftDownwelling: Downwelling In areas of convergence Surface water piles up in center of gyre Sea level in the center of gyre increases Surface layer of water thickens Accumulation of water causes it to sink Process known as downwellingEquatorial Divergence: Equatorial Divergence Areas of the ocean where divergence of surface currents occurs Equatorial divergence (e.g., Atlantic) In N. hemisphere, NW trades result in westward flowing N. equatorial current Eckman transport moves water to N In S. hemisphere, SW trades result in westward flowing S. equatorial current Eckman transport moves water to S Divergence occurs along the equatorEquatorial Upwelling: Equatorial Upwelling As surface water diverges, sea level falls, surface layer thins and cold water “upwells”Eckman Transport Along Coasts: Eckman Transport Along Coasts Winds along a coast may result in Eckman transport that moves water towards or away from the coast Divergence from easterly winds and southward moving currents SW coast of N. America W coast of N. Africa Divergence from northward moving currents West coasts of S. America and S. AfricaCoastal Upwelling: Coastal Upwelling Coastal divergence results in upwelling as cold water rises to replace surface waterGeostrophic Currents: Geostrophic Currents Eckman transport from wind-driven currents piles water up in gyre center Gravity pulls water down slope Slope is opposite to Coriolis effect Net effect is flow 90° to slope Result is a geostrophic current Geostrophic currents push water in the same direction as the wind-driven flowBoundary Currents: Boundary Currents Gyre circulation pushes water to the west Flow of water around gyres is asymmetric In the western part of gyre water is confined to a narrow fast-moving flow Western boundary current In the eastern part of gyre flow is diffuse, spread out and slow Eastern boundary current Eastern currents tend to be divergent Eckman transport away from continentGulf Stream: Gulf Stream Western boundary current in Atlantic Narrow, fast-moving from Cuba to Cape Hatteras Decreases speed across N. Atlantic Flow broadens and slows becoming N. Atlantic Drift Movement to the south along the Canary Current is very slow, shallow and broadDeep Ocean Circulation: Deep Ocean Circulation Driven by differences in density Density of seawater is a function of Water temperature Salinity Quantity of dissolved salts Chlorine Sodium Magnesium Calcium PotassiumThermohaline Circulation: Thermohaline Circulation Deep ocean circulation depends on temperature (thermo) & salinity (hals) Controls seawater density Density increases as: Salinity increases Temperature decreases Horizontal density changes small Vertical changes not quite as small Water column is stable Densest water on bottom Flow of water in deep ocean is slow However, still important in shaping Earth’s climateVertical Structure of Ocean: Vertical Structure of Ocean Surface mixed layer Interacts with atmosphere Exchanges kinetic energy (wind, friction) and heat Typically well mixed (20-100 m)Vertical Structure of Ocean: Vertical Structure of Ocean Pychnocline (~1 km) Zone of transition between surface and deep water Characterized by rapid increase in density Some regions density change due to salinity changes – halocline Most regions density change due to temperature change – thermocline Steep density gradient stabilizes layerBottom Water Formation: Bottom Water Formation Deep-ocean circulation begins with production of dense (cold and/or salty) water at high latitudes Ice formation in Polar oceans excludes salt Combination of cold water and high salinity produces very dense water Dense water sinks and flows down the slopes of the basin towards equatorAntarctic Bottom Water (AABW): Antarctic Bottom Water (AABW) Weddell Sea major site of AABW formation AABW circles Antarctica and flow northward as deepest layer in Atlantic, Pacific and Indian Ocean basins AABW flow extensive 45°N in Atlantic 50°N in Pacific 10,000 km at 0.03-0.06 km h-1; 250 yNorth Atlantic Deep Water (NADW): North Atlantic Deep Water (NADW) Coastal Greenland (Labrador Sea) site of NADW formation NADW comprises about 50% of the deep water to worlds oceans NADW in the Labrador Sea sinks directly into the western Atlantic NADW forms in Norwegian Basins Sinks and is dammed behind sills Between Greenland and Iceland and Iceland and the British Isles NADW periodically spills over sills into the North AtlanticDeep Atlantic Water Masses: Deep Atlantic Water Masses Deep Atlantic water comes from high latitude N. Atlantic, Southern Ocean and at shallower depth, the Mediterranean SeaAABW and NADW Interact: AABW and NADW Interact NADW flowing south in the Atlantic joins the Antarctic Circumpolar Current NADW and AABW combine Spin around Antarctica Eventually branch off into the Pacific, Indian and Atlantic ocean basinsOcean Circulation: Ocean Circulation Surface water at high latitudes forms deep water Deep water sinks and flows at depth throughout the major ocean basins Deep water upwells to replace the surface water that sinks in polar regions Surface waters must flow to high latitudes to replace water sinking in polar regions Idealized circulation – Thermohaline Conveyer BeltThermohaline Conveyor Belt: Thermohaline Conveyor Belt NADW sinks, flows south to ACC and branches into Indian and Pacific Basins Upwelling brings cold water to surface where it eventually returns to N. AtlanticOcean Circulation and Climate: Ocean Circulation and Climate Warm surface waters move from equator to poles transferring heat pole-ward and into the deep oceans Oceans vast reservoir of heat Water heats and cools slowly Pools of water warmer than normal heat the atmosphere Pools of water colder than normal cool the atmosphere Timescale of months to years Time needed for heating/cooling of waterOcean Circulation and Climate: Ocean Circulation and Climate On long timescales, average ocean temperature affects climate Most water is in deep ocean Average temperature of ocean is a function of Process of bottom-water formation Transport of water around ocean basins Deep water recycle times is ~1000 y Thermohaline circulation moderates climate over time periods of ~ 1000 yIce on Earth: Ice on Earth Important component of climate system Ice properties are different from water, air and land Two important factors affecting climate High albedo Latent heat stored in ice Sea Ice: Sea Ice Salt rejection during sea ice formation Important for bottom water formation Sea ice stops atmosphere from interacting with surface mixed layerSea Ice Distribution: Sea Ice Distribution Most sea ice in Southern Ocean Enormous amount form and melt each season Average thickness ~1 m Landmasses in Arctic prevent sea ice movement Arctic sea ice persists for 4-5 years Reach thickness of 4 m in central Arctic and 1 m on marginsGlacial Ice: Glacial Ice Mountain glaciers Equatorial high altitude or polar lower altitude Few km long, 100’s m wide and 100’s m thickGlacial Ice: Glacial Ice Continental ice sheets Large ice cube Existing ice sheets Antarctica and Greenland ~3% of Earth’s surface or 11% of land surface 32 million km3 (= 70 m of sea level)