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Meteo 1020 – Lecture 4 The Natural Variability of the Earth-Atmosphere System • Natural variability can be classified by its forcing type (internal or external to the climate system) and whether it is periodic/cyclic or episodic. Modes of Natural Variability that we know of: timescale 1. Seasonal 90 days 2. El Niño Southern Oscillation 3-5 yrs 3. North Atlantic Oscillation decadal 4. Volcanism none 5. Ice ages 40,000 yrs 6. Pacific Decadal 20-50 yrs form forcing cyclic external cyclic internal cyclic internal?? episodic external cyclic internal cyclic ???? Ocean structure: on average: warm and relatively fresh mixed layer lying on top of a nearly isothermal (same temperature) cold and salty water mass Meteo 1020 – Lecture 4 The Natural Variability of the Earth-Atmosphere System Air-Sea Interactions: Ocean and atmosphere communicate with one another: 1. constituents: water (precipitation and evaporation), carbon dioxide, oxygen, trace gasses, etc 2. Energy – momentum through wind stress driving the surface currents 3. Heat – sensible heat and latent heat due to evaporation http://science.hq.nasa.gov/oceans/images/ water_cycle.jpg How does ocean circulation affect local climates? Answer: Heat release locations are warmer! http:// www. wbgu .de/I mage s/sn_ 2006 _en/2 .14.png Warm surface current- Less Dense Cold deep water current–More Dense Salty water anywhere- More Dense Intergovernmental Panel on Climate Change (IPCC), "Climate Change 2001: The Scientific Basis" What directions do warm and cold water currents travel? Is it true that the North Atlantic current could shut down? The ocean surface transfers heat to the atmosphere! Animation by Jack Cook (Woods Hole Oceanographic Institute) Animation by Jack Cook (Woods Hole Oceanographic Institute) Meteo 1020 – Lecture 4 The Natural Variability of the Earth-Atmosphere System What process could change the ocean circulation? http://www.whoi.edu/page.do?pid=12455&tid=282&cid=10046 go to bookmarks The global thermohaline circulation: Cold Salty water in the north Atlantic becomes dense and convects downward, spreads southward and contributes to vertical overturning of deep ocean water on millennial timescales. Importance: Climate of northern Europe and Asia rely on heat and moisture supplied to atmosphere to keep climate habitable in extreme northern latitudes. Is freshwater increasing in the North Atlantic? • http://www.whoi.edu/templates/files/multim edia.jsp?pid=12455&cid=7466&cl=6732 • Meteo 1020 – Lecture 4 The Natural Variability of the Earth-Atmosphere System Even though the oceans and atmosphere are both fluids, they have a fundamental difference – their density: Atmosphere 1 kg/cubic meter, Ocean – approximately 1000 kg/cubic meter. This density difference leads to large difference in heat capacity. Heat capacity is defined as the amount of temperature change in kelvin degrees for a unit input of heat energy. The ocean’s heat capacity is approximately 41 times that of the atmosphere. A 1 degree change in atmospheric temperature is equivalent to an 0.02 change in ocean temperature change. http://www.whoi.edu/institutes/occi/images/occi_abrclimate_jk_lev_en.gif Meteo 1020 – Lecture 4 The Natural Variability of the Earth-Atmosphere System El Nino is an example of air-sea interactions that occur on annual time scales Note figures 4.8 and 4.9: Sea surface temperature (SST) patterns change fundamentally with the el nino cycle The atmosphere both forces and responds to the el nino cycle. Normal sst patterns: atmospheric forcing of sst is accomplished through easterly trade winds cooling the central and eastern equatorial pacific. Atmosphere responds to warm western pacific water by the occurrence of strong thunderstorms in that region http://teacherresourceexchange.org/science/coriolis/index.php ENSO Outline ENSO Animation • • http://www.cpc.noaa.gov/ products/precip/CWlink/ MJO/enso.shtml#curren t http://sealevel.jpl.nasa.gov/science/images/el-nino-la-nina.jpg • • Mean state of the ocean and atmosphere across the tropical Pacific Mean ocean surface temperatures Mean tropical Pacific rainfall, winds, and subsurface ocean temperatures Mean wintertime jet streams over the North Pacific and South Pacific The ENSO cycle El Niño and La Niña Ocean Temperature Patterns The Southern Oscillation and its link to the ENSO cycle The Southern Oscillation Index (SOI) El Niño El Niño (ENSO) related rainfall patterns over the tropical Pacific El Niño-related winds, the state of the equatorial Walker circulation, subsurface ocean structure El Niño-related global temperature and rainfall patterns El Niño - related changes in atmospheric circulation in the subtropics and middle latitudes La Niña La Niña-related rainfall patterns over the tropical Pacific La Niña-related winds, the state of the equatorial Walker circulation, subsurface ocean structure La Niña-related global temperature and rainfall patterns La Niña- related changes in atmospheric circulation in the subtropics 2. Mean tropical Pacific rainfall, winds, and subsurface ocean temperatures • NOAA Image and text • NOAA Image and text Summary: Normally in the equatorial pacific El Niño and La Niña Ocean Temperature Patterns • Trade winds blow from the east to the west • Warm water piles up on the western side of the equatorial pacific ocean • Cool water upwells along the coast of South America • Low pressure is observed over Indonesia and the western pacific ocean and heavy rainfall occurs there • High pressure is observed in the eastern pacific ocean. • The Southern Oscillation and its link to the ENSO cycle • NOAA Image and text How are high and low pressures related to rainfall and winds? NOAA Image and text Pressure Force • More air on the left hand side (higher pressure). • The pressure difference over that distance of the sheet (the pressure gradient force), pushes the sheet to the right. Pressure Force • More air on the left hand side (higher pressure). • The pressure difference on either side of the parcel (the pressure gradient force), pushes the parcel to the right. Pressure Gradient Force http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/fw/pgf.rxml Ifhttp://teacherresourceexchange.org/science/coriolis/index.php the earth was not spinning, air would move directly from high to low pressure areas. Coriolis Force http://teacherresourceexchange.org/science/coriolis/index.php El Nino Related Rainfall • NOAA Image and text http://ww2010.at mos.uiuc.edu/(Gh )/guides/mtr/fw/gif s/coriolis.mpg Video 2. Mean tropical Pacific rainfall, winds, and subsurface ocean temperatures • NOAA Image and text El Niño-related winds, the state of the equatorial Walker circulation, subsurface ocean structure Ocean productivity and El Niño – easterly trade winds weaken, • allowing warmer waters of the western Pacific to migrate eastward and eventually reach the South American Coast. – The cool nutrient-rich sea water normally found along the coast of Peru is replaced by warmer water depleted of nutrients, resulting in a dramatic reduction in marine fish and plant life. • NOAA Image and text El Niño El Niño • El Niño NOAA Image and text La Niña-Related Rainfall Patterns over the Tropical Pacific • NOAA Image and text 2. Mean tropical Pacific rainfall, winds, and subsurface ocean temperatures • La Niña-Related Winds, Walker Circulation, and Subsurface Ocean Temperatures NOAA Image and text La Niña-Related Global Temperature and Precipitation Patterns • • World Connections of weather patterns shift in the distribution of heat in the atmosphere and ocean which moves things around (Boiling pot) NOAA Image and text La Niña NOAA Image and text • NOAA Image and text • NOAA Image and text Current Data • Stronger easterly (coming from the east) winds occur moving surface water away from the western coast of South America. • La Niña (female child) • La Niña occurs roughly half as often as El Niño. Current La Niña Sea Surface Temperatures • NOAA Image and text Upper ocean heat changes • NOAA Image and text Meteo 1020 – Lecture 4 The Natural Variability of the Earth-Atmosphere System An el nino is characterized by a general warming of the water in the central and eastern pacific. Atmosphere forces the ocean by a weakening of the easterly trades in the central and eastern pacific. Atmosphere responds by shifting thunderstorm activity eastward to the central pacific. Implications: Interruption of fishery along western margins of South America, failure and/or weakening of the Indian Monsoon impacting agriculture in that region. • NOAA Image and text • NOAA Image and text Ocean Anomalies Meteo 1020 – Lecture 4 The Natural Variability of the Earth-Atmosphere System El nino remote forcing: the modulation of the normal patterns in the equatorial pacific influence weather patterns around the world: In the U.S., the pacific storm track is shifted southward leading resulting in storminess over the southwestern U.S. and droughts over the Pacific Northwest. Precipitation is often reduced over the southeastern U.S. Meteo 1020 – Lecture 4 The Natural Variability of the Earth-Atmosphere System • Natural variability can be classified by its forcing type (internal or external to the climate system) and whether it is periodic/cyclic or episodic. Modes of Natural Variability that we know of: timescale 1. Seasonal 90 days 2. El nino 3-5 yrs 3. North Atlantic Oscillation decadal 4. Volcanism none 5. Ice ages 40,000 yrs 6. Pacific Decadal 20-50 yrs • The negative NAO index phase shows a weak subtropical high and a weak Icelandic low. • The reduced pressure gradient results in fewer and weaker winter storms crossing on a more westeast pathway. • They bring moist air into the Mediterranean and cold air to northern Europe • The US east coast experiences more cold air outbreaks and hence snowy weather conditions. Meteo 1020 – Lecture 4 The Natural Variability of the Earth-Atmosphere System Natural variability can be classified by its forcing type (internal or external to the climate system) and whether it is periodic/cyclic or episodic. Modes of Natural Variability that we know of: timescale 1. Seasonal 90 days 2. El nino 3-5 yrs 3. North Atlantic Oscillation decadal 4. Volcanism none 5. Ice ages 40,000 yrs 6. Pacific Decadal 20-50 yrs The NAO index is defined as the anomalous difference between the polar low and the subtropical high during the winter season (December through March) form forcing cyclic external cyclic internal cyclic internal?? episodic external cyclic internal cyclic ???? The Negative NAO • North Atlantic Oscillation • form forcing cyclic external cyclic internal cyclic internal?? episodic external cyclic internal cyclic ???? Positive NAO Index • The Positive NAO index phase shows a stronger than usual subtropical high pressure center and a deeper than normal Icelandic low. • The increased pressure difference results in more and stronger winter storms crossing the Atlantic Ocean on a more northerly track. • This results in warm and wet winters in Europe and in cold and dry winters in northern Canada and Greenland • The eastern US experiences mild and wet winter conditions Volcanic eruptions and climate: • The present atmospheric composition, Nitrogen-78%, Oxygen-21%, Argon-<1%, water vapor-0.4%, carbon dioxide-0.036% • How did the present atmospheric composition evolve? • Assume outgassing from early volcanoes provided the first atmosphere. • Composition of volcanic gasses: Water vapor-80%, Nitrogen-1%, Oxygen-0%, carbon dioxide12%, sulphur compounds and others-7% Volcanism and the early atmosphere: So how did the atmosphere evolve from the volcanic composition to our present composition? Earth’s Atmosphere Develops 1. Water began to precipitate early – forming oceans 2. Carbon Dioxide dissolved rapidly in the early oceans reaching saturation and leading to precipitate of Calcium carbonate to the deep ocean 3. Nitrogen and argon built up slowly since it does not dissolve in sea water 4. Oxygen built up in the atmosphere due to by product of photosynthesis. http://www.globalchange.umich.edu/globalchange1/current/lectures/first_ billion_years/first_billion_years.html EFFECTS OF LARGE EXPLOSIVE TROPICAL VOLCANOES ON WEATHER AND CLIMATE Volcanoes produced the atmosphere and the oceans EFFECT/MECHANISM Volcanic emissions 1. Enhance or reduce El Niño? BEGINS DURATION 1-2 weeks 1-2 months Tropospheric absorption of shortwave and longwave radiation, dynamics N2 remains N2 CO2 photosynthesis O2 H2O condensation 2. Reduction of diurnal cycle Immediately 1-4 days Blockage of shortwave and emission of longwave radiation 99% of atmosphere 3. Summer cooling of NH tropics, subtropics Immediately 1-2 years Blockage of shortwave radiation 4. Reduced tropical precipitation Immediately ~1 year Blockage of shortwave radiation, reduced evaporation oceans 5. Reduced Sahel precipitation (?) 1-3 months 1-2 years Blockage of shortwave radiation, reduced land temp., reduced evaporation Tambora in 1815, together with an eruption from an unknown volcano in 1809, produced the “Year Without a Summer” (1816) EFFECTS OF LARGE EXPLOSIVE TROPICAL VOLCANOES ON WEATHER AND CLIMATE EFFECT/MECHANISM BEGINS 6. Ozone depletion, enhanced UV DURATION 1 day 1-2 years Dilution, heterogeneous chemistry on aerosols 7. Global cooling Blockage of shortwave radiation Immediately 1-3 years multiple eruptions: 10-100 years 8. Stratospheric warming Immediately 1-2 years Stratospheric absorption of shortwave and longwave radiation 9. Winter warming of NH continents ½-1½ years 1 or 2 winters Stratospheric absorption of shortwave and longwave radiation, dynamics High latitude eruptions: 10. Cooling of continents Immediately 1-2 years Blockage of shortwave radiation 11. Reduction of Indian summer monsoon ½-1½ years 1 or 2 summers Continental cooling, reduction of land-sea temperature contrast Tambora, 1815, produced the “Year Without a Summer” (1816) “The Scream” Edvard Munch Percy Bysshe Shelley Mary Shelley George Gordon, Lord Byron Painted in 1893 based on Munch’s memory of the brilliant sunsets following the 1883 Krakatau eruption. These two photos show the Earth’s limb at sunset before and after the Mt. Pinatubo eruption. The first view (STS41D-32-14) shows a relatively clear atmosphere, taken August 30, 1984. Astronauts were looking at the profiles of high thunderstorms topping out at the tropopause at sunset; different atmospheric layers absorbed the last rays of light from the sun as the spacecraft moved eastward. Pinatubo June 12, 1991 Three days before major eruption of June 15, 1991 The same type of photograph (STS043-22-23) was taken August 8, 1991, less than two months after the Pinatubo eruption. Two dark layers of aerosols make distinct boundaries in the atmosphere. The estimated altitude of aerosol layers in this view is 20 to 25 km. Photo from USGS. From http://earthobservatory.nasa.gov/Study/AstronautPinatubo/astronaut_pinatubo2.html Casadevall et al. (1996) After Pinatubo, Clark Air Force Base 25 km from volcano Bataan Photo by R. P. Hoblitt, June 15, 1991 After Pinatubo, Cubi Point Naval Air Station, 40 km from volcano After Pinatubo, Subic Bay Naval Base 35 km from volcano Photo by Tom Grzelak U.S. Navy photograph by R. L. Rieger The climate effects of volcanic eruptions: What makes an eruption climatically significant? • nature of the eruption – lava vs. ash (ash is more significant) • composition – need high sulfur dioxide gas content • location – Tropical eruption spread globally In most eruptions, the particulates have only a minor effect. If the sulfur dioxide gas can reach the stratosphere, it converts to small sulfuric acid droplets that have long residence times in the stable stratosphere. It is this cloud of particles that spread and influence climate over long periods. Note Figure 4.3 in the book. Pacific Decadal Oscillation • Natural variability can be classified by its forcing type (internal or external to the climate system) and whether it is periodic/cyclic or episodic. Modes of Natural Variability that we know of: timescale 1. Seasonal 90 days 2. El nino 3-5 yrs 3. North Atlantic Oscillation decadal 4. Volcanism none 5. Ice ages 40,000 yrs 6. Pacific Decadal 20-50 yrs form forcing cyclic external cyclic internal cyclic internal?? episodic external cyclic internal cyclic ???? Pacific Decadal Oscillation warm phase phase cool http://teacherresourceexchange.org/science/coriolis/index.php http://teacherresourceexchange.org/science/coriolis/index.php How does weather move the energy (heat) move from equator to the poles? Vertical winds, horizontal winds, and the release of latent heat transport the energy! Our atmosphere is a three cell model. http://teacherresourceexchange.org/science/coriolis/index.php These three cells transport energy to the poles. Winds Patterns Balance of 3 forces 1. The pressure gradient force causes wind to blow from high pressure toward low pressure. 2. The coriolis force causes wind to be deflected to the right of the motion in the northern hemisphere. 3. Friction which slows the wind. Pressure Force • More air on the left hand side (higher pressure). • The pressure difference over that distance of the sheet (the pressure gradient force), pushes the sheet to the right. Pressure Force Pressure Gradient Force • More air on the left hand side (higher pressure). • The pressure difference on either side of the parcel (the pressure gradient force), pushes the parcel to the right. http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/fw/pgf.rxml Pressure Gradient Force Pressure Gradient Force • Hurricane’s have a strong pressure gradient force! • This generates fast winds! Winds Patterns are a balance of 3 forces Ifhttp://teacherresourceexchange.org/science/coriolis/index.php the earth was not spinning, air would move directly from high to low pressure areas. 1. The pressure gradient force causes wind to blow from high pressure toward low pressure. 2. The coriolis force causes wind to be deflected to the right of the motion in the northern hemisphere. 3. Friction which slows the wind. Coriolis Force • Stronger as you move AWAY from the equator (dependant on latitude). • There must be initial motion for the coriolis to take place (there must be a wind). • Reference information: Coriolis force = 2 * the rotation rate of the earth * sin (degree latitude) * velocity of the wind Coriolis Force Southern hemisphere video (earth spinning from the point of view “underneath” the earth. Video Coriolis Coriolis (Northern Hemisphere- air moves to the right of the initial motion) (Northern Hemisphere- air moves to the right of the initial motion) Direction of initial motion • Highs – clockwise rotation • Lows – counterclockwise rotation (cyclonic) • Northern Hemisphere Surface map • Northern Hemisphere Satellite map Coriolis Coriolis (Southern Hemisphere - Air moves to the left of the initial motion) (Southern Hemisphere - Air moves to the left of the initial motion) • Highs- counterclockwise rotation • Lows- clockwise rotation Direction of initial motion • Southern Hemisphere Satellite • Southern Hemisphere Pressure Coriolis (earth turns underneath the slower wind) Direction of initial motion http://teacherresourceexchange.org/science/coriolis/index.php Geostrophic Balance • Coriolis Pressure Gradient Movement Animation Geostrophic Wind Pressure Gradient Force = Coriolis Force H L Initial Motion • Balance of forces summary • Pressure • Coriolis • Friction Winds Patterns are a balance of 3 forces Geostrophic Balance Lines of constant pressure Arrows show wind flow Frictional Force 1. The pressure gradient force causes wind to blow from high pressure toward low pressure. 2. The coriolis force causes wind to be deflected to the right of the motion in the northern hemisphere. 3. Friction which slows the wind. Pressure Gradient and Coriolis and Friction H L Initial Motion http://teacherresourceexchange.org/science/coriolis/index.php