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Review for Midterm 3 What we have discussed after Midterm 2 • • • • Tropical cyclones Tropical and extratropical climate Observed global climate change Projection of global climate change Global Climate System Spatial Scale Globe Global warming Multi-decadal Oscillation Ice age Glacial cycle El Nino Biennial Oscillation Continent Monsoon Madden-Julian Oscillation Tropical waves Annular modes Diurnal variation Heat wave Midlatitude cyclone Tropical cyclone State Mesoscale convective system Thunderstorm Tornado Shallow convection Boundary layer turbulence City Football field 1 mm 1 m 10-4 m Vapor/Cloud/precipitation Radiation Composition 10-15sec 1sec 1min 1day 1mon 1yr 10yr 100yr 100,000yr Time Scale The most common atmospheric circulation structure H L Cooling or No Heating Spiritual Social Health Economy Heating Radiation Convection Conduction Greenhouse Gases Pollution Clouds Precipitation (Latent heat) Latent/Sensible H L Imbalance of heating Imbalance of temperature Imbalance of pressure Wind Biosphere Land/Ocean/Ice/Stra tosphere Feedback Standard units of measurement SI (System International) Quantity Length Mass Time Temperature Density Speed Force Pressure Energy Power Name meter kilogram second Kelvin kilogram per cubic meter meter per second newton pascal joule watt Units m kg s K kg/m3 Symbol m kg s K kg/m3 m/s m/s m.kg/s2 N/m2 N.m J/s N Pa J W Scientific Notation nano micro milli centi deci deka hecto kilo mega giga … yotta one-billionth one-millionth one-thousandth one-hundredth one-tenth ten one hundred one thousand one million one billion 10-9 10-6 10-3 10-2 10-1 101 102 103 106 109 1024 0.000000001 0.000001 0.001 0.01 0.1 10 100 1000 1000000 1000000000 Tropical cyclones • Tropical cyclone genesis: Western Pacific has the highest averaged number per year. 6 necessary conditions. 4 stages. • Tropical cyclone structure: 3 major components, rotation direction of inflow and outflow, location of maximum wind and rainfall, 3 feedbacks • Tropical cyclone intensity scale. Category 1: 74mph, category 5: 155mph • Tropical cyclone destruction: 4 reasons. Which side has the most intense destruction? • Trends and variability in tropical cyclone activity Necessary conditions for tropical cyclone formation 1. SST > 27 oC (Poleward of about 20o SST too cold for formation. Highest frequency in late summer to early autumn when water is warmest.) 2. Warm ocean mixed layer is thick enough to supply energy (this is why they weaken quickly upon landfall) 3. Unstable atmosphere with a moist lower/middle troposphere (central and western ocean basins) 4. Low vertical windshear (Otherwise upward transfer of latent heat disrupted) 5. Coriolis force (hurricanes do not form between 5N-5S) 6. Pre-existing low-level rotating circulations (tropical waves and other disturbances) Structure of tropical cyclones • Size and lifetime: about 600km, last up to a week or more • Make up: many thunderstorms arranged in pinwheel formation • Three components: 1. Central eye - clear skies, light winds (25 km diameter) 2. Eye wall - maximum rainfall and wind speed. 3. Spiral rainbands • Cylonic inflow, anticyclonic outflow. Tropical cyclone Destruction and Fatalities Destruction caused by: • Hurricane-scale winds (>74 mph) • Rainfall (10 in/day) • Storm surge (winds blowing coast-ward + lower atmosphere pressure) • Fine-scale Tornadoes Destruction most intense on right side of cyclone (wind + storm speed) Tropical and extratropical climate Tropical climate: • Mean state: The two basic regions of SST? Which region has stronger rainfall? What is the Walker circulation? • Mean state: Two types of ocean upwelling, ocean-atmosphere feedback • El Nino and La Nina: Which region has warm SST anomaly during El Nino? 4-year period. • Land-sea contrasts: seasonal monsoon Extratropical climate: • Mean state: westerly winds, polar vortex • What is the primary way El Nino affect extratropics? (Pacific/North American Oscillation) • The oscillations associated with strengthening/weakening of polar vortex: Arctic Oscillation, Antarctic Oscillation Tropical mean state • Determined by east-west sea surface temperature contrast: Indo-Pacific warm pool, eastern Pacific cold tongue • Walker circulation, which interacts with underlying ocean and causes equatorial upwelling and coastal upwelling 2 basic regions Indo-Pacific warm pool Eastern Pacific cold tongue Ocean upwelling • is an oceanographic phenomenon that involves wind-driven motion of dense, cooler, and usually nutrient-rich water towards the ocean surface, replacing the warmer, usually nutrient-depleted surface water. • Equatorial upwelling: Due to Coriolis effect • Coastal upwelling: Due to Coriolis effect El Nino/Southern Oscillation (ENSO): The 4-year oscillation • El Nino: Very warm sea surface temperature over central and eastern tropical Pacific, which occurs every 3-7 years. The Walker Circulation becomes disrupted during El Niño events, which weakens upwelling in eastern Pacific. • La Nina: the opposite condition to El Nino • Southern Oscillation: The atmospheric oscillation associated with the El Nino-La Nina cycle. • The whole phenomena is now called El Nino /Southern Oscillation (ENSO) Land-Sea Contrast: Seasonal “Monsoon” • A seasonal reversal of wind due to seasonal thermal differences between landmasses and large water bodies (landsea contrast) • Orographic lifting often enhances precipitation totals Observed global climate change • 3 ways human activities affect the climate. • Rapid increase of greenhouse gases (CO2, CH4, N2O) since 1750: far exceed pre-industrial values determined from ice core measurements spanning the last 650,000 years, which is mainly caused by CO2 fossil fuel use. Lead to strong radiative heating. • The developed countries and developing countries contribute almost equally to the emissions of GHGs. • Observed change of mean: air temperature, ocean temperature, melting of arctic sea ice, Greenland ice sheet, snow and glaciers, rising of sea level. • Observed change of extreme events: extreme precipitation events, heat waves, strongest hurricanes How do human activities change the global climate? Human beings are changing the global climate system in three different ways: • Release or cleanse greenhouse gases • Release or cleanse pollutants (aerosols) • Change land cover (deforestation and urbanization) Observed change of greenhouse gases Global atmospheric concentrations of CO2 and CH4 have increased markedly as a result of human activities since 1750 and now far exceed pre-industrial values determined from ice core measurements spanning the last 650,000 years! GHG Emissions by Sector Greenhouse gas emissions per capita The developed countries and developing countries contribute almost equally to the emissions of GHGs. Global map of temperature change: Largest warming in Arctic (“Arctic amplification”) Larger warming over land than ocean Retreat of Mountain Glaciers: a major contributor to sea level rise Glacier retreat is a world-wide phenomena. Will affect water supply for millions: • Kenya/Tanzania • Northern India • Andes Mountains IPCC (2001) Projection and mitigation of global climate change • Global climate models: Earth system models (5 components) • Global climate models can reproduce the observed warming in the 20th century. The warming is largely caused by human activities. • Projected change: mean temperature (largest warming over Arctic, larger over land), mean precipitation, sea level, extreme temperature, extreme precipitation, fresh water, ecosystems • Abrupt climate change and tipping points • Future climate scenarios show that reducing greenhouse gas emissions can substantially mitigate warming in the latter half of this century. • Mitigation: International (Kyoto Protocol), Green economy (Renewable energy, Sustainable transportation, Green buildings, Energy-efficient industry and carbon capture, Land management, afforestation, waste management) • We can make a difference by reducing waste of energy, food and other materials, and by purchasing environment-friendly products. Framework of Earth System Model Atmosphere Sea Ice Coupler Biogeochemistry Ocean Land • Include 5 components: atmosphere, ocean, land, sea ice, biogeochemistry • Based on the conservation laws of mass, energy, momentum, water vapor and other chemical species (e.g. CO2, CH4) • Based on future assumptions of external forcing (GHG concentrations, solar variability, pollution, land use changes) Can the GCMs Reproduce the 20th Century Temperature Trend? The GCMs can reproduce the 20th century temperature trend The warming is caused by anthropogenic forcings! Projected Change in Global Mean Temperature Global map of projected change Temperature: Largest warming over Arctic, larger over land Precipitation: Increase in tropics/poles, decrease in midlatitudes Impacts on ecosystems 4.0 3.0 Green economy About Midterm 3 • There will be <50 multiple-choice questions