1AnnouncementsModern climate system• Mean atmospheric circulation• Mean ocean circulation• Variability:– El Niño– Monsoons– North Atlantic Oscillation• Shortwave (gain) >> longwave (loss) at equator• Longwave (loss) >> shortwave (gain) at poles• Ocean and atmosphere move to redistribute thisheat; that is the source of weather and climateSun’s radiation is not the same everywhereexcessdeficitdeficitHow does energy transport happen?Mid-latitude stormsLow-latitude currentexample: Gulf Stream2http://www.newmediastudio.org/DataDiscovery/Hurr_ED_Center/Hurricane_Science.htmlHadley circulation• Mean pattern;simplification• Drives oceancurrents atsurface• Sets up rainy,dry zones• How stable isthis?Ocean surface currentsGlobal rainfallNote ITCZ, subtropical dry, and wetter midlatsAlso exceptions: monsoons, continental effectsClimate patterns: ENSO, monsoon,NAO, annular, PDO, AMO…• Reflect a natural organization of the climate system inspace and time– Impacts that go beyond physical climate– Time scales often irregular, not well predicted• Expect that ongoing/future changes in forcing will act onthese systems– How to distinguish natural and forced variability?– Examples from past: Holocene monsoon and ENSO• Not a lot of consensus on whether we are actually seeinghuman imprint yet– (but MUCH debate!)– Clearest indication: contraction of annular modes around poles3El Niño, La Niña, and the Southern OscillationENSO = El Niño/SouthernOscillation systemEl Niño is the interannualwarming of the eastern andcentral PacificLa Niña indicates cooling in thesame area.Southern Oscillation is theinverse relationship betweenatmospheric pressure in theE and W tropical PacificSea surface temperature anomalies from http://ingrid.ldeo.columbia.edu/MAY 1999DEC 1997El Niño and La NiñaLa Niña El NiñoWalker circulation breaksdown; ocean temperaturewarms up. Pressure high inW, low in E/central. Sealevel drops in W, rises in E.Walker circulation: east-westatmospheric circulation over thePacific: easterly trade winds,rising in W (low P), sinking in E(high P), westerly up high. Sealevel high in west.http://www.pmel.noaa.gov/tao/elnino/el-nino-story.htmlIndex of ENSO 1950-present• Interannual variations• Shift in 1976 to warmer state– fewer/weaker La Niñas, more/stronger El Niñoshttp://www.cdc.noaa.gov/ENSO/enso.mei_index.html00.020.040.060.080.1std. dev.(‰ !18O)Amplitude of ENSO variability in living and fossil corals(std. dev. of 2.5-7 yr bandpass filtered coral !18O timeseries)2.5ka 2.7ka 6.5ka 8.9-9.3ka 9.1-9.5kaMODERNage:length (years):(112) (108) (40) (95) (49) (83) (95)(A. Tudhope et al, unpublished)Past changes in El Niño4El Niño, Dec-FebLa Niña, Dec-FebENSO impacts beyondclimate: Extreme events (floods,storms, drought) Agricultural impacts Fire frequency Health, e.g. disease and airquality Biogeochemical consequencesthrough rainfall, plant growth,and upwelling changes Fisheries disruptions Ecosystem perturbation ofmarine and terrestrial systemsTucson during El Niño (1983)In the SW US, wetterwinters and morePacific storms increasethe potential for floodsWhat about La Niña…?• La Niña events may be worse forthe US than El Niño’s…–Drought–Fire–Atlantic hurricanes–Locally (Tucson): dry winters5What’s thecurrent statusof El Niño?“Weak La Niñaconditions aredeveloping”(NOAA requires 5months ofanomalous SST tobe a real LaNiña/El Niño)“Ensemble” of 40 model runsgives a mean result and a largespread.What should you believe?Largest events of20th centurySummer: land heatsfaster than ocean; risingair over land pulls inmoist air from ocean;this air rises andproduces rain.Winter: land coolsfaster than ocean; risingair over ocean producesrain; air over land is dryand no rain falls.Link to radiative forcing on other time scales (>seasonal)4050607080901001101201965 1970 1975 1980 1985 1990YEARRICE PRODUCTION IN INDIA AND PRECIPITATION1501601701801902002102202302402502602700.00.10.20.30.40.50.60.70.80.91.0123451979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989YEAREFFICIENCY IN MAIZE PRODUCTION IN MEXICOAND PRECIPITATION RATE DURING SUMMERRain and food supplyoften coupled.General trend ofincreasing production,but year to yearvariations often relatedto climate (rainfall).Figure from Magana andWebster 1998;http://webster.eas.gatech.edu/Archives/CLIVAR/paristalk/6Monsoons highly variableacross time and space20042003Monsoon and radiative forcing:what’s in store?• GHG forcing: intensify land-ocean contrast;stronger monsoon• Aerosol direct forcing: reflect radiation over landleading to reduced contrast; weaker monsoon• Aerosol indirect forcing: more clouds, morereflection over land, reduced contrast: weakermonsoon• New obs of semidirect forcing: upper level heatingcreates upper-level circulation pattern thatstimulates monsoon to come earlier, with highermonsoon rain totals in India (lower for E Asia)North American monsoonS of line:≥50% ofprecip insummer (JJA)http://geochange.er.usgs.gov/sw/changes/natural/monsoon/Annular modes• Annular = ring-shaped• Centered on poles (±)• Figs are results of “empirical orthogonalfunction” analysis ==> characteristicpatterns of sea level pressure.• In warmer world: pressure shifts to higherover poles, westerlies move poleward andintensify• Link to stratosphere; O3; solar variabilitySAM trend7The North Atlantic Oscillation• Large scale seesaw in atmospheric pressure (mass)between subtropical high and polar low in the N. Atlantic• A measure of this is the contrast in SLP between thesubtropical Atlantic and Iceland• Recent trend to positive values; linked to annular modehttp://tao.atmos.washington.edu/data_sets/nao/Positive NAO phase• Stronger subtropicalhigh, deeper Icelandiclow (greater contrast)• Europe: more andstronger winter storms,a more northerly track.• warm and wet wintersin N. Europe; dry Med.;cold and dry winters innorthern Canada andGreenland• eastern US: mild andwet winter conditionshttp://www.ldeo.columbia.edu/NAO/Negative NAO phase• Weaker subtropicalhigh and weakerIcelandic low (reducedcontrast)• Europe: Fewer andweaker winter storms,a more southerly track.• Moist air to Med. andcold to N. Europe; mildin Greenland• eastern US: cold airoutbreaks, snowyhttp://www.ldeo.columbia.edu/NAO/A few trends to think about• All from IPCC AR4, some from TS andsome from Ch 3• These are observations; model-basedpredictions