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Annular Modes, Blocks and the Solar Influence A look at three separate, but arguably important influences on climate prediction Annular Modes A different view of the zonal index – global sea level pressure at 55N/S – positive index: westerlies are strong – negative index: more meridional flow averaged by day, week, month, season most significant in the winter (NH) Annular Mode NAM averaged for Jan-Feb-Mar (high) NAM averaged for Jan-Feb-Mar (low) Annular Mode NAM averaged Jan-Feb-Mar (high) NAM averaged Jan-Feb-Mar (low) Annular Mode Blue shading indicates ratio of cold days (T<1.5sd) to low values of NAM Annular Mode Annular Mode The Polar Night Jet (PNJ) oscillates in the stratosphere – develops each autumn at about 20km and reaches speeds of 50m/s – Northern Hemisphere PNJ is asymmetric due to thermal contrasts of land/oceans – PNJ is perturbed by upward propagating velocity waves (due to baroclinic waves) Annular Mode PNJ Dissipation – In Northern Hemisphere, deformation of the polar vortex plus upward propagating planetary waves leads to rapid weakening of the jet – lower polar stratosphere can warm by 50C as upper stratospheric air replaces cold core jet. Annular Mode Stratosphere Temps - Feb 22 2002 Annular Mode Global Warming and the NAM – Many GCM predict warming in troposphere and cooling in stratosphere – This causes a steep thermal gradient in the lower stratosphere due to tilted tropopause – In turn, leads to stronger than average PNJ which locks coldest air near the Pole – Explains warmth of most winters since 1980’s and patches of frigid air in far north Blocking Patterns Stagnation at High Latitudes Blocking Patterns Definition: – a ridge of high pressure aloft that bridges up to 45 degrees latitude and persists for more than 10 days. This causes a split in the jet stream leading to a meridional flow. – First studied by D.F Rex (rex block) and later by Austin, et al. Blocking Patterns Example of 500 mb flow Blocking Patterns Result of uneven distribution of land and ocean – leads to intense baroclinic waves – disrupts upper air flow due to anomalous thermal pools Result of dynamic flow on a rotating annulus – normal disruption of flow pattern that has axis of rotation at it pole – numerous model simulations lead to blocking patterns without topography Blocking Patterns “Chicken and the Egg” complex – NAO, ENSO, PNA - NAM all describe to some extent blocking patterns – Do these effects cause or are they the result of blocking patterns? – Once again, ocean temperature departures seem to be at the core of this conundrum Solar Contributions Sol - the weather’s best friend Solar Contributions Solar Flux - largest impact in the Tropics or middle latitudes during their summers – Must be considered for polar latitudes during winter because of ‘ionization’ effect of fewer neutrons when solar flux is high. – The ‘Svensmark’ effect has a purported role – Fewer neutrons, less clouds, more warmth Solar Contributions Svensmark Effect: Solar Contributions The connection: Solar Contributions Svensmark claims that concentration of neutrons explains much of the variance in satellite integrated cloud cover: Solar Contributions This effect seems to explain drift upward in global temperatures: Solar Contribution http://cloudws.web.cern.ch/cloudws/do cuments_talks/Henrik_Svensmark/index