Dear Alistair, Someone said that there were 3 new ideas in 20th century physics - relativity, quantum mechanics and chaos theory.
ENSO is endlessly fascinating. Deep oceanic currents are driven by thermohaline circulation and by the rotation of the planet. The deep currents interact with, and tend to be suppressed by, a sun warmed surface layer that is a hundred or more metres deep. Deep ocean currents occasionally surface in the south eastern Pacific in one of the major areas for upwelling on the planet. Upwelling subsurface water is both frigid and rich in nutrients leading to booms and busts in biological activity affecting fisheries, mammals and birds off the Pacific coast of South America. This area is designated as Large Marine Ecosystem (LME) No. 13, is amongst the most productive environments in the world and is known as the Humboldt Current. A good introduction is provided by National Oceanic and Atmospheric Administration (NOAA) at their LME/Humboldt Current web page. The thermodynamic evolution of the Humboldt Current is dominated by ENSO. ENSO is an oscillation between El Niño and La Niña states over a 2 to 7 year cycle. An El Niño is defined as sustained sea surface temperature anomalies greater than 0.5O degree C (in the Nino 3 region) over the central pacific. Conversely, a La Niña is defined as sustained sea surface temperature anomalies less than -0.5O degrees C. The oscillations are driven by complex interactions of cloud, wind, sea surface pressure and temperature, planetary rotation and surface and subsurface currents. See for instance Klaus Wolter's Multivariate ENSO Index. The short explanation is that the Pacific trade winds set up conditions for a La Niña. Trade winds, south-easterly in the Southern Hemisphere and north-easterly in the Northern Hemisphere, pile up warm surface water against Australia and Indonesia. Water vapour rises in the western Pacific creating low pressure cells that strengthen the trade winds piling yet more warm water up in the western Pacific. Cool, subsurface water rises in the eastern Pacific and spreads westward. At some point the trade winds falter and warm water spreads out westward across the Pacific. It is worth having a good mental picture of SST in La Nina and El Niño - big differences and this is where the link to surface temperature variation is found. see: http://www.elnino.noaa.gov/lanina.html There are two Pacific Ocean modes. One is the 2 to 7 years ENSO mode. I think this can very usefully be viewed as a bimodal phase space. The other is the 20 to 30 year mode identified in the Pacific Decadal Oscillation. The PDO is a tendency for enhanced upwelling in the north eastern Pacific for 2 or 3 decades followed by 2 to 3 decades of reduced upwelling. There are huge biological implications but the PDO is simply an indication of a balance between a warm surface layer and cold turbulent upwelling. There is less ocean heat for 2 to 3 decades and more upwelling followed by 2 to 3 decades of more ocean heat and less upwelling. Again a bimodal phase space but over a longer period. The cool PDO mode is associated with more frequent and intense La Niña and the warm mode with more frequnet and intense El Niño. This is a great site for following the fortunes of ENSO and other indices: http://ioc3.unesco.org/oopc/state_of_the_ocean/all/ The question is - what are the 'bifurcation parameters'? A mate of mine has a wild theory that it is driven by UV radiation changes from the Sun - itself a complex system. If you pull up yesterdays SST anomaly satellite image from NOAA - you can see a tongue of cold water extending up the Antarctic Peninsula to the west coast of South America. http://www.osdpd.noaa.gov/data/sst/anomaly/2010/anomnight.2.11.2010.gif The idea is that UV changes result in warming and cooling of stratospheric ozone. This in turn influences downwelling in the polar vortex (an effect related to planetary spin - dynamic environments indeed). A cooler stratosphere leads to more downwelling and a more intense vortex. The vortex drives cold surface (Ekmann) flows (perpendicular to the wind direction) which flow up the Antarctic Peninsula to South America where the cool Antarctic waters interact with upwelling currents and drive 'thermal evolution' of ENSO. The thermal evolution of ENSO influences Walker and Hadley circulation, cools or warms the planet and influences the formation of extratropical cloud in reinforcing processes. The ISCCP cloud analysis is particularly revealing - a decrease from about a 69% cover in the mid 1980's to about a 64% cover in 2000. It increased a little around 2001 - and has been more or less constant since. http://isccp.giss.nasa.gov/zD2BASICS/B8glbp.anomdevs.jpg The cloud cover directly changes incident short wave radiation and ocean heat content and therefore the dynamic balance of warm surface and cold upwelling. Greenhouse gases should of course also change the dynamic balance. We are basically messing about with stuff we know little about. But both 'the science is certain' and cap and trade are losing strategies albeit for different reasons. Cheers Robert On Feb 11, 9:38 pm, Alastair <[email protected]> wrote: > I am currently rereading "Chaos" by Gleick, and hoping this time I > will master it. So it would probably be better if I keep quiet at the > moment. > > But I see ENSO as a strange attractor, with quasi-random movement > within bounds. I also think El Nino is one phase of the ENSO cycle, > and that the idea of a permanent El Nino is as sensible as the sound > made when clapping with one hand. > > Cheers, Alastair. > > On Feb 10, 9:27 pm, Robert Indigo Ellison > > <[email protected]> wrote: > > Gear Alistair > > > 'Most commonly applied to the mathematical study of dynamical > > systems, a bifurcation occurs when a small smooth change made to the > > parameter values (the bifurcation parameters) of a system causes a > > sudden 'qualitative' or topological change in its behaviour.' > > > But the term entering chaos does also seem to be used to used as an > > equivalent to bifurcation. > > > Slowing down refers to a state of maximum autocorrelation. That is > > minimum change in values in a sliding window in a time series. > > Oscillations tend to a minima - in detrended data in the case of Dakos > > et al. For decadal climate shifts - I think we might be better off > > looking at ENSO rather than surface temperature. Decadal scale > > climate shifts are accompanied by large ENSO events (La Nina and El > > Nino) and the oscillations then tend to a minima (slowing down) just > > before another shift. > > > I believe you can see hints of this pattern in the ENSO graph > > approaching and following the 1998/2001 climate shift. > > >http://ioc-goos-oopc.org/state_of_the_ocean/sur/pac/nino3.4.php > > > Surface temperature changes are strongly correlated to ENSO - 70% > > according to McLean et al (sorry can't help myself). But instead of > > looking at decadal trends - detrend it and look at the magnitude of > > interannual variations to detect autocorrelation maxima. > > > Cheers > > Robert > > > On Feb 10, 10:14 pm, Alastair <[email protected]> wrote: > > > > On Feb 9, 10:53 pm, Robert Indigo Ellison > > > > <[email protected]> wrote: > > > > >look at how we can describe and analyze > > > > > systems in order to recognize and predict when they'll become > > > > > chaotic...." > > > > > One way of looking at trying to predict phase shifts is with > > > > autocorrelation. > > > > > I think perhaps the systems are always chaotic but the tipping point > > > > is known as bifurcation. > > > > I don't think so. The first bifurcation happens when the system > > > enters chaos. > > > > "Here, we analyze eight ancient abrupt climate shifts and show that > > > they were all preceded by a characteristic slowing down of the > > > fluctuations starting well before the actual shift. Such slowing down, > > > measured as increased autocorrelation, can be mathematically shown to > > > be a hallmark of tipping points. Therefore, our results imply > > > independent empirical evidence for the idea that past abrupt shifts > > > were associated with the passing of critical thresholds. Because the > > > mechanism causing slowing down is fundamentally inherent to tipping > > > points, it follows that our way to detect slowing down might be used > > > as a universal early warning signal for upcoming catastrophic change > > > > >http://www.pnas.org/content/105/38/14308.full > > > > We have now entered a period when the temperature rise has slowed > > > down. That is what they say happens as we are about to pass a tipping > > > point :-! > > > > Cheers, Alastair. > > -- You received this message because you are subscribed to the Google Groups Global Change ("globalchange") newsgroup. 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