The 30 day Southern Oscillation Index is at +12 – will El Niño fade again next month?

click for larger image

click for larger image

Here is what the current SST map looks like:

clickable global map of SST anomalies

From Nine News in Australia:

The Southern Oscillation Index (SOI) is calculated from the monthly or seasonal fluctuations in the air pressure difference between Tahiti and Darwin.

A strongly and consistently positive SOI pattern (e.g. consistently above about +6 over a two month period) is related to a high probability of above the long-term average (median) rainfall for many areas of Australia, especially areas of eastern Australia (including northern Tasmania) – La Niña.

Conversely, a ‘deep’ and consistently negative SOI pattern (less than about minus 6 over a two month period, with little change over that period) is related to a high probability of below median rainfall for many areas of Australia at certain times of the year – El Niño.

However, it is important to remember that the pattern of relationship between SOI and rainfall (and temperature) can vary depending on the particular season and region. Additionally, the change in SOI over a specified period can be as important in understanding relationships between SOI and rainfall as is the absolute value in SOI.

Here is what BoM has to say about it. While they note that we “remain at El Niño levels” they also note that “The latest 30-day value (+12) is unusual for a developing El Niño”.

Summary: Ocean indicators remain at El Niño levels

Ocean conditions in the Pacific Basin remain at El Niño levels. Should they persist at such levels through the remainder of the southern winter and into spring, as predicted by the world’s leading climate models, 2009 will be considered an El Niño year.

While El Niño indicators have fluctuated over the past few weeks, the overall picture remains one of a developing El Niño event. Pacific Ocean surface temperatures, which drive El Niño events, currently exceed El Niño thresholds and are around 1°C above average. Cloud patterns and rainfall along the equator are becoming consistent with a developing El Niño event.

However, some indicators run contrary to a normal El Niño development. The Southern Oscillation Index (SOI) is currently strongly positive: persistent negative values are a feature of El Niño events. Similarly, ocean temperatures in the western Pacific, Coral Sea and off northern Australia have been much warmer than during previous El Niño events.

El Niño periods are usually (but not always) associated with below normal rainfall in the second half of the year across large parts of southern and inland eastern Australia.

The value of the Indian Ocean Dipole (IOD), as measured by the Dipole Mode Index (DMI), has fallen steadily since the middle of June. The Bureau’s POAMA model suggests the IOD may increase over the coming months.

See IOD forecast, DMI values.

Map showing recent winds and temperatures in the tropical Pacific. Click on the map for a larger version. From NOAA/PMEL/TAO website.

From the NOAA/PMEL/TAO website.

In Brief

  • The sea surface is significantly warmer than the long-term average across most of the tropical Pacific Ocean, with El Niño thresholds met in central to eastern areas.
  • A large amount of the sub-surface water of the tropical Pacific is also warmer than the long-term average, particularly in the east.
  • The latest 30-day SOI value is +12, while the monthly value for June was −2. The latest 30-day value is unusual for a developing El Niño; persistent negative values are a feature of El Niño events.
  • Trade winds have been consistently weaker than normal in the far western equatorial Pacific in recent months. Trade winds have fluctuated over the central to eastern tropical Pacific, with winds generally slightly stronger in July than in June.
  • Consistent with an emerging El Niño, there is increasing cloudiness near the date-line.
  • All international climate models predict the tropical Pacific to continue to warm and to be above El Niño thresholds throughout most of the second half of 2009.

Graph of 30-day Southern Oscillation Index values from 2006.
This graph is updated automatically each day. Download data.

Details

The central and eastern equatorial Pacific sea surface warmed through June and has remained warm through the first part of July. This warming is a continuation of a steady warming trend that has been observed since February 2009. Positive SST anomalies are now well established across most of the equatorial Pacific, with the monthly indices for June being +0.8°C, +0.7°C and +0.6°C for NINO3, NINO3.4 and NINO4 respectively.

In terms of weekly data, the most recent NINO indices are +1.1°C, +0.9°C and +0.6°C for NINO3, NINO3.4 and NINO4 respectively. Although the most recent NINO3 and NINO3.4 values are significantly warmer than their June values, over the past two weeks there has been little change in the weekly NINO index values. Consistent with the establishment of an El Niño, the 7-day SST anomaly map shows a persistence of positive anomalies of greater than +1.0°C across most of the central and eastern equatorial Pacific. Should these warm anomalies persist through the remainder of the southern winter and into spring, 2009 will be classed as an El Niño year. However, contrary to normal SST conditions during El Niño events, ocean temperatures in the western Pacific, Coral Sea and off northern Australia have been warmer than average. An animation of recent SST changes is available.

The sub-surface of the equatorial Pacific has steadily warmed since February 2009. A large volume of warmer than normal sub-surface water has been evident across most of the tropical Pacific since May. A four-month sequence of Pacific Ocean equatorial temperature anomaly is available here. The sequence shows a slight cooling of the sub-surface in the western tropical Pacific through July. A recent map for the 5 days ending 20 July shows warmer than normal sub-surface water extending across most of the equatorial Pacific, with anomalies exceeding +2.0°C over much of the eastern Pacific. When compared with two weeks ago, the sub-surface has cooled slightly, particularly in the west, however, most of the sub-surface remains significantly warmer than the long-term mean. An animation of recent sub-surface changes is available.

An archive of past SST and sub-surface temperature charts is available.

Trade Winds have been consistently weaker than average over the far west of the tropical Pacific in recent months. The Trade Winds have fluctuated over the central to eastern equatorial Pacific with Trades being generally weaker than the average in June and slightly stronger, closer to the long term mean in July. The latest weekly wind anomalies are shown in the TAO/TRITON map (small image above) for the five days ending 20 July.

The Southern Oscillation Index (SOI) is currently strongly positive with a 30 day value (30 July) of +12. The SOI is usually negative during normal El Niño development, therefore the current positive SOI trend is unusual. Ocean temperatures in the western Pacific, Coral Sea and off northern Australia have been warmer than average. The warmer waters near Darwin may have impacted on the SOI by keeping mean sea level pressure (MSLP) lower at Darwin, while recent weather patterns have kept Tahiti MSLP high. Some cooling of the warm waters off northern Australia has occurred in the past week. As the equatorial Pacific continues to warm and Trade Winds remain generally weak the SOI is expected to fall to negative values again. (SOI graph, SOI table).

Cloudiness near the date-line over the central to western Pacific is another important indicator of warm/cool ENSO conditions, as it normally increases/decreases (negative OLR/positive OLR anomalies) during these episodes. Cloudiness near the date-line has increased steadily in recent months. Consistent with a developing El Niño, cloudiness near the date-line has generally been greater than normal over the past few weeks. This is supported by satellite measurements of rainfall, which now show above average in rainfall in these areas.

All international dynamic computer models surveyed by the Bureau of Meteorology predict further warming of the Pacific Ocean SST in coming months. All models predict SST to be above El Niño thresholds throughout most of the second half of 2009. One of the surveyed models shows less vigorous warming than other models, however all models predict El Niño conditions to be established by the southern spring at the latest. As all models surveyed agree El Niño conditions will persist, and as historically the southern winter is a time of good model predictability, the probability of El Niño conditions remaining through 2009 is high. If this occurs, 2009 will be declared an El Nino year. Recent forecasts from the POAMA model, run daily at the Bureau of Meteorology, show a steady warming with El Niño conditions developing in July. Pacific conditions and model predictions will continue to be monitored closely.

For the mathematically minded (from Australia’s BoM)

There are a few different methods of how to calculate the SOI. The method used by the Australian Bureau of Meteorology is the Troup SOI which is the standardised anomaly of the Mean Sea Level Pressure difference between Tahiti and Darwin. It is calculated as follows:


         [ Pdiff - Pdiffav ]
SOI = 10 -------------------
             SD(Pdiff)      

where

Pdiff   =   (average Tahiti MSLP for the month) – (average Darwin MSLP for the month),
Pdiffav   =   long term average of Pdiff for the month in question, and
SD(Pdiff)   =   long term standard deviation of Pdiff for the month in question.

The multiplication by 10 is a convention. Using this convention, the SOI ranges from about –35 to about +35, and the value of the SOI can be quoted as a whole number. The SOI is usually computed on a monthly basis, with values over longer periods such a year being sometimes used. Daily or weekly values of the SOI do not convey much in the way of useful information about the current state of the climate, and accordingly the Bureau of Meteorology does not issue them. Daily values in particular can fluctuate markedly because of daily weather patterns, and should not be used for climate purposes. A table of monthly SOI values is available here. Approximate 30-day values are often included in the weekly El Niño Wrap-Up.

h/t to WUWT reader rtgr

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36 thoughts on “The 30 day Southern Oscillation Index is at +12 – will El Niño fade again next month?

  1. @Ted Annonson

    I suspect errors in the NOAA map. For example, it shows warm to hot (+5!)anomalies off the coast of Buenos Aires, which we know is having temperatures 5F below average and had unusual freezing conditions a couple of days ago. It would be valuable to study the whole map to see if there are more discrepancies.

  2. I have been watching the BOM site for several weeks now and their reasons for the SOI rising (local weather conditions near Darwin and Tahiti, high mean sea level pressure at Tahiti, warmer waters near Darwin, etc etc) yet they continue to predict with some confidence that the SOI will fall and an El Nino will be established.

    Can’t say I would like to put my house on an El Nino developing looking at the SST anomaly loop:

    But whether we have record snowfalls, flood, famine, fire or drought in the coming months, it does seem certain that an Emissions Trading Scheme will be voted in by both Government and Opposition as according to Opposition Leader Turnbull today, the vast majority of Australians want some action on Climate Change.

  3. I fear El Nino will be frozen in his crib by the White Witch-La Nina-by October.
    Just in time for Boreal Winter…

  4. Am I right in saying that the reason it is called ‘El Niño’ is that its effects were usually felt around Christmas time? If so, isn’t July a little early to be thinking about it!?

  5. Just stirring up the moisture for Northern Winter to come along and bury the playground in white stuff. A gathering fleet of Big Snow dumptrucks.

  6. Scott Gibson (20:14:06) :

    That would explain the warmer than normal GISS, wouldn’t it? Doesn’t GISS use NOAA’s SST data in it’s anomaly measurements? Or am I mistaken?

  7. It looks as if the +12 was the peak. July has 4 days to go and the last four June SOI values contributing to the current 30 day SOI averaged +30. The mean for the 26 days of July so far is +4.4. Although, as noted above, one should be careful about using daily values, there hasn’t been a daily value above 10 for nearly two weeks so it is likely the the July mean will end up at around +3 to +4 which is neutral territory.

    Daily values are at http://www.longpaddock.qld.gov.au/SeasonalClimateOutlook/SouthernOscillationIndex/30DaySOIValues/ They are calculated slightly differently than those at BOM.

  8. OK, I see some tension and an insufficient separation between the “definition of ENSO regimes” and “predictions of its consequences”. As far as I am concerned, El Nino is defined in a way, by the SST anomalies in the ENSO regions, inequalities, and their persistence etc.

    So if the models work for a few months, the El Nino conditions will become an episode and there’s no reason for mysterious and ambiguous statements here.

    Whether such an episode will have all the consequences that we normally associate with an El Nino is an entirely different question. Each such a correlation may fail to be a general rule. Even if it used to be a rule and not a series of coincidences, each such a rule may break down if the climate jumps into a different system.

    I would bet that a positive contribution to the global mean temperature will remain a property of El Ninos, as defined from Pacific SST anomalies, simply because the Pacific Ocean is so big and El Nino makes it warmer.

    But even if many such conclusions and detailed weather predictions from El Nino fail this year or in the future, one should be careful to keep the definitions seriously. If the consequences become completely detached from the SSTs, in the way we were used to, we should invent new terminology. El Nino has been taken by science, so the definition should be scientific. If the weather patterns decouple from the SSTs, the weather patterns will really be “new” and a new term for them would be appropriate.

    I don’t think that the evidence that this is gonna happen is too strong.

  9. Is there a tropical Cu-Nim index? Warm western waters allow earlier cu-nims each day which will pump up the trade winds and kill the Nino by Christmas?

  10. What is the level of hurricane/typhoon activity so far this year and how does that play into the picture?

  11. Scott Gibson (20:14:06) :

    @Ted Annonson

    I suspect errors in the NOAA map. For example, it shows warm to hot (+5!)anomalies off the coast of Buenos Aires, which we know is having temperatures 5F below average and had unusual freezing conditions a couple of days ago. It would be valuable to study the whole map to see if there are more discrepancies.

    Which coast are you looking at. Buenos Aires is on the East Coast and considerably further south than the funnel of warm SST in the Pacific.

  12. In general, the variations in the SOI agree with those of NINO3.4 SST anomalies, though they do so in opposite directions. The qualifier in that sentence was “in general”. Since this is a post about the SOI, I’ve scaled and inverted NINO3.4 SST anomalies in the following comparison chart.

    While they do follow one another, there can be periods of divergence, so using the SOI as a predictor of an ENSO event has to consider that fact.

    As of last Monday’s NOAA/NCDC update of the weekly (OI.v2) SST anomaly data…

    http://bobtisdale.blogspot.com/2009/07/mid-july-sst-anomaly-update.html

    …NINO3.4 SST anomalies have been flat for a few weeks. Does that mean they won’t climb more? No, just means they took a breather. They are presently above the threshold of an El Nino.

    Looking at the subsurface temperature anomalies…

    http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_update/wkxzteq.shtml

    …if the subsurface anomalies rise to the surface (and there’s no reason to believe they won’t), there would be a moderate El Nino.

  13. There are two types of predictive models used by NOAA. One is a dynamical model that kind of uses calculated mechanisms to predict what will happen. This is a new type of model that has yet to be proven and uses massive amounts of computing power. It is being compared against the standard statistical model. The statistical model uses past conditions and affect sets to predict future events. If conditions now mimic conditions in the past, then the affect will be whatever happened in the past. This kind of model continues to improve itself statistically as more “sets” are added to the mix of historical data. It can be run on a single PC with statistical software and follows the standard of “more data means higher confidence”. The dynamical model does not improve itself unless someone tinkers with it.

    The current NOAA models diverge based on what kind of model is run. The dynamical models predict El Nino. The statistical models not so much.

  14. Scott Gibson: You wrote, “I suspect errors in the NOAA map. For example, it shows warm to hot (+5!)anomalies off the coast of Buenos Aires, which we know is having temperatures 5F below average and had unusual freezing conditions a couple of days ago. It would be valuable to study the whole map to see if there are more discrepancies.”

    I assume the +5 deg C anomalies you’re talking about on the NOAA July 23rd map are the small area located about 38S, 54W. The Unisys map dated two days later (July 25th) also shows an elevated anomaly there. The Unisys data has also been smoothed. So why is the NOAA data bad but the Unisys data dated two days later okay?

    Additionally, the Brazil Current (travels toward the southwest) and the Malvinas Current (travels toward the northeast) meet right about that spot.

    Eddies result where two currents meet. Warm water or cool water can accumulate in eddies. So, regardless of what the weather is like 570 km away in Buenos Aires, the SST anomalies in that area are not likely to represent it on a daily, weekly, or monthly basis.

  15. All these indicators are strongly correlated with the ENSO:

    - the Southern Oscillation Index just west of the Nino regions, the Trade Winds over the Nino regions, Atmospheric Angular Momentum, Equatorial Upper Ocean Heat Content Anomaly in the Nino regions, Outgoing Long-Wave Radiation just west of the Nino regions.

    Since they are all correlated with the ENSO, they are also strongly correlated with each other.

    They are all part of the same system – whatever that really is.

    Here is a couple of charts I haven’t posted before – Nino 3.4 versus the Equatorial Upper Ocean Heat Content Anomaly and versus Outgoing Long-Wave Radiation.

    All together, these indicators are not pointing to a strong long-lasting El Nino (with the ocean heat content being the lone indicator saying it will strengthen) but I guess we’ll have to watch and see.

    About 80% of El Ninos and La Ninas peak in the November to January period and they start slowly building up in the spring and strengthen throughout the summer and fall.

  16. Jimmy Haigh

    “Am I right in saying that the reason it is called ‘El Niño’ is that its effects were usually felt around Christmas time? If so, isn’t July a little early to be thinking about it!?”

    As a Canadian who has spent about 1/4 of his life in Peru, I believe I can answer that.

    The warm currents usually reache the general area of the Peru-Ecuador border around December. For this reason the change in current was named “El Niño” – the Christ child.

    I first became aware of this in the 1982-83 southern summer when I was working on a hydro project in northern Peru and we had double the annual rainfall in one month (Feb 83). The damage was very extensive and paleohydrologists estimated that the event was of a recurrence interval of 1:600 years.

    Locals were astonished because they had never seen anything like it before.

    I would like to see what the paleohydrologists have to say about ENSO/AGW/PDO etc. They’re a pretty reticent bunch.

  17. Global Warming or Global Cooling? A New Trend in Climate Alarmism

    by Dr. David Evans

    http://www.globalresearch.ca/index.php?context=va&aid=14504

    The ocean data that the alarmists are relying on to establish their warming trends is all pre-Argo, from XBTs. Now that we are measuring ocean temperatures properly, the warming trend has disappeared. And by coincidence, it disappeared just when we started measuring it properly!
    Notice how the Minister’s graph above shows rising ocean heat content for 2004 through 2006, but the Argo data shows a cooling trend? There is a problem here.

    The Argo data is extraordinarily difficult to find on the Internet. There is no official or unofficial website showing the latest ocean temperature. Basically the only way to get the data is to ask Josh Willis (above). The graph above come from Craig Loehle, who got the data from Willis, analysed it, and put the results in a peer reviewed paper available on the Internet. Given the importance of the ocean temperatures, don’t you think this is extraordinary?

    If the Argo data showed a warming trend, don’t you suppose it would be publicised endlessly?

    So what’s going on? Our best data, from satellites and Argo, says that both the air and oceans have not warmed for at least five years now. In the short term, some cooling force is overpowering the warming due to human emissions.

    Let’s look at the long-term trend. The medieval warm period around AD 1000 – 1300 was a little warmer than now: crops grew in Greenland, and there were many signs around the world of extra warmth during that period. That gave way to the bitter cold of the little ice age from 1400 to 1800: animals in Europe died from cold even inside barns, and the River Thames in London would freeze over every winter (it last froze over in 1804).

    Global air temperatures have been rising at a steady trend rate of 0.5°C per century since about 1750, as the world recovers from the little ice age:

    On top of that trend are oscillations that last about 30 years in each direction:

    1882 – 1910 Cooling
    1910 – 1944 Warming
    1944 – 1975 Cooling
    1975 – 2001 Warming

    In 2009 we are where the green arrow points in Figure 5, with temperature levelling off and beginning to fall slightly. The pattern suggests that the world has entered a period of cooling until about 2030.

    The long-term trend suggests that the last warming period (1975-2001) was like the previous one (1910-1944), and that once the effects of the little ice age have finally passed, the temperature will get back to where it was in the medieval warm period (which is also where it was during the Roman Optimum, and in the Holocene optimum before that).

    What about human influence? Human emissions of CO2 were virtually non-existent before 1850, and were insignificant compared to current levels until after 1945.

    It is worth bearing in mind that there is no actual evidence that carbon dioxide was the main cause of recent warming—it’s only an assumption, and the calculations of future temperature rises derive most of their warming from an assumed water vapor feedback for which there is only counter-evidence.

  18. @Bob Tisdale–Thanks, an eddy makes sense to make for a disconnected hot area. I also wasn’t aware that the Unisys map also shows that anomaly.

    However, I was also concerned it shows the warm anomaly going right into the bay where Buenos Aires and Montevideo are located, knowing that the area has been extraordinarily cold and not warm. And for John Finn, of course Buenos Aires is on the east coast. It is in the bay at the Rio Uruguay mouth, which is shown as a warm anomaly on the map referenced above.

  19. Ha, and right on cue, a tiny spot of cool over Buenos Aires. Which suggests the entire warm belt is interpolated between two data points, emphasizing the warm point and de-emphasizing the cool point. It would really help if they published all the data at a scale we could really see, showing the places where the readings come from.

  20. As the el nino (warm waters) and la nina (cold waters) accounts for the fish catch in the pacific. It increases with cold waters (La Nina). FAO forecasts the catches: (paper link below)

    Years Peruvian Anchovy Japanese Anchovy
    2005 6.7 2.5
    2010 8.6 3.0
    2015 10.5 3.1
    2020 8.5 2.6
    2025 6.8 2.0
    2030 4.6 1.0
    2035 2.6 0.7
    2040 2.4 0.4
    And FAO forecasts only a variation of temperatures ranging from -0.1 to +0.1 degrees to the year 2099, which contradics alarmist IPCC predictions. (both of the same UN organization)
    ftp://ftp.fao.org/docrep/fao/005/y2787e/

  21. Ed Scott (09:35:50) :

    Your summary of the multiple cycles (800 year peak-to-peak major (Medieval Warm period – LIA – Modern Warming Period) cycle with a 30 year minor cycle superimposed on it can explain much of the apparent proxy “errors” in the LIA and MWP.

    A “high” point in the 30 year short cycle can easily “add” 1/4 to 1/2 of one degree temperature to a true low period, and thus hide the actual overall coolness for the actual date in question. (Add in errors in the date of the measurement itself, plus actual weather changes, plus the usual error bars) and you can easily get isolated “proof” that “this proxy proves that the LIA does not exist.

    Equally, you can get” as well proxies showing “This record proves the Medieval Warming Period does not exist” when a short low point in the 30 year cycle subtracts from the overall higher general temperatures for actual date in question.

  22. I think the widespread and generally elevated ocean temperatures will continue, and not just in the Pacific. This is not a warm PDO el nino like ’98. It is heat accumulated in the oceans during the long run of high amplitude-short duration solar cycles coming back out at this time of solar quiet. The longer the solar minimum drags on, the greater the momentum will be of upwelling warm water being released. Because the air is cool, the heat release will continue until cloudiness helps to restore the balance.

    If you look at the historical SST’s back in the late 1800′s, there were some big el nino events as the oceans cooled down to the minimum around 1900.
    This will give false support to the AGW camp, but we will have the last laugh in 18 months or so when temperatures fall below the Jan 2007 value again.

    Meantime, enjoy the balmy weather. ;-)

  23. In physiology (I am a Physiologist), life systems have mainly negative feedback. Maybe in Nature (the Earth), the same thing happens. The sun is dying (very temporary in millenian terms), but could be very significant for the next 20-30 years). The Oceans may have reserve heat systems (such as El Nino) to compensate. This minimun may not be enough so we may go into a small ice age. Even NASA is acknowledging that the Sun ain’t doing what they expected (see Hathaways predictions etc..)

  24. Speaking of forecasting fish tonnage, I predict today I will catch my limit in trout. The fishing has been very good with lots of fish in the rivers here in NE Oregon. So far, an 18 incher was landed by my aunt. I have caught 10″ to 16″ fish nearly every day that I have not been in bed fighting off whooping cough. The increased presence of fish is likely due to colder waters off the coast on up to Alaska. Cold waters there nearly always predict increased fish tonnage. La Nina’s are great for those of us hooked on hooks and the lag keeps em coming for a while. If ENSO conditions remain neutral to cool (as I believe they will), the fishing season now and next year will continue to be enjoyable.

  25. Slightly OT, but involving the surge in fish populations that occur during La Ninas:

    A.) A lot has to do with an increase of upwelling, which brings an increase in nutrient-rich water from down deep. The change can be quite abrupt and startling. Besides the water getting abruptly colder, it changes its color because there is an immediate plankton bloom. This plankton bloom feeds a swift population-explosion of fish. Also the sky is abruptly filled with terns and gulls.

    B.) As I understand it, anchovy population-explosions alternate with sardine population-explosions. No one is exactly sure why one species has the advantage one cycle, while the other has the advantage another cycle.

    C.) For the most part people seem to look upon the cold upwelling as a responce to other factors. In other words, pressure gradients and trade winds cause the upwelling to turn on, or else squelch it. I wonder about this. Are there occations when the upwelling is what changes the winds and pressure gradients?

    When you experience any sort of upwelling episode, out at sea, you get the sense a tremendous power is involved, lifting all this cold and heavy water from down deep. (Cold water wants to sink, and upwellings in a sense defy gravity.) I tend to wonder what is happening upstream, in the thermohaline circulation, to generate such a push from below, rather than imagining one can always blame the breezes overhead.

  26. Those breezes can be strong enough to move ice bergs, most of which are below sea level. If they are strong enough, alarmists think the Arctic is melting away because of heat. Those trade winds can move a LOT of water. By the way, didn’t catch my limit but did catch a 17″ and 15″ trout.

  27. Caleb (16:12:57) : “…C.) For the most part people seem to look upon the cold upwelling as a respon(s)e to other factors. In other words, pressure gradients and trade winds cause the upwelling to turn on, or else squelch it. I wonder about this. Are there occa(s)ions when the upwelling is what changes the winds and pressure gradients?”

    Yeah, I keep wondering the same thing. Upwelling cold water raises both the surface viscosity and the air density (via lower humidity) above it, both of which will present more resistance to wind and thus lower the net wind velocity. The reverse is true, thus the system will oscillate.

  28. Pamela Gray (17:02:02) :
    Don’t get me wrong. I don’t doubt that the wind has effects which can be great. I just wonder if there are OTHER effects as well.

    Let us imagine a wind shift causes west-moving ice up at the pole to halt and move east. You get the formation of a lead’s open water in one place, but the ice piles up into a pressure ridge in another place.

    OK. Assume a pressure ridge’s jumble of ice sticks up twenty feet above sea level. It forms a sail that sticks up twenty feet into the wind. However, if nine tenths of ice is above water, the roots of that pressure ridge stick down 9 times twenty feet, or 180 feet. That is one heck of a keel sticking down into the current. Might it deflect the current? Might it steer the movement of the ice in some way?

    When I have insomnia, (like tonight,) I amuse my mind by considering such stuff.

    For example, some talk a lot about the volume of the sea-ice, these days.
    Others talk about the sea-ice area. Yet a simple calculation shows it takes a large area of six-foot-thick ice to make a pressure ridge twenty feet high that also juts 180 feet downwards. Are pressure ridges included in volume calculations? Also, if ice juts down into a current which is warmer than normal, does it increase the rate of melt? Does this in turn create some sort of wave in the thermohaline circulation? Are wave-like rises and falls ever noted in the level of the thermocline? When the thermocline reaches the surface as upwellings, are wave-like patterns ever noted?

    My day-job involves a lot of contact with kids. They are full of questions, and perhaps their mind-set has affected me, because I am full of questions as well. My questioning can be quite annoying to people who feel they have all the answers, (especially when Global Warming comes up at a cocktail party,) and some even suggest my science is questionable, (especially after a third cocktail.) I can only reply I’m not pretending to be a scientist with answers; rather I am filled with child-like wonder over the amazing way our planet works, and wonder expresses itself with questions.

  29. Caleb,

    I am not an expert, but I doubt that a pressure ridge of twenty feet results in a corresponding downwards spike of 180 feet. The force (weight) of the pressure ridge would probably be distributed throughout the ice sheet to which it was attached. As new ice was not created (it was just rearranged, so to speak) there should be no or very little net increase in the depth of the ice.

  30. Tamara,

    I am no expert, either. However I do know that subs have to avoid downward-jutting protusions of ice. Exactly how far down they stick, I am unsure of.

    I do like to wonder about this stuff. One neat thing about this site is that often people answer your wonderings.

    If we don’t get an answer about how deep the roots of pressure ridges go on this thread, I’ll bring it up on a future thread, as a direct question. Then maybe we’ll meet someone who has an answer.

    Or maybe we’ll just start a debate. You never can tell.

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