What triggers el nino events?

  • #1

Main Question or Discussion Point

What triggers the onset of an el nino event?
Are my conclusions listed below reasonable?
The southward conduction and flow of cold air and water from the arctic region in the north are inhibited by local air and sea currents in and around the arctic warming the pacific ocean around indonesia and new guinea.
In some years warmer water from the arctic sea thermocline
heads south.El nino occurs even when the south flowing Bering strait
cold current is cut off by glacial periods and this is why the reduction of cold air flow to the south must also be a factor
in triggering el nino.With the flow of cold air reduced the trade winds warm a little around indonesia and new guinea causing small changes
in local wind patterns and warming the local winds.
These changes in temperature and direction of local winds are small but a door is opened allowing a burst of a much larger volume of hot air
north of australia to move east causing a Kelvin wave which warms the ocean in an easterly direction along the equator.
In 1997 el nino became hotter then colder and then hotter again.This was a particularly
intense el nino episode.There must have been a larger than average number of kelvin waves
generated by air coming in waves ( a lot of cold air followed by a little) from the arctic
and periods when no waves were generated allowing the equator to cool a lot.The complex currents of air and water in the arctic give el nino its unpredictable nature - it is hard to say when el nino will occur and how intense it will be in a given year..The 1997 el nino started in spring time when water from the arctic that was mixed in
december approached the equator ( bottom waters mix with top waters in december in arctic).This water may have been particularly warm that year opening many "doors" around northern australia.
The hot zone that forms around the antarctic peninsula -in the sea - is warm air carried
south from the equator in the mid-pacific ocean -air that forms part of the westerly wind flow.
El nino is triggered by a relatively small change in heat distribution in the northern hemisphere
and this is why the trigger is hard to detect.
Since people don't report seeing changes in local surface wind temperatures and directions could the changes be higher in the atmosphere?Or out at sea? I have heard that vertical convection occurs in the so-called Madden Julian oscillations and that these can precede el nino and that in one particular year a 4 month spell of Madden Julian oscillations was followed by a particularly intense el nino?
Why doesn't el nino occur every year? Surely heat is not getting stored in the atmosphere from one year to the next
waiting to burst out as el nino - the air cools so fast in one night!Isn't it more likely that something like the arctic trigger
I suggested determines when el nino occurs?
 
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Answers and Replies

  • #2


La nina events are the opposite of el nino events - the eastern pacific becomes colder and the western pacific warmer than usual.
La nina occurs 50 per cent of the time after el nino events.
Is this simple explanation for la nina likely to be right?
If sufficient warm water from an el nino event moves on the south equatorial current to eastern australia,it can lower atmospheric pressure and encourage the south easterly trade winds to move faster from the east pacific to australia,
cooling the east pacific by drawing in cold air from the antarctic ocean.So for la nina to happen the
heat energy of el nino would disperse less to the west south and north of the equator than in a non la nina year.
So would there be higher pressure in these compass directions at the start of a la nina year?Higher pressure keeping
the heat contained and unable to move away apart from to the east.
 
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  • #3
Is this a more convincing explanation for the onset of el nino:Warmer air and water than normal pass from the arctic
through the bearing strait area and warm the westerly winds.
The westerlies pass heat on to the equatorial current via the california
current. This warmer air passes north of the equator to the west pacific
and the lower pressure it produces causes more warm air to move from
the area of indonesia and new guinea towards the east.The trade winds oppose
this easterly motion less because of the warmth brought by the warmer
than usual current of water that passes through the bering strait and that heads south
close to japan.
The jet stream in the north may also be more southerly and warmer than usual
due to lower pressure around the bering strait , and the jet stream takes
heat to the west coast of the usa,some of which may be transferred
to the california current and then to the equator.
Lower pressure at the bering strait than average may indicate the onset of el nino.



Is the intensity of an el nino event determined by how much warm water
vapour is in the air around the equator? Air with lots of water in it is more dense and can
push its way through other drier air masses around it.Perhaps this is why madden julian oscillations
can be followed by intense el ninos - the vertical convection of air and water
results in more humid and warm air above the sea on the equator.This air could then pass
its heat energy to the sea itself.The water vapour must be drawn from a large area and concentrated
in a smaller area or else there would be noticeable changes in salinity of the sea.
El nino would then take a year or two to reoccur because more humid air has to be "pumped in"
after an el nino event.
When el nino occurs the antarctic peninsula has warmer sea water
but more sea ice.This suggests that water from the equator evaporated and passed from high
altitude to the antarctic peninsula, lowering the salinity of the sea and warming the sea too.
Ice can form in less saline and higher temperature water (freezing point is raised).
The ross ice shelf gets bigger in an el nino year - this may be the cold high pressure
over the antarctic shifting towards the ross shelf in response to lower
pressure at the antarctic peninsula.The warm water south of austalia during el nino
may be due to warm air moving from the indian ocean to the westerly moving air masses at sea level
in the south.Do you think all this is plausible?
Can el nino be predicted by measuring the temperature and humidity of the upper and lower atmosphere at lots of places in a fixed area between for example
australia and indonesia (where there are large climate fluctuations due to el nino).When the equatorial pacific
starts to cool and no more energy is being pumped into it then presumably the el nino pump is
exhausted of fuel and needs to recharge with warm humid air.Would measurements of temperature and humidity
at the time of exhaustion tell us how long it would be until another el nino i.e how much fuel needs to go
back in the tank.
 
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  • #4
Since el nino is unaffected by ice ages the most likely scenario is that el nino only depends on the tropics for its creation.So it is most likely self-triggering.
The humidity and temperature of air east of indonesia (droughts come to indonesia in el nino years) and new guinea must reach such a high point that the heat can no longer be contained and it bursts eastwards into the sea.The indonesian and guinean land masses
stop heat spreading through the sea to the west.The heat must be pumped out of the atmosphere into the sea and air to the east consistently or else the temperature in the guinea indonesia region would be unbearable.So the question surrounding the el nino phenomenon is why does heat which normally exists over a large area around indonesia and guinea become funelled along a narrow strip on the equator.How does the internal energy of the atmosphere in the indonesia guinea area become chanelled.Perhaps the el nino of 1997 in which the el nino oscillated and the equator heated up then cooled and then heated up again can help get to the answer.What was switching the heat pump on and off? The answer probably lies in the weather of the previous year -1996.Something damaged the heat pump.But what? The answer is unlikely to be ocean currents bringing in cold water because ice ages do not affect el nino.
The indian ocean dipole was strong and hot and close to indonesia in the months leading up to el nino of 1997.
This may have had profound effects on the surface layers of the sea and on the atmosphere around indonesia.
A lot of warm pacific ocean water passes by indonesia to the indian ocean.
In 1997 the sea around indonesia and north western australia was particularly cooler than usual.We can hypothesise that more heat than usual was being transferred to the air around indonesia and pumped out of the region eastwards along the equator giving the intense el nino.And there was a period of three months from july to september when there was a more sustained period of cooling than usual in the sea around indonesia. This must have caused the peak of the heat oscillation that year on the equator and elsewhere.

http://wn.com/Indian_Ocean_Dipole

Around southern indonesia heat can be removed from the sea by humid air from northern australia- the dampest part of australia.
The walker circulation shifts east
http://www.weeklytimesnow.com.au/images/uploadedfiles/editorial/pictures/2009/06/24/Drying_Up.jpg [Broken]
http://en.wikipedia.org/wiki/Walker_circulation
The walker circulation may be affected by the Hadley Cell which accounts for the trade winds and also has its origin at the equator.

Heat may also be transferred to the equator north east of australia from northern australia.

The stratosphere has a 2 yearly cycle of winds and 2 years is the minimum time between el ninos although
no suggestions have yet been made by scientists to suggest there is a link
http://en.wikipedia.org/wiki/QBO
Any phenomenon that slows the walker circulation or changes its direction is a suspect as the trigger for el nino.

If the equatorial thermocline became more dense north of new guinea and less dense west of chile then the vertical circulation
in the ocean caused by the walker circulation in the atmosphere would be impeded.This could be caused by cold antarctic water
running along the ocean floor rising upwards in response to topographical features in its path.Like a kalman vortex around a flagpole that oscillates from side to side the antarctic cold water current would oscillate over a period of years.The floor of the pacific is not smooth and topographically very complex and many such cold water currents could be interacting and modifying each other's paths giving the unpredictable nature of el nino.The source of energy for the oscillations would be the gravitational acceleration of cold water descending from the antarctic ice shelf.
La nina events could be initiated after el nino events by heat shifting from the same area north of new guinea to australia on the south equatorial surface current.
It is doubtful that a build up of electricity from thunderstorms is responsible for changes in walker circulation.Aircraft would be affected by such changes (which would have to be large in a small area)at all altitudes in the atmosphere.
It is of great interest to note that the Japan Trench and the Marianas Trench (the deepest part of the ocean in the world) lead from the cold water of the northern pacific to the equatorial current north of new guinea (west edge of a walker cell) and that the Chile trench leads from the antarctic to the east edge of a walker cell.These trenches may guide or perturb the flow of cold deep water and account for el nino oscillations.
 
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  • #5
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El Nino's don't happen every year, because they occur near the equator where seasonal variations of the sun are minimal.

It's is an oscillation of hot and cold waters. The time to charge and discharge are influenced by weather systems which are chaotic. Typical frequency if 5 years, but can range from 2 to 7. It is also not clear how climate change may impact El Nino.
 
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