Journal of Theoretics

Commentary  Vol.3-5



El Nino, A Possible Trigger Mechanism

by Joseph F. Cuny <cuny@jps.net>

Science now realizes that the El Nino weather phenomenon has been around for centuries. Recognition that El Nino is real, has led to a search for its cause. The public perception of this phenomenon is a reversed link with the weather, whereby atmospheric conditions trigger the warm water flow that then modifies the weather. This ‘closed loop’ perception, of course, is due to the work of many meteorologists and other scientists who have identified the El Nino-Southern Oscillation link.

According to that link, which seems to fit the known data, the east-west air circulation is driven by air pressure differences between that over the Pacific near South America and that near Indonesia/northern Australia. The upper surface waters of the Pacific are alternately driven to the east and then to the west. The so-called trade winds that are low-level easterlies, along with subsurface Kelvin waves, help carry the sun warmed surface water to South America. This heats the air and thereby intensifies the trade winds. The mass of warm water distributed across the Pacific affects the humidity and weather patterns, producing the El Nino phenomenon.

Even though this ‘explains’ the phenomenon, it does not seem to explain the trigger that initiates the Kelvin waves and the reversal of the air circulation pattern. As the warm water approaches South America, the change in local air pressure reinforces and intensifies the new weather pattern produced by the collapse of the high air pressure near Indonesia/Australia. Since the repeatability of the phenomenon is unpredictable, it is considered anomalous. There is a strong possibility, however, that the trigger or the engine driving El Nino is actually deep in the ocean rather than being in the atmosphere. Although the following is extremely simplistic, it presents the necessary concepts.

The key to understanding this engine is the knowledge that hydraulic flow patterns may be present in bi-stable states, or at least quasi-stable states. In effect these are the repetitive creation and destruction of eddy currents. At the end of the El Nino phase, rotation of the ocean in the vertical plane is essentially a single rotating mass from the ocean floor to the surface. The sub-surface ridges and canyons, however, partition the lower region into pockets or compartments.

The lower portion of this flow sweeping these pockets (the initial bi-stable state) gradually rises in elevation, until there is a ‘clean’ relatively unobstructed main circulation pattern. As this bottom flow rises, it drives a reversed flow eddy current beneath it. The interface between the two flows provides for the momentum/energy transfer to the eddy with virtually no mass exchange between the two. This second bi-stable state has lower total energy because the speed of the eddy current may be significantly less than of the main flow. The second state evolves from the first, due to the (mini-max) principle of minimum energy.

At this point the thermal energy from the ocean floor (rifts, vents, etc.) begins to heat the water in the eddy. As this water warms up, the interface greatly restricts thermal diffusion but salt diffusion across this boundary may partly compensate for the reducing density of the eddy flow. When this water becomes warm enough, the thermal energy added to the rotational energy allows the warm water to ‘punch through’ the upper mass. The upwelling occurs where the upward moving kinetic energy of the eddy can displace the down-flow of the main circulation. This is on the west end of the eddy where it simply bypasses or displaces easterly the down-flow of the main circulation. This upwelling then begins to move in all directions but primarily to the east as a surface sheet flow.

During the transitional period as the warm water is rising on the west, the residual rotational momentum/energy allows the eddy to continue to retain its integrity. As the upper cold water ‘fills in’ behind the eastern end, the eddy is driven to the surface in one long, continuous pulse. In effect the cold water sweeps the warm water out of the pockets, reinforcing the upwelling. When the cold water begins to fill in behind the lower eddy, the upper main circulation pattern is disrupted. The additional energy provided by the fill in process aids in the energy transfer necessary to reverse the surface flow.

When all of the warm water of the eddy current has been displaced to the surface, the residual momentum carries a large mass of cold water to the surface. This cold water causes a collapse of the local high pressure thereby reversing the atmospheric flow patterns and yielding the traditional El Nino flow. Additionally, since the upwelling discharge of the eddy is affected by various local conditions such as wave action, this flow tends to oscillate at various frequencies. These oscillations are then propagated horizontally as Kelvin waves.

In this scenario, the engine driving the phenomenon is the heat released on the ocean floor. This heat gradually warms one or more large pockets of water that form contiguous eddies or eddies that may become contiguous as their upper boundaries are lifted by the thermal expansion. They may also be close enough together that the onset of upwelling from one pocket may ‘drag’ enough additional water to provide a flow path for the nearby pockets. The mechanism that makes this phenomenon possible is the hydraulics allowing two flow conditions, one stable main circulation with its eddy currents, and one quasi-stable circulation without the eddies.

The time from one stable condition to the next stable condition is the cycle time. This cycle time depends on many variables including recovery time for the minimum energy flow (the main water circulation pattern), heat transfer to the eddy currents or pockets, and upper surface flow patterns that affect the amount of energy needed to punch through. There may also be heated pockets to the north and south of the major circulation; these would have different cycle times and would lead to ‘beat frequencies’ yielding variations in the El Nino strength and timing. They would, however, show up in the El Nino surface flow because they would join the upwelling from the major eddy.

It might also be noted that as stated above, the pockets of water expand as they are heated. This expansion, however, is minimal due to the intense pressure near the bottom of the ocean. When this heated water reaches the surface and flows eastward as a surface sheet flow, the water expands to its full potential thereby raising the surface elevation of the ocean.

 

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