The Pacific coast of South America is similar to our own. The continent steeply drops off into deep ocean. In normal (non-ESNO) conditions at the equator, the prevailing winds blow east to west, gently pushing the warm surface water away from land, allowing cooler nutrient-rich deep ocean water to rise (upwelling) to the surface. This nutrient-rich water is the source of the "food chain", supporting high levels of primary productivity, diverse marine ecosystems, and major fisheries. The weather onshore is cool, because of the sea temperatures, and rainfall is low. Normal (non-ESNO) conditions in the western Pacific are tropical, with warm ocean temperatures and standard rainfall conditions.

When an ENSO begins, the tradewinds (easterlies) blowing off South America intensify, usually lasting for a few months. The warmer surface water is pushed westward and collects east of the Malay Peninsula, creating lower barometric pressures in the western Pacific and higher barometric readings in the eastern Pacific. (Generally winds blow from high pressure areas to low pressure areas.) As the barometric differences increase, the winds intensify and warm water accumulates faster in the western Pacific. The warm water, not as dense as cool water, changes the mean sea level at either peak of an ENSO as much as 18". The satellite images below show sea level. These readings loosely conform to sea surface temperatures (SST).

Eventually, the winds weaken, upwelling in the eastern Pacific diminishes and barometric pressure drops. The warm water or energy stored in the western Pacific has to go somewhere. Sea level drops in the west and rises in the east as warm water surges east along the equator in the form of a pulse. The average energy of the warmer water associated with one of the ENSO events is 30 times the energy consumed by the United States this year alone. This is the beginning of what we call El Nino.

The moist air over the ocean warms and rises, creating strong low pressure systems and heavy tropical rainfall. As the pool of warm water moves east, barometric pressure rises in the western Pacific and westerly winds increase accelerating the pulse. The warm water can move across the Pacific in as little as a month. When the warm water reaches Ecuador it surges both north and south along the American coast. The effects have been seen as far north as Canada and as far south as central Chile. At the peak of the event we see tropical conditions, heavy rainfall, and flooding in South America. The high pressure in the West Pacific creates drought conditions in Australia, Malaysia, and the western and central pacific.

Satellite imagery of this year's El Nino. Data shown is variation from mean sea level. The warm water associated with the ENSO is red with a white center.

Recent history of El Nino events:

There have been ten ENSO events in the last 40 years. Reports from NOAA, National Oceanic and Atmospheric Administration, show most of them raised water temperatures along the South American coast out as far as the Galapagos Islands and along a belt stretching 5,000 miles across the equatorial Pacific.

I found a report posted at the NOAA website dated early 1995 and it states: "The weaker events raised ocean temperatures by only 2 to 4C, having only minor impacts on South American fisheries; however, the strong events, like the El Nino of 1982-83, had a major effect on the weather in South America, and significantly disrupted climatic conditions around the globe. The 1982-83 event, during which sea surface temperature increased by as much as 20C, will probably go on record as the strongest El Nino in this century. (Recent developments suggest that the 1994-95 El Nino may have been as strong, if not stronger than the 1982-83 event.) "

The Jet Propulsion Laboratory has been collecting data as part of the Special ENSO Project. The 1994-1995 event now is considered to have started in 1990 and lasted until 1995. I quote from a posting at the University of Iowa website: Kevin E. Trenberth and Timothy J. Hoar. Geophysical Research Letters, Vol. 23, No. 1, pp 57-60. January 1, 1996.

"Sea- surface temperatures in the central Pacific Ocean have remained high over the 1990-1995 period, which is highly unusual over the 113-year record for which data are available. This has led to a persistence in the Southern Oscillation, even though temperatures in the traditional El Nino region have fluctuated. Both the recent trend toward more ENSO occurrences since 1976 and the extended ENSO event of 1990-1995 are unexpected from the previous record. Statistical analysis shows that such events would occur only once in 2,000 years, based on natural variability of the last 113 years. This raises the possibility that changes in the ENSO pattern may be in part due to observed increases in greenhouse gases."

Our observations this year, as fishermen, would lead us to believe that this year's ENSO is a major event. There is one difference with this ENSO and past events, however. Satellite images of SSTs show that a higher than normal proportion of the warm water associated with the ENSO turned north when it hit the Americas. I received a fishing report from Cabo San Lucas last week. The marlin have disappeared and the water temperature is in the 90's. There are no records of such conditions.

Although the scientific community has made great strides in the last ten years to understand the ENSO phenomenon, they still don't know what causes an event or if there is a triggering mechanism. The increased frequency and intensity of ENSO events does provide much food for thought.

Most current Sea Surface Temperature Map. Temperature shown Celcius. 16C = 61F, 30C = 93F

Possible impact on the California Fishery

There is a connection between ENSO events and higher rainfall in Northern California. Increased runoff will cause reduced salinity and increased turbidity next spring in our coastal waters. This could have an impact on the schools of baitfish. It will be interesting to note the size of the salmon next season.

The increased amount of storms anticipated over the course of the winter will affect the runs of all migratory species, but this is more a factor of timing than increased river flows.

There is a possibility that the baitfish schools in our coastal waters will be affected by the feeding of species not native to the area, such as tuna. It is also possible that there are baitfish that have been pushed here by the ENSO.

In the last month we have witnessed the largest run of king salmon on the Sacramento River in recent memory and currently we find a high concentration of striped bass in the north bay.