New satellite imagery shows that in the last 18 months a giant horseshoe pattern of higher than normal sea surface heights has begun to dominate the entire western Pacific and Asiatic oceans, supplanting the dominant pattern of the last 20 years. The new pattern covers an area two to three times larger than El Niño or La Niña and is believed to have significant implications for global climate change, especially over North America.

“The persistence of these abnormally high and low Pacific sea-surface patterns, along with warmer and colder than average ocean temperatures, tells us there is much more than an isolated La Niña occurring in the Pacific Ocean,” says Dr. William Patzert, an oceanographer at NASA’s Jet Propulsion Laboratory (JPL) in Pasadena. American scientists and media have long focussed on localised weather patterns like El Niño and La Niña, in lieu of global changes.

Sea-surface heights are a measure of how much heat is stored in the ocean below: higher sea-surface heights indicate higher temperatures below. These temperatures are a direct influence on the atmosphere. “When you put these two pieces of the climate puzzle together, they will tell us both about what is influencing today’s weather and how much heat is being stored in the ocean to fuel future planetary climate events,” says Patzert.

Patzert believes the newly-identified cycle of higher sea-surfaces and temperatures may be part of a ‘Pacific decadal oscillation’ (PDO). If it is, it would evolve over decades, unlike the more spectacular but shorter-lasting El Niño and La Niña events.It is thought the PDO alternates between two phases over a period of approximately 20 to 30 years: in the present phase, a warm horseshoe pattern of higher than normal sea-surface heights connects the north, west and southern Pacific, in conjunction with a contrasting wedge of cool temperatures and lower than normal sea-surface heights in the eastern equatorial Pacific. After that the Pacific switches to the opposite phase, showing a reversal of the warm and cool regions; the horseshoe becomes cool and the wedge warms.

This climate trend can be seen in TOPEX/Poseidon satellite imagery (see image) taken between December 30, 1999 and January 8, 2000. Sea-surface height is shown relative to normal (green) height and reveals cooler water (blue and purple) measuring between 8 and 24 cm lower than normal along the coast of Central and South America, and stretching out into the equatorial Pacific. The giant horseshoe of warmer water (red and white) dominating the western and mid-latitude Pacific has higher than normal sea- surface heights of between 8 and 24 cm.

JPL scientists caution that it is still too early to definitively label the conditions as a PDO. In the coming year, TOPEX/Poseidon data will be used to continue to monitor the development of these conditions and their implications for climate in the next several years.

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