Friday, 26 June 2015

The intensifying el-Nino

Third Warm Kelvin Wave to Raise Extreme El Nino by Fall?


25, June, 2015
More fuel for El Nino’s fire and a record hot 2015 on the way…
Last week, a set of climate models predicted the emergence of a large and moderately strong westerly wind burst running against the trades associated with an eastward propagating cloudy and rainy phase of the Madden-Julian Oscillation (MJO). And, over the past few days a moderate strength, but very wide-ranging, westerly wind pattern appeared.

image
(A strengthening westerly wind burst over the Western Equatorial Pacific could produce a third warm Kelvin Wave and further heighten an El Nino that already has a potential to be very intense come Fall. Image source: Earth Nullschool.)

Today, 20 to 35 mile per hour westerly winds are prevalent along a 2,500 mile stretch of ocean running from just east of the Philippines, across an equatorial zone just north of New Guinea, and on eastward for hundreds more miles in the direction of the Date Line. The winds are associated with numerous low pressure systems developing both north and south of the Equator — their cyclonic wind patterns joining in a daisy chain like feature to drive a large synoptic westerly wind back-burst (WWB).
Over the next few days, winds within the zone are predicted to strengthen to near gale force intensity. But it’s the size of the zone that may have the greatest impact.
Strong, long-fetch westerlies in this region of the world have a tendency to push warm surface waters, now topping off at 31 degrees Celsius (and 1-2 C above the already hotter than normal 1979 to 2000 average), downward and eastward. This heat pump action generates what, in meteorological parlance, are known as warm Kelvin Waves. And warm Kelvin Waves are high energy fuel for strengthening El Ninos.
Two Warm Kelvin Waves
(Warm water propagation through the upper 300 meters of the central and eastern Equatorial Pacific serves as oceanic fuel for El Nino events. In the above graph by NOAA, not one but two warm Kelvin Waves are indicated — one peaking during April and May, and a second ongoing now. Will a significant westerly wind burst, now lighting off in the Western Pacific, generate a third warm Kelvin Wave by August? Image source: NOAA’s Climate Prediction Center.)

During mid-March, the Strongest Madden Julian Oscillation on record drove an extreme westerly wind burst (WWB) and produced a very strong Kelvin Wave. This Kelvin Wave ensured the progression to El Nino during 2015, an El Nino event that would have probably reached moderate strength by summer on the force of this single Kelvin Wave’s heating alone. An El Nino ensuring, when combined with the greenhouse gas heat forcing produced by humans, that 2015 would march into the record books as yet one more hottest year in the global climate record.

By early May, a second, albeit somewhat weaker, WWB generated another warm Kelvin Wave, heightening the potential for strong El Nino yet again. This time El Nino model forecasts picked up the doubled Kelvin Wave signal and began to produce some rather extreme predictions for El Nino come Fall. Late spring is an uncertain time for El Nino models due to an ocean tendency to cool down by September. So the impact of strong Kelvin Waves during spring can be somewhat muted. However, as June arrived, the model consensus for a strong El Nino emerging by Fall had solidified, if not along a range quite so extreme as some of the May numbers indicated.

Meanwhile, in the Central Pacific, anomalous warm sea surface temperatures were continuing to build. By mid-May, Central Pacific sea surface temperatures exceeded the moderate El Nino threshold of 1 C above average. By Monday, June 22, NOAA’s weekly El Nino statement had indicated that the Central Pacific region had warmed to a 1.4 degree Celsius positive anomaly. A level just 0.1 C short of strong El Nino intensity.

Adding a third significant Westerly Wind Burst on top of an already warming Equatorial Pacific throws yet one more variable into the dynamic El Nino forecast. 
A variable that could heighten the already strong potential for a major El Nino event late this Summer through to Fall. And one that could further heighten extreme global record hot temperatures during 2015. For the late June WWB is likely to produce an extraordinary third Warm Kelvin Wave, giving the currently strengthening El Nino yet one more shove toward increasingly extreme conditions.

Links:
NOAA’s Climate Prediction Center (Please support public, non-special interest based, science like the quality research and data provided to us daily by NOAA.)
 

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