Record Warm World’s ‘Weird’ 2015 El Nino Sees Westerly Gales, Growing Kelvin Wave

“The 2015 El Nino is finally here, but it’s weak, weird and late,” said Mike Halpert, deputy director of the Climate Prediction Center last week.

And the current El Nino is certainly an odd bird. According to reports from NOAA and the National Weather Service, the center of highest sea surface temperatures for the El Nino this year is offset westward — coming closer to the date line than it typically does. This is a weird heat disposition for El Nino which is, at least, a mid ocean event and often pushes warming well across the Pacific to South American shores.

(Pacific sea surface temperature anomaly [SSTA]. Note the hot water pools off both Australia and North America. These zones are joined by a vast blanket of warmer than average waters arranged diagonally across the Pacific from SW to NE. This disposition includes the warm anomaly along the Equator which is hot enough to reach weak El Nino status. But the disposition of sea surface temperatures throughout the Pacific, with highest equatorial anomalies near the date line and warmer spikes near Australia and the North American West Coast is unusual. SSTA graphic provided by Earth Nullschool. Data Source: Global Forecast System Model and NCEP.)

It’s also late in coming, as typical El Ninos have tended to arrive in full form during late fall or early winter. A Christmas-time warming of waters off the West Coast of South America was a traditional call-sign for El Nino and one that resulted in its name — which is Spanish for “The Christ Child.” Late winter and early spring are more typical times for the formation of deeper warmer water that may trigger an El Nino later in the year but often do not herald a fully-developed event (see What is El Nino? for more related information).

Lastly, the El Nino is currently rather weak — barely meeting a requirement for El Nino from NOAA and still not reaching the threshold that Australia’s Bureau of Meteorology applies.

But despite all this relative oddity, the 2015 El Nino is here. And it appears to be growing.

Intense West Wind Back-burst Coincident with Powerful Cyclone Formation

For earlier this week strong westerly winds began to roar against the typical flow of the trades along the Equator. The west wind back-bursts (WWB) push warmer West Pacific waters eastward and downward, enhancing the sea surface temperature anomaly spikes that fuel El Nino.

(Very strong West Wind Back-Burst hosting 85 kph 10 minute west wind at 7.45 South Latitude on early March 11. Image source: Earth Nullschool.)

As of early Wednesday, March 11, these west winds had formed a gale force wall stretching just past the date line from about 5 North Latitude to 10 South Latitude. A gale driven by parallel cyclones — a weaker system to the north (Bavi) and the newly gathering Pam, which may challenge south Pacific records as the strongest storm ever to form in that region. In the above graphic we see a related ten minute sustained WWB of a rather extraordinary 85 kilometers per hour (about 50 mph) along the 7.45 degree South Latitude line.

Strengthening Kelvin Wave in a Record Warm World

Just before the formation of these strong westerlies, sub-surface temperatures also began to spike. A warm Kelvin wave that had already started its run beneath the sea surface, as of March 4, was beginning to show signs of strengthening well in advance of the added shove coming from the vigorous WWB shown above.

(A new Monster Kelvin wave? Sub surface temperature anomalies are again entering the far above normal range for the Equatorial Pacific. Image source: Climate Prediction Center.)

Peak temperatures in the wave as of a week ago had hit more than +6 C above average. A heat signature that is starting to look, more and more, like the very powerful Kelvin Wave of early 2014 that belched so much warmth into the atmosphere and likely contributed to both the current strongly positive PDO as well as 2014’s new record high temperatures.

An event that top ocean and atmospheric scientists Kevin Trenberth and Axel Timmerman attribute to signalling a possible start to much more rapid atmospheric temperature increases.

The Kind of Mid-Ocean Event That Some Scientists Say we Should See More of

If this is the case, then what we may be seeing is a slow start to an El Nino that could be much stronger and longer than expected. Last year’s intense Kelvin Wave may have simply been preparation for a slowly building event in conjunction with what was, during December, a record broader warming of the Pacific called positive Pacific Decadal Oscillation (PDO). Some model runs, especially those at Australia’s BoM, appear to have picked up this track.

In addition, NOAA sea surface temperature models now are predicting continued Central Pacific Warming (CPW) in association with the current El Nino over the coming months. If this El Nino continues to progress along CPW warming lines, then it is likely to be more indicative of what Japanese scientists call an El Nino Modoki event:

(Sea surface temperature signature of an El Nino Modoki, which is closer to what we are seeing now, even if the higher temperature levels are currently shifted more toward the Date Line. Image source: Japan Agency for Marine-Earth Science.)

During recent years, some scientific reports have indicated that Central Pacific Warming or El Nino Modoki will be more prevalent as a result of human-caused climate change. Study authors Tong Lee and Michael J McPhaden, in the 2010 paper entitled Increasing Intensity of El Nino in the Central Equatorial Pacific note that increases in Pacific Ocean temperatures are primarily expressed through more intense warming of the central regions:

Satellite observations suggest that the intensity of El Niño events in the central equatorial Pacific (CP) has almost doubled in the past three decades, with the strongest warming occurring in 2009–10. This is related to the increasing intensity as well as occurrence frequency of the so-called CP El Niño events since the 1990s. While sea surface temperature (SST) in the CP region during El Niño years has been increasing, those during neutral and La Niña years have not. Therefore, the well-documented warming trend of the warm pool in the CP region is primarily a result of more intense El Niño events rather than a general rise of background SST.

If so, it seems possible that global warming may well be influencing the rather strange El Nino evolution we are witnessing now.

In any case, Central Pacific Warming El Ninos have a somewhat different impact than Eastern Pacific Warming El Ninos. For one, they tend to ramp up, rather than cool down North Atlantic Hurricanes. They also tend to result in more, not less, drought for the US West Coast. For India, mid-ocean warming of the kind we are seeing now can result in an enhanced disruption of the Asian monsoon — kicking off drought and related food security risks.

Tong Lee and Michael J McPhaden continue by adding:

…. the amplitude of this new type of El Niño has increased in recent decades (Lee and McPhaden 2010). For convenience, hereinafter we refer this new type of El Niño as to CP warming (CPW). Compared with the canonical EPW, the CPW exhibits distinctly different impacts on worldwide climate. For example, the CPW shifts the anomalous convection westward and usually forms two anomalous Walker circulations in the tropical Pacific (Ashok et al. 2007; Weng et al. 2007; Weng et al. 2009). The westward displaced convection was suggested to be more effective in causing Indian drought (Kumar et al. 2006). The CPW increases hurricane frequency both in the Atlantic Ocean (Kim et al. 2009) and western North Pacific (Chen and Tam 2010), and also shifts tropical cyclone tracks in the western North Pacific (Hong et al. 2011).

But the authors’ research doesn’t directly point toward the odd seasonal change we are witnessing now, nor the off-setting of the initial hot pool about 1,500 kilometers further west than even during a typical El Nino Modoki event. For this reason, our ‘weird’ El Nino and equally weird and warm Central Pacific bear close watching.

Links:

El Nino Finally Here, But it’s Weak, Weird, and Late
NOAA
National Weather Service
What is El Nino?
NOAA’s ONI Index
BoM ENSO Wrap-up
Earth Nullschool
Global Forecast System Model
NCEP
Pam at Category 5 Strength
Warming Pacific Drives Global Temperatures
Bad Climate Outcomes
2015 El Nino to Bring Back-to-Back Hottest Years on Record?
Increasing Intensity of Central Pacific El Nino — Links to Climate Change
Japan Agency for Marine-Earth Science
El Nino Declared as Climate Scientists Watch on With Amazement

Hat tip to Phil

Hat tip to Wili

Hat tip to Timothy Chase

Posted by robertscribbler on March 12, 2015

https://robertscribbler.wordpress.com/2015/03/12/weird-2015-el-nino-fed-by-strong-west-winds-growing-kelvin-wave/