Guest Post by Bob Tisdale
Note: See Update at the end of the post.
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Last month on November 10, NOAA issued a La Niña Advisory, indicating weak La Niña conditions existed and that those conditions were “slightly favored to persist (~55% chance) through winter 2016-17.” Let’s see how things are progressing.
NOAA’S WEEKLY SATELLITE-ENHANCED REYNOLDS OI.v2 SEA SURFACE TEMPERATURE DATA SHOW A WEAKENING TO ENSO-NEUTRAL CONDITIONS
The sea surface temperature anomalies of the NINO3.4 region of the tropical Pacific (coordinates 5S-5N, 170W-120W) are a commonly used index for the timing, strength and duration of El Niño and La Niña events.
NOAA’s weekly sea surface temperature anomaly data for the NINO3.4 region based on their original Reynolds OI.v2 data show that surface temperatures there have been in ENSO neutral conditions (not La Niña, not El Niño) for 3 weeks. As of the week centered on Wednesday November 30 and for the two prior weeks, NINO3.4 sea surface temperature anomalies were at -0.4 deg C, which is above the -0.5 deg C threshold of La Niña conditions. (Rounding out the month of November, for the first week, the value was -0.7 deg C.) See the time-series graph in Figure 1.
Note that the horizontal green line is the most recent weekly value, not a trend line.
This data are based on NOAA’s original version of their Reynolds OI.v2 satellite-enhanced sea surface temperature dataset. The anomalies are referenced to the base period of 1981-2010. This is not the dataset that NOAA uses for their “official” ENSO indices.
NOAA’S MONTHLY IN SITU-ONLY ERSST.v4 SEA SURFACE TEMPERATURE DATA (WITH A FIXED SET OF BASE YEARS FOR ANOMALIES, 1981-2010) SHOW TEMPERATURES WELL WITHIN WEAK LA NIÑA CONDITIONS FOR NOVEMBER AND STRENGTHENING SLIGHTLY
Again we’re looking at sea surface temperature data for the NINO3.4 region, but this time we’re looking at a version based on NOAA’s ERSST.v4 monthly “pause buster” sea surface temperature data, which is based solely on observations from buoys and ship inlets, no satellite-based data. This is the dataset that NOAA uses for their “official” ENSO index but it is referenced to the fixed base years of 1981-2010…while NOAA takes a few additional steps for their “official” Oceanic NINO Index.
The monthly ERSST.v4-based data for November 2016 show NINO3.4 sea surface temperature anomalies well within the realm of weak La Niña conditions, at -0.82 deg C. See Figure 2. The October value was -0.8 deg C.
NOAA’S MONTHLY IN SITU-ONLY ERSST.v4 SEA SURFACE TEMPERATURE DATA (WITH SHIFTING BASE YEARS FOR ANOMALIES) SHOW SLIGHTLY STRONGER LA NIÑA CONDITIONS WITH A MORE NOTICEABLE STRENGTHENING
As opposed to using a fixed 30-year based period for the ERSST.v4-based NINO3.4 anomalies in their “official” Oceanic NINO Index, NOAA uses multiple 30-year periods that shift every 5 years. See the NOAA explanation here. NOAA claims they’ve taken this curious approach “to remove this [global] warming trend” on the equatorial Pacific sea surface temperature data. We revealed, however, in the 2012 post Comments on NOAA’s Recent Changes to the Oceanic NINO Index (ONI) that the global “warming trend” in NINO3.4 sea surface temperature data resulted primarily from the impact of the well-known and naturally occurring 1976 Pacific climate shift. Apparently, NOAA doesn’t want mother nature to be responsible for even localized warming. This, of course, renders the Oceanic NINO Index useless for realistic climate studies.
Regardless, NOAA has adopted this odd approach to calculate the sea surface temperature anomaly values for their “official” Ocean NINO Index. The monthly NINO3.4 values that are input to the Ocean NINO Index are shown in Figure 3. The November 2016 NINO3.4 sea surface temperature “anomaly” for this altered dataset is -0.92 deg C, which is approaching the -1.0 deg C threshold of a moderately strong La Niña. From October to November 2016, this modified dataset shows a noticeable strengthening of -0.05 deg C.
So it appears that NOAA is working hard at making the 2016/17 La Niña an “official” reality.
Note: NOAA then uses a 3-month running average of this altered monthly NINO3.4-based data for their Oceanic NINO Index.
THE SOUTHERN OSCILLATION INDEX FROM AUSTRALIA’S BOM CONTINUES TO SHOW ENSO NEUTRAL CONDITIONS
The Southern Oscillation Index (SOI) from Australia’s Bureau of Meteorology is another widely used reference for the strength, frequency and duration of El Niño and La Niña events. We discussed the Southern Oscillation Index in Part 8 of the 2014/15 El Niño series. It is derived from the sea level pressures of Tahiti and Darwin, Australia, and as such it reflects the wind patterns off the equator in the southern tropical Pacific. With the Southern Oscillation Index, El Niño events are strong negative values and La Niñas are strong positive values, which is the reverse of what we see with sea surface temperature-based indices. The November 2016 Southern Oscillation Index shows ENSO neutral conditions exist in the tropical Pacific…with a value is -0.7, which is the sign opposite to those of La Niña conditions. (The BOM threshold for La Niña conditions is an SOI value of +8.0.) According to the SOI, we briefly made it into La Niña conditions in September and since then, ENSO neutral. Figure 4 presents a time-series graph of the SOI data.
Again, the horizontal green line is the most recent monthly value, not a trend line.
Also see the BOM Recent (preliminary) Southern Oscillation Index (SOI) values webpage. The current 30-day running average and the 90-day average are still in ENSO neutral conditions.
As noted in the title, we’re getting mixed signals from NOAA and BOM, and from NOAA itself, about the existence of La Niña conditions on the tropical Pacific.
WANT TO LEARN HOW EL NIÑO AND LA NIÑA EVENTS CONTRIBUTE TO LONG-TERM GLOBAL WARMING?
I published On Global Warming and the Illusion of Control (25MB .pdf) back in November 2015. The introductory post is here. That 700+ page climate change reference is free. Chapter 3.7 includes detailed discussions of El Niño events and their aftereffects…though not as detailed as in Who Turned on the Heat?
My ebook Who Turned on the Heat? – The Unsuspected Global Warming Culprit: El Niño-Southern Oscillation (23MB .pdf) goes into a tremendous amount of detail to explain El Niño and La Niña processes and the long-term global-warming aftereffects of strong El Niño events. It too is free. See the introductory post here. Who Turned on the Heat? weighs in at a whopping 550+ pages, about 110,000+ words. It contains somewhere in the neighborhood of 380 color illustrations. In pdf form, it’s about 23MB. It includes links to more than a dozen animations, which allow the reader to view ENSO processes and the interactions between variables.
Within hours of my publishing this post, Australia’s BOM has cancelled their La Niña watch. They write in their December 6th ENSO Update:
La Niña no longer likely in the coming months
The El Niño–Southern Oscillation (ENSO) in the tropical Pacific Ocean remains neutral (neither El Niño nor La Niña). Although some very weak La Niña-like patterns continue (such as cooler than normal ocean temperatures and reduced cloudiness in the central and eastern Pacific), La Niña thresholds have not been met. Climate models and current observations suggest these patterns will not persist. The likelihood of La Niña developing in the coming months is now low, and hence the Bureau’s ENSO Outlook has shifted from La Niña WATCH to INACTIVE.
Will NOAA follow?