>A Discontinuity In 1945 Or A Missing ENSO Event?

>UPDATE – September 28, 2009

The post has been updated to include brief discussions of the other datasets in which the 1945 discontinuity appear.

OVERVIEW

For those still concerned about the upcoming adjustments to the Hadley Centre’s SST data, and because the methods used by Thomspon et al as discussed in Thompson et al (2009) – High-Tech Wiggle Matching Helps Illustrate El Nino-Induced Step Changes left significant ENSO residuals, I investigated the possibility that the discontinuity revealed in Thompson et al (2008) was the result of an unrecorded El Nino event in 1943/44 or 1944/45. It appears as though global temperatures are responding to an El Nino event in 1943 and 1944, with sharp rises and falls in Sea Surface Temperature (SST) and Land Surface Temperature (LST). This could then be the cause of the severe drop in 1945 (the discontinuity) if the global temperatures were then responding to the subsequent unrecorded La Nina event. But, using the Southern Oscillation Index (SOI) as a second reference, there is no evidence of an ENSO event during those years. But this assumes that the measurement of sea level pressure in Darwin and Tahiti was not impacted by the war years.

Keep in mind, though, that the discontinuity also exists in COADS and Hadley Centre’s Marine Air Temperature data (as does the appearance of an El Nino beforehand) and in the COADS Cloud Cover and Wind Speed data.

INTRODUCTION

The Hadley Centre is rewriting the Global SST record to reflect the findings of Thompson et al (2008). In the 2008 paper “A large discontinuity in the mid-twentieth century in observed global-mean surface temperature”, Thompson et al write, “The discontinuity in global-mean surface temperatures in late 1945 is evident in the unfiltered global-mean time series, but its prominence and unique character are highlighted by the removal of the ENSO and COWL-related variability (Fig. 2).” They continue in the next paragraph, “The step in late 1945 does not appear to be related to any known physical phenomenon. No substantial volcanic eruptions were reported at the time, and the nuclear explosions over Hiroshima and Nagasaki are estimated to have had little effect on global-mean temperatures…” The discontinuity is illustrated in Figure 1.

http://i35.tinypic.com/28r2ow3.png
Figure 1

Thompson et al (2009) “Identifying signatures of natural climate variability in time series of global-mean surface temperature: Methodology and Insights” reinforces the 1945 discontinuity and provide advanced notice of the Hadley Centre’s intent. They write, “THE SST DATA CORRECTED FOR INSTRUMENT CHANGES IN THE MID 20TH CENTURY ARE EXPECTED TO BECOME AVAILABLE IN 2009, and it will be interesting to see how the corrections affect the time history of global-mean temperatures, particularly in the middle part of the century.” [Emphasis added.]

But Thompson et al (2009) acknowledged that there was also a drop in land surface temperatures at that time. They wrote, “It is worth noting that the land data also exhibit a small drop in the mean ~1945, albeit much smaller than that found in the residual SST time series (Figure 10).”

A simultaneous drop in the land data? This leads to the question…

IS THERE A MISSING ENSO EVENT IN THE SST RECORD?

Thompson et al base their claim of a 1945 discontinuity in the Global SST dataset on the fact that, after they eliminated the effects of ENSO and COWL, there was no corresponding volcanic eruption to cause the drop in temperature. This assumes the volcano records and the SST records for the NINO regions are correct. It is difficult to imagine that an explosive volcanic eruption that would have lowered global temperatures 0.3 deg C could be missed, but can the same be said about ENSO events? Also, the methods used by Thompson et al (2008) to extract the ENSO signal from the global temperature record are similar to those in Thompson et al (2009), but as illustrated in Thompson et al (2009) – High-Tech Wiggle Matching Helps Illustrate El Nino-Induced Step Changes, they left significant ENSO residuals in their adjusted data. With this in mind, I resorted to raw HADISST Global and NINO3.4 SST anomaly data and to raw CRUTEM3 Land Surface Temperature anomaly data for this post.

Figure 2 illustrates the global SST anomalies from January 1935 to December 1974 for three datasets: HADISST, ERSST.v2, and ERSST.v3b. The data has been smoothed with a 13-month filter to remove the rough edges. Note how the discontinuity now appears to be a gradual decrease from late 1944 to late 1946. Scaled NINO3.4 SST anomalies have also been provided for comparison. All three global SST datasets appear as if they’re responding to an El Nino event when none exists in the NINO3.4 SST anomaly data. Also note that there is also little agreement between NINO3.4 SST anomalies and the global SST datasets between 1943 and 1950, while global SST anomalies do appear to respond to NINO3.4 SST anomalies at other times.
http://i36.tinypic.com/kceyoy.png
Figure 2

In Figure 3, HADISST Global SST anomaly data from January 1935 to December 1974 are compared to CRUTEM3 Land Surface Temperature data. Again, the data have been smoothed with a 13-month filter. And again, scaled HADISST NINO3.4 SST anomalies are provided for comparison. Global land surface temperatures also appear to be responding to an El Nino event around that time. But looking at other ENSO events, global land surface temperatures do exaggerate some ENSO events but not others. And looking at the land surface temperature data for 1938/39, there was also a similar anomalous rise and fall without an El Nino event.
http://i37.tinypic.com/292tohw.png
Figure 3

THE SOI INDICATES NO EL NINO EVENT IN 1943 OR 1944

Figure 4 is a comparison chart of NINO3.4 SST anomalies and inverted and scaled Southern Oscillation Index (SOI) data, the surface pressure component of ENSO. The SOI represents the sea level pressure difference between Tahiti and Darwin Australia, and would, therefore, not be impacted by the transition between SST measurement types. This assumes that the sea level pressure measurements during those war years were accurate. However, if there were shifts in sea level pressure measurements during those years as there were in SST, the anomalous rises and falls in global SST and LST data may reflect El Nino events.
http://i38.tinypic.com/106g5c7.png
Figure 4

CLOSING

Seeing how poorly global SST anomalies track NINO3.4 SST anomalies in the 1940s, the upcoming modifications by the Hadley Centre could be a good thing. Maybe they’ll try to clean up the data from 1910 to 1940 next.

Will the Hadley Centre attempt to flatten out the appearance of a 1943/44 and/or 1944/45 El Nino in the Global SST data. That rise and fall also appears in the COADS and MOHMAT Marine Air Temperature datasets, and, as illustrated above, in the CRUTEM3 LST data. Global Ocean Cloud Cover and Wind Speed datasets also indicate anomalous variations during the war years, and cloud cover and wind speed are major drivers of SST. Refer to my posts The Large 1945 SST Discontinuity Also Appears in Cloud Cover and Marine Air Temperature Data and Part 2 of The Large SST Discontinuity Also Appears in Cloud Cover and Marine Air Temperature Data.

SOURCE

SST and LST anomaly data used in this post is available through the KNMI Climate Explorer:
http://climexp.knmi.nl/selectfield_obs.cgi?someone@somewhere

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About Bob Tisdale

Research interest: the long-term aftereffects of El Niño and La Nina events on global sea surface temperature and ocean heat content. Author of the ebook Who Turned on the Heat? and regular contributor at WattsUpWithThat.
This entry was posted in CAGW Proponent Arguments, El Nino-La Nina Processes. Bookmark the permalink.

12 Responses to >A Discontinuity In 1945 Or A Missing ENSO Event?

  1. Andrew says:

    >Bob, that still leaves the puzzling issue of why a discontinuity would also occur in the marine air temps, doesn't it?

  2. John says:

    >Hi Bob – I believe you made an older post noting that the 1945 discontinuity was reflected in other measures – marine air temp, cloud cover, etc. Is this correction by Hadley meant to eliminate this bump one way or another? Are they ignoring that it happened, whatever the source? If the other measurements confirm there was some sort of event, why is there a need to a adjustment? Or are the adjustments more far-reaching?

  3. Andrew says:

    >By the way Bob, what about the three year, 2 sigma ENSO event beginning circa 1940? Could it not have caused a step change which then rapidly dissipated?

  4. Bob Tisdale says:

    >Andrew: You wrote, "Bob, that still leaves the puzzling issue of why a discontinuity would also occur in the marine air temps, doesn't it?" It also appears in a number of other datasets: cloud cover, surface winds. If I read Thompson et al (2009) correctly, they are attributing the spikes in the other datasets to the transition between U.S. and British measurements and back again during the war. They don't come right out and call attention to the other datasets. Then again, I may be reading between the lines too much, knowing that the discontinuity (or ENSO response)also appears in the other datasets. I think I'll ammend the end of the post and link those posts that show the discontinuity in the other datasets.

  5. Bob Tisdale says:

    >John: You asked, "Is this correction by Hadley meant to eliminate this bump one way or another?" They've discussed eliminating the drop but have said nothing about the rise that preceeds it.You asked, "Are they ignoring that it happened, whatever the source?"In the Thompson et al papers, they present that it is caused by changes in SST measurements. If there's another motive, I can't speculate on what it is.You asked, "If the other measurements confirm there was some sort of event, why is there a need to a adjustment?"They're either ignoring the other datasets or they will address their marine air temperature dataset later. The Hadley Centre can't do anything about the raw COADS data, so the data will still exist. The discontinuity will also remain in the NOAA datasets, so they won't disappear.You asked, "Or are the adjustments more far-reaching?"Are they trying to make it easier for GCMs to hindcast SST and surface temperature anomalies? Dunno.

  6. Bob Tisdale says:

    >Jenette: You asked about the NOAA press realease on the recent record SSTs.The record is only for the NOAA ERSST.v3b data. It does not occur in the NOAA satellite-based OI.v2 SST data or in the Hadley Centre SST data. Refer to:http://bobtisdale.blogspot.com/2009/09/record-sea-surface-temperatures-are.html

  7. Bob Tisdale says:

    >Andrew: You asked, "By the way Bob, what about the three year, 2 sigma ENSO event beginning circa 1940? Could it not have caused a step change which then rapidly dissipated?"In other words, could it have generated a "secondary wave" in global SST anomalies? Good question. I don't have an answer for it. When I think of that three-year El Nino, I think of the response of the Indian Ocean. That's an extreme reaction. I'll have to break down the SST anomalies in the 1940s into individual ocean subsets and see if anything shows up. Almost forgot. Here's a link to my look at the Indian Ocean SST anomalies. Check out the response in the early 1940s to that three year El Nino.http://bobtisdale.blogspot.com/2008/09/indian-ocean-more-detailed-look.html

  8. John says:

    >Hi Bob -Do you know if they are blaming the raw COADS and NOAA on dataset transition as well? Or is it just not addressed? I couldn't quite tell from your response – sorry for my confusion.

  9. Bob Tisdale says:

    >John: I don't know that the Hadley Centre is blaming anyone. They're just trying to sort through the reasons for the wiggles in the data. The Hadley Centre and NOAA both use the data that's collected and archived in COADS.

  10. John says:

    >Hi Bob – Off topic, but I was looking at the UAH anomaly graph (http://www.drroyspencer.com/wp-content/uploads/UAH_LT_1979_thru_Aug_091.jpg) , and I couldn't help but notice the more cyclical nature of the UAH temperature anomalies prior to 1998. After 1998 it seems to be much flatter (prior to the 2008 La Nina). Is this a reflection of the small bump ups via the 2000s El Ninos that prevented the lowering portion of the "cycle?" Have you posted about this in the past?I also noticed in a response you posted on WUWT about a paper that predicted more frequent, but less powerful, El Ninos. If true, would we expect to see this flattening at this level to be more the norm? More frequent small bumps keeping the SSTs elevated and preventing a return to lower anomalies?Thanks as always, and I hope that was coherent!

  11. Bob Tisdale says:

    >John: You wrote, “I couldn't help but notice the more cyclical nature of the UAH temperature anomalies prior to 1998. After 1998 it seems to be much flatter (prior to the 2008 La Nina).”That's mostly due to volcanos, plus two significant El Nino events.Prior to the 1997/98 El Nino there were two significant volcanic eruptions. Mount Pinatubo is responsible for the dip from 1991 to 1995. It overwhelmed the two little El Nino events then. El Chichon counteracted (suppressed) the 1982/83 El Nino and amplified the 1983/84/85 La Nina. Between the two volcanic eruptions was a significant 2-year El Nino in 1986/87/88.After the 1997/98 El Nino, there were no explosive volcanic eruptions to add the additional dips. The only major dip was from the 1998/99/00 La Nina.You wrote, “I also noticed in a response you posted on WUWT about a paper that predicted more frequent, but less powerful, El Ninos.”Was that the news report that predicted more frequent El Nino Modoki events? If so, I believe I replied that that should be a good thing since the significant traditional El Nino events are what cause the upward step changes in SST and TLT.If the La Nina events outweigh El Nino events (frequency and amplitude), TLT and SST should decline.

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