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Saturday, June 11, 2016

Willis Eschenbach wonders about ENSO events and rain

Sou | 6:24 PM Go to the first of 5 comments. Add a comment
Willis Eschenbach is one of the resident pseudo-scientists at WUWT. Today he decided to tackle ENSO events and precipitation (archived here). As is usual, he went to satellite data to get precipitation, which is probably not the best approach. While the Tropical Rainfall Measuring Mission (TRMM) is a worthwhile project, I don't think it was intended to be used in the way Willis has used it.


Wet and dry regions during ENSO events


Willis took issue with a recent paper in Nature Communications from a team led by Michael Griffiths. (Anthony Watts had earlier said the paper was a bombshell. I don't know why. It's an interesting paper, but not what I'd call a bombshell.) The paper itself was about multi-century shifts in weather patterns in the Pacific.  Willis wasn't writing about that. What he wanted to do was dispute the fact that El Niño years tend to be drier and La Niña years tend to be wetter.

Willis didn't accurately reflect what was in the paper. This excerpt from the paper will give you an idea of how the scientists describe an El Niño-like state and a La Niña-like state. It's about how there's a possible link between the strength of the Pacific Walker circulation and multi-century shifts in rainfall in the western Pacific:
Evidence for a potential link between the PWC [Pacific Walker circulation] and multi-century changes in western Pacific rainfall is provided by the inverse relationship between the AISM [Australian-Indonesian Summer Monsoon] and rainfall in the central-eastern equatorial Pacific (Fig. 4) over the past millennium. Specifically, the western Pacific and Peruvian Andes (Fig. 4a–e) were generally wetter during the LIA [Little Ice Age], whereas the central and eastern equatorial Pacific (EEP) experienced drier conditions (Fig. 4f) or reduced heavy precipitation events (Fig. 4g,h), similar to La Niña events today when the PWC strengthens (Fig. 1). Conversely, drier conditions in Indonesia and Peru (along with Panama) during the MCA [Medieval Climate Anomaly] were matched by wetter conditions in the central and EEP, signifying a more ‘El Niño-like’ mean state.



I think that Willis just looked at the pictures and didn't bother with the text, because he wrote:
The paper made a curious claim, that La Nina conditions were wetter, and El Nino conditions were dryer. Here’s the graphic from their paper:
He didn't get that from the text, he only got that from Figure 4 in the paper where on the right hand side he saw Wet/La Niña-like and Dry/El Niño-like:

Figure 1 | (a) Flores LLPC1 record. (b) Marine foraminifera δ18Osw (ref. 5) and (c) terrestrial δDleaf-wax (ref. 6) records recovered from marine sediment cores located in the Makassar Strait on the Sulawesi margin. (d) δ18O of lake sediment calcite in Laguna Pumacocha in the central Peruvian Andes (proxy for the strength of the South American summer monsoon)44. (e) Speleothem δ18O record from Cascayunga cave in northeast Peru46. (f) δDleaf-wax record from Washington Island in the central equatorial Pacific8. (g) Red-colour intensity from Laguna Pallcacocha, southern Ecuador47. (h) Percent sand in El Junco lake, Galápagos Islands10. For clarity, all records have been converted to standard (z) scores with blue indicating wetter conditions (a–f) or heavier precipitation events (g–h) and vice versa for red. Vertical bars indicate the approximate timing of the MCA (yellow), LIA (blue) and CWP (pink) in Flores. Source: Griffiths16


Even though Willis missed the details in the paper, as you'll see, La Niñas are wetter than El Niños averaged over the land surface as a whole. That is, water tends to shift from the sea to the land in La Niña years, and there's a shift from the land to the sea in El Niño years.


Willis thinks he knows more than scientific experts. He doesn't.


Willis bases most of his pronouncements about climate on his days fishing in the Pacific. (He saw lots of clouds while he was fishing so, in his mind, clouds are the answer to everything climate.) Today was no exception. Willis oddly wrote about a general rule while at the same time saying there was no general rule:
Now I was born yesterday, but having lived in the South Pacific I do know that there is no general rainfall rule for El Nino and La Nina. Some places like Southern California get wetter in an El Nino year, and some places like Australia get drier. So I found it odd that they identified “wetter” with La Nina and “drier” with El Nino. 
Then he proceeded to put up some charts from his interpretation of satellite data and pronounced:
This shows what I started out by saying, which was that an El Nino increases the rain in Southern California and decreases the rain in Australia. In other words, we cannot say “Wet/La Niña-like” or “Dry/El Niño-like” as the authors do.
The thing is that while he's correct about some of the places that tend to wet and dry during ENSO events, he missed out on a lot of the world, which is why the scientists are right and Willis is wrong.


Sea level and ENSO


I figured that another way to look at wet vs dry was to see what happens with sea level. At the global level, precipitation is very difficult to monitor using rain gauges or satellites. You can get an idea of the coverage with satellites, but in many areas you'll lose intensity. Rain gauges only measure the rain that falls where the gauges are. Sea level isn't perfect either. The advantage is that it shows where the water is. If there's a dip in sea level it's an indication that more water evaporated and the rain fell over land rather than over the ocean. If there's a rise in sea level it's an indication that there was less rain on land and that more rain fell over the oceans than evaporated. (There are other reasons for sea level rising and falling, too.)

Anyway, I put together a chart, marked blue for La Niña and pink for El Niño, and shading a bit darker when there was a stronger event. This is the result (click to enlarge as always):

Figure 2 | Sea level and ENSO events. Blue is La Nina and pink is El Nino. Data sources: U Colorado and BoM

That's a bit rough and ready. However what you can see is that more often during El Niño years (pink) the sea level is above the trend line, whereas during La Niña years (blue) it's more often below. The 2010/12 La Nina is an extreme case, when water evaporated from the ocean, the sea level dropped, and there was massive flooding in various parts of the world (including South America and Australia).

Fortunately for you, the Sea Level Research Group at the University of Colorado has a nice chart that I came across which shows this much more clearly. It's a plot of the Multivariate ENSO Index (MEI) against global mean sea level with seasonal signals removed.

Figure 3 | ENSO events as indicated by MEI and sea level. The Multivariate ENSO Index (MEI) is the unrotated, first principal component of six observables measured over the tropical Pacific (see NOAA ESRL MEI, Wolter & Timlin, 1993,1998).  To compare the global mean sea level to the MEI time series, the mean, linear trend, and seasonal signals are removed from the 60-day smoothed global mean sea level estimates and each time series is normalised by its standard deviation. The normalized values plotted above show a strong correlation between the global mean sea level and the MEI, with the global mean sea level often lagging changes in the MEI. Source: U Colorado
You can see the relationship much more easily. A positive MEI is El Niño and a negative MEI is La Niña. The sea level drops with La Niña because there's more rain on land. It rises with El Niño when there's less rain on land.

That's why La Niña is thought of as "wet" and El Niño is thought of as "dry", even though in some places the reverse happens.

I also found a really good article by Tamino on the subject, which he wrote back in 2012.


Long term upward trend in sea level, with ENSO fluctuations


One thing you probably noticed right away is just how high the sea level is now. That's in part because of the recent El Niño. The upward trend is because the oceans are getting warmer so the water is expanding, plus melting ice is adding to the volume. The wiggles about the long term upward trend are caused by internal variability as happens with ENSO events.


A word about Willis' silly last word


Before finishing his article, Willis wrote something that further indicated that he didn't understand the paper he was criticising:
Now, the authors of the study say:
“The composite record shows pronounced shifts in monsoon rainfall that are antiphased with precipitation records for East Asia and the central-eastern equatorial Pacific. These meridional and zonal patterns are best explained by a poleward expansion of the Australasian Intertropical Convergence Zone and weakening of the Pacific Walker circulation (PWC) between ~1000 and 1500 CE.

I see no need to invoke any such special mechanisms to explain rainfall shifts that are “antiphased” to rainfall shifts in other areas. From an examination of Figure 2 above, such antiphasing is the rule rather than the exception. In La Niña times California gets drier, Australia gets wetter, and the world goes on.
Regards to all on a sunny evening,
w.
Why he objected to that passage is not at all clear to me. The authors were discussing a "2,000-year, multiproxy reconstruction of western Pacific hydroclimate". In particular, they were writing about century-scale shifts in weather patterns. Willis seems to have missed the point completely.


From the WUWT comments


Nobody seems very interested in making a comment on Willis' article. There were only five "thoughts", including one from Nick Stokes, who pointed out that, unsurprisingly, the scientists are quite familiar with what regions tend to wetter and what regions tend to drier in ENSO events.


References and further reading


Michael L. Griffiths, Alena K. Kimbrough, Michael K. Gagan, Russell N. Drysdale, Julia E. Cole, Kathleen R. Johnson, Jian-Xin Zhao, Benjamin I. Cook, John C. Hellstrom, Wahyoe S. Hantoro. "Western Pacific hydroclimate linked to global climate variability over the past two millennia." Nature Communications, 2016; 7: 11719 DOI: 10.1038/NCOMMS11719 (open access)

Sea Level and la Niña - article by Tamino, November 2012



From the HotWhopper archives

5 comments:

JCH said...

This confirms everything Tisdale has ever written!!!

MarkR said...

I don't see a problem with Willis' use of TRMM - if you do the analysis right then you should be able to use it for this sort of thing.

The paper identified rainfall pattern changes over thousands of years and tried to explain why. Willis looks at patterns over 15 years and decides there's "no need to invoke any such special mechanisms to explain rainfall shifts that are “antiphased” to rainfall shifts in other areas" because "such antiphasing is the rule...and the world goes on."

Willis' problem seems to be that scientists are doing science to try and explain the real world rather than just accepting that's how things are.

That hints at a basic difference in outlook and approach that helps to explain why people like Willis haven't convinced climate scientists, and climate scientists haven't convinced Willis.

D.C.Petterson said...

You are correct. Willis et. al. seem to think things just happen, and there is no need or possibility to explain them. Yet it is the job of scientists to explain things that happen. That is the basic difference in mindset.

D.C.Petterson said...

Sou, a bit OT, but you continue to amaze with the thoroughness and clarity of your analysis and your writing. Thank you for your dedication.

@whut said...

ENSO model based on Laplace's original wave equation formulation (1776) solved for the equatorial latitudes.

https://web.archive.org/web/20160613123314/http://contextearth.com/2016/06/10/pukites-model-of-enso/

No GCMs involved because it's first-order physics!

I don't think Willis would understand this math because his head is in the clouds.