Saturday, July 22, 2017

NOAA's new ERSST V5 Sea surface temperature and TempLS

The paper describing the new version V5 of ERSST has been published in the Journal of Climate. The data is posted, and there is a NOAA descriptive page here. From the abstract of the (paywalled) paper, by Huang et al:
This update incorporates a new release of ICOADS R3.0, a decade of near-surface data from Argo floats, and a new estimate of centennial sea-ice from HadISST2. A number of choices in aspects of quality control, bias adjustment and interpolation have been substantively revised. The resulting ERSST estimates have more realistic spatio-temporal variations, better representation of high latitude SSTs, and ship SST biases are now calculated relative to more accurate buoy measurements, while the global long-term trend remains about the same.
A lot of people have asked about including ARGO data, but it may be less significant than it seems. ARGO floats only come to the surface once every ten days, while the more numerous drifter buoys are returning data all the time. There was a clamor for the biases to be calculated relative to the more accurate buoys, but as I frequently argued, as a matter of simple arithmetic it makes absolutely no difference to the anomaly result. And sure enough, they report that it just reduces all readings by 0.077°C. That can't affect trends, spatial patterns etc.

The new data was not used for the June NOAA global index, nor for any other indices that I know of. But I'm sure it will be soon. So I have downloaded it and tried it out in TempLS. I have incorporated it in place of the old V3b. So how much difference does it make? The abstract says
Furthermore, high latitude SSTs are decreased by 0.1°–0.2°C by using sea-ice concentration from HadISST2 over HadISST1. Changes arising from remaining innovations are mostly important at small space and time scales, primarily having an impact where and when input observations are sparse. Cross-validations and verifications with independent modern observations show that the updates incorporated in ERSSTv5 have improved the representation of spatial variability over the global oceans, the magnitude of El Niño and La Niña events, and the decadal nature of SST changes over 1930s–40s when observation instruments changed rapidly. Both long (1900–2015) and short (2000–2015) term SST trends in ERSSTv5 remain significant as in ERSSTv4.
The sea ice difference may matter most - this is a long standing problem area in incorporating SST in global measures. On the NOAA page, they show a comparison graph:

There are no obvious systematic trend differences. The most noticeable change is around WWII, which is a bit of a black spot for SST data. A marked and often suspected peak around 1944 has diminished, with a deeper dip around 1942.

TempLS would be expected to reflect this, since most of its data is SST. Here is the corresponding series for TempLS mesh plotted:

Global trends (in °C/century) are barely affected. Reduced slightly in recent decades, increased slightly since 1900:

start yearend yearTempLS with V4TempLS with V5

Almost identical behaviour is seen with TempLS grid.


  1. Off topic, but NOAA STAR has had a TLT product for a few years, which has been updated with latest Po-Chedley derived corrections. The difference is that it is AMSU-A only (1998 to present). It documented here (pre-Po-Chedley)

    Is this something that could be added to your trend/time series pages? Unfortunately, it is only available as a netcdf file.

    1. Yes, I meant channel 4.

    2. CCE,
      Thanks, I'll check that out.

  2. I think you are referring to AMSU channel 4 which has a TLT-like weighting profile.
    However, the AMSU-only 2.0 datasets has not been updated recently and have the old faulty diurnal drift correction, like RSS v3 and STAR v3.
    Hence, I think it is better to use the latest STAR v4 MSU/AMSU dataset (with Po Chedley corrections) and make a TTT-index ( 1.1*TMT-0.1*TLS), alternatively make a UAH v6 TLT analogue with the formula TLT= 1.538*TMT-0.548*TTP+0.01*TLS
    Both these indices would have trends of about 0.18-0.19 C/decade in the satellite era

    1. I spoke with Dr. Zou and he said the Po-Chedley corrections have been applied. I believe V2 of their AMSU-A only dataset linked above contains these corrections, but V1 does not.

      The "near nadir" channel 4 profile (solid line) can be seen in this graph:

    2. cce,
      As I remember, AMSU-only v2 channel 5 had a lower trend than v4 TMT, also after 2005 when the last MSU-satellite NOAA-14 was discontinued. They should be identical after 2005 so I concluded that the newest drift corrections had not yet been applied. I may be wrong though...

      You could mail Dr Zou and ask him if the AMSU-only 2.0 dataset actually have the Po Chedley drift corrections like STAR v4. It would be interesting to know..

    3. I did email him and the corrections have been applied. This has happened sometime in the last year or so.

    4. Thanks cce, good to know..
      I'm away from my pc right now, but my latest download of AMSU-only ended June 2016, so things may have changed since..

      As I remember the global trends Nov 1998 - Jun 2016 were about:
      AMSU 7, 0.14 C/dec
      AMSU 6, 0.12 C/dec
      AMSU 5, 0.08 C/dec
      AMSU 4, 0.15 C/ dec

      These figures suggest a global hotspot, or that something is wrong with channel 5, being much lower than the neighbour channels.

      I used AMSU-only data for the following chart which covers the MSU/AMSU overlap 1999-2005.

      I kind of of demonstrates that NOAA-14 is right and NOAA-15 wrong, and that UAH's arbitrary low trend satellie cherrypick isn't supported by evidence..

      But now we are way of the topic, new SST..

    5. The latest files were modified July 3rd, so it looks like they're being updated on a monthly basis.

  3. Another paper that makes claims about the impact on ENSO from AGW without understanding what causes ENSO in the first place.

    Why does this kind of tenuously-argued science happen?
    There is a real gap between the phony science of WUWT and the glacially-evolving world of consensus science influenced by confirmation bias.

  4. That study shows a weakening meridional gradient and southward itcz are about to boost extreme El Ninos. What's wrong with that, according to your phony science ?

    1. The title actually refers to frequency: "Continued increase of extreme El Niño frequency .."

      There's no consensus on the cause of El Ninos. I say that, because if the consensus was that changes in the prevailing winds was isolated as a cause, we would still have to ask what causes the changes in those winds.

      So it's quite a leap of faith to go from a no-consensus root cause for ENSO and then to assert that the frequency of El Ninos will go up with additional global warming. I see several steps missing in the scientific explanation. For example, what sets the frequency in the first place? If it based on the results of GCMs, I have a problem with that because GCMs have no input or parameters for the lunar gravitational forcing, which provides an alternate model.

      So if the frequency of El Ninos is a result of lunisolar cycles alone, how can that frequency change with additional global warming?

      In other words, a secondary assertion requires a primary assertion to build from, and yet there is no consensus to the primary cause.

    2. The study is based on models. The meridional sst gradient is supposed to boost extreme El Ninos. That's What the models show, if I'm correct. The key may bé weather it will hapen or not. If it hapens, a southward shift of the Itcz could fuel the most extreme events.

  5. More precisely, from Wenju Cai (2014) :"The weakening of the SST gradients is induced by faster warming in the background state along the equatorial than in the off-equatorial Pacific, and in the eastern equatorial Pacific than in the west, a feature produced even without a dynamical ocean. These slight changes in climatological SST gradient translate into a large increase in the occurrences of a diminished or reversed meridional SST gradient. This is associated with more occurrences of maximum SSTs, and hence convection, in the eastern equatorial Pacific for a given SST anomaly, leading to increased extreme El Niño occurrences".

    1. OK, here is an explanation in plain language. Remember that the title of the paper refers to an increase in frequency of ElNino events. If there is a threshold in what defines an El Nino event, then an increase in energy to the system will cause more below-threshold events to cross into an El Nino regime.

      Now do a thought experiment. If AGW increases the thermal energy by 10 degrees, it is extremely likely that El Ninos will become more pronounced. The same is true if AGW is only 1 degree. Don't really need a paper for that as that is really just thermal physics/thermodynamics.

      My point is that there is still no consensus on what causes ENSO. It is nowhere near the 97% for AGW. If there is a consensus for ENSO and it drops below 50%, it really ceases to be a consensus.

  6. The study rather refers to more frequent big El Niño events, not average ones...
    El Nino causes may not be fully understood but... Models show conditions could lead to the most extreme evens, i.e EP El Ninos.Those events are both atmosphere-ocean. A meridional shift leads to more extreme El Ninos. The question is : will we se such a meridional shift ?

  7. True that El Nino causes are not fully understood. They are still at the point of making only observational connections with other measures, such as wind velocity. Yet this does not address the root cause if these are causally linked by a common mode.

    Only when the root is isolated as being due to an external forcing such as the combined lunisolar pull will we be able to make decent headway with ENSO research. They really are spinning their wheels until that time.