E-Mail Exchange With Josh Willis On The Ability To Monitor The Transfer Of Heat In The Oceans To Levels Below 700m

Several weeks ago, I had an interesting exchange of viewpoints with Gavin Schmidt and a few others on Real Climate which I summarized in my post

Response To Gavin Schmidt’s Post Of October 3 2011 “Global Warming And Ocean Heat Content”

My Recent Discussion with Gavin Schmidt On Real Climate

One of the issues is whether the existing Argo network can resolve the transfer of heat through the upper 700m of the ocean. I contacted Josh Willis of Jet Propulsion Laboratory and have (with his permission) reproduced them below (with minor edits and the insertion of the abstract of a paper and the figures referred to).

My E-Mail

Hi Josh

In a discussion on Real Climate, this question came up from Gavin  Schmidt in response to my comment  [http://www.realclimate.org/index.php/archives/2011/10/global-warming-and-ocean-heat-content/comment-page-3/#comment-216615]

My Comment on Real Climate

 On your question regarding heat transfer downward, if the models show warming at depth, why don’t you show plots as to the magnitude of its fluxes over time and space through the upper 700m of the ocean. Then one could look at the observations to see if this flux is there with the same pattern and magnitude as the real world data.  I assume our disagreement is in the form of these fluxes. If they are diffuse and distributed across the upper oceans, I agree they would be hard to see in the Argo data. However, if this transfer occurs in globs  associated with mesoscale and larger ocean circulation features (as suggested in the ECMWF data), we should clearly see this movement of  heat.

 [[Gavin’s] Response: Model estimates of total heat flux through 700m are possible of course, but non-trivial to compute (including effects of the resolved circulation, isopycnal diffusion, and vertical mixing) – though this might well be worth doing for the CMIP5 models. However, I don’t have the answers handy. But I have no confidence that the observations will be sufficient to distinguish the anomalous heat flux from the climatological mean with sufficient precision to be helpful. If you think it is,please point to a study that has attempted this. – gavin]

Can you let me know if this has been done from the observations?

Best Regards
Roger

Josh’s Reply

Hi Roger,

 The way I would answer this is that we can probably diagnose the amount of warming between 700 and 2000 m in the Argo data for the past 5 to 7 years. Using the data to determine the cause of this, however, can be tricky.  For example, if an isotherm at 1000 m is depressed in one region by 10 meters, is this caused by a simple downward advection of the isopycnal, or is it due to vertical or horizontal mixing with a nearby warm water mass?

 Questions like this can be difficult to answer with the Argo data. Nevertheless, with some basic knowledge of the local oceanographic conditions and use of additional data, like salinity and horizontal advection, it might be possible to tease apart the causes of this temperature change.  There are some efforts to do this for the abyssal warming signal published by Purkey & Johnson, by asking the question: how big of a reduction in bottom water formation would be needed to account for the observed warming of the abyssal waters?  I’m not sure if that work is published yet, however.

Hope this helps.

Cheers,

Josh

My E-Mail

Hi Josh

 This is helpful; thanks!

 I do have several questions/comments.

 Regarding

 ” if an isotherm at 1000 m is depressed in one region by 10 meters, is  this caused by a simple downward advection of the isopycnal, or is it due  to vertical or horizontal mixing with a nearby warm water mass?:

 I agree this could be difficult. However, in terms of moving heat through  the entire upper 700m, the critical question, in my view, is whether the Argo network has the spatial and temporal resolution to see coherent regions of warm and cold anomalies e.g. seen in  http://www.ecmwf.int/products/forecasts/d/charts/ocean/real_time/xzmaps/ ?

 Or are they there only for one sampling period and than gone?

 If it is the former, we should be able to track these “globs” of  anomalies.

 Have you (or anyone) looked at the coherency of these anomalies over time?

 In the same context, if one integrated horizontally at different levels  over regions in each ocean, the region-time integrated movement of heat upwards and downwards would seem to be possible IF the space and time  resolution of Argo is good enough. If not, what would need to be added to the Argo network to accomplish this?

 It seems this subject would benefit from a paper.

 With Best Regards

 Roger

Josh’s Reply

Hi Roger,

You are more than welcome to post these comments.  For interannual or longer time scales, the Argo networks should easily resolve the large-scale movement of heat between the upper (<700 m) and mid-depth (700 to 2000 m) layers of the ocean.  For interannual signals the global coverage is now quite good:

http://www-hrx.ucsd.edu/www-argo/statusbig.gif

So in short, yes, the “globs: of heat anomalies that change on yearly time scales are resolved by Argo.  There is now a vast literature on the use of Argo data (more than 150 papers per year).  Here is one of interest:

Roemmich, D., and J. Gilson (2011), The global ocean imprint of ENSO, Geophys. Res. Lett., 38, L13606, doi:10.1029/2011GL047992.

[the abstract of this paper reads

“The ENSO-related spatial patterns and global averages of ocean temperature, salinity, and steric height are estimated from over 7 years of Argo data, 2004–2011. Substantial extratropical variability is seen in all variables in addition to familiar tropical ENSO signals. Surface layer (0–100 dbar) and subsurface (100–500 dbar) temperature variations are both important in determining steric height and sea surface height patterns. For the two years prior to the 2009 El Niño, the upper 100 dbar of the ocean gained 3.3 × 1022 J yr−1 of heat, while the 100–500 dbar layer lost a similar amount. The ENSO-related vertical redistribution of globally-averaged heat content between surface and subsurface layers, occurring throughout the record, is due primarily to changes in the east-west tilting of the equatorial Pacific thermocline. The large temperature changes in the individual layers mask the smaller vertically-averaged temperature change, in which the ocean loses heat when the surface layer is anomalously warm and gains heat when the surface layer is cool.”]

Cheers,
Josh

My E-Mail

Hi Josh

 Thank you for the quick reply. This is very helpful.

 I guess the remaining question is whether significant amounts of heat could be transferred below 700m without being seen in the upper 700m? The curious conclusion of recent accumulation but not in the past; e.g. see

http://bobtisdale.wordpress.com/2011/10/24/introduction-to-the-nodc-ocean-heat-content-anomaly-data-for-depths-of-0-2000-meters/

is curious [Bob’s figure is reproduced below].

This accumulation started when Argo came online. Any comments you have on this issue would be welcome.

The paper you sent is quite relevant to this discussion!

Best Regards

Roger

Josh’s Reply

This is a tough question to answer, and I would say the jury is still out over how quickly the 700 to 2000 m layer can warm (or cool).  I think we need more Argo data and more time with the data that we have before we say for sure…

Cheers,
Josh

Also, Josh alerted us to the video of his presentation

Hot Water: The Oceans and Global Warming

with the abstract

Water covers nearly 70 percent of its surface, so it’s no wonder that the world’s oceans play such an important role in global climate changes. As the planet heats up, the oceans wind up being by far the biggest reservoir for taking up the extra heat. This talk will cover the ins and outs of global warming as they pertain to the world ocean.

source of image

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