PMIP 2 Water-Hosing Experiments


The PMIP 2 water-hosing experiments will follow the guidelines specified in the sensitivity to surface water flux forcing subproject of the CMIP project.

You can find more details in the mail that Ron Stouffer sent to CMIP participants:

CMIP Common Experiments Letter
May 14, 2003

Dear modeler,

Last year, two sets of Coordinated Coupled Model Experiments were approved by CMIP's Working Group on Coupled Models.

The goal of the first set of experiments is to understand the role of the various surface fluxes in the weakening of the Atlantic meridional overturning circulation when CO2 increases in the atmosphere. This effort includes some partially coupled integrations.

The second set of experiments focus on a so-called water hosing integration. In this experiment, an external source of freshwater is applied to the Atlantic Ocean surface from 50N to 70N at a rate of 0.1SV for 100 years. (A third less publicized experiment has been initiated as an offshoot of the 0.1SV hosing: a 1.0SV hosing in the same area, for the same length of time). The water hosing effort is also a PMIP 2 project.

It is time for us to begin collecting and comparing data from these experiments. It is important to remember that each group is primarily responsible for analyzing its own integrations. We have planned only a limited amount of common analysis, but hope that the coordinated experiments will stimulate coordination among those involved as we seek to develop a greater understanding of the differences in the model results.

A few months ago, Keith Dixon and Bill Hurlin agreed to take the lead in collecting the role of the surface flux data. Ron Stouffer and Mike Spelman will collect the water hosing data. This arrangement will continue for the next year or so.

Those four people plus Jonathan Gregory developed a list of variables (subproject : [1] - [2]) to be shared amongst the participants of the two subprojects. The list of variables and suggested options for how the data can be shared are described on a web site developed for these Coordinated Coupled Model Experiments. The options include having the modeling groups transfer copies of their data to GFDL where it can be stored on a password protected server accessible to other participants. Alternatively, groups can place their data files on a distributed data server of their own.

We have tested this arrangement by having Jonathan Gregory (HadCM3) and Andrew Weaver/Mike Eby (UVic) send their data to GFDL. It has worked well and we are now ready to begin the larger effort of collecting data from all participants. (FYI - Much of Jonathan's CMIP talk at the recent EGS was prepared using these preliminary data sets.)

Please complete the integrations and begin the process of transferring the data as soon as possible. Instructions for the data transfer are also found on the web site (subproject : [1] - [2]). We want to have the preliminary analysis of these projects complete by late summer in time for the mid-September climate meetings in Hamburg (the Climate Conference and CMIP workshop). For this reason, we would like to have your model data here at GFDL (or accessible via another distributed server) as soon as possible. The data we collect will be available to all participants via a password protected web site. Our intention is produce Intercomparison papers of the basic results with joint authorship by the individuals from the participating centers. The papers will be written some time after the September meetings.

The main web page for these coordinated experiments is

Keith Dixon will maintain the web pages for the Atlantic Meridional Overturning Response To Time-Dependent Climate Change On The Century Time scale subproject (includes the partially-coupled experiments).

Ron Stouffer will maintain the web pages for the Sensitivity To Surface Water Flux Forcing subproject (the so-called water-hosing experiments).

During the analysis phase of this project, access to the individual subproject web pages and the model data sets will be password protected. Each participating modeling group will be sent a username and password that will allow them to access these web pages and data files. Please contact us if you have questions regarding password access. We are using this security to limit outside access to our results. Once papers are published on this data, we plan to revisit the issue of making the information public.

The desired data format is netCDF, using the CF convention. Documentation for the CF convention can be found at:

One can also learn about the CF convention by inspecting the CDL information for defining the variables - information that can be found on our web site.

Ron Stouffer
Keith Dixon
Jonathan Gregory
Mike Spelman
Bill Hurlin

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