The PMIP Subprojects

Note: the PMIP subprojects were originally defined in the Workshop Letter 5.

Climate sensitivity

Coordinators: Karl Taylor, David Rind, John Mitchell

The objective of this subproject is to estimate climate sensitivity for paleoclimate simulations, and compare it to other climatic conditions.

Procedure and tasks:

1. Calculate radiative forcing due to various changes in boundary conditions (insolation, changes in surface albedo, greenhouse gas forcing).
2. Calculate climate sensitivity.
3. Evaluate importance of different feedbacks.
4. Compare climate sensitivity for different experiments and also to sensitivity to doubling of CO2.

Tropical climates, 6 kyr BP

Coordinators: John Kutzbach, John Mitchell, Pascale Braconnot, Nathalie de Noblet

The primary objectives of this sub-project are to:

1. evaluate and quantify the sensitivity of Asian and African monsoons to changes in insolation and CO2;
2. find out which mechanisms are robust (i.e. present in most of the models) and which are not;
3. see whether we can rank the sensitivity of the monsoons according to the complexity of their parameterizations.

Model-model as well as model-data comparisons will be used to achieve these goals.

This subprojet will consider:

1. Diagnostics of the large scale dynamics and energetics, and relationship with the regional scale (involving the study of Hadley and Walker circulations, diabatic heating, position of the ITCZ, tropical waves, subtropical jet, ...)
2. Regional study of monsoons: Asia and/or Africa, summer and/or winter. Three main points will be developed:
   • intercomparison of the simulated land-surface climatologies, and comparing them with lake and pollen data;
   • study of onset, duration and intensity of the summer monsoon in relation to changes in the length of the season and insolation at the top of the atmosphere;
   • impact of model parameterizations, with particular emphasis on land surface processes and clouds.

Very simple diagnostics (zonal/meridional means, P-E maps, runoff and monsoon index) will be output first, to provide an overview of the model behaviour. Comparison with data will also be made at that point. Some of these results will serve as a basis for the gross features to be contributed to the 6 kyr BP overview paper. More sophisticated diagnostics will then be developed.

Extra-tropics, 6 kyr BP

Coordinators: Patrick Bartlein, Nathalie de Noblet

The objective of this subproject is to study the impact of insolation changes on the mid-latitude large-scale circulation.

Procedure and tasks:

1. Circulation changes: planetary waves, storm tracks, surface energy and moisture balance
2. Data-model comparisons

Extra-tropics, 21 kyr BP

Coordinator: Paul Valdes

The objective of this subproject is to study the impact of the Last Glacial Maximum boundary conditions on the simulated mid-latitude large-scale circulation.

Analyses will be carried out as follows:

1. Circulation changes: planetary waves, Southern and Northern Hemisphere westerlies, storm tracks.
2. Impact of sea-ice on the simulated surface fluxes. Comparison of simulations with computed versus simulations with prescribed SSTs.
3. Study of the simulated local circulation over ice-sheets (seasonal cycle, energy balance)
4. Surface climate : model-data comparison

Ocean forcing at the last glacial maximum

Coordinators: Klaus Herterich, Michael Lautenschlager, Tony Broccoli

This subproject is already divided in two parts

The forcing of ocean circulation during glacial times

Coordinators: Klaus Herterich, Michael Lautenschlager

The objective here is to study the simulated surface heat fluxes that are used to drive ocean general circulation models

Procedure and tasks:

1. U. Bremen/DKRZ will compute the vertical heat fluxes at the ocean surface (annual mean), from the different models, in order to determine and intercompare the meridional heat transports.
2. Obtain boundary conditions (fresh water flux, heat fluxes, wind stresses, surface air temperature) from the PMIP simulations needed to force ocean models and carry out ocean simulations.

The problem of Q-flux in mixed-layer ocean models

Coordinator: Tony Broccoli

The objective here is to study the impact of computed SSTs on the simulated climate of the Last Glacial maximum.

The procedure will be to compare the different technics used, and see what this implies for ocean heat transport.

Ice sheet mass balance

Coordinators: Dave Pollard, Gerhard Krinner, Karl Taylor

The objective of this subproject is to study the impact of the simulated climate changes on ice-sheets.

Procedure and tasks:

1. Diagnostic calculations will be carried out, using all PMIP simulations, to study the net balance for each icesheet, in most models, for 0, 6, and 21 kyr.
   A rather detailed description of the different methodologies, including a brief questionnaire has already been sent to one member of each AGCM group by Dave Pollard.
2. Global (x,y) fields of net annual sow/ice accumulation-ablation will be plotted for most models, to see if any "initiation" is simulated.
3. Global fields of "potential" net balance (x,y,z), necessary to drive ice sheet models, will be derived and studied for some models.

Tropical climates, 21 kyr BP

Coordinator: Gilles Ramstein

The objective of this subproject is to study the impact of LGM boundary conditions on the simulated climates of the tropics.

Procedure and tasks:

1. Study the simulated changes in the african and asian monsoons. What is the relative impact of the different prescribed boundary conditions?
2. Compare computed SSTs to fixed SSTs (CLIMAP).
3. Model-Data comparisons.