6 June 2001

Summary Report for Climate Simulation Laboratory Project

Climate Change Simulations

Warren M. Washington - Principal Investigator

Ocean and Sea Ice Component Developments 

The Parallel Climate Model (PCM) uses a 2/3 degree (on average) displaced pole, global configuration of the Parallel Ocean Program (POP) with the computational pole over the Hudson’s Bay region. The Climate System Model (CSM) is developing similar version with numerical pole point over Greenland. During the past year there was an effort to have closer collaboration between the CSM and PCM efforts. The PCM-CSM-Transitional-Model (PCTM) model has been developed using the same parallel execution method used in PCM version 1. This Model has the same atmospheric component of CCM3.2 but it has the new ocean and sea ice components. Working with the Oceanography Section and LANL scientists, the Gent-McWilliams diffusion scheme and K Profile Parameterization (KPP) vertical upper ocean scheme have been added into POP. The PCM ocean model version includes increased latitudinal resolution near the equator to resolve the strong tropical current systems.  The ocean simulations revealed remarkable smaller scale structure that compared quite favorably with higher resolution versions and limited observations. Also, the narrow flows along the coastal regions were in good agreement with observations. The meridional overturning in the North Atlantic and worldwide conveyor belt circulation were well represented in the simulations. 

The sea ice component has been upgraded to use the LANL sea ice model of Hunke and the sea ice thermodynamics of C. Bitz of the University of Washington. Weatherly, Briegleb, Holland, and Schramm have included further refinements.

Examples of the ocean and sea ice simulations of the model can be found on the Parallel Climate Model web page at www.cgd.ucar.edu/pcm/.

Coupled Model Simulation with PCM (Version 1)

The PCM makes use of the NCAR Community Climate Model (CCM3) and Land Surface Model (LSM) for the atmospheric and land surface components, respectively, the Los Alamos National Laboratory POP, and the NPS sea-ice model. The PCM executes on several distributed and shared memory computer systems. The coupling method is similar to that used in the CSM in that a flux coupler ties the components together, with interpolations between the different grids of the component models. Flux adjustments or corrections are not used in the PCM. The ocean component has 2/3° average horizontal grid spacing with 32 vertical levels and a free surface that allows calculation of sea level changes. Near the equator, the grid spacing is approximately 1/2° in latitude to better capture the ocean equatorial dynamics. The North Pole is rotated over northern North America, thus, producing resolution smaller than 2/3 degree in the North Atlantic where the sinking part of the world conveyor circulation largely takes place. Because this ocean model component does not have a computational point at the North Pole, the Arctic Ocean circulation systems are more realistic and similar to the observed. The elastic viscous plastic sea-ice model has a grid spacing of 27 km to represent small-scale features, such as ice transport through the Canadian Archipelago and the East Greenland current region.  

Results from a 300-year present-day coupled climate control simulation by Washington, Weatherly, Meehl, Semtner, Thomas Bettge, Craig, Gary Strand, Julie Arblaster, Wayland, Rodney James (SCD) and Yuxia Zhang (NPS) showed that the PCM gave a very stable simulation with approximately the observed interannual and decadal variability.  Five transient 1% per year CO₂ increase experiments have been carried out that showed a global warming of about 1.26°C for a 10 year average at the doubling point of CO₂.One of the experiments was allowed to go to the quadrupling point and the global average warming was 2.89°C. There was a gradual warming beyond the doubling and quadrupling points. A 0.5% per year CO₂ increase experiment also was performed showing a global warming of 1.49°C and a similar geographic warming pattern to the 1% per year doubling experiment. Globally averaged sea level rise at the time of CO₂ doubling was approximately 7cm and at the time of quadrupling it was 23 cm. The regional sea level changes were much larger and reflect the adjustments in the temperature, salinity, internal ocean dynamics, surface heat flux, and wind stress on the ocean. El Niņo and La Niņa events in the tropical Pacific Ocean show approximately the observed frequency distribution and amplitude, which leads to realistic variability on interannual timescales of tropical and extratropical planetary wave patterns. Washington et al (2000) and Weatherly and Zhang (2000) show the early results from these simulations in two articles accepted for publication and a paper by Meehl et al., (2000) is in preparation and shows more details on the factors that affect El Niņo amplitude.

Ensemble historical and future climate model simulations have been conducted.  The simulations make use of the same forcing as the CSM (the business as usual (BAU) and policy limited ACACIA scenarios). They simulate from 1870 to year 2100.  Additional simulations with the added effect of solar forcing on the climate system are also being conducted.  

The following are scientists and programming staff involved in the PCM effort or its components in alphabetical order: J. Arblaster (NCAR), T. Bettge (NCAR), A. Craig (NCAR), J. Dennis (NCAR), J. Dukowicz (LANL), J. Hack (NCAR), S. Hammond (NCAR), E. Hunke (LANL), R. James (NCAR), P. Jones (LANL), R. Loft (NCAR), R. Malone (LANL), M. Maltrud (LANL), W. Maslowski (NPS), G. Meehl (NCAR), A. Middleton (NCAR) A. Semtner (NPS), R. Smith (LANL), G. Strand (NCAR), W. Washington (NCAR), J. Weatherly (CRREL), V. Wayland (NCAR), D. Williamson (NCAR), and Y. Zhang (NPS). 

CSL Usage 

The following is the breakdown by case configuration (type of simulation), years of simulation. Over the last year we have used only the IBM system. Over the last year we have carried out many simulations on the NCAR IBM system, which is shown in the following table:

 PCM1

Type of Simulation                                                                    Years 

Control                                                                                         240

Historical (1870-2000) Ensemble 4                                         480                         

Solar Forcing Historical Ensemble 2                                        240

Climate Change Scenarioe (A2, B2, BAU, STAB)                 400

 PCTM development simulations                                              1500

 Total number of years simulated                                              3960                                              

Estimates of Computer Time Used at Other Centers

 We estimate that we have conducted about 2500 years of simulation at LANL, ORNL, and NERSC over the last year.

Data Availability to the Community 

We have made the data available to the community. For example, the simulations of climate change will be a part of the ongoing IPCC assessment as well as the U. S. National Assessment. We have also provided data to the Scripps Oceanographic Institution, University of Washington, GFDL, etc. Arrangements have been made to make all of the atmospheric, ocean and sea ice data available to any scientist through the DOE’s PCMDI capability. The data is on a large file server system at PCMDI (Lawrence Livermore National Laboratory).