Climate and Global Dynamics Division
|NCAR | UCAR | NSF | ASR 98|
Climate Change Research Section
|The Climate Change Research (CCR) Section
uses appropriate climate system models to study the response of the Earth system to a
variety of forcings, including changes of carbon dioxide, and other greenhouse gases and
aerosols. CCR provides a focal point for paleoclimate and serves as a resource to the
paleoclimatic research community in the use of CSM.
is also involved with Los Alamos National Laboratory (LLNL) and the Naval Postgraduate
School (NPS) in developing and using a high-peformance coupled model, the Parallel Climate
Model (PCM). This collaborative effort between UCAR and the Department of Energy is
managed under a Cooperative Agreement that is aimed at using massively parallel processor
Bette Otto-Bliesner (Climate Change Research Section, CCR), Esther Brady (CCR), and Christine Shields (CCR) continued work on the PaleoCSM. The PaleoCSM is a version of the CSM that uses a T31 resolution for the atmosphere and land models and the new x3' grid for the ocean and sea ice models. The ocean model version incorporates a spatially varying, three-dimensional eddy viscosity coefficient (anisotropic viscosity). In addition, this version of the model allows specification of the solar constant, atmospheric trace gases, Milankovitch orbital variations of the solar insolation, continental configuration and ocean bathymetry, vegetation, and soil characteristics. The new ocean grid enhanced the latitudinal resolution to 0.9° from 10°S to 10°N and 1.8° at middle and high latitudes. This version better resolves tropical currents than the previous version with the x3 resolution and isotropic viscosities. The equatorial undercurrent at 140°W now has zonal velocities of 80cm/s and a realistic latitudinal width. A version of the PaleoCSM is now being developed with reduced background vertical diffusivity (fkph) to improve the simulation of interannual variability in the tropical Pacific Ocean. Results show an improved signal with standard deviation of the NINO3 sea surface temperatures (SSTS) of 0.68°C in the simulation with fkph=0.15 compared to 0.71°C for the observational record from 1950-1979.
This figure (49K) showsthe annual-mean ocean zonal velocity at 140°W in PaleoCSM simulations with the x3- isotropic viscosity (top) and x3'-anisotropic viscosity (bottom). A realistic estimate of the observed undercurrent is about 100 cm/s.
This figure (11K) shows the NINO3 (red) and NINO4 (blue) standard deviations as a function of the background vertical diffusivity (fkph) in 40-year PaleoCSM simulations.
A tutorial for the PaleoCSM can be found on the Paleoclimate Model Working Group web page.
Present and Past Climate Coupled Simulations
Otto-Bliesner, Brady, and Shields have used the PaleoCSM (with fkph=0.5) to complete three fully coupled simulations for present-day, for pre-industrial times, and for the mid-Holocene (6000 years before present). The present-day simulation was forced by modern-day insolation (1367 W m-2) and atmospheric trace gas concentrations (CO2= 354.4 ppm, CH4=1722.3 ppb, N2O=308.4 ppb, CFC11=513.95 ppt, CFC12=462.67 ppt). The pre-industrial simulation was forced with insolation and trace gas concentrations appropriate to 1800 A.D. (1365 W W m-2, CO2= 280 ppm, CH4=700 ppb, N2O=275 ppb, CFC11=CFC12=0). The mid-Holocene simulation was forced with Paleoclimate Modeling Intercomparison Project (PMIP)-specified boundary conditions for orbital parameters but used the same insolation and trace gas concentrations as the pre-industrial simulation. The pre-industrial simulation was run for 400 years, the present-day was run for 200 years, and the mid-Holocene was run for 50 years.
Trends in the volume mean ocean potential temperatures were small: -0.06°C/century in the pre-industrial run and 0.003°C/century in the present-day run. Annual-average, global surface temperatures were 1.3°C cooler in the pre-industrial simulation compared to the present-day simulation with the largest cooling in the middle and high latitude oceans in regions of sea-ice formation. Ice areas were 10% greater in both polar regions in the pre-industrial run. Increased summer and early fall insolation at northern middle latitudes during the mid-Holocene led to delayed sea-ice formation during the fall and a 5% decrease of sea-ice annually compared to pre-industrial times.
Interannual variability of tropical Pacific SSTs has been better defined compared to previous versions with increased variability in the central and eastern Pacific. Atmospheric modes, such as the Arctic Oscillation and North Atlantic Oscillation were reproduced realistically, as was their expression on northern continental climates. A one-standard deviation positive change in the NAO index led to warming over Europe and extending into northern Asia and into central North America and cooling over the northwest Atlantic, Greenland, and eastern Canada.
The Paleoclimate Group (Otto-Bliesner, Brady, and Shields) is also involved in a multi-model intercomparison of coupled model simulations for the mid-Holocene as a subproject of PMIP and PAIN (Pan-Arctic Initiative), an international consortium of ecologists, paleoecologists, paleoclimatologists, and climate modelers studying changes in the diversity of tundra vegetation for past and future climates.
This figure (90K) shows annual-average SSTs for the pre-industrial simulation (top), present-day simulation (middle), and difference map, pre-industrial minus present-day.
This figure (21K) shows daily Northern and Southern Hemisphere ice areas smoothed by a 365-day running mean for present-day (green), pre-industrial (red), and mid-Holocene (blue) simulations. Present-day observed values are approximately 1x1013 m2 for the Northern Hemisphere and 0.85x1013 m2 for the Southern Hemisphere.
This figure (27K) shows the time series of winter values of the NAO simulated for years 100 to 199 in the present-day simulation and corresponding changes in surface temperature (°C) corresponding to unit deviations of the NAO index.
Visiting student Caspar Ammann from the University of Massachusetts, Amherst, in collaboration with Jeffrey T. Kiehl (Climate Modeling Section, CMS) and Charles Zender (ACD, now University of California at Irvine), added stratospheric aerosol into the radiation code of CRM/CCM/CSM. Single eruption simulations of Pinatubo aerosol are currently underway. The experiments include sensitivity analysis of the effects of aerosol size, spatial and temporal resolution of the forcing, and vertical resolution of the stratosphere. The following three projects are being performed with the volcanic aerosol code:
Ammann, Kiehl, and Zender are involved in a model
intercomparison of the Pinatubo eruption among several GCMs, coordinated by G. Stenchikov
of the Rutgers University.
Brady and Otto-Bliesner continued investigating the effect initial conditions have on ocean model spinup. For past climate periods, temperatures and salinities of deep and surface oceans are not known in sufficient detail to specify initial conditions for the ocean spinup phase of the coupled integration. Ocean simulations were done for the warm climate period of 80 million years ago when the continental configuration and ocean bathymetry were significantly different than present, atmospheric CO2 may have been as high as 6 times pre-industrial levels, and proxy evidence suggests deep ocean temperatures 8-12°C warmer than present. Four experiments were done to examine the effect of different temperature profiles and atmospheric forcing on the spinup of a paleo-ocean. Simulations with high CO2 (1680 ppm) and low CO2 (1120 ppm) atmospheric forcing combined with warm (12°C) and cold (10°C) initial deep water temperatures were compared. The ocean component was integrated forward 100 surface years and 5000 deep years. In terms of volume-integrated ocean temperature, the simulations with initially warm deep ocean temperatures equilibrated after approximately 1000 deep years. A choice of cold initial deep ocean temperatures require significantly longer spinup times. Atmospheric forcing also affected the solution with higher CO2 levels resulting in higher salinity levels in the South Atlantic and a more intense Southern Hemisphere meridional overturning cell.
This figure (12K) shows the time series of the globally and vertically integrated temperature over the 100 surface years of the simulations.
This figure (37K) shows the meridional overturning stream function in Sverdrups (106 m3s-1) averaged over the last 10 years of the spinups.
More results are described on the Paleoclimate Ocean Spinup Experiments web page.
Ocean Component Development
Albert Semtner (Affiliate Scientist, Naval Postgraduate School, NPS), Anthony Craig (CCR), Warren Washington (CCR), John Weatherly (visitor, U.S. Army Cold Regions Research Engineering Laboratory, CRREL), Gerald Meehl (CCR), and Frank Bryan, (Oceanography Section, OS) continued to evaluate, improve, and optimize a modified version of the Parallel Ocean Program (POP). The Parallel Climate Model (PCM) uses a 2/3 degree (on average) displaced pole, global configuration of POP, while the Climate System Model (CSM) is developing a 2 degree version with a different numerical pole point. During the past year there was an effort to have closer collaboration between the CSM and PCM efforts. An attempt is being made to introduce the Gent-McWilliams diffusion scheme and K Profile Parameterization (KPP) vertical upper ocean scheme. This latter activity is being done in collaboration with scientists at Los Alamos National Laboratory. The PCM ocean model includes increased latitudinal resolution near the equator to resolve the strong tropical current systems. This version of POP was integrated for over a century with acceleration at the bottom of the ocean of a factor of 10 to bring the ocean simulation closer to equilibrium. The ocean model component of PCM continues to be in production mode on the 128 Silicon Graphics Inc. (SGI) Origin 2000 at NCARs Climate Simulation Laboratory (CSL) and on the SGI machines at Los Alamos National Laboratory. Recently, the PCM components have started production on the NCAR IBM SP2. The ocean simulations revealed remarkable eddy 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. This version of POP is an integral component of the PCM, a coupled model developed as part of a multi-institutional, distributed research effort for use on current and future generations of Massively Parallel Processors (MPP). A discussion of the ocean model simulation in the coupled model can be found in two papers by Semtner (2000) and Washington et al.(2000) to be published in Climate Dynamics.
This figure (93K) shows a simulation of the Arctic and the North Atlantic upper ocean flow. In both ocean basins there are realistic eddie structures. The Arctic simulation shows the strong flow across the pole showing no evidence of numerical difficulties near the North Pole.
This figure (106K) of Gulf Stream simulation shows a relatively warm and narrow flow that cannot be captured by coarser resolution models. We do note that in the simulations of the 1/10th degree version of POP that the eddies are even more realistic and the 2/3 degree resolution is able to capture some of the eddy details.
The PCM version of POP was optimized by Vincent Wayland (CCR) for the National Energy Research Scientific Computing Center (NERSC) Cray T3E and demonstrated excellent scalability using 8, 16, 32, 64, and 256 processing elements (PEs). Semtner and colleagues provided ferret analysis tools for POP that allows for diagnosis of the simulations in comparison with observations. This series of plots has allowed for a better analysis of the ocean simulation characteristics.
Examples of the ocean simulation of the model can be found on the Parallel Climate Model web page.
Coupled Model Simulation
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 (CCR), Craig, Gary Strand (CCR), Julie Arblaster (CCR), Wayland, Rodney James (Scientific Computing Division, SCD) and Yuxia Zhang (NPS) showedthat the PCM gave a very stable simulation with approximately the observed interannual and decadal variability. Five transient 1% per year CO2 increase experiments that showed a global warming of about 1.26°C for a 10 year average at the doubling point of CO2 have been carried out. 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 was also 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 17cm and at the time of quadrupling it was 15 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 Niño and La Niña 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.
Presently, historical future climate model ensemble simulations are being conducted. The simulations make use of the same forcing as the CSM. They simulate from 1870 to year 2100. Additional simulations with the added effect of solar forcing on the climate system are also being conducted.
This figure (93K) shows the near surface Arctic Ocean pattern for one instance in time. Ocean eddy structures are shown along with a transpolar flow.
This figure (111K) shows three transient climate change simulations using 0.5% CO2 per year and 1% CO2 per year increases. December, January, and February (DJF) and June, July, and August (JJA) are surface temperature 10-year difference means. The top figure shows a warming pattern (°C) for the 0.5% per year simulation at the doubling point (140 years), the middle figure shows the warming pattern for a 1% CO2 per year simulation at 70 years, and the bottom is the warming at 1% CO2 per year at the quadrupling point (140 years). As expected the warming is largest in the winter hemisphere season and half the rate of warming, 0.5% per year, over 140 years gives a pattern very similar to that of 1% CO2 per year over 70 years. This warming is proportionally amplified at the quadrupling point.
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).
Climate System Ice Model (CSIM)
Weatherly analyzed the sea ice and polar climate in the
control and transient CO2 PCM simulations. The doubled CO2 run
showed significant thinning of Arctic sea ice and decreased summer ice concentrations,
similar to the recent observational evidence from submarine- and satellite-based data. The
ice and snow albedos used in PCM and CSM were compared with observations from the
year-long Surface Heat Budget of the Arctic (SHEBA) field program by Weatherly and Donald
Arblaster and Meehl analyzed observations and results from
the DOE PCM. They showed that coherent decadal climate variability extended over the
entire Pacific basin, and affected El Niño teleconnections between equatorial
Pacific SSTs and Australian rainfall. Such time-varying links between decadally-varying
tropical Pacific SSTs and El Niño teleconnections with Australian rainfall noted in
observations were shown to arise in the model due to a combination of decadal modulation
of El Niño amplitude and longitudinal shifts of the Walker Circulation.
Climate Change Projections
Meehl, Washington, Arblaster, Bettge, and Strand analyzed