Maurice L. Blackmon

The Community Climate System Model version 3 (CCSM3)

Abstract The Community Climate System Model version 3 (CCSM3) has recently been developed and released to the climate community. CCSM3 is a coupled climate model with components representing the atmosphere, ocean, sea ice, and land surface connected by a flux coupler. CCSM3 is designed to produce realistic simulations over a wide range of spatial resolutions, enabling inexpensive simulations lasting several millennia or detailed studies of continental-scale dynamics, variability, and climate change. This paper will show results from the configuration used for climate-change simulations with a T85 grid for the atmosphere and land and a grid with approximately 1° resolution for the ocean and sea ice. The new system incorporates several significant improvements in the physical parameterizations. The enhancements in the model physics are designed to reduce or eliminate several systematic biases in the mean climate produced by previous editions of CCSM. These include new treatments of cloud processes, aerosol ...

Surface Climate Variations over the North Atlantic Ocean during Winter: 1900–1989

Abstract The low-frequency variability of the surface climate over the North Atlantic during winter is described, using 90 years of weather observations from the Comprehensive Ocean–Atmosphere Data Set. Results are based on empirical orthogonal function analysis of four components of the climate system: sea surface temperature (SST), air temperature, wind, and sea level pressure. An important mode of variability of the wintertime surface climate over the North Atlantic during this century is characterized by a dipole pattern in SSTs and surface air temperatures, with anomalies of one sign cast of Newfoundland, and anomalies of the opposite polarity off the southeast coast of the United States. Wind fluctuations occur locally over the regions of large surface temperature anomalies, with stronger-than-normal winds overlying cooler-than-normal SSTs. This mode exhibits variability on quasi-decadal and biennial time scales. The decadal fluctuations are irregular in length, averaging ∼9 years before 1945 and ∼1...

On the Relationship between Tropical and North Pacific Sea Surface Temperature Variations

Abstract Empirical orthogonal function analysis of winter sea surface temperature (SST) anomalies over the Pacific domain (60°N–20°S) reveals an El Nino-Southern Oscillation (ENSO) mode that is linked to the eastern North Pacific, and a North Pacific mode that is linearly independent of ENSO. The North Pacific mode exhibits maximum amplitude and variance explained along ∼40°N, west of ∼170°W. SSTs in this region have decreased by ∼1.5°C from 1950 to 1987. The cooling in winter has been associated with a strengthening of the overlying westerly winds.

How Can We Advance Our Weather and Climate Models as a Community

Abstract A common modeling infrastructure ad hoc working group evolved from an NSF/NCEP workshop in 1998, in recognition of the need for the climate and weather modeling communities to develop a more organized approach to building the software that underlies modeling and data analyses. With its significant investment of pro bono time, the working group made the first steps in this direction. It suggested standards for model data and model physics and explored the concept of a modeling software framework. An overall software infrastructure would facilitate separation of the scientific and computational aspects of comprehensive models. Consequently, it would allow otherwise isolated scientists to effectively contribute to core U.S. modeling activities, and would provide a larger market to computational scientists and computer vendors, hence encouraging their support.

Simulating the Atmospheric Response to the 1985–87 El Niño Cycle

Abstract The atmospheric response to the evolution of global sea surface temperatures (SSTS) from 1985 to 1987 is studied using the NCAR Community Climate Model (CCM1). Five separate 2-year integrations are performed, and results are presented for the ensemble-averaged response during the pre-El Nino 1985/86 winter and the mature El Nino 1986/87 winter. No skill is found in CCM1s simulation for 1985/86. The simulation for the following winter, when tropical Pacific SST anomalies approached 2°C, is more successful. A large-amplitude wave train extends poleward and eastward from the location of anomalous central Pacific convection in CCM1, although the models wave train is shifted 30° too far east compared to observations. A linear barotropic stationary wave model is used to diagnose CCM1s response during 1986/87. The eastward-shifted PNA response is easily excited by a dipole pattern of upper-level forcing with convergence over the western tropical Pacific and divergence over the central tropical Pacifi...