In this paper, the teleconnections from the tropical Atlantic to the Indo-Pacific region from inter-annual to centennial time scales will be reviewed. Identified teleconnections and hypotheses on mechanisms at work are reviewed and further explored in a century-long pacemaker coupled ocean-atmosphere simulation ensemble. There is a substantial impact of the tropical Atlantic on the Pacific region at inter-annual time scales. An Atlantic Niño (Niña) event leads to rising (sinking) motion in the Atlantic region, which is compensated by sinking (rising) motion in the central-western Pacific. The sinking (rising) motion in the central-western Pacific induces easterly (westerly) surface wind anomalies just to the west, which alter the thermocline. These perturbations propagate eastward as upwelling (downwelling) Kelvin-waves, where they increase the probability for a La Niña (El Niño) event. Moreover, tropical North Atlantic sea surface temperature anomalies are also able to lead La Niña/El Niño development. At multidecadal time scales, a positive (negative) Atlantic Multidecadal Oscillation leads to a cooling (warming) of the eastern Pacific and a warming (cooling) of the western Pacific and Indian Ocean regions. The physical mechanism for this impact is similar to that at inter-annual time scales. At centennial time scales, the Atlantic warming induces a substantial reduction of the eastern Pacific warming even under CO₂ increase and to a strong subsurface cooling.

The present paper describes the Variability of the American Monsoon Systems (VAMOS) Ocean–Cloud–Atmosphere–Land Study (VOCALS), an international research program focused on the improved understanding and modeling of the southeastern Pacific (SEP) climate system on diurnal to interannual time scales. In the framework of the SEP climate, VOCALS has two fundamental objectives: 1) improved simulations by coupled atmosphere–ocean general circulation models (CGCMs), with an emphasis on reducing systematic errors in the region; and 2) improved estimates of the indirect effects of aerosols on low clouds and climate, with an emphasis on the more precise quantification of those effects. VOCALS major scientific activities are outlined, and selected achievements are highlighted. Activities described include monitoring in the region, a large international field campaign (the VOCALS Regional Experiment), and two model assessments. The program has already produced significant advances in the understanding of major issues in the SEP: the coastal circulation and the diurnal cycle, the ocean heat budget, factors controlling precipitation and formation of pockets of open cells in stratocumulus decks, aerosol impacts on clouds, and estimation of the first aerosol indirect effect. The paper concludes with a brief presentation on VOCALS contributions to community capacity building before a summary of scientific findings and remaining questions.

This paper contrasts the sea surface temperature (SST) and surface heat flux errors in the Tropical Pacific simulated by the University of California, Los Angeles, coupled atmosphere–ocean general circulation model (CGCM) and by its atmospheric component (AGCM) using prescribed SSTs. The usefulness of such a comparison is discussed in view of the sensitivities of the coupled system. Off the equator, the CGCM simulates more realistic surface heat fluxes than the AGCM, except in the eastern Pacific south of the equator where the coupled model produces a spurious intertropical convergence zone. The AGCM errors are dominated by excessive latent heat flux, except in the stratus regions along the coasts of California and Peru where errors are dominated by excessive shortwave flux. The CGCM tends to balance the AGCM errors by either correctly decreasing the evaporation at the expense of cold SST biases or erroneously increasing the evaporation at the expense of warm SST biases. At the equator, errors in simulated SSTs are amplified by the feedbacks of the coupled system. Over the western equatorial Pacific, the CGCM produces a cold SST bias that is a manifestation of a spuriously elongated cold tongue. The AGCM produces realistic values of surface heat flux. Over the cold tongue in the eastern equatorial Pacific, the CGCM simulates realistic annual variations in SST. In the simulation, however, the relationship between variations in SST and surface latent heat flux corresponds to a negative feedback, while in the observation it corresponds to a positive feedback. Such an erroneous feature of the CGCM is linked to deficiencies in the simulation of the cross-equatorial component of the surface wind. The reasons for the success in the simulation of SST in the equatorial cold tongue despite the erroneous surface heat flux are examined.

The ozone evolution in the lower stratosphere of the Southern Hemisphere during the period 5–10 August 1994 is analyzed. The analysis focuses on the ozone “collar” (the band of maximum values in ozone mixing ratio around the Antarctic ozone “hole” at these altitudes) and the development of “collar filaments.” Ozone mixing ratios provided by the Microwave Limb Sounder (MLS) on board the Upper Atmosphere Research Satellite and by an ER-2 aircraft participating in the Airborne Southern Hemisphere Ozone Experiment/Measurements for Assessing the Effects of Stratospheric Aircraft campaign are compared with values at corresponding locations in high-resolution isentropic maps obtained by using the numerical scheme of “contour advection with surgery” (CAS). The CAS reconstructed ozone maps provide a view of the way in which air masses are exported from the outskirts of the collar to form the “tongues” of higher mixing ratios observed at lower latitudes on MLS synoptic maps. There is an overall consistency... Abstract The ozone evolution in the lower stratosphere of the Southern Hemisphere during the period 5–10 August 1994 is analyzed. The analysis focuses on the ozone “collar” (the band of maximum values in ozone mixing ratio around the Antarctic ozone “hole” at these altitudes) and the development of “collar filaments.” Ozone mixing ratios provided by the Microwave Limb Sounder (MLS) on board the Upper Atmosphere Research Satellite and by an ER-2 aircraft participating in the Airborne Southern Hemisphere Ozone Experiment/Measurements for Assessing the Effects of Stratospheric Aircraft campaign are compared with values at corresponding locations in high-resolution isentropic maps obtained by using the numerical scheme of “contour advection with surgery” (CAS). The CAS reconstructed ozone maps provide a view of the way in which air masses are exported from the outskirts of the collar to form the “tongues” of higher mixing ratios observed at lower latitudes on MLS synoptic maps. There is an overall consistency...

The distribution of a climate model across homogeneous and heterogeneous computer environments with nodes that can reside at geographically different locations is investigated. This scientific application consists of an atmospheric general circulation model (AGCM) coupled to an oceanic general circulation model (OGCM). Three levels of code decomposition are considered to achieve a high degree of parallelism and to mask communication with computation. First, the domains of both the gridpoint AGCM and OGCM are divided into subdomains for which calculations an carded out concurrently (domain decomposition). Second, the model is decomposed based on the diversity of tasks performed by its major components (task decompositions). Three such components are identified: (a) AGCM/physics which computes the effects on the grid-scale flow of subgrid-scale processes such as convection and turbulent mixing; (b) AGCM/dynamics, which computes the evolution of the flow governed by the primitive equations; and (c) the OGCM. Task decomposition allows the AGCM/dynamics and OGCM calculations to be carried out concurrently. Last, computation and communication are organized in such a way that the exchange of data between different tasks is carded out in subdomains of the model domain (110 decomposition). In a dedicated computer network environment, the wall-clock time required by the resulting distributed application is reduced to that for the AGCMJ physics, with the other two components and interprocess communications running in parallel. The network bandwidth requirements for the distributed application are analyzed. It is assumed that the wall-clock time required to run the AGCM/physics for the model atmosphere in a dedicated computer environment is fixed at a value corresponding to high network efficiency. The analysis shows that, for computer environments based an nodes equivalent to the Intel Touchstone Delta, a bandwidth approaching that of the Gigabit Network is required for an efficient operation of the distributed application with model resolution double that used in current studies of the climate system if output is visualized in real time. It is argued that distribution of a climate model based on domain, task, and 110 decomposition has the potential for significant and eventually superlinear speedup in model execution, which will facilitate performance of the long integrations required by climate studies.