Edwin K. Schneider

A review of the predictability and prediction of ENSO

A hierarchy of El Nino-Southern Oscillation (ENSO) prediction schemes has been developed during the Tropical Ocean-Global Atmosphere (TOGA) program which includes statistical schemes and physical models. The statistical models are, in general, based on linear statistical techniques and can be classified into models which use atmospheric (sea level pressure or surface wind) or oceanic (sea surface temperature or a measure of upper ocean heat content) quantities or a combination of oceanic and atmospheric quantities as predictors. The physical models consist of coupled ocean-atmosphere models of varying degrees of complexity, ranging from simplified coupled models of the “shallow water” type to coupled general circulation models. All models, statistical and physical, perform considerably better than the persistence forecast in predicting typical indices of ENSO on lead times of 6 to 12 months. The TOGA program can be regarded as a success from this perspective. However, despite the demonstrated predictability, little is known about ENSO predictability limits and the predictability of phenomena outside the tropical Pacific. Furthermore, the predictability of anomalous features known to be associated with ENSO (e.g., Indian monsoon and Sahel rainfall, southern African drought, and off-equatorial sea surface temperature) needs to be addressed in more detail. As well, the relative importance of different physical mechanisms (in the ocean or atmosphere) has yet to be established. A seasonal dependence in predictability is seen in many models, but the processes responsible for it are not fully understood, and its meaning is still a matter of scientific discussion. Likewise, a marked decadal variation in skill is observed, and the reasons for this are still under investigation. Finally, the different prediction models yield similar skills, although they are initialized quite differently. The reasons for these differences are also unclear.

Decadal climate prediction: An update from the trenches

This paper provides an update on research in the relatively new and fast-moving field of decadal climate prediction, and addresses the use of decadal climate predictions not only for potential users of such information but also for improving our understanding of processes in the climate system. External forcing influences the predictions throughout, but their contributions to predictive skill become dominant after most of the improved skill from initialization with observations vanishes after about 6–9 years. Recent multimodel results suggest that there is relatively more decadal predictive skill in the North Atlantic, western Pacific, and Indian Oceans than in other regions of the world oceans. Aspects of decadal variability of SSTs, like the mid-1970s shift in the Pacific, the mid-1990s shift in the northern North Atlantic and western Pacific, and the early-2000s hiatus, are better represented in initialized hindcasts compared to uninitialized simulations. There is evidence of higher skill in initialize...

Axially Symmetric Steady-State Models of the Basic State for Instability and Climate Studies. Part II. Nonlinear Calculations

Abstract The linearized model presented in Part I of this study (Schneider and Lindzen, 1977) is extended to include the nonlinear advections of angular momentum by the meridional circulation. A crude cumulus heating parameterization is also introduced in certain calculations to simulate the effect of an internal hydrological cycle. The nonlinear (steady-state) boundary value problem is solved by means of an iterative scheme. The results from the nonlinear model are viewed as a reasonable basic state whose stability may be studied. It is seen that this basic state is similar in many respects to the observed zonally averaged general circulation. Surface easterlies and westerlies appear at the correct latitudes with the right magnitudes, the tropical Hadley cell has near the observed mass flux and geometry, with an ITCZ forming at the sea surface temperature maximum, mid-latitude Ferrel cells appear (although fluxes by baroclinic eddies are not modeled) with somewhat less mass flux than the observations ind...

Effects of Implementing the Simple Biosphere Model in a General Circulation Model

Abstract The Simple Biosphere Model (SiB) of Sellers et al. was designed to simulate the interactions between the Earths land surface and the atmosphere by treating the vegetation explicitly and realistically, thereby incorporating the biophysical controls on the exchanges of radiation, momentum, sensible and latent heat between the two systems. This paper describes the steps taken to implement SiB in a modified version of the National Meteorological Centers global spectral general circulation model (GCM) and explores the impact of the implementation on the simulated land surface fluxes and near-surface meteorological conditions. The coupled model (SiB-GCM) was used to produce summer and winter simulations. The same GCM was used with a conventional hydrological model (Ctl-GCM) to produce comparable “control” summer and winter simulations for comparison. It was found that SiB-GCM produced a more realistic partitioning of energy at the land surface than Ctl-GCM. Generally, SiB-GCM produced more sensible h...

Multiseasonal Predictions with a Coupled Tropical Ocean–Global Atmosphere System

The Center for Ocean‐Land‐Atmosphere Studies anomaly coupled prediction system, using a sophisticated dynamical model of the tropical Pacific Ocean and the global atmosphere, is described. The resolution of the component models is moderate, with the atmospheric spectral model truncated at triangular total wavenumber 30 and 18 vertical levels. The ocean model is a Pacific Basin model with 0.58 latitude and 1.58 longitude resolution in the waveguide and 20 vertical levels. The performance of the uncoupled component models motivates the anomaly coupling strategy and has led to the development of a simple empirical technique for converting the 850-mb zonal wind into a zonal surface stress that is used in the prediction experiments described here. In developing ocean initial conditions, an iterative procedure that assimilates the zonal wind stress based on the simulated sea surface temperature anomaly error is applied. Based on a sample of 78 18-month hindcasts, the predictions have useful skill in the Nino-3 region for at least 12 months. The systematic error of the predictions is shown to be relatively small because the ocean initial conditions are in reasonable equilibrium with the ocean

Tropospheric Water Vapor and Climate Sensitivity

Abstract Estimates are made of the effect of changes in tropospheric water vapor on the climate sensitivity to doubled carbon dioxide (CO2), using a coarse resolution atmospheric general circulation model coupled to a slab mixed layer ocean. The sensitivity of the model to doubled CO2 is found as the difference between the equilibrium responses for control and doubled CO2 cases. Clouds are specified to isolate the water vapor feedback. Experiments in which the water vapor distribution is specified rather than internally calculated are used to find the contribution of water vapor in various layers and latitude belts to the sensitivity. The contribution of water vapor in layers of equal mass to the climate sensitivity varies by about a factor of 2 with height, with the largest contribution coming from layers between 450 and 750 mb, and the smallest from layers above 230 mb. The positive feedback on the global mean surface temperature response to doubled CO2 from water vapor above 750 mb is about 2.6 times a...

The Simulated Indian Monsoon: A GCM Sensitivity Study

Abstract A series of sensitivity experiments are conducted in an attempt to understand and correct deficiencies in the simulation of the seasonal mean Indian monsoon with a global atmospheric general circulation model. The seasonal mean precipitation is less than half that observed. This poor simulation in seasonal integrations is independent of the choice of initial conditions and global sea surface temperature data used. Experiments are performed to test the sensitivity of the Indian monsoon simulation to changes in orography, vegetation, soil wetness, and cloudiness. The authors find that the deficiency of the model precipitation simulation may be attributed to the use of an enhanced orography in the integrations. Replacement of this orography with a mean orography results in a much more realistic simulation of Indian monsoon circulation and rainfall. Experiments with a linear primitive equation model on the sphere suggest that this striking improvement is due to modulations of the orographically force...

The COLA Global Coupled and Anomaly Coupled Ocean–Atmosphere GCM

Abstract The Center for Ocean–Land–Atmosphere Studies (COLA) global coupled and anomaly coupled ocean–atmosphere GCM models are described. The ocean and atmosphere components of these coupled models are identical. The only difference between them is in the coupling strategy. The anomaly coupling strategy guarantees that the climatology of the coupled model is close to the observed climatology, whereas the global coupled model suffers from serious climate drift. This climate drift is largest in the eastern tropical Pacific where the coupled model is too warm by as much as 5°C. The climate drift in the coupled model can also be seen by the predominance of an erroneous double intertopical convergence zone (ITCZ) in the eastern tropical Pacific. Despite the climate drift, both models exhibit robust interannual variability in the tropical Pacific. Composite analysis, however, reveals that the characteristics of interannual variability in the coupled and the anomaly coupled models are markedly different. For ex...

Forcing of Northern Hemisphere climate trends

The impact of observed global SST trends during the second half of the twentieth century on the Northern Hemisphere extratropical winter atmospheric circulation is investigated using ensembles of simulations with the Center for Ocean‐Land‐Atmosphere Studies (COLA) atmospheric GCM. In contrast to some other studies, the simulated ensemble mean 500-hPa trends in the North Atlantic sector do not resemble the observed trend. However, the intraensemble variability of the trends is large, with the dominant structure of that variability resembling the Arctic Oscillation ‘‘annular mode.’’ The model results are consistent with the interpretation that the observed trend is dominated by the forced signal in the Pacific‐North America sector, while over the rest of the Northern Hemisphere, and especially the North Atlantic sector, the trend is primarily interdecadal timescale internal atmospheric noise with an annular structure. In order to diagnose the origins of the forced component of the model trend, a series of equilibrium response simulations is performed using constant-in-time SST anomalies with the structure of the trend superimposed on the annually varying climatological SST. It is found that the SST trend in the latitude belt from 20 8 St o 208N is responsible for forcing much of the extratropical trend, and that the dominant tropical forcing is the SST trend in the Indian Ocean/western Pacific and eastern Pacific sectors. The idealized experiments show that the precipitation response in the Tropics is linearly related to the SST trend, and that the NH December‐January‐ February height response to SST anomalies in various regions is quasi-linear. Some additional analysis and interpretation is given. The extratropical response to low-latitude SST trends in the idealized experiments has characteristics reminiscent of Rossby wave trains forced by tropical deep convection. The intraensemble variability in the model’s extratropical zonal mean height trend, which cannot be explained by external forcing, appears to be due to variability in the trends of midlatitude eddy stirring. The observed zonal mean trend also shows evidence of forcing by trends in the eddy stirring.

Understanding Differences between the Equatorial Pacific as Simulated by Two Coupled GCMs

Abstract Numerical experiments are performed to isolate the cause of differences between the simulations of SST in the low-latitude Pacific of two coupled atmosphere–ocean general circulation models, the Center for Ocean–Land–Atmosphere (COLA) coupled model and the NCAR Climate System Model (CSM). The COLA model produces a more realistic simulation of the annual cycle of SST and interannual SST variability. The CSM has the more realistic annual mean wind stress and east–west SST gradient. The approach to finding the causes of these differences is to systematically eliminate differences in the physical parameterizations and numerics of the two models, and to examine the effects of these changes on the simulations. The results indicate that the atmospheric models rather than the ocean models are primarily responsible for differences in the simulations. There is no dominant process in the atmospheric models that explains the differences; both physical parameterizations (convection, surface flux formulation, ...