Forecasting global ENSO-related climate anomalies

Long-range global climate forecasts have been made by use of a model for predicting a tropical Pacific sea surface temperature (SST) in tandem with an atmospheric general circulation model. The SST is predicted first at long lead times into the future. These ocean forecasts are then used to force the atmospheric model and so produce climate forecasts at lead times of the SST forecasts. Prediction of the wintertime 500 mb height, surface air temperature and precipitation for seven large climatic events of the 1970 to 1990s by this two-tiered technique agree well in general with observations over many regions of the globe. The levels of agreement are high enough in some regions to have practical utility. -Author

Forecasting global ENSO-related climate anomalies

Long-range global climate forecasts have been made by use of a model for predicting a tropical Pacific sea surface temperature (SST) in tandem with an atmospheric general circulation model. The SST is predicted first at long lead times into the future. These ocean forecasts are then used to force the atmospheric model and so produce climate forecasts at lead times of the SST forecasts. Prediction of the wintertime 500mb height, surface air temperature and precipitation for seven large climatic events of the 1970 1990s by this two-tiered technique agree well in general with observations over many regions of the globe. The levels of agreement are high enough in some regions to have practical utility

Climate predictability experiments with general circulation model

The atmospheric response to the evolution of the global sea surface temperatures from 1979 to 1992 is studied using the Max-Planck-Institut 19 level atmospheric general circulation model, ECHAM3 at T 42 resolution. Five separate 14-year integrations are performed and results are presented for each individual realization and for the ensemble-averaged response. The results are compared to a 30-year control integration, using a climate monthly mean state of the sea surface temperatures. It is found that the ECHAM3 model, by and large, does reproduce the observed response pattern to El Nino and La Nina. During the El Nino events, the subtropical jet streams on both hemispheres are intensified and displaced equatorward, and there is a tendency of weak upper easterlies over the equator. The Southern Oscillation is a very stable feature of the integrations and accurately reproduced in all experiments. The inter-annual variability at middle and high latitudes, on the other hand, is strongly dominated by chaotic dynamics, and the SST forcing does only weakly modulate the atmospheric circulation. The potential predictability of the model is investigated for eight different regions. Signal to noise ratio is large in most parts of the tropical belt, of medium strength in the Western hemisphere and generally small over the European area. The ENSO signal is most pronounced during the boreal spring. A particular strong signal in the precipitation field during spring can be found over southern United States and over southwestern Asia. Western Canada is normally warmer during the warm ENSO phase, while northern Europe is warmer than normal during the ENSO cold phase. The reason is advection of warm air due to a more intense Pacific low than normal during the warm ENSO phase and a more intense Icelandic low than normal during the cold ENSO phase, respectively. It is suggested, that inter-annual extratropical SST anomalies are, at least partly, secondary effects and forced by the atmospheric winter circulation, in its turn affected by the ENSO events. (orig.)Available from TIB Hannover: RR 1347(145) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

The atmospheric general circulation model ECHAM-4: Model description and simulation of present-day climate

A detailed description of the fourth-generation ECHAM model is presented. Compared to the previous version, ECHAM3, a number of substantial changes have been introduced in both the numerics and physics of the model. These include a semi-Lagrangian transport scheme for water vapour, cloud water and trace substances, a new radiation scheme (ECMWF) with modifications concerning the water vapour continuum, cloud optical properties and greenhouse gases, a new formulation of the vertical diffusion coefficients as functions of turbulent kinetic energy, and a new closure for deep convection based on convective instability instead of moisture convergence. Minor changes concern the parameterizations of horizontal diffusion, stratiform clouds and land surface processes. Also, a new dataset of land surface parameters have been compiled for the new model. The climatology of the model, derived from two extended AMIP simulations at T42L19 resolution, is documented and compared with ECMWF operational analyses. Some of the biases noted for the previous model version remain virtually unchanged. For example, the polar upper troposphere and lower stratosphere is much too cold, and the zonal wind errors become very large above the 200 hPa level. Furthermore, the low-frequency variability is still too small but the errors are reduced by about 50% compared to ECHAM397 refs.SIGLEAvailable from TIB Hannover: RR 1347(218) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Simulation of the present-day climate with the ECHAM model: Impact of model physics and resolution

Available from TIB Hannover: RR 1347(93) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman