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1996 .

(2 publications)

K. Layal, R. Raghava, J. Polcher, R. Sadourny, and M. Forichon. Simulations of the 1987 and 1988 Indian Monsoons Using the LMD GCM. Journal of Climate, 9:3357-3372, December 1996. [ bib | DOI | ADS link ]

Results from 90-day simulations with the LMD GCM are described, where sea surface temperatures of 1987 or 1988 years are respectively prescribed. The initial states correspond to 1 June 1987 and 1 June 1988. The simulated precipitation rates over India show a strong contrast between the two years, with drought occurring during summer 1987 and abundant rainfall during summer 1988. The dry regime simulated during 1987 corresponds to an eastward displacement of the outflow at 200 mb and a weaker westerly flow at the surface as compared with 1988, both features being in agreement with reality. Because it is more difficult for models to simulate rainfall differences than to simulate wind variations between the two years, the changes in simulated rainfall over India are studied in more detail. In particular, more integrations are carried out to test the sensitivity of rainfall variations to initial conditions, and the result is that the decrease of rainfall in 1987 compared to 1988 is a robust feature of the model.Very early, the importance of evapotranspiration in simulating land rainfall was emphasized. Additional integrations are performed in order to study the impact of the new vegetation scheme introduced in the LMD GCM. It is shown that the contrast in rainfall between the two years is better simulated when the evapotranspiration rate of vegetation cover is represented. When vegetation is not represented in the model, the model does not simulate accurately the interannual variation of the precipitation rates.

A. Harzallah, J. O. Rocha de Aragão, and R. Sadourny. Interannual Rainfall Variability in North-East Brazil: Observation and Model Simulation. International Journal of Climatology, 16:861-878, August 1996. [ bib | DOI | ADS link ]

The relationship between interannual variability of rainfall in north-east Brazil and tropical sea-surface temperature is studied using observations and model simulations. The simulated precipitation is the average of seven independent realizations performed using the Laboratoire de Météorologie Dynamique atmospheric general model forced by the 1970-1988 observed sea-surface temperature. The model reproduces very well the rainfall anomalies (correlation of 091 between observed and modelled anomalies). The study confirms that precipitation in north-east Brazil is highly correlated to the sea-surface temperature in the tropical Atlantic and Pacific oceans. Using the singular value decomposition method, we find that Nordeste rainfall is modulated by two independent oscillations, both governed by the Atlantic dipole, but one involving only the Pacific, the other one having a period of about 10 years. Correlations between precipitation in north-east Brazil during February-May and the sea-surface temperature 6 months earlier indicate that both modes are essential to estimate the quality of the rainy season.

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