Impact of moisture variations on the circulation of the south-west monsoon

The impact of moisture anomalies on the circulation of the south-west Indian monsoon has been studied with a general circulation model. Newtonian relaxation is adopted to subject the model atmosphere under sustained moisture anomalies. The impact of negative anomalies of moisture was seen as a divergent circulation anomaly, while the positive anomaly was a stronger convergent anomaly. Although the humidity fields display a resilient behaviour, and relax back to normal patterns 1–2 days after the forcing terms in humidity are withdrawn, the circulation anomalies created by the moisture variation keeps growing. A feedback between positive moisture anomalies and low level convergence exists, which is terminated in the absence of external forcings

Multimodel Ensemble Forecasts for Weather and Seasonal Climate

In this paper the performance of a multimodel ensemble forecast analysis that shows superior forecast skills is illustrated and compared to all individual models used. The model comparisons include global weather, hurricane track and intensity forecasts, and seasonal climate simulations. The performance improvements are completely attributed to the collective information of all models used in the statistical algorithm. The proposed concept is first illustrated for a low-order spectral model from which the multimodels and a "nature run" were constructed. Two hundred time units are divided into a training period (70 time units) and a forecast period (130 time units). The multimodel forecasts and the observed fields (the nature run) during the training period are subjected to a simple linear multiple regression to derive the statistical weights for the member models. The multimodal forecasts, generated for the next 130 forecast units, outperform all the individual models. This procedure was deployed for the multimodel forecasts of global weather, multiseasonal climate simulations, and hurricane track and intensity forecasts. For each type an improvement of the multimodel analysis is demonstrated and compared to the performance of the individual models. Seasonal and multiseasonal simulations demonstrate a major success of this approach for the atmospheric general circulation models where the sea surface temperatures and the sea ice are prescribed. In many instances, a major improvement in skill over the best models is noted

Improved Weather and Seasonal Climate Forecasts from Multimodel Superensemble

A method for improving weather and climate forecast skill has been developed. It is called a superensemble, and it arose from a study of the statistical properties of a low-order spectral model. Multiple regression was used to determine coefficients from multimodel forecasts and observations. The coefficients were then used in the superensemble technique. The superensemble was shown to outperform all model forecasts for multiseasonal, medium-range weather and hurricane forecasts. In addition, the superensemble was shown to have higher skill than forecasts based solely on ensemble averaging

The Effect of Urban Expansion in Metro Manila on the Southwest Monsoon Rainfall

Model simulations of historical climate changes often do not take into account the climatic effects of changes in land use. Modifications in land cover such as urbanization, affect the partitioning of the water and energy balances, which in turn influences temperature and rainfall magnitudes and patterns. The local climate impacts of major urban expansion in metropolitan Manila (Metro Manila) in the Philippines is examined, particularly during the peak of the Southwest monsoon (SWM) rainfall season from July to September. MM5 is used to perform an ensemble simulation of experiments consisting of three-month runs for ten different years using two land cover scenarios representative of the urban cover of Metro Manila in 1972 and its expanded urban area in 2001. Results show that the SWM rainfall may be enhanced by up to 20% due to extensive urban growth. Comparison of model results with observation data indicates that without urban expansion, rainfall increases only by about 17%. When expanded urban impacts are included, the modeled increase in rainfall is about 29%, which is much closer to the observed value. This study therefore illustrates the significance of incorporating land use changes together with CO2 changes in climatic change modeling especially at the scale of local impacts