A model study of the 30-50 day oscillation In the tropical atmosphere

Using a global spectral model with wave-CISK formulation we have generated an eastward de which. Resembles the observed 30-50 day mode. This has a scale of global wave number one and two years structure in the vertical. It has the structure of a composite of Kelvin and Rossby waves. This composite system moves eastwards. We have also studied a linear two-level analytical model to understand the nonlinear spectral model response. In the linear as well as in the nonlinear spectral model, as we Increase the moisture availability factor the speeds of the waves decrease. In the linear model this speed is found to be independent of drag for all types of waves. In the nonlinear spectral model for a given drag there is a critical value of the moisture availability factor for which the wave becomes stationary and beyond which even shows westward propagation. Thus both moisture availability and nonlinearity appear to contribute to the slow eastward speed of the equatorial 30-50 day mode.

Medium range prediction of tropical cyclogenesis of intense vortices over Indian Seas by a Global Spectral Model

The performance of a Global Spectral Model (T-80) operational at the National Centre for Medium Range Weather Forecasting (NCMRWF), New Delhi in predicting the cyclogenesis of six tropical cyclones over Indian Seas formed during 1995-96 has been evaluated. It has been found that the model has the capability to predict cyclogenesis in wind field at least 72 hours in advance although the positions of predicted vortices are seen to be displaced from those of analysed ones in some cases. The quantitative estimates of the atmospheric conditions favourable for cyclogenesis also confirm the conclusions drawn from the qualitative analysis of cyclogenesis predictions of the model in terms of appearance of cyclonic circulation. It also follows from this analysis that the predicted circulations at the cyclogenesis stage are in general more intense and stronger as compared to the corresponding analysis in terms of wind and mass fields. On examining the model systematic errors of prediction it is found that the model has a clear bias for predicting more intense vortex during genesis and weakening stages. On the order hand it predicts relatively less intense vortex during intensification process.

A Simplified Approach for Evaluating the Flexural Response of Concrete Beams Reinforced With FRP Bars

This paper is proposed for modelling concrete beams reinforced with fiber reinforced polymer (FRP) bars in a simplified way. In order to appropriately model the FRP-reinforced concrete beams the stiffness matrix is developed in the frequency domain using fast Fourier Transform. Numerical results with the proposed spectral model for the load-displacement response and the shear stress distribution between FRP reinforcement and surrounding concrete are obtained for beams statically tested. Tens of elements are deployed in this work due to the simplicity of the proposed model. Using the same spectral model the natural frequency and mode shapes are evaluated since the frequency-dependent stiffness matrix enables it to apply for dynamic study, e.g. modal analysis. The feasibility of the proposed numerical approach for performing dynamic analysis especially for high frequency excitations in an efficient way makes it a promising tool for use in the field of structural health monitoring according to the changes in dynamic characteristics.