Browsing by Author "Alam, Dr. Md. Mahbub"

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Prediction of Formation and Tracks of Bay of Bengal Cyclones
(Dhaka University (DU), Dhaka, Bangladesh., 1998-12) Alam, Dr. Md. Mahbub; Shafee, Prof. Sultana
Rawindsonde data of 0000 UTC for standard isobaric surfaces at the surface, 850, 700, 500, 400, 300, 200, 150 and 100 hPa levels for the periods of different cyclones in the last decade were considered to study the different meteorological parameters. The vertical wind shear, the vertical variation of zonal wind speed and meridional wind speed and temperature were studied for different cyclones in the surroundings of the Bay of Bengal in relation to the movement of cyclones. The dry static energy, the latent heat energy, the moist static energy, the total energy, the meridional and zonal fluxes of moist static energy and their vertical distribution were studied in the surroundings of the Bay of Bengal in relation to the movement of cyclones and their ultimate landfall. A two dimensional model is developed for the prediction of cyclone tracks in the Bay of Bengal. The boundary value problem is then solved by using the complex potentials. The different cyclones are integrated in different time steps to find the relationship between the actual travel time and observed time by the models. The results obtained for cyclone tracks by this model are almost the same as the actual track. The cyclonic track data were collected from the Storm Warning Centre (SWC) of Bangladesh Meteorological Department (BMD). A simplified system of equations that can simulate the evolution and mature stages of tropical cyclones is presented. The study has been done using a three-dimensional numerical model constructed which produces circularly symmetric feature of the tropical cyclone. It has 5 layers in the vertical with the horizontal extent of 1200 km. The horizontal grid length of the model is 80 km. The model equations have been solved using the Leapfrog scheme. Numerical simulation shows that the model sensitivity to the vertical stability is similar to results obtained from other general models. Latent heat release associated with condensation is calculated from the moisture equation. The sensible heating parameter is added to the heating term. Initially the model atmosphere is assumed to be at rest and is then excited by a large scale heating to generate an initial vortex. The evolution of surface pressure drop, tangential wind, radial wind, heat released due to condensation, temperature anomaly, D-value, horizontal structure of vertical p-velocity, vertical structure of vertical p-velocity, vorticity and static stability parameter have been discussed based on the results obtained from the tropical cyclone modelling experiment.
Study of Rainfall Distributions over Bangladesh associated with Tropical Disturbances in the Bay of Bengal
(Khulna University of Engineering & Technology (KUET), Khulna, Bangladesh., 2009-02) Ferdousi, Morsheda; Alam, Dr. Md. Mahbub
Tropical cyclone is the most disastrous natural phenomenon for Bangladesh. Only preparedness can reduce the losses of lives as well as properties. Rain, one of the three means of destruction due to Tropical cyclone, is closely related with the Tropical cyclone. From its birth to death tropical cyclone produces rain, but the amount and region of rainfall at different stage of the tropical cyclone is different. Keeping this information in mind, in this dissertation, we have studied the rainfall distribution over Bangladesh with the movement of the tropical disturbances in the Bay of Bengal that crossed the Bangladesh coast. As our interest was limited over Bangladesh only, we have chosen those events whose eventual landfall was in the Bangladesh coast from the database created with the help of Bangladesh Meteorological Department (BMD). The main objective of this study is to identify the relationship between the amount of rainfall that is observed in different meteorological stations all over Bangladesh and the track of the tropical disturbances affecting Bangladesh. For that purpose rainfall data of 30 stations located all over Bangladesh is analyzed. We have plotted the isolines to identify the rainfall pattern over Bangladesh map along with the track of the disturbances. Then these figures are analyzed to identify the relationship between the rainfall and the track of the disturbances. In this study, 17 cyclonic disturbances of different categories, 8 Severe Cyclonic Storms with a core of hurricane wind (SCS (H)), 2 Severe Cyclonic Storm (SCS), 3 Cyclonic Storm (CS), 3 Deep Depression (DD) and 1 depression, have been considered that occurred during 1974 to 2001. The analysis shows that heavy to very heavy rainfall occurred on the front-right quadrant of the track on the day and the day before the system approached the Bangladesh coast.