This paper investigates the spatial distribution of precipitable water contents over Indian region for the southwest monsoon 2005. The precipitable water contents are derived from the objective analysis field of operational Numerical Weather Prediction system of India Meteorological Department. The study shows that the distribution of PWC is capable to capture large scale features of monsoon precipitation system. Real-time availability of this product is expected to be useful in monitoring and prediction of heavy rainfall events.
Maximum wind speeds associated with tropical cyclones are estimated operationally by a very widely used tool, the satellite‐based Dvorak technique (SDT) of cloud pattern matching and infrared cloud‐top temperature analyses, but it still has its own limitations. To make a good forecast and its proper verification it is essential to estimate the location and current intensity of a cyclone accurately. This study compares intensity estimates of tropical cyclones over the north Indian Ocean by the Joint Typhoon Warning Center (JTWC) and the Regional Specialized Meteorological Centre, New Delhi (RSMCND). The results show that, except for super cyclones, the differences in intensity estimates are a function of intensity, the 12 hr intensity trend and the translation speed. The intensity estimates by the JTWC are often higher than RSMCND estimates. The mean absolute difference (MAD) and the root mean square difference (RMSD) are 9.7 kt and 13.3 kt respectively. The MAD ranges from 5.9 kt to 15.6 kt and the RMSD ranges from 7.6 kt to 19.0 kt. The average difference in location estimation and the corresponding standard deviation are found to be 67 km and 54 km respectively. In view of the subjectivity in SDT‐based intensity estimation which largely depends on the skill of the individual analyst, a robust objective method should be adopted to achieve uniformity in intensity estimates across agencies. The results of this study and the factors affecting intensity estimates quantified in the study will help operational forecasters for better monitoring of tropical cyclones and better post storm best‐track data analysis.
In recent years, physical initialization has emerged as a powerful tool to improve initial state of dynamical model during assimilation phase. This improved initial state at high resolution global spectral model is able to provide a tropical meso-scale coverage. In this paper, model out-put is used to study some dynamical aspects of meso-scale rainfall events. Major findings of this study are : (i) Meso-scale rainfall event carries a distinct dynamic structure in vertical profiles of divergence and vertical upward motion, (ii) Meso-scale event exhibits a large diurnal variation in these vertical profiles and (iii) Vertical motion field of meso-scale organisation appears to play a significant role in tropical storm formation.
There is an operational requirement to formulate an objective procedure to handle operational cyclone forecasting work in a more efficient and effective way. In this paper we propose a four-step statistical-dynamical scheme for the real time application in cyclone forecasting work. The four-step scheme consists of (a) Analysis of Genesis Potential Parameter (GPP), (b) Estimation of Maximum Potential Intensity (MPI), (c) 72 hours Intensity Prediction and (d) Prediction of decaying intensity after the landfall. In November 2007, a very severe cyclonic storm 'SIDR' formed over the Bay of Bengal and hit the Bangladesh coast. In this paper, a four-step procedure is demonstrated for real time forecasting this cyclone. The results show that the GPP analysis at early stages of development can strongly indicate that the cyclone »SIDR« had enough potential to reach its cyclone stage. The MPI of the cyclone based on the SST (Sea Surface Temperature) values along the cyclone track is estimated to be 146 knots. The observed maximum intensity of the cyclone is found to be 79 % of its MPI. The 72 hours intensity prediction based on 00 UTC on 12 November could reproduce the intensity value of 109 knots, an underestimation of 6 knots. The subsequent updated forecasts are found to be realistic and useful. The 6-hourly decaying intensity forecast after the landfall shows an underestimation of 10 knots at 12 hours forecast and a significant improvement is noticed with the incorporation of correction factor. The study has documented the potentiality of the procedure for operational application.
Three monsoon depression events of 2011 have been simulated using WRF (ARW) model with five different cumulus parameterizations namely Betts-Miller-Janjic (BMJ), Kain-Fritsch (KF), Grell-3dimensional (G3D), Tiedtke (TDK) and new simplified Arakawa-Schubert (NSAS) schemes.The forecast skills of the model have been verified with observed TRMM-3B42 rainfall analysis.The validation of forecasts is conducted through two approaches.The standard categorical skill scores have used for grid-point by grid-point verification over India domain.The contiguous rain area (CRA) method, one of the object oriented verification techniques in recent times also has been applied for further analysis.The rainfall forecasts of the model performed variedly with different cumulus physics schemes.The comparative performance of 5 schemes through categorical have been analyzed over whole India and seven separated zones as well to capture spatial variation.Using CRA method the rain objects in the observed analysis and model forecasts have been compared in terms of displacement, volume and structure errors.Consequently, the percentage match of rain objects between observation and model forecast has been computed for all cumulus physics separately for comparison.As the displacement error is found to be major contributor, the linear displacements of forecast objects from the location of respective observed objects have also been computed for further clarity.The comparison of verification results for all 5 schemes has been completed separately for all selected weather events to bring a generalized view.
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