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A Comparative Study of Storm Surge Phenomenon Associated with the Tropical Cyclone Aila Over the Bay of Bengal Using Nwp Models

Md. Idris Ali*
Department of Physics, Khulna University of Engineering & Technology, Khulna – 9203, Bangladesh

Ashik Imran
Department of Physics, University of Dhak, Dhaka – 1000, Bangladesh

I. M. Syed
Department of Physics, University of Dhak, Dhaka – 1000, Bangladesh

Md. Jafrul Islam
Department of Physics, University of Dhak, Dhaka – 1000, Bangladesh

M. A. K Mallik
Bangladesh Meteorological Department, Agargaon, Sher-E-Bangla Nagar, Dhaka – 1207, Bangladesh

Abstract/ Executive Summary:

The coastal area of the North Bay of Bengal (BoB) is one of the most vulnerable places of tropical cyclone-induced storm surge. The funneling shape of the coast cannot drive water towards the coast but amplify the surge height. Meteorological force drives seawater to the coast. In this study, prediction of cyclone-induced storm surge for cyclone Aila is done by using the India Institute of Technology-Delhi (IIT-D) storm surge model and the Japan Meteorological Agency (JMA) storm surge model. The input files for both the models are provided by using simulated data of the Weather Research and Forecasting (WRF) model and estimated data of the India Meteorological Department (IMD). The results are compared with available recorded data of surge height for this cyclone. The differences in simulated output for two different input files are also studied. The maximum surge height for Aila from the IIT-D model is found 3 m and from the JMA model is 2 m using WRF simulated data. For IMD estimated data, it is found 3 m from the IIT-D model and 2.5 m from the JMA model. The simulated surge heights are found in good agreement with the available reported data of storm surges.

Keywords: TC, Storm Surge, JMA, IIT-D

Location: In Bangladesh

Start Date:

End Date:

Program Area: Risk Management in Agriculture

Commodity: Modeling, Storm

Objectives:

In this study, we have used Weather Research and Forecasting (WRF) model to simulate minimum central pressure, maximum sustained wind and track of the cyclone. For model physics parameterization, WRF Single Moment 3 (WSM3) scheme is used as microphysics scheme, Kain-Fritch (KF) scheme is used as cumulus parameterization because this scheme includes a downdraft in the cloud (Kain, 2004) which is essential for this study and Yonsei State University (YSU) scheme is more sensitive with observed variables than other planetary boundary layer schemes which is founded by Rahul et al. (2015) in this case YSU scheme have been used as planetary boundary layer scheme. The IIT-D and JMA storm surge models are used to simulate maximum storm surge.

Methodology:

2.1 Data and WRF model Description The National Centre for Environmental Prediction (NCEP) high-resolution Global Final (FNL) Analysis data on 1.0°×1.0° grids covering the entire globe every 6-hourly has been taken as initial and lateral boundary conditions for the WRF model. WRF Model is a numerical weather prediction (NWP) system that is the composition of some fully compressible non-hydrostatic equations with different prognostic variables is designed to serve both atmospheric research and operational forecasting needs. NWP refers to the simulation and prediction of the atmosphere with a computer model, and WRF is a set of software of this. The development of WRF is a joint effort by several organizations to build a next-generation mesoscale forecast model and data assimilation system to advance the understanding and prediction of mesoscale weather and accelerate the transfer of research advance into two operations. The WRF effort has a collaborative one among the National Center for Atmospheric Research (NCAR), Mesoscale and Microscale Meteorology (MMM) Division (ARW version 3.8.1).

2.3 IIT-D Model Description IIT-D is fully non-linear and is forced by wind stress and quadratic bottom friction. It is a vertically integrated parametric storm surge model. It is used as a menu-driven stand-alone system. In this model, the applied surface wind stress is determined from a bulk quadratic law. For the numerical solution of the model equations, a stable semi-explicit finite difference scheme with the staggered grid is used. The staggered grid consists of three distinct types of computational points as the sea surface elevations, the zonal and meridional components. In this model, the bottom stress is computed from depth-integrated current with a constant co-efficient of 0.0026 (Johns et al., 1983).

To simulate storm surge from IIT-D model, observed track data from WRF model-simulated data and IMD estimated data are used. The input parameters of the model include the oceanographic and meteorological parameters, hydrological input, basin characteristics, coastal geometry, wind stress and information about the astronomical tides. In this model time, position, radius of maximum wind and pressure drop are used as input file.

2.4 JMA Storm Surge Model Description This model was developed by the Meteorological Research Institute (MRI) of JMA. JMA mainly operates two storm surge models, one is the Japan area storm surge model and the other is the Asia area storm surge, model. JMA has developed the next generation’s storm surge predictions system using the Finite Element Method (FEM). The technique to divide regions to finite elements and make unstructured grids are established (Hasegawa et al. 2015). This parametric storm surge model used two-dimensional shallow water formulae without advection terms as its model equations. Pressure drop due to inverse barometric effect and wind setup because of a strong wind is included in the model. For the JMA-SSM model observed track information from WRF simulated data and IMD estimated data are used. The input file of this model contains cyclones latitudes, longitudes, maximum sustained surface wind, minimum sea level pressure, drag coefficient, and normal atmospheric pressure.

Source of Information: Journal of Engineering Science 09(2), 2018, 33-40

Article Link (Online Journal):

Funding Source:

1.

Budget:

Total Budget (Tk.) :

Achievement/Findings:

The WRF model simulated MCP for tropical cyclone Aila and is found 978 hPa and IMD estimated MCP was 970 hPa. The model simulated maximum wind speed for cyclone Aila is found 24ms' and IMD and Joint Typhoon Warning Center (JTWC) estimated maximum wind speed is 30 ms-1. The model underestimated the maximum sustained wind speed by 6ms-1 (i.e. by 30%). IIT-D storm surge model simulated maximum surge heights using both WRF model-simulated data and IMD estimated data are found approximately 3 m. JMA storm surge model simulated maximum surge height using WRF model-simulated data is 2 m and using IMD estimated data it is 2.5 m. The maximum surge height was reported as 3 m for cyclone Aila. Therefore, the IITD model predicted maximum storm surge is in good agreement with the reported maximum surge height.

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