Ajit Tyagi

Best track parameters of tropical cyclones over the North Indian Ocean: a review

India Meteorological Department has the responsibility of monitoring and prediction of cyclonic disturbances (CDs) including tropical cyclone (TC) and depression, collection, processing and archival of all data pertaining to CDs and preparation of best track data over the North Indian Ocean (NIO). The process of post-season analysis of CDs to determine the best estimate of a CD’s position and intensity along with other characteristics during its lifetime is described as ’best tracking’. The best tracking procedure has undergone several changes world-over including NIO due to change in definition and classification of TCs, monitoring and analysis tools and procedure and physical understanding of TCs. There have been a few attempts to document the temporal changes in the best track procedure including changes in observational network, monitoring technique, area of responsibility for monitoring, terminology and classification of the TCs over the NIO. Hence, a study has been undertaken to review the temporal variations in all the above aspects of best tracking procedure and its impact on quality of best track parameters over the NIO. The problems and prospective with the best track data over the (NIO) have been presented and discussed. Based on quality and availability, the whole period of best track information may be broadly classified into four phases, viz. (i) pre-1877, (ii) 1877–1890, (iii) 1891–1960 and (iv) 1961–2010. The period of 1961–2010 may be further classified into (a) 1961–1973, (b) 1974–1990 and (c) 1991–2010. As optimum observational network including satellite leading to better estimation of location and intensity without missing of CDs was available since 1961, the climatology of genesis, location, intensity, movement (track) and landfall can be best represented based on the data set of 1961–2010. The best track parameters need to be reanalysed since 1891, based on the present criteria/classification of CDs to develop a digital data set of every six hourly position, intensity and other characteristics throughout the life period of each recorded CD over the NIO to meet the world standard. At least attempt should be made from 1974 when all types of major data including satellite, radar, surface and upper air observations are available for best track analysis. The reanalysis of best track parameters can help in better understanding and prediction of CDs and address the issues related to climate change aspects over the NIO region.

Construction and Quality of Best Tracks Parameters for Study of Climate Change Impact on Tropical Cyclones over the North Indian Ocean during Satellite Era

India Meteorological Department (IMD) has the responsibility of monitoring and prediction of cyclonic disturbances (CDs) including tropical cyclone (TC) and depressions; collection, processing and archival of all data pertaining to CDs and preparation of best track data over the North Indian Ocean (NIO). A CD is classified based on the associated sustained surface wind (MSW) (IMD, 2003). The detailed classification over the NIO adopted by IMD is shown in Table 1. This classification has been used in this study for analyzing interannual variation of frequency and intensity of CDs over the NIO during satellite era (1961-2010).

Characteristics of Very Severe Cyclonic Storm “NARGIS” over the Bay of Bengal During 27 April to 3 May 2008

A very severe cyclonic storm crossed southwest coast of Myanmar near latitude 16.0°N between 1200 and 1400 UTC of 2 May 2008. It caused loss of more than 22,000 human lives in Myanmar. The special features of “Nargis” are given below. (i) The system continued to intensify even after the recurvature. (ii) The system moved almost in the easterly direction from 0600 UTC of 1 May till 1500 UTC of 2 May. (iii) The system maintained the intensity of very severe cyclonic storm for about 12 h after the landfall. (iv) It was the most devastating cyclone over the Bay of Bengal after the 1991 Bangladesh cyclone in term of loss of life and property.

Status and Plans for Operational Tropical Cyclone Forecasting and Warning Systems in the North Indian Ocean Region

The tropical warm Indian Ocean, like the tropical North Atlantic, the South Pacific and the northwest Pacific, is a breeding ground for the disastrous tropical cyclone (TC) phenomenon. TCs are accompanied by very strong winds, torrential rains and storm surges. The reduction of cyclone disasters depends on several factors including hazard analysis, vulnerability analysis, preparedness and planning, early warning, prevention and mitigation. The early warning is a major component and it includes skill in monitoring and prediction of cyclone, effective warning products generation and dissemination, coordination with emergency response units and the public perception about the credibility of the official predictions and warnings.

An Evaluation of the Simulation of Monthly to Seasonal Summer Monsoon Rainfall over India with a Coupled Ocean Atmosphere General Circulation Model (GloSea)

The performance of the UK Met Office’s coupled ocean-atmosphere General Circulation Model (GCM) is evaluated in simulation of summer monsoon rainfall over Indian monsoon region. The UK Met Office’s Global Seasonal (GloSea) forecasting model is initialized at 0000 UTC of 1st May and integrated for a period of 6 month with 15 ensemble members to generate the model forecast. These experiments have been conducted in similar approach from 1987 to 2002 (16 years) to have monthly as well as seasonal forecast of individual year. The model simulated rainfall is compared with the verification analysis (Xie-Arkin) during the monsoon season from June to September (JJAS). The monthly forecast climatology from June to September separately and the seasonal forecast climatology (June to September; JJAS) of rainfall are well simulated by the model with two maxima viz., one over the west coast of India and other over the head Bay of Bengal region. However, the rainfall magnitude over the west-coast of India is less in the model simulation for monthly as well as in seasonal simulation. The model has shown good skill in simulation of seasonal (JJAS) mean rainfall over the Indian monsoon region. However, a little overestimation in rainfall is noted (approximately 4%) when considered the Indian monsoon region covering the land region and surrounding oceanic regions. The pattern correlation during JJAS shows highly significant correlation coefficients (CCs) over the global tropics (0.91) and Indian monsoon region (0.82). Similarly the Root Mean Square Error (RMSE) during JJAS is found to be less (1.01) over the global tropics than the Indian monsoon region (1.68). The interannual variability of forecast ensemble mean rainfall over the Indian monsoon region shows similar behaviour with that of verification rainfall variability with Correlation Coefficient of about 0.43 during the 16 years period from 1987 to 2002. The Anomaly Correlation Coefficients (ACCs) between verification and simulated rainfall during 1987–2002 over the Indian monsoon region is quite significant (more than 0.6 during some years). Overall, it can be stated that the performance of the UK Met Office’s seasonal mean simulation is reasonably good.

Modernization of Observation and Forecasting System in IMD in Support of Agromet Services

India Meteorological department has added many data and research networks during the 135 years for climate-dependent sectors, such as agriculture, forestry, and hydrology, rendering a modern scientific background to atmospheric science in India. The inclusion of the latest data from satellites and other modern observation platforms, such as Automated Weather Stations (AWS), and ground-based remote-sensing techniques in recent years has strengthened India’s long-term strategy of building up a self-reliant climate data bank for specific requirements, and also to fulfill international commitments of data exchange for weather forecasting and allied research activities. It has augmented forecasting capabilities to meet the operational requirements of day to day seamless weather forecasts in various ranges.

Characteristics of Very Severe Cyclonic Storm “SIDR” over the Bay of Bengal During 11-16 November 2007

The year 2007 showed increased cyclonic activity over the Bay of Bengal, compared to recent years with the formation of nine cyclonic disturbances. Out of these disturbances, two cyclonic storms, including a very severe cyclonic storm “SIDR”, formed over the Bay of Bengal. This system crossed Bangladesh coast around 1700 UTC of 15 November 2007. The system caused heavy to very heavy rainfall over Bangladesh and northeastern states of India. According to media report, the wind speed of about 200 km/h prevailed over Bangladesh coast at the time of landfall and tidal wave of about 6 m inundated low lying areas of Bangladesh. It caused a loss of about 3,400 human lives and huge loss of property. The special features of “SIDR” are as follows. It was the first ever very severe cyclonic storm crossing Bangladesh after 1991 and first severe cyclonic storm after 1998 (Table 1). The system moved in a near northerly direction till a few hours before landfall and recurved northeastwards during landfall. It moved faster during 12 h before landfall. The size of the storm was less, though it had severe damage potential. The very severe cyclonic storm was monitored by the latest technological tools like Doppler Weather Radar (DWR), Automatic Weather Stations (AWS), and satellite derived products including atmospheric motion vectors (AMV).

The First Ever Super Cyclonic Storm “GONU” over the Arabian Sea During 1-7 June 2007: A Case Study

Four cyclonic storms including a super cyclonic storm (Gonu) formed over the north Indian Ocean during 2007. The first ever super cyclonic storm Gonu developed over the Arabian Sea as per the history recorded by IMD since 1877. It made its first landfall over Oman as a very severe cyclonic storm, and then emerged into the Gulf of Oman and made a second landfall over Iran as a cyclonic storm. Heavy to very heavy rainfall occurred over the eastern coast of Oman, causing flood and heavy damage. Gale winds with a speed of 100 km/h were recorded at Muscat at the time of landfall. About 50 persons died and estimated damage to property was about

Classification of cyclone hazard prone districts of India

4.2 billion in Oman. The number of human deaths was 28 and loss of property was

The SAARC STORM: A Coordinated Field Experiment on Severe Thunderstorm Observations and Regional Modeling over the South Asian Region

215 million over Iran. The special features of “Gonu” are as follows. It was the first ever super cyclonic storm developed over the Arabian Sea as per recorded history of IMD (1979, 1996, 2008) The super cyclonic storm, GONU made two landfalls over Oman and Iran. This was the second landfalling cyclonic storm over Iran after 4 June 1898 (IMD 1979, 2008).