P. K. Kundu

Development of NWP-Based Cyclone Prediction System for Improving Cyclone Forecast Service in the Country

India Meteorological Department (IMD) operationally runs two regional model WRF and Hurricane WRF (HWRF) model for short-range prediction and Global model T574L64 for medium range prediction (7 days). As part of WMO programme to provide a guidance of tropical cyclone (TC) forecasts in near real-time for the ESCAP/WMO member countries based on the TIGGE Cyclone XML (CXML) data, IMD also implemented JMA supported software for real-time TC forecast over North Indian Ocean (NIO).

Growth of cyclone Viyaru and Phailin – a comparative study

The tropical cyclone Viyaru maintained a unique quasi-uniform intensity during its life span. Despite being in contact with sea surface for >120 hr travelling about 2150 km, the cyclonic storm (CS) intensity, once attained, did not intensify further, hitherto not exhibited by any other system over the Bay of Bengal. On the contrary, the cyclone Phailin over the Bay of Bengal intensified into very severe cyclonic storm (VSCS) within about 48 hr from its formation as depression. The system also experienced rapid intensification phase (intensity increased by 30 kts or more during subsequent 24 hours) during its life time and maximum intensity reached up to 115 kts. In this paper, a comparative study is carried out to explore the evolution of the various thermodynamical parameters and possible reasons for such converse features of the two cyclones. Analysis of thermodynamical parameters shows that the development of the lower tropospheric and upper tropospheric potential vorticity (PV) was low and quasi-static during the lifecycle of the cyclone Viyaru. For the cyclone Phailin, there was continuous development of the lower tropospheric and upper tropospheric PV, which attained a very high value during its lifecycle. Also there was poor and fluctuating diabatic heating in the middle and upper troposphere and cooling in the lower troposphere for Viyaru. On the contrary, the diabatic heating was positive from lower to upper troposphere with continuous development and increase up to 6∘C in the upper troposphere. The analyses of cross sections of diabatic heating, PV, and the 1000–500 hPa geopotential metre (gpm) thickness contours indicate that the cyclone Viyaru was vertically tilted (westward) and lacked axisymmetry in its structure and converse features (axisymmetric and vertical) that occurred for the cyclone Phailin. In addition, there was a penetration of dry air in the middle troposphere of Viyaru, whereas high moisture existed in the middle troposphere of Phailin. The vertical wind shear (5–10 ms−1) near the core of the storm region between 850 and 200 hPa was favourable for both the systems but was higher in the northern region of the cyclone Viyaru. The divergent development of these thermodynamic features conspired to produce converse characteristic of the two cyclones.

Sensitivity of WRF-ARW Model to Cumulus Parameterisation Schemes in Prediction of TC Intensity and Track Over the North Indian Ocean

Tropical cyclones (TCs) are one of the most devastating extreme weather events causing tremendous loss to human civilisation. With the growing population and economic developments, more life and property are getting exposed to the nature’s fury, particularly, along the coastal areas and these vulnerable groups always look forward to efficient real time forecasting to minimise their losses. Numerical Weather Prediction (NWP) models with its reasonable strength to forecast for several days in advance especially for the data sparse regions over the oceans are extremely handy for the operational forecasters. There has been considerable improvement during the past decades in the prediction of track and intensity of TC (Mohapatra et al. J Earth Syst Sci 122:433–451. doi: 10.1007/s12040-013-0291-1, 2013a, Nat Hazard 68:589–601. doi: 10.1007/s11069-013-0624-z, 2013b, Mausam 61:1–15, 2013c) using NWP models (Kotal et al. Trop Cycl Res Rev 3:162–177, 2014). Hence, the operational forecasters across the globe look forward to the NWP models’ products.

Decadal variation of ocean heat content and tropical cyclone activity over the Bay of Bengal

The upper ocean heat content up to 700 m depth (OHC700) is an important climatic parameter required for atmospheric and oceanographic studies like a cyclone. In this study, therefore, an attempt has been made to examine the inter-decadal variations of tropical cyclone (TC) activity and OHC700 over the Bay of Bengal (BOB) for the post-monsoon season (October–December) during 1955–2013 periods. The sea-surface temperature (SST), geopotential height at 500 hPa, low-level vorticity at 850 hPa, vertical wind shear between 200 and 850 hPa, middle tropospheric humidity at 500 hPa and outgoing long-wave radiation are also being studied using seasonal mean data. The results show a significant inter-decadal variation during 1955–2013, with two distinct decadal periods: active decadal period (ADP) (1955–1988) and inactive decadal period (IDP) (1989–2013). The anomalies of these parameters are opposite in phase for two periods. It is found that the large scale atmospheric features and oceanic parameters have significant inter-decadal variability, but frequency of the tropical cyclone is attributed to the variation in the atmospheric dynamic and thermodynamic conditions rather than the variation of oceanic parameters OHC700 and SSTs during the post-monsoon season.

Retrieval of Atmospheric Temperature Profiles from AMSU-A Measurement Using Artificial Neural Network and Its Applications for Estimating Tropical Cyclone Intensity for ‘Gonu’ and ‘Nargis’

The vertical structure of temperature and water vapour plays an important role in the meteorological processes of the atmosphere. For years the radiosonde network has been the primary observing system for monitoring tropospheric temperature and water vapour. Routine observations are very difficult over the oceanic region due to logistic problems and high cost factors. The radiosonde networks are limited only over land regions. The interpretation of satellite radiances requires the inversion of the radiative transfer equation (RTE), where measurements of radiation performed at different frequencies are related to the energy from different atmospheric regions. The solution, thus obtained, is highly indeterminate for a set of observed radiances. The degree of indetermination is associated with the spectral resolution and the number of spectral channels. These radiances are basically a function of the vertical distribution of water vapour and temperature in the atmosphere and not simply of their average values. The retrieval of these vertical profiles from the radiances is an illposed problem that cannot be solved directly (Isaacs et al., 1986). Due to the difficulty of obtaining correct RTE solutions, several approaches and methods were developed to extract information from the satellite data by retrieving geophysical parameters from satellite radiances.

Forecasting of cyclone Viyaru and Phailin by NWP-based cyclone prediction system (CPS) of IMD - an evaluation

An objective NWP-based cyclone prediction system (CPS) was implemented for the operational cyclone forecasting work over the Indian seas. The method comprises of five forecast components, namely (a) Cyclone Genesis Potential Parameter (GPP), (b) Multi-Model Ensemble (MME) technique for cyclone track prediction, (c) cyclone intensity prediction, (d) rapid intensification, and (e) predicting decaying intensity after the landfall. GPP is derived based on dynamical and thermodynamical parameters from the model output of IMD operational Global Forecast System. The MME technique for the cyclone track prediction is based on multiple linear regression technique. The predictor selected for the MME are forecast latitude and longitude positions of cyclone at 12-hr intervals up to 120 hours forecasts from five NWP models namely, IMD-GFS, IMD-WRF, NCEP-GFS, UKMO, and JMA. A statistical cyclone intensity prediction (SCIP) model for predicting 12 hourly cyclone intensity (up to 72 hours) is developed applying multiple linear regression technique. Various dynamical and thermodynamical parameters as predictors are derived from the model outputs of IMD operational Global Forecast System and these parameters are also used for the prediction of rapid intensification. For forecast of inland wind after the landfall of a cyclone, an empirical technique is developed. This paper briefly describes the forecast system CPS and evaluates the performance skill for two recent cyclones Viyaru (non-intensifying) and Phailin (rapid intensifying), converse in nature in terms of track and intensity formed over Bay of Bengal in 2013. The evaluation of performance shows that the GPP analysis at early stages of development of a low pressure system indicated the potential of the system for further intensification. The 12-hourly track forecast by MME, intensity forecast by SCIP model and rapid intensification forecasts are found to be consistent and very useful to the operational forecasters. The error statistics of the decay model shows that the model was able to predict the decaying intensity after landfall with reasonable accuracy. The performance statistics demonstrates the potential of the system for improving operational cyclone forecast service over the Indian seas.