G. R. Iyengar

Impact of a nonlocal closure scheme in a simulation of a monsoon system over India

Abstract The impact of two parameterization schemes for the atmospheric boundary layer in predicting monsoon circulation over the Indian region has been studied using a Global Spectral Model. The performance of the nonlocal closure scheme for the boundary layer has been tested in the operational global model of the National Centre for Medium Range Weather Forecasting (NCMRWF) for its possible implementation and operational use. Keeping the parameterization schemes for all other physical processes the same, the performance of the nonlocal closure scheme is studied and compared with the performance of the operational local closure scheme of the boundary layer processes. Incorporation of the nonlocal closure scheme shows marginal impact in the prediction of the flow pattern. However, systematic improvement in the precipitation distribution over the Indian region is seen with the incorporation of a nonlocal closure scheme during the month of August 1999. Location of the precipitation maximum along the west co...

Improvements in medium range weather forecasting system of India

Medium range weather forecasts are being generated in real time using Global Data Assimilation Forecasting System (GDAFS) at NCMRWF since 1994. The system has been continuously upgraded in terms of data usage, assimilation and forecasting system. Recently this system was upgraded to a horizontal resolution of T574 (about 22 km) with 64 levels in vertical. The assimilation scheme of this upgraded system is based on the latest Grid Statistical Interpolation (GSI) scheme and it has the provision to use most of available meteorological and oceanographic satellite datasets besides conventional meteorological observations. The new system has an improved procedure for relocating tropical cyclone to its observed position with the correct intensity. All these modifications have resulted in improvement of skill of medium range forecasts by about 1 day.

Behaviour of predicted convective clouds and precipitation in the high resolution Unified Model over the Indian summer monsoon region

National Centre for Medium Range Weather Forecasting (NCMRWF) high resolution regional convective scale Unified Model (NCUM-R) with latest tropical science settings is used to evaluate vertical structure of cloud and precipitation over two prominent monsoon regions: Western Ghats (WG) and Monsoon Core Zone (MCZ). Model radar reflectivity generated using Cloud Feedback Model Inter-comparison Project (CFMIP) observation simulator package (COSP) along with CloudSat profiling radar reflectivity is sampled for an active synoptic situation based on a new method using Budykos index of turbulence (BT). Regime classification based on BT-precipitation relationship is more predominant during the active monsoon period when convective scale models resolution increases from 4 km to 1.5 km. Model predicted precipitation and vertical distribution of hydrometeors are found to be generally in agreement with Global Precipitation Measurement (GPM) products and BT based CloudSat observation respectively. Frequency of occurrence of radar reflectivity from model implies that the low level clouds below freezing level is underestimated compared to the observations over both regions. In addition, high level clouds in the model predictions are much lesser over WG than MCZ.

Verification of Medium Range Probabilistic Rainfall Forecasts Over India

Forecasting rainfall in the tropics is a challenging task further hampered by the uncertainty in the numerical weather prediction models. Ensemble prediction systems (EPSs) provide an efficient way of handling the inherent uncertainty of these models. Verification of forecasts obtained from an EPS is a necessity, to build confidence in using these forecasts. This study deals with the verification of the probabilistic rainfall forecast obtained from the National Centre for Medium Range Weather Forecasting (NCMRWF) Global Ensemble Forecast system (NGEFS) for three monsoon seasons, i.e., JJAS 2012, 2013 and 2014. Verification is done based on the Brier Score (BS) and its components (reliability, resolution and uncertainty), Brier Skill Score (BSS), reliability diagram, relative operating characteristic (ROC) curve and area under the ROC (AROC) curve. Three observation data sets are used (namely, NMSG, CPC-RFE2.0 and TRMM) for verification of forecasts and the statistics are compared. BS values for verification of NGEFS forecasts using NMSG data are the lowest, indicating that the forecasts have a better match with these observations as compared to both TRMM and CPC-RFE2.0. This is further strengthened by lower reliability, higher resolution and BSS values for verification against this data set. The ROC curve shows that lower rainfall amounts have a higher hit rate, which implies that the model has better skill in predicting these rainfall amounts. The reliability plots show that the events with lower probabilities were under forecasted and those with higher probabilities were over forecasted. From the current study it can be concluded that even though NGEFS is a coarse resolution EPS, the probabilistic forecast has good skill. This in turn leads to an increased confidence in issuing operational probabilistic forecasts based on NGEFS.

Performance of NCMRWF Model TC Track Forecasts During 2013

There are two tropical cyclone (TC) seasons over the North Indian Ocean (NIO), (including the Bay of Bengal (BOB) and the Arabian Sea (AS)), i.e. during the pre-monsoon months (April–early June) and the post-monsoon months (October–December) (Mohanty et al., Mar Geod 33:294–314, 2010). Further the Indian subcontinent happens to be one of the world’s highly vulnerable areas since the coastal population density is very high leading to an extensive damage to life and property. Therefore, forecasting of TC track and landfall location is critical for early warnings and mitigation of disaster. Track forecast errors over the NIO though improved significantly in recent years (Mohapatra et al., J Earth Syst Sci 122:589–601, 2013, J Earth Syst Sci 124:861–874. doi: 10.1007/s12040-015-0581-x, 2015) are still high relative to those over the Atlantic and Pacific Oceans. With advancements in computational power, development of better NWP models (both global and regional), the forecasting capability of meteorologists have greatly increased. Several meteorological centers like NCEP, UKMet office, ECMWF, JMA, JTWC etc give a real time forecast of TC tracks from their global NWP models (deterministic as well as Ensemble Prediction Systems (EPS)) (Hamill et al. Mon Weather Rev 139:3243–3247, 2011; Froude et al. Mon Weather Rev 135:2545–2567, 2007; Buckingham et al. Weather Forecast 25:1736–1754, 2010; Heming et al. Meteorol Appl 2:171–184, 1995; Heming and Radford Mon Weather Rev 126:1323–1331, 1998). TC track prediction from an ensemble forecasting system besides providing a track from each ensemble member also provides the strike probability (Weber Mon Weather Rev 133:1840–1852, 2005). For the TCs of NIO, Mohapatra et al. (J Earth Syst Sci 122:589–601, 2013, J Earth Syst Sci 124:861–874. doi: 10.1007/s12040-015-0581-x, 2015) provided a detailed verification of the official forecast tracks and its improvements in the recent past. This study provides a detailed verification of the NCMRWF NWP model forecasts of 2013 TC cases. Some of the earlier studies (Ashrit et al. Improved track and intensity predictions using TC bogusing and regional assimilation. In: Mohanty UC, Mohapatra M, Singh OP, Bandyopadhyay BK, Rathore LS (eds) Monitoring and prediction of TCs in the Indian ocean and climate change, Springer, Dordrecht, p 246–254, 2014; Chourasia et al. Mausam 64:135–148, 2013 and Mohandas and Ashrit Nat hazard 73:213–235, 2014) focused on the NCMRWF model TC forecasts and the impact of bogusing, assimilation and cumulus parameterisation etc. The present study is focused on the real time operational forecasts provided to India Meteorological Department (IMD). During May–December 2013, there were five TCs observed in the Bay of Bengal namely: Viyaru (May10–17), Phailin (October 4–14), Helen (November 19–23), Lehar (November 19–28) and Madi (December 6–13). This report summarises the performance of the real time prediction of these TC tracks by the NCMRWF Global Forecast Systems.

Spatial Verification of Rainfall Forecasts During Tropical Cyclone ‘Phailin’

During October 2013 Bay of Bengal (BOB) tropical cyclone (TC) ‘Phailin’ hit east coast of India. This was the most intense cyclone that made landfall over India after the Odisha Super Cyclone (29 October 1999). This TC originated from a remnant cyclonic circulation from the South China Sea. It intensified into a cyclonic storm on the 9 October 2013 and moved northwestwards. It further intensified into a very severe cyclonic storm on 10 October 2013 over east central BOB. It crossed Odisha coast near Gopalpur around 2230 h IST of 12 October 2013 with a sustained maximum surface wind speed of 200–210 kmph gusting to 220 kmph. Some of its unique features included the rapid intensification of the system from 10 October to 11 October 2013 resulting in an increase of wind speed from 83 to 215 kmph. Also, at the time of landfall on 12 October, maximum sustained surface wind speed in association with the cyclone was about 215 kmph and estimated central pressure was 940 hPa with pressure drop of 66 hPa at the center compared to surroundings (RSMC, New Delhi, 2014).