The performance of the operational extended range forecast issued by the India Meteorological Department in the nil,low,moderate and high categories of probability of cyclogenesis has been evaluated based on 868 forec...The performance of the operational extended range forecast issued by the India Meteorological Department in the nil,low,moderate and high categories of probability of cyclogenesis has been evaluated based on 868 forecasts issued every Thursday for week 1 and week 2 for the Arabian Sea(AS),Bay of Bengal(BoB)and north Indian Ocean(NIO)as a whole during April 2018 to December 2023.The forecast is biased towards under-warning for low and moderate categories over the NIO,BoB&AS and towards over-warning for high categories over NIO and BoB in week 1.It is biased towards over-warning for moderate&high categories and under-warning for low category forecast over NIO and BoB for week 2.It is biased towards under-warning for low and high categories and over-warning for moderate category forecasts over AS in week 2.The Brier score(Brier skill score)for week 1 and week 2 are 0.051(48.7%)and 0.087(8.6%)over NIO respectively.The association of Madden Julian Oscillation(MJO),equatorial Rossby waves(ERW)and Kelvin waves(KW)with genesis increases and that of low-frequency background waves(LW)and inter-tropical convergence zone(ITCZ)decreases with an increase in the intensity of storms from depression to very severe cyclonic storms(VSCS).About 100%,92%,92%,92%and 100%of the cases of the genesis of VSCS&above category storms over the NIO are associated with stronger westerlies to the south,stronger easterlies to the north,convective phase of MJO,ERW and KW over the region of genesis.展开更多
The Tropical Cyclone(TC)track prediction using different NWP models and its verification is the critical task to provide prior knowledge about the model errors,which is beneficial for giving the model guidance-based r...The Tropical Cyclone(TC)track prediction using different NWP models and its verification is the critical task to provide prior knowledge about the model errors,which is beneficial for giving the model guidance-based real-time cyclone warning advisories.This study has attempted to verify the Global Forecast System(GFS)model forecasted tropical cyclone track and intensity over the North Indian Ocean(NIO)for the years 2019 and 2020.GFS is one of the operational models in the India Meteorological Department(IMD),which provides the medium-range weather forecast up to 10 days.The forecasted tracks from the GFS forecast are obtained using a vortex tracker developed by Geophysical Fluid Dynamics Laboratory(GFDL).A total of 13 tropical cyclones formed over the North Indian Ocean,eight during 2019 and five in 2020 have been considered in this study.The accuracy of the model predicted tracks and intensity is verified for five days forecasts(120 h)at 6-h intervals;the track errors are verified in terms of Direct Position Error(DPE),Along Track Error(ATE)and Cross-Track Error(CTE).The annual mean DPE over NIO during 2019(51–331 km)is lower than 2020(82–359 km),and the DPE is less than 150 km up to 66 h during 2019 and 48 h during 2020.The positive ATE(76–332 km)indicates the predicted track movement is faster than the observed track during both years.The positive CTE values for most forecast lead times suggest that the predicted track is towards the right side of the observed track during both years.The cyclone Intensity forecast for the maximum sustained wind speed(Max WS)and central mean sea level pressure(MSLP)are verified in terms of mean error(ME)and root mean square error(RMSE).The errors are lead time independent.However,most of the time model under-predicted the cyclone intensity during both years.Finally,there is a significant variance in track and intensity errors from the cyclone to cyclone and Bay of Bengal basin to the Arabian Sea basin.展开更多
文摘The performance of the operational extended range forecast issued by the India Meteorological Department in the nil,low,moderate and high categories of probability of cyclogenesis has been evaluated based on 868 forecasts issued every Thursday for week 1 and week 2 for the Arabian Sea(AS),Bay of Bengal(BoB)and north Indian Ocean(NIO)as a whole during April 2018 to December 2023.The forecast is biased towards under-warning for low and moderate categories over the NIO,BoB&AS and towards over-warning for high categories over NIO and BoB in week 1.It is biased towards over-warning for moderate&high categories and under-warning for low category forecast over NIO and BoB for week 2.It is biased towards under-warning for low and high categories and over-warning for moderate category forecasts over AS in week 2.The Brier score(Brier skill score)for week 1 and week 2 are 0.051(48.7%)and 0.087(8.6%)over NIO respectively.The association of Madden Julian Oscillation(MJO),equatorial Rossby waves(ERW)and Kelvin waves(KW)with genesis increases and that of low-frequency background waves(LW)and inter-tropical convergence zone(ITCZ)decreases with an increase in the intensity of storms from depression to very severe cyclonic storms(VSCS).About 100%,92%,92%,92%and 100%of the cases of the genesis of VSCS&above category storms over the NIO are associated with stronger westerlies to the south,stronger easterlies to the north,convective phase of MJO,ERW and KW over the region of genesis.
文摘The Tropical Cyclone(TC)track prediction using different NWP models and its verification is the critical task to provide prior knowledge about the model errors,which is beneficial for giving the model guidance-based real-time cyclone warning advisories.This study has attempted to verify the Global Forecast System(GFS)model forecasted tropical cyclone track and intensity over the North Indian Ocean(NIO)for the years 2019 and 2020.GFS is one of the operational models in the India Meteorological Department(IMD),which provides the medium-range weather forecast up to 10 days.The forecasted tracks from the GFS forecast are obtained using a vortex tracker developed by Geophysical Fluid Dynamics Laboratory(GFDL).A total of 13 tropical cyclones formed over the North Indian Ocean,eight during 2019 and five in 2020 have been considered in this study.The accuracy of the model predicted tracks and intensity is verified for five days forecasts(120 h)at 6-h intervals;the track errors are verified in terms of Direct Position Error(DPE),Along Track Error(ATE)and Cross-Track Error(CTE).The annual mean DPE over NIO during 2019(51–331 km)is lower than 2020(82–359 km),and the DPE is less than 150 km up to 66 h during 2019 and 48 h during 2020.The positive ATE(76–332 km)indicates the predicted track movement is faster than the observed track during both years.The positive CTE values for most forecast lead times suggest that the predicted track is towards the right side of the observed track during both years.The cyclone Intensity forecast for the maximum sustained wind speed(Max WS)and central mean sea level pressure(MSLP)are verified in terms of mean error(ME)and root mean square error(RMSE).The errors are lead time independent.However,most of the time model under-predicted the cyclone intensity during both years.Finally,there is a significant variance in track and intensity errors from the cyclone to cyclone and Bay of Bengal basin to the Arabian Sea basin.
