Showing papers by "National Centre for Medium Range Weather Forecasting published in 2001"

A mesoscale model intercomparison: A case of explosive development of a tropical cyclone (COMPARE III)

Abstract: The performance of current mesoscale numerical models is evaluated in a case of model intercomparison project (COMPARE III). Explosive development of Typhoon Flo (9019) occurred in the case in September 1990 during the cooperative three field experiments, ESCAP/WMO-led SPECTRUM, US-led TCM-90, and former USSR-led TYPHOON-90 in the western North Pacific. Sensitivity to initial fields as well as impact of enhanced horizontal resolution are examined in the model intercomparison. Both track and intensity predictions are very sensitive to the choice of initial fields prepared with different data assimilation systems and the use of a particular synthetic tropical cyclone vortex. Horizontal resolution enhanced from 50km through 20km down to a 10km grid has a large impact on intensity prediction. This is presumably due to a better presentation of inner structure with higher resolution. There is little impact on track prediction in this target period when the typhoon was in its before-recurvature stage. While most models show large biases in underestimating central pressure deepening, some of the participating models with a particular initial field succeed in reproducing qualitatively the time evolution of central pressure, including slow deepening in the first half and rapid deepening in the second half of the simulation period of 72 hours. However, differences leading to different intensity predictions among models have yet to be identified. Intercomparison of the simulation results shows that wind field has a close relationship with precipitation distribution. This suggests that better prediction of precipitation distribution is crucial for better prediction of wind field, and vice versa. Through the COMPARE III experiments, it has become clear that precise simulation of tropical cyclone structure, especially in the inner-core region, is very important for accurate intensity prediction. Consideration, therefore, should be given to this point, when improvements in resolution, initialization, and physics of numerical models for tropical cyclone intensity prediction are reviewed.

Interannual Variability of the Indian Summer Monsoon and Internal Variability in the JMA Global Model Simulations

Abstract: In this investigation, we study the monsoon variability using an ensemble of long integration (34 years) of the JMA model at T42 resolution. It was noted that a major part of the interannual variability of the Indian monsoon is by internal dynamics. Leading modes of atmospheric variability are examined using a multivariate EOF analysis. EOF-1 (obtained from a model-run with observed SST) represents the model’s response to SST variations associated with ENSO, and it has a dominant periodicity of around 4-5 years. ENSO related variability is mostly confined to the equatorial region. Over the Indian land region, the loadings of this EOF are not large. Loading associated with EOF-2 are large over the Indian region. Large-scale SST variation in the equatorial region is not seen in the spatial pattern of this mode. The rainfall pattern is characterised by positive anomalies over the Indian region, and over the central Pacific north of the equator. Rainfall anomalies of opposite sign are noticed in the warm pool regions of the western Pacific and the south-central Pacific Ocean. This EOF has a dominant periodicity on the quasi-biennial time scale (with spectral peaks at about 30 months and another at about 15 months). Spatial pattern of the EOF-1 from a climatological SST run resembles that of the EOF-2 obtained from the observed SST run and it is a natural mode of the atmospheric system. Similar analyses have been made using monthly anomalies of June to September (monsoon months). Interannual variability of rainfall has been examined using filtered rainfall anomalies during the monsoon season retaining the variability on the time scales of 15-30 months, and 36-84 months. Large rainfall variability in the climatological SST run occurs on the time scales of the QBO and ENSO as in the observed SST run. Over the Indian region, magnitudes of interannual variability in these two time scales obtained from the climatological SST run is comparable to those obtained from the observed SST run.

Impact of satellite derived moisture in a global numerical weather prediction model

Abstract: EN ANOS RECIENTES, INSTRUMENTOS ESPECIALES Y HERRAMIENTAS DE PERCEPCION REMOTA NOS HAN PERMITIDO VER A LA TIERRA DE MEJOR MANERA, AMPLIFICANDO EL AMBITO DE LA VISION. INDIA TIENE EL SISTEMA MUNDIAL MAS GIGANTESCO QUE ES MUY IMPORTANTE PARA SU AGRICULTURA. OBTIENE LA MAYORIA DE SU LLUVIA DURANTE LOS MESES DE JUNIO A OCTUBRE DE LA TEMPORADA DE MONZON. EN JULIO OBTENEMOS EL MAXIMO NUMERO DE PERTURBACIONES TROPICALES EN LA REGION CITADA. EL PRESENTE ESTUDIO PRETENDE DEDUCIR LOS PERFILES DE HUMEDAD PARA EL MES DE JUNIO DE 1996 MEDIANTE EL USO DE TECNICAS DE PERCEPCION REMOTA Y SU IMPACTO SOBRE EL SISTEMA DE ANALISIS-PRONOSTICO. LA INCLUSION DE LA HUMEDAD DERIVADA MEDIANTE LOS SATELITES EN EL MODELO DE PREEDICION NUMERICA (NWP) RESULTA EN: (I) EL DEBILITAMIENTO DE LA CONFIGURACION DE FLUJO MONZONICA SOBRE L A REGION DE SOMALIA (II) LA REDUCCION DE LAS VELOCIDADES DEL VIENTO EN EL SUR DE LA BAHIA DE BENGALA, (III) LA FORMACION DE UNA VAGUADA EN LA COSTA OESTE DEL SUBCONTINENTE Y (IV) LA PREDICCION REALISTA DE LA LLUVIA SOBRE LA REGION DE ORISSA Y ANDHARA PRADESH, ETC. TODOS ESTOS EFECTOS CONTRASTAN CON EL CONTROL EXISTENTE Y PODRIA AYUDAR A MEJORAR LA PREDICCION DE LA PRECIPITACION PLUVIAL Y LAS CONFIGURACIONES DE FLUJO DURANTE LA TEMPORADA MONZONICA.