Improving multimodel weather forecast of monsoon rain over China using FSU superensemble   总被引：3，自引：0，他引：3  

T. N. KRISHNAMURTI  A. D. SAGADEVAN  A. CHAKRABORTY  A. K. MISHRA  A. SIMON 《大气科学进展》2009,26(5):813-839

In this paper we present the current capabilities for numerical weather prediction of precipitation over China using a suite of ten multimodels and our superensemble based forecasts. Our suite of models includes the operational suite selected by NCARs TIGGE archives for the THORPEX Program. These are: ECMWF, UKMO, JMA, NCEP, CMA, CMC, BOM, MF, KMA and the CPTEC models. The superensemble strategy includes a training and a forecasts phase, for these the periods chosen for this study include the months February through September for the years 2007 and 2008. This paper addresses precipitation forecasts for the medium range i.e. Days 1 to 3 and extending out to Day 10 of forecasts using this suite of global models. For training and forecasts validations we have made use of an advanced TRMM satellite based rainfall product. We make use of standard metrics for forecast validations that include the RMS errors, spatial correlations and the equitable threat scores. The results of skill forecasts of precipitation clearly demonstrate that it is possible to obtain higher skills for precipitation forecasts for Days 1 through 3 of forecasts from the use of the multimodel superensemble as compared to the best model of this suite. Between Days 4 to 10 it is possible to have very high skills from the multimodel superensemble for the RMS error of precipitation. Those skills are shown for a global belt and especially over China. Phenomenologically this product was also found very useful for precipitation forecasts for the Onset of the South China Sea monsoon, the life cycle of the mei-yu rains and post typhoon landfall heavy rains and flood events. The higher skills of the multimodel superensemble make it a very useful product for such real time events.  相似文献   

A paradoxical situation in determining relative competence from wavelength/arclength ratios within buckle folded multilayers     

S. K. Ghosh  Sudipta Sengupta 《Journal of the Geological Society of India》2010,75(1):13-17

By measuring the ratio of wavelength to arclength of folds in closely associated disharmonically folded competent layers, it is possible to determine which layer has undergone a greater layer-parallel strain and has a smaller competence. This method may lead to a paradoxical situation. For example when foliated quartzite and mica schist layers are folded together, the mica schist laminae show a much larger buckle shortening than the quartzite layers. On the other hand, the geometry of folds in quartzite indicates that quartzite was more competent than the mica schist. The structure can be explained by different modes of buckling, general buckling in quartzite layers and internal buckling in strongly anisotropic mica schists.  相似文献   

The time scales of magma mixing and mingling involving primitive melts and melt–mush interaction at mid-ocean ridges     

Fidel Costa  Laurence A. Coogan  Sumit Chakraborty 《Contributions to Mineralogy and Petrology》2010,159(3):371-387

We have studied the chemical zoning of plagioclase phenocrysts from the slow-spreading Mid-Atlantic Ridge and the intermediate-spreading rate Costa Rica Rift to obtain the time scales of magmatic processes beneath these ridges. The anorthite content, Mg, and Sr in plagioclase phenocrysts from the Mid-Atlantic Ridge can be interpreted as recording initial crystallisation from a primitive magma (~11 wt% MgO) in an open system. This was followed by crystal accumulation in a mush zone and later entrainment of crystals into the erupted magma. The initial magma crystallised plagioclase more anorthitic than those in equilibrium with any erupted basalt. Evidence that the crystals accumulated in a mush zone comes from both: (1) plagioclase rims that were in equilibrium with a Sr-poor melt requiring extreme differentiation; and (2) different crystals found in the same thin section having different histories. Diffusion modelling shows that crystal residence times in the mush were <140 years, whereas the interval between mush disaggregation and eruption was ≤1.5 years. Zoning of anorthite content and Mg in plagioclase phenocrysts from the Costa Rica Rift show that they partially or completely equilibrated with a MgO-rich melt (>11 wt%). Partial equilibration in some crystals can be modelled as starting <1 year prior to eruption but for others longer times are required for complete equilibration. This variety of times is most readily explained if the mixing occurred in a mush zone. None of the plagioclase phenocrysts from the Costa Rica Rift that we studied have Mg contents in equilibrium with their host basalt even at their rims, requiring mixing into a much more evolved magma within days of eruption. In combination these observations suggest that at both intermediate- and slow-spreading ridges: (1) the chemical environment to which crystals are exposed changes on annual to decadal time scales; (2) plagioclase crystals record the existence of melts unlike those erupted; and (3) disaggregation of crystal mush zones appears to precede eruption, providing an efficient mechanism by which evolved interstitial melt can be mixed into erupted basalts.  相似文献   

Non‐mass‐dependent oxygen isotopic fractionation in smokes produced in an electrical discharge     

Yuki Kimura  Joseph A. Nuth  Subrata Chakraborty  Mark H. Thiemens 《Meteoritics & planetary science》2007,42(7-8):1429-1439

Abstract— We report the first production of non‐mass‐dependently fractionated silicate smokes from the gas phase at room temperature from a stream of silane and/or pentacarbonyl iron in a molecular hydrogen (or helium) flow mixed with molecular oxygen (or nitrous oxide). The smokes were formed at the Goddard Space Flight Center (GSFC) at total pressures of just under 100 Torr in an electrical discharge powered by a Tesla coil, were collected from the surfaces of the copper electrodes after each experiment and sent to the University of California at San Diego (UCSD) for oxygen isotopic analysis. Transmission electron microscopy studies of the smokes show that they grew in the gas phase rather than on the surfaces of the electrodes. We hypothesize at least two types of fractionation processes occurred during formation of the solids: a mass‐dependent process that made isotopically lighter oxides compared to our initial oxygen gas composition followed by a mass‐independent process that produced oxides enriched in ¹⁷O and ¹⁸O. The maximum Δ¹⁷O observed is + 4.7‰ for an iron oxide produced in flowing hydrogen, using O2 as the oxidant. More typical displacements are 1–2‰ above the equilibrium fractionation line. The chemical reaction mechanisms that yield these smokes are still under investigation.  相似文献   

Preference of echo features for classification of seafloor sediments using neural networks     

Chanchal De  Bishwajit Chakraborty 《Marine Geophysical Researches》2010,31(3):215-221

Selection of a set of dominant echo features to classify seafloor sediments using a multilayer perceptron neural network is investigated at two acoustic frequencies (33 and 210 kHz). Several sets of inputs with different combinations of two, three, four, five, and six echo features are exploited with three-layer neural networks. The performances of the networks are analyzed to assess the most discriminating set of echo features for classification of seafloor sediments. The results of the overall average performances reveal that backscatter strength and time spread are the two most important echo features at 33 kHz, whereas backscatter strength has higher discriminating characteristics at 210 kHz for seafloor sediment classification. In addition, a set of four echo features consisting of backscatter strength, time-spread, statistical skewness, and Hausdroff dimension gives the highest success at both the acoustic frequencies.  相似文献   

An analytic representation of the three-dimensional structure of monsoon depressions     

S. K. Mishra  D. R. Chakraborty  S. S. Desai 《Meteorology and Atmospheric Physics》1982,31(4):329-337

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Deformation of pebbles in relation to associated structures in parts of Singhbhum Shear Zone,Eastern India     

Dr. Sudipta Sengupta 《International Journal of Earth Sciences》1977,66(1):175-192

The Singhbhum Shear Zone separates the rocks of a highly metamorphosed northern group from an unmetamorphosed southern group. It had been recognised by earlier workers as a thrust zone in which the thrust movements were achieved by slip along a pre-existing schistosity. Deformed conglomerates crop out in discontinuous bands along the Shear Zone. Strain determinations from these conglomerates have been made to ascertain the strain pattern within the Shear Zone. None of the existing methods of determining strain from stretched pebbles can be applied to these conglomerates. An approximate value for shortening perpendicular to the schistosity can however be obtained from cross-cutting buckled veins. Detailed study of various small-scale structures clearly indicates that the principal structures of this region cannot be explained simply by a slipping on the schistosity.

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Zusammenfassung Die Singhbhum-Scherzone trennt die Gesteine der stark metamorphen nördlichen Gruppe von denjenigen einer nicht metamorphen südlichen Gruppe. Nach früheren Autoren ist es eine Überschiebungszone, worin die Überschiebungsbewegungen durch das Gleiten entlang einer älteren Schieferung zustande kamen. Deformierte Trümmergesteine treten in ununterbrochenen Bändern entlang der Scherzone auf. Man hat Deformationsbestimmungen von diesen Trümmergesteinen gemacht, um das Deformationsbild in der Scherzone zu erklären. Eine ausführliche Untersuchung der verschiedenen kleinmaßstäblichen Strukturen zeigt deutlich, daß die Hauptstrukturen dieser Gegend nicht einfach durch das Gleiten auf der Schieferung erklärt werden können.

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Résumé La zone de cisaillement de Singhbhum sépare les roches très métamorphiques au nord, de celles d'un groupe non-métamorphique au sud. Elle avait été reconnue lors de recherches précédentes comme étant la base de charriages suivant laquelle la poussée se serait faite par glissement le long d'une schistosité pré-existante. Des conglomérats déformés affleurent par bandes discontinues le long de cette zone. Grâce à ces conglomérats, des estimations sur la déformation ont été faites pour définir le style de déformation dans la zone de glissement. Une étude détaillée de différentes structures à petite échelle indique clairement qu'on ne peut pas expliquer les principales structures de cette région uniquement par un glissement sur la schistosité.

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Tropical systematic and random error energetics based on NCEP (MRF) analysis-forecast system — A barotropic approach     

S. De  D. R. Chakraborty 《Journal of Earth System Science》2004,113(2):167-195

Systematic and random error and their growth rate and different components of growth rate budget in energy/variance form are investigated at wavenumber domain for medium range tropical (30‡S-30‡N) weather forecast using daily horizontal wind field of 850 hPa up to 5-day forecast for the month of June, 2000 of NCEP (MRF) model. Part I of this paper deals with the study at physical domain. The following are the major findings in this paper:

–	•Tropical systematic error is associated with large scale wave of wavenumber 2, unlike the tropical random error, in which case dominant spectra of random error are observed at higher spectral band of wavenumbers 4–7 in comparison to that of systematic error.
–	•Systematic error growth rate peak is observed at wavenumber 2 up to 4-day forecast then the peak is shifted to wavenumber 1 at 5-day forecast. Random error energy shows maximum growth at wavenumber 4 for 2-day forecast, wavenumber 6 for 3–4 day forecasts and at wavenumber 7 for 1-day and 5-day forecasts.
–	•In the error growth rate budget, flux of systematic error shows the net increase of error energy at wavenumber 1 through the triad interactions with the pairs of waves of other wavenumbers. Flux and pure generation of random error energy are found to be accumulated at wavenumber 4. Resolving the possible triads in wavenumber 4 associated with these terms, it is shown that the wave receives more energy from the pairs of waves of different wavenumbers than it loses, leading to the error energy peak at wavenumber 4. However, the significant triad interaction occurs among the wavenumber 2 and higher wavenumbers in systematic error energy flux.

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Pull-apart origin of the Satpura Gondwana basin, central India     

Chandan Chakraborty  Sanjoy Kumar Ghosh 《Journal of Earth System Science》2005,114(3):259-273

The Gondwana basins of peninsular India are traditionally considered as extensional-rift basins due to the overwhelming evidence of fault-controlled synsedimentary subsidence. These basins indeed originated under a bulk extensional tectonic regime, due to failure of the attenuated crust along pre-existing zones of weakness inherited from Precambrian structural fabrics. However, disposition of the basins and their structural architecture indicate that the kinematics of all the basins cannot be extensional. To maintain kinematic compatibility with other basins as well as the bulk lateral extension, some basins ought to be of strike-slip origin. The disposition, shape and structural architecture of the Satpura basin, central India suggest that the basin could be a pull-apart basin that developed above a releasing jog of a left-stepping strike-slip fault system defined by the Son-Narmada south fault and Tapti north fault in consequence to sinistral displacement along WSW-ENE. Development of a sedimentary basin under the above-mentioned kinematic condition was simulated in model experiments with sandpack. The shape, relative size, stratigraphic and structural architecture of the experimental basin tally with that of the Satpura basin. The experimental results also provide insights into the tectono-sedimentary evolution of the Satpura basin in particular and pull-apart basins in general.  相似文献   

Simulation of Indian summer monsoon: experiments with SSTs     

S. K. Deb  H. C. Upadhyaya  O. P. Sharma  A. Chakraborty 《Meteorology and Atmospheric Physics》2006,94(1-4):43-64

Summary Hindcasts for the Indian summer monsoons (ISMs) of 2002 and 2003 have been produced from an ensemble of numerical simulations performed with a global model by changing SST. Two sets of ensemble simulations have been produced without vegetation: (i) by prescribing the weekly observed SST from ECMWF (European Centre for Medium Range Weather Forecasting) analyses, and (ii) by adding weekly SST anomalies (SSTA) of April to the climatological SST during the simulation period from May to August. For each ensemble, 10 simulations have been realized with different initial conditions that are prepared from ECMWF data with five each from April and May analyses of both the years. The predicted June–July monsoon rainfall over the Indian region shows good agreement with the GPCP (observed) pentad rainfall distribution when 5 member ensemble is taken from May initial conditions. The All-India June–July simulated rainfall time series matches favourably with the observed time series in both the years for the five member ensemble from May initial condition but drifts away from observation with April initial conditions. This underscores the role of initial conditions in the seasonal forecasting. But the model has failed to capture the strong intra-seasonal oscillation in July 2002. Heating over equatorial Indian Ocean for June 2002 in a particular experiment using 29th May 12 GMT as initial conditions shows some intra-seasonal oscillation in July 2002 rainfall, as in observation. Further evaluation of the seasonal simulations from this model is done by calculating the empirical orthogonal functions (EOFs) of the GPCP rainfall over India. The first four EOFs explain more than 80% of the total variance of the observed rainfall. The time series of expansion coefficients (principal components), obtained by projecting on the observed EOFs, provide a better framework for inter-comparing model simulations and their evaluation with observed data. The main finding of this study is that the All-India rainfall from various experiments with prescribed SST is better predicted on seasonal scale as compares to prescribed SST anomalies. This is indicative of a possible useful seasonal forecasts from a GCM at least for the case when monsoon is going to be good. The model responses do not differ much for 2002 and 2003 since the evolution of SST during these years was very similar, hence July rainfall seems to be largely modulated by the other feedbacks on the overall circulation.  相似文献