Influence of Future Tropical Cyclone Track Changes on Their Basin-Wide Intensity over the Western North Pacific: Downscaled CMIP5 Projections

The possible changes of tropical cyclone（TC） tracks and their influence on the future basin-wide intensity of TCs over the western North Pacific（WNP） are examined based on the projected large-scale environments derived from a selection of CMIP5（Coupled Model Intercomparison Project Phase 5） models. Specific attention is paid to the performance of the CMIP5 climate models in simulating the large-scale environment for TC development over the WNP. A downscaling system including individual models for simulating the TC track and intensity is used to select the CMIP5 models and to simulate the TC activity in the future.The assessment of the future track and intensity changes of TCs is based on the projected large-scale environment in the21 st century from a selection of nine CMIP5 climate models under the Representative Concentration Pathway 4.5（RCP4.5）scenario. Due to changes in mean steering flows, the influence of TCs over the South China Sea area is projected to decrease,with an increasing number of TCs taking a northwestward track. Changes in prevailing tracks and their contribution to basin-wide intensity change show considerable inter-model variability. The influences of changes in prevailing track make a marked contribution to TC intensity change in some models, tending to counteract the effect of SST warming. This study suggests that attention should be paid to the simulated large-scale environment when assessing the future changes in regional TC activity based on climate models. In addition, the change in prevailing tracks should be considered when assessing future TC intensity change.

The Simulation of Five Tropical Cyclones by Sample Optimization of Ensemble Forecasting Based on the Observed Track and Intensity

The quality of ensemble forecasting is seriously affected by sample quality.In this study,the distributions of ensemble members based on the observed track and intensity of tropical cyclones(TCs)were optimized and their influence on the simulation results was analyzed.Simulated and observed tracks and intensities of TCs were compared and these two indicators were combined and weighted to score the sample.Samples with higher scores were retained and samples with lower scores were eliminated to improve the overall quality of the ensemble forecast.For each sample,the track score and intensity score were added as the final score of the sample with weight proportions of 10 to 0,9 to 1,8 to 2,7 to 3,6 to 4,5 to 5.These were named as“tr”,“91”,“82”,“73”,“64”,and“55”,respectively.The WRF model was used to simulate five tropical cyclones in the northwestern Pacific to test the ability of this scheme to improve the forecast track and intensity of these cyclones.The results show that the sample optimization effectively reduced the track and intensity error,“55”usually had better performance on the short-term intensity prediction,and“tr”had better performance in short-term track prediction.From the overall performance of the track and intensity simulation,“91”was the best and most stable among all sample optimization schemes.These results may provide some guidance for optimizing operational ensemble forecasting of TCs.

A SIMULATION STUDY OF THE INFLUENCE OF LAND FRICTION ON LANDFALL TROPICAL CYCLONE TRACK AND INTENSITY

A quasi-geostrophic barotropic vorticity equation model is used to simulate the influences of topographic forcing and land friction on landfall tropical cyclone track and intensity. The simulation results show that tropical cyclone track may have sudden deflection when the action of topographic friction dissipation is considered, and sudden deflection of the track is easy to happen and sudden change of tropical cyclone intensity is not clear when the intensity of tropical cyclone is weak and the land friction is strong. The land friction may be an important factor that causes sudden deflection of tropical cyclone track around landfall.

Tracking molecular structure deformation of nitrobenzene and its torsion-vibration coupling by intense pumping CARS

The structural deformation induced by intense laser field of liquid nitrobenzene（NB） molecule,a typical molecule with restricting internal rotation,is tracked by time- and frequency-resolved coherent anti-Stokes.Raman spectroscopy（CARS） technique with an intense pump laser.The CARS spectra of liquid NB show that the NO2 torsional mode couples with the NO2 symmetric stretching mode,and the NB molecule undergoes ultrafast structural deformation with a relaxation time of 265 fs.The frequency of NO2 torsional mode in liquid NB（42 cm-1） at room temperature is found from the sum and difference combination bands involving the NO2 symmetric stretching mode and torsional mode in time- and frequency-resolved CARS spectra.

EXPERIMENTAL STUDY ON A DYNAMIC ASYMMETRICAL TYPHOON INITIALIZATION SCHEME BASED ON 4D-VAR

Axisymmetric bogus vortexes at sea level are usually used in the traditional bogus data assimilation （BDA） scheme. In the traditional scheme, the vortex could not accurately describe the specific characteristics of a typhoon, and the evolving real typhoon is forced to unreasonably adapt to this changeless vortex. For this reason, an asymmetrical typhoon bogus method with information blended from the analysis and the observation is put forward in this paper, in which the impact of the Subtropical High is also taken into consideration. With the fifth-generation Penn State/NCAR Mesoscale Model （MM5） and its adjoint model, a four-dimensional variational data assimilation （4D-Var） technique is employed to build a dynamic asymmetrical BDA scheme to assimilate different asymmetrical bogus vortexes at different time. The track and intensity of six surmner typhoons much influenced by the Subtropical High are simulated and the results are compared. It is shown that the improvement in track simulation in the new scheme is more significant than that in the traditional scheme. Moreover, the periods for which the track cannot be simulated well by the traditional scheme can be improved with the new scheme. The results also reveal that although the simulated typhoon intensity in the new scheme is generally weaker than that in the traditional scheme, this trend enables the new scheme to simulate, in the later period, closer-to-observation intensity than the traditional scheme. However, despite the fact that the observed intensity has been largely weakened, the simulated intensity at later periods of the BDA schemes is still very intensive, resulting in overly development of the typhoon during the simulation. The limitation to the simulation effect of the BDA scheme due to this condition needs to be further studied.

Passive tracking and size estimation of volume target based on acoustic vector intensity

The special sections of volume target are observed with acoustic vector intensity according to the difference among their radiated-noise characteristics, then three sections are tracked with Kalman filtering, and target size is estimated. Simulation results indicate that in ideal condition three sections of a ship can be tracked and ship's size can be estimated even though one of three sections can not be observed.

HWRF BASED ENSEMBLE PREDICTION SYSTEM USING PERTURBATIONS FROM GEFS AND STOCHASTIC CONVECTIVE TRIGGER FUNCTION

In this study, an ensemble prediction system(EPS) for the operational Hurricane Weather Research and Forecast(HWRF) model at the Environmental Modeling Center(EMC) of National Centers for Environmental Prediction(NCEP) is introduced and evaluated. The HWRF-EPS takes into account two main sources of uncertainties related to the initial/boundary conditions and the model physics by 1) using the large scale fields from NCEP Global Ensemble Forecast System(GEFS);and 2) stochastically perturbing the convective trigger function in the cumulus convection parameterization scheme.Verification for the 2011-2012 North Atlantic hurricane seasons shows that HWRF-EPS outperforms its deterministic versions at all lead times for both track and intensity forecast errors. Statistical characteristics are investigated and analyzed to demonstrate the effectiveness and robustness of the HWRF-EPS. The relationship between ensemble spread and forecast error for track and intensity in the HWRF-EPS indicated that the spread is likely more useful as a predictor of forecast error when it has moderately low values. Rank histogram analysis shows that the HWRF-EPS is well dispersed in both track and intensity forecasts except for the systematic errors inherited from the deterministic version. Further comparison with 2012 hurricane season’s top-flight models shows improved track and intensity forecasts from the HWRF-EPS.