A Time Neighborhood Method for the Verification of Landfalling Typhoon Track Forecast

Landfalling typhoons can cause disasters over large regions.The government and emergency responders need to take measures to mitigate disasters according to the forecast of landfall position,while slight timing error can be ignored.The reliability of operational model forecasts of typhoon landfall position needs to be evaluated beforehand,according to the forecasts and observation of historical cases.In the evaluation of landfalling typhoon track,the traditional method based on point-to-point matching methods could be influenced by the predicted typhoon translation speed.Consequently,the traditional track evaluation method may result in a large track error even if the predicted landfall position is close to observation.The purpose of this paper is to address the above issue using a simple evaluation method of landfalling typhoon track forecast based on the time neighborhood approach.In this new method,the timing error was lessened to highlight the importance of the position error during the landfall of typhoon.The properties of the time neighborhood method are compared with the traditional method based on numerical forecast results of 12 landfalling typhoon cases.Results demonstrated that the new method is not sensitive to the sampling frequency,and that the difference between the time neighborhood and traditional method will be more obvious when the moving speed of typhoon is moderate(between 15−30 km h^(−1)).The time neighborhood concept can be easily extended to a broader context when one attempts to examine the position error more than the timing error.

Application of Direct Assimilation of ATOVS Microwave Radiances to Typhoon Track Prediction

In order to solve the difficult problem of typhoon track prediction due to the sparsity of conventional data over the tropical ocean, in this paper, the No. 0205 typhoon Rammasun of 4-6 July 2002 is studied and an experiment of the typhoon track prediction is made with the direct use of the Advanced TIROS-N Operational Vertical Sounder (ATOVS) microwave radiance data in three-dimensional variational data assimilation. The prediction result shows that the experiment with the ATOVS microwave radiance data can not only successfully predict the observed fact that typhoon Rammasun moves northward and turns right, but can also simulate the action of the fast movement of the typhoon, which cannot be simulated with only conventional radiosonde data. The skill of the typhoon track prediction with the ATOVS microwave radiance data is much better than that without the ATOVS data. The typhoon track prediction of the former scheme is consistent in time and in location with the observation. The direct assimilation of

A nowcasting model for the prediction of typhoon tracks based on a long short term memory neural network

It is of vital importance to reduce injuries and economic losses by accurate forecasts of typhoon tracks. A huge amount of typhoon observations have been accumulated by the meteorological department, however, they are yet to be adequately utilized. It is an effective method to employ machine learning to perform forecasts. A long short term memory（LSTM） neural network is trained based on the typhoon observations during 1949–2011 in China＇s Mainland, combined with big data and data mining technologies, and a forecast model based on machine learning for the prediction of typhoon tracks is developed. The results show that the employed algorithm produces desirable 6–24 h nowcasting of typhoon tracks with an improved precision.

Prediction of Typhoon Tracks Using Dynamic Linear Models

This paper presents a study on the statistical forecasts of typhoon tracks. Numerical models have their own systematic errors, like a bias. In order to improve the accuracy of track forecasting, a statistical model called DLM (dynamic linear model) is applied to remove the systematic error. In the analysis of typhoons occurring over the western North Pacific in 1997 and 2000, DLM is useful as an adaptive model for the prediction of typhoon tracks.

Sensitivity of WRF simulated typhoon track and intensity over the South China Sea to horizontal and vertical resolutions

To determine the grid resolutions of the WRF model in the typhoon simulation,some sensitivity analysis of horizontal and vertical resolutions in different conditions has been carried out.Different horizontal resolutions(5,10,20,30 km),nesting grids(15 and 5 km),different vertical resolutions(35-layers,28-layers,20-layers)and different top maximum pressures(1 000,2 000,3 500,5 000 Pa)had been used in the mesoscale numerical model WRF to simulate the Typhoon Kai-tak.The simulation results of typhoon track,wind speed and sea level pressure at different horizontal and vertical resolutions have been compared and analyzed.The horizontal and vertical resolutions of the model have limited effect on the simulation effect of the typhoon track.Different horizontal and vertical resolutions have obvious effects on typhoon strength(defined by wind speed)and intensity(defined by sea level pressure,SLP),especially for sea level pressure.The typhoon intensity simulated by the high-resolution model is closer to the real situation and the nesting grids can improve computational accuracy and efficiency.The simulation results affected by vertical resolution using 35-layers is better than the simulation results using 20-layers and 28-layers simulations.Through comparison and analysis,the horizontal and vertical resolutions of WRF model are finally determined as follows:the two-way nesting grid of 15 and 5 km is comprehensively determined,and the vertical layers is 35-layers,the top maximum pressure is 2 000 Pa.

ENSEMBLE PREDICTION EXPERIMENTS OF TYPHOON TRACK BASED ON THE STOCHASTIC TOTAL TENDENCY PERTURBATION

The GRAPES-TCM is used to make ensemble prediction experiments for typhoon track.Three kinds of ensemble schemes are designed for the experiments.A total of 109 experiments are made for the nine typhoons in 2011 and the integral time is 72 h.The experiment results are shown as follows.In the three ensemble schemes,on the whole,scheme 1 has the best track prediction.Its average absolute track error and overall deviations of typhoon moving speed and moving direction are all the smallest in the three schemes.For both scheme 1 and scheme 2,they are all smaller than those of their control predictions.Both of their ensemble predictions show superiority to their deterministic predictions.Overall,compared with the observations,the typhoon moving directions of the three schemes mainly skew to the right,and in the late integration they mainly tend to be relatively slow.In the three schemes,the track dispersion of scheme 1 is the largest and that of scheme 3 the smallest.In scheme 1 it is much larger than in schemes 2 and 3.The difference of dispersion between scheme 2 and scheme 3 is small.The track dispersions of the three schemes are all much smaller than their rational dispersions.Compared with the eight domestic and overseas operational numerical weather prediction(NWP) models,scheme 1 has better predictions than the other seven operational models except ECMWF NWP model.Scheme 1 has the value of operational application.

TYPHOON TRACK PREDICTION EXPERIMENTS USING T_(106)L_(19)

A series of 96-h typhoon track prediction experiments were carried out using medium range forecasting system of NMC by adding BOGUS typhoon (simplified as B-TC) into the first guess field or the analysis field in order to provide longer time typhoon track forecast. The results show that T106L19 could provide a better forecast to typhoon tracks when the B-TC was added, especially when the typhoon vortex is even weaker. The sensitive experiments on where to add the B-TC show that the results from adding the B-TC into the first guess field are better. The results also show that the initialization smoothes the B-TC a lot and this will affect the typhoon track prediction.

THE IMPACT OF CUMULUS PARAMETERIZATIONS AND MICROPHYSICS SCHEMES UNDER DIFFERENT COMBINATIONS ON TYPHOON TRACK PREDICTION

This study examines the effects of cumulus parameterizations and microphysics schemes on the track forecast of typhoon Nabi using the Weather Research Forecast model. The study found that the effects of cumulus parameterizations on typhoon track forecast were comparatively strong and the typhoon track forecast of Kain-Fritsch (KF) was superior to that of Betts-Miller (BM). When KF was selected, the simulated results would be improved if microphysics schemes were selected than otherwise. The results from Ferrier, WSM6, and Lin were very close to those in the best track. KF performed well with the simulations of the western extension and eastern contraction changes of a North Pacific high as well as the distribution and strength of the typhoon wind field.

APPLICATION OF BDA SCHEME IN TYPHOON TRACK PREDICTION

The MM5,which is the PSU/NCAR mesoscale nonhydrostatic limited-area model,and its adjoining modeling system are used in this paper.Taking T106 analysis data as background field the authors generate an optimal initial condition of a typhoon by using two bogus data assimilation schemes,and conduct some numerical simulating experiments.The results of No.9608 typhoon(Gloria)show that the optimal initial field have some dramatic improvements,such as inaccurate position of typhoon center,weaker typhoon circulation and incomplete inner structure of the typhoon,which are caused by shortage of data over the sea.Some improvements have been made in the track forecast.Through several comparing experiments,the initialization optimized by BDA scheme is found to be more reasonable than GFDL scheme and its typhoon track forecast is better.

AN IMPROVEMENT OF STATISTICAL PREDICTION OF TYPHOON TRACKS

In this paper, a statistical interpretation composite forecast model for typhoon track is set up by us-ing numerical forecast products and several forecast schemes. Tested in 1994 typhoon season, its forecastperformance is much better than that of a previous statistical forecast model. The test shows that it is aneffective method that sufficiently Anproves objective forecast of typhoon track using the numerical fore-cast output products obtained in forecast and adopting several schemes in composition.

AN EXPERIMENT WITH THE CONSENSUS FORECAST OF TYPHOON TRACK

Obvious results have been achieved in the forecast of typhoon track that is improved with a consensus procedure Forecast experiments were conducted with the analogue model (TSF) and the Markov type model (MTSF)that are widely used and the results show that there has been significant increase in the capability of forecasting with the improvement by the consensus procedure.

EXPERIMENTS OF ENSEMBLE FORECAST OF TYPHOON TRACK USING BDA PERTURBING METHOD

A new method, BDA perturbing, is used in ensemble forecasting of typhoon track. This method isbased on the Bogus Data Assimilation scheme. It perturbs the initial position and intensity of typhoons and gets aseries of bogus vortex. Then each bogus vortex is used in data assimilation to obtain initial conditions. Ensembleforecast members are constructed by conducting simulation with these initial conditions. Some cases of typhoonare chosen to test the validity of this new method and the results show that: using the BDA perturbing method toperturb initial position and intensity of typhoon for track forecast can improve accuracy, compared with the directuse of the BDA assimilation scheme. And it is concluded that a perturbing amplitude of intensity of 5 hPa isprobably more appropriate than 10 hPa if the BDA perturbing method is used in combination with initialposition perturbation.

A TWO-WAY INTERACTIVE MOVABLE NESTED MESH MODEL FOR TYPHOON TRACK PREDICTION

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COMPARISONS OF EOF AND CCA METHODS IN EXPERIMENTS WITH TYPHOON TRACK

A predictive model for 24-120 h track of the tropical cyclone over the South ChinaSea is set upusing the predictors of CLIPER and with reference to those 0f EOF and CCA. This EOF-and CCA-basedmodel is compared with dependent and independent samples in veritring forecasts’Analpees appltwg themeth0ds to 500-hPa geopotential heights have shown that the CCA method is able toconcentrate moreoriginal information of variable fleld that has the best global correlation withtropical cycl0ne track andthus reduces more efficiently error arisen in forecast,despite that can0nicaldistribution of weighted vari-able coefficients derived by it is less well-defined or smoothed 0f a spacialpattern as is done by eigenvec-tor in the EOF method. The verification indicates a certain degree of skill inb0th track predictive model,though better results are yielded in the CCA-based one, whose mean vector err0rare 159. 27, 314. 84,524. 12, 813. 03, and 987. 12 km, respectively for periods of 24, 48, 72, 96, and120 h. The modelmakes an objective approach for prediction of short-and medium-range track of tropical cyclone in theSouth China Sea.

A STUDY ON THE APPLICATION OF FY-2E CLOUD DRIFT WIND HEIGHT REASSIGNMENT IN NUMERICAL FORECAST OF TYPHOON CHANTHU(1003) TRACK

In this paper, we first analyzed cloud drift wind(CDW) data distribution in the vertical direction, and then reassigned the height of every CDW in the research domain in terms of background information, and finally, conducted contrast numerical experiments of assimilating the CDW data before and after reassignment to examine the impacts on the forecast of the track of Typhoon Chanthu(1003) from 00:00(Coordinated Universal Time) 21 July to 00:00 UTC23 July, 2010. The analysis results of the CDW data indicate that the number of CDWs is mainly distributed in the midand upper-troposphere above 500 h Pa, with the maximum number at about 300 h Pa. The height reassigning method mentioned in this work may update the height effectively, and the CDW data are distributed reasonably and no obvious contradiction occurs in the horizontal direction after height reassignment. After assimilating the height-reassigned CDW data, especially the water vapor CDW data, the initial wind field around Typhoon Chanthu(1003) became more reasonable, and then the steering current leading the typhoon to move to the correct location became stronger. As a result, the numerical track predictions are improved.

THE IMPACTS OF INTERACTION OF A TYPHOON WITH THE MIDLATITUDE TROUGH ON ITS TRACK AFTER THE RECURVATURE

Three typhoon cases are selected to conduct a series of simulations that are initialized from sequential analyses. The results show that the forecast error in crucial area where a tropical cyclone(TC) interactes with the upstream trough is highly correlated to the track forecast error after the TC recurvature. Furthermore, sensitivity experiments confirm that the developments of the midlatitude downstream circulations and then the TC track after its recurvature are highly sensitive to the TC intensity and its location relative to the upstream trough, which can give an example or one way of sensitivity of the TC track to the TC-trough interaction. If the TC interacts with the upstream trough more strongly(e.g., the TC being intensified or getting closer to the upstream trough), the downstream circulations will be more meridional, thus the TC track will be more northerly and westerly; otherwise, the downstream circulations will be more zonal, and the TC track will be more southerly and easterly.

THE EFFECT OF THE LONG WAVE OVER THE NORTHERN HEMISPHERE ON TYPHOON TRACKS OVER THE NORTHWESTERN PACIFIC

The normal typhoon paths with 109 cases during the period from 1960 to 1979 have been analysed in this study. These paths are divided into 7 categories. The effect of the position and intensity of large- scale wave on each category has been examined. It has been discovered, as a result, that this effect is rather evident. On the other hand, the teleconnection between different centers of anion does exist. A simple theoretical analysis indicates that the teleconnection is related to the propagation of wave energy. Thus, to predict correctly typhoon path, not only the steering flow of typhoon, but also, more significantly, the behavior of large-scale wave over the Northern Hemisphere must be taken into consideration.

The application of the orthogonal conditional nonlinear optimal perturbations method to typhoon track ensemble forecasts

The orthogonal conditional nonlinear optimal perturbations (CNOPs) method, orthogonal singular vectors (SVs)method and CNOP+SVs method, which is similar to the orthogonal SVs method but replaces the leading SV (LSV) with the first CNOP, are adopted in both the Lorenz-96 model and Pennsylvania State University/National Center for Atmospheric Research (PSU/NCAR) Fifth-Generation Mesoscale Model (MM5) for ensemble forecasts. Using the MM5, typhoon track ensemble forecasting experiments are conducted for strong Typhoon Matsa in 2005. The results of the Lorenz-96 model show that the CNOP+SVs method has a higher ensemble forecast skill than the orthogonal SVs method, but ensemble forecasts using the orthogonal CNOPs method have the highest forecast skill. The results from the MM5 show that orthogonal CNOPs have a wider horizontal distribution and better describe the forecast uncertainties compared with SVs. When generating the ensemble mean forecast, equally averaging the ensemble members in addition to the anomalously perturbed forecast members may contribute to a higher forecast skill than equally averaging all of the ensemble members. Furthermore, for given initial perturbation amplitudes, the CNOP+SVs method may not have an ensemble forecast skill greater than that of the orthogonal SVs method, but the orthogonal CNOPs method is likely to have the highest forecast skill. Compared with SVs, orthogonal CNOPs fully consider the influence of nonlinear physical processes on the forecast results; therefore, considering the influence of nonlinearity may be important when generating fast-growing initial ensemble perturbations. All of the results show that the orthogonal CNOP method may be a potential new approach for ensemble forecasting.

Effects of 4DVAR with multifold observed data on the typhoon track forecast

Effects of 4-dimension variational data assimi-lation (4DVAR) with multifold observed data on the typhoontrack forecast are studied, by using the MM5V3 model, theRTTOVS-5 model and their adjoint models. The data usedfor assimilation include large-scale background fields data,bogus data, cloud-derived wind data, satellite inverse data,and high resolution infrared radiation sounder data (HIRS).There are 5 typhoon cases are used to perform the numericalexperiments and assimilation experiments. The numericalresults show that with 4DVAR the initial fields can be greatlyimproved and the initial typhoon structure can be clearlydescribed.