Typhoon Position Research Articles

Investigation of the Atmospheric Boundary Layer Height Using Radio Occultation: A Case Study during Twelve Super Typhoons over the Northwest Pacific

This study investigated the relationship between variations in the atmospheric boundary layer height (ABLH) and typhoons over the Northwest Pacific using global navigation satellite system (GNSS) radio occultation (RO) data during the local summer typhoon season (July–October in the Northern Hemisphere) from 2007 to 2020. The minimum gradient of refractivity derived from COSMIC and COSMIC-2 was used to determine the ABLH. The RO profiles were co-located with the position of a typhoon track base within a 600 km space window and different time windows. ABLH climatology with a 2.5° × 2.5° horizontal resolution was developed, which can be used to obtain the interpolated mean ABLH at any target position. The mean ABLH at the central typhoon position in a specific year was compared with the results interpolated from the climatology of the same location (excluding the year in which the investigated typhoon occurred). In this paper, the results indicate that the ABLH is lower in the vicinity of typhoons relative to the undisturbed atmosphere by a significant amount, and that the reduction in ABLH ranges from 0.13 km to 0.39 km. It was also found that the ABLH was negatively correlated with wind speed, and that the mean correlation coefficient was −0.607. Moreover, similar results can be obtained via the RO water vapor partial pressure profile compared to the refractivity results.

Fast Storm Surge Ensemble Prediction using Searching Optimization of a Numerical Scenario Database

AbstractAccurate storm surge forecasts provided rapidly could support timely decision-making with consideration of tropical cyclone (TC) forecasting error. This study developed a fast storm surge ensemble prediction method based on TC track probability forecasting and searching optimization of a numerical scenario database (SONSD). In a case study of the Fujian Province coast (China), a storm surge scenario database was established using numerical simulations generated by 93,150 hypothetical TCs. In a GIS-based visualization system, a single surge forecast representing 2562 distinct typhoon tracks and the occurrence probability of overflow of seawalls along the coast could be achieved in 1–2 min. Application to the cases of Typhoon Soudelor (2015) and Typhoon Maria (2018) demonstrated that the proposed method is feasible and effective. Storm surge calculated by SONSD had excellent agreement with numerical model results (i.e., mean MAE/RMSE: 7.1/10.7 cm, correlation coefficient: >0.9). Tide prediction also performed well with MAE/RMSE of 9.7/11.6 cm versus the harmonic tide, and MAE/RMSE of phase prediction for all high waters of 0.25/0.31 h versus observations. The predicted high-water level was satisfactory (MAE of 10.8 cm versus observations) when the forecasted and actual positions of the typhoon were close. When the forecasted typhoon position error was large, the ensemble surge prediction effectively reduced prediction error (i.e., the negative bias of −58.5 cm reduced to −5.2 cm versus observations), which helped avoid missed alert warnings. The proposed method could be applied in other regions to provide rapid and accurate decision-making support for government departments.

Assimilation of Himawari-8 imager radiance data with the WRF-3DVAR system for the prediction of Typhoon Soudelor

Abstract. Himawari-8 is a next-generation geostationary meteorological satellite launched by the Japan Meteorological Agency. It carries the Advanced Himawari Imager (AHI) on board, which can continuously monitor high-impact weather events with high frequency in space and time. The assimilation of AHI radiance data was implemented with the three-dimensional variational data assimilation system (3DVAR) of the Weather Research and Forecasting Model for the analysis and prediction of Typhoon Soudelor (2015) in the Pacific typhoon season. The effective assimilation of AHI radiance data in improving the forecast of the tropical cyclone during its rapid intensification has been realized. The results show that, after assimilating the AHI radiance data under clear-sky conditions, the typhoon position in the background field of the model was effectively corrected compared with the control experiment without AHI radiance data assimilation. It is found that the assimilation of AHI radiance data is able to improve the analyses of the water vapor and wind in a typhoon's inner-core region. The analyses and forecasts of the minimum sea level pressure, the maximum surface wind, and the track of the typhoon are further improved.

Assimilation of GPM Microwave Imager Radiance data with the WRF hybrid 3DEnVar system for the prediction of Typhoon Chan-hom (2015)

The impact of assimilating radiances from the global satellite precipitation program (GPM) Microwave Imager (GMI) on the track prediction of typhoon Chan-hom was studied with a hybrid three-dimensional ensemble-variational (3DEnVar) data assimilation (DA) system. It is found that the data assimilation of clear-sky GMI radiance is able to depict the structure of typhoon well by warming the typhoon inner core area. The bias correction coefficients obtained by the off-line model along with the variational bias correction method can reduce the bias. GMI radiance data assimilation experiment can effectively adjust the core area of Typhoon “Chan-hom” and systematically correct the typhoon position in the background of the model. The sensitivity of the hybrid 3DEnVar DA behaviors on the choice of the ensemble members is also investigated. Results show that the 3DEnVar Global Ensemble Forecast System (3DEnVar_GEFS)-based ensemble spread is essentially dominated in the vicinity of Typhoon Chan-hom, which is less disturbed by random errors. In general, the track forecasts from 3DEnVar_RCV match better with the best track by adding Gaussian noise randomly based on the background error than those from the 3DVAR, and 3DEnVar_GEFS.

The relationship between typhoons' peripheral circulation and ground-level ozone concentrations in central Taiwan

Surface data of meteorological parameters (wind speed, wind direction, and mixing height) and air pollutant concentrations (O3, NO, and NO2) were collected for a 92-day period associated with typhoon formation in 2005. The influence of typhoons on O3 concentration were defined by azimuth and distance from Taiwan, and Types A, B, and C correspond to typhoons less than 1,500km from Taiwan and located between azimuths 45° and 135°, 135° and 225°, and 225° and 45°, respectively. Type D corresponds to typhoons more than 1,500km from Taiwan. Titration reactions were conducted at three temporal phases: 2000-0700, 0800-1100, and 1200-1400 LST (Local Standard Time). The air pollution model (TAPM) was used to simulate wind fields and trajectories of air masses. It was determined that typhoon position affected O3 concentration, temporal and spatial patterns of O3 titration and vertical meteorological characteristics, which were not all at the statistically significant level.

Estimation of a possible maximum flood event in the Tone River basin, Japan caused by a tropical cyclone

AbstractThe damage to society caused by tropical cyclones depends largely on the storm track relative to geography. A procedure is proposed to generate different typhoon tracks deviating from the original track of a given reference case. In this procedure, the position of a typhoon is artificially shifted at a certain time before landing in a physically consistent way by applying potential vorticity inversion methodology. After shifting the typhoon position, the subsequent progress is again simulated by a mesoscale weather model. The procedure is applied to a strong typhoon that emerged in a global warming experiment using an atmospheric general circulation model. Various realizations of typhoon landfall cases are generated. Using the output of a suite of realization of different tracks, the worst case scenario is discussed in terms of the river discharge in the Tone River basin, Japan. Copyright © 2013 John Wiley & Sons, Ltd.

ニューラルネットワークを用いたリアルタイム高潮予測における学習パラメータの感度分析に関する研究

In the paper, the sensitivity of real-time storm surge forecast models to the input parameters is described based on the artificial neural network in order to predict the storm surge at Sakai Minato in the Sanin coast. In addition, the forecast time spans of 01, 02, 03, 04, 05, 12 and 24 hours are investigated. The study reveals that the real-time forecast model for the 24 forecast successfully predicted the observation at Sakai Minato. The performance of the real time forecast model for the 24h forecast was best when using the data set consisting of the storm surge, the sea level pressure, the depression rate of the sea level pressure and the typhoon position.

A Vortex Relocation Scheme for Tropical Cyclone Initialization in Advanced Research WRF

Abstract This paper introduces a relocation scheme for tropical cyclone (TC) initialization in the Advanced Research Weather Research and Forecasting (ARW-WRF) model and demonstrates its application to 70 forecasts of Typhoons Sinlaku (2008), Jangmi (2008), and Linfa (2009) for which Taiwan’s Central Weather Bureau (CWB) issued typhoon warnings. An efficient and dynamically consistent TC vortex relocation scheme for the WRF terrain-following mass coordinate has been developed to improve the first guess of the TC analysis, and hence improves the tropical cyclone initialization. The vortex relocation scheme separates the first-guess atmospheric flow into a TC circulation and environmental flow, relocates the TC circulation to its observed location, and adds the relocated TC circulation back to the environmental flow to obtain the updated first guess with a correct TC position. Analysis of these typhoon cases indicates that the relocation procedure moves the typhoon circulation to the observed typhoon position without generating discontinuities or sharp gradients in the first guess. Numerical experiments with and without the vortex relocation procedure for Typhoons Sinlaku, Jangmi, and Linfa forecasts show that about 67% of the first-guess fields need a vortex relocation to correct typhoon position errors while eliminates the topographical effect. As the vortex relocation effectively removes the typhoon position errors in the analysis, the simulated typhoon tracks are considerably improved for all forecast times, especially in the early periods as large adjustments appeared without the vortex relocation. Comparison of the horizontal and vertical vortex structures shows that large errors in the first-guess fields due to an incorrect typhoon position are eliminated by the vortex relocation scheme and that the analyzed typhoon circulation is stronger and more symmetric without distortions, and better agrees with observations. The result suggests that the main difficulty of objective analysis methods [e.g., three-dimensional variational data assimilation (3DVAR)], in TC analysis comes from poor first-guess fields with incorrect TC positions rather than not enough model resolution or observations. In addition, by computing the eccentricity and correlation of the axes of the initial typhoon circulation, the distorted typhoon circulation caused by the position error without the vortex relocation scheme is demonstrated to be responsible for larger track errors. Therefore, by eliminating the typhoon position error in the first guess that avoids a distorted initial typhoon circulation, the vortex relocation scheme is able to improve the ARW-WRF typhoon initialization and forecasts particularly when using data assimilation update cycling.

Case Study of the Storm Surges in the Seto Inland Sea Caused by Typhoon Chaba

Typhoon Chaba hit southeastern Kyushu and passed through Chugoku (western part of Japan's main island) on August 30, 2004, causing large storm surges in the Seto Inland Sea (SIS). Record-high storm tides were recorded at tide stations in Takamatsu and Uno Ports. We analyzed the tidal data and simulated this case with numerical storm surge models. The results revealed that the wind setup basically played a key role in causing the large storm surges. Since the time of the maximum storm surge (MSS) approximately corresponded to the time of high spring tide in Takamatsu, a record-breaking storm tide was observed there. However, the MSS occurred not when the typhoon was closest to the city but two hours later. We also investigated the mechanism and the degrees of contribution of the two main factors of storm surges, the inverse barometer effect and the wind setup, in each local area. The results revealed that the peak time of each effect was influenced by geographical features, as well as the wind field and the typhoon position, and had different characteristics in these areas. They also revealed that the Kanmon Strait, which is very narrow and supposed to be negligible in effect, had an important role in sea water inflow into the SIS.

Relation between the Induced Flow and the Position of Typhoon:Chanchu 2006

Using a special solution of the Euler equation, the relation between theposition of the typhoon centre and the induced flow (background wind) isfound. The relation can be used to predict the typhoon track. Theprediction of the track for No 1 tropical cyclone, CHANCHU, isconcretely provided.

A fuzzy–neural hybrid system of simulating typhoon waves

This study addresses a fuzzy–neural hybrid system of simulating typhoon waves. A membership function based on the fuzzy theory is expressed by a union Gaussian function to illustrate the rapid wave decaying. Four areas separated by two lines which intersect at the Hua-Lien harbor indicate the case of typhoon's position and propagation. Better simulation performance of the peak wave heights and their occurrence time in both the learning stage and the verification stage simulated by the NF2 model than by the NF1 model is identified. The wave decaying due to land effect is well described by the NF2 model. The NF2 model is applicable for well simulating typhoon waves during the whole period of a typhoon approaching to Taiwan.

階層結合された分解型ファジィモデルによる台風の進路予測モデル

本論文では,階層結合分解型ファジィモデル,周辺風速場情報,層別化を導入した台風の進路予測モデルを提案する.本モデルは,多入力1出力システムを複数のファジィ推論による1入力1出力に分解表現し,それらの出力を階層結合して記述することに特徴がある.入力として,従来用いられていなかった台風の周辺風速場情報を導入している.台風に関するデータは膨大なものであるが,重回帰分析や主成分分析を上手く用いて,本提案モデルの構築過程を示している.最後に,気象庁で用いられている時系列解析に基づくPC法とスーパーコンピュータを用いる台風モデルと比較し,本モデルが台風モデルには及ばないものの,PC法を上回る予測精度を有することを示す.

GFDLハリケーンモデルを用いた台風予報

A hurricane model developed at GFDL, NOAA, was combined with each of AN and NO GAPS global analyses to construct typhoon prediction systems GFDS and GFDN, respl~ctively. The GFDS system performed 125 (178) forecast experiments for 16 (24) storms in the western North Pacific basin during 1995 (1996). It exhibited considerable skill in the forecast of tropical cyclone tracks. The average forecast position errors at 12, 24, 36, 48 and 72 h in 1995 (1996) were 95 (108), 146 (178), 193 (227), 249 (280), and 465 (480) km. The improvement with GFDS in the typhoon position forE~cast over CLIPER was roughly 30 %. The reduction of position errors in both average and standard deviations indicates superior forecast accuracy and consistency of GFDS, although there existed systematic; northward bias in the forecast motion at low latitudes. On the other hand, intensity forecast was not satisfactory, showing a tendency to overpredict weak storms and underpredict strong storms, similar to the tendency in the Atlantic. Two sets of forecasts performed in the 1996 season, the one by GFDS ,I.nd the other by GFDN, were compared with each other. Forecast skills of the storm position with the 1~\1ro systems were comparable. However, the two forecast positions tended to be systematically biased toward different directions. As a result, when the two forecasts were averaged, the mean error was 10 % smaller than that of each forecast. Also, overall improvement in track forecast was obtained in supplemental experiments in which individual forecasts were corrected for systematic biases. Though systematic bias is not steady, there may be ways to utilize it for improvement of tropical cyclone forecasts.

GMS赤外雲画像を用いた台風中心位置の自動推定

It is indispensable to know the position and the intensity of the typhoon for the safety navigation of ships. This paper presents a new method for automatically estimating the position of the typhoon center using only GMS IR images. The method is based on the fact that the center position of the typhoon is to be a focus of the ridge lines of cloud bands which curves like as a spiral. First, we assume the center position and find the most reliable focus of these ridge lines using tangent lines whose distance from that point is all the same. Next, we regard the reliable focus as assumed center positioin and repeat above operation. We get the center position of typhoon because the assumed center moves toward the true center. Experimental results using GMS IR images show that the method estimates the typhoon center with the accuracy reported in SAREP.