Sangwook Park

Technical note on a track-pattern-based model for predicting seasonal tropical cyclone activity over the western North Pacific

Recently, the National Typhoon Center (NTC) at the Korea Meteorological Administration launched a track-pattern-based model that predicts the horizontal distribution of tropical cyclone (TC) track density from June to October. This model is the first approach to target seasonal TC track clusters covering the entire western North Pacific (WNP) basin, and may represent a milestone for seasonal TC forecasting, using a simple statistical method that can be applied at weather operation centers. In this note, we describe the procedure of the track-pattern-based model with brief technical background to provide practical information on the use and operation of the model. The model comprises three major steps. First, long-term data of WNP TC tracks reveal seven climatological track clusters. Second, the TC counts for each cluster are predicted using a hybrid statistical-dynamical method, using the seasonal prediction of large-scale environments. Third, the final forecast map of track density is constructed by merging the spatial probabilities of the seven clusters and applying necessary bias corrections. Although the model is developed to issue the seasonal forecast in mid-May, it can be applied to alternative dates and target seasons following the procedure described in this note. Work continues on establishing an automatic system for this model at the NTC.

Comparison of extended medium-range forecast skill between KMA ensemble, ocean coupled ensemble, and GloSea5

This article describes a three way inter-comparison of forecast skill on an extended medium-range time scale using the Korea Meteorological Administration (KMA) operational ensemble numerical weather prediction (NWP) systems (i.e., atmosphere-only global ensemble prediction system (EPSG) and ocean-atmosphere coupledEPSG) and KMA operational seasonal prediction system, the Global Seasonal forecast system version 5 (GloSea5). The main motivation is to investigate whether the ensemble NWP system can provide advantage over the existing seasonal prediction system for the extended medium-range forecast (30 days) even with putting extra resources in extended integration or coupling with ocean with NWP system. Two types of evaluation statistics are examined: the basic verification statistics - the anomaly correlation and RMSE of 500-hPa geopotential height and 1.5-meter surface temperature for the global and East Asia area, and the other is the Real-time Multivariate Madden and Julian Oscillation (MJO) indices (RMM1 and RMM2) - which is used to examine the MJO prediction skill. The MJO is regarded as a main source of forecast skill in the tropics linked to the mid-latitude weather on monthly time scale. Under limited number of experiment cases, the coupled NWP extends the forecast skill of the NWP by a few more days, and thereafter such forecast skill is overtaken by that of the seasonal prediction system. At present stage, it seems there is little gain from the coupled NWP even though more resources are put into it. Considering this, the best combination of numerical product guidance for operational forecasters for an extended medium-range is extension of the forecast lead time of the current ensemble NWP (EPSG) up to 20 days and use of the seasonal prediction system (GloSea5) forecast thereafter, though there exists a matter of consistency between the two systems.

A possible relationship between East Indian Ocean SST and tropical cyclone affecting Korea

Abstract In this study, a strong negative correlation was found between East Indian Ocean (EIO) SST and frequency of summertime tropical cyclone (TC) affecting Korea. For the Warm EIO SST years, the TCs mostly occurred in the southwestern region of tropical and subtropical western Pacific, and migrated west toward the southern coast of China and Indochinese peninsula through the South China Sea. This is because the anomalous easterlies, induced by the development of anomalous anticyclone (weakening of monsoon trough) from the tropical central Pacific to the southern coast of China, served as the steering flows for the westward migration of TCs. In contrast, for the cold EIO SST years, the TCs mostly occurred in the northeastern region of tropical and subtropical western Pacific and migrated toward Korea and Japan located in the mid-latitudes of East Asia through the East China Sea. This is because the northeastward retreat of western North Pacific subtropical high was more distinct for the cold EIO SST years compared to the warm EIO SST years. Therefore, the TCs of warm EIO SST years weakened or dissipated shortly due to the effect of geographical features as they land on the southern coast of China and Indochinese peninsula, whereas the TCs of cold EIO SST years had stronger intensity than the TCs of warm EIO SST years as sufficient energy is supplied from the ocean while moving toward Korea and Japan.

Operational Wind Wave Prediction System at KMA

An overview of the current operational wind wave prediction system and of new developments at the Korea Meteorological Administration (KMA) is presented. KMA has operated a numerical ocean wave prediction system since 1992. The first major upgrade was done in 1999 with the adaptation of a third-generation wave model (WAM) for both regional (ReWAM-0.25 deg resolution, covering Northeast Asia) and global (GoWAM-1.25 deg resolution) domains. In 2005, the KMA replaced its NEC SX5 computer with a 1024-CPU Cray X1E system, a Parallel Vector Processor (PVP) machine with 128 node modules. A coastal ocean wave prediction system (CoWAM) has been designed and is currently under test mode. Six CoWAM domains, each of 3 deg longitude by 2 deg latitude in size, with a mesh size of 1 km, are nested inside the regional ocean wave prediction system. The directional wave spectra at the boundaries of the CoWAM are provided from a 1/12° resolution upgraded version of the operational ReWAM. The WAVEWATCH-III code (developed at NOAA) is used for the upgraded ReWAM and new CoWAM system. To ensure the required model performance in the Massively Parallel Processor (MPP) architecture of the new supercomputer, a Message Passing Interface (MPI) has been implemented in the model source code. The sea surface wind and significant wave height are verified routinely on a monthly basis. The global moored buoy data (including the coastal buoys operated by KMA) and remote sensing data from Topex/Poseidon, and Jason (retrieved wave heights) and QuikSCAT (retrieved wind data) are used for verification of the wave prediction system. This validation and a comparison of results from the new ReWAM and CoWAM against buoy data off the coast of Korea are discussed.

An Analysis of Model Bias Tendency in Forecast for the Interaction between Mid-latitude Trough and Movement Speed of Typhoon Sanba

Typhoon Sanba was selected for describing the Korea Meteorological Administration (KMA) Global Data Assimilation Prediction System (GDAPS) model bias tendency in forecast for the interaction between mid-latitude trough and movement speed of typhoon. We used the KMA GDAPS analyses and forecasts initiated 00 UTC 15 September 2012 from the historical typhoon record using Typhoon Analysis and Prediction System (TAPS) and Combined Meteorological Information System-3 (COMIS-3). Sea level pressure fields illustrated a development of the low level mid-latitude cyclogenesis in relation to Jet Maximum at 500 hPa. The study found that after Sanba entered the mid-latitude domain, its movement speed was forecast to be accelerated. Typically, Snaba interacted with mid-latitude westerlies at the front of mid-latitude trough. This event occurred when the Sanba was nearing recurvature at 00 and 06 UTC 17 September. The KMA GDAPS sea level pressure forecasts provided the low level mid-latitude cyclone that was weaker than what it actually analyzed in field. As a result, the mid-latitude circulations affecting on Sanba`s movement speed was slower than what the KMA GDAPS actually analyzed in field. It was found that these circulations occurred due to the weak mid-tropospheric jet maximum at the 500 hPa. In conclusion, the KMA GDAPS forecast tends to slow a bias of slow movement speed when Sanba interacted with the mid-latitude trough.

Possible Relationship between NAO and Western North Pacific Typhoon Genesis Frequency

National Typhoon Center, Korea Meteorological Administration, Jeju 699-942, KoreaAbstract: This study examined a strong positive correlation between the North Atlantic Oscillation (NAO) index duringJune and the total tropical cyclone (TC) genesis frequency in the western North Pacific during July and August. Toinvestigate a possible cause for this relationship, the mean difference between the highest positive NAO years and thelowest negative NAO years was analyzed by dividing into when the El Nino and La Nina years were included and whenthe El Nino and La Nina years were not included. When the El Nino and La Nina years were included, for the positiveNAO years, the TCs mostly occurred in the northwestern region of tropical and subtropical western Pacific, and showed apattern that migrate from the sea northeast of the Philippines, pass the East China Sea, and move toward the mid-latitudesof East Asia. In contrast, for the negative NAO years, the TCs mostly occurred in the southeastern region of tropical andsubtropical western Pacific, and showed a pattern that migrate westward from the sea southeast of the Philippines, passthe South China Sea, and move toward the southern coast of China and Indochinese peninsula. These two different TCmigration patterns affect the recurving location of TC, and for the positive NAO years, the recurving of TC wasaveragely found to take place in the further northeast. In addition, the migration patterns also affect the TC intensity, andthe TCs of positive NAO years had stronger intensity than the TCs of negative NAO years as sufficient energy can beabsorbed from the ocean while moving north in the mid-latitudes of East Asia. The TCs of negative NAO years showedweak intensity as they get weaken or disappear shortly while landing on the southern coast of China and the Indochinesepeninsula. On the other hand, the above result of analysis is also similarly observed when the El Nino and La Nina yearswere not included.Keywords: North Atlantic Oscillation, typhoon, TC genesis frequency요약: 이 연구는 지역특별기상센터-동경 태풍 센터에서 제공하는 태풍의 최적 경로 자료와 미국 국립 환경예측센터/미국 국립 대기연구센터의 재분석 자료를 이용하여 6월 북대서양 진동 지수와 7, 8월 총 북서태평양 태풍발생빈도 사이에 강한 양의 상관관계가 있음이 분석되었다. 이러한 관계의 가능한 원인을 알아보기 위해 엘니뇨, 라니냐 해를 포함한경우와 포함 하지 않은 경우로 구분하여 가장 높은 양의 북대서양 진동 해와 가장 낮은 음의 북대서양 진동 해 사이의평균 차를 분석하였다. 엘니뇨 해와 라니냐 해를 포함한 경우 양의 북대서양 진동 해에는 태풍이 열대 및 아열대 서태평양의 북서쪽에서 주로 발생하였으며, 필리핀 북동쪽 해상으로부터 동중국해를 지나 동아시아 중위도 지역으로 이동하는 패턴을 나타냈다. 반면, 음의 북대서양 진동 해에는 태풍이 열대 및 아열대 서태평양의 남동쪽에서 주로 발생하였으

Comparing the Effect of Both Thermal and Mechanical Forcing on the Error of Typhoon Track

To compare the effects of two external forcing on track of typhoon, TWRF(Typhoon WRF) based ensemble experiments are carried out in the case of Typhoon Morako which is the 8th typhoon at Northwest Pacific region in 2009. The two forcing are tropical SST and topography induced thermal and mechanical forcing, respectively. According to the result of numerical experiment for five-day forecast, the effect of mechanical forcing is about two times stronger than thermal forcing on the track error of the typhoon. More case study for other typhoon will be done as a next paper.