• 대기
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• 제29권2호
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• pp.219-226
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• 2019

Generally, the weather forecast system has been run using prescribed ocean condition. As it is widely known that coupling between atmosphere and ocean process produces consistent initial condition at all-time scales to improve forecast skill, there are many trials on the application of data assimilation of coupled model. In this study, we implemented a weakly coupled data assimilation (short for WCDA) system in global NWP model with low horizontal resolution for coupled forecast with uncoupled initialization, following WCDA system at the Met Office. The experiment is carried out for a typhoon evolution forecast in 2017. Air-sea exchange process provides SST cooling and gives a substantial impact on tendency of central pressure changes in the decaying phase of the typhoon, except the underestimated central pressure. Coupled data assimilation is a challenging new area, requiring further work, but it would offer the potential for improving air-sea feedback process on NWP timescales and finally contributing forecast accuracy.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2007년도 Proceedings of ISRS 2007
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• pp.153-155
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• 2007

Korea Meteorological Administration (KMA) has operationally produced Atmospheric Motion Vector (AMV) from the consecutive MTSAT-1R satellite image dataset. Comparing with radiosonde data, our current AMV scheme shows more than 10 m/s RMSE. Therefore we need to improve continuously its accuracy. Many AMV producers have stated that the bad performance of the Height Assignment (HA) algorithm is the main reason of degrading the accuracy of AMV. The uncertainties in AMV HA can occur in the algorithm itself, used NWP profiles, and the performance of Radiative Transfer Model (RTM) etc. This study introduces currently operated AMV HA schemes and the impacts of NWP profile data and RTM that these schemes use were investigated. Finally we analyzed the relationship between vectors by vector tracking and heights assigned to each vector by using collocated wind profile dataset with radiosonde data. This study is a preliminary work to improve the accuracy of AMV by removing or decreasing the uncertainties in AMV estimation.

• 한국해안·해양공학회논문집
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• 제23권3호
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• pp.236-247
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• 2011

지구온난화로 인한 북서태평양 및 한반도 근해의 미래 해수면 상승을 IPCC AR4 기후 예측모델들의 결과를 이용하여 조사하였다. 본 연구에서는 대부분의 기후모델에서 제시하지 않은 지역적인 열팽창에 의한 해수면 상승을 3차원 수온과 염분 자료를 이용한 역학고도의 계산을 통해 분석하였다. 해수면 자료의 분석결과, 열팽창을 고려한 북서태평양 및 한반도 근해의 해수면 상승률은 전 지구 평균보다 최대 두 배까지 높게 나타났다. 특히, 쿠로시오 확장지역에서 가장 높은 해수면 상승 경향을 보였다. 열팽창을 고려한 A1B 시나리오에 의한 MPI_ECHAM5와 GFDL_CM2.1 모델 결과에서는 향후 100년 동안 북서태평양에서 각각 24 cm와 28 cm 그리고 한반도 근해에서 27 cm와 31 cm의 해수면이 상승하는 것으로 예측되었다. 통계분석 결과, 이러한 해수면 상승은 겨울철 시베리아 고기압의 약화와 북서태평양 해역의 기압장 변화 그리고 이로 인한 바람장 및 해류의 변화로 발생한 수온변화가 그 원인으로 분석된다. 특히, 쿠로시오 확장지역의 북상에 따른 수온 변화가 북서태평양에서 가장 큰 해수면 상승을 유발한 것으로 사료된다.

• 대기
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• 제15권1호
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• pp.35-46
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• 2005

Today, the outreach of National Meteorological Service such as PC cluster based Numerical Weather Prediction (NWP) technique is vigorous in the world wide. In this regard, WMO (World Meteorological Organization) asked KMA (Korea Meteorological Administration) to formulate a regional project, which cover most of RA II members, using similar technical system with KMA's. In that sense, Meteorological Research Institute (METRI) in KMA developed Mongolian NWP System (MNWPS) based on PC cluster and transferred the technology to Weather Service Center in Mongolia. The hybrid parallel algorithm and channel bonding technique were adopted to cut cost and showed 41% faster performance than single MPI (Message Passing Interface) approach. The cluster technique of Beowulf type was also adopted for convenient management and saving resources. The Linux based free operating system provide very cost effective solution for operating multi-nodes. Additionally, the GNU software provide many tools, utilities and applications for construction and management of a cluster. A flash flood event happened in Mongolia (2 September 2003) was selected for test run, and MNWPS successfully simulated the event with initial and boundary condition from Global Data Assimilation and Prediction System (GDAPS) of KMA. Now, the cluster based NWP System in Mongolia has been operated for local prediction around the region and provided various auxiliary charts.

• Journal of Astronomy and Space Sciences
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• 제24권4호
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• pp.285-296
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• 2007

시 공간 분해능이 우수한 GPS 가강수량 자료를 활용하면 강수나 구름과 같이 변동성이 큰 기상현상에 대한 수치예보모델의 예측성 한계를 줄일 수 있다. 이 연구에서는 GPS 가강수량 자료를 수치 예보모델에 초기치로서 적용하기 위해 한국천문연구원과 해양수산부가 운영하고 있는 GPS 상시관측소 자료로부터 GPS 가강수량을 계산하였다. 시 공간적 규모가 작아 기존 수치예보모델에서 예측하기 어려운 국지적 집중호우사례를 선정하였다. 차세대 수치예보모델인 WRF(Weather Research & Forecasting)모델의 3차원 변분동화(3D-Var)기법을 이용하여 GPS 가강수량 자료를 초기치에 동화하였다. 이 연구는 GPS 가강수량 자료가 수치예보모델의 결과에 미치는 영향을 분석하였다. 분석결과를 바탕으로 하여 수치예보모델의 예측성 향상을 위한 연구방향을 제시 하였다.

• 대기
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• 제21권1호
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• pp.85-93
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• 2011

UK Met Office Unified Model (UM) is a grid model applicable for both global and regional model configurations. The Met Office has developed a 4D-Var data assimilation system, which was implemented in the global forecast system on 5 October 2004. In an effort to improve its Numerical Weather Prediction (NWP) system, Korea Meteorological Administration (KMA) has adopted the UM system since 2008. The aim of this study is to provide the basic information on the effects of satellite data assimilation on UM performance by conducting global satellite data denial experiments. Advanced Tiros Operational Vertical Sounder (ATOVS), Infrared Atmospheric Sounding Interferometer (IASI), Special Sensor Microwave Imager Sounder (SSMIS) data, Global Positioning System Radio Occultation (GPSRO) data, Air Craft (CRAFT) data, Atmospheric Infrared Sounder (AIRS) data were assimilated in the UM global system. The contributions of assimilation of each kind of satellite data to improvements in UM performance were evaluated using analysis data of basic variables; geopotential height at 500 hPa, wind speed and temperature at 850 hPa and mean sea level pressure. The statistical verification using Root Mean Square Error (RMSE) showed that most of the satellite data have positive impacts on UM global analysis and forecasts.

• 대기
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• 제31권4호
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• pp.395-404
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• 2021

In order to investigate downslope windstorm by using more detailed observation, we observed 6 cases at 3 sites - Inje, Yongpyeong, and Bukgangneung - during "3-D Meteorological Observation Project in Yeongdong region of Gangwon province, South Korea in 2020." The results from analysis of the project data were as follows. First, AWS data showed that a subsidence inversion layer appeared in 800~700 hPa on the windward side and 900~850 hPa on the leeward side. Second, before strong wind occurred, the inversion layer had descended to about 880~800 hPa. Third, with mountain wave breaking, downslope wind was intensified at the height of 2~3 km above sea level. After the downslope wind began to descend, the subsidence inversion layer developed. When the subsidence inversion layer got close to the ground, wind peak occurred. In general, UM (Unified Model) GDAPS (Global Data Assimilation Prediction System) have had negative bias in wind speed around peak area of Taebaek mountain range, and positive bias in that of East Sea coast area. The stronger wind blew, the larger the gap between observed and predicted wind speed by GDAPS became. GDAPS predicted strong p-velocity at 0600 LST 25 Apr 2020 (4^th case) and weak p-velocity at 2100 LST 01 Jun 2020 (6^th case) on the lee-side of Taebaek mountain range near Yangyang. As hydraulic jump theory was proved, which is known as a mechanism of downslope windstorm in Yeongdong region, it was confirmed that there is a relationship between p-velocity of lee-side and wind speed of eastern slope of Taebaek mountain range.

• 대기
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• 제30권4호
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• pp.319-333
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• 2020

Aircraft observations constitute one of the major sources of temperature observations which provide three-dimensional information. But it is well known that the aircraft temperature data have warm bias against sonde observation data, and therefore, the correction of aircraft temperature bias is important to improve the model performance. In this study, the algorithm of the bias correction modified from operational KMA (Korea Meteorological Administration) global model is adopted in the preprocessing of aircraft observations, and the effect of the bias correction of aircraft temperature is investigated by conducting the two experiments. The assimilation with the bias correction showed better consistency in the analysis-forecast cycle in terms of the differences between observations (radiosonde and GPSRO (Global Positioning System Radio Occultation)) and 6h forecast. This resulted in an improved forecasting skill level of the mid-level temperature and geopotential height in terms of the root-mean-square error. It was noted that the benefits of the correction of aircraft temperature bias was the upper-level temperature in the midlatitudes, and this affected various parameters (winds, geopotential height) via the model dynamics.

• 대기
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• 제30권2호
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• pp.103-113
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• 2020

In this study, we analyzed and developed the monitoring system in order to confirm the effect of observations on forecast sensitivity on ensemble-based data assimilation. For this purpose, we developed the Ensemble Forecast Sensitivity to observation (EFSO) monitoring system based on Local Ensemble Transform Kalman Filter (LETKF) system coupled with Korean Integrated Model (KIM). We calculated 24 h error variance of each of observations and then classified as beneficial or detrimental effects. In details, the relative rankings were according to their magnitude and analyzed the forecast sensitivity by region for north, south hemisphere and tropics. We performed cycle experiment in order to confirm the EFSO result whether reliable or not. According to the evaluation of the EFSO monitoring, GPSRO was classified as detrimental observation during the specified period and reanalyzed by data-denial experiment. Data-denial experiment means that we detect detrimental observation using the EFSO and then repeat the analysis and forecast without using the detrimental observations. The accuracy of forecast in the denial of detrimental GPSRO observation is better than that in the default experiment using all of the GPSRO observation. It means that forecast skill score can be improved by not assimilating observation classified as detrimental one by the EFSO monitoring system.

• 한국수자원학회논문집
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• 제53권3호
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• pp.181-191
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• 2020

본 연구에서는 전지구수치예보모델의 예측성능에 주요한 영향을 주는 요소 중 하나인 토양수분 초기장을 적절히 생산하기 위해, 오프라인 Noah 지면모델을 구축하여 스핀업실험을 수행하고 그 변동특성을 살펴보았다. 스핀업실험은 지면기후장 생성과 목표연도에 대한 현실화의 2단계로 구성되었다. 첫 번째 단계의 지면기후장 생성은 2008~2017년 기간에 대해 평균한 대기강제력으로 10년 동안 지면모델을 반복적으로 수행하는 방식으로 이루어졌으며, 토양수분 모의가 평형상태에 도달하는데 소요되는 시간은 토양깊이와 코펜 정의에 기반한 기후구 특성에 따라 차이가 컸다. 토양 첫 번째 층은 극지역에서 가장 길었고, 두 번째 층 부터 네 번째 층까지는 건조지역에서 평형상태에 도달하는 시간이 가장 늦어 최대 7년 내외의 시간이 소요되었다. 결과적으로 10년의 spin-up을 거치면 지면모델이 평형상태에 도달함을 알 수 있다. 이 소요시간은 지상기온과 강수량과 음의 상관관계를 보였다. 두 번째 단계에서는 2018년을 목표연도로 설정하고 지면기후장을 이용하여 추가 적분을 수행하고, 그 결과 6개월 이내에 지면모델에서 모의된 토양수분, 지표기온, 증발산량은 2018년 지면상태에 도달하는 것을 확인하였다. 이에 구축된 오프라인 Noah 지면모델 스핀업 시스템은 안정적으로 전구수치예보모델의 토양수분 초기장을 생산함으로써 전지구수치모델에 결합된 지면모델의 물리과정과 기초자료가 변하더라도 유연하게 대응할 수 있는 가능성을 확인하였다.