전지구 해양 해빙 예측시스템인 NEMO-CICE/NEMOVAR의 해빙 초기조건의 특성을 2013년 6월부터 2014년 5월까지 북극영역에 대하여 분석하였다. 이를 위하여 관측 자료와 재분석 자료를 모델의 초기조건과 비교하였다. 모델 초기조건은 관측에서 나타나는 해빙 면적과 해빙 두께의 월 변동을 잘 보이는 반면, 분석 기간 동안 관측과 재분석 자료보다 북극의 해빙 면적을 좁게, 해빙 두께를 얇게 나타내었다. 모델 초기조건의 북극 해빙 면적이 좁은 것은 해빙의 경계 지역에서 해빙 농도 초기조건이 약 20% 정도 재분석자료보다 낮기 때문이다. 또한 북극 평균 해빙 두께가 얇게 나타나는 이유는 연중 두꺼운 해빙이 유지되는 그린란드 및 북극 군도와 인접한 북극해 영역에서 모델의 초기조건이 약 60 cm 정도 얇기 때문이다.

강수는 다양한 대기 변수들의 영향으로 나타나기 때문에 비선형성이 매우 강하다. 따라서 역학 모형을 통해 예측된 강수의 보정은 비선형 모형인 인공 신경망 등을 통해 가능할 것이지만, 인공 신경망의 경우 초기 가중치 선택, 지역 최소화 문제, 뉴런의 수 결정 등의 문제로 인한 한계가 있다. 그러므로 본 연구에서는 가장 보편적으로 사용되는 다중 선형 회귀 모형을 이용하여 CGCM에 의해 모사된 강수를 보정하였으며, 예측성을 살펴보았다. 이를 위하여 우선 PNU/CME 접합 대순환 모형(Coupled General Circulation model, CGCM)(박혜선과 안중배, 2004)을 이용하여 1979년부터 2005년까지 매해 4월부터 8월까지 5개월간 앙상블 적분을 하였다. 적분 결과 중 한반도를 포함한 동북아시아 지역(110˚E-145˚E, 25˚N-55˚N)의 여름철인 6월(리드 2), 7월(리드 3), 8월(리드 4) 및 여름철 평균인 JJA(from June to August) 기간의 PNU/CME CGCM에 의해 모사된 강수를 보정하기 위해 다중 선형 회귀(Multiple Linear Regression, MLR)를 이용하였다. PNU/CME 접합 대순환 모형의 결과 중 강수, 500 hPa 연직 속도, 200 hPa 발산장, 지상 기온 등의 예측 인자와 관측 강수와의 선형적인 관계를 이용하여 MLR 모형을 구축하였다. 그리고 교차 검증(cross- validation)을 수행하여 PNU/CME 접합 대순환 모형의 결과와 교차 검증 결과를 비교하였다. 상관계수, 적중률 (hit rate), 오보율(false alarm rate) 그리고 Heidke 기술 점수(Heidke skill score) 등을 살펴본 바, 보정하지 않은 모형의 결과에 비해 MLR 모형을 이용하여 보정한 결과의 강수에 대한 예측성이 뛰어난 것을 알 수 있었다.

We projected the temperature changes in the mid-21st century with Representative Concentration Pathway (RCP) 4.5 and RCP8.5 using the temperature data simulated by four regional climate models (RCMs: WRF, CCLM, MM5, RegCM4) in Korea. The simulation area and spatial resolution of RCMs were the CORDEXEA (COordinated Regional Climate Downscaling Experiment-East Asia) area and 25 km, respectively. We defined the temperature change as the difference (ratio) between the average annual temperature (IAV: Interannual Variation) over the projected 25 years (2026-2050) and that over the present 25 years (1981-2005). The fact that the average annual temperature bias of the four RCMs is within ±2.5°C suggests that the RCM simulation level is reasonable in Korea. Across all RCMs, scenarios, and geographic locations, we observed increased temperatures (IAV) in the mid-21st century. In RCP4.5 and RCP8.5, 1.27°C and 1.57°C will be increased by 2050, respectively. The ensemble suggests that the temperature increase is higher in winter (RCP4.5: 1.36°C, RCP8.5: 1.75°C) than summer (RCP4.5: 1.25°C, RCP8.5: 1.49°C). Central Korea exhibited a higher temperature increase than southern Korea. A slightly larger IAV is expected in the southeastern region than in the Midwest of Korea. IAV is also expected to increase significantly in RCP4.5 (summer) than in RCP8.5 (winter).

In this study, the impact of cumulus parameterization usage in Weather Research and Forecasting (WRF) model on reproducing summer precipitation in South Korea is evaluated. Two sensitivity experiments are set up with using cumulus parameterization (ON experiment) and without using cumulus parameterization, which is called Convection Permitting Model (OFF experiment). For the both ON and OFF experiments, the horizontal grid resolution is 2.5km, and initial and lateral boundary conditions are derived from ERA5 reanalysis data. Overall, both of the two experiments can capture the spatial distribution of 2014 summer mean and extreme precipitation but show dry biases in the southern region of Korean Peninsula. Occurrence percentage analyses for different precipitation intensity reveal that OFF experiments show better performance than ON experiment for extreme precipitation. In the case of heavy rainfall over Gyeongnam region for 25 August 2014, OFF experiment shows similar characteristic of rainfall to the observations, although it simulates earlier precipitation peak. On the other hand, ON experiment underestimates the amount of precipitation. Also, vertical distribution of equivalent potential temperature and strong southerly wind which play an important role in developing heavy rainfall on 25 August 2014 are better simulated in OFF experiment.

A statistical forecast model for early spring (March and April) precipitation over South Korea is developed by using multiple linear regression method. Predictors are selected among the forty five large-scale atmospheric and oceanic indices. Because the model is meant to use for real-time forecast, the predictors are chosen from the indices that have statistically significant lag correlation with observed early spring precipitation. The selected predictors of early spring precipitation are North Pacific Pattern with 6-month lead, Siberian High Index with 5-month lead and Indian Ocean Basin Mode Index with 3-month lead from March, and they are statistically independent. We applied leave-two-out cross validation. According to the regression map between these indices and synoptic circulations around Korean peninsula, these indices represent the induction of early spring rainfall by controlling East Asian jet and low level moisture flux. The regression coefficients for each training period show that three indices affects evenly at every forecast year and they show stable variability, indicating that the influence of each index does not depend on training period. The developed statistical model significantly predicted early spring precipitation over South Korea (r=0.63, p-value<0.01). Also it marks 61% of hit rate according to the three-category deterministic forecast.

In this study, global climate change scenario by Hadley Centre Global Environmental Model version 2-Atmosphere and Ocean (HadGEM2-AO) is dynamically downscaled using four regional climate models (RCMs). All RCMs with 12.5-km and 50-km resolution are integrated for continuous 27 years (1979-2005). In general, RCMs with higher horizontal resolution more reasonably capture the spatial distribution of precipitation over South Korea compared to those with lower resolution. In particular, heavy precipitation regions related to complex mountain ranges are well simulated due to detailed topography in RCMs with higher resolution. Difference between RCMs with dissimilar resolutions is relatively robust in summer compared to other seasons. This could be associated with that higher resolution and detailed topography lead to more realistic simulation of heavy summer precipitation related to mesoscale phenomena.

In this study, long term simulations for current(1979-2010) and future(2019-2050) climate over North-East Asian region were performed using RegCM4 driven by HadGEM2-AO provided by the KMA(Korean Meteorological Administration). The spatial resolution is 12.5㎞ and two RCP scenarios(4.5, 8.5) are applied for the future climate simulation. The RegCM4 simulates well the spatial and temporal variations of air temperature of current climate. However, it weakly simulates the intensity of rain band associated with the seasonal march of the East Asian summer monsoon and thereby significantly under simulates the summer rainfall and fails in reproducing the seasonal and spatial variations of precipitation. The 20-year averaged differences between current(1986-2005) and future(2031-2050) simulations showed that the temperature increases are generally greater in RCP8.5(1.93K) than RCP4.5(1.86K) and all the changes are statistically significant at 1% level. In general, the temperature increases are greater in the northern region(autumn, winter) than in the southern region(spring, summer) irrespective of RCP scenarios. The temperature over South Korea is expected to increase by 1.53K to 1.87K irrespective of RCP scenarios and seasons. The precipitation changes vary significantly according to the season and region irrespective of RCP scenarios and the changes of spring and autumn in the certain regions are statistically significant at 5% level. The precipitation over South Korea is expected to increase by +0.42㎜/day in RCP4.5 during spring but it is expected to significantly decrease during autumn(-0.35㎜/day) and in RCP 8.5 during summer(-0.30㎜/day).

본 연구에서는 겨울철에 나타나는 전지구 규모 패턴과 한반도 겨울철 기온과의 관계를 알아보았다. 500hPa 지위고도에 대한 EOF 분석을 통해 겨울철 평균(DJF) 주요 모드는 AO이고 12월, 1월, 2월 각각에 WP, PNA, EA, NAO, EU 패턴이 잘 나타나는 것을 알았다. EOF 분석에서 나타난 전지구 규모 패턴들은 한반도 겨울철 평균 기온과 높은 상관관계를 가지고 있었다. 한반도 겨울철 기온은 DJF 평균으로 보면 AO패턴, 월 별로 따져보면 12월에는 WP, 1월에는AO 뿐만 아니라 PNA 그리고 WP, 그리고 2월에는 AO와 EU의 영향을 받는 것으로 나타났다.

한반도의 몬순 특성을 알아보기 위해 한반도 61개 지점 자료를 가지고 EOF 분석을 수행하였다. 기온의 EOF 분석 결과 한반도에는 동북아시아 몬순과 반도규모의 몬순이 주요 모드로 나타났다. 가장 큰 모드는 동북아시아 몬순에 대해서 한반도 전체가 추워지는 겨울철 패턴은 북풍이나 반대로 한반도 전체가 따뜻해지는 여름철 남풍과 관계가 있다. 이러한 몬순의 형태는 잘 알려진 시베리아 고기압이나 북태평양 고기압과 같은 대륙규모의 해양-육지 간의 비열 차이와 이에 따른 순환과 연관이 있다. 본 연구에서는 이러한 대륙 규모의 몬순과 더불어 반도규모의 한반도 몬순순환이 존재하는 것을 밝혔는데, 이 순환은 기온과 동서류와의 관계로 잘 설명되며 한반도 중심이 냉각/가열될 때 한반도 중심에서부터 해양으로 동서류가 발산/수렴하는 전형적인 몬순의 패턴이 구조를 나타났다. 강수의 주요 모드는 연주기 변동으로 여름철에 강수가 집중되는 현상을 나타내었다.

In order to simulate and investigate the major characteristics of El Nino/Southern Oscillation(ENSO) and Madden Jullian Oscillation(MJO), an intermediate type atmosphere-ocean coupled model is developed and their results are examined. The atmosphere model is a time-dependent non-linear perturbation moist model which can determine the internal heating for itself. The counterpart of the atmosphere model is GCM-type tropical ocean model which has fine horizontal and vertical grid resolutions. In the coupled experiment, warm SST anomaly and increased precipitation and eastward wind and current anomalies associated with ENSO and MJO are properly simulated in Pacific and Indian Oceans. In spite of some discrepancies in simulation MJO, the observed atmospheric and oceanic low-frequency characteristics in the tropics are successfully identified. Among them, positive SST anomalies centered at the 100m-depth of tropical eastern-central Pacific due to the eastward advection of warm water and reduced equatorial upwelling, and negative anomalies in the Indian and western Pacific seem to be the fundamental features of tropical low-frequency oscillations.

In this research, two stochastic models are considered to detect and estimate the effect of air temperature change due to industrialization in Ulsan area. Using the monthly mean minimum air temperature anomalies, the data are divided into pre-industrialization part and industrialization one for analysis. The ARMA(autoregressive moving-average) model and intervention model have been applied to the data for the analysis. The results show that the variability of minimum temperature anomalies are very significant in 1989, and also significant in 1971 when the industrialization have started. Therefore, it is stochastically possible to estimate the time when the affection of increase of the temperature concerning industrialization to climate change in Ulsan area has happened.

One-dimensional thermodynamic mixed layer model to simulate variations of meteorological variables within the planetary boundary layer has been developed in this study. This model consists of 2 prognostic equations, which can predict the variations of potential temperature and mixing ratio and several diagnostic equations. Physics within the surface and mixed layers has been considered seperately in the model. For the variations of the model, its result has been analysed and compared with observated data over the Dukyang Bay for one day, July 23, 1992. The simulated height of mixed layer is comparable to the observation and the variations of temperature and mixing ratio in the mixed layer are also reasonably simulated. Those imply that the model responds appropriately with given boundary conditions in spite of its simplified assumptions applied to the model and insufficient boundary and initial conditions.

The atmospheric responses to a Sea Surface Temperature Anomaly(SSTA) over the equatorial eastern Pacific Ocean have been investigated using the horizontally fine resolution model based on OSU 2-layer Atmospheric General Circulation Model(AGCM). The SSTAs during the peak phase of 1982-83 El Nin∼o have been applied to the model as the boundary conditions of the experiment. The model simulates the eastward movement of the rising branch of the Walker circulation. That is, the major features associated with the El Nin∼no such as the increase of the precipitation rate over the center of the Pacific and decrease over the Indonesia, and the 500hPa geopotential height anomaly in the middle latitude are properly described in the fine resolution model experiment. The model results indicate that this horizontally fine resolution GCM can successfully simulate the ENSO anomalies and be more effectivelly used for the study of the climate and the climate changes.

An intermediate atmosphere-ocean coupled model appropriate for the study of El Nin~o has been developed. The model is not only economic to use but also contains several most important physical processes. The geometrical effects which were not consided in the previous intermediate model study of Ahn (1990), are included in the model for more realistic simulation of the event. The results show hat the individual models respond appropriately to the given boundary conditions. At the same time, in the coupled model experiment, ENSO-like oceanic and atmospheric anomalies are also well simulated under an external triggering similar to the initiation forcing of ENSO. It is expected that this type of model can be effectively used for the study and simulation of El Nin~o. More improvement of modeling may be possible after inclusion of subsequent processes such as inclusion of ocean mixed layer dynamics.