As global warming continues, we expect extreme climate events to occur more frequently and intensively and the extremes to become normal eventually. Such timing of when the climate extremes in the present climate become normal in a future climate has been estimated in previous studies, but these studies used different methods and definitions, making an interpretation and application of the results difficult. Defining the year of beginning of a new normal climate as the timing of unprecedented climate (TUC), this study suggests a new estimation method using a return level of extreme temperatures. The TUC was estimated using CMIP5 climate model simulation data with an application to the wintertime daily maximum and minimum temperatures in Korea. With a 50-year return level obtained from Generalized Extreme Value distribution of the CMIP5 historical experiment data, overall in the models, TUC was estimated to come in the 2070s under RCP 8.5 (a business- as-usual) scenario and in the 2090s under RCP 4.5 (an intermediate level of emissions) scenario. Using this new method, TUC can be estimated for various fields globally or regionally in different seasons with different variables, providing a useful guideline for climate change mitigation and adaption policy and also a timetable for the actions.

This study evaluated the performance of GFDL HiRAM, a fine resolution AGCM, in the simulation of GPI (Genesis Potential Index) of tropical cyclone and its temporal variation over the Western North Pacific (WNP). We analyzed the AMIP simulation by the AGCM for the 30-year (1979-2008) forced by observed sea surface temperatures as the lower boundary condition. Since GPI depends on the five large-scale environmental factors(850 hPa absolute vorticity, 700 hPa relative humidity, vertical wind shear, maximum potential intensity, and 500 hPa vertical velocity), the biases of the simulation are examined for these factors as well as GPI itself. The results are compared with the ECMWF Interim reanalysis (ERA-I), and the analyses show that both the mean spatial pattern and the seasonal cycle of GPI over the WNP are reasonably simulated by HiRAM. But the magnitude of GPI is significantly underestimated due to the combined contribution of negative biases in four factors excluding the low-level vorticity. It is demonstrated that the three leading modes of spatio-temporal variability of GPI in EOF analysis for ERA-I are associated with ENSO, climate change with long-term trends, and SST anomalies over the WNP. The response of GPI to ENSO is more or less captured by HiRAM, including the east-west shift of Typhoon genesis location. However, it is supposed that unrealistic response of GPI and its factors to La-Nina or eastern Pacific El-Nino is an important shortcoming of HiRAM. In addition, HiRAM fails to reproduce the characteristic spatiotemporal variation associated with the climate change mode of GPI. The key findings from this study provide helpful guidance for improvement of HiRAM.

The interannual variability of summer temperature during June-August (JJA) in South Korea was associated with geopotential height averaged in the East Sea (Korea-Japan Index, KJI) and in the subtropical western North Pacific (Western North Pacific Subtropical High Index, WNPSHI). The KJI was coupled with a decaying El Niño one month in advance, while the WNPSHI was influenced by Sea Surface Temperature (SST) anomaly in the western North Pacific and a developing El Niño one to three months ahead. Additionally, the JJA temperature over South Korea was affected by SST anomaly in the western North Pacific in May. Based on these teleconnections, a multivariate regression model using the SST surrogates for the KJI and WNPSHI and an univariate model using an area-averaged May SST were developed to reconstruct the JJA temperature over South Korea. Both of the empirical models reproduced the JJA and monthly temperatures reasonably well. However, when the simulated SSTs from global climate models were used, the multivariate model outperformed the univariate model. Further, for JJA temperature prediction, the multivariate model with 6-month lead SST outstripped one-month lead prediction of global climate models. Therefore, the empirical-dynamical approach can pave a promising way for summer temperature prediction in South Korea.

In this study, we tried to assess the future projection of the climate as a tourism resource in Gangwon region based on Tourism Climatic Index (TCI) and two RCP scenarios(RCP4.5 and RCP8.5) datasets. TCI combines ve climatic aspects relevant for outdoor tourism activity: daytime comfort(CID), average (or daily) comfort(CIA), sunshine(S), precipitation(P) and wind(W). The mean annual variation of TCI at most of stations shows bi-modal peak pattern, but the variation at Daegwallyeong shows unique summer peak pattern. During the 21st century, TCI in summer has distinct declining trend, and this tends to be more rapid in higher emission scenario(RCP8.5) than in lower emission scenario(RCP4.5). We found Daegwallyeong is expected to experience the most distinguished change in the late 21st century as annual variation pattern of TCI is likely to shift from summer peak to bi-modal peaks. Spatial distribution of the future TCI shows that maximum changes are likey to occur along high mountains(Backdudaegan), and summertime( June to September) climate conditions for tourism activities are expected to be increasingly deteriorated, while wintertime conditions are expected to be preferable more or less. It notes that magnitude of the change in RCP8.5 scenario estimates 2-3 times larger than in RCP4.5 scenario. To identify causes of the long-term TCI trends, we analyzed the contribution level of each sub-index to the trends. Consequently, it reveals that the most primary contributor is CID. However, CIA, P, and S also can highly contribute in some cases.

Agreement in the vertical profiles of the temperature trends from radiosonde observation (HadAT) and four kinds of reanalysis dataset (ERA40, ERA-I, NCEP-DOE, and 20CR) are examined for the period of 1979-2000. There are noticeable spread among reanalysis and observation datasets in the temperature trend depending on region and vertical level. East Asia shows large discrepancy among datasets, while Europe shows relatively good agreement. Generally, biases in temperature trends are larger in the upper troposphere (above 300 hPa) than in the lower and middle troposphere. Comprehensive comparison of the long-term temperature trends among reanalyses is made for horizontal distributions with height, latitude-pressure cross-sectional distributions, zonally-averaged meridional distributions with height, and area-averaged vertical profiles in both DJF and JJA. Consequently, we find that the degree of agreement among reanalyses significantly varies with vertical level, region, and season. The highest discrepancy is found over southern high-latitudes and in the upper troposphere over southern tropics. In the tropical upper troposphere above 200 hPa, observation (HadAT) shows cooling trend increases with height, but three reanalyses show warming trends except NCEP-DOE reanalysis in which cooling trend is overestimated. In conclusion, discrepancies in the vertical profiles of long-term temperature trends among four kinds of reanalysis datasets are quite large, and then a scrupulous approach should be needed when reanalysis dataset is used for climate change study.

TCI(tourism climatic index) is a measure of the suitability of climate for outdoor sightseeing, which combines seven climate variables. Based on the TCI, we analyse the present climate resources for tourism in Gangwon-do and assess the recent changes. We use daily meteorological data from 11 stations in Gangwon-do. First, we compare mean annual cycles of the TCI for 5 stations(Gangneung, Sokcho, Wonju Chuncheon, and Daegwallyeong). This comparison reveals that range of the annual cycle is from minimum 35(for Daegwallyeong in January) to maximum 80(for Wonju in May and September). Daegwallyeong which is located in highland is characterized by summer season peak pattern while other regions have low TCI values in hot summer. In long-term trend of the TCI, Gangneung has increasing trends in February, April and December, whereas it has significant decreasing trends in summer and fall(June to October). In case of Daegwallyeong, increasing trends are found in February, November and December, and relatively steep declining trends in summer season. The overall decreasing trend in summer season is a common feature in Gangwon-do. Decreasing trends at Gangneung in August and September might be mostly explained by the increasing trend of rainfall amount in those months. Meanwhile, increasing trends of the TCI in winter season might be a positive impact of climate warming on the tourism sector.

Many recent studies have concentrated upon the radiative effects of atmospheric aerosols. Though their scattering and absorption of radiation, aerosols can also induce some other important environment effects. In this study, new radiation code and aerosol data within Atmosphere General Circulation Model (AGCM) is used to assess the aerosol radiative forcing and to analyze relative climate effects. The new Kangnung National University AGCM Stratospheric-15 (KNU AGCM ST15) was integrated by using two sets of radiative effect of aerosols : CTRL as not a radiative effect of aerosols and AERO as a radiative effect of aerosols. Two cases show the difference of net shortwave radiation budget at top-of-atmosphere (TOA) is found to be about -3.4 Wm-2, at the surface (SFC) is about -5.6 Wm-2. Consequently the mean atmospheric absorption due to aerosol layer in global is about 2.2 Wm-2. This result confirms the existence of a negative forcing due to the direct effect of aerosols at the surface and TOA in global annual mean. In addition, it is found that cooling over at the surface air temperature due to radiative effect of aerosols is about 0.17 ℃. It is estimated that radiative forcing of the net upward longwave radiation taken as the indirect effect of aerosol is much smaller than that of the direct effect as there is about 0.2 Wm-2 of positive forcing both at TOA and at SFC. From this study, It made an accurate estimation of considering effect of aerosols that is negative effect. This may slow the rate of projected global warming during the 21st century.