This research investigated the meteorologically relevant characteristics of high PM2.5 episodes in Busan. The number of days when daily mean PM10 concentration exceeded 100 ㎍/m3 and the PM2.5 concentration exceeded 50 ㎍/m3 over the last four years in Busan were 24 and 58, respectively. Haze occurrence frequency was 37.6% in winter, 27.4% in spring, 18.6% in fall, and 16.4% in summer. Asian dust occurrence frequency was 81.8% in spring, 9.1% in fall and winter, and 0% in summer. During summer in Busan, high PM2.5 episode occurred under the following meteorological conditions. 1) Daytime sea breeze. 2) Mist and haze present throuout the day. 3) Anti-cyclone located around the Korean peninsula. 4) Stable layer formed in the lower atmosphere. 5) Air parcel reached Busan by local transport rather than by long-range transport. These results indicate that understanding the meteorological relevance of high PM2.5 episodes could provide insight for establishing a strategy to control urban air quality.

In this study, the spatio-temporal patterns of summertime thermal environments in the two subtropical cities (Jeju and Seogwipo) of Jeju Island, Korea are examined. Long-term average data from Jeju and Seogwipo show that higher human sensible temperature (HST) than air temperature (T) due to the high humidity effects associated with warm sea surface temperature around Jeju Island is most distinct during mid-summer period (late July-early August). Comparatively, their trend analyses reveal that summertime intra-seasonal changes with more increasing HST than T are most obviously observed in late summer (late September-early October) and regionally in Seogwipo. According to the hourly temperature-humidity data measured at approximately 30 HOBO temperature-humidity sensors deployed in the two subtropical cities during 2019 summer, the greater HST than T during mid-summer period maximizes up to 6.2°C and 7.0°C across the urban areas of Jeju and Seogwipo, respectively in early afternoon, leading to consecutive inter-daily heat wave events. The examination of their spatial patterns demonstrates that bioclimatic heat waves in these two subtropical cities are affected primarily by the urban heat island phenomenon. However, it should not be overlooked that local moisture advection from the warm ocean adjacent to the subtropical cities can modify the stronger heat wave pattern toward urban cores. It is also notable that according to comparisons of local HST and T distributions between impervious urban cores and neighboring urban parks, not only the size of green space but also other ecological properties including species of vegetation may be crucial factors to the mitigation of hot thermal environments in subtropical cities during summers.

Climate change affects the occurrence of heat waves in Korea. Heat wave gives significant impacts not only to human health, but also adversely affects on traffic accidents both directly and indirectly. This study analyzed heat wave impacts on traffic accidents in summer time (JJA) from 2012 to 2017 timely. To consider some occupations work in earlier or later than regular working hour, 04~20h is set for this study. Generalized additive model is used to analyze the relation between the temperature and traffic accidents. The results showed that the traffic accidents in high temperature increases in 04~08h, 08~12h, and especially 18~20h. The percent difference for relative risk of traffic accidents is 2.34% (95% confidence interval: 1.140, 3.269) when the temperature increase by 1°C in 18~20h. The results of this study suggest some requirements for measures to prevent traffic accidents in the morning and evening hours with increasing temperatures.

This study investigated the relationship between heat-related illnesses obtained from healthcare big data and daily maximum temperature observed in seven metropolitan cities in summer during 2013~2015. We found a statistically significant positive correlation (r = 0.4~0.6) between daily maximum temperature and number of the heat-related patients from Pearson's correlation analyses. A time lag effect was not observed. Relative Risk (RR) analysis using the Generalized Additive Model (GAM) showed that the RR of heat-related illness increased with increasing threshold temperature (maximum RR = 1.21). A comparison of the RRs of the seven cities, showed that the values were significantly different by geographical location of the city and had different variations for different threshold temperatures. The RRs for elderly people were clearly higher than those for the all-age group. Especially, a maximum value of 1.83 was calculated at the threshold temperature of 35℃ in Seoul. In addition, relatively higher RRs were found for inland cities (Seoul, Gwangju, Daegu, and Daejeon), which had a high frequency of heat waves. These results demonstrate the significant risk of heat-related illness associated with increasing daily maximum temperature and the difference in adaptation ability to heat wave for each city, which could help improve the heat wave advisory and warning system.

Agricultural or rural landscape provides various ecosystem services. However, the ecosystem services function is declining due to various environmental problems such as climate change, land use change, stream intensification, non-point pollution and garbage. The A1B scenario predicts that the mean air temperature of South Korea will rise 3.8℃ degrees celsius in 2100. Agricultural sector is very vulnerable to climate change, so it must be thoroughly predicted and managed. In Korea, the facility horticulture complex is 54,051ha in 2016 and is the 3rd largest in the world(MAFRA, 2014). Facilities of horticultural complexes are reported to cause problems such as groundwater decrease, vegetation and insects diversity reduction, landscapes damage and garbage increase, compared with the existing land use paddy fields. Heat island phenomenon associated with climate change is also accelerated by the high heat absorption of horticultural sites. Therefore, we analyzed the heat island phenomenon occurring in the facility of horticultural complex in Korea. As an improvement measurement, I examined how much air temperature is reduced by putting the channel and the open space. In the case of the Buyeo area, the Computational Fluid Dynamics (CFD) simulation was analyzed for the average summer temperature distribution in the current land use mode at 38.9℃. As an improvement measurement, CFD simulation after 10% of 6m water channel was found to have an effect of lowering the summer temperature of about 2.7℃ compared with the present average of 36.2℃. In addition, CFD simulations after analyzing 10% of the open space were analyzed at 34.7℃, which is 4.2℃ lower than the present. For the Jinju area, CFD simulations were analyzed for the average temperature of summer at 37.8℃ in the present land use pattern. As an improvement measure, CFD simulations after 10% of 6m water channel were found to have an effect of lowering the summer temperature of about 2.6℃ compared to the current average of 35.2℃. In addition, CFD simulations after analyzing 10% of the open space were analyzed at 33.9℃, which is 3.9℃ lower than the present. It can be said that the effect of summer temperature drop in open space and waterway has been proven. The results of this study are expected to be reflected in sustainable agriculture land use and used as basic data for government - level policy in land use planning for climate change.

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.

Persistent Extreme Temperature Events (PETEs) are defined in two steps; first, to define extreme temperature events, the 80th and 20th percentiles of daily maximum and minimum temperature were chosen. Then individual PETE was defined as an event which lasted three or longer consecutive extreme temperature days. In this study, we examined characteristics and changes of PETEs in Republic of Korea (ROK) using 14 weather stations with a relatively long-term period of data, 1954-2016. In ROK, PETEs lasted four-five days on average and occurred two-three times a year. PETEs lasted longer in summer than in winter and in maximum temperature than in minimum temperature. PETEs which lasted greater than seven days account for a greater proportion in summer than in winter. However, intensities of PETEs were greater in winter because of a larger temperature fluctuation. In both summer and winter, durations and intensities of persistent extreme high temperature events increased while those of persistent extreme low temperature events decreased. Changes of PETEs were closely related with both global warming and diverse large-scale climate variabilities such as AO, NAO and Nino 3.4.

In order to investigate the effect of air temperature reduction on an urban neighborhood park, air temperature data from five inside locations (forest, pine tree, lawn, brick and pergola) depending on surface types and three outside locations (Suwon, Maetan and Kwonsun) depending on urban forms were collected during the summer 2016 and compared. The forest location had the lowest mean air temperature amongst all locations sampled, though the mean difference between this and the other four locations in the park was relatively small (0.2-0.5℃). In the daytime, the greatest mean difference between the forest location and the two locations exposed to direct beam solar radiation (brick and lawn) was 0.5-0.8℃ (Max. 1.6-2.1℃). In the nighttime, the mean difference between the forest location and the other four locations in the park was small, though differences between the forest location and locations with grass cover (pine tree and lawn) reached a maximum of 0.9-1.7℃. Comparing air temperature between sunny and shaded locations, the shaded locations showed a maximum of 1.5℃ lower temperature in the daytime and 0.7℃ higher in the nighttime. Comparing the air temperature of the forest location with those of the residential (Kwonsun) and apartment (Maetan) locations, the mean air temperature difference was 0.8-1.0℃, higher than those measured between the forest location and the other park locations. The temperatures measured in the forest location were mean 0.9-1.3℃ (Max. 2.0-3.9℃) lower in the daytime than for the residential and apartment locations and mean 0.4-1.0℃ (Max. 1.3-3.1℃) lower in the nighttime. During the hottest period of each month, the difference was greater than the mean monthly differences, with temperatures in the residential and apartment locations mean 1.0-1.6℃ higher than those measured in the forest location. The effect of air temperature reduction on sampling locations within the park and a relatively high thermal environment on the urban sampling locations was clearly evident in the daytime, and the shading effect of trees in the forest location must be most effective. In the nighttime, areas with a high sky view factor and surface types with high evapotranspiration potential (e.g. grass) showed the maximum air temperature reduction. In the urban areas outside the park, the low-rise building area, with a high sky view factor, showed high air temperature due to the effect of solar (shortwave) radiation during the daytime, while in the nighttime the area with high-rise buildings, and hence a low sky view factor, showed high air temperature due to the effect of terrestrial (longwave) radiation emitted by surrounding high-rise building surfaces. The effect of air temperature reduction on the park with a high thermal environment in the city was clearly evident in the daytime, and the shading effect of trees in the forest location must be most effective. In the nighttime, areas with high sky view factor and surface types (e.g., grass) with evapotranspiration effect showed maximum air temperature reduction. In the urban areas outside the park, the high sky view factor area (low-rise building area) showed high air temperature due to the effect of solar (shortwave) radiation during the daytime, but in the nighttime the low sky view factor area (high-rise building area) showed high air temperature due to the effect of terrestrial (longwave) radiation emitted surrounding high-rise building surfaces.

We studied the distribution of air temperature using the high density urban climate observation network data of Daegu. The observation system was established in February 2013. We used a total of 38 air temperature observation points (23 thermometers and 18 AWSs). From the distribution of monthly averaged air temperatures, air temperatures at the center of Daegu were higher than in the suburbs. The daily minimum air temperature was more than or equal to 25℃ and the daily maximum air temperature was more than or equal to 35℃ at the elementary school near the center of Daegu. Also, we compared the time elements, which are characterized by the diurnal variation of surface air temperature. The warming and cooling rates in rural areas were faster than in urban areas. This is mainly due to the difference in surface heat capacity. These results indicate the influence of urbanization on the formation of the daily minimum temperature in Daegu.

This study was carried out to elucidate the chemical compositions of water-soluble inorganic ions in PM10 and PM2.5 aerosols collected during summer and winter in downtown Jejusi city. The ratios of NO3 - to the total mass of ionic species in PM10 and PM2.5 aerosols largely increase in winter compared to summer, while SO4 2- ratios in both aerosols appear to follow the opposite trend. Moreover, concentrations of Na+, Mg2+, Ca2+ and Cl- in PM10 and PM2.5-10 aerosols are higher in winter than in summer. The nitrate concentrations in PM10 and PM2.5 aerosols increase with an identical increase in excess ammonium during winter, however, nitrate formation during summer is not important owing to ammonium-poor conditions.

Chemical properties of aerosols were investigated by analyzing the inorganic water-soluble content in PM2.5 collected in the downtown area of Jeju City in Jeju Island. Due to an increase in both the number of visiting tourists and the size of local population, the number of cars in this area is increasing, causing an increase in PM2.5. Eight PM2.5-bound major inorganic ions were analyzed during the summer and winter periods. The water-soluble inorganic component represents a significant fraction of PM2.5. In particular, secondary inorganic aerosols contribute 36.2% and 47.5% of PM2.5 mass in summer and winter, respectively. Nitrate concentrations increase for [NH4 +]/[SO4 2-]>1.5, and excess ammonium, which is necessary for ammonium nitrate formation, is linearly correlated with nitrate. These results are clearly observed during the winter because conditions are more conducive to the formation of ammonium nitrate. A significant negative correlation between Nitrogen Oxidation Ratio (NOR) and temperature was observed. The obtained results can be useful for a better understanding of the aerosol dynamics in the downtown area in Jeju City.

The APHRODITE (Asian Precipitation - Highly-Resolved Observational Data Integration Towards Evaluation of water resources) data has been widely used for the evaluation of the numerical model due to its higher spatial and temporal resolutions. However, some studies have indicated that it significantly underestimates the extreme precipitation values for several regions such as South Asia compared with station-based observation. In this study, therefore, the 25 year (1981-2005) APHRODITE precipitation data over South Korea during June to September was improved using Automated Synoptic Observing System (ASOS) data from Korea Meteorological Administration (KMA). After the spatial resolution and temporal interval of the ASOS data were changed to be same as those in the APHRODITE data, the GEV (Generalized Extreme Value) distribution for each data was calculated. After then, the GEV distribution of the APHRODITE data was corrected through the quantile mapping method with ASOS data. The corrected APHRODITE data was similar to the annual mean precipitation of the ASOS data. In particular, the corrected annual mean precipitation over South Korea reasonably increased by ~10% and the extreme value of precipitation have significantly improved compared to those from the original APHRODITE data.

High temporal resolution precipitation data can provide information about rainfall intensity, and can better reveal the essential physical process of precipitation intensity than daily totals do. Using hourly precipitation data at 14 stations during 1961-2014, the changes in the characteristics of summer precipitation in South Korea analysed. Although the precipitation amount in summer has increased at all stations, hourly precipitation in summer shows different directions and magnitudes of changes at each station in South Korea. Results showed that the change pattern of hourly precipitation is mostly attributed to change in the frequency of hourly precipitation of 10mm or more.

We analyzed diurnal variations in the surface air temperature using the high density urban climate observation network of Daegu in summer, 2013. We compared the time elements, which are characterized by the diurnal variation of surface air temperature. The warming and cooling rates in rural areas are faster than in urban areas. It is mainly due to the difference of surface heat capacity. In addition, local wind circulation also affects the discrepancy of thermal spatiotemporal distribution in Daegu. Namely, the valley and mountain breezes affect diurnal variation of horizontal distribution of air temperature. During daytimes, the air(valley breeze) flows up from urban located at lowlands to higher altitudes of rural areas. The temperature of valley breeze rises gradually as it flows from lowland to upland. Hence the difference of air temperature decreases between urban and rural areas. At nighttime, the mountains cool more rapidly than do low-lying areas, so the air(mountain breeze) becomes denser and sinks toward the valleys(lowlands). As the result, the air temperature becomes lower in rural areas than in urban areas.

In this study, we analyzed the characteristics of summer extreme rainfall over South Korea and their relationships with the synoptic and large-scale circulation anomalies during 1979-2014. Heavy rainfall (R90p) is related with the strong convection surrounded by dry zone over Korean peninsula and the moist air delivered from the convection area over Bay of Bengal-South China Sea-Philippine Sea. The upper-level anticyclonic flow with the low-level dipole of anticyclonic circulation in the Southeast and cyclonic circulation to the northwest of Korean peninsula are the main characteristics when the extreme rainfall occurs. The barotropic Rossby wave developed over the Korean peninsula transfers its energy farther downstream to the western coast of North America. It is also found that the dominant lowfrequency oscillation over the tropics (intraseasonal oscillation) play an important background role for the enhancement of extreme rainfall over South Korea.

To investigate thermal environment and effect of clean-road system over a broad way, we conducted the filed meteorological observation during 12~13 August 2014. The clean-road system was employed over a part of the broad way of Dalgubul(Dalgubul-Daero) by Daegu Metropolitan city in 2011. The clean–road system in general is operated two times(4 am, 2 pm) during summertime. In case of scorching alert, the system is operated 3 times a day(4 am, 2 pm and 4 pm). To evaluate the present thermal condition and the improvement effects due to the system, we analyzed the time variation of discomfort index and WBGT(wet-bulb and globe temperature). WBGT was more than 25 during 8 a.m. ~ 9 p.m. And discomfort index was more than 75 during 8 a.m. ~ 11 p.m. The thermal improvement effect of the clean-road system was restrictive during daytime.

This study analyzed the climate regime shift using statistical change-point analysis on the time-series tropical cyclone (TC) frequency that affected Japan in July to September. The result showed that there was a significant change in 1995 and since then, it showed a trend of rapidly decreasing frequency. To determine the reason for this, differences between 1995 to 2012 (9512) period and 1978 to 1994 (7894) period were analayzed. First, regarding TC genesis, TCs during the 9512 period showed a characteristic of genesis from the southeast quadrant of the tropical and subtropical western North Pacific and TCs during the 7894 period showed their genesis from the northwest quadrant. Regarding a TC track, TCs in the 7894 period had a strong trend of moving from the far east sea of the Philippines via the East China Sea to the mid-latitude region in East Asia while TCs in the 9512 period showed a trend of moving from the Philippines toward the southern part of China westward. Thus, TC intensity in the 7894 period, which can absorb sufficient energy from the sea as they moved a long distance over the sea, was stronger than that of 9512. Large-scale environments were analyzed to determine the cause of such difference in TC activity occurred between two periods. During the 9512 period, anomalous cold and dry anticyclones were developed strongly in the East Asia continent. As a result, Korea and Japan were affected by the anomalous northerlies thereby preventing TCs in this period from moving toward the mid-latitude region in East Asia. Instead, anomalous easterlies (anomalous trade wind) were developed in the tropical western Pacific so that a high passage frequency from the Philippine to the south China region along the anomalous steering flows was revealed. The characteristics of the anomalous cold and dry anticyclone developed in the East Asia continent were also confirmed by the analysis of air temperature, relative humidity and sensible heat net flux showing that most regions in East Asia had negative values.

This study analyzed a correlation between South China Sea summer (June to September) monsoon (SCSSM) and the ENSO for the last 32 years (1979 to 2010). There was a correlation that the higher (lower) the SST in the Niño-3.4 region was, the weaker (stronger) the SCSSM intensity was. To identify the reason for this correlation, a difference of means between 8 El Niño years and 8 La Niña years (June to September). The analysis on the difference between two groups with respect to the 850 hPa stream flows showed that there were anomalous huge cyclones in the subtropical Pacific in the both hemispheres so that cold and dry anomalous northerlies were strengthened in the South China Sea relatively while anomalous westerlies were strengthened from the Maritime Continent to the off the coast of Chile. The analysis on the difference between two groups with respect to the 200 hPa stream flows showed that the opposite anomalous pressure system pattern to that in the 850 hPa stream flows were shown. In the subtropical Pacific of the both hemispheres, anomalous anticyclones existed so that anomalous easterlies were strengthened from the Maritime Continent to the equatorial central Pacific. Considering the anomalous atmospheric circulations in the upper and lower layers of the troposphere, upward airflows from the equatorial central and eastern Pacific were downward in the South China Sea and the Maritime Continent, which was a structure of anomalous atmospheric circulations. This means that the Walker Circulation was weakened and it was a typical structure of atmospheric circulations revealed in El Niño years.