Do-Yong Kim

Remotely sensed retrieval of midday air temperature considering atmospheric and surface moisture conditions

Near-surface air temperature (T a) is an important variable for various scientific communities, and many previous studies have attempted to estimate T a with high spatial resolution using remotely sensed data. The present study proposes a new, practical method for estimating T a near the land surface based on moisture conditions of the atmosphere and surface. First, match-up data sets of ground observations from 76 meteorological stations and satellite remote-sensing observations were established over the Republic of Korea during 2006. Four cases of atmospheric and surface moisture conditions were then determined using Moderate Resolution Imaging Spectroradiometer brightness temperatures (at 11 and 12 μm) and the normalized difference water index for all match-ups. Using stepwise multiple regression analysis for each case, land surface temperature and the normalized difference vegetation index were statistically selected as significant independent variables for estimating T a using the development data set (75% of the match-ups for each case). The T a values estimated from the multiple regression algorithm with different constants and coefficients for each case showed reasonably good performance (nearly zero mean bias and approximately 3°C root mean square error) compared with the measured T a values used as the validation data set (25% of the match-ups for each case). Thus, the proposed T a estimation approach based on moisture conditions of the atmosphere and surface is not confined to a specific season or land type and can be applied to all areas and seasons in the Republic of Korea.

Mesoscale simulations of multi-decadal variability in the wind resource over Korea

This study investigated multi-decadal variability in the wind resource over the Republic of Korea using the Weather Research and Forecasting (WRF) mesoscale meteorological model. Mesoscale simulations were performed for the period from November 1981 to November 2010. The typical wind climatology over the Korean Peninsula, which is influenced by both continental and oceanic features, was represented by the physics-based mesoscale simulations. Winter had windier conditions with northwesterly flows, whereas less windy with southwesterly flows appeared in summer. The annual mean wind speeds over the Republic of Korea were approximately 2 m s−1 with strong wind in mountainous areas, coastal areas, and islands. The multi-decadal variability in wind speed during the study period was characterized by significant increases (positive trend) over many parts of the study area, even though the various local trends appeared depending on the station locations. The longterm trend in the spatially averaged wind speed was approximately 0.002 m s−1 yr−1. The annual frequency of daily mean wind speeds over 5 m s−1 at the turbine hub height also increased during the study period throughout the Republic of Korea. The present study demonstrates that multi-decadal mesoscale simulations can be useful for climatological assessment of wind energy potential.

Spatio-temporal characteristics of wind observations over South Korea: 1982–2011

In this study, we investigate the spatial and temporal characteristics of long-term (1982–2011) wind measurements over South Korea. First, ground-based measurements are adjusted to standard 10 m above ground level using a modified wind-profile power law, to account for wind variation in the actual measurement height. Then, wind climatology, variability, and long-term trends were calculated using the daily wind-speed series. The spatially averaged annual mean wind speeds over South Korea were found to be characterized by a light breeze (approximately 2 m s−1). Seasonality in the mean wind speed was generally influenced by the monsoonal flow; wind speeds were higher in winter and spring than in summer and autumn. However, the tendencies of near-surface wind speed showed opposite values at clustered stations regardless of season. There were negative trends with −0.028 m s−1 a−1 for 25% of the stations (R1) and positive trends with 0.020 m s−1 a−1 for 75% of the stations (R2). We found that the annual trends in the two regions (R1 and R2) were statistically significant and homogenous for all time-varying percentiles over 12 months of the year. Our study also identified that geo-spatial features such as elevation, land-use, geographical setting, and urbanization have large impacts on the spatiotemporal characteristics of the local wind speed.

A regression-based statistical correction of mesoscale simulations for near-surface wind speed using remotely sensed surface observations

Wind speed is an important meteorological variable for various scientific communities. In this study, numerical mesoscale simulations were performed over the Republic of Korea in 2006, to produce wind information distributed homogeneously with space. Then, an attempt was made to statistically correct the simulated nearsurface wind speed using remotely sensed surface observations. The weak wind season (WWS, from May to October) and strong wind season (SWS, from November to April) were classified on the basis of the annual mean wind speed. Although the spatial features and monthly variation pattern of the near-surface wind speed were reasonably simulated in the Weather Research and Forecasting (WRF) model, the simulations overestimated the observed values. To correct the simulated wind speeds, a regression-based statistical algorithm with different constants and coefficients for WWS and SWS was developed using match-up datasets of wind observations and satellitederived variables (land surface temperature and normalized difference water index). The corrected wind speeds showed reasonable performance for both WWS and SWS with respect to observed values. The monthly variation in the corrected wind speeds over the Republic of Korea also matched better with observations throughout the year, within a monthly bias range of approximately ± 0.2 m s−1. The proposed algorithm using remotely sensed surface observations may be useful for correcting simulated near-surface wind speeds and improving the accuracy of wind assessments over the Republic of Korea.

Atmospheric Photochemistry in Low-and High-Nox Regimes

Atmospheric photochemistry of were considered theoretically, to clarify the reasons for the different trends of between the formation of photochemical oxidants (Ox) and its primary pollutants for the Low-and High-NOx regimes. Equations of OH, , and production of ozone () as a function of nitrogen oxides (NOx) and reactive hydrocarbons (RH) were represented in this study. For the Low-NOx regime, radical is proportional to RH but independent of NOx. OH radical is proportional to NOx but inversely-proportional to RH. production is proportional to NOx but has a weak dependence on RH. For the High-NOx regime, OH and radicals concentrations and production are proportional to RH but inversely-proportional to NOx. In addition, the Osaka Bay and surrounding areas of Japan were evaluated with the mass balance of odd-hydrogen radicals (Odd-H) using CBM-IV photochemical mechanism, in order to distinguish the Low- and High-NOx regimes. The Harima area (emission ratio, RH/NOx = 6.1) was classified to the Low-NOx regime. The Hanshin area (RH/NOx = 3.5) and Osaka area (RH/NOx = 4.3) were classified to the High-NOx regime.