Recently, the surface ozone concentration in the Korean peninsula has been increasing more rapidly than in the past, and seasonal changes are appearing such as increases in the number of ozone alerts in springtime. We examined changes in the timing of annual maximum South Korean O3 levels by fitting a sine function to data from 54 air-quality monitoring sites over a 10-year period (2005-2014). The analytical results show that the date of maximum ozone concentration at 23 points in the last 10 years has been advanced by about 2.1 days per year (E-sites), while the remaining 31 points have been delayed by about 2.5 days per year (L-sites). We attribute these differences to seasonal O3 changes: E-sites show a larger increase in O3 level in March-April (MA) than in June-July (JJ), while L-sites show a larger increase in JJ than in MA. Furthermore, these shifts are significantly larger in magnitude than those reported for Europe and North America. We also examined one possible reason for these seasonal differences: the relationship between O3 and precursors such as NO2 and CO. E-sites showed a rapid decrease in NO2 (NO) concentration in MA over the last decade. As a result, the ozone concentration at E-sites seems to have increased due to the absence of ozone destruction by NOx titration in early spring. In L-Sites, the concentrations of ozone precursors such as NO2 and CO in JJ showed a smaller decrease than those at other sites. Therefore, in L-sites, relatively large amounts of ozone precursors were distributed in JJ, implying that more ozone was generated. We suggest that shifts in the South Korean O3 seasonal cycle are due to changes in early spring and summer NO2 (NO) and CO levels; this should be tested further by modeling studies.

The negative impact of extreme high-temperature days (EHDs) on people’s livelihood has increased over the past decades. Therefore, an improved understanding of the fundamental mechanisms of EHDs is imperative to mitigate this impact. Herein, we classify the large-scale atmospheric circulation patterns associated with EHDs that occurred in South Korea from 1982 to 2018 using a self-organizing map (SOM) and investigate the dynamic mechanism for each cluster pattern through composite analysis. A common feature of all SOM clusters is the positive geopotential height (GPH) anomaly over the Korean Peninsula, which provides favorable conditions for EHDs through adiabatic warming caused by anomalous downward motion. Results show that Cluster 1 (C1) is related to the eastward-propagating wave train in the mid-latitude Northern Hemisphere, while Cluster 2 (C2) and 3 (C3) are influenced by a northward-propagating wave train forced by enhanced convection in the subtropical western North Pacific (WNP). Compared to C2, C3 exhibits strong and eastward-extended enhanced convection over the subtropical WNP, which generates an anomalous high-pressure system over the southern part of the Kamchatka Peninsula, reinforcing EHDs via atmospheric blocking. Our results can contribute to the understanding of East Asia climate variability because wave trains influence the climate dynamics of this region.

Recently, Earth system models (ESMs) have begun to consider the marine ecosystem to reduce errors in climate simulations. However, many models are unable to fully represent the ocean-biology-induced climate feedback, which is due in part to significant bias in the simulated biogeochemical properties. Therefore, we developed the Generic Ocean Turbulence Model–Tracers of Phytoplankton with Allometric Zooplankton (GOTM–TOPAZ), a single-column ocean biogeochemistry model that can be used to improve ocean biogeochemical processes in ESMs. This model was developed by combining GOTM, a single-column model that can simulate the physical environment of the ocean, and TOPAZ, a biogeochemical module. Here, the original form of TOPAZ has been modified and modularized to allow easy coupling with other physical ocean models. To demonstrate interactions between ocean physics and biogeochemical processes, the model was designed to allow ocean temperature to change due to absorption of visible light by chlorophyll in phytoplankton. We also added a module to reproduce upwelling and the air–sea gas transfer process for oxygen and carbon dioxide, which are of particular importance for marine ecosystems. The simulated variables (e.g., chlorophyll, oxygen, nitrogen, phosphorus, silicon) of GOTM–TOPAZ were evaluated by comparison against observations. The temporal variability in the observed upper-ocean (0–20 m) chlorophyll is well captured by the GOTM–TOPAZ with a correlation coefficient of 0.53 at point 107 in the Sea of Japan. The surface correlation coefficients among GOTM–TOPAZ oxygen, nitrogen, phosphorus, and silicon are 0.47, 0.31, 0.16, and 0.19, respectively. We compared the GOTM–TOPAZ simulations with those from MOM–TOPAZ and found that GOTM–TOPAZ showed relatively lower correlations, which is most likely due to the limitations of the single-column model. Results also indicate that source–sink terms may contribute to the biases in the surface layer (250 m). Despite this limitation, we argue that our GOTM–TOPAZ model is a good starting point for further investigation of key biogeochemical processes and is also useful to couple complex biogeochemical processes with various oceanic global circulation models.

South Korea has frequently suffered from heat waves, which are mainly attributable to anomalously prolonged high-pressure systems. There have been many studies regarding the role of large-scale circulation in the Korean Peninsula heatwaves, but the contribution of local-scale circulation and sea surface temperature has not been analyzed. This study investigates the impact of local circulation and sea surface temperature (SST) of the East Sea (Sea of Japan) on the surface temperature variations of the Korean Peninsula. Based on empirical orthogonal function (EOF) analysis of the detrended daily surface temperature anomalies from July to August, 1991–2020, high-temperature days were classified into three categories: high pressure (HP), easterly wind (EW), and both high pressure and easterly wind (HPEW). On EW days, the mean surface temperatures in the western part of the peninsula are 1.75 °C higher than those on the eastern part of the windward side, indicating foehn wind warming on the leeward side. Under the synergistic effects of foehn wind warming and high-pressure anomalies, the surface temperature is the highest on HPEW days. Regression analysis also shows that, when the SST of the East Sea increased by 1 °C, the surface temperatures in the western region on HPEW and EW days increased by 0.36 °C and 0.22 °C, respectively. In contrast, the SST effect in the western region is negligible on HP days owing to the lack of foehn wind warming. Sensitivity experiments using the high-resolution Weather Research and Forecasting (WRF) model also showed that foehn wind warming becomes stronger on EW and HPEW days with warmer East Sea SST. Our results suggest that local circulation and SST are important factors in high-temperature events in the Korean Peninsula.