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This study investigates the impacts of near-term climate forcers (NTCFs) and ozone precursor emissions on particulate matter (PM2.5) concentrations in East Asia (EA). Our analysis used the Coupled Model Intercomparison Project Phase 6 Aerosols and Chemistry Model Intercomparison Project (AerChemMIP) dataset to assess the potential changes in air quality under varying emission scenarios for the present day (1995–2014) and near-term future (2015–2054). Present-day PM2.5 concentrations in EA averaged 14.3 ± 2.6 μg/m3, with significant regional variation: East China (32.43 μg/m3), Korea (13.71 μg/m3), and Japan (7.51 μg/m3). A reduction in historical NTCF emissions would lower PM2.5 concentrations by approximately 43% across EA, whereas reducing O3 precursors would yield an approximately 10% decrease. Under the SSP370 scenario, PM2.5 concentrations are projected to increase by 16% in the near-term future (2045–2054). However, robust NTCF mitigation could reduce PM2.5 levels by approximately 40%, primarily by decreasing sulfate and organic aerosols, which are the dominant contributors of historical PM2.5 variability. Despite substantial projected improvements, achieving the World Health Organization’s stringent air quality guidelines remains challenging, highlighting the necessity for enhanced emissions control targeting key pollutant sources. These insights are crucial to East Asian policymakers aiming to implement effective air quality management strategies.

The maximum significant wave height ( H s m a x ) induced by a tropical cyclone (TC) can be estimated from an empirical fetch formula using the TC’s size, maximum wind speed, and translation speed, in which larger, stronger, and faster-moving TCs generally have higher the H s m a x . In the formula, the radius of maximum wind (RMW) has been widely used as the TC size parameter under the assumption that H s m a x is mainly generated by strong winds near the RMW. This study investigates whether RMW is the optimal parameter for determining TC-induced H s m a x through extensive wave model simulations for North Atlantic hurricanes from 1988–2017. The correlation analysis between the estimated H s m a x and TC size parameters revealed that the radius of the 34-kt wind speed (R34, r = 0.84–0.95) was much higher than the widely used RMW ( r = 0.33–0.58), which suggests that R34 is a more important TC size parameter for determining TC-induced H s m a x than RMW. This result can be explained by the fact that R34 showed a significantly higher correlation ( r = 0.96) than RMW ( r = 0.31) with cumulative TC wind speeds, which are closely related to H s m a x . These findings also indicate that the TC-induced H s m a x is more affected by the region containing moderately strong winds outside the TC than by the region of maximum wind speed near the RMW. Our paper provides additional insight into the mechanisms by which extreme wave heights, which cause severe damage during TC passage, occur.

The two-way Lagrangian particle-tracking model (PTM) is proposed for specifying sources of objects drifting with random-walk processes on the sea surface. First, to determine object source candidates, modeled particles are released from the point (hereafter, “receptor”) where an observer finds the objects using a backward-in-time PTM with modeled ocean currents of which directions are reversed in sign. Second, the modeled particles are released from these source candidates in a forward-in-time PTM using ocean currents originally computed in hydrographic models. Third, the source candidates are considered to be reliable at a 5% significance level if the observed receptor is located inside the ellipse whose center is the mean position of the modeled particles at the time when the observer found the objects and whose axis length is twice the standard deviation computed using all modeled particle positions. The two-way PTM experiments are carried out in a realistic hydrographic model over the East China Sea shelf for the period from June through August 2004. Statistically significant sources are well specified close to the true source because 58%–90% of source candidates are rejected in the experiments.

A regional wave forecasting system in East Asia, including the Korean Peninsula, was built based on WAVEWATCH III using offshore wind forecast data from the Global Data Assimilation Prediction System. The numerical simulations were performed on the sensitivity of the interaction between input wind and wave development. The forecasts for each condition were compared and verified with the observational data of marine meteorological buoys from 1 August to 30 September 2020. The sensitivity conditions were configured to have a specific range of variables related to the directional distribution of input winds (SINA0) and variables indicating the development of input wind–wave (CDFAC) in the ST6. The results were presented by calculating the mean error and root mean square error for all observation points. Overall, as the CDFAC increased, the mean error tended to decrease according to the forecast time and the root mean square error increased. Although the effect of SINA0 at the same CDFAC was insignificant, when SINA0 increased in sections where the significant wave height decreased rapidly, the significant wave height tended to decrease. In addition, the main variables that affect the physical process of wind–wave interaction should be considered to improve wave model forecasting performance and accuracy.

The seasonal variation of water circulation in the Seto Inland Sea is investigated using a high resolution, three-dimensional numerical ocean model. The model results are assessed by comparison with long-term mean surface current and hydrographic data. The simulated model results are consistent with observations, showing a distinct summer and winter circulation patterns. In summer the sea water is highly stratified in basin regions, while it is well mixed near the straits due to strong tidal mixing there. During this period, a cold dome is formed in several basins, setting up stable cyclonic eddies. The cyclonic circulation associated with the cold dome develops from May and disappears in autumn when the surface cooling starts. The experiment without freshwater input shows that a basin-scale estuarine circulation coexists with cyclonic eddy in summer. The former becomes dominant in autumn circulation after the cold dome disappears. In winter the water is vertically well mixed, and the winter winds play a significant role in the circulation. The northwesterly winds induce upwind (downwind) currents over the deep (shallow) water, forming a “double-gyre pattern” in the Suo-Nada, two cyclonic eddies in Hiuchi-Nada, and anticyclonic circulation in Harima-Nada in vertically averaged current fields.

A wave forecast numerical simulation was performed for Typhoon Lingling around the Korean Peninsula and in the East Asia region using sea winds from 24 members produced by the Ensemble Prediction System for Global (EPSG) of Korea Meteorological Administration (KMA). Significant wave height was observed by the ocean data buoys used to verify data of the ensemble wave model, and the results of the ensemble members were analyzed through probability verification. The forecast performance for the significant wave height improved by approximately 18% in the root mean square error in the three-day lead time compared to that of the deterministic model, and the difference in performance was particularly distinct towards mid-to-late lead times. The ensemble spread was relatively appropriate, even in the longer lead time, and each ensemble model runs were all stable. As a result of the probability verification, information on the uncertainty that could not be provided in the deterministic model could be obtained. It was found that all the Relative Operating Characteristic (ROC) curves were 0.9 or above, demonstrating good predictive performance, and the ensemble wave model is expected to be useful in identifying and determining hazardous weather conditions.

The interannual variation of the behavior of Changjiang freshwater has been investigated using the Princeton Ocean Model (POM). Five experiments are described in this study. Three basic experiments (Exps. B1, B2 and B3) were performed to examine the freshwater behavior in response to annual variations of the Changjiang discharge in normal, wet and dry years, respectively. Thereafter, the freshwater variation was investigated with the model forced by primary-interannual variations of river discharge with an 8-year period (Exp. I1) and a wind field with a 3.6-year period (Exp. I2). In Exp. B1, the average residence time of freshwater is roughly estimated to be 681.4 days in the Yellow Sea (YS) and 353.4 days in the combined area of the East China Sea (ECS) and the Chinese Coast (CC). This difference is attributed to the current pattern in each region and freshwater exchange among the regions. The interannual variation of freshwater volume in Exp. I1 has a large amplitude and long phase lag in the YS (38 km^sup 3^ and 1.6-year against primary-interannual discharge variation), while there are relatively small amplitudes and short phase lags in the ECS (18 km^sup 3^ and 0.7-year) and the CC (14 km^sup 3^ and 0.5-year). It is concluded that the difference in the freshwater behavior results from the difference in the average residence time in each region.[PUBLICATION ABSTRACT]

To investigate technical issues associated with the particle-tracking numerical models frequently used to reproduce the behavior of objects drifting in the actual ocean, the trajectories of satellite-tracked drifters released in 2003, 2004, and 2007 were reproduced using a numerical model. In particular, the wind stress driving the surface currents which carried the drifters has been computed using satellite-observed QuikSCAT/Seawinds data provided twice daily in conjunction with in-situ Ieodo-station wind data. Although it is difficult to reproduce the trajectory of a single drifter using numerical models because of the uncertainty induced by random-walk processes, the similarity between the modeled particle and observed buoy trajectories is statistically significant, except for the experiment in 2007. In general, the satellite-derived wind field modified using in situ data is likely to be able to reproduce observed drifter motion. However, it is found that the model is unable to reproduce drifter trajectories in windy 2007. The numerical modeling result demonstrates that wind-induced leeway drift prevails in drifter motion in 2007, in spite of the wind-resistant drogue attached to the drifters, and that this drift shows non-negligible spatiotemporal variability, suggesting that leeway drift is not simply proportional to wind speeds, as in previous studies have maintained.

The reliability of a numerical tide model for detiding acoustic Doppler current profiler (ADCP) data is examined on the East China Sea shelf. The process is adopted for the ADCP data obtained on 12–13 May 2003. The ocean model accompanied by the most precise harmonic constants available to public is used to compute external tides. The root mean square difference is less than 10 cm/s between the detided currents and those using the least squares method, and so the detiding process using the numerical model is available to detect the East China Sea shelf circulation faster than this speed.