Asia-Pacific Journal of Atmospheric Sciences最新文献

Long-range transport (LRT) often drives episodic fine particulate matter (PM_2.5) pollution in the Republic of Korea. In this study, an LRT-driven episode that occurred from March 2 to 4, 2024 was examined during the ASIA-AQ campaign in Seoul (January 23 to March 12, 2024), using nationwide monitoring, satellite observations, trajectory analysis, and aircraft measurements over the Yellow Sea. During the LRT, PM_2.5 increased to 49.43 µg/m³, and the fraction attributable to long-range transport accounted for approximately 56% of the observed PM_2.5. The significant increases in nitrate, sulfate, and ammonium indicate the import of regionally aged aerosols and their precursors. Transport diagnostics, utilizing ERA5 winds and HYSPLIT backward trajectories with concentration-weighted trajectory analysis, as well as GK-2B GEMS aerosol optical depth, pointed to inflow from eastern China and the North China Plain. Additionally, independent aircraft measurements using PTR-ToF-MS onboard a 1900D platform detected heightened low-altitude benzene levels over the Yellow Sea during the LRT, which aligns with transboundary combustion influences. Elevated CO/CO₂ ratios further supported the presence of aged inflow. Overall, these multi-platform observations demonstrate that LRT can significantly overshadow typical domestic conditions, leading to PM_2.5 compositions rich in nitrate, sulfate, and ammonium, which are chemically processed. This underscores the necessity for coordinated regional air quality management and international collaboration to mitigate cross-border pollution and its associated health risks in Northeast Asia.

In this study, a new double-moment warm rain Goddard 4ICE scheme (GCEDM) is developed based on the Goddard 4ICE single-moment (GCESM) scheme and then tested using idealized 2D squall line and 3D supercell simulations. The addition of the total number concentrations for cloud water ((:{N}_{TC})) and rainwater ((:{N}_{TR})) enables this new scheme to simulate more diverse raindrop size distributions, making it more realistic. GCEDM has similar overall thermal and dynamic characteristics to GCESM but produces higher evaporation rates, predicted particle number concentrations, and mass mixing ratios than GCESM, leading to stronger cold pools than with GCESM. In addition, comparisons are made versus the Weather Research and Forecasting Model Double-Moment Microphysics 7-class scheme (WDM7), which was also improved from a single-moment 4-class ice scheme to a double-moment warm-rain scheme. WDM7 also shows a stronger cold pool, but the system characteristics and microphysical processes are quite different from the single-moment version of this scheme.

To investigate urban enhancements of greenhouse gases (GHGs), CO₂ and CH₄ were measured in Seoul from January to March 2024 including the Airborne and Satellite Investigation of Asian Air Quality (ASIA-AQ) campaign. Mean concentrations of both CO₂ and CH₄ exceeded those reported for other major urban cities during winter. Identified four high-concentration episodes occurred under elevated CO and low wind speeds, consistent with suppressed ventilation after long-range transport. The footprint analysis indicated that the contribution of South Korea was dominant in most episodes indicating mainly influenced by local emission sources; however, episode 4 showed a relatively larger upwind (other) contribution suggesting the long-range transport. The contribution of emission sectors indicated that buildings/heating and power generation dominated ΔCO₂ (subtracted by background concentration) variability, whereas waste management led ΔCH₄, with secondary contributions from agriculture, buildings, and fuel exploitation. Despite different major emission sectors, ΔCO₂ and ΔCH₄ converged with a narrow range with high correlation coefficient (R), reflecting co-located anthropogenic sources during wintertime. A diurnal variation of both ΔCO₂ and ΔCH₄ peaked in the morning, then reached local minimum in mid-afternoon with increasing PBL height. However, the diurnal variation of the simulated ΔCO₂ and ΔCH₄ from the Stochastic Time-Inverted Lagrangian Transport (STILT) model showed late-afternoon minimum compared to measured values because the STILT overestimates the afternoon vertical gradient of CO₂, likely owing to biases in diagnosed PBL height. This approach might provide scientific evidence to policy makers to attain the carbon neutral by suitable regulation for major emission sources when more dense spatial resolution of bottom-up inventory and meteorological fields are available.

The accuracy of PM_2.5 forecasts in Seoul from 2019 to 2023 was assessed using multiple methods. Daily short-term PM_2.5 forecasts, which were provided as four categories (good, moderate, bad, and very bad), were directly compared with the corresponding PM_2.5 observation data. Although the probability of detection for days with high PM_2.5 concentrations increased, a simultaneous rise in the false alarm rate resulted in no improvement in the total accuracy and F1-score. To analyze these trends in more detail, the forecast accuracy was further examined based on the PM_2.5 categories. The results showed an annual improvement of 3.65% in the accuracy for the bad category. An analysis based on the announcement time also indicated an increase of over 20% in the accuracy for the bad category for next-day and day-after forecasts. The confusion matrices of forecasted and observed PM_2.5 categories confirmed this improvement, which was primarily due to a reduction in the number of instances where the moderate category was forecasted as bad. However, the accuracy for the good category showed no significant change and that for the moderate category even declined. These findings highlight the importance of category-specific evaluation in air quality forecasting and improving the forecast accuracy, particularly for the good and moderate categories. The reliability of forecasts and their policy relevance may be improved by utilizing these insights and addressing temporal and spatial limitations.

This study investigates the influence of the Quasi-BiWeekly Oscillation (QBWO) on the onset, monsoon breaks, and extreme rainfall events in the Philippines during the southwest monsoon season from 1980 to 2019. Findings show that the occurrence of extreme rainfall events over the Philippines follows the northward to northwestward movement of QBWO-related convective anomalies. These events initially appear in Mindanao and Visayas (Phase 5), then shift toward Luzon (Phases 7–8), and may persist along Luzon’s western coast up to Phase 2. The contribution of tropical cyclones (TCs), low-pressure systems (LPSs), and other disturbances to extreme rainfall was also assessed. Although their percentage contribution to the total extreme rainfall varies substantially across stations, their impacts are more apparent in Phase 6, coinciding with northward/northwestward propagation of the convective anomalies of the QBWO towards the Philippines. Monsoon breaks, which is defined as the period when the average rainfall across the western coastal stations in Luzon Island decreases below 5 mm day^-1 for at least three consecutive days, also show distinct QBWO-phase preferences such that short to medium breaks are more frequent in Phases 3–5, coinciding with the movement of the anticyclonic anomaly of the QBWO from the South China Sea toward East Asia in these phases. In contrast, longer breaks occur more frequently in Phases 4–6 and may persist until Phase 7, when the northeasterlies at the northern flank of the cyclonic circulation anomaly of the QBWO weaken the southwest monsoon. The southwest monsoon onset in the Philippines typically begins during Phase 1 and Phases 6–8. Notably, about 82% of monsoon onset events occurred during these phases when the QBWO amplitude exceeded 0.5, suggesting that a real-time QBWO index could aid in monitoring the monsoon onset.

This study conducts an observation-constrained intercomparison of 23 CMIP6 global climate models (GCMs) for precipitation over Japan. We quantify relative agreement between models and a regional reference analysis from the JMA mesoscale system (GPV-MSM) for 2015–2023. Eight precipitation indices (mean, 90th percentile, max5d, CWD, etc.) and four statistical metrics (correlation, Pbias, NRMSE, Taylor skill score) are synthesized via entropy-weighted TOPSIS to obtain a proximity-to-reference coefficient and a similarity-based ordering. To limit interpolation artifacts, all fields are remapped to a 1.0° × 1.0° common grid. Because the CMIP6 Historical experiment ends in 2014, ScenarioMIP SSP585 simulations are used for 2015–2023. Axis-specific results show a stable latitudinal top-tier cohort comprising ACCESS-CM2, KACE-1-0-G, and UKESM1-0-LL, each with Top-3 inclusion probabilities ≥ 89%. In the longitudinal direction, a distinct three-model cohort—KACE-1-0-G, CNRM-ESM2-1, and CESM2-WACCM—emerges with Top-3 probabilities near 60%. Bootstrap resampling　indicates consistent rank structures (median Kendall’s Tau = 0.87 for latitude and 0.72 for longitude), with wider intervals in the longitudinal rankings indicating larger sampling variability. Across indices, the intercomparison indicates systematic model-reference differences: many models show lower amplitudes in extreme-intensity indices (90P, max5d) together with positive differences in wet-spell persistence (CWD, CWD10). The synthesis therefore identifies cohorts with comparatively higher similarity across multiple indicators (e.g., ACCESS-CM2, KACE-1-0-G, UKESM1-0-LL) and others with lower similarity (e.g., INM-CM4-8, IPSL-CM6A-LR). All findings are interpreted as relative agreement with an observation-constrained regional analysis over 2015–2023 and are intended to support bias-aware, purpose-specific use of CMIP6 precipitation in regional applications.

This study analyzed the characteristics and mechanisms of low-level wind shear at Incheon International Airport (IIA), which is located in a coastal region with gentle terrain, using 1-minute wind data from the Aerodrome Meteorological Observation System (AMOS) and hourly ERA5 reanalysis data. Wind measurements from 8 AMOS stations positioned along runways revealed a dominant channeling effect along the runway, with prevailing northwesterly and southeasterly winds, along with small-scale horizontal variability. The analysis of joint frequency distributions between near-surface and upper-level winds indicated that the northwesterly winds resulted from downward momentum transport, while the southeasterly winds occurred due to baroclinicity and pressure-driven channeling under stable stratification. These southeasterly winds were enhanced by the land breezes. Thermally-driven circulations, including land-sea breezes and slope winds, further contributed to the horizontal heterogeneity in wind patterns. On strong-synoptic forcing days, wind heterogeneity increased with wind speed, whereas on weak-synoptic forcing days, it peaked in the early afternoon due to local sea breeze development. Vertical wind shear events exceeding 7.7 m s^-1 (15 knots) between the surface and 975 hPa were more frequent at night, accounting for 3.0% (headwind) and 4.2% (crosswind) of study period. Strong shear events were often accompanied with strong synoptic winds, but some events were associated with moderate synoptic southeasterly and southwesterly winds due to interactions with land-breeze forcing. The results emphasize the importance of the interaction between synoptic forcing and land breeze forcing in low-level wind shear in coastal regions and provide insights for enhancing flight safety and small air mobility operations.

Non-landfalling tropical cyclones (TCs) traversing north and northeast of the Philippines during the southwest monsoon season (locally, Habagat) often enhance the prevailing moisture-laden southwest monsoon flow, inducing heavy rainfall and flooding events, particularly along the western coast of the country. One such event occurred last July 23–24, 2024 (Habagat 2024), when the Habagat was enhanced by TC GAEMI (locally, Super Typhoon CARINA) and some parts of the country received a month’s worth of rainfall. This study examines its unique features and compares it with recent Habagat events. Events with rainfall amounts above the 95th percentile in weather stations within Metro Manila in July and August for at least two days from 2012 to 2024 were selected for the analysis. Habagat 2024 produced exceptionally high rainfall, most of which occurred within 24 h. This record rainfall was accompanied by higher than normal magnitudes of the horizontal winds, vertically integrated moisture flux convergence (VIMFC), stream function, vertically integrated moisture flux (VIMF), and surface latent heat flux. The Moisture Conveyor Belt for the Habagat 2024 event, in particular, was noticeably more pronounced, which explains the higher rainfall rate relative to previous Habagat events. Furthermore, the VIMF anomalies were further separated into the basic flow (monsoon only) and the TC perturbation flow using spatial Fourier decomposition analysis to identify which contributes more to rainfall enhancement over Metro Manila. Habagat 2024 exhibited the strongest basic monsoon flow and TC perturbation flow among all events, with the latter contributing more to the rainfall enhancement.

This study examines the synoptic-scale environment for heavy rainfall over the Korean Peninsula (KP) during the Changma (late June through mid-July) and August using a 30-year dataset (1990–2019). The K-means clustering of geopotential height and equivalent potential temperature at 850 hPa has produced nine clusters of synoptic-scale environment, which are classified into 4 patterns. For the Changma, 1) the pattern 1 (C2, C4 and C6 clusters): a synoptic cyclone to the north, the western North Pacific Subtropical high (WNPSH) to the southeast of the KP, a significant trough to the southeast of the Tibetan plateau, and the strong southwesterly band from SW China to the KP, 2) the pattern 2 (C3 and C5) is similar to the pattern 1 except for the ridge over northeastern China, 3) the pattern 3 (C1 and C7) is similar to the pattern 2, except for the synoptic-scale trough over the South China Sea, and 4) the pattern 4 (C8 and C9) is not a typical Changma pattern. For August, 1) the pattern 1 (A3, A8 and A9) is similar to the Changma pattern 1, however, the Tibet trough and the southwesterly belt are relatively weak, 2) the pattern 2 (A7 and A2) shows heavy rainfall along the western edge of the WNPSH accompanied by relatively frequent tropical cyclones (TCs), 3) the pattern 3 (A5 and A6) shows heavy rainfall along the western edge of the WNPSH with a trough over the Yellow Sea, and 4) the pattern 4 (A4 and A1) shows heavy rainfall away from the WNPSH.