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국제학술지

공지 (2024. 9. 4.)

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Development of a monthly PM2.5 forecast model for Seoul, Korea, based on the dynamic climate forecast and CNN algorithm

Abstract: A convolutional neural network (CNN) model has been developed to predict monthly concentrations of particulate matter with a diameter ≤ 2.5 μm (PM2.5) in Seoul, Republic of Korea, during winter months (November through February). Seven meteorological variables influencing PM2.5 concentrations were selected as predictors: geopotential heights at 1000 and 500 hPa, zonal and meridional winds, relative humidity and temperature at 850 hPa, and boundary layer height. These predictors were obtained from the fifth generation of the European Centre for Medium-Range Weather Forecasts reanalysis (ERA5) for model construction and from the Korea Polar Prediction System (KPOPS) dynamic forecasts for operational predictions. From the 11-year ERA5 dataset for 2008-2020, one year was allocated for testing, while the remaining 10 years were randomly assigned for either training (80%) or validation (20%). This process was repeated until all 11 years were allocated for testing, resulting in 11 CNN models. The benchmark which used the ERA5 dataset as the predictors yielded a mean bias error (MBE) of 0.05 μg m-3, root mean square error (RMSE) of 2.41 μg m-3, Pearson correlation coefficient (R) of 0.85, and 71% hit rate in predicting the months of high PM2.5 concentrations (≥ 30 μg m-3) for the testing periods. The 11-CNN-model ensemble predictions using the KPOPS forecasts resulted in an MBE of 0.1 μg m-3, RMSE of 3.19 μg m-3, R of 0.74, and hit rate of 62.5% for the period 2008-2020. Considering that the average temporal correlation coefficients between the ERA5 and the KPOPS forecasts for the seven predictors ranged from 0.20 to 0.66, the CNN-based PM2.5 prediction model has demonstrated good performance in overcoming the adverse effects of the KPOPS forecast errors on predicting PM2.5 concentrations. The CNN model showed limitations for unusual period such as the COVID-19 period, November 2020 through February 2022, when the emissions in East Asia were substantially below their climatological normal levels. In conclusion, the CNN model developed in this study showed potential applicability to operational monthly PM2.5 concentration predictions for the years of normal emissions using solely meteorological data. This can provide professionals in various fields, such as health care and environmental science, with valuable insights for long-term planning. Full title: Development of a monthly PM2.5 forecast model for Seoul, Korea, based on the dynamic climate forecast and a convolutional neural network algorithm
- 작성자Park et al.
- 작성일2024.08.22
- 조회수30
- 2024
Modulations of MJO and QBWO on early summer tropical cyclone genesis over Bay of Bengal and South China Sea

Abstract: The Madden–Julian oscillation (MJO) and the quasi-biweekly oscillation (QBWO) are prominent components of the intraseasonal oscillations over the tropical Indo-Pacific Ocean. This study examines the tropical cyclone (TC) genesis over the Bay of Bengal (BOB) and the South China Sea (SCS) on an intraseasonal scale in May–June during 1979–2021. Results show that the convection associated with the two types of intraseasonal oscillations simultaneously modulates TC genesis in both ocean basins. As the MJO/QBWO convection propagated, TCs form alternately over the two basins, with a significant increase (decrease) in TC genesis frequency in the convective (nonconvective) MJO/QBWO phase. Based on the anomalous genesis potential index associated with the MJO/QBWO, an assessment of the influence of various factors on TC genesis is further assessed. Middle-level relative humidity and lower-level relative vorticity play key roles in the MJO/QBWO modulation on TC genesis. The MJO primarily enhances large-scale cross-equatorial moisture transport, resulting in significant moisture convergence, while the QBWO generally strengthens the monsoon trough and induces the retreat of the western North Pacific subtropical high, increasing the regional lower-level relative vorticity. The potential intensity and vertical wind shear make small or negative contributions. This study provides insights into the neighboring basin TC relationship at intraseasonal scales, which has a potential to improve the short-term prediction of regional TC activity. Full title: Modulations of Madden-Julian oscillation and quasi-biweekly oscillation on early summer tropical cyclone genesis over Bay of Bengal and South China Sea
- 작성자Chen et al.
- 작성일2024.08.22
- 조회수19
- 2024
Geostationary satellite-derived positioning of a TC center using artificial intelligence algorithms over the WNP

Abstract: Artificial intelligence (AI) models were developed to determine the center of tropical cyclones (TCs) in the western North Pacific. These models integrated information from six channels of geostationary satellite imagery: the brightness temperature of four infrared (IR) and one shortwave IR channels, as well as the reflectivity of one visible channel. The first model is a convolutional neural network designed for spatial data processing, and the second is a convolutional long short-term memory model that effectively captures spatiotemporal information. For training, verification, and testing purposes, spatial images from six channels were obtained from the Japanese Himawari-8 satellite from 2016 to 2021. The position of the European Centre for Medium-Range Weather Forecasts 6- or 12-h prediction was assigned as an initial value to the AI models. Errors in the initial value were 20–50 km compared to the Joint Typhoon Warning Center best track, depending on TC intensity. Weak (strong) TCs exhibited large (small) errors. This error dependency was found in Automated Rotational Center Hurricane Eye Retrieval (ARCHER) product, which is currently used by several operational organizations. ARCHER errors were typically small when observations from both geostationary and polar-orbiting satellites were included. Significant errors remained in the absence of microwave channel information from polar-orbiting satellites. This study successfully developed two AI models that consistently determined the location of the TC center using only six-channel images from geostationary satellites. These models exhibited comparable or better performance than the ARCHER products. The newly developed AI models can potentially be implemented for operational use. Full title: Geostationary satellite-derived positioning of a tropical cyclone center using artificial intelligence algorithms over the western North Pacific
- 작성자Ho et al.
- 작성일2024.06.13
- 조회수21
- 2024
Development of interpretable probability ellipse in TC track forecasts using multiple operational EPSs

Abstract: Most tropical cyclone (TC) forecasting centers have implemented a probabilistic circle to represent track uncertainty at a specified lead time. Recent studies suggest that probability ellipses constructed from ensemble prediction systems can convey the anisotropy of track predictability. In this study, a new probability ellipse model is developed to interpret the extent of forward speed and heading uncertainties in ensemble forecasts by selecting an equal proportion of members in the along- and cross-track directions. This method is validated using the 2019–2021 western North Pacific (WNP) TC track forecasts from the ensemble predictions of the European Centre for Medium-Range Weather Forecasts, the United States National Centers for Environmental Prediction, and the Korea Meteorological Administration. When the proportion of ensemble members in the ellipse is set to 70%, more than one-half (50.0%–73.6%) of the forecasts, depending on the lead time, indicate reduced area compared with that of the circle. The mean areas of the probability ellipses are 4.9%, 7.0%, 10.0%, and 11.5% smaller than those of the circle in 48-, 72-, 96-, and 120-hr forecasts, respectively. The forward speed shows greater uncertainty than the heading, as evidenced by the along-track radii being larger than the cross-track counterpart in ∼60% of the samples, regardless of the lead time. In addition, the regional distribution of the along-track/cross-track ratio in the probability ellipses can explain the dominant direction of the track error in a particular location. The proposed probability ellipse shows potential for application in operational TC track predictions. Full title: Development of interpretable probability ellipse in tropical cyclone track forecasts using multiple operational ensemble prediction systems
- 작성자Yoo and Ho
- 작성일2024.06.13
- 조회수18
- 2024
Sea surface temperature warming to inhibit mitigation of tropical cyclone destructiveness over East Asia in El Niño

Abstract: Given their conditions to reside in and intensify longer over warm oceans, tropical cyclones (TCs) in the western North Pacific (WNP) present a stronger lifetime maximum intensity during El Niño than during La Niña. By using observational data, we found that the anomalously cool sea surface temperature (SST)s in the basin act as effective barriers against intense TCs approaching East Asia during El Niño, weakening their destructiveness at landfall. Based on our high-resolution pseudo-global-warming simulations, the basin-wide 2K SST warming within the WNP basin can, however, shatter this cool SST barrier, exposing East Asia to more destructive TCs during El Niño, compared to those during La Niña. Considering that the 2K warmer WNP will likely occur in the mid-21st century under a high emission scenario and in the late 21st century under a moderate emission scenario, our findings support that more aggressive efforts of global warming mitigation are needed.
- 작성자Park et al.
- 작성일2024.08.22
- 조회수14
- 2024
Polarimetric radar signatures in various lightning activities during Seoul (Korea) flood on August 8, 2022

Abstract: On August 8 and 9, 2022, a record-breaking rain rate of 142 mm h-1, with an accumulated rainfall of more than 500 mm, was observed in the Seoul metropolitan area, Republic of Korea. This study focuses on analyzing the concentration of lightning in southern Seoul, which occurred solely on August 8. It is worth noting that the daily rainfall of August 8 was approximately twice that of August 9 (381 mm on August 8 vs. 198 mm on August 9). The RKSG (located in Yongin, 40 km south of Seoul) Weather Surveillance Radar-1988 Doppler was used to explore the characteristics of cloud microphysics associated with lightning activity. Four major heavy rain periods on August 8 were grouped into three categories of lightning rate (e.g., intense, moderate, and none), and their polarimetric signatures were compared. Significant differences in the vertical distribution of graupel were found within the temperature range of 0 °C and − 20 °C, as indicated by radar reflectivity (ZH) > 40 dBZ and differential reflectivity (ZDR) < 0.5 dB. Although graupel was detected in all three categories at the relatively warm temperatures of 0 °C to − 10 °C, its presence extended into colder regions exclusively in the intense category. This observation preceded the appearance of lightning by approximately 6 min. At heights with temperature ≤ − 20 °C, a high concentration of vertically aligned ice crystals was observed in lightning-prone regions, leading to a decrease in differential phase (ΦDP). In summary, this study provides valuable insights into the microphysical characteristics of thunderstorms and their relationship to lightning activity in the Seoul metropolitan area.
- 작성자Kim et al.
- 작성일2024.08.22
- 조회수9
- 2024
Centennial analysis in tropical cyclone induced precipitation in Korea

Abstract: Tropical cyclone (TC)-induced precipitation has undergone significant multidecadal changes over the last 117 years (1904–2020) on the Korean Peninsula, as determined through the analysis of affected TCs and surface-observed precipitation at ten stations in the Republic of Korea (hereafter Korea). Information on TCs that have affected Korea over a century was collected from the National Typhoon Center of the Korea Meteorological Administration (KMA). The information was cross-validated by referring to the International Best Track Archive for Climate Stewardship archive, while the information for 1904–1950 was cross-validated by also examining extreme weather reports in newspapers. A significant regime shift in the annual total heavy rainfall (confined to rain events ≥100 mm day−1), and its frequency associated with the affected TCs was found before and after 1979. The regime-shift signal is robust regardless of the methodology. Heavy rainfall from non-TC events, however, has presented a regime-shift increase since 1997. Based on a detailed review of historical documents describing instrument type, measuring method, altitude, and site location, this rainfall increase in regime-shift is likely a non-climatic signal coming from updates in measurement tools (i.e., the weather station automation project of KMA) during 1995–2000. However, increases in heavy rainfall of TC events in 1979 are comprehensively supported by the intensity and track changes in Korea affecting TC and changes in large-scale atmospheric and oceanic environments. The present results provide an earnest validation of TC records over the Korean Peninsula and confirm a regime-shift increase in TC hazards over Korea, thus providing grounds for further global analysis.
- 작성자Chang et al.
- 작성일2024.09.04
- 조회수20
- 2023
Critical contribution of moisture to the air quality deterioration in a warm and humid weather

Abstract: The deterioration of air quality that threatens human health is recognized as focal compound hazard. Here, decisive thermodynamic conditions for activation of secondary aerosol formation have been investigated focused on Korea. In a dry environment with relative humidity < 60%, gas phase reaction to form fine particles depended largely on surface temperature. In a wet environment (relative humidity ≥ 60%), however, aqueous phase reaction of secondary inorganic aerosols, which are sulfate, nitrate, and ammonium, accounting for 67% of the total aerosol mass, was more activated. Thus, humidity is as important as temperature in the secondary production of aerosol; air quality often worsened when a low-pressure system was predominant over the Korean Peninsula. It is rather different from the general synoptic conditions of high concentrations of particulate matters characterized by high pressure and atmospheric stagnation. This study suggests additional favorable condition and responsible mechanism of air quality hazards that may be frequent in future.
- 작성자Choi et al.
- 작성일2024.09.04
- 조회수22
- 2023
Ineffective implementation of emergency reduction measures against high concentrations of particulate matter in Seoul...

Abstract: Since December 30, 2017, the Seoul Metropolitan Government, Republic of Korea, has been implementing emergency reduction measures (ERMs) restricting the operation of industrial sites, thermal power plants, and vehicles when air quality is expected to deteriorate. ERMs are implemented when the present observed concentration of particulate matter (PM) of aerodynamic diameter less than 2.5 μm (PM2.5) and/or the predicted values for the following day exceed a threshold value. In this study, the effectiveness of ERMs was evaluated for 33 days with and 6 days without ERM implementation but where the PM2.5 concentration exceeded the threshold value, until March 15, 2021. Of the 33 days of ERM implementation, on 7 days it was executed despite the thresholds not being met. The ERM on these days might have been properly executed because the pre-notice and implementation of ERM might have reduced the local emissions of air pollutants. Our major findings are that even on days of ERM implementation, there were marginal reductions in vehicle traffic, thermal power generation, and industrial emissions. Second, the concentrations of PM2.5 and related air pollutants in Seoul were almost unchanged for most ERM implementation episodes. Third, most of the 39 (= 33 + 6) days when the air quality worsened were caused by the transboundary transport of air pollutants from China. In conclusion, it was revealed that the currently executed ERM law is insufficient for effectively reducing PM2.5. To achieve the required reductions, it is necessary to undertake stricter policies in Seoul and its neighboring regions. Full title: Ineffective implementation of emergency reduction measures against high concentrations of particulate matter in Seoul, Republic of Korea
- 작성자Ho and Kim
- 작성일2024.09.04
- 조회수15
- 2023
Major decisive factors of tropical cyclone risk in the Republic of Korea: Intensity, track, and extratropical transition

Abstract: After the catastrophic damage caused by the extratropical transitioned North Atlantic hurricane Sandy (2012), the decaying stage of a tropical cyclone (TC) have received more attention. TC undergoing extratropical transition (ET) in mid-latitudes may become hazardous with torrential rain and violent wind over a vast area. In this study, a decision tree analysis was applied to evaluate the relative importance of TC parameters such as intensity category, entry location, and distance from coastlines, in determining damage occurrence. All 123 landfalling TCs in the Republic of Korea (hereafter Korea) during 1979–2015 were analyzed. The results reveal that intense TCs (severe tropical storms and typhoons) incur damages regardless of entry location and distance from coastlines. TCs with tropical storm intensity are expected to incur damages only when they approach the southwest of the Korean Peninsula. Weak TC with maximum wind speeds smaller than 17 m s−1 does not have the potential to incur damages unless the TC was undergoing extratropical transition (ET) during landfall in Korea. ET storms that make a landfall approaching 1.22° (~130 km) to the coastline cause substantial damages especially in the west coast and capital area of Korea. The present results suggest that accurate forecasting that also considers ET, and not only intensity and track, is essential for successful disaster risk mitigation.
- 작성자Nam et al.
- 작성일2024.09.04
- 조회수11
- 2023