Asia-Pacific Journal of Atmospheric Sciences最新文献

During Octobers of 1970–2019, no tropical cyclones (TCs) affected Taiwan in 32 out of 50 years (64%). Suppressed TC activity in these years results from different modulating processes imposed by various climatic features. During Octobers of El Niño years, TC genesis in the western North Pacific (WNP) shifts eastward and decreases in the western WNP to the southeast of Taiwan. An anomalous anticyclone across the South China Sea (SCS) and Taiwan hinders TC movement toward Taiwan. In La Niña years, TC genesis increases in the region southeast of Taiwan. These TCs are guided by an anomalous cyclone centering in the SCS to have major TC tracks to the southwest of Taiwan toward the SCS. A year with a September–November value on the Oceanic Niño Index (ONI) of between 0°-0.5 °C (-0.5°-0 °C) is categorized as a positive (negative) Normal year. During the positive Normal years, an anomalous cyclone over the WNP enhances TC genesis in its southern section and guides these TCs northward along the regions east of Taiwan. An anomalous anticyclone across the SCS and Taiwan hinders TC movement toward Taiwan. During the negative Normal years, a westward elongation of warm sea surface temperature anomalies from the WNP into the eastern Indian Ocean forces an anomalous anticyclone to extend westward from the WNP toward the SCS. TC genesis to the south of this anomalous anticyclone decreases and is accompanied by reduced TC movement toward Taiwan.

Increasing heatwave frequency due to climate change threatens outdoor workers’ health. We aimed to assess the on-site heat strain level of outdoor workers using wearable sensors and identify the factors for consideration in developing individual-based heat adaptation strategies. Seven road construction workers were recruited and asked to wear necklace-form temperature loggers and smartwatches monitoring heart rate (HR). The questionnaire was delivered daily to ask about their psychological comfort level during work. Workers were exposed to up to 5.4 °C higher temperature than the official air temperature, indicating that the national heatwave alarm does not reflect on-site heat conditions. Based on the measured HR data, heat strain levels were defined. When HR exceeded the level of “180-age,” we assumed extreme heat strain occurred, which requires immediate cessation of work. When HR exceeded 40% of the individual heart rate reserve (the difference between the maximum and resting HR), we assumed high heat strain occurred, indicating a stressed condition. High heat strain occurred in all workers on 9 of the 13 monitored days, whereas the official heatwave alarms were issued only on four dates. Additionally, three workers experienced extreme heat strain on two dates. The main factor for workers experiencing extreme heat strain was age. Comparing the heat strain levels from HR with the survey results, we found that the older workers considered their condition comfortable even under extreme and high heat strain. Thus, an individual sensor-based early-warning system is needed to prevent heat strain not perceived by outdoor workers. The findings emphasize the need for a personalized adaptation strategy for heatwaves and will be a baseline for developing a new work manual that mainstreams climate change impacts.

Synoptic-scale weather systems play dominant roles in inducing high tropospheric dust over the Tibetan Plateau (TP). However, few studies have summarized the typical synoptic-scale weather patterns when high tropospheric dust occurs over the TP, as well as the difference between the distribution and transport methods of dust under weather patterns. Based on dust optical depth (DOD) from remote sensing data and reanalysis data during 2000 to 2019, two typical synoptic-scale weather patterns (T1 and T2) in the middle troposphere in association with high DOD in spring over the TP were obtained by using the self-organizing map (SOM) clustering method. The results show that the T1 features a deep trough over the Altai Mountains and the westerly wind increases over the TP. As a result, dust is transported from the Taklimakan Desert and Qaidam Basin to the upper troposphere and extends to the TP and northern China. T2 shows a low-pressure system over the western TP and decreased westerly winds over the TP, resulting in dust from the Taklimakan Desert, Qaidam Basin, and western TP to downstream areas. T1 (T2) contributes more to DOD over the eastern (western) TP. Therefore, we believe that a small increase (decrease) in DOD in the western (eastern) part of the TP from 2000 to 2019 may be related to an increase (decrease) in the occurrence of the T2 (T1). This work may provide a new possibility for projecting dust transport and its influence on tropospheric dust over the TP.

Severe spatiotemporal heterogeneity of emissions sources and limited measurement networks have been hampering the monitoring and understanding of CO₂ fluxes in large cities, a great concern in climate research as big cities are among the major sources of anthropogenic CO₂ in the climate system. To understand the CO₂ fluxes in Seoul, Korea, CO₂ fluxes at eight surface energy balance sites, six urban (vegetation-area fraction < 15%) and two suburban (vegetation-area fraction > 60%), for 2017–2018 are analyzed and attributed to the local land-use and business types. The analyses show that the CO₂ flux variations at the suburban sites are mainly driven by vegetation and that the CO₂ flux differences between the urban and suburban sites originate from the differences in the vegetation-area fraction and anthropogenic CO₂ emissions. For the CO₂ fluxes at the urban sites; (1) vehicle traffic (traffic) and heating-fuel consumption (heating) contribute > 80% to the total, (2) vegetation effects are minimal, (3) the seasonal cycle is driven mainly by heating, (4) the contribution of heating is positively related to the building-area fraction, (5) the annual total is positively (negatively) correlated with the commercial-area (residential-area) fraction, and (6) the traffic at the commercial sites depend further on the main business types to induce distinct CO₂ flux weekly cycles. This study shows that understanding and estimation of CO2 fluxes in large urban areas require careful site selections and analyses based on detailed consideration of the land-use and business types refined beyond the single representative land-use type widely-used in contemporary studies.

Tropical cyclone (TC) with genesis in the South China Sea (SCS) has been a major concern because of their high landfall frequency and associated serious hazards to the surrounding coastal areas. The classification of TCs from records of historical tracks is an important way to obtain their characteristics and to help predict their future behavior. According to the generation location, intensity, direction, and track length of TC, TCs with genesis in the SCS from 1950 to 2020 are classified into four clusters by the K-means clustering method, including northwestward track cluster A, westward track cluster C and two long northeastward track clusters B and D. The landfall probability, peak season, climate trend, lifespan, maximum wind speed, and power dissipation index show a significant distinction for each cluster. All clusters had a landfall probability exceeding 50%, with the highest probability in cluster A (90.44%), followed by cluster C, cluster B, and cluster D with the lowest probability (54.55%). The clustering results indicate that tracks of TCs are strongly affected by the distribution pattern of the Western Pacific Subtropical High. When the WPSH moves southward, the southwesterly anomalies provide a significantly favorable steering flow for TC northeastward. Conversely, the WPSH located northward in July-September, the strong southeasterly anomaly favoring the northwestward movement of TC. From October to November, the WPSH shrinking in size gives way to the prevailing anomalous easterlies that steer the TCs westward. Further concerning the influence of TCs in the different clusters by the WPSH movement will be helpful for prediction in terms of the occurrence, track and landfall probability of TCs in the SCS.

Abstract

Selecting a reliable global climate model as the driving forcing in simulations with dynamic downscaling is critical for obtaining a reliable regional ocean climate. With respect to their accuracy in providing physical quantities and long-term trends, we quantify the performances of 17 models from the Coupled Model Inter-comparison Project Phase 6 (CMIP6) over the North Pacific (NP) and Northwest Pacific (NWP) oceans for 1979–2014. Based on normalized evaluation measures, each model’s performance for a physical quantity is mainly quantified by the performance score (PS), which ranges from 0 to 100. Overall, the CMIP6 models reasonably reproduce the physical quantities of the driving variables and the warming ocean heat content and temperature trends. However, their performances significantly depend on the variables and region analyzed. The EC-Earth-Veg and CNRM-CM6-1 models show the best performances for the NP and NWP oceans, respectively, with the highest PS values of 85.89 and 76.97, respectively. The EC-Earth3 model series are less sensitive to the driving variables in the NP ocean, as reflected in their PS. The model performance is significantly dependent on the driving variables in the NWP ocean. Nevertheless, providing a better physical quantity does not correlate with a better performance for trend. However, MRI-ESM2-0 model shows a high performance for the physical quantity in the NWP ocean with warming trends similar to references, and it could thus be used as an appropriate driving forcing in dynamic downscaling of this ocean. This study provides objective information for studies involving dynamic downscaling of the NP and NWP oceans.

Abstract

The state of the El Niño-Southern Oscillation (ENSO) has chaotic yet deterministic seasonal patterns and inter-annual fluctuations over the equatorial Pacific Ocean. ENSO has impacts and global teleconnections on regional temperature, precipitation, and mid-tropospheric atmospheric circulation and has been used as a predictor of regional weather. Despite being developed over several decades, dynamical and statistical models are still unable to reliably predict seasonal ENSO. This paper presents the unique utilization of several deep convolutional neural networks, identified preferable model parameters, and an optimized ensemble output to extend the ENSO forecast by up to 36 months in advance. While individual models performed differently depending on the forecasting lead month, the ensemble output is the only model that produces a correlation of 0.52 with an index of agreement of 0.60 for the 36th month forecast, a 4% and 7% improvement in the cumulative index of agreement and r score, respectively, over the best single model. The results demonstrate the moderate ENSO forecasting capability of the system and the next step in extending the prediction lead time to previous generations of ENSO forecasting models.

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.