Asia-Pacific Journal of Atmospheric Sciences最新文献_第8页

Intra-urban Variations of the CO2 Fluxes at the Surface-Atmosphere Interface in the Seoul Metropolitan Area 首尔市区地表大气界面CO_ 2通量的城市内部变化

IF 2.3 4区地球科学

Asia-Pacific Journal of Atmospheric Sciences Pub Date : 2023-04-12 DOI: 10.1007/s13143-023-00324-6

Seon-Ok Hong, Jinwon Kim, Young-Hwa Byun, Jinkyu Hong, Je-Woo Hong, Keunmin Lee, Young-San Park, Sang-Sam Lee, Yeon-Hee Kim

{"title":"Intra-urban Variations of the CO2 Fluxes at the Surface-Atmosphere Interface in the Seoul Metropolitan Area","authors":"Seon-Ok Hong, Jinwon Kim, Young-Hwa Byun, Jinkyu Hong, Je-Woo Hong, Keunmin Lee, Young-San Park, Sang-Sam Lee, Yeon-Hee Kim","doi":"10.1007/s13143-023-00324-6","DOIUrl":"10.1007/s13143-023-00324-6","url":null,"abstract":"<div><p>Severe spatiotemporal heterogeneity of emissions sources and limited measurement networks have been hampering the monitoring and understanding of CO<sub>2</sub> fluxes in large cities, a great concern in climate research as big cities are among the major sources of anthropogenic CO<sub>2</sub> in the climate system. To understand the CO<sub>2</sub> fluxes in Seoul, Korea, CO<sub>2</sub> 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 CO<sub>2</sub> flux variations at the suburban sites are mainly driven by vegetation and that the CO<sub>2</sub> flux differences between the urban and suburban sites originate from the differences in the vegetation-area fraction and anthropogenic CO<sub>2</sub> emissions. For the CO<sub>2</sub> 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 CO<sub>2</sub> 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.</p></div>","PeriodicalId":8556,"journal":{"name":"Asia-Pacific Journal of Atmospheric Sciences","volume":"59 4","pages":"417 - 431"},"PeriodicalIF":2.3,"publicationDate":"2023-04-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s13143-023-00324-6.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47716914","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 1

Cluster Analyses of Tropical Cyclones with Genesis in the South China Sea Based on K-Means Method 基于K-Means方法的南海有成因热带气旋聚类分析

IF 2.3 4区地球科学

Asia-Pacific Journal of Atmospheric Sciences Pub Date : 2023-04-12 DOI: 10.1007/s13143-023-00322-8

Yafeng Yin, Yangyang Yong, Shandong Qi, Kai Yang, Yizhao Lan

{"title":"Cluster Analyses of Tropical Cyclones with Genesis in the South China Sea Based on K-Means Method","authors":"Yafeng Yin, Yangyang Yong, Shandong Qi, Kai Yang, Yizhao Lan","doi":"10.1007/s13143-023-00322-8","DOIUrl":"10.1007/s13143-023-00322-8","url":null,"abstract":"<div><p>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.</p></div>","PeriodicalId":8556,"journal":{"name":"Asia-Pacific Journal of Atmospheric Sciences","volume":"59 4","pages":"433 - 446"},"PeriodicalIF":2.3,"publicationDate":"2023-04-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s13143-023-00322-8.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42237936","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Trends and Spatio-Temporal Variability of Summer Mean and Extreme Precipitation across South Korea for 1973–2022 1973-2022年韩国夏季平均降水量和极端降水量的趋势和时空变异性。

IF 2.3 4区地球科学

Asia-Pacific Journal of Atmospheric Sciences Pub Date : 2023-04-06 DOI: 10.1007/s13143-023-00323-7

Hye-Ryeom Kim, Mincheol Moon, Junghee Yun, Kyung-Ja Ha

{"title":"Trends and Spatio-Temporal Variability of Summer Mean and Extreme Precipitation across South Korea for 1973–2022","authors":"Hye-Ryeom Kim, Mincheol Moon, Junghee Yun, Kyung-Ja Ha","doi":"10.1007/s13143-023-00323-7","DOIUrl":"10.1007/s13143-023-00323-7","url":null,"abstract":"<div><h2>Abstract\u0000</h2><div><p>Climate change has altered the frequency, intensity, and timing of mean and extreme precipitation. Extreme precipitation has caused tremendous socio-economic losses, and severe impacts on human life, livelihood, and ecosystems. In recent years, heavy rainfall events occurred during the boreal summer (June-to-August) frequently and sporadically over South Korea. Given that its severity, a call for an urgent investigation of summer extreme rainfall is needed. Although many previous studies have addressed daily extreme precipitation, hourly extreme rainfall still needs to be thoroughly investigated. Therefore, in this study, we investigated the trends, spatio-temporal variability, and long-term variations in mean and extreme precipitation over South Korea during the boreal summertime using daily and hourly observational data through various analysis methods. During the past 50 years (1973–2022), there has been a notable escalation in maximum hourly precipitation, although the boreal summer mean precipitation has increased only marginally. Regionally, an increase in mean and extreme rainfall occurred in the northern part of the central region and the southern coast of the Korean peninsula. Moreover, the increase in intensity and frequency of extreme precipitation as well as in dry day have contributed more to the total summer precipitation in recent years. Our findings provide scientific insights into the progression of extreme summer precipitation events in South Korea.</p></div></div>","PeriodicalId":8556,"journal":{"name":"Asia-Pacific Journal of Atmospheric Sciences","volume":"59 3","pages":"385 - 398"},"PeriodicalIF":2.3,"publicationDate":"2023-04-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s13143-023-00323-7.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"9705649","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 1

Quantification of The Performance of CMIP6 Models for Dynamic Downscaling in The North Pacific and Northwest Pacific Oceans CMIP6模式对北太平洋和西北太平洋动力降尺度性能的量化

IF 2.3 4区地球科学

Asia-Pacific Journal of Atmospheric Sciences Pub Date : 2023-03-30 DOI: 10.1007/s13143-023-00320-w

Seok-Geun Oh, Bong-Gwan Kim, Yang-Ki Cho, Seok-Woo Son

{"title":"Quantification of The Performance of CMIP6 Models for Dynamic Downscaling in The North Pacific and Northwest Pacific Oceans","authors":"Seok-Geun Oh, Bong-Gwan Kim, Yang-Ki Cho, Seok-Woo Son","doi":"10.1007/s13143-023-00320-w","DOIUrl":"10.1007/s13143-023-00320-w","url":null,"abstract":"<div><p>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.</p></div>","PeriodicalId":8556,"journal":{"name":"Asia-Pacific Journal of Atmospheric Sciences","volume":"59 3","pages":"367 - 383"},"PeriodicalIF":2.3,"publicationDate":"2023-03-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s13143-023-00320-w.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42810838","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Comments on “Numerical Errors in Ice Microphysics Parameterizations and Their Effects on Simulated Regional Climate” 对“冰微物理参数化的数值误差及其对模拟区域气候的影响”一文的评论

IF 2.3 4区地球科学

Asia-Pacific Journal of Atmospheric Sciences Pub Date : 2023-03-29 DOI: 10.1007/s13143-023-00321-9

Song-You Hong, Jimy Dudhia

引用次数: 0

Development of Deep Convolutional Neural Network Ensemble Models for 36-Month ENSO Forecasts 36个月ENSO预测的深度卷积神经网络集成模型的发展

IF 2.2 4区地球科学

Asia-Pacific Journal of Atmospheric Sciences Pub Date : 2023-03-01 DOI: 10.1007/s13143-023-00319-3

Yannic Lops, Yunsoo Choi, Seyedali Mousavinezhad, Ahmed Khan Salman, Delaney L. Nelson, Deveshwar Singh

{"title":"Development of Deep Convolutional Neural Network Ensemble Models for 36-Month ENSO Forecasts","authors":"Yannic Lops, Yunsoo Choi, Seyedali Mousavinezhad, Ahmed Khan Salman, Delaney L. Nelson, Deveshwar Singh","doi":"10.1007/s13143-023-00319-3","DOIUrl":"10.1007/s13143-023-00319-3","url":null,"abstract":"<div><p>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 <i>r</i> 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.</p></div>","PeriodicalId":8556,"journal":{"name":"Asia-Pacific Journal of Atmospheric Sciences","volume":"59 5","pages":"597 - 605"},"PeriodicalIF":2.2,"publicationDate":"2023-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45863112","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Major Decisive Factors of Tropical Cyclone Risk in the Republic of Korea: Intensity, Track, and Extratropical Transition 韩国热带气旋风险的主要决定因素:强度、路径和温带过渡

IF 2.3 4区地球科学

Asia-Pacific Journal of Atmospheric Sciences Pub Date : 2023-02-27 DOI: 10.1007/s13143-023-00318-4

Chaehyeon Chelsea Nam, Doo-Sun R. Park, Chang-Hoi Ho

{"title":"Major Decisive Factors of Tropical Cyclone Risk in the Republic of Korea: Intensity, Track, and Extratropical Transition","authors":"Chaehyeon Chelsea Nam, Doo-Sun R. Park, Chang-Hoi Ho","doi":"10.1007/s13143-023-00318-4","DOIUrl":"10.1007/s13143-023-00318-4","url":null,"abstract":"<div><p>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<sup>−1</sup> 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.</p></div>","PeriodicalId":8556,"journal":{"name":"Asia-Pacific Journal of Atmospheric Sciences","volume":"59 3","pages":"359 - 366"},"PeriodicalIF":2.3,"publicationDate":"2023-02-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42370944","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Extreme Weather and Climate Events: Dynamics, Predictability and Ensemble Simulations 极端天气和气候事件:动力学、可预测性和集合模拟

IF 2.3 4区地球科学

Asia-Pacific Journal of Atmospheric Sciences Pub Date : 2023-02-14 DOI: 10.1007/s13143-023-00317-5

Christian L. E. Franzke, June-Yi Lee, Terence O’Kane, William Merryfield, Xuebin Zhang

引用次数: 1

Preliminary Results of Cloud Seeding Experiments for Air Pollution Reduction in 2020 2020年减少空气污染云播试验初步结果

IF 2.3 4区地球科学

Asia-Pacific Journal of Atmospheric Sciences Pub Date : 2023-02-13 DOI: 10.1007/s13143-023-00315-7

Jung Mo Ku, Ki-Ho Chang, Sanghee Chae, A.-Reum Ko, Yonghun Ro, Woonseon Jung, Chulkyu Lee

{"title":"Preliminary Results of Cloud Seeding Experiments for Air Pollution Reduction in 2020","authors":"Jung Mo Ku, Ki-Ho Chang, Sanghee Chae, A.-Reum Ko, Yonghun Ro, Woonseon Jung, Chulkyu Lee","doi":"10.1007/s13143-023-00315-7","DOIUrl":"10.1007/s13143-023-00315-7","url":null,"abstract":"<div><p>In previous studies, cloud seeding has been primarily used to increase precipitation; however, its use for the purpose of reducing particulate matter concentration has not yet been adequately addressed. In this study, we investigated the effect of cloud seeding on the reduction of fine dust concentration by conducting two airborne experiments in west Korea along the Yellow Sea coast on November 1, 2020. Numerical simulations showed that the seeding material diffused in Seoul, Gyeonggi-do, and Chungcheongnam-do as observed from the prevailing wind direction. We also observed enhanced radar reflectivity in these areas, and analysis of aircraft observation data revealed that the average concentration of cloud, drizzle, and precipitation particles increased after seeding as compared with the observations before and during seeding. Further, the precipitation particles had large diameters after seeding; particularly, PM<sub>10</sub> (particulate matter with size ≤ 10 µm) concentration tended to decrease owing to precipitation in the areas affected by cloud seeding; however, it remained unchanged in the unaffected areas. Although it is necessary to conduct further experiments to obtain more comprehensive results, the findings of this study highlight the possibility of reducing fine dust concentration in the atmosphere via cloud seeding.\u0000</p></div>","PeriodicalId":8556,"journal":{"name":"Asia-Pacific Journal of Atmospheric Sciences","volume":"59 3","pages":"347 - 358"},"PeriodicalIF":2.3,"publicationDate":"2023-02-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s13143-023-00315-7.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46291036","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 1

Evaluation of a CMIP6 Multi-GCM Ensemble for Atmospheric Rivers and Precipitation Over East Asia CMIP6多GCM集合对东亚大气河流和降水的评估

IF 2.3 4区地球科学

Asia-Pacific Journal of Atmospheric Sciences Pub Date : 2023-02-02 DOI: 10.1007/s13143-022-00311-3

Tae-Jun Kim, Jinwon Kim, Chanil Park, Seok-Woo Son, Jin-Uk Kim, Sang-Hoon Kwon, Hyejin Moon, Young-Hwa Byun

{"title":"Evaluation of a CMIP6 Multi-GCM Ensemble for Atmospheric Rivers and Precipitation Over East Asia","authors":"Tae-Jun Kim, Jinwon Kim, Chanil Park, Seok-Woo Son, Jin-Uk Kim, Sang-Hoon Kwon, Hyejin Moon, Young-Hwa Byun","doi":"10.1007/s13143-022-00311-3","DOIUrl":"10.1007/s13143-022-00311-3","url":null,"abstract":"<div><h2>Abstract\u0000</h2><div><p>Atmospheric rivers (ARs) are closely related to water resources and hydrological extremes in East Asia (EA) that has been historically susceptible to extreme hydrological events. Thus, projecting the climate change impact on ARs in EA has become an important research topic. This study evaluates a CMIP6 multi-model ensemble (MME) for the climatology of ARs, AR-related variables and precipitation over EA in the present-day climate by comparing the MME against those from the ECMWF Reanalysis version 5 (ERA5). The MME represents well the seasonal-regional variations of AR frequency as well as the integrated water–vapor transport, precipitable water and precipitation. The most notable biases are the underestimation of these variables over the western North Pacific where ARs are most active. The MME biases vary regionally with the largest (smallest) biases in southern China (Korea-western Japan); the biases in the highly populated and industrialized mid-latitude EA coastal regions, the main region of interest in the climate change study to follow, are below 10% of the ERA5-derived values. The MME represents the seasonal-meridional evolution of ARs and precipitation related to the EA summer monsoon rainfall over the longitudes of the Korean peninsula (124.5E-130.5E), at least qualitatively, despite underestimation of these for June–August over the latitudes of 30 N-40 N, i.e., much of the early summer monsoon season in Korea. Overall, these results suggest that the CMIP6 MME possesses skill acceptable for projecting the climate change impacts on ARs and precipitation over the population and industrial centers in EA.</p></div></div>","PeriodicalId":8556,"journal":{"name":"Asia-Pacific Journal of Atmospheric Sciences","volume":"59 3","pages":"327 - 345"},"PeriodicalIF":2.3,"publicationDate":"2023-02-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49425943","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 2