Atmospheric and Oceanic Science Letters最新文献

This paper documents the westward extension of the summer atmospheric circulation over the North Pacific (NP circulation) around the 1990s and investigates the possible reason, based on the North Pacific index. The NP circulation was centered in the Northeast Pacific during 1961–1983 and in the central North Pacific during 1994–2016. Further results show that the westward movement of the NP circulation was closely linked with an intensification of the relationship between the NP circulation and the previous spring sea surface temperature of the midlatitude North Pacific (SST_NP) after the 1990s. The spring SST_NP anomalies exerted considerable impacts on surface heat flux (i.e., sensible heat flux and latent heat flux) and vertical motion anomalies over the central North Pacific during the following summer, facilitating a westward shift in the summer NP circulation. Additionally, the interannual variability of the sea level pressure over the central North Pacific increased after the 1990s, which was likely a contributing factor to the westward extension of the NP circulation.

摘要

本文研究了20世纪90年代前后夏季北太平洋大气环流 (NP circulation) 向西扩展, 并探讨了其可能的原因. 结果表明, 在1961–1983年期间NP中心主要位于东北太平洋, 而在1994–2016年期间NP中心发生西移, 至北太平洋中部. 进一步分析指出, 90年代以后NP活动中心的西移和春季中纬度北太平洋海温(SST_NP) 与NP关系的加强有关. 春季SST_NP异常通过引起后期夏季北太平洋中部地表热通量(即感热通量和潜热通量)和垂直运动异常, 有利于NP活动中心向西移动. 此外, 20世纪90年代以后, 北太平洋中部海平面气压的年际变率增加, 这可能是NP向西扩展的另一原因.

Based on the impact of large-scale circulation anomalies on sea-ice melting, this paper develops a statistical forecasting model for the seasonal sea-ice early melt onset (EMO) in the Bering Sea using the interannual increment prediction method. The prediction model considers three physically meaningful predictors: the January Beaufort High (P1-H500), the November sea-level pressure (P2-SLP) over eastern Siberia, and the November snow cover over the eastern European Plain (P3-Snowc). P1-H500 can influence the sea surface temperature (SST) anomaly in the Bering Sea through ocean–atmosphere interactions, and this SST anomaly can persist from January to March. Subsequently, it affects the EMO in the Bering Sea. P2-SLP exhibits a close association with the east part of the midlatitude North Pacific SST in November. The colder midlatitude North Pacific SST anomalies, which persist from November until January and February of the following year, will be accompanied by warmer SST anomalies in the Bering Sea, which result in a decreased sea-ice extent and a later-than-usual EMO. The Arctic dipole anomaly in January is one of the ways in which P3-Snowc affects the EMO in the following year. The predicted EMO shows good agreement with the observed EMO in the cross-validation test for 1981–2022, with a temporal correlation coefficient of 0.45, exceeding the 99% confidence level. The prediction accuracy of the prediction model for positive and negative abnormal years of EMO is 60% and 41%, respectively.

摘要

基于大尺度环流异常对海冰消融的影响过程, 本文采用年际增量预测方法研制了白令海季节性海冰早期消融开始日期(EMO)的统计预测模型. 预测模型选取了3个具有明确物理意义的预测因子: 1月波弗特高压, 前期11月东西伯利亚地区海平面气压, 以及11月东欧平原积雪覆盖率. 1月波弗特高压可以通过海气相互作用影响白令海地区海温异常, 该海温异常能够从1月持续到3月, 进而影响白令海EMO. 11月东西伯利亚地区海平面气压与11月至次年2月北太平洋中纬度东部海温密切相关. 伴随着北太平洋中纬度东部冷海温异常的出现, 白令海地区会出现暖海温异常, 进而导致白令海海冰范围减少, EMO较晚. 1月北极偶极子异常是11月东欧平原积雪覆盖率影响次年白令海EMO的桥梁之一. 1981−2022年的交叉检验结果表明: 统计模型对白令海EMO具有较好的预测能力, 预测与观测的EMO之间时间相关系数达到了0.45, 超过了99%的置信水平. 统计模型对白令海EMO正常年份和异常年份的预测准确率分别为60%和41%.

In recent years, the issue of photochemical pollution in the Guangxi region of China has escalated considerably. However, there remains a notable dearth of related research in this area. Peroxyacetyl nitrate (PAN), recognized as a reliable indicator of photochemical pollution, was the focus of our study. This study marks the inaugural observation of PAN levels in Guilin, a renowned world tourist destination situated in a typical karst region, during 1–31 October 2021. Throughout this observation period, the average volume concentration of PAN ranged from 0.087 to 2.559 ppb, which was 3.61 times higher than the South China background site of the Nanling. Combined with meteorological factors and potential source analysis, the causes of a typical high-value PAN process were explored during 24–29 October. The results showed that, during this high-value PAN event, pollution primarily originated from the horizontal transport of polluted air masses and the descent of high-altitude air masses from Hunan Province in the northeast direction. Additionally, the meteorological conditions, including high temperatures, intense radiation, and low humidity, fostered local PAN formation. Notably, traffic emissions emerged as the primary source of PAN's locally generated precursor volatile organic compounds. Furthermore, we estimated the background concentration of O₃ to be approximately 20.347 ppb based on PAN monitoring data, constituting 44.4% of the total O₃ levels in Guilin City. This study offers valuable insights for addressing and mitigating photochemical pollution in southern Chinese cities, while providing a theoretical foundation for regional pollution control efforts.

摘要

桂林是世界著名的地处喀斯特地区的旅游胜地, 其光化学污染问题日益严重.过氧乙酰硝酸酯(PAN)被认为是光化学污染的可靠指标, 也是本研究的重点. 本研究于2021年10月首次观测了桂林的PAN的浓度为0.087–2.559 ppb, 同时探讨了PAN典型高值过程的成因. 此次污染主要来源于东北方向污染气团的水平和高空输送, 同时, 高温, 强辐射和低湿度等气象条件也促进了本地PAN的形成. 本研究同时估算了桂林市的O₃背景浓度为20.347 ppb.这项研究为城市的光化学污染控制工作提供了理论基础.

This study examines the possible impacts of western North Pacific (WNP) monsoon break events on the cross-equatorial flows (CEFs) over the Maritime Continent using daily data from ERA5 for 1979–2020. It reveals that WNP monsoon break events can cause significant weakening of CEF in the both upper and lower troposphere, i.e., weaker southerlies in the lower level and northerlies in the upper level. These CEF anomalies are associated with a baroclinic structure of circulation anomalies over the WNP, consisting of upper-level cyclonic and lower-level anticyclonic anomalies. Furthermore, statistical analysis indicates that WNP monsoon break events correspond more closely to weakening of upper-level CEF, in comparison with lower-level CEF: 92% of WNP monsoon break events correspond to upper-level CEF weakening, while this decreases to 70% for lower-level CEF. This relatively lower proportion for lower-level CEF is largely attributable to the impact of the warm phase of ENSO.

摘要

本文利用ERA5逐日再分析资料, 探讨了1979–2020年间西北太平洋季风中断事件对海洋性大陆越赤道气流的影响. 合成结果表明, 西北太平洋季风中断事件会造成高, 低空越赤道气流减弱, 即高层南风异常, 低层北风异常, 与此相关的环流异常表现为西北太平洋高层气旋, 低层反气旋的斜压结构. 特别的是, 西北太平洋季风中断对高空越赤道气流的影响更为显著, 92%的季风中断事件都导致高空越赤道气流减弱, 而只有70%的事件造成低空越赤道气流减弱, 这是由于低空越赤道气流同时还受到赤道中东太平洋海温异常的调控.

Net ecosystem production (NEP) over northern latitudes has an obvious seasonal variation, which dominantly drives the seasonal variation in atmospheric CO₂. Investigating these carbon processes and understanding the underlying drivers is a key issue of climate research. This study focuses on the seasonal amplitude of northern NEP (40°–90°N) and investigates its trend in the period 1990–2014 by using the dynamic global vegetation model (IAP DGVM) in the second version of the Chinese Academy of Sciences Earth System Model (CAS-ESM2). Basing on a spin-up simulation, the authors conduct a control simulation to evaluate the modeled trend in the seasonal amplitude of northern NEP, and three sensitivity simulations to detect the contributions of the climate and atmospheric CO₂. The results show that the modeled seasonal amplitude of northern NEP increases significantly from 1990 to 2014, with a trend of 9.69 TgC month⁻¹ yr⁻¹, which is mainly because of the increasing maximum NEP. The positive trend is largely reduced when CO₂ fertilization effects and climatic effects are separately excluded. These significant reductions suggest important effects of atmospheric CO₂ and climate change on the seasonal amplitude of northern NEP. Even though model uncertainties remain, the results favor further development of IAP DGVM in accurately simulating the terrestrial carbon cycle, and also provide an important reference for the application of CAS-ESM in further investigating carbon–climate interactions.

摘要

北方陆地净生态系统生产力(NEP)具有明显的季节变化特征, 这是大气CO₂季节变化的关键驱动. 研究这些碳循环过程并理解潜在的驱动因素是气候研究的一个关键问题. 本文利用第二代中国科学院地球系统模式(CAS-ESM2)中的全球植被动态模型(IAP DGVM), 研究了1990−2014年北方NEP(40°−90°N)的季节振幅及其变化趋势. 在初始化试验的基础上, 本文开展了一个控制试验来评估模拟的北方NEP季节幅度的变化趋势, 同时开展了三个敏感性试验来研究气候和大气CO₂的贡献. 结果表明: 1990−2014年, 模拟的北方NEP季节振幅显著增加, 趋势为9.69 万吨碳/月/年, 这主要是由于最大NEP增加所致. 当分别排除CO₂施肥效应和气候效应时, 上述增加趋势大大减弱.这些显著的减少表明大气CO₂和气候变化对北方NEP的季节性振幅有重要影响. 尽管模式存在不确定性, 但这些结果有利于进一步提升IAP DGVM对陆地碳循环的精确模拟, 也为CAS-ESM研究碳-气候相互作用的应用提供了重要参考.

A comprehensive understanding of energy and water cycle characteristics in different regions is crucial for studying local land–atmosphere interactions and predicting regional weather and climate change. To explore similarities and differences in land–atmosphere energy and water exchanges between two regions—the Tibetan Plateau (TP), characterized by higher elevation and a drier climate, and the Yangtze River Region (YRR), with lower elevation and a wetter climate—this study analyzed and compared the radiation components and the turbulent heat fluxes at eight sites covering various land-cover types, including alpine desert and alpine grassland on the TP, as well as urban and grassland on the YRR. The following results were obtained: (1) Over the TP, the annual mean incoming and outgoing shortwave radiation are 251.3 and 59.6 W m⁻², which are 1.70 and 2.87 times the values in the YRR, respectively. The incoming and outgoing longwave radiation are 231.5 and 338.0 W m⁻², which are 0.64 and 0.83 times those in the YRR, respectively. However, the difference in net radiation is relatively small. (2) In grassland over both the TP and YRR, the latent heat fluxes have higher values of 35.0 and 38.8 W m⁻², respectively, leading to a higher heating efficiency. Alpine desert has the highest sensible heat flux (SH) value of 42.1 W m⁻², due to sparse vegetation and lower soil moisture, followed closely by urban land cover with an average SH value of 38.2 W m⁻². These results highlight the different characteristics of land–atmosphere interaction across different land covers in different climatic contexts, laying the groundwork for future investigations of additional land–atmosphere coupling processes.

摘要

正确认识不同区域能量和水分循环特征是研究局地地气相互作用及准确预测区域天气, 气候变化的关键. 为了研究属于干旱/半干旱气候的青藏高原 (TP) 和湿润/半湿润气候的长江流域 (YRR) 之间地表能量和水分交换的异同, 本文对比分析了两个区域8个不同地表类型 (包括高山荒漠, 高山草地, (平原) 城市和 (平原) 草地等) 观测站点的地表辐射和能量通量数据. 结果显示: (1) TP由于高原大气层稀薄且空气洁净, 年平均入射短波辐射为251.3 W m⁻², 是YRR的1.7倍. 加之高原地表反照率高导致反射辐射 (59.6 W m⁻²⁾ 是YRR的2.87倍. 入射及出射的长波辐射为231.5和338.0 W m⁻², 分别为YRR的0.64和0.83. 而两个区域的净辐射差异不大; (2) 草地站更多的潜热释放使得地表总加热效率高于城市和高山荒漠, TP和YRR的草地站的年平均潜热分别为35.0 和 38.8 W m⁻², 而植被稀疏且土壤干燥的高山荒漠地区感热最大, 年平均感热为42.1 W m⁻²; 其次是城市下垫面, 其年平均感热为37.7 W m⁻². 研究结果揭示了不同气候背景下典型下垫面地气相互作用特征, 为地气相互作用过程深入分析奠定了基础.

In 2022, eastern China was wet in the north and dry in the south, and characterized particularly by a persistent compound extreme event with high temperatures, low precipitation, and dry soil during the warm season. Here, the authors investigate the evolution and possible underlying mechanism of this compound extreme event. From May to September in eastern China, there was a clear climate pattern transition from north to south, with noticeable intraseasonal changes in temperature, precipitation, and soil moisture. Different from the long-term climatology of 1940–2022, an enhanced influence of soil moisture on evaporation occurred in the Yangtze River Valley and Southeast China in 2022. These regions, however, are typically where evapotranspiration is limited by the land-surface available energy. Strong feedback between soil moisture and climate elements may have played a crucial role in the evolution and persistence of extreme climate events during the warm season in 2022.

摘要

2022年暖季, 中国东部地区遭受持续性高温, 少雨和土壤干旱的复合极端事件. 特征分析指出, 在研究时段内, 中国东部地区的气温, 降水和土壤湿度呈现明显的季节内变化和南北差异. 由1940–2022年的气候态可知, 长江流域和东南地区的土壤含水充足, 蒸散主要受限于陆面有效能量. 然而, 潜在机制研究指出, 2022年土壤湿度对蒸散的限制作用在上述区域异常偏强. 土壤湿度与气候要素之间的强反馈可能在2022年复合极端事件的演变和持续中发挥了关键作用.

This paper assesses the performance of 20 CMIP6 models in simulating the relationship between spring Arctic Oscillation (AO) and summer precipitation in the Yangtze River valley (YRP) over the period 1980–2014. Their relationship during 2015–2100 under SSP2-4.5 is also projected. The assessment indicates that four models (ACCESS-ESM1-5, CMC-CM2-SR5, MRI-ESM2-0, and NorESM2-LM) can reasonably simulate the observed interdecadal weakening of the AO–YRP connection in the late 1990s. During 1980–1998, corresponding to the positive phase of spring AO, the East Asian jet (EAJ) shifts northward in summer, favoring descending anomalies over the Yangtze River valley. Meanwhile, the western Pacific subtropical high is weaker than normal and anomalous northeasterlies prevail in the lower troposphere of the Yangtze River valley, reducing the water vapor transport to the target region. These situations are unfavorable for the occurrence of precipitation, consequently resulting in a decrease in summer YRP. During 1999–2014, however, the association of the above atmospheric circulations with spring AO becomes insignificant, thus diluting the AO–YRP connection. The ensemble of the four models projects that the significant out-of-phase relationship between spring AO and summer YRP will recover in the near term (2015–2040) and weaken again afterwards. Such projected relationships are supported by the changes in the linkage of summer atmospheric circulations to spring AO.

摘要

评估了20个CMIP6模式对春季北极涛动 (AO) 与长江流域夏季降水 (YRP) 关系的模拟能力. 结果表明, 4个模式 (ACCESS-ESM1-5, CMC-CM2-SR5, MRI-ESM2-0, NorESM2-LM)) 能合理模拟出1990年代后期AO–YRP关系的减弱. 1980–1998年, 当春季AO位于正位相时, 夏季东亚急流北移, 长江流域为异常下沉运动, 同时西太平洋副热带高压减弱, 减少向长江流域的水汽输送, 结果导致降水减少. 1999–2014年, 上述大气环流与春季AO的联系不显著, 从而减弱AO–YRP的关系. 利用这四个模式进一步预估了RCP4.5情景下2015–2100年期间AO–YRP的关系. 两者在2015–2040年为显著负相关关系, 随后再次减弱.

Given the inherent imperfections in models and the inevitability of initial condition errors, subseasonal prediction ability faces ongoing limitations. Most international numerical models employ ensemble forecasts to enhance the accuracy of subseasonal prediction. The prediction skill for the Madden–Julian Oscillation (MJO), as a vital source of subseasonal predictability, depends on both model performance and the physical nature of the events. Based on the reforecast results of the CAMS-CSM subseasonal prediction system, the differences in MJO prediction skill among ensemble members are classified and compared together with the characteristics of different kinds of MJO events. In the category with generally high ensemble member prediction skill, MJO events often have extended durations, stronger intensities, and the intense convection primarily locates in the Indian Ocean, gradually shifting eastward to the western Pacific. In the category with mostly poor ensemble member prediction skill, the convection strength during MJO event propagation is weakest. In the category with mixed prediction skill among ensemble members, MJO events tend to have shorter durations and lower intensities, and the convection centers during subsequent propagation exhibit stationary characteristics over Maritime Continent regions.

摘要

由于模式误差和初始误差所致, 次季节-季节预报技巧整体偏低. 国际上多数模式都采用集合预报的方式来提高次季节预报的准确率. 热带大气季节内振荡 (MJO) 作为次季节尺度可预报性的重要来源, 其预测水平取决于模式性能和MJO事件本身的物理特性. 根据中国气象科学研究院气候系统模式次季节预测系统的回报结果, 结合不同类型MJO事件的特征, 对模式集合成员间的预报技巧进行了分类和比较. 在集合成员预报技巧普遍较高的一类MJO事件中, 对流异常信号持续时间较长, 强度较大, 强对流异常中心主要位于印度洋区域, 并逐渐东传至西太平洋. 在集合成员预报技巧多数较差的MJO事件中, 对流异常信号的强度最弱, 维持时间最短. 在集合成员预报技巧优劣参半的类别中, MJO往往持续时间较短, 强度较低, 在后续传播过程中, 对流异常中心多停驻在海洋性大陆区域.

How extreme weather and climate events change is an intriguing issue under global warming. By investigating the frequency of extreme cold events (Frexces) in winter over North China (NC), this paper presents robust interdecadal changes in Frexces in NC since the late 1980s. Two shift points are detected at about 2003 and 2013 through a Mann–Kendall test. Three periods are then identified as 1989–2002 (P1), 2003–2012 (P2), and 2013–2021 (P3). Frexces increases from P1 to P2 and then decreases from P2 to P3. Correspondingly, the winter mean Siberian–Ural High (SUH), polar jet stream (PJS), and North Atlantic Oscillation (NAO) show interdecadal changes. The winter SUH gets stronger and the PJS and NAO weaker during P2, while the SUH is weakened and the PJS and NAO strengthened in P3. The stronger SUH and weaker PJS is favourable for cold-air intrusion into NC in P2, and the opposite is true for the weaker SUH and stronger PJS in P1 and P3. The weaker NAO in P2 relates to long-distance wave propagation to Eurasia to strengthen the SUH, while wave activity accompanying the stronger NAO in P3 is confined to western Eurasia. For the all-extreme cold events composite, the area affected by the cold air inducing extreme cold events in NC enlarges northwestward to the West Siberian Plain, and the intensity of the cold air also gets strengthened from P1 to P3.

摘要

全球变暖背景下, 极端天气气候事件的变化受到关注. 本文研究发现, 1989–2021年期间, 华北地区极端冷日数在2003和2013年发生了年代际变化. 极端冷日数先增加后减少. 2003–2012年, 西伯利亚–乌拉尔高压偏强, 极地西风急流偏弱, 有利于冷空气南下入侵华北地区, 华北极端冷日数偏多. 而在1989–2002年和2013–2021年, 情况相反. 虽然三个时段华北极端冷日的强度没有显著差异, 但与其相联系的冷空气强度变得更强, 2013–2021年冷空气中心区域往西北扩张到了贝加尔湖以西地区.