Atmospheric and Oceanic Science Letters最新文献

Previous studies have demonstrated that boreal summer intraseasonal oscillation (BSISO) active in the Indian Ocean can affect precipitation over the Yangtze River Valley (YRV). In this study, the impacts of three types of BSISO modes on precipitation over the YRV were investigated and found to vary significantly. First, moisture budget analysis indicated that the process responsible for the precipitation anomalies in all BSISO modes is moisture convergence, while moisture advection is insignificant. In the canonical mode, precipitation anomalies are negative (positive) at pentad −2 (−1 to 3) owing to a BSISO-related cyclone over the northwestern Pacific (anticyclone moving from the subtropical western to northwestern Pacific) accompanied by enhanced (suppressed) convection propagating northeastward. Comparatively, in the eastward expansion mode, precipitation anomalies are positive (negative) at pentad −2 to 0 (1 to 3) via a BSISO-related anticyclonic (cyclonic) circulation over the northwestern Pacific induced by the teleconnection effect of enhanced (suppressed) convection over the Indian Ocean. Different from the previous two BSISO modes, in the northward dipole mode, precipitation anomalies are negative (positive) at pentad −2 to 0 (1 to 3) owing to a BSISO-related cyclonic (anticyclonic) circulation, which moves from the South China Sea to the northwestern Pacific because of the propagation of enhanced (suppressed) convection.

The contribution of the tropical sea surface temperature in the Arctic tropospheric warming during 1979–2013 was studied through simulations using the CAM6-Nor atmospheric general circulation model. Results showed that the tropical sea surface temperature explained about 30%–40% of the autumn warming and the January warming in the historical simulation. This implies that the tropical sea surface temperature could have been one of the main drivers of Arctic winter tropospheric warming between 1979 and 2013. The tropical sea surface temperature impacts generally came from a combination of the effects of the tropical central-eastern Pacific, the tropical Indo-western Pacific, and the tropical Atlantic, except for the January warming below 850 hPa, which was dominated by the tropical Indo-western Pacific impacts.

The Last Interglacial (LIG), with its many reconstructions and simulations, provides an ideal analog for investigating the future warmer climate. However, there has been a persistent mismatch between simulated and reconstructed LIG climates in East Asia, with simulations generally indicating a colder and drier climate than reconstructions. In this study, utilizing the Norwegian Earth System Model (NorESM1-F), the authors investigated whether incorporating the global mean sea-level rise in LIG simulation experiments can reduce the model–data mismatch. The new experiments reveal a discernible, yet insufficient, warming and wetting effect in East Asia resulting from the sea-level rise. Therefore, the model–data mismatch remains unresolved. Based on these results, the authors explore alternative factors that may contribute to this mismatch, offering insights for future studies.

In the past 60 years, the global climate has undergone both rapid warming and a brief warming hiatus, while regional precipitation patterns in China have also experienced diverse and complex changes. Specifically, the factors behind the opposing trends in summer precipitation between two adjacent regions—Southwest China and the Qinghai–Tibet Plateau—are particularly intricate. After evaluating the historical runs from CMIP6 models, the authors assessed the contributions of various external forcing factors that simulated the summer precipitation trends observed over the Qinghai–Tibet Plateau and Southwest China from 1961 to 2014. The findings show that, compared to other forcing factors, greenhouse gases had a significant impact on the increase in summer precipitation over the Qinghai–Tibet Plateau, while aerosols played an important role in the decrease in summer precipitation in Southwest China.

摘要

在过去的60年中, 全球气候经历了快速变暖和短暂的变暖停滞, 而中国的区域降水也经历了多样而复杂的变化. 本文分析了1961年至2014年外强迫因子对青藏高原和中国西南地区夏季降水趋势的影响. 观测数据显示, 青藏高原的夏季降水呈增加趋势, 而中国西南地区的夏季降水呈减少趋势, 这两个相邻地区的夏季降水变化趋势相反. 利用CMIP6数据, 本文研究了不同外强迫因子对两个区域夏季降水趋势的影响. 结果表明, 温室气体对青藏高原夏季降水的增加具有显著影响, 而气溶胶在中国西南地区夏季降水减少中起主要作用.

A distinct characteristic of the Arctic summer atmospheric circulation is the anomalous anticyclonic circulation centered over the Arctic Ocean associated with significant Arctic warming. Previous studies have related the underlying mechanisms to the earlier spring Eurasian snowmelt and the tropical Pacific forcing. Here, the authors show that the Arctic summer anomalous anticyclonic circulation is significantly related to the extratropical North Pacific sea surface temperature anomalies (SSTAs) in spring, indicating a teleconnection from the extratropical North Pacific to the Arctic. The SSTA pattern is characterized by warm anomalies in the midlatitudes of the extratropical North Pacific surrounded by significant cold anomalies, resembling the negative phase of the Pacific Decadal Oscillation (PDO) but without significant signals in the tropics (referred to as the negative PDO-like pattern). This negative PDO-like pattern in May can stimulate a Rossby wave propagating from the Bering Sea to the Arctic and lead to an anomalous Arctic anticyclone which can be sustained during summer. Meanwhile, the negative PDO-like pattern can persist to summer and induce an anomalous surface low pressure over the Bering Sea in summer. This anomalous surface low causes anomalous rising motions and induces upper-level divergence anomalies which further intensify the summer Arctic anticyclone. The upper-level tropospheric Arctic anticyclone can force anomalous adiabatic descent over the Arctic and sub-Arctic, leading to significant adiabatic heating in the Arctic. As a result, a significant warming emerges over the Arctic with the center located in the middle troposphere. The connection between the negative PDO-like SSTAs and the summer Arctic anticyclone has been confirmed by numerical experiments.

Inter-monthly winter temperature variation in East Asia has been remarkable in recent years, showing reversed or alternating extreme cold and extreme warm events in different months or in different stages of the winter. There are many challenges in climate prediction in the winter months because the inter-monthly climate variation is often within the seasonal mean variation. It is therefore urgent to understand the variation of inter-monthly winter temperatures in East Asia, to identify their predictability and predictive sources, and to propose effective prediction methods and prediction models for the inter-monthly winter climate. This paper reviews progress in research during the last five years on the main characteristics, physical processes, mechanisms, predictability, and prediction of inter-monthly winter temperatures in East Asia, considering several related systems including the winter monsoon, Siberian high, and stratospheric polar vortex. The authors also discuss future research prospects.

摘要

近年来, 东亚冬季气温的月际间变化十分显著, 冬季不同月份或不同阶段之间极端冷暖事件的转折或交替频发. 由于月际间变化常常被季节平均掩盖, 东亚冬季气候预测面临众多的挑战. 因此, 亟需研究东亚冬季气温月际间变化的特征和机理, 明确其可预测性和预测来源, 进而研制考虑月际变化的东亚冬季气温的有效预测方法和预测模型. 本文回顾了过去5年对东亚冬季气温月际间变化的主要特征, 物理过程, 机制, 可预测性和预测的研究进展, 同时考虑了多个与气温相联系统的变化, 包括冬季风, 西伯利亚高压, 平流层极涡. 本文也进一步讨论了未来的研究前景.

Based on Japanese 55-year daily reanalysis data, the present study reveals that a strong Siberian high (SH) is preceded by three teleconnection patterns—namely, the Scandinavian (SCA) pattern, western Pacific (WP) pattern, and Polar/Eurasian (POL) pattern. Accordingly, strong SH events are classified into three types. Composite results show that there are evident differences among the three types in their typical circulation characteristics and impacts on surface air temperature (SAT) in East Asia. The SCA type is characterized by a wave-train anomaly over mid- and high-latitude Eurasia, while the WP type is characterized by a western expansion of circulation anomalies from the downstream western North Pacific/Far East. The significant signal of the POL type is a gradual southward movement of anticyclonic anomalies from the North Pole. In terms of the impact on SAT in East Asia, the SCA type and POL type are similar since they can cause a wide range of cold anomalies in East Asia. However, the cold anomalies caused by the POL type in northern China show significant signals earlier. The WP type causes only modest cold anomalies over northern and eastern China, but the persistence of SAT anomalies is obvious.

摘要

本文利用日本55年逐日再分析资料, 发现在SH异常增强前, 有三种不同的大气遥相关型前兆信号, 即斯堪的纳维亚 (SCA) 型, 西太平洋 (WP) 型, 极地-欧亚 (POL) 型. 据此, 本文将异常增强的SH分为对应的三类事件. 合成结果表明, 三类事件在典型环流特征和对东亚气温的影响上存在着明显的不同. 具体而言, SCA类事件主要表现为在欧亚中高纬度上自西向东的波列异常, WP类事件表现为环流异常自下游太平洋/俄罗斯远东地区向西发展的特征, POL型事件的显著信号则来源于自极区向南移动的反气旋式环流异常. 在对东亚地表气温的影响上, SCA类与POL类事件类似, 它们均可造成大范围的低温异常. 而WP类仅在我国北方和东部地区造成强度较弱的地表气温异常, 但该异常的持续性特征较明显.

Wind substantially impacts human activity and electricity generation. Thus, accurately forecasting the short-term wind speed is of profound societal and economic significance. Based on 100 weather stations in eastern China, the authors first evaluate the performance of the 10-m wind forecast products from five operational forecast models. Among them, the Japan Meteorological Agency (JMA) model performs best in reducing the forecasting errors. Then, the authors establish a 10-m wind speed multimodel ensemble forecast based on the five numerical models’ outputs and machine learning methods, combining dynamic and statistical methods. Feature engineering and machine learning algorithm optimization are conducted for each site separately. The forecast performance of this method is compared to the JMA model and multimodel ensemble forecast by ridge regression at lead times of 24–96 h. The results demonstrate that the multimodel ensemble method based on machine learning optimization can reduce the forecast error of JMA by more than 39%, and the improvement in forecast skill is most evident in November. In addition, it performs better than the ensemble forecast by ridge regression.

The tropical easterly jet (TEJ) is an easterly jet stream that occurs from the upper troposphere to lower stratosphere in boreal summer. Owing to its wide vertical extension from 300 to 70 hPa, the TEJ may exhibit distinct characteristics at different levels, the details of which remain thus far unclear. In this study, two empirical orthogonal function (EOF) modes of the year-to-year variability in the vertical structure of the TEJ were investigated. The leading EOF mode represents a consistent strengthening or weakening of the TEJ's main body in the vertical direction and varies on both interannual and interdecadal time scales. It has been suggested that ENSO can modulate this vertically consistent mode interannually, whereas the Atlantic Multidecadal Oscillation and Pacific Decadal Oscillation can influence its interdecadal variability. In contrast, the second EOF mode exhibits an out-of-phase relationship between the zonal wind anomalies of the upper troposphere and lower stratosphere, linked with the changes in the TEJ's vertical movement and dominating on the quasi-biennial time scale. The Quasi-Biennial Oscillation could contribute to variations in the TEJ's vertical movement by changing the tropopause winds as a direct pathway and inducing anomalous convection over the tropical Indian Ocean and Maritime Continent as an indirect pathway.