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2023 Vol. 40, No. 9

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News & Views
Mongolia Contributed More than 42% of the Dust Concentrations in Northern China in March and April 2023
Siyu CHEN, Dan ZHAO, Jianping HUANG, Jiaqi HE, Yu CHEN, Junyan CHEN, Hongru BI, Gaotong LOU, Shikang DU, Yue ZHANG, Fan YANG
2023, 40(9): 1549-1557. doi: 10.1007/s00376-023-3062-1
Dust storms are one of the most frequent meteorological disasters in China, endangering agricultural production, transportation, air quality, and the safety of people’s lives and property. Against the backdrop of climate change, Mongolia’s contribution to China’s dust cannot be ignored in recent years. In this study, we used the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem), along with dynamic dust sources and the HYSPLIT model, to analyze the contributions of different dust sources to dust concentrations in northern China in March and April 2023. The results show that the frequency of dust storms in 2023 was the highest observed in the past decade. Mongolia and the Taklimakan Desert were identified as two main dust sources contributing to northern China. Specifically, Mongolia contributed more than 42% of dust, while the Taklimakan Desert accounted for 26%. A cold high-pressure center, a cold front, and a Mongolian cyclone resulted in the transport of dust aerosols from Mongolia and the Taklimakan Desert to northern China, where they affected most parts of the region. Moreover, two machine learning methods [the XGBoost algorithm and the Synthetic Minority Oversampling Technique (SMOTE)] were used to forecast the dust storms in March 2023, based on ground observations and WRF-Chem simulations over East Asia. XGBoost-SMOTE performed well in predicting hourly PM10 concentrations in China in March 2023, with a mean absolute error of 33.8 μg m−3 and RMSE of 54.2 μg m−3.
Super Typhoon Hinnamnor (2022) with a Record-Breaking Lifespan over the Western North Pacific
Qian WANG, Dajun ZHAO, Yihong DUAN, Shoude GUAN, Lin DONG, Hongxiong XU, Hui WANG
2023, 40(9): 1558-1566. doi: 10.1007/s00376-023-2336-y
Super Typhoon Hinnamnor (2022) was a rare and unique western North Pacific typhoon, and throughout its lifespan, it exhibited all of the major features that pose current challenges in typhoon research. Specifically, during different stages of its lifespan, it experienced a sudden change of track, underwent rapid intensification, interacted and merged with another vortex, expanded in size, underwent rapid weakening, produced a strong cold wake, exhibited eyewall replacement, and underwent extratropical transition. Therefore, a timely identification and review of these features of Hinnamnor (2022), as reported in this article, will help update and enrich the case sets for each of these scientific issues and provide a background for more in-depth mechanistic studies of typhoon track, intensity, and structural changes in the future. We also believe that Hinnamnor (2022) can serve as an excellent benchmark to quickly evaluate the overall performance of different numerical models in predicting typhoon’s track, intensity, and structural changes.
Original Paper
Rainfall Monitoring Using a Microwave Links Network: A Long-Term Experiment in East China
Xichuan LIU, Kun ZHAO, Mingzhong ZOU, Kang PU, Kun SONG
2023, 40(9): 1567-1583. doi: 10.1007/s00376-023-2104-z
The first long-term rainfall monitoring experiment using the commercial microwave links (CMLs) network in East China is introduced. The network, located in Jiangyin, Jiangsu Province, consists of 49 links with frequencies ranging from 15 GHz to 26 GHz and lengths from 1.14 km to 4.78 km. An OTT PARSIVEL disdrometer is deployed to refine the local rain-induced attenuation relationship, and the CML observations are compared simultaneously with five rain gauges. The inversion parameters of the CML are optimized by minimizing the error of the accumulated rainfall of historical rainfall events. The inversion results show that the daily accumulated rainfall retrieved by the CMLs agrees well with the rain gauge measurements. As an opportunistic approach to monitor near-surface rainfall with high spatiotemporal representativeness and accuracy, the CML network can be used to monitor and forecast urban flood disasters, especially in regions where the widepread deployment of conventional meteorological instruments is impractical.
Interdecadal Variations of the March Atmospheric Heat Source over the Southeast Asian Low-Latitude Highlands
Dayong WEN, Jie CAO
2023, 40(9): 1584-1596. doi: 10.1007/s00376-023-2146-2
Based on the fifth-generation reanalysis dataset from the European Centre for Medium-Range Weather Forecasts for 1979–2019, we investigated the effects of the circumglobal teleconnection (CGT) on the interdecadal variation of the March atmospheric heat source (AHS) over the Southeast Asian low-latitude highlands (SEALLH). The dominant mode of the March AHS over the SEALLH features a monopole structure with an 8–11-year period. Decadal variations in the AHS make an important contribution to the 11-year low-pass filtered component of the AHS index, whichexplains 54.3% of the total variance. The CGT shows a clear interdecadal variation, which explains 59.3% of the total variance. The March AHS over the SEALLH is significantly related to the CGT on interdecadal timescales. When the CGT is optimally excited by a significant cyclonic vorticity source near northern Africa (i.e., in its positive phase), the SEALLH is dominated by anomalous southerly winds and ascending motions on the east of the anomalous cyclone. The enhanced advection and upward transfer result in a high-enthalpy air mass that converges into and condenses over the SEALLH, leading to a larger-than-average March AHS over this region. The key physical processes revealed by this diagnostic analysis are supported by numerical experiments.
Recent Enhancement in Co-Variability of the Western North Pacific Summer Monsoon and the Equatorial Zonal Wind
Minmin WU, Xugang PENG, Baiyang CHEN, Lei WANG, Jinwen WENG, Weijian LUO
2023, 40(9): 1597-1616. doi: 10.1007/s00376-023-2215-6
The western North Pacific summer monsoon (WNPSM) is an important subcomponent of the Asian summer monsoon. The equatorial zonal wind (EZW) in the lower troposphere over the western Pacific may play a critical role in the evolution of the El Niño-Southern Oscillation (ENSO). The possible linkage between the EZW over the western Pacific and the off-equatorial monsoonal winds associated with the WNPSM and its decadal changes have not yet been fully understood. Here, we find a non-stationary relationship between the WNPSM and the western Pacific EZW, significantly strengthening their correlation around the late 1980s/early 1990s. This observed shift in the WNPSM–EZW relationship could be explained by the changes in the related sea surface temperature (SST) configurations across the tropical oceans. The enhanced influence from the springtime tropical North Atlantic, summertime tropical central Pacific, and maritime continent SST anomalies may be working together in contributing to the recent intensified WNPSM–EZW co-variability. The observed recent strengthening of the WNPSM–EZW relationship may profoundly impact the climate system, including prompting more effective feedback from the WNPSM on subsequent ENSO evolution and bolstering a stronger biennial tendency of the WNPSM–ENSO coupled system. The results obtained herein imply that the WNPSM, EZW, ENSO, and the tropical North Atlantic SST may be closely linked within a unified climate system with a quasi-biennial rhythm occurring during recent decades, accompanied by a reinforcement of the WNPSM–ENSO interplay quite possibly triggered by enhanced tropical Pacific–Atlantic cross-basin interactions. These results highlight the importance of the tropical Atlantic cross-basin influences in shaping the spatial structure of WNPSM-related wind anomalies and the WNPSM–ENSO interaction.
Linkage of the Decadal Variability of Extreme Summer Heat in North China with the IPOD since 1981
Tiejun XIE, Ji WANG, Taichen FENG, Ting DING, Liang ZHAO
2023, 40(9): 1617-1631. doi: 10.1007/s00376-023-2304-6
Extreme summer heat can have serious socioeconomic impacts in North China. Here, we explore the decadal variability of the number of extreme heat days in early-to-mid summer (June and July) and a related potential mechanism consistent with the major seasonal occurrence period of extreme heat events in North China (NCSH). Observational analyses show significant decadal variability in NCSH for 1981–2021, potentially linked to the Indo-Pacific warm pool and Northwest Pacific Ocean dipole (IPOD) in early-to-mid summer. Dynamic diagnostic analysis and the linear baroclinic model (LBM) show that the positive IPOD in early-to-mid summer can excite upward vertical wind anomalies in the South China-East China Sea region, shifting the position of the western Pacific subtropical high (WPSH) to the east or weakening the degree of its control of the South China-East China Sea region, thus generating a positive geopotential height quadrupole (EAWPQ) pattern in the East Asia-Northwest Pacific region. Subsequently, the EAWPQ can cause air compression (expansion) over North China by regulating the tropospheric thickness anomalies in North China, thus increasing (decreasing) NCSH. Finally, an empirical model that incorporates the linear trend can better simulate the decadal NCSH compared to an empirical model based solely on the IPOD index, suggesting that the decadal variability of NCSH may be a combined contribution of the decadal IPOD and external linear forcing.
Enhanced Seasonal Predictability of Spring Soil Moisture over the Indo-China Peninsula for Eastern China Summer Precipitation under Non-ENSO Conditions
Chujie GAO, Gen LI
2023, 40(9): 1632-1648. doi: 10.1007/s00376-023-2361-x
Seasonal prediction of summer precipitation over eastern China is closely linked to the East Asian monsoon circulation, which is largely affected by the El Niño-Southern Oscillation (ENSO). In this study, results show that spring soil moisture (SM) over the Indo-China peninsula (ICP) could be a reliable seasonal predictor for eastern China summer precipitation under non-ENSO conditions. When springtime SM anomalies are present over the ICP, they trigger a structured response in summertime precipitation over most of eastern China. The resultant south-to-north, tri-polar configuration of precipitation anomalies has a tendency to yield increased (decreased) precipitation in the Yangtze River basin and decreased (increased) in South and North China with a drier (wetter) spring soil condition in the ICP. The analyses show that ENSO exerts a powerful control on the East Asian circulation system in the ENSO-decaying summer. In the case of ENSO forcing, the seasonal predictability of the ICP spring SM for eastern China summer precipitation is suppressed. However, in the absence of the influence of ENSO sea surface temperature anomalies from the preceding winter, the SM anomalies over the ICP induce abnormal local heating and a consequent geopotential height response owing to its sustained control on local temperature, which could, in turn, lead to abnormal eastern China summer precipitation by affecting the East Asian summer monsoon circulation. The present findings provide a better understanding of the complexity of summer climate predictability over eastern China, which is of potential significance for improving the livelihood of the people.
Hybrid Seasonal Prediction of Meridional Temperature Gradient Associated with “Warm Arctic–Cold Eurasia”
Tianbao XU, Zhicong YIN, Xiaoqing MA, Yanyan HUANG, Huijun WANG
2023, 40(9): 1649-1661. doi: 10.1007/s00376-023-2226-3
The meridional gradient of surface air temperature associated with “Warm Arctic–Cold Eurasia” (GradTAE) is closely related to climate anomalies and weather extremes in the mid-low latitudes. However, the Climate Forecast System Version 2 (CFSv2) shows poor capability for GradTAE prediction. Based on the year-to-year increment approach, analysis using a hybrid seasonal prediction model for GradTAE in winter (HMAE) is conducted with observed September sea ice over the Barents–Kara Sea, October sea surface temperature over the North Atlantic, September soil moisture in southern North America, and CFSv2 forecasted winter sea ice over the Baffin Bay, Davis Strait, and Labrador Sea. HMAE demonstrates good capability for predicting GradTAE with a significant correlation coefficient of 0.84, and the percentage of the same sign is 88% in cross-validation during 1983−2015. HMAE also maintains high accuracy and robustness during independent predictions of 2016−20. Meanwhile, HMAE can predict the GradTAE in 2021 well as an experiment of routine operation. Moreover, well-predicted GradTAE is useful in the prediction of the large-scale pattern of “Warm Arctic–Cold Eurasia” and has potential to enhance the skill of surface air temperature occurrences in the east of China.
The Processes-Based Attributes of Four Major Surface Melting Events over the Antarctic Ross Ice Shelf
Wenyi LI, Yuting WU, Xiaoming HU
2023, 40(9): 1662-1670. doi: 10.1007/s00376-023-2287-3
The Ross-Amundsen sector is experiencing an accelerating warming trend and a more intensive advective influx of marine air streams. As a result, massive surface melting events of the ice shelf are occurring more frequently, which puts the West Antarctica Ice Sheet at greater risk of degradation. This study shows the connection between surface melting and the prominent intrusion of warm and humid air flows from lower latitudes. By applying the Climate Feedback-Response Analysis Method (CFRAM), the temporal surge of the downward longwave (LW) fluxes over the surface of the Ross Ice Shelf (RIS) and adjacent regions are identified for four historically massive RIS surface melting events. The melting events are decomposed to identify which physical mechanisms are the main contributors. We found that intrusions of warm and humid airflow from lower latitudes are conducive to warm air temperature and water vapor anomalies, as well as cloud development. These changes exert a combined impact on the abnormal enhancement of the downward LW surface radiative fluxes, significantly contributing to surface warming and the resultant massive melting of ice.
Coupling of the Calculated Freezing and Thawing Front Parameterization in the Earth System Model CAS-ESM
Ruichao LI, Jinbo XIE, Zhenghui XIE, Binghao JIA, Junqiang GAO, Peihua QIN, Longhuan WANG, Si CHEN
2023, 40(9): 1671-1688. doi: 10.1007/s00376-023-2203-x
The soil freezing and thawing process affects soil physical properties, such as heat conductivity, heat capacity, and hydraulic conductivity in frozen ground regions, and further affects the processes of soil energy, hydrology, and carbon and nitrogen cycles. In this study, the calculation of freezing and thawing front parameterization was implemented into the earth system model of the Chinese Academy of Sciences (CAS-ESM) and its land component, the Common Land Model (CoLM), to investigate the dynamic change of freezing and thawing fronts and their effects. Our results showed that the developed models could reproduce the soil freezing and thawing process and the dynamic change of freezing and thawing fronts. The regionally averaged value of active layer thickness in the permafrost regions was 1.92 m, and the regionally averaged trend value was 0.35 cm yr–1. The regionally averaged value of maximum freezing depth in the seasonally frozen ground regions was 2.15 m, and the regionally averaged trend value was –0.48 cm yr–1. The active layer thickness increased while the maximum freezing depth decreased year by year. These results contribute to a better understanding of the freezing and thawing cycle process.
A Lagrangian Trajectory Analysis of Azimuthally Asymmetric Equivalent Potential Temperature in the Outer Core of Sheared Tropical Cyclones
Yufan DAI, Qingqing LI, Xinhang LIU, Lijuan WANG
2023, 40(9): 1689-1706. doi: 10.1007/s00376-023-2245-0
In this study, the characteristics of azimuthally asymmetric equivalent potential temperature (\begin{document}$ {\theta }_{e} $\end{document}) distributions in the outer core of tropical cyclones (TCs) encountering weak and strong vertical wind shear are examined using a Lagrangian trajectory method. Evaporatively forced downdrafts in the outer rainbands can transport low-entropy air downward, resulting in the lowest \begin{document}$ {\theta }_{e} $\end{document} in the downshear-left boundary layer. Quantitative estimations of \begin{document}$ {\theta }_{e} $\end{document} recovery indicate that air parcels, especially those originating from the downshear-left outer core, can gradually revive from a low entropy state through surface enthalpy fluxes as the parcels move cyclonically. As a result, the maximum \begin{document}$ {\theta }_{e} $\end{document} is observed in the downshear-right quadrant of a highly sheared TC. The trajectory analyses also indicate that parcels that move upward in the outer rainbands and those that travel through the inner core due to shear make a dominant contribution to the midlevel enhancement of \begin{document}$ {\theta }_{e} $\end{document} in the downshear-left outer core. In particular, the former plays a leading role in such \begin{document}$ {\theta }_{e} $\end{document} enhancements, while the latter plays a secondary role. As a result, moist potential stability occurs in the middle-to-lower troposphere in the downshear-left outer core.
Modulation of the Wind Field Structure of Initial Vortex on the Relationship between Tropical Cyclone Size and Intensity
Kexin CHEN, Guanghua CHEN, Donglei SHI
2023, 40(9): 1707-1721. doi: 10.1007/s00376-023-2233-4
This study investigates the modulation of initial wind field structure on the relationship between the size and intensity of a simulated vortex. A series of idealized experiments are conducted by varying the radius of maximum wind (RMW) and shape parameter \begin{document}$ b $\end{document} of the initial vortices. The size–intensity relationship is quantified by the linear regression coefficient of the azimuthally-averaged gale-force wind radius against the maximum wind during the development stage, reflecting the degree of size expansion at the same intensity increment. The regression coefficient increases with increased RMW and decreased \begin{document}$ b $\end{document}, with the RMW being the primary constraint. The effect of lowering \begin{document}$ b $\end{document} on the elevation of the regression coefficient gradually stands out when the initial RMW is large. Enlarging the RMW leads to a secondary circulation with a horizontally elongated structure, which retards the intensification while promoting size expansion, thus substantially enhancing size expansion as the vortex intensifies. Broadening the wind field outside the RMW by reducing \begin{document}$ b $\end{document} results in abounding convection in the outer region, which promotes size expansion. Based on the axisymmetric tangential wind tendency and Sawyer–Eliassen equations, when the RMW is large, the active convection in the outer region can weaken the radial inflow induced by the eyewall heating in the inner region, thus retarding the intensification by reducing the radial imports of vorticity near the RMW.
Meeting Summary
The 17th Workshop on Antarctic Meteorology and Climate and 7th Year of Polar Prediction in the Southern Hemisphere Meeting
Anastasia J. TOMANEK, Matthew A. LAZZARA, David E. MIKOLAJCZYK, Taylor P. NORTON, Isabella I. ONSI, David H. BROMWICH, Mariana F. LITELL
2023, 40(9): 1722-1729. doi: 10.1007/s00376-023-3049-y