应用气象学报

2019, 30(4)

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Abstract:

Advances of Research and Application on Major Rainy Seasons in China

Chen Lijuan, Zhao Junhu, Gu Wei, Liang Ping, Zhi Rong, Peng Jingbei, Zhao Shuyun, Gao Hui, Li Xiang, Zhang Peiqun

2019, 30(4): 385-400. DOI: 10.11898/1001-7313.20190401

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Abstract:
The pre-rainy season in South China, Meiyu, rainy season in North China and autumn rainfall in West China are important phenomena influenced by the process of the East Asian summer monsoon (EASM). These regional rainy seasons determine the distribution and evolution of drought and flood during the flood season over mid-eastern China. Therefore, the prediction of regional rainy seasons plays an important role in the meteorological service of flood season.The research progress on characteristics and influencing factors of major rainy seasons during flood season in China are reviewed. In order to meet the demand of prediction operation, the influence and mechanism of the previous sea surface temperature (SST) and related atmosphere circulation systems on climatic events are analyzed firstly, and the statistical prediction models can be established based on that.Recent studies show that SST anomalies (SSTAs) are important forecast signals of rainy seasons. However, the influence and spatial-temporal pattern of SST vary with the interannual and interdecadal variation characteristics of different events. For instance, the interannual variation of precipitation in the pre-rainy season in South China can be better explained using the east-west SST contrast index in the tropical Pacific. Multiple timescale variation characteristics of Meiyu over the Yangtze River correspond to different SST forcing. Key regions of SST associated with interannual variation of Meiyu over the Yangtze River are in tropics. For the interdecadal or mutli-decadal time scale of Meiyu variations, the SST in middle and high latitudes may play an important role. The intensity of rainy-season precipitation in North China is not only coincident with the ENSO phase-switching, but also influenced by the developing speed of ENSO event. The key SST region that influences autumn rain in West China has changed with the inter-decadal changing background, which requires updating impact factors and models.These results provide strong support for the real-time prediction of climate events in recent years. During 2015-2018, the prediction accuracy of the onset date and intensity (rainfall) of Meiyu and rainy season in North China is 75% and 81%, respectively.

Recent Advances on Sub-seasonal Variability of East Asian Summer Monsoon

Zhu Congwen, Liu Boqi, Zuo Zhiyan, Yuan Naiming, Liu Ge

2019, 30(4): 401-415. DOI: 10.11898/1001-7313.20190402

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Abstract:
The sub-seasonal (10-90 days) variability of East Asian summer monsoon (EASM) is crucial for extreme climate disasters (e.g., persistent heavy rainfall and heat waves) in China, which is a blind spot between the upper weather forecast and the seasonal prediction. Recent advances of EASM on sub-seasonal timescale are reported, including features of EASM sub-seasonal variation, influences of mid-latitudinal Eurasian soil moisture and snow cover, as well as the tropical air-sea interaction. Results show the potential predictability of EASM sub-seasonal variability depends on the phase-locking between the sub-seasonal variability and seasonal cycle of EASM. The sub-seasonal variation of EASM is the intrinsic physical mode, which is different from the Madden-Julian Oscillation. It is featured by the intra-seasonal interaction among the western Pacific subtropical high (WPSH), the South Asian High (SAH) and the Mongolian cyclone (MC), along with the alternation of sub-seasonal rain belt in China. The onset of South China Sea summer monsoon (SCSSM), the emergence of Meiyu over the Yangtze River and the starting of rainy season in North China are critical for both the seasonal and sub-seasonal prediction of summer rainfall in China. In mid-May, the eastward extension of SAH onto the South China Sea is vertically coupled with the retreat of WPSH, leading to the onset of SCSSM. Afterwards, the temporal evolution of sub-seasonal modes induced by WPSH, SAH and MC determines the beginning of rainy season over the Yangtze River and North China. Another predicting source of EASM sub-seasonal variation is the interaction between underlying forcing and atmospheric circulation. On one hand, the spring soil moisture over East China acts as an important precursor of summer monsoon onset and anomalous summer rainfall, and the spring snow cover over Eurasian continent could modulate the rainfall over South China. On the other hand, the relationship between tropical air-sea interaction and SCSSM onset shows evident interdecadal variation. The decaying rate of ENSO events and the mid-latitudinal wave activity in the upper troposphere can alter the sub-seasonal variation of EASM on interannual timescale. In addition, a new detrended DPCCA method is developed to investigate the interaction among multi-factors of EASM on multi-timescales. Unsolved questions about the sub-seasonal variation of EASM include objectively qualifying EASM sub-seasonal modes, the crucial process affecting year-by-year changes of EASM sub-seasonal modes, and co-effects of underlying factors on EASM sub-seasonal modes.

Advances on the Predictability and Prediction Methods of 10-30 d Extended Range Forecast

Zhang Daquan, Zheng Zhihai, Chen Lijuan, Zhang Peiqun

2019, 30(4): 416-430. DOI: 10.11898/1001-7313.20190403

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Abstract:
The 10-30 d extended range forecast (ERF) fills the gap between traditional weather forecast and short-term climate prediction, and it plays an important role in the decision making of disaster prevention and mitigation. Therefore, ERF becomes one hot topic in both scientific research and predictive operations. The research progress and operational status of ERF are reviewed from three aspects, the source of predictability, sub-seasonal climate phenomenon and operational predictions. The research achievements on predictability of ERF and its applications are specially emphasized, and some new forecasting methods of ERF in recent years are summarized. At last, key scientific issues and technical problems are raised and some thoughts and possible ways enhancing the predictive skills of ERF are proposed.ERF exceeds time limits of traditional daily weather forecast, largely beyond the atmospheric memory of initial conditions, while it is too short to consider the variability of the ocean, which makes it difficult to beat persistence. Fortunately, recent years, some research work indicates the existence of some important sources of predictability at this time range, such as Madden-Julian oscillation (MJO), ENSO, soil moisture, snow cover and sea ice, stratosphere-troposphere interaction, ocean conditions, tropics-extratropics teleconnections, etc. Verification results of numerical model indicate that upper bounds of the prediction skill can be extended to 4 weeks. However, the complexity and diversity of mechanisms associated with the connection between source of predictability and climate variables prevent the potential predictability from being transformed into realized forecast skill. The effective forecast of most climate variables of numerical model is still limited within 2 weeks.Although the direct application of numerical dynamical model output in ERF is unsatisfactory, some research institutes and operational centers still conduct a series of scientific research and propose some practical methods. According to utilization of numerical model data, those forecast methods can be divided into two categories, i.e., statistical methods and the combination of both statistical and dynamical methods. Based on dynamical forecast model, Beijing Climate Center develops several methods, including Dynamical-Analogue Ensemble Forecasting (DAEF), statistical downscaling, ensemble forecast of ERF based on predictable components and probabilistic calibration of model biases. On the other side, based on predictable signals of extended range, such as low frequency variation of atmosphere, MJO and periodic relationship, some statistical forecast methods are proposed, which show considerable predictive skill and good prospects of application.

Dynamic Linkages Between Heat Wave Events in Jianghuai Region and Arctic Summer Cold Anomaly

Dong Xiaoyao, Wu Bingyi

2019, 30(4): 431-442. DOI: 10.11898/1001-7313.20190404

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Abstract:
Summer high temperature events have been occurring with increasing frequency since 2000, which have disastrous consequence for society, economy and human production and life. During recent years, causes and effects of high temperature events in East Asia have been focused in many research efforts. However, relationships between high temperature events in East Asia summer and cold or warm anomalies in the Arctic during the same period, especially in the seasonal time scale, attract little attention.Based on reanalysis data of NCEP/NCAR, main characteristics of atmospheric circulation anomalies and its possible dynamics of Arctic cold anomalies during the summer of 2010, 2013 and 2016, are analyzed by using both composite analysis and correlation analysis. Results show that the frequency of high temperature events in East Asia is complex. High temperature events occurred in Jianghuai Region accompanied by 500 hPa positive geopotential height anomalies, warm anomalies in the middle and low tropospheric, weakened westerly winds throughout the troposphere and stratosphere over middle and low latitudes of East Asian. And meanwhile, over most of the Arctic, 500 hPa height negative anomalies are corresponded with 500-1000 hPa negative thickness anomalies, cold anomalies in the middle and low tropospheric and strengthened westerlies throughout the troposphere and stratosphere. Results show that the high temperature events in Jianghuai Region of 2010, 2013 and 2016 are closely related to the tropospheric zonal wind. It shows that high temperature events in Jianghuai Region is negatively correlated with the tropospheric zonal wind in middle and low latitudes of East Asia, while positively correlated with that over Arctic areas. It's also found that this correlation is not limited to 200 hPa, which occurs through the troposphere and stratosphere. Evidence suggests that during the high temperature events in Jianghuai Region of 2010, 2013 and 2016, weakened upper westerly winds over the middle and low latitudes of East Asian enhance barotropy and decrease baroclinity in this area, which suppress convection and have great contributions to the generation and maintenance of anticyclone. Thereby resulting in reduced cloud cover and enhancing the downwelling surface shortwave radiation, which contributes to increase heat waves. Possible causes of westerly winds anomalies over the Arctic and mid-and low-latitudes of East Asia during high temperature events in Jianghuai Region are also discussed through dynamic diagnosis.

The Impact of Cloud Microphysical Processes on Typhoon Numerical Simulation

Chang Wanting, Gao Wenhua, Duan Yihong, Deng Lin

2019, 30(4): 443-455. DOI: 10.11898/1001-7313.20190405

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Abstract:
Previous studies show that the cloud microphysical process affects the precipitation, as well as the intensity, internal structure and evolution process of tropical cyclones. Thus, the rational description of the cloud microphysical process is crucial. And the correctness of the cloud microphysical process is the basis of the high-resolution model in simulating precipitation and fine-scale structure of typhoon. The two-moment bulk microphysics scheme developed by Chinese Academy of Meteorological Sciences (CAMS) is a mixed phase two-moment cloud microphysics scheme, which can simulate cloud microphysics processes in different weather systems. However, whether it can be applied to the simulation of tropical cyclones is still uncertain.Four numerical experiments of typhoon Usagi (2013) are conducted by using the Weather Research and Forecasting (WRF) model with Chinese Academy of Meteorological Sciences two-moment microphysics scheme (CAMS). The simulated track, intensity, cloud microphysics and rainfall are compared with the observed typhoon best track dataset and satellite observations to evaluate performances of CAMS microphysics scheme and investigate the possible impacts of cloud microphysical processes on Typhoon Usagi. To overcome the overestimation of snow content in control experiment (CTRL), three sensitivity experiments are designed:Modifying coefficients of snow particle mass and falling velocity (EXP1), using the typical oceanic cloud droplet parameter (EXP2), and including changes in both EXP1 and EXP2 (EXP3). It shows that the snow content is significantly reduced in the EXP1 and EXP3 due to the increased rate of accretion of snow by graupel and the slightly reduced snow mass flux, and the content of whole ice-phase hydrometeors are also reduced. The rapid intensification process in the early stage of typhoon Usagi is well captured in EXP2 and EXP3 owing to the better simulated CAPE in eye region, and their intensity and track are also better than those in CTRL. Although the hourly precipitation rate in each experiment is generally stronger, the spatial distribution of precipitation in EXP3 is more consistent with the observation. As a result, modifying coefficients of snow mass and falling velocity as well as using the typical oceanic cloud droplet concentration in CAMS microphysics will significantly reduce the snow content and improve the simulated track, intensity and precipitation. These results could not only provide ideology for improving the cloud microphysical parameterizations in simulating typhoon, but also improve the understanding of cloud microphysics impacts on typhoon process and help improving the cloud microphysical parameterization schemes in simulating typhoons.

Interaction and Influence of Binary Typhoons

Zhang Xiaohui, Zhang Lifeng, Zhou Haishen, Wei Tongfeng

2019, 30(4): 456-466. DOI: 10.11898/1001-7313.20190406

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Abstract:
The non-static mesoscale numerical model WRF V3.3 is used to study the influence of the interaction between binary typhoons on their moving path, intensity and precipitation. Data of NCEP FNL are used as initial field and side boundary conditions, and satellite data of ATOVS such as AMSUA, AMSUB, HIRS (3/4) are assimilated. Simulation results of binary typhoons in control runs, which are based on hybrid ensemble three-dimensional variational data assimilation (Ens-3DVar) system, are very close to the real intensity, moving path and precipitation. Beyond that, 6 sensitive experiments based on control runs are designed. The 96-hour simulations are conducted after one of the binary typhoons (Fitows/Danas/Goni/Morakot) is removed from the initial field which adopts the first step of vortex reconstruction technology in WRF ARW in the sensitive experiments (C1-RMF/C1-RMD/C2-RMG/C2-RMM). Experiment C2-WEM (C2-STM) is conducted by weakening or enhancing one of the binary typhoons in order to study effects of typhoon Morakot on typhoon Goni, but the typhoon radius is unchanged. Results of sensitive experiments and control runs are further compared and analyzed.In Case 1, the role of typhoon Danas leads typhoon Fitow to move southward and slower. The role of typhoon Fitow causes typhoon Danas to move northward but has little effects on the shifting speed. The strength of binary typhoons Fitow and Danas have been changed by the interaction between them. Specifically, the interaction of binary typhoons makes the intensity of typhoon Fitow and typhoon Danas stronger in the strong stage and weaker in the dying stage of typhoon Fitow. From 6 October to 9 October in 2013, the heavy precipitation in East China is mainly affected by typhoon Fitow. Affected by typhoon Danas, the precipitation intensity brought by typhoon Fitow is enhanced, and the heavy precipitation center moves southward.In Case 2, the interaction of binary typhoons makes typhoon Goni move southward and faster, but typhoon Goni has little influence on the movement and speed of typhoon Morakot. The winding path and direction change of typhoon Goni are all associated with typhoon Morakot. The bending extent of typhoon Goni is positively correlated with the strength of typhoon Morakot. Main causes are the interaction and transportation mechanism of vorticity, water vapor flux between binary typhoons.

Impact of Crop Residue Burning on PM_2.5 Inorganic Components in Beijing-Tianjin-Hebei and Surrounding Areas

Zhang Fangjian, Xu Jing, Ma Jianzhong, Kou Xingxia

2019, 30(4): 467-478. DOI: 10.11898/1001-7313.20190407

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Abstract:
Tremendous advances in atmospheric aerosol particle research have taken place in the last decade in the context of climate and global change science. Biomass burning, one of the largest sources of accumulation mode particles globally, is closely studied for its radiative, geochemical, and dynamic impacts. In addition to primary aerosols such as organic carbon (OC) and black carbon (BC), straw burning emits a large amount of gaseous precursor of aerosols. The transformation of these gaseous precursors to secondary aerosols is one of the important ways to the formation of heavy pollution episodes. Due to rapid economic growth and urbanization in China, crop residues are often burnt in a couple of days post harvests to prepare for planting the next season's crops. The North China Plain is a major agricultural base in China with straw burning widely in the field. Remote sensing data, ground monitoring data, meteorological data are used for analyzing effects on the haze pollution from autumn crop residue burning over Beijing-Tianjin-Hebei area. Results indicate that lots of heavy pollution processes are related to the pollutant transmission from the crop residue burning in surrounding regions. Emission characteristics of straw burning during the autumn harvest season (October 2014) are analyzed, using the regional chemical transport model WRF-Chem. Effects of straw burning on gaseous precursors of inorganic aerosols and their oxidation products as well as resulting changes of sulfate, nitrate and ammonium in PM_2.5 are studied. It's found that during the autumn harvest season of 2014, the straw burning emissions in Henan and Shandong provinces tend to affect Beijing-Tianjin-Hebei urban areas under the influence of the southeast wind. A large number of VOCs emitted by straw burning lead to an increase in the concentration of major oxidants in the atmosphere which enhances the regional atmospheric oxidation capacity. When the straw burning plume carrying a large number of VOCs is mixed with the urban air mass mainly composed of fossil fuel emissions, the increase of atmospheric oxidation accelerates the oxidation process of gaseous precursors such as NO₂ and SO₂ emitted by anthropogenic sources and increases the conversion rate of sulfate and nitrate. Ammonia-rich state in Beijing-Tianjin-Hebei area are favorable for the formation of secondary inorganic aerosols, and straw burning intensifies the development of this process, and then results in a significant increase in the concentration of nitrate, sulfate and ammonium.

Vertical Profiles of Raindrop Size Distribution Observed by Micro Rain Radar

Song Can, Zhou Yuquan, Wu Zhihui

2019, 30(4): 479-490. DOI: 10.11898/1001-7313.20190408

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Abstract:
Raindrop size distribution (DSD) is of great importance for understanding the microphysical process of precipitation, as well as improving the microphysical parameterization scheme in numerical model. Most studies of DSD focus on precipitation characteristics on the surface. However, vertical profiles of DSD and rain parameters are important for quantitatively accurate precipitation estimation from weather radars. Based on data observed by the ground-based PARSIVEL disdrometer and a vertical pointing micro rain radar (MRR) at Xingtai, Hebei Province located in North China from June to September in 2016, the vertical evolution of precipitation microphysical parameters and DSD of different rain rate classed for stratiform precipitation are analyzed. Measurements from MRR, rain gauge and ground PARSIVEL disdrometer are compared. Results show that measurements from MRR, rain gauge and PARSIVEL disdrometer have good agreement in rain rate. MRR and PARSIVEL disdrometer show good consistency in medium sized (1-2.5 mm) range of DSD but have slight differences for small and large raindrops. MRR observes much more small particles than PARSIVEL disdrometer. When the rain rate is low, with low relative humidity around the ground, both large and small drops decrease with the altitude decreasing, so as to the liquid water content and rain rate, which is explained by the evaporation. When the rain rate is high, the concentration of particles for precipitation is much larger, and the vertical variation of DSD is more obvious. The profiles of radar reflectivity show a positive slope(dZ/dH>0). The concentration of medium-sized and large raindrops increases obviously with decreasing altitude at the cost of reducing small raindrops for precipitation with rain rate between 2-20 mm·h^-1, indicating that the coalescence is the dominant process for 2-20 mm·h^-1. The largest contribution to the total number concentration is small drops (0-0.5 mm) with diameters between 0-1 mm and can reach up to 50% above altitude of 2 km. Small particles contribute less to the precipitation intensity as the altitude decreasing. These small raindrops account only 15% to the surface precipitation, while the medium-sized raindrops can contribute 60% with rain rate between 2-20 mm·h^-1. Large raindrops (>2 mm) is about 50% of the surface rainfall for the largest rain rate class. These results provide useful information for better understanding rain processes and quantitative estimation of precipitation in the future.

A Statistical Study of Gravity Wave with Second-level Radiosonde Data in Sichuan

Wu Hongkun, Chen Qiying, Hua Wei, Li Fangfang, Li Zechun

2019, 30(4): 491-501. DOI: 10.11898/1001-7313.20190409

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Abstract:
High vertical resolution radiosonde data of Sichuan Province from June 2014 to September 2017 are analyzed to derive important gravity wave parameters, such as wave energy, intrinsic frequencies, vertical and horizontal wavelengths, and propagation directions. The sampling period of these data is 1.2 s and the vertical resolution is 5-8 m. Five representative stations of Sichuan Province are investigated, including Ganzi, Hongyuan, Chengdu, Xichang and Dazhou. Data in troposphere (2-10 km) and stratosphere (18-25 km), and the latest upper-air wind measurement algorithm for L-band radiosonde sounding system are used to process the original data. Results show that there are obvious seasonal variabilities of gravity waves energy at various areas in Sichuan, strong in winter and weak in summer. In the troposphere, due to the influence of terrain, the energy in the western Sichuan and northern Sichuan regions is significantly smaller than that in other regions. And gravity wave activity is also affected by latitudes. There is no obvious spatial variation in vertical wavelength, and vertical wavelength in winter is slightly larger than summer. The vertical wavelength is concentrated at 1.5-3 km and 1.5-3.5 km in the troposphere and stratosphere, respectively. The horizontal wavelength is quite different, distributed in 0-300 km and 100-700 km, or averaged of 100 km and 350 km in the troposphere and stratosphere, respectively. The ratio of horizontal wavelength to vertical wavelength is 35:1 in the troposphere and 150:1 in the stratosphere. It indicates that gravity waves mainly propagate vertically in the troposphere and propagate horizontally in the stratosphere. In order to get more accurate intrinsic frequency of gravity waves, filtering is essential perform before calculation. There is a large regional difference for intrinsic frequency in the troposphere. The averaged intrinsic frequency in the Plateau regions in northwestern Sichuan is 3 (represents the Coriolis force parameter), while only 2.4 in other regions. There is no obvious spatial difference in the stratosphere, and the mean value is about 2. The vertical propagation directions of gravity waves at different stations in Sichuan are similar, with about 50% of the waves propagating upward in the troposphere and more than 90% in the stratosphere. Horizontal propagation direction of gravity wave is always influenced by background wind field, and it has significant uncertainty, especially in the troposphere. The horizontal propagation of gravity waves in stratosphere strongly depends on season, eastward in summer and westward in other seasons.

Optimizing BCCAGCM on Sunway TaihuLight

Wei Min, Wang Bin, He Xiang, Sun Jun, Jiang Xiaocheng, Xiao Sa, Zhang Li, Xu Jinxiu

2019, 30(4): 502-512. DOI: 10.11898/1001-7313.20190410

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Abstract:
With the rise of many-core processors such as Intel MIC, GPU and SW26010, the architecture of supercomputer systems has undergone great changes. The supercomputer transitions from a homogeneous system containing only multi-core CPUs to a heterogeneous system with coexistence of CPU and many-core accelerators. Heterogeneous architectures provide powerful computing power for large, complex applications. However, since the numerical model is basically based on conventional CPU development different from the many-core accelerator, the existing tens of thousands of lines of legacy code cannot take full advantage of the parallel computing capacity of the new architecture. Carrying out the porting and optimization of the weather and climate numerical model on the new system is of great significance to improve the adaptability of the model in the new computing architecture.The Sunway TaihuLight System is the world's first supercomputer with a peak performance greater than 100 PFlops based on homegrown SW26010 heterogeneous many-core chip. Each SW26010 processor consists of management processing elements (MPEs) and clusters of computing processing elements (CPEs). To support parallel computing for heterogeneous architectures, the system provides a set of compilation tools, including basic C/C++, Fortran compilers. In addition to that, there is also a customized Sunway OpenACC tool that supports the OpenACC2.0 syntax.As the atmospheric component of BCCCSM, BCCAGCM is the most computationally expensive component in typical configurations. Since BCCAGCM has not been operated in the Sunway system, BCCAGCM is first ported to the Sunway system, using only MPE to perform the computation. And then, the calculation framework is analyzed to determine the major kernels that take the most time to calculate. BCCAGCM uses a hybrid parallelization scheme combining MPI and OpenMP to complete the calculation. In the Sunway system, MPI and OpenACC are used to obtain appropriate parallelism from the CPE cluster. On one hand, by adjusting the computational sequence and the loop structures to aggregate more parallel computations, the parallelism from the CPE cluster is fully utilized. On the other hand, the design optimizes data access and transmission strategy, improves the LDM availability, and minimizes the proportion of data moving and computation overhead.The efficiency of the MPE+CPE heterogeneous calculation after optimization is compared with the calculation efficiency of the original MPE only. The optimized kernel calculation efficiency is basically about 3 times as before, and up to about 14 times. Kernels are integrated, and the new version is integrated with a computing efficiency of 1.9 times as before. Although the overall acceleration effect of the model is not very obvious, the formation of the BCCAGCM heterogeneous many-core basic version add to the experience for the optimization and refactoring of the new computing architecture for the meteorological numerical model.

Vol.30, NO.4, 2019