应用气象学报

2024, 35(3)

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Abstract:

Characteristics and Causes of Extreme Heavy Rainfall in Heilongjiang Province During August 2023

Qi Duo, Wang Chengwei, Bai Xuemei, Gong Yanduo, Sun Qi, Luan Chen, Tang Kai, Zhao Yujie

2024, 35(3): 257-271. DOI: 10.11898/1001-7313.20240301

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Abstract:
From 2 August to 4 August in 2023, a prolonged and extensive extreme heavy rainfall event occurrs in the southeast of Heilongjiang Province. Utilizing multiple observations and ERA5 reanalysis data, characteristics of the precipitation process are analyzed focusing on large-scale circulation background, mesoscale circulation system evolution, environmental conditions from perspectives of climate statistics, weather analysis, and physical quantity diagnosis. Factors contributing to the prolonged extreme heavy rainfall event are explored. Main causes for the long duration of this heavy precipitation event are the stable maintenance of favorable large-scale conditions, such as the persistent divergence of the upper troposphere, the stable location of the west Pacific subtropical high (WPSH) and Northeast China cold vortex (NCCV), and continuous water vapor transport by the southwest jet. Due to the strong southwest jet, there is abundant moisture transfer, primarily through the advection of water vapor, which is the primary source for heavy rainfall. The process can be divided into two stages due to significant differences of rainfall, atmospheric stratification, and local circulation characteristics. In the first stage, the meridional water vapor inflow layer and the saturated layer are thick, resulting in high tropospheric humidity. The atmospheric condition is characterized by weak convective instability. Under the control of the northwest airflow at 500 hPa, the development of southwest jet, along with the influence of a weak eastward-moving vortex system at 850 hPa, results in horizontal wind speed convergence and systematic upward motion, leading to widespread and prolonged precipitation. The heavy rainfall area is mainly composed of cumulus embedded stratus, with a large coverage area of the cloud system, low echo centroid height, and high precipitation efficiency. With weak convective instability that promotes the development of convection and train effect in some periods, extreme hourly precipitation and large cumulative precipitation occur. In the second stage, the meridional water vapor inflow is concentrated in the lower troposphere with high intensity. The lower troposphere is close to saturation, with high humidity and temperature, while the middle and upper troposphere is dry and cold, and the atmospheric condition is more unstable than that in the first stage. Convection is developed and strengthened by the combined action of systematic uplift by a trough at 500 hPa, warm shear at 850 hPa, topographic convergence, and uplift. The cloud system is dominated by local strong cumulus clouds, and the distribution of precipitation intensity is uneven. At the beginning of this stage, convective cells continue to form at the trumpet-shaped terrain and move towards the eastern mountainous areas, organizing into linear convection. This is accompanied by the development and southward movement of surface convergence lines, leading to the generation of new convection and continuously causing localized intense short-duration rainfall.

Characteristics of Precipitation Cloud System in Northeast China Cold Vortex at Changbai Mountain Foothills

Wang Xiujuan, Qi Yanbin, Jiang Xiaoling, Yu Dongjia, Wang Tianqi

2024, 35(3): 272-284. DOI: 10.11898/1001-7313.20240302

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Abstract:
Utilizing the microwave radiometer data and hourly rainfall data in Jilin Cloud Physics Field Scientific Test Base, CMA, the precipitation cloud system in Northeast China cold vortex at the Changbai Mountain foothills is analyzed. Rainfall events are divided into heavy precipitation, moderate intensity precipitation, and weak precipitation. Assisted by ERA5 reanalysis data, results show that the middle and high clouds appear first by 6 hours before the precipitation occurrence at the Changbai Mountain foothills. Water vapor and cloud water are both important for the occurrence and maintenance of heavy precipitation induced by Northeast China cold vortex. The cloud liquid water appears approximately with the height of 5-6 km by 4 hours before the precipitation induced by Northeast China cold vortex. Two hours before precipitation, the cloud descendes sharply. During one hour after the three types precipitation occurrence, the vapor density respectively leap to 13-14 g·m^-3, 9-12 g·m^-3, and 7-9 g·m^-3 below 1 km height. Integrated water vapor during three types of precipitation increase to 5.8 cm, 4.2 cm, and 3.5 cm, respectively. The water vapor increases 5 hours before the occurrence of strong precipitation below 6 km height. The vapor density increases to 12-14 g·m^-3 below 1 km height. There is cloud liquid water with 1.0-1.6 g·m^-3 at the height of 5-6 km in the temperature layers of -5--10 ℃, which contributes to the formation of ice and snow crystals. Six hours before the heavy precipitation, moderate intensity precipitation, and weak precipitation, the integrated cloud liquid water are 4.2-4.8 mm, 3.0 mm, 2.3 mm, respectively. There are middle and high clouds in the temperature layers of -6 ℃ and -16 ℃. The height of cloud base drops sharply from 5.5-7 km to the ground, while the relative humidity drops sharply. These characteristics continue until the beginning of heavy rainfall. For moderate and weak precipitation induced by Northeast China cold vortex, there is middle cloud before the precipitation, and the cloud liquid water is 0.4-0.8 g· m^-3 at the height of 5-6 km. However, there is no characteristic of water vapor jumping or relative humidity decreasing.Through the study of these physical quantity characteristics, indicators with indicative and predictive significance for precipitation induced by Northeast China cold vortex have been established.

Moisture Transfer Characteristics of Extreme Precipitation During the Warm Season in the Mid-south Section of the Taihang Mountains

Qiu Guiqiang, Wu Yongli, Dong Chunqing, Sun Yingshu, Ma Li

2024, 35(3): 285-297. DOI: 10.11898/1001-7313.20240303

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Abstract:
Extreme precipitation events in China have increased significantly in recent decades. Extreme precipitation can easily trigger natural disasters such as urban waterlogging, landslides, and mudslides, which poses a serious threat to the social economy, human lives and property. Currently, research on extreme precipitation has attracted widespread attention.To increase the accuracy of extreme precipitation forecasts, precipitation data from automatic meteorological stations, ERA5 reanalysis data, and Global Data Assimilation System (GDAS) data are used to summarize the synoptic circulation affecting 75 extreme precipitation events in the mid-south section of the Taihang Mountains during the warm season (May-September) for the period of 2012-2021 on the basis of self-organizing maps (SOMs) neural network, synoptic verification method, and hybrid single-particle Lagrangian integrated trajectory (HYSPLIT) model. Characteristics of moisture transfer and the resulting precipitation for various types of synoptic circulation are also discussed. Results show that there are five types of synoptic circulation that affect extreme precipitation during the warm season in the mid-south section of the Taihang Mountains, namely the upper trough type, low vortex type, zonal subtropical high type, meridional subtropical high type, and northwest airflow type. The upper trough type is the most frequent, accounting for 40.0%, while the northwest airflow type is the least common, representing less than 5%. The daily extreme, maximum hourly intensity, and impact range of precipitation resulting from the low vortex circulation are the highest among all types. There are three moisture transfer passages for the low vortex type: The Bay of Bengal, South China Sea, and Northwest Pacific. Compared to the low vortex type, the upper trough type cannot transfer moisture through the Northwest Pacific passage, while neither the zonal subtropical high type nor the meridional subtropical high type can transfer moisture through the Bay of Bengal passage. Air mass tracking results indicate that the contribution of moisture transfer from the Northwest Pacific is the highest for both the low vortex type and the zonal subtropical high type, the contribution of moisture transfer from the Yellow Sea coast is the highest for the upper trough type, and the contribution of moisture transfer from the South China Sea is the highest for the meridional subtropical high type. Analysis of the moisture budget in the whole troposphere reveals that the main moisture inflow of extreme precipitation during the warm season in the mid-south section of the Taihang Mountains comes from the southern boundary. Other inflow boundaries and the relative contribution of all inflow boundaries is related to the synoptic circulation. The moisture budget at the boundaries of the lower troposphere differs from that in the whole troposphere.

Climatology of Winter Cold Waves and Associated Atmospheric Circulation Anomalies in China During the Last 40 Years

Wang Miaomiao, Ding Minghu, Lü Junmei, Chen Junming

2024, 35(3): 298-310. DOI: 10.11898/1001-7313.20240304

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Abstract:
Based on daily high-resolution temperature observations at 1941 meteorological stations in China from 1980 to 2023, stations reaching standard for cold wave and 418 cold wave processes (including 152 strong cold waves processes) in winter are identified according to the monitoring indices of cold air processes. And cold wave processes are objectively classified according to their intensity and influencing areas using K-means++ clustering method. The temporal and spatial characteristics of the single-station cold waves and 418 cold wave events are discussed. Results show that the frequency of cold waves in the high affecting areas of China has not increased significantly but has shown a decreasing trend over the last 40 years. The increasing trend of frequency and intensity of single-station cold waves in the middle-lower reaches of the Yangtze River Plain is significant. Additionally, the intensity of single-station cold waves in South China is also noticeably enhanced. The frequency of winter cold wave events in China has decreased significantly in the last 40 years with an expanding range of influence, while the intensity of strong cold wave events has increased significantly, accompanied by a marked increase in the amplitude of interannual variations. The cold air associated with cold waves in China mainly originates from the southeast of Novaya Zemlya, and its trajectory varies depending on the type of cold wave. Based on the fifth-generation European Centre for Medium-Range Weather Forecasts (ECMWF) atmospheric reanalysis data (ERA5), characteristics of atmospheric circulation anomalies in the preceding and the simultaneous period for cold wave processes in the countrywide, Northeast-North China and Northwest-North China are analyzed. It is found that the deep warm high pressure in Greenland is an important precursor of the countrywide cold wave, and the zonal wave train in the middle and upper troposphere of Eurasia is a prominent feature of the cold wave outbreak. The cold wave in Northeast-North China is related to the eastward movement of the cold vortex under the block of anomalous high-pressure system in the mid-low latitudes. The cold wave in Northwest-North China is closely related to the development of a warm high ridge over the East European Plain and the circulation situation of two-ridge-one-trough in mid-high latitudes of Eurasia. All types of cold waves are preceded by the maintenance of the Ural blocking high and the accumulation of cold air in Siberia.

Aerosol Characteristics of Dust Weather on North Slope of the Qilian Mountains

Xi Lizong, Ba Li, Pang Zhaoyun, Li Baozi, Huang Shan

2024, 35(3): 311-322. DOI: 10.11898/1001-7313.20240305

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Abstract:
Understanding the vertical distribution characteristics of aerosols in dust weather is crucial for further discussion of aerosol-cloud interaction and its impacts on weather and climate. In response to a dust storm in Northwest China on 6 September 2023, Gansu Weather Modification Office conducts aircraft detection and operational flights on north slope of the Qilian Mountains, obtaining the vertical detection data of aerosols. The vertical distribution of aerosols in dust weather is analyzed, and causes of vertical distribution of dust aerosols, related meteorological factors and air mass sources are studied. Results show that the dust weather is formed under the combined action of the upper front area and the surface cold high pressure. Affected by the dust weather, the peak mass concentration of PM₁₀ and PM_2.5 reaches 1150 μg·m^-3 and 282 μg·m^-3, respectively, at Wuwei Environmental Monitoring Station on north slope of the Qilian Mountains. Under the influence of dust weather, aerosol particles across all size segment show an increase in number concentration and particle size. Most of the dust particles are 1.2-1.8 μm and 6.5-16.6 μm in size, and there is a large concentration of aerosol particle number at the height of 4000-4500 m and 3000-4000 m. In addition, compared with the average concentration of particles in the fine particle segment and the coarse particle segment, the average concentration of particles increases by 2 times and 3.5 times, respectively. The average particle size increases by 3 times and 1.5 times, respectively. After the transit of sand and dust, the spectrum width widens, and the high-value region of the number concentration shows an overhanging state. In the coarse particle segment, the distribution of aerosol particle spectra changes from bimodal to trimodal. The increase in aerosol particle number concentration is more pronounced in the coarse particle segment and the lower layer. At the altitude of 500-2000 m above the ground, aerosol particles mainly come from the Gurbantunggut Desert in Xinjiang, while at the altitude of 2000-3000 m, aerosol particles mainly come from the Badain Jaran Desert in Inner Mongolia. In addition, the vertical upward movement in the middle layer and the strong northwest wind speed in the lower layer may play an important role in the vertical and spectral distribution of aerosols. Various sources and transport layers of aerosols, along with the vertical distribution evolution of meteorological elements, play an important role in the vertical distribution and spectral distribution of aerosols.

Cloud Observation by Aircraft During Dust Storms

Ma Xincheng, Bi Kai, Wang Fei, Gao Yang, Huang Mengyu

2024, 35(3): 323-336. DOI: 10.11898/1001-7313.20240306

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Abstract:
Aerosols influence cloud microphysical properties by acting as cloud condensation nuclei and ice nuclei. Aerosols have the potential to modify the location and intensity of precipitation by changing cloud properties. However, identifying precipitation changes induced by aerosols remains a significant challenge for current research. Dust aerosol carried by dust storms is an important source of ice nuclei. China and Mongolia are the primary desert regions in Asia and the world. The Mongolian cyclone in northern China is one of the significant weather systems that cause sandstorms in both countries. Studying the impact of dust aerosols on clouds under the weather conditions of Mongolian cyclones and sandstorms is of great significance. Due to challenges of aerial observations during dust storms, the impact of dust aerosols on clouds is minimally understood during Mongolian cyclone dust storms. In order to investigate the impact of dust aerosols on clouds, a study is conducted based on the comprehensive observation experiment of clouds in Beijing Area carried out by Beijing Weather Modification Center. An extremely rare case of strong sandstorm weather caused by a Mongolian cyclone and cold front is observed on 24 April 2009. The vertical macro and micro physical structure characteristics of dust cloud and clean cloud are compared and analyzed, and the potential influence of dust aerosols on clouds is discussed. Results show that dust aerosol transferred from China-Mongolia areas is an important source of ice nuclei in North China. It can be transferred vertically to a height of 3200 meters above the cloud top. The concentration of ice nuclei in the dust background area is significantly increased by 10 times compared to that in the clean background area. This increase further affects the microphysical structure of cumulus and stratocumulus clouds with high cloud top temperatures (-6 ℃ to -3 ℃) by altering the process of ice crystal formation. At the same temperature, the average concentration of ice crystals in the dust cloud increases significantly by nearly 10 times compared to that in the clean cloud. The liquid water content is reduced, leading to the formation of a large number of small ice crystal particles in the cloud. It inhibits the rime process and results in a significant reduction in the average concentration of precipitation particles compared to that in the clean cloud. Additionally, the spectral width of cloud droplets, ice and snow crystals, and precipitation particles is significantly narrower than that in the clean cloud. It will eventually weaken the precipitation, which will have a significant impact on the weather and climate in North China. It is helpful to enhance our understanding of the indirect effects of aerosols.

Raindrop Size Distribution Characteristics of Summer Precipitation at Xinmin, Northeast China

Zhou Renran, Wang Gaili, Gao Yunyi

2024, 35(3): 337-349. DOI: 10.11898/1001-7313.20240307

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Abstract:
Raindrop size distribution (DSD) is a basic characteristic for describing the microphysical process of rainfall. A better understanding of DSD and its variations is not only crucial for improving microphysical parameterization schemes in numerical weather forecasting models, but also important for radar quantitative precipitation estimation. It shows that DSD characteristics are not only related to geographical location, climate, terrain, and humidity, but also vary among different rainfall types and rain rate in the same region. At present, there are still some uncertainties and limitations in the understanding of microphysical characteristics of rainfall in Northeast China, and the microphysical parameterization scheme still lacks accurate description of rainfall microphysical process. Based on observations of the precipitation phenomenon instrument at Xinmin of Liaoning Province in summer, DSD characteristics of different rainfall rate classes are investigated and compared with those of other regions in China. Spectral width of DSD increases with an increase in rain rate (R). The spectral width of raindrops is close to 8 mm when R>20 mm·h^-1. Small drops are predominant in rainfall of Xinmin, but moderate drops make the most significant contribution to total rainfall. Observed DSD samples are also categorized into convective and stratiform rainfall types. The convective rainfall at Xinmin has large raindrop size and low raindrop concentration. Convective rainfall can be identified as continental clusters, with average D_m and lgN_w of 2.14 mm and 3.40, while average D_m and lgN_w of stratiform rainfall at Xinmin are 1.23 mm and 3.30, respectively. The μ-Λ and Z-R relationships for convective and stratiform rainfall at Xinmin are thus fitted. Fitted μ-Λ relationship at Xinmin is similar to that in other regions fitted with data observed by PARSIVEL disdrometers, but different from the empirical relationship fitted from two-dimensional video raindrop spectrometers (2DVD) observations in other regions, and the difference of instruments is the main cause for the discrepancies of μ-Λ relationships. Compared with East China and North China, Xinmin rainfall has larger D_m, lower lgN_w, and higher exponent value of fitted Z-R power-law relationship for convective rainfall, indicating that the radar reflectivity factor at Xinmin increases more rapidly with the increase of rain rate. Using the Z-R empirical formula fitted at Xinmin can reduce the error of radar-based quantitative precipitation estimation. Results would contribute to the understanding of microphysical characteristics of rainfall in Northeast China and the accuracy of radar quantitative precipitation estimation.

Modeling and Verification of Microwave Scattering Characteristics of Typical Global Tropical Rainforests

Wang Yitong, Hu Xiuqing, Shang Jian, Gu Lingjia, Yin Honggang

2024, 35(3): 350-360. DOI: 10.11898/1001-7313.20240308

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Abstract:
To ensure the microwave scatterometer is accurately calibrated, natural targets with stability, homogeneity, and isotropy are selected as references. The broad and continuous spatial distribution of the tropical rainforest, along with its relatively consistent vegetation cover, makes it an ideal choice.A tropical rainforest optimal stable area selection algorithm, combining mean, standard deviation, and relative standard deviation, is proposed using measurements from the advanced scatterometer (ASCAT) onboard the second Meteorological Operational satellite (MetOp-B) from 2019 to 2021. It is used to identify stable areas within the Amazon, Congo, and Southeast Asian rainforests. Results show that the Amazon rainforest has a larger stable area compared to the Congo and Southeast Asian rainforests, indicating more consistent backscatter across space. However, the Southeast Asian rainforest exhibits scattered stable areas and unstable backscatter properties.To accurately model the intrinsic characteristics of targets within stable areas, influences of seasonal variations, incidence angles and azimuth angles are comprehensively considered. The scatterometer, as an independently measured remote sensing instrument, is not affected by seasonal variations on the earth and experiences minimal temperature-related fluctuations. Therefore, seasonal characteristics of backscatter coefficients in rainforests can be modeled to reduce their impact. Different incidence and azimuth angles can cause variations in the backscatter coefficient. To address this issue, responses to these aspects are also modeled. It is observed that daytime data, with lower model errors, shows greater stability in the stable areas of the Amazon and Congo rainforests. Therefore, daytime data from these areas should be selected to assess instrument stability.A stability verification of ASCAT measurements from the stable areas of the Amazon and Congo rainforest on MetOp-C, covering the period from 1 July 2019 to 31 October 2023, is carried out based on model coefficients derived from the continuous three-year data of ASCAT on MetOp-B. The calibration stability verification quantifies the magnitude of variations in ASCAT measurements over different periods. Through analysis, it's found that measurements from the ASCAT on MetOp-C shows regular fluctuations of about 0.05 dB, indicating relatively stable characteristics.

Applicability Evaluation of Provincial Precipitation Real-time Analysis Product in Beijing

Zhao Wenfang, Wang Huiying, Meng Huifang, Miao Yupeng, Huang Mingming, Fan Min, Tang Wei

2024, 35(3): 361-372. DOI: 10.11898/1001-7313.20240309

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Abstract:
The national precipitation real-time analysis product is a gridded product developed using probability density matching, Bayesian model averaging, multi grid variation, optimal interpolation and other technologies by National Meteorological Information Center. It has advantages of high accuracy, high quality, and spatiotemporal continuity, and is widely used in national nowcasting forecasting operations. In September 2022, National Meteorological Information Center issues a provincial multi-source fusion real-time analysis system to promote the collaborative application of precipitation analysis in different provinces. The same core multi-source fusion algorithms for real-time precipitation analysis products are applied in this system, allowing access to additional provincial local observations. The consistency and accuracy of the provincial precipitation analysis products in Beijing from September 2022 to August 2023 are evaluated by automatic weather station observations, error analysis, effective precipitation time proportion, and other methods. "23·7" extreme precipitation event is also analyzed in terms of cumulative precipitation, precipitation intensity, and hourly precipitation error. Results show that root mean square error of the provincial precipitation analysis product is less than 1 mm, and the average absolute deviation is below 0.16 mm, which closely aligns with observations from automatic weather stations. The bias of provincial precipitation real-time analysis product increases with magnitude of precipitation. The intensity of light rain exceeds the observation, while the spatial distribution difference of bias is evident. The maximum negative deviation occurs in both moderate rain and rainstorm magnitudes of Yanqing, while the maximum positive deviation is observed at Changping. During the extreme precipitation event of "23·7", the spatial distribution of provincial precipitation real-time analysis product is largely consistent with observations from automatic weather stations. The precipitation intensity is consistent with the trend of time variation observed by automatic weather stations, with an average root mean square error of 1.8 mm and an average absolute deviation of 0.806 mm, which more accurately reflects the trend of precipitation intensity variation. Overall, the provincial precipitation real-time analysis product has high accuracy in Beijing and can reflect the spatial distribution of precipitation, but the estimate is lower than the observation in the precipitation course of local heavy rainstorm.

The Design and Implementation of Stream Processing for Data of Ground Automatic Weather Stations

Xiao Weiqing, Xue Lei, Liu Zhen, Luo Bing, Wang Ying, Zhang Laien, Guo Ping, Huo Qing, Han Shuli, He Wenchun

2024, 35(3): 373-384. DOI: 10.11898/1001-7313.20240310

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Abstract:
To process the high-density and high-frequency mass data generated by ground automatic weather stations, a real-time stream processing system based on Storm is designed and implemented in the Meteorological Big Data Cloud Platform (Tianqing). It leverages the advantages of large-scale parallel computing to enhance processing speed. For BUFR messages, a Storm topology is designed to process the standardized BUFR format data transmitted by RabbitMQ directly on the service, reducing the intermediate steps from transmission to processing of observations. In the spout design, the manual confirmation mode of RabbitMQ messages is adopted to ensure that each message is effectively processed. In the decoding process, bolt is anchored to the spout using message identification (ID) to ensure reliable processing of each message. Format and time checks are performed during data decoding to filter out abnormal data. A batch timing monitoring strategy is applied to address the issue of data ingestion loss caused by port occupancy during extensive monitoring data transmission. A startup strategy with a configurable number of spout and bolt is designed for quick optimization and adjustment based on system resources. During cluster deployment, some resources are reserved to enable automatic task migration without disrupting business operations in case of node corruption within the cluster. System design involves automatically reconnecting message queues and databases to enhance system stability and enable self-healing capabilities. Application results show that the service efficiency of 2442 national stations has decreased from 175 s with CIMISS to 78 s with Tianqing. Additionally, the service efficiency of hourly data from over 60000 regional stations has decreased from 5 min with CIMISS to 2 min with Tianqing. After switching the data source of the ART (analysis of real time) system to Tianqing, the number of stations that can be retrieved simultaneously is doubled compared to CIMISS. It can effectively improve the quality of ART live products while keeping other conditions unchanged. By implementing specialized stream processing, it can effectively handle various business scenarios where data access process of the provincial Tianqing ground automatic weather stations differ from that of other provinces. It enables the provincial Tianqing to quickly process nationwide data from ground automatic weather stations. In December 2021, Storm-based stream processing is implemented in the national and provincial meteorological information departments alongside Tianqing. It has been running smoothly over two years, delivering reliable ground automatic weather station data to users, including MICAPS4, SWAN2.0, ART systems and others.

Vol.35, NO.3, 2024