ISSN 1000-0526
CN 11-2282/P

Volume 50,Issue 11,2024 Table of Contents

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  • 1  Thermodynamic and Dynamic Mechanism of Maintenance of Typhoon Doksuri Remnant Vortex After Its Landfall in 2023
    XIANG Chunyi DONG Lin LIU Da WANG Qian ZHUGE Xiaoyong
    2024, 50(11):1289-1305. DOI: 10.7519/j.issn.1000-0526.2024.081901
    [Abstract](99) [HTML](77) [PDF 14.81 M](561)
    Abstract:
    This study utilized ERA5 reanalysis data and multiple observations to investigate the weakening and strengthening of the remnant vortex of Typhoon Doksuri (2023) in the Northwest Pacific after its landfall. It caused significant damages in northern China. The main maintenance and recovery period were observed from the night of July 29th to the daytime of July 30th. The study result reveals that during the maintenance of the remnant vortex, it had a warm-core structure and was not influenced by dry and cold air. During the recovery process, a noticeable increase in water vapor convergence and moist potential vorticity were observed on the northeastern side of the remnant vortex center. Additionally, the northward movement of the remnant vortex was hindered by a zonal subtropical high belt, causing a reduction in its northward-moving speed. Under the guidance of a mid- and high-level high-pressure system, the dry and cold air further intensified the temperature and moisture gradients between the mid- and low-level remnant vortex and warm-moist air masses, resulting in a clear tilt of isentropic surfaces on the northern side of the vortex. This tilt in isentropic surfaces led to the vertical development of cyclonic vortex. Furthermore, during the maintenance and recovery period, the remnant vortex continued to receive some heating from the increased soil moisture. Additionally, significant condensation latent heat was released due to radial moisture inflow and vertical upward motion on the northeastern side of the remnant vortex. This release of latent heat provided necessary conditions for the maintenance and strengthening of the remnant vortex.
    2  Analysis on Structure Changes of Landfall Northbound Typhoons and the Heavy Precipitation in Liaodong Peninsula Induced by Them
    LIANG Jun ZHANG Shengjun JIA Xuxuan FENG Chengcheng LI Tingting LI Sixu
    2024, 50(11):1306-1316. DOI: 10.7519/j.issn.1000-0526.2024.101201
    [Abstract](63) [HTML](41) [PDF 4.78 M](413)
    Abstract:
    The landfall tropical cyclones can often bring heavy precipitation to Liaodong Peninsula when they move northward into the Bohai Sea. Using CMA Tropical Cyclone Yearbook, cloud top brightness temperature and ERA-Interim reanalysis data, we conduct dynamic synthesis and diagnostic analysis of seven typhoons that caused heavy precipitation over the Liaodong Peninsula during their northward moving. The major conclusions are as follows. The typhoons experienced extratropical transition when approaching westerly troughs and had hybrid structures with remarkable baroclinic instability. Meanwhile, the vertical wind shear was enhanced, the vertical structure of the typhoon vortex slanted with height, and mesoscale convection developed on their north sides. The locations of heavy precipitation mainly occurred in the left side along with the direction of vertical wind shears. The standing link of typhoon with a deep southwestern or southeastern jet was favorable for the development of sustained convective activities in the typhoon rain belts, and the typhoons decayed slowly due to abundant moisture supply. Basically, strong-rainfall typhoons moved northward near the entrance area of the westerly jet stream in front of the trough, characterized by strong divergence in the upper layers. The coupling dynamical structure of positive divergence zone and the positive vorticity at lower levels formed, which was favorable for genesis of heavy precipitation and long-time substation of typhoon circulation. The cold air in the middle and upper troposphere invaded into typhoons’ northwest sides and the frontal zone slanted towards northwest with height, increasing the convective instability in the low-level front zone. The coupling dynamic structure of positive vorticity region and the divergence center further uplifted the air on their northeast sides and southeast sides. Liaodong Peninsula was in the north side of the typhoons, possessing strong low-level convergence, vertical wind shear, and deep and persistent vertical motion, thus the precipitation intensity was high and the duration was long over the Liaodong Peninsula.
    3  Analysis on Rapid Weakening of Typhoon Bavi (No.2008) After Its Landfall Northward
    CUI Jin ZHANG Aizhong PARK Jungsuk LI Deqin TIAN Li YI Xue JIAO Min
    2024, 50(11):1317-1330. DOI: 10.7519/j.issn.1000-0526.2024.061801
    [Abstract](60) [HTML](27) [PDF 10.31 M](368)
    Abstract:
    To study the causes for rapid weakening and dissipation of Typhoon Bavi (No.2008) after its landfall in the north, in this study a numerical simulation is carried out with the non-hydrostatic mesoscale model WRF, and the simulated results are verified by the observation data. Furthermore, based on the high-resolution simulation results, the changes of the weather circulation background, ambient field and structural characteristics of Typhoon Bavi before and after its landfall are analyzed. The results indicate that “Bavi” was guided by the southwest airflow ahead of the mid-latitude westerly trough, and was located on the right side of the upper-level jet entrance area before its landfall. The divergence field at the upper level was conducive to maintaining the typhoon circulation. However, after its landfall, the intrusion of dry and cold air into the center of typhoon and the strong vertical wind shear were the main reasons for its loss in structure features and rapid weakening. After its landfall, the upper-level jet on the north side of typhoon decreased and the upper-level divergence weakened. Under such unfavorable upper-level circulation conditions, on the one hand, the strong vertical wind shear, especially from middle to high levels, increased the dispersion of warm air from the high-level warm core, which made the heat unable to concentrate and destroyed the upper warm core structure. On the other hand, the sinking cold air invaded the center of typhoon from the low level on the northwest side, and the vertical structure of “Bavi” was destroyed, then the height of warm core decreased and tilted to the northeast, so “Bavi” dissipated rapidly after its gradual loss of structure features. At the same time, insufficient water vapor supply after the landfall of “Bavi” was not good for its maintenance.
    4  Forecast Difficulties and Model Performances in Typhoon Haikui (2311) Forecasting
    WANG Haiping ZHANG Ling DONG Lin XIANG Chunyi XU Yinglong NIE Gaozhen
    2024, 50(11):1331-1342. DOI: 10.7519/j.issn.1000-0526.2024.082101
    [Abstract](70) [HTML](38) [PDF 11.26 M](372)
    Abstract:
    Typhoon Haikui (2311) moved west-northwestward and repeatedly wobbled, forming a serpentine path. It strengthened into a super typhoon category before landing on Taiwan Island. Then, it moved slowly after entering the Taiwan Strait. After it landed again, its residual vortex sustained for about 5 days, resulting in the long-time precipitation and large accumulated rainfall. Different models and different members of ensemble forecast also had large errors and uncertainties in forecasting the landing spots and landfall strength of Haikui, which brought great challenges to forecast correction. ECMWF, NCEP and CMA deterministic forecast and ensemble forecast data are used to analyze the main characteristics of Haikui and critical difficulties in the process of operational forecast. There exist large errors and differences in the forecast of typhoon track in the offshore waters of China, and the operational correction problems in the intensity forecast are affected by the uncertainty of the track forecast. Besides, it is difficult to quantitatively estimate the time of the typhoon’s slowly moving that was caused by weak steering flow and terrain influence after the typhoon crossed Taiwan Island and entered the Taiwan Strait. Moreover, it is also difficult to quantitatively estimate the time of typhoon’s residual circulation maintenance, track and precipitation influence after the typhoon made landfall weakening.
    5  Severe Convection Prediction Method Based on XGBoost Classified Algorithm and Numerical Model Ingredients
    LI Wenjuan LI Minjie MA Hao HUANG Xuanxuan ZHANG Zhicha
    2024, 50(11):1343-1358. DOI: 10.7519/j.issn.1000-0526.2024.081902
    [Abstract](64) [HTML](33) [PDF 6.91 M](408)
    Abstract:
    Improving the accuracy of objective classification and spatio-temporal forecast of severe convective weather has always been a challenge in meteorological forecasting. This paper integrates mesoscale models with machine learning classification algorithms, achieving hourly forecasting of classified severe convection. The specific algorithm is as follows. First, the XGBoost classification algorithm and historical data over 10 years are used to establish a classification potential forecast model for severe convection. Secondly, by statistically analyzing the optimal spatial neighborhood radius and probability density distribution characteristics of CMA-SH9 model elements, and extracting element thresholds based on the combination of optimal scores, a spatial neighborhood graded element ingredient model is established. Finally, through joint discrimination, the machine learning classification method and the spatial neighborhood element “ingredient method” are integrated to establish hourly forecast models for thunderstorm gales and short-time heavy rainfall. The validation results show that this fusion algorithm significantly outperforms numerical model forecast results and national guidance products. For short-time heavy rainfall forecasts on an hourly basis over 24 h during 2021-2022, the average hit rate is 0.51 and the TS (threat score) is 0.15, which reflects the improvements of 82% and 36% respectively compared to the model. For thunderstorm gale forecasts on an hourly basis over 24 h, the average hit rate reaches 0.37 and the TS is 0.07, representing improvements of 68% and 133% respectively relative to the model (reflectivity factor ≥45 dBz). Thus, the forecast accuracy of thunderstorm gale is significantly improved.
    6  Study of Hail Potential Forecast in Chengde Mountains Based on Bayesian Method
    GAO Yanchun HU Zhiqun WANG Hong HU Saian HU Qilu
    2024, 50(11):1359-1372. DOI: 10.7519/j.issn.1000-0526.2024.022102
    [Abstract](82) [HTML](37) [PDF 3.57 M](359)
    Abstract:
    A total of 184 hail weather cases in Chengde Mountains from April to September in 2000-2020 are analyzed by means of multi-source data including the hail observation, CINRAD/CB weather radar data, NCEP FNL reanalysis data, and NCEP-GFS forecasts. Firstly, the distribution characteristics and forecast thresholds of relevant ambient parameters such as water vapor, thermal instability, dynamic lift and characteristic height are analyzed in the form of box plots. Then, the initial optimal threshold values are set according to the results of box plots. The hail labels are determined according to the hail observation records or composite reflectivity greater than or equal to 60 dBz from April to September in 2014-2020. The hail labels are matched to the grids of reanalysis data according to the principle of near location and proximity time to construct the positive and negative sample dataset for feature parameter selection, interval segmentation and probability calculation. Next, five models for 3, 6, 9, 12 and 24 h hail potential forecast are established by the Bayesian method. The models are tested focusing on the weather processess from June to August during 2021-2022. The results suggest that the Bayesian-based hail potential prediction models have a certain feasibility in daily weather forecasting. The hit rates of all the models are above 90%, and the average critical success index is over 40.3%. Differing from the traditional probability and ingredient methods, the method can provide a better objective forecast of hail occurrence, which has a certain reference value for forecasting severe convective weather in mountainous areas. However, there are some false alarms as the spatio-temporal scale of the reanalysis data is much larger than that of severe convective weather, which needs to be improved in the future.
    7  Verification of FY-3D Satellite Humidity Profiles Using Descending Phase Data of Round-Trip Drifting Sounding
    ZHOU Xuesong HONG Guan XIA Yuancai LUO Haowen BAO Weizhi TIAN Hong
    2024, 50(11):1373-1385. DOI: 10.7519/j.issn.1000-0526.2024.063002
    [Abstract](56) [HTML](22) [PDF 11.03 M](344)
    Abstract:
    The round-trip drifting sounding system (RDSS) can detect the atmospheric temperature profile vertically from ground to the lower stratosphere and the horizontal temperature distribution in the lower stratosphere continuously for 4 hours. Round-trip drifting sounding observation tests have been carried out in the middle and lower reaches of the Yangtze River, Guangdong, Inner Mongolia and other places, and the results are very successful. Based on the data of round-trip drifting sounding tests in the middle and lower reaches of the Yangtze River from March to September 2021, this paper conducts the verification of atmospheric humidity profile data of satellite. The verification results of the descending phase data of the round-trip drifting sounding indicate that the average absolute error of the satellite humidity profile is about 15%, and the root mean square error is approximately 20%. At noon and night, the quality of humidity profile data of satellite is better than that in the morning and evening. The humidity average absolute error of the satellite decreases with increasing altitude and increases with increasing humidity. Below the 50% humidity, the satellite-retrieved humidity is relatively large, but for the humidity above 50%, the satellite-retrieved humidity is relatively small.
    8  Experiments and Verification on Doppler Radar Network Wind Fields Retrieved by the IVAP Method
    YAO Xiaojuan SUN Xin JI Yanxia LIU Linchun MENG Xuefeng
    2024, 50(11):1386-1396. DOI: 10.7519/j.issn.1000-0526.2024.070301
    [Abstract](64) [HTML](13) [PDF 4.90 M](349)
    Abstract:
    Wind observation data are very important in weather research and forecasting. The IVAP technique, which is based on the azimuth uniform assumption retrieval relationship, offers good compatibility and practical simplicity for 2-D wind field retrieval. In this paper, the large-scale precipitation events from July to August 2020 are selected, and the wind fields from the Doppler radar network are retrieved by the IVAP method. At the same time, the quality of the retrieved wind fields is evaluated and analyzed with the seconds-sounding data as a reference. The results indicate that the retrieved wind fields of Doppler radar network have a high correlation with the sounding data, and the quality of wind direction data is better than the wind speed data with altitude rising. The quality of the retrieved winds is better in precipitation areas than in the non-precipitation areas. Moreover, the quality of wind field and the stability of vertical profile are the best in precipitation areas, but the quality of the retrieved winds is the worst in clear sky areas, especially when the altitude is higher than 4 km. The retrieved winds of a scattered precipitation process on 6 July 2019 are further analyzed, which demonstrates that the retrieved wind field can reasonably reproduce the dynamic field characteristics such as vortex structure and shear line of the upper wind field. This study shows that based on the single Doppler radar wind field retrieval, the IVAP method has the ability to retrieve wind fields of Doppler radar network, so the method will have a good application prospect in practical operations, and can provide a better basis for weather forecasting services and wind data assimilation.
    9  Refined Evaluation of Spring Temperature Forecast in Beijing During 2019-2021
    LI Nina LIU Couhua LIN Jian DAI Kan WEI Qing ZHAO Shengrong
    2024, 50(11):1397-1408. DOI: 10.7519/j.issn.1000-0526.2024.050601
    [Abstract](67) [HTML](60) [PDF 2.62 M](339)
    Abstract:
    Using the 3 h observation data from national-level stations in Beijing Region in spring (February to April) during 2019-2021, we evaluate the temperature forecasts made by numerical models including European Centre for Medium-Range Weather Forecasting (ECMWF) and Global and Regional Assimilation and Prediction System (CMA-GFS), and by national gridded guidance forecast product (SCMOC) as well as the revised feedback gridded forecast product at provincial level (SMERGE). The results show that the spring temperature forecasts in Beijing by the models of ECMWF and CMA-GFS often show negative biases. The biases have no significant difference in mountainous and plain areas, but more prominent during nighttime periods. The gridded forecast products (SCMOC and SMERGE) have a good ability to correct the temperature forecasted by the models (ECMWF and CMA-GFS). The temperature forecast biases of the gridded products are concentrated in the range of -1-1℃, meanwhile the forecast accuracy is higher and the mean absolute error is lower than that of model forecast. Some problems are found in the forecasts of 24 h temperature change and diurnal temperature range from the four products. The amplitude of intense 24 h temperature change forecasted by all products is relatively smaller than that of observation, and the gridded forecast products fail to demonstrate significant correction ability. In addition, the diurnal temperature range forecasted by all products has a positive deviation of 1-3℃ compared to the observation. SCMOC has a better correction ability for the diurnal temperature range by the models, while SMERGE overestimates the difference more prominently than that by models. The positive deviation of diurnal temperature range forecast is closely related to the underestimation of low temperature at 05:00 BT in the models, while the overestimation of high temperature at 14:00 BT can not be ignored in the grid forecasts. The refined analysis suggests that gridded forecast products should not only focus on improving overall accuracy (reducing biases), but also on the development and evolution of synoptic processes.
    10  Analysis of August 2024 Atmospheric Circulation and Weather
    LI Xiaomeng SONG Qiaoyun YANG Yin
    2024, 50(11):1409-1416. DOI: 10.7519/j.issn.1000-0526.2024.102301
    [Abstract](80) [HTML](56) [PDF 3.09 M](584)
    Abstract:
    The main characteristics of the general atmospheric circulation in August 2024 are as follows. There were two polar vortex centers in the Northern Hemisphere and they were stronger than normal. The circulation at middle-high latitude of the Eurasia showed a two-trough and two-ridge pattern. The location of the western Pacific subtropical high was more westward and northward compared to that in normal years. In August, the monthly average precipitation in China was 96.5 mm, 9.9% lower than normal (107.1 mm), and the monthly average temperature was 22.6℃, higher than normal (21.1℃) by 1.5℃. During this month, the high temperature days were more than normal for the same period of the year. The continuous high temperature weather in southern China was highly extreme, and meteorological drought developed along the middle and upper reaches of the Yangtze River. Five torrential rain processes occurred in China, and rainstorm events appeared frequently in northern China, with high overlap of rainstorm-hit areas and strong disaster causing ability. There were six tropical cyclones active over the Northwest Pacific in August, and no tropical cyclones formed or passed through the South China Sea or landed in China. Severe convection events occurred frequently and dispersedly, causing localized serious damages.


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