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30 June 2021, Volume 37 Issue 3 Previous Issue    Next Issue

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Improvement of nowcasting for a squall line using cycling assimilation radar data Qi-ru DONG, Xiao-bin QIU, Ying WANG, Ze-lin WANG, Ji LI, Mian LIANG 2021, 37 (3):  1-11.  doi: 10.3969/j.issn.1673-503X.2021.03.001 Abstract ( 240 )   HTML ( 17 )   PDF (9087KB) ( 98 )   Save Using the Weather Research Forecast (WRF) model and the Three-Dimensional Variational (3DVar) assimilation system, numerical sensitivity experiments were conducted to examine the performance of using radar data cycling assimilation to predict a squall line event in the surrounding areas of Beijing on July 7, 2017.Among the experiments, the best prediction occurred when the squall line reached the mature period with the use of the cycling assimilation of radar data.The main reason is that with the use of the cycling assimilation of radar data, the forecasted low-level northwesterly cold air is relatively strong, which leads to strong low-level wind shears.This is favorable for the maintaining of the squall line's development, in conjunction with strong thermal instability conditions.The comparison of 7 sensitivity experiments showed that for single radar data, the timing of assimilation is more important.The assimilation of radar reflectivity data at the mature stage of the squall line can improve the low-level thermal stratification and provide unstable energy for the development of the squall line.For cycling assimilation, the flow fields can be well modified through the observation influence and the thermodynamic adjustment of the model itself, which provides sufficient dynamic conditions for the continuous development of the convective system. Figures and Tables | References | Related Articles | Metrics

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Causes of a weak rainfall event during the opening ceremony of the Beijing International Horticultural Exhibition Lu GAN, Jin-lan GUO, Lei LEI, Nan XING 2021, 37 (3):  12-18.  doi: 10.3969/j.issn.1673-503X.2021.03.002 Abstract ( 160 )   HTML ( 5 )   PDF (4302KB) ( 57 )   Save From the evening to the night on April 28, 2019, a weak rainfall occurred in the northern area of Beijing, which had a certain impact on the preparations for the opening ceremony of the Beijing World Horticultural Exposition in China.This article analyzes the causes of the weak-intensity and high-impact rainfall weather and discusses the major concerns of the on-site meteorological service of the major events of the opening ceremony.The results showed that during the opening ceremony of the Expo, it is affected by a weak short-wave trough and the dynamic conditions are relatively weak.Beijing is located at the rear of high pressure and the front of the convergence zone of low pressure, with descending or weak ascending movements at low levels.Various numerical models can forecast the occurrence of this rainfall event, but they do not show obvious advantages in the time and scope of the occurrence of rainfall.Using ground automatic stations, wind profilers, and cloud radars, and other high-resolution detection data, combined with refined model forecast products, it is helpful for forecasters to accurately study the short-term evolution of the precipitation system.Meteorological support for major events often focuses on single-point forecasts.Combining weather-affected risk forecasting services with response plans, and adopting certain service strategies can effectively make up for the shortcomings of forecasts and better bring out the benefits of meteorological services. Figures and Tables | References | Related Articles | Metrics

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Evaluation of multi-model precipitation forecast of Northeast Cold Vortex in Fuxin Xu ZHANG,Bao-li SUN,Jia-ning BAI,Dan-mei ZHANG,Ke SUN,Xiao-tong YANG,Zhen-yu ZHAO,Xi-long NING 2021, 37 (3):  19-24.  doi: 10.3969/j.issn.1673-503X.2021.03.003 Abstract ( 227 )   HTML ( 3 )   PDF (701KB) ( 107 )   Save This study evaluated forecast performance of the 24-h precipitation induced by Northeast Clod Vortex using the European Center for Mesoscale Weather Forecast (ECMWF) model, the Global/Regional Assimilation and Prediction System (GRAPES), and Global Forecast System of the National Centers for Environmental Prediction (NCEP_GFS), in order to improve the prediction capability of numerical models in Fuxin and provide scientific references for the choice and adjustment of physical parameter schemes in models.Using the precipitation products from May to August of 2019, the tests for the accuracy of sunny/rainy weather, general precipitation, and grading precipitation, as well as their mean absolute errors and mean errors were conducted at two national observation stations (Fumeng station and Zhangwu station) in Fuxin.The results showed that the precipitation forecast of the ECMWF model is better than that of the other two models.The TS score of ECMWF products is higher during the cold vortex development period and the mature period and is lower during the decay period.In terms of the mean absolute error, the ECMWF has the smallest error at Fumeng station from May to August, and the forecast performance of GRAPES and NCEP_GFS is unstable.At the Zhangwu station, the ECMWF has no obvious advantage, the GRAPES performs best from May to June, and the NCEP_GFS performs best in July and August.The mean error analysis shows that all three models underestimate precipitation at Fumeng and Zhangwu stations except for an overestimation of precipitation at Zhangwu station in June.All models underestimate the precipitation of heavy rain and above, with the highest TS score of 40.2% from the ECMWF model.Moreover, all three models have higher precipitation TS scores at Fumeng station than Zhangwu station. Figures and Tables | References | Related Articles | Metrics

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Comparison of visibility measurements using DNQ1 and FD12 visibility meters and their major influencing factors Xiao-lan LI, Wei-jun QUAN, Dong-dong WANG, Di WANG 2021, 37 (3):  25-32.  doi: 10.3969/j.issn.1673-503X.2021.03.004 Abstract ( 222 )   HTML ( 7 )   PDF (6252KB) ( 227 )   Save The DNQ1 forward scattering visibility meter is currently one of the most widely used visibility meters at weather stations in China.However, rare studies have evaluated and compared the performance of DNQ1 visibility meters with other similar visibility instruments worldwide.Therefore, we conducted a comparative study using observation data of DNQ1 and FD12 visibility meters at the Shangdianzi National Atmosphere Watch Station from January to March 2015.The characteristics of observed differences between the two visibility meters and their relationships with major meteorological parameters and atmospheric components were analyzed in this study.The results indicated that hourly mean visibility measured by two instruments exhibits a consistent variation trend, with a correlation coefficient of 0.98.Except for rainfall, the difference in visibility observed by DNQ1 and FD12 instruments is less affected by different weather conditions (including sunny days, sand-dust, fog, haze, rainfall, and snowfall), but the difference range and dispersion increase as visibility level increases.The visibility difference shows an exponential decrease with the increase of relative humidity, a linear positive correlation with air temperature, and an insignificant relationship with air pressure, wind speed, and wind direction.The mean relative deviation between DNQ1-and FD12-measured visibility at different times of the day is on average less than ±10%, which indicates that the NDQ1 visibility meter meets observation needs.The correlation between the two visibility at night is better than that during the day, which may be related to the daily variation of relative humidity and temperature. Figures and Tables | References | Related Articles | Metrics

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Impacts of precipitation and wind on PM2.5 concentration and its region transport in Tai'an Zhao-peng LUAN,Hui-chao LU,Tian LI,Xiang-qian CUI,Tian-liang ZHAO,Qing-rui ZHU 2021, 37 (3):  33-39.  doi: 10.3969/j.issn.1673-503X.2021.03.005 Abstract ( 143 )   HTML ( 9 )   PDF (1178KB) ( 157 )   Save Using the hourly observation data of precipitation, wind, and PM2.5 in Tai'an from 2018 to 2019, the impacts of precipitation and wind on PM2.5 concentration as well as the source of PM2.5 were analyzed.The results showed that precipitation has a certain scavenging effect on PM2.5.The average mass concentration of PM2.5 on rainy days is about 7.2% lower than that on non-rainy days, especially in autumn and winter.The scavenging rate of PM2.5 by precipitation is related to precipitation intensity, initial PM2.5 concentration before precipitation, and precipitation duration.The scavenging rate of PM2.5 is higher than 40% when the precipitation intensity is greater than 4 mm·h-1.The PM2.5 concentration tends to rebound under conditions of precipitation intensity < 2 mm·h-1, or the initial PM2.5 concentration < 75 μg·m-3 and precipitation intensity < 1 mm·h-1, or the initial PM2.5 concentration within the range of 75-100 μg·m-3 and precipitation duration < 5 h.Different wind directions and wind speeds show different impacts on the scavenging of haze particles in Tai'an.The west-southwesterly wind and the east-northeasterly wind are more likely to cause haze pollution in the Tai'an area.During heavy pollution, the southerly winds > 5 m·s-1 and the northerly winds > 3 m·s-1 can effectively remove pollutants.PM2.5 is mainly transported from Guangxi-Hu'nan-Jiangxi provinces, southern Anhui province, and northern Zhejiang province to Tai'an by southwesterly airflows, and less contribution is from the local emissions. Figures and Tables | References | Related Articles | Metrics

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Analysis of the characteristics of O3 concentration and its influencing factors in summer from 2017 to 2019 in the southern urban area of Taiyuan Sheng-dong LU, Jun-xia LI, Fen LI, Jun-jie ZHAO, Ze-hui JIN, Ying LI, Xiao LIU 2021, 37 (3):  40-46.  doi: 10.3969/j.issn.1673-503X.2021.03.006 Abstract ( 146 )   HTML ( 8 )   PDF (868KB) ( 120 )   Save Based on the hourly data of pollutant concentration and relative meteorological factors during summer (June to August) from 2017-2019, the distribution characteristics of O3 concentration and its influencing factors in Taiyuan were analyzed using the neural network method.The results show that, during the summer from 2017-2019, the numbers of days in which the O3 concentration exceeds the limit in Taiyuan are 55 d, 39 d, 59 d, respectively.The cases that the O3 concentration exceeds the limit mostly occur in June and July.The diurnal variation of O3 concentration is unimodal, with the lowest around 06:00, and the peak around 15:00.The conditions such as high temperature, strong radiation, low humidity, low pressure, and southwest wind can easily lead to an increase of O3 concentration in Taiyuan urban areas.The NW wind is beneficial to the diffusion of O3 concentration.The relationships of NO2 and CO with O3 concentration are negative, and the influence of NO2 is more significant.The selected cases show that the O3 concentration fluctuates with the influencing factors.The relationship between O3 concentration and the influencing factors is constructed using the neural network method, with the correlation coefficient of 0.96, the mean square root and average absolute error of 8 μg·m-3 and 6%, respectively, and TS score of 0.95.The neural network model is valuable for the O3 concentration prediction and ozone pollution control in the Taiyuan area. Figures and Tables | References | Related Articles | Metrics

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Effects of low-frequency oscillation on the persistent extreme precipitation in Western Sichuan Yao HUANG,Jia-xing YOU,Tian-gui XIAO,Jie GUO 2021, 37 (3):  47-56.  doi: 10.3969/j.issn.1673-503X.2021.03.007 Abstract ( 337 )   HTML ( 2 )   PDF (8935KB) ( 48 )   Save Based on the precipitation data from the surface meteorological stations and the NCEP/NCAR (the National Centers for Environmental Prediction-the National Center for Atmospheric Research Reanalysis) data during 1981-2016, the effects of low-frequency oscillation on the persistent heavy precipitation in Western Sichuan were analyzed using the synthetic analysis and Butterworth filtering methods which provided a theoretical reference for the extended period forecast.The results show that the precipitation in Western Sichuan is mainly characterized by low-frequency oscillation in 15-30 d.During the precipitation period, the low-frequency northeast wave and southwest wave in the low level merge and form a convergence area over Western Sichuan.Before precipitation, a low-frequency anticyclone and a cyclone are generated over the Kara Sea and northwest Asia, respectively.These two systems move southeast to the vicinity of Lake Baikal and the Sea of Japan, respectively, which transport cold air for precipitation in Western Sichuan.The low-frequency cyclone over the Indian Peninsula converts into an anticyclone to transport water vapor from the Arabic Sea to Western Sichuan.On the middle level, the low-frequency northeast airflows from the mid-high latitude propagate southward to the rain area.The low-frequency high pressure and low-frequency low pressure correspond to the low-frequency anticyclone and cyclone in the low level, respectively, which propagates to the southeast and affects the Western Sichuan region.On the upper layer, the propagation of low-frequency waves mainly occur in the mid-high latitude.Before the precipitation, the low-frequency anticyclone and the divergence center formed in the west of Lake Baikal first move to the southeast and then extend to the southwest, which controls the beginning of precipitation over the Western Sichuan area. Figures and Tables | References | Related Articles | Metrics

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Analysis of precipitation variation and water vapor flux characteristics in summer under the background of global warming in Liaoning province Shu-ting CHANG,Xue BAI,Zi-yi QU,Zhou WEN,Yu-xiu XU,Ming GAO,Cui-yan ZHANG 2021, 37 (3):  57-64.  doi: 10.3969/j.issn.1673-503X.2021.03.008 Abstract ( 269 )   HTML ( 3 )   PDF (2222KB) ( 102 )   Save Based on the precipitation data from the daily surface climate data set (V3.0) provided by China Meteorological Data Network and the monthly reanalysis data from ERA (European centre for medium-range weather forecasts Re-Analysis) Interim, the characteristics of summer precipitation and the influence of water vapor transport over Liaoning province under the background of global warming since 1999 were studied.The results show that under the background of slowing down of global warming, the summer precipitation in Liaoning province has a certain increasing trend, but the trend is weak.The increasing trend of precipitation in the southern part of Liaoning province is more significant than that in other regions, which contributes a high degree to the overall precipitation change in Liaoning province.There is a high positive correlation between water vapor flux and precipitation over the northern and southern border of Liaoning province in summer.The southern boundary has the most significant correlation.The contribution of meridional water vapor flux to precipitation is higher than that of zonal water vapor flux, and the high-value area is mainly located in the lower troposphere of eastern and southern Liaoning province, which has an impact on local precipitation.The meridional water vapor flux in the troposphere of southern Liaoning province has a significantly positive correlation with precipitation in Liaoning province.Based on the analysis of the influence of atmospheric circulation background field on the water vapor flux the northward movement of western Pacific subtropical high ridge is an important factor causing the increase of water vapor flux in Liaoning province which directly affects precipitation variation and results in an increasing trend of precipitation in summer in Liaoning province under the background of global warming. Figures and Tables | References | Related Articles | Metrics

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Projection of climate change over Centre China by high-resolution simulation data under RCP4.5 scenario Miao WANG,Min LIU,Yong-jian REN 2021, 37 (3):  65-72.  doi: 10.3969/j.issn.1673-503X.2021.03.009 Abstract ( 184 )   HTML ( 6 )   PDF (3484KB) ( 96 )   Save Based on the data from the high-resolution RegCM4.4 (Regional Climate Model version 4.4) and the daily meteorological observations from 1986-2005, the climate change in the future in Central China was estimated under the temperature rising threshold of 1.5℃ and 2℃.The model simulation performance was tested.The results show that the simulation results can accurately reflect the annual variation and spatial distribution characteristics of regional air temperature and precipitation.Compared with the observed values, the simulated values of temperature are lower and the simulated values of precipitation are larger.Compared with 1986-2005, under the future RCP4.5 (Representative Concentration Pathway 4.5) greenhouse gas emission scenario, the increase of air temperature in Central China during 2020-2098 is 2.1℃, and the increasing trend is 0.3℃/10 a, while the precipitation trend has no significant change.The long-term (2080-2098) temperature will rise by 2.88℃, and the precipitation will increase by 7.58%, which are both higher than the recent (2020-2035) and medium-term (2046-2065) 1.5℃ temperature rise scenarios in Central China, where the temperature will rise by 1.22℃, and the precipitation will increase by 1.93%.Under the 2℃ temperature rise scenario, the temperature in Central China increases by 1.36℃, and the precipitation increases by 3.57%. Figures and Tables | References | Related Articles | Metrics

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Study on the characteristics of temperature change in Yingkou city in the past hundred years Li LI,Yan CUI,Hao-yu WANG,Guo-zhen WU,Ming YANG,Yun-zhi ZHANG,Xiao-chuan ZHAO 2021, 37 (3):  73-80.  doi: 10.3969/j.issn.1673-503X.2021.03.010 Abstract ( 195 )   HTML ( 4 )   PDF (2014KB) ( 247 )   Save Based on the temperature data from the national meteorological observation station from 1904-2019, the variation law and characteristics of temperature in Yingkou city in recent 116 years were analyzed using the linear trend estimation, 7 years moving average, Mann-Kendall test, Morlet wavelet analysis, and other methods.The results show that the annual mean temperature in Yingkou city illustrates a clear increasing trend, with an increasing rate of 0.17℃ per decade.The average temperature of each season also shows an obvious upward trend, with the fastest rising rate in winter, followed by spring and autumn, and the slowest rising rate in summer.The annual mean temperature has obvious interdecadal variation characteristics, which roughly experiences the change process of "cold-warm-cold-warm", and also presents different change processes in each season.There were abrupt changes in annual mean temperature, spring, summer, autumn, and winter mean temperature in 1987, 1988, 2015, 1991, and 1979, respectively.The annual mean temperature has periodic oscillation of 6 years, 20 years, 37 years, and 64 years, of which 64 years is the main period.The seasonal mean temperature also has periodic oscillation of different time scales in Yingkou city. Figures and Tables | References | Related Articles | Metrics

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Spatial and temporal variation characteristics of extreme temperature in Shaanxi province from 1961 to 2018 Xiao-hua ZHENG, Pan-xing LOU, Yong-yong MA 2021, 37 (3):  81-87.  doi: 10.3969/j.issn.1673-503X.2021.03.011 Abstract ( 304 )   HTML ( 7 )   PDF (1962KB) ( 354 )   Save Based on the daily temperature data of 94 meteorological stations in Shaanxi province from 1961 to 2018, ten types of extreme temperature indices proposed by WMO were employed to analyze the spatio-temporal characteristics of extreme temperature events in three climate regions of Shaanxi province i.e.Shanbei, Guanzhong, and Shannan using linear trend rate, Mann-Kendall and wavelet methods.The results show that the extreme temperature indices significantly change in the past 60 years in Shaanxi province.The increasing trend of the thermal index is more obvious than the decreasing trend of the cold index with a large inter-annual variation.The change of the night index is more prominent than that of the corresponding day index.Among them, the warm night days increase with a rate of 7.4 d per decade.Except for the extreme minimum temperature, the other cold indices change abruptly around 1995, while the abrupt changes for the numbers of warm night and warm day both occur after 2005.The change trends of ice days, cold days, and hot night days all indicate the most obvious zonal characteristics.The change trends of extreme minimum temperature, cold night days, warm night days, frost days, and summer days in Guanzhong are more significant than in the other two regions.The cyclical changes of the extreme index are mainly concentrated between 2 years and 8 years.Compared with the extreme index, the changes of the relative index and the absolute index are capable to better reflect the change trends in the annual average maximum and minimum temperatures in Shaanxi province. Figures and Tables | References | Related Articles | Metrics

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Correlation analysis of NDVI and meteorological factors in the West Liao River Basin Bao-xing TIAN,Dan LIU,Li-juan GONG,Fang ZHAO,Sheng-tai JI,Hui-ying ZHAO,Cheng-long YU 2021, 37 (3):  88-93.  doi: 10.3969/j.issn.1673-503X.2021.03.012 Abstract ( 122 )   HTML ( 3 )   PDF (937KB) ( 214 )   Save The paper aims to understand the distribution rule and trend change of the normalized difference vegetation index(NDVI) and its response to climate change in the West Liao River Basin.Linear regression and correlation analysis were used to analyze the delay of NDVI and meteorological factors in each month of the growing season, and the correlation between NDVIs of different vegetation types and meteorological factors in the 10 km buffer zone around the meteorological station based on the daily meteorological data of 11 meteorological stations and MODIS normalized difference vegetation index data set from 2000 to 2018.The results showed that the annual temperature, the highest temperature, the lowest temperature, and the precipitation in the West Liao River Basin all saw an uptrend.The NDVI of different vegetation types was on the rise in the West Liao River Basin, and the vegetation was improved.The increased rate of cultivated land was the largest, which benefited from the improvement and promotion of agricultural activities.The spatial distribution of NDVI was characterized by low value in the middle and high value around the West Liao River Basin.NDVI in each month lagged obviously behind precipitation in the growing season with a lag period of one month, only the NDVI in August lagged behind the average and maximum temperatures in the previous month.NDVIs of different vegetation types were closely related to the average and maximum temperatures in the West Liao River Basin.There were better correlations between NDVI of cultivated land and meteorological factors.The results provide a reference for maintaining the balance of the ecosystem in the West Liao River Basin. Figures and Tables | References | Related Articles | Metrics

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Study on relationships between highway traffic accidents and meteorological factors in Jilin province Yun-feng LI, Yong XIE, Shun-mei JIN, Ye-jun LIU 2021, 37 (3):  94-101.  doi: 10.3969/j.issn.1673-503X.2021.03.013 Abstract ( 174 )   HTML ( 3 )   PDF (1446KB) ( 241 )   Save Based on the daily traffic accident data of 27 major highways in Jilin province from 2009 to 2019, combined with the observational data of 24 national meteorological stations in Jilin province corresponding to the accident points of the highways, the spatio-temporal distribution characteristics of highway traffic accidents and their relationships with meteorological elements were analyzed and studied using the k-mean cluster, data standardization, Principal Component Analysis (PCA) and accident ratio methods from SPSS software.The results show that the accidents were the most in winter, followed by summer, fewer in spring and autumn.The highway accidents were basically divided into four grades i.e.high risk, second high risk, medium risk, and low risk.Specifically, the central region was the high-risk area, and the northern region was the low-risk area, and the most accidents occurred in the area from Changchun to Jiaohe and the eastern part of Yanbian on the Huiwu line.Meteorological elements including rain, overcast, and snow were the main causes of traffic accidents.Only considering the influence of a single factor, rainfall and snowfall were positively related to the traffic accidents.Visibility was able to be adopted to quantify the influence of overcast on highway traffic safety and was the most important influence factor on traffic accidents when it was below 50 meters, especially under the wind force of level 6 or above. Figures and Tables | References | Related Articles | Metrics

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Analysis of the soil temperature corresponding to the frozen point based on manual frozen soil observation Yan-yun SUN,Chuan-hai MIAO,Yu CONG,Ruo-nan WANG,Chang HOU,Ying HAN,Lin LI,Nan-shu AO 2021, 37 (3):  102-109.  doi: 10.3969/j.issn.1673-503X.2021.03.014 Abstract ( 205 )   HTML ( 1 )   PDF (1744KB) ( 35 )   Save Based on the data observed with the manual frozen soil apparatus (MFSA) and the temperature-measuring automatic frozen soil apparatus (TMMFSA) from December 2018 to March 2020 at four national surface meteorological stations i.e.Kazuo, Shenyang, Liaoyang, and Manzhouli, the freezing point obtained from MFSA and soil temperature measured with TMMFSA were compared.The results show that the freezing point temperature from MFSA was generally consistent with 0℃ with some small differences.At 0-35 cm soil depth, soil temperature corresponding to the freezing point was between -2 to 6℃ with a jumping change.Below 35 cm soil depth, soil temperature corresponding to the freezing point ranged from -0.5 to 1℃, and the mean temperature corresponding to the freezing point in the melting process was higher than that in the freezing process.The completely melting time observed with MFSA was later than that when the 0℃ lines observed by TMMFSA disappeared completely.The essence of artificially frozen soil observation is to obtain the position of soil temperature of 0℃.Under the same temperature conditions, there is no obvious difference between freezing and melting state in the inner pipe of the frozen soil observation instrument filled with water from different stations.The freezing process of the inner pipe of MFSA was closely related to the temperature and duration of the persistent freezing.Specifically, slow change of soil temperature in the deep layer causes the increase of duration of freezing and melting of water in the pipe.As a contact temperature measuring device, reducing the time delay caused by external reasons is very important to improve its sensitivity.It is suggested that the metal outer tube with less temperature lag effect should be used in TMMFSA, and the soil temperature with high spatio-temporal resolution obtained by TMMFSA should be applied to business.More importantly, soil temperature data measured by TMMFSA can provide sufficient data to support the study of the characteristics of soil temperature change and the heat exchange between soil and atmosphere. Figures and Tables | References | Related Articles | Metrics

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Analysis of the structure characteristics and seeding possibility of low trough cold front stratiform cloud in winter in Hebei province Wei LIU,Yu-wen SUN,Xiang-yong XIE,Xiao-shen SUN,Zhi-jun ZHAO,Yi HUANG 2021, 37 (3):  110-116.  doi: 10.3969/j.issn.1673-503X.2021.03.015 Abstract ( 132 )   HTML ( 4 )   PDF (3755KB) ( 41 )   Save A low trough cold front precipitation process occurred on January 6, 2018, in Hebei province.Based on two sets of aircraft detection data, macro and micro cloud structure and cloud development process were analyzed, and the catalytic condition and seeding opportunity for the stratiform cloud in low trough cold front system in winter were investigated.The results show that when the wind center of southwest wind occurred at an altitude of 6500 m at the beginning of the weather system, the wind speed was discontinuously distributed with the height, the cloud top temperature of stratiform cloud was around-29.2℃, and the low and middle clouds were thin.At the same time, cloud particles above 3000 m were glaciated, the supercooled water content in the cloud was less than 0.05 g·m-3, and the solid water content was about 0.1 g·m-3.Meanwhile, there were a lot of natural ice crystals in the cloud below 3000 m, and the supercooled water content was less than 0.15 g·m-3, which was not available for seeding.At the height of 700-3000 m, the southwesterly wind was strengthened, the supercooled water content in the cloud was generally larger than 0.1 g·m-3, and the wind speed at the wind center at 2200 m was 16 m·s-1, and the maximum liquid water content at this height was 0.38 g·m-3, and ice crystal concentration was 6 L-1, and the temperature was-9℃, which was suitable for seeding.The structure characteristics and seeding conditions of stratiform clouds in this low cold front weather system were affected by the intensity of the southwest wind ahead of the trough and the height of the wind center.Because the top of the stratiform cloud was too high and the temperature was too low in the early stage of the weather system, this cloud system was not in favor of seeding.As the trough line moved eastward, the wind center height decreased and the southwesterly wind below 3000 m was intensified, this stratiform cloud was transformed into the cloud available for seeding. Figures and Tables | References | Related Articles | Metrics

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Research on lightning forecast and early warning in Shaoyang area based on lightning location and radar data Ming-wei ZHOU,Dao-ping WANG,Long-you LUO,Shao-juan WANG,Bin GUO 2021, 37 (3):  117-124.  doi: 10.3969/j.issn.1673-503X.2021.03.016 Abstract ( 117 )   HTML ( 1 )   PDF (581KB) ( 58 )   Save Based on lightning location data and radar data, the 30 dBz, 35 dBz, and 40 dBz echo peaks of the 17 thunderstorm cells and 9 non-thunderstorm cells, as well as the relationship between the echo area exceeding 30 dBz, 35 dBz and 40 dBz at 0℃, -10℃, and-20℃ layer and the occurrence of lightning in Shaoyang in the summer of 2018, were analyzed.Using 40 dBz echo top height, the echo area above the-10℃ layer exceeding 40 dBz and its ratio to the total area of the cell, the lightning in this area was forecasted.The results show that when the echo intensity of thunderstorm cell and non-thunderstorm cell is 40 dBz, the difference of percentage of three stratification heights exceeding 0℃, -10℃, and-20℃ is the largest.The 40 dBz echo top height of the-10℃ layer can better distinguish thunderstorm cells and non-thunderstorm cells in the Shaoyang area than other stratification heights.When the percentage of the area above the-10℃ layer exceeding 40 dBz in the total cell area is greater than 1% of the threshold, it can be used as an effective early warning indicator to distinguish between thunderstorm cells and non-thunderstorm cells.Comprehensive use of 40 dBz echo top height, -10℃ layer above the echo area of more than 40 dBz and the percentage of the total area of the monomer to test 12 monomer samples, the accuracy rate of thunderstorm forecast is 66.7%.The accuracy rate of non-thunderstorm cell judgment is 83.3%. Figures and Tables | References | Related Articles | Metrics

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The relationship between climate characteristics of wire icing days in Liaoning province and atmospheric general circulation anomalies Xiu-bo SUN,Wan-ying ZHANG,Jian-qiang ZHANG,Cong LUO 2021, 37 (3):  125-131.  doi: 10.3969/j.issn.1673-503X.2021.03.017 Abstract ( 147 )   HTML ( 4 )   PDF (1659KB) ( 206 )   Save Using data from 11 meteorological stations with wire icing observation projects in Liaoning province from 1980 to 2019, NCEP reanalysis data, and Hadley sea surface temperature data, the climatic characteristics of the icing days of Liaoning electrical generators and the circulation characteristics that were conducive to the occurrence of icing were analyzed.The results show that there are three high value regions for the occurrence of wire icing phenomenon in Liaoning province, which are in the northern area of Liaoning province, the mountainous area in eastern Liaoning, and the coastal area of central and western Liaoning province.The wire icing phenomenon in Liaoning province mainly occurs from October of the current year to April of the following year, and the number of wire icing days from 1980 to 2019 shows a significant decrease.The number of wire icing days has a significant interannual variation cycle, the main interannual variation period is 5-7 years, and the interannual oscillation energy has undergone 3 changes of strength-weakening in the recent 40 years.The difference of SST anomaly between high index years and low index years in Autumn from September to November in Liaoning province shows the distribution of El Nino type.The SST in the Pacific presents El Nino type in the more wire icing year, the overall SST in the Northwest Pacific is relatively cold, and the SST in the sea of Japan has an obvious negative anomaly.At the same time, there is a high pressure center over Lake Baikal on the mainland, and the latitudinal direction of the northern hemisphere in Asia is "high in the north and low in the south".The winter monsoon is stronger, and the cold air moves southward frequently.Liaoning province is controlled by the northeast airflow, on the southeast side of the abnormal anticyclonic circulation of Lake Baikal, and there is a weak anticyclonic circulation over the Sea of Okhotsk which leads to an abnormal east wind over the Sea of Japan.When the southbound cold air and the east side of the Sea of Japan transport cold water vapor intersection, it is easy to lead to the cold fog, causing the rime phenomenon.The supercooled water vapor condenses on the wires and causes the wires to become iced. Figures and Tables | References | Related Articles | Metrics

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Navigation risk assessment of Guangzhou port based on Monte Carlo method Jing ZHANG,Zhi-jian ZHANG,Xin-yu ZHOU 2021, 37 (3):  132-138.  doi: 10.3969/j.issn.1673-503X.2021.03.018 Abstract ( 192 )   HTML ( 3 )   PDF (845KB) ( 74 )   Save To obtain the characteristics of navigation risk of Guangzhou port at different visibility levels, the qualitative navigation risks of Guangzhou port under different visibility were quantified, to enhance the risk control ability of navigation accidents and improve the resources utilization rate of Guangzhou port.By analyzing the frequency of ship accidents and the severity of the consequences under different visibility, the Monte Carlo simulation of the accident data under three levels of visibility was carried out after the probability statistics of the two, which effectively increased the navigation accidents samples of Guangzhou port.The simulation results under three levels of visibility were obtained, and then the risk distribution characteristics of visibility within 0 and 12 km were acquired.The results show that the probability distribution model based on the Monte Carlo simulation method can effectively solve the problem of small samples of navigation risk, and the risk result is reliable.The risk is lowest at poor visibility (Vis ≤ 5 km), followed by good visibility (Vis ≥ 10 km).When it is restricted (5 km <Vis < 10 km), the risk is approximately 1.7-2.4 times of the other two cases.It can be seen that this method can well assess the navigation risk of Guangzhou port with visibility within 0-12 km, and provide a reference for delineating risk level standards. Figures and Tables | References | Related Articles | Metrics

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Study on assessment model of typhoon disaster in Guangxi based on genetic-neural network method Yan-lan LI,Long JIN,Xu-ming SHI,Dan CHEN 2021, 37 (3):  139-144.  doi: 10.3969/j.issn.1673-503X.2021.03.019 Abstract ( 110 )   HTML ( 2 )   PDF (394KB) ( 78 )   Save Using 86 typhoon cases that affected Guangxi with relatively complete disaster records from 1981 to 2018, the typhoon disaster was classified and the disaster causing factors were selected based on the number of casualties and direct economic losses.The assessment model of the typhoon disaster in Guangxi was established by combining genetic algorithm and neural network.The results show that there is a significant correlation between the selected disaster factors and the typhoon disaster grades.The genetic-neural network ensemble prediction model which is constructed has a good effect on the typhoon disaster prediction.The fitting consistency rate of training samples is 86.1%, and the prediction accuracy of test samples is 71.4%.Among them, the prediction results of severe and heavy typhoon disaster grades are generally consistent with the actual situation, and the prediction accuracy of lighter grades is 83.3%. Figures and Tables | References | Related Articles | Metrics