ISSN 1000-0526
CN 11-2282/P

Volume 46,Issue 7,2020 Table of Contents

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  • 1  Multi-Scale Mechanisms of EF3 Tornado in Linear Convection
    ZHANG Nan YANG Xiaojun LIN Xiaomeng LI Cailing WANG Ying
    2020, 46(7):873-884. DOI: 10.7519/j.issn.1000-0526.2020.07.001
    [Abstract](747) [HTML](212) [PDF 3.08 M](1082)
    Based on NCEP reanalysis data, surface observation data, Doppler radar data, wind profiler radar data, FY-4A satellite data and VDRAS data, the EF3 tornado event that occurred in Jinghai Area of Tianjin at 17:30 BT 13 August 2018 was analyzed. The results show that this tornado process was a strong tornado occurring in linear convection, and the convective storm causing tornado did not have the typical characteristics of supercell storm. After the formation of the tornado, on the basis of the continuous enhancement of the vortices, the center of rotation was declining, and the extension thickness of TVS was increasing. The formation and development of new convections between two linear convections promoted the merger of linear convections.There was a good correspondence between the grounding time of strong echoes of new convection and the occurrence time of the tornado. Twenty minutes before the tornado, the northerly wind on the north and west sides of the two convergence lines in boundary layers and the easterly wind constituted the convergent rotating flow field of the mesoscale low pressure. When the thunderstorm outflow met the local vertical shear center (up to 90×10-3 s-1 at the height of 180 meters), the uneven upward motion along the convergence line forced the horizontal vortex tube to tilt, forming a vertical vortex tube and being stretched in the vertical direction. According to the law of conservation of angular momentum, the strong tornado parent vortex was caused by the intensification of rotation. Thus, although the convective mode of non-supercell tornado in linear convection is different from that of supercell tornado, the physical mechanism of tornado parent vortex formation is the same.
    2  Characteristics of Three Types of Convective Storms During the Beijing Extreme Precipitation Event in 15-17 July 2018
    CAO Yancha ZHENG Yongguang SHENG Jie LIN Yinjing ZHU Wenjian ZHANG Xiaowen
    2020, 46(7):885-897. DOI: 10.7519/j.issn.1000-0526.2020.07.002
    [Abstract](696) [HTML](280) [PDF 41.86 M](1832)
    An extremely severe precipitation event took place in Beijing during 15-17 July 2018. This event was characterized by long duration, large accumulated precipitation amount and locally strong intensity. According to the features of hourly precipitation decrease stage by stage, the three types of convective storms and their precipitation characteristics are analyzed and compared. The results show that the extreme precipitation at the edge of the subtropical high in the morning of 16 July was mainly caused by the low-echo-centroid convective storms, during which the warm and wet layer was deep and the vertical wind shear was weak. The characteristics of convective storms, 〖JP2〗which were similar to the severe tropical precipi-〖JP〗tation storms, along with the impact of “train effect” were the direct causes for the extreme severe precipitation in Minyun District of Beijing. The high-echo-centroid convective storms mainly took place during the daytime of 16 to the early morning of 17 July, when the westerly trough and the subtropical high affected this area together. During this period, the dry air intruded into the middle layer and the vertical wind shear of the whole layer was stronger. The convective storms had some characteristics such as high-echo-centroid, draping structure, strong local features and rapid movement, and the maximum precipitation intensity caused by the high-echo-centriod convective storms was weaker than it caused by low-echo-centroid convective storms. Hybrid convective storms corresponded to heavy precipitation during the transit of westerly trough on the 17th July. Compared with the early stage, the energy and water vapor conditions during this period decreased significantly. The echoes and precipitation intensity of hybrid convective storms were the weakest of the three types. The intensity and magnitudes of precipitation in different stages of this process were determined by the corresponding environmental conditions, structural characteristics and moving propagation characteristics of different types of convective storms.
    3  Construction and Application of Extreme Rainstorm Index Based on Environmental Parameters
    ZHANG Xia WANG Xinmin LI Han LYU Linyi
    2020, 46(7):898-912. DOI: 10.7519/j.issn.1000-0526.2020.07.003
    [Abstract](550) [HTML](239) [PDF 3.97 M](1142)
    Using percentile method and the 1981-2010 daily precipitation data, this paper proposed extreme rainstorm threshold and regional extreme rainstorm standard of Henan Province. Aiming at the selected 13 extreme rainstorm cases in 1981-2016, this paper analyzed the environment parameters of these cases using the ECMWF reanalysis datasets. The results show that the average values of environment parameters such as specific humidity and vorticity at 850 hPa, vertical speed and V wind component at 700 hPa, divergence at 200 hPa, whole-layer precipitatle water, K index and 0-3 km vertical wind shear, which represent the water vapor, dynamics and instability conditions, deviate far from their climatic ave-rage during the extreme rainstorms. This means these environment parameters are instructive to extreme rainstorm forecasting. The standard deviation multiple of environment parameters has good correlations with rainfall, and their quantile values are distributed along the diagonal line. When quantile value of standard deviation multiple of environment parameters is greater than or equal to 80%, it is positively correlated to abnormal precipitation (quantile values ≥90%). However there are more light precipitations when standard deviation multiple of environment parameters is at lower quantile value (<40%). The anomaly of single environment parameter cannot reflect the degree of precipitation anomaly in general. Thus we build the extreme rainstorm index (ERI) based on the eight environment parameters discussed above and also test it with the 13 extreme rainstorm cases. The test results show that the TS, missing rate and false rate are 35%, 27%, 49% respectively when ERI is greater than or equal to 0.7. These values can be used as the reference thresholds for the forecasting of extreme rainstorm. The practical application of ERI during “Rumbia” typhoon extreme rainstorm process indicated that ERI has good reference meaning for the forecast of extreme rainstorm location.
    4  Construction of Heavy Rain THWC Index and Its Diagnosis Application to Northward-Moving Typhoon Affecting Haihe River Basin
    CONG Jing WU Zhenling LI Deshuai DONG Chang
    2020, 46(7):913-925. DOI: 10.7519/j.issn.1000-0526.2020.07.004
    [Abstract](502) [HTML](146) [PDF 3.43 M](991)
    Based on the physical mechanism of heavy rain occurrence, a new heavy rain index THWC (temperature, helicity and water condensation) was constructed by using the ingredients based method to diagnose the dynamic, water vapor and unstable conditions signals. The THWC index calculated with NCEP/NCAR reanalysis data was used to diagnose the northward-moving Typhoon Yagi (No.14 in 2018) affec-ting Haihe River Basin. The results indicated that the THWC index is accurate for forecasting the northerly rainstorm location of typhoon and the center magnitude in the following 6 hours. Then the universality of THWC index was tested according to the northward-moving typhoons affecting Haihe River Basin du-ring 2012-2018. The results showed that the standardized ZTHWC index is more universal than the THWC index, and it has solved unstable problem of THWC index in forecasting quantitative prediction of the central precipitation magnitude. The ZTHWC index has a good correspondence with the main rainstorm location near typhoon center and the central precipitation magnitude in the following 6 hours. The more integrated the atmospheric circulation of northward-moving typhoon is, the better coincidence between ZTHWC and the typhoon main rainstorm area is. Therefore, the ZTHWC index can be used as a quantitative index for forecasting the main rainstorm of the northward-moving typhoon.
    5  Simulation Study of the Impact of Urban Environment on a Local Precipitation Process in Tianjin
    LI Yinghua LIU Lili QIU Xiaobin DONG Gaohong SONG Wei WU Bingui WANG Xuelian
    2020, 46(7):926-937. DOI: 10.7519/j.issn.1000-0526.2020.07.005
    [Abstract](450) [HTML](128) [PDF 3.83 M](919)
    Using mesoscale numerical prediction model WRF combined with dataset from automatic weather stations, focused on a local convective precipitation process which occurred in and near Tianjin urban area, this paper conducts numerical simulations and sensitivity test to investigate the impact of urban environments (surface features, urban air pollution) on the convective precipitation. The results show that the heat island circulation caused by urban surface changed the position and intensity of convergence line after superimposing sea breeze circulation, which directly affected occurrence and falling area of convective precipitation. Once convection develops, the air pollution over cities can affect the intensity and rainfall. The sensitivity test shows that the increase of aerosol concentration makes the regional average precipitation increased by about 25%. The increase of precipitation is related to the formation of more liquid water in convective clouds.The enhancement effect of aerosol is mainly manifested in enhancing the content of liquid water and ice phase substances in convective clouds.The increased liquid water is transported to a higher level by strong updraft and froze to form ice crystals. The increased latent heat release during this process can also enhance the ascending motion and eventually lead to the increase of total precipitation on the surface. In this experiment, the increase of aerosol concentration can increase the latent heating rate by 110 K·h-1.
    6  Weather Radar Identification of Directional Biological Migrations Across the Sea
    TENG Yupeng CHEN Hongbin MA Shuqing WU Dongli ZHOU Yan CUI Kai
    2020, 46(7):938-947. DOI: 10.7519/j.issn.1000-0526.2020.07.006
    [Abstract](419) [HTML](175) [PDF 3.41 M](889)
    By filtering the Doppler velocity of S-band weather radar, the wind radial velocity deviation caused by biological directional migration is obtained, which can effectively distinguish the cross-sea migration activities of directional migratory organisms. The results show that the low-pass filtering of radar Doppler velocity at the same range can effectively separate the directional migratory organisms from the clear-sky echoes generated by undirected plankton and atmospheric turbulence. It also can realize the monitoring of the directional migratory organisms’ cross-sea migration activities, and provide the data of their migration paths in the process of migration. In order to verify the algorithm, through the verification of a biological migration process of the US KICT radar over the night of 30 September 2012, the successful seperation of the birds, which is migrated from the insects, was successfully relied on the Doppler velocity and reflectivity factors. According to the artificial observation results of Changdao Pest Control Field Scien-tific Observation Station, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, the radar data analysis of the night migration period of armyworm in the Bohai Strait on 30 May 2017 shows that this method can effectively identify and monitor the activities of orientated migrating organisms over the Bohai Strait.
    7  Study of the Vertical Distribution of Aerosol Optical Properties During a Heavy Pollution Event in Chengdu
    XU Dongfu CAO Pingping WANG Yuancheng
    2020, 46(7):948-958. DOI: 10.7519/j.issn.1000-0526.2020.07.007
    [Abstract](422) [HTML](232) [PDF 3.91 M](906)
    An event of heavy pollution in Chengdu during 1-6 January 2017 was analyzed in this study by using the data of micro-pulse lidar, the concentration of PM2.5, surface meteorological observations and vertical soundings. The results show that the extinction coefficient calculated by the lidar data is highly consistent with the change of PM2.5 concentration. When PM2.5 concentration increases, the near-surface extinction coefficient increases. Conversely, the near-surface extinction coefficient decreases. For this particular case, when there is no influence of cold air, diurnal variations of mixing layer height and relative humidity have obvious influence on the profile of extinction coefficient. The decrease of mixing layer height and the increase of relative humidity result in the increase of extinction coefficient and the aggravation of the pollution. The sky condition has a significant effect on the vertical distribution of aerosol. In sunny or cloudy days, the water vapor and a large number of aerosols concentrate in the area below the top of inversion layer because of the strong inversion in the morning. As the aerosol layer thickens, the near-surface extinction coefficient decreases significantly due to the evenly mixing of aerosols in the mixed layer with the development of mixed layer at noon. When the previous day was sunny or cloudy and the very day is overcast, the aerosol is obviously divided into two layers in the morning, one is near the ground and the other one is near the top of the residual layer. Part of residual layer aerosol is mixed downward into the mixed layer because the vertical turbulence at noon makes the extinction coefficient in the mixed layer increase significantly. The strong inversion layer near the surface, the decrease of the height of the mixed layer, the downward mixing of the residual aerosol layer and the increase of relative humidity are all responsible for the aggravation of the pollution.
    8  Analysis on the Variation Characteristics and Meteorological Conditions of Haze in Lianyungang City in Recent Decade
    LIU Ruixiang LIU Duanyang YAO Lei ZHU Yunfeng YAN Jiaren
    2020, 46(7):959-970. DOI: 10.7519/j.issn.1000-0526.2020.07.008
    [Abstract](478) [HTML](222) [PDF 3.21 M](947)
    Based on the meteorological and environmental observation data, the variation characteristics and meteorological conditions of haze in Lianyungang City were analyzed during 2008-2018. The synoptic backgrounds and pollutant sources of moderate and heavy haze events in this region were also emphatically discussed. The results indicated that the number of haze days in Lianyungang main urban area increased significantly from 2011, which reached the peak from 2013 to 2015, and then decreased year by year. The haze days appeared most frequently in winter while the number of heavy haze days in January ranked the most. The wind speed 1-2 m·s-1 was most conducive to the formation of moderate and heavy haze. The frequencies of haze hours ranked higher under the wind directions of WNW, WSW and SSW in Lianyun-gang main urban area, and the frequency of haze hours under easterly wind from the sea was also higher duing to factors like terrain features and industrial layout. The haze appeared at a highest frequency with the relative humidity between 70% and 80%, while higher relative humidity was more conducive to the formation of moderate and heavy haze hours. The correlation coefficients of PM2.5 concentration and meteo-rological factors such as visibility, wind speed and relative humidity were higher than that of PM10. The surface circulation backgrounds of moderate and heavy haze events can be divided into five types, which were low pressure or inverted trough type, prefrontal type, front of high pressure type, back of high pressure type and uniform pressure field type, among which the uniform pressure field type accounted for the largest proportion of 35.8%. The inversion layer played an important role in the formation of moderate and heavy haze events, and the average intensity and frequency of inversion at 08:00 BT and 20:00 BT were both higher than that at 14:00 BT. Analysis of trajectory clustering showed that the source, path and moving distance of air masses corresponding to moderate and heavy haze events under different weather types were of significant differences.
    9  Impacts of Drought and Irrigation on Root and Yield of Winter Wheat
    MA Qingrong LIU Ronghua HU Chengda WANG Hongzhen YU Hui WANG Yanling
    2020, 46(7):971-981. DOI: 10.7519/j.issn.1000-0526.2020.07.009
    [Abstract](395) [HTML](164) [PDF 467.25 K](784)
    By carrying out different degrees of drought, rehydration test at Zhengzhou Agricultural Meteorological Experimental Station, we studied the effects of different water conditions on the root vigor morphology and yield of winter wheat, to establish an optimized irrigation system for winter wheat in Henan Province, improve water use efficiency and achieve the goal of water saving and yield increasing. The results showed that under drought conditions, the root vigor and stem diameter of winter wheat decreases significantly, but the root length increases significantly, and the proportion of lower soil roots volume increases. In addition, with the development of the growth stages, the proportion of the lower soil roots volume increases, and the water use efficiency improves significantly. Along with the increase of drought degree, the above trend is more obvious. In the case of same amount of water recovery, overwintering irrigation is beneficial to the increase of root vigor and root diameter of winter wheat, but unfavorable for roots to extend downward. In the greening and jointing stages, irrigation is good for the roots stretching down, water use efficiency, grain weight and theoretical increase of yield, but not conducive to the increase of root vigor and diameter. For the purpose of improving water use efficiency, it is appropriate to increase irrigation volume and reduce the times of irrigation. Comprehensive analysis of root morphology and vitality, water use efficiency and yield shows that under the condition of persistent drought in winter wheat, irrigation is about 600 m3·hm-2 at the turning green stage and booting stage, so the amount of irrigation can be increased or decreased appropriately according to the degree of drought. Irrigation times can be increased appropriately under severe drought conditions. In severe drought years, under difficult irrigation conditions, only 600 m3·hm-2 can be irrigated at jointing stage to achieve the loss reduction of yield and water saving effect.
    10  Characteristics and Causes Analysis of the Warm and Wet Winter in China in 2019/2020
    ZHAO Junhu SONG Wenling KE Zongjian
    2020, 46(7):982-993. DOI: 10.7519/j.issn.1000-0526.2020.07.010
    [Abstract](517) [HTML](385) [PDF 6.26 M](1087)
    The temperature in most areas of China was significantly higher than normal, and the precipita-tion was more than normal in the 2019/2020 winter. The main causes are as follows. The East Asian winter monsoon (EAWM) and Siberian high were both weaker than normal during the 2019/2020 winter, with significant intraseasonal variation of EAWM. The Arctic polar vortex (APV) was contracting in the polar region, with a strong intensity. The Arctic oscillation (AO) was in a positive phase with a strong intensity. The activity of Ural blocking high and the East Asian trough were all weak. The Euro-Asia was controlled by zonal circulation. The West Pacific subtropical high (WPSH) was significantly stronger than normal with westward and northward position. India-Burma trough (IBT) was active periodically. The WPSH and IBT were beneficial to water vapor transportation from Pacific Ocean and Indian Ocean to China. Diagnostic analysis of possible mechanism for weak EAWM in the 2019/2020 winter indicates that the warm SST in the equatorial Pacific in the fall and winter of 2019 and aroused strong and northward anticyclone in the northwestern Pacific, suppressing the development and southward invasion of the EAWM. In addition, the strong APV, and positive AO were not conducive to the development of Ural blocking high. And the East Asian trough was obviously weak. All these elements jointly lead to the zonal circulation in the middle and high latitudes of Euro-Asia and the weak EAWM.
    11  Analysis of the April 2020 Atmospheric Circulation and Weather
    GUAN Liang ZHANG Tao LIU Zimu
    2020, 46(7):994-1000. DOI: 10.7519/j.issn.1000-0526.2020.07.011
    [Abstract](2933) [HTML](503) [PDF 7.28 M](1233)
    The main characteristics of the general atmospheric circulation in April 2020 are as follows. There was one polar vortex center in the Northern Hemisphere, the 500 hPa geopotential height presented the distribution of a three-wave pattern in the high latitude of Northern Hemisphere. The strength of Western Pacific subtropical high was closed to that in normal years, but the south branch though was a little weaker. The monthly mean temperature was 11.2℃, closed to normal, and a total of 18 stations across the country measured the sharp drop in temperature, which reached the standard of extreme events. The monthly mean precipitation amount was 33.7 mm, 25.3% less than in normal period (45.1 mm). Two cold air processes and four rainfall processes occurred in China this month. The meteorological drought condition in Yunnan Province got alleviated, but continued in many areas north of the Yangtze River. Only one sand-dust event happened in the northern part of China, significantly less than in normal period.

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