ISSN 1000-0526
CN 11-2282/P

Volume 47,Issue 2,2021 Table of Contents

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  • 1  Study on Spatio-Temporal Distribution of Hourly Precipitation in Yunnan Province
    SU Jinlan ZHANG Wancheng SONG Jinmei XU Anlun
    2021, 47(2):133-142. DOI: 10.7519/j.issn.1000-0526.2021.02.001
    [Abstract](221) [HTML](311) [PDF 6.98 M](929)
    Based on the hourly precipitation data of 125 national stations from 2005 to 2018, the spatio-temporal distribution characteristics of hourly precipitation in Yunnan were studied. The results show that the spatial distributions of annual total precipitation, different duration precipitation, extremely severe precipitation and diurnal variation of precipitation are significantly different. The annual rainfall increases from northwest to south, and intensity enhances from north to south. The rainfall duration in west is more than in the east, and that in south is slightly more than in the north. The annual rainfall is affected commonly by rainfall duration and intensity. The influence of duration is stronger than that of intensity, especially in northwest Yunnan, but the rainfall in northeast Yunnan has better correlation with intensity. Most areas of Yunnan receive more rainfall at night than in the daytime, especially in northeast and northern margin of Yunnan. The diurnal variation of precipitation features a single peak at night in the northern part, a single peak in early morning in the western edge, double peaks at night and in the afternoon in the central and southern part, but the occurrence times of major peak and secondary peak are different in southern part. The precipitation southern Yunnan is mainly from the short and medium duration precipitations, while that in the north is mainly from long and ultra-long duration precipitations. Times of short-time severe precipitation increase from northwest to southeast, and its annual change has an increasing trend. Its daily distribution shows a significant single peak from dusk to night, but extreme short-time severe precipitation is more likely to occur in the early hours of the morning. These spatio-temporal characteristics of hourly precipitation largely represent the characteristics of the low-latitude plateau. The spatial distribution difference of hourly precipitation characteristics is related to the weather system. The low-value weather system mostly affects the central and northern part of the low-latitude plateau, while the southern part is mostly affected by tropical weather system. Moreover, the topography is complex, and the local thermal conditions are greatly distinct. All these factors contribute to the significant differences in the spatio-temporal distribution characteristics of hourly precipitation in this region.
    2  Analysis on Severe Wind Characteristics During Typhoon Rammasun Landing Process Based on the Observation at Wind Tower
    HUANG Haohui CHEN Wenchao ZHI Shiqun WANG Binglan
    2021, 47(2):143-156. DOI: 10.7519/j.issn.1000-0526.2021.02.002
    [Abstract](164) [HTML](278) [PDF 2.30 M](738)
    Based on the representative observation data obtained by the 90 m wind tower in Xilian Town, Xuwen County, Guangdong Province during the landfall of No.1409 Super Typhoon Rammasun, and the observation data of 100 m wind tower in Bohe Town, Maoming City, Guangdong Province, which is located in the periphery of the typhoon, the characteristics of the severe winds near surface layer are analyzed. The results of Xilian Tower show that time variations of the wind speed present clear “M” pattern. The wind direction counterclockwise deflects about 170° as the typhoon center passes through the tower. The wind speed increases with the increase of height, and the wind speed profile fits well with the laws of logarithm and power index. Wind shear index and roughness length decrease first and then gradually increase during the typhoon passing period. The wind shear index and roughness length on rough land underlying surface are large. The turbulence intensity and gust coefficient are larger in the front or back outer-vortex, but smaller in the front or back eye-wall. The turbulence intensity and gust coefficient decrease with the increase of height, which basically accords with the power law with negative exponent. The turbulence intensity and the gust coefficient are amplified under the influence of the rough underlying surface. The variation of the 10 min wind direction is more stable in the outer-vortex and eye-wall compared with that in wind eye in which it is rather intense. The maximum amplitude of the 10 min wind direction occurred when the wind speed reaches the minimum in the typhoon eye. The results of the Bohe Tower show that the situation is similar to that of the Xilian Tower when it is located in the front outer-vortex and the front eye-wall of the typhoon.
    3  Microphysical Structure Analysis of a Spring Sea Fog Event in Southern Coastal Area of Fujian
    ZHANG Wei CHEN Dehua HU Yajun XUN Aiping JIANG Yongcheng SUN Xuejin
    2021, 47(2):157-169. DOI: 10.7519/j.issn.1000-0526.2021.02.003
    [Abstract](215) [HTML](215) [PDF 5.57 M](828)
    Based on the data of automatic weather station, windprofiling radar, ERA5 reanalysis, Himawari 8 high resolution satellite and FM120 fog droplet spectrometer, we discuss the circulation pattern and microphysical characteristics of an sea fog event that happened in southern coastal area of Fujian Province on 7 April 2019. Circulation analysis shows that this sea fog event occurred under the control of westtonorthwest flow at 500 hPa trough bottom, while from 700 hPa to surface there was uniform southerly flow. The sounding situation was stable. Before sea fog event, lowlevel wind speed decreased significantly, increasing the thickness of lowwind speed. This situation provided stable circulation for sea fog. Himawari 8 satellite images show that the sea fog rapidly formed in the Taiwan Strait first and then advected to coastal area affected by lowlevel southerly airflow. Hydrological analysis indicates that there existed a cold water band and large temperature gradient near the shore. Sea surface temperature (SST) varied between 18 ℃ and 24 ℃. The air and sea temperature difference was between 0 ℃-2 ℃ with sea surface colder than the air above, which contributed to the formation of advective sea fog. Fog droplet spectrum analysis shows that visibility decreased dramatically while particle number concentration (PNC), liquid water content (LWC) and droplet spectrum increased significantly at the same time. During the sea fog process, 5 min average PNC exceeded 200 cm-3 and instantaneously reached 468 cm-3 maximum, and the average PNC during the fog process reached 100 cm-3. The 5 min average LWC reached 0.41 g·m-3 and 1.35 g·m-3 instantaneously. The average LWC during the fog process reached 0.17 g·m-3. Fog droplet size featured double peaks with 4-6 μm and 22-26 μm intervals respectively during the fog process. This indicates that small and big particles both can contribute to the formation of sea fog. 
    4  Analysis of Evolution Mechanism and Characteristics of Dual Polarization Radar Echo of a Hail Caused by Long-Life Supercell
    GAO Li PAN Jiawen JIANG Lulu WENG Zhimei
    2021, 47(2):170-182. DOI: 10.7519/j.issn.1000-0526.2021.02.004
    [Abstract](173) [HTML](110) [PDF 8.45 M](774)
    On 21 March 2019, a hail process caused by long-life supercell occurred in Zhejiang Province. In order to study the environmental background and microphysical characteristics of supercell which maintained for a long time, we analyze the evolution of this process by using conventional data, Ningbo S-band dual polarization radar data and hydrometeor classification algorithm. The results show that the high-level trough, 850 hPa shear line and the surface cold front provided suitable background for the supercell. The increase of effective convective potential energy in the storm propagation area, high speed of storm bearing layer, the similarity of the mean wind direction of the storm bearing layer and moving direction of the storm, as well as the eastward propagation of the convective storm along the high pseudo-equivalent potential temperature gradient of surface, and the increase of rotation speed and thickness of mesocyclone produced by the enhancement of strong vertical wind shear in the coastal area, all these factors are the causes of making the convective storm maintain for a long time. Through the analysis of the structure of the hailstorm, the vigorous convection (the maximum reflectivity above 60 dBz, the storm top above 8 km) was found in the whole life cycle, and three obvious fluctuations in the height of storm centroid appeared, corresponding to three hail processes. In this case the vertical integrated liquid water content (VIL) jump increment was lower than the traditional index, but the combination of the vertical integrated liquid water content density (VILD), the maximum VIL and the maximum reflectivity factor could still indicate the hailstorm. The analysis of the dual polarization characteristics, suggest that the tumbling of falling hail resulted in the Zdr close to 0 dB, and the difference between horizontal and vertical polarization waves led to the appearance of large Zdr region at the root of TBSS. The water coated phenomenon made the Zdr value increase and CC value decrease. The polarization parameters Zdr and CC could be used to identify hail in high altitude; Zdr column, near BWER, could not only indicate the ascending motion, but also reveal the different growth stages of hail cell.
    5  Parameterizations of Downward Longwave Radiation in Clear Sky Considering Air Pressure and Their Applicability Analysis
    MENG Qi
    2021, 47(2):183-191. DOI: 10.7519/j.issn.1000-0526.2021.02.005
    [Abstract](145) [HTML](133) [PDF 2.60 M](540)
    Based on Prata parameterization of clear sky downward longwave radiation and in view of its poor theoretical accuracy in plateau areas and areas with small precipitable water vapor, three new parameterizations of clear sky downward longwave radiation are proposed in this paper, in which air pressure is considered because longwave radiation from different length of atmosphere column is different. Empirical constants are obtained by least square fitting of global ERA5 reanalysis data and their applicability is analyzed in different regions of the world. The simulation results show that parameterizations with consideration of air pressure can effectively improve the convergence of atmospheric emissivity of Prata scheme when the precipitable water vapor can be reduced. The mean bias errors and the root mean square errors of the simulation values of the downward longwave radiation of the new schemes in Amdo Area and San Luis from the observation values are obviously smaller than that of Prata’s 〖JP2〗parameterization scheme. Compared with Prata’s scheme, the simulation accuracies of the new schemes are improved and the applicabilities are better.
    6  Forecast on Convective Cloud Condition and Analysis on Seeding Plan of an Artificial Rainfall Mitigation Case
    SHI Yueqin LIU Weiguo WANG Fei GAO Yang
    2021, 47(2):192-204. DOI: 10.7519/j.issn.1000-0526.2021.02.006
    [Abstract](152) [HTML](184) [PDF 21.84 M](1041)
    In order to do well artificial rainfall mitigation on specific target period and area, cloud seeding condition such as cloud properties and structure, moving speed and direction, cloud evolution, precipitation mechanism and so on was forecast by using Cloud Precipitation Explicit Forecast System (CPEFS). The results showed that on 8 August 2017 in Hohhot there were scattering convective clouds, with coldwarm mixed vertical structure and strong updrafts. Horizontal scale of single convective cloud was about tens of kilometers, and lifetime was about 1.5-3.0 hours. 〖JP2〗Cloud top (bottom) height of 10 (3) km, 〖JP〗and 0℃ layer height of 4.3 km. Cloud microphysics aspects were with high content of snow and graupel, low cloud water content in warm regions, maximum content of supercooled water of 0.7 g·kg-1, less ice crystals in areas with rich supercooled water, mainly with cold precipitation mechanism. Convective clouds first appeared in the northwest direction of the core zone in Hohhot, rapidly developing and moving eastward and southward gradually to the core zone at the speed about 30-40 km·h-1. Satellite and radar observations also showed there were convective clouds. The forecasted generation time of convective clouds was 1-2 hours later than observation, but moving direction was consistent with observation. Moving speed was 10-20 km·h-1 slower. The maximum liquid water content was 0.6 g·m-3 at the 5 〖KG-*5〗400 m height (-8℃) by airborne cloud physical detection. The forecasted cloud water content was consistent with detection. The seeding plan was made based on cloud condition forecast. The area 30-50 km northwest of the core zone was chosen as key defense zone. AgI overseeding would be suitable to be implemented in the 5.1-7.0 km height. In the morning of 8 August the aircraft would carry out detection in weak echo areas of the first defense line. Ground operations would focus on the implementation of overseeding in the initial stage of convective clouds in the third defense line to achieve the goal of rainfall mitigation. Based on the plan, additional five sets of ground mobile seeding equipment were added to reinforce the capability of rainfall mitigation ahead of 24 hours of target time. Rainfall mitigation was carried out with the 5 sets equipment. In summary, the cloud seeding condition forecast was proper, and the seeding plan was reasonable, which provided strong support for field rainfall mitigation action.
    7  Analysis of a Precipitation-Fog Process Detected by Millimeter-Wave Radar
    CEN Juhui TANG Shihao HU Lijun TU Xiaoping YAO Risheng
    2021, 47(2):205-215. DOI: 10.7519/j.issn.1000-0526.2021.02.007
    [Abstract](142) [HTML](263) [PDF 3.68 M](665)
    The characteristics of a precipitation-fog process, which caused the occurrence of low visibility weather, were analyzed by using the imagery of millimeter-wave radar detection. The analysis of horizontal distribution characteristics of the process showed that its spatial scale was about 15 km, and the radar wave intensity ranged from -20 dBz to 25 dBz. We also analyzed the vertical structure of the process, finding that the process experienced a series of varying processes from precipitation to fog as it passed through the radar-scanned region. The analysis of radar radial velocity suggests that the main structure of the system was stable, and the edge area was compensated for the main area, so that the system could maintain and develop. The visibility began to decline when the process was approaching the visibility stations, and reached the minimum value when the process was about to leave. The visibility became better after the process left for a period of time, and no effective precipitation was observed in the millimeter- wave radar scanning area during the process.〖JP2〗 In addition, according to the empirical formula, the relationship between low-level radar reflectivity intensity and near-surface visibility in this process was well simulated, and the specific formula was Vis=2.283Z-0.121.
    8  Analysis of the 13 April 2019 Strong Tornado in Xuwen County, Guangdong Province
    HUANG Xianxiang YU Xiaoding YAN Lijun CAI Kanglong ZHI Jiangling WANG Shuofu
    2021, 47(2):216-229. DOI: 10.7519/j.issn.1000-0526.2021.02.008
    [Abstract](206) [HTML](275) [PDF 4.65 M](800)
    An EF3 strong tornado in Xuwen County of Zhanjiang City, Guangdong Province on 13 April 2019 was analyzed by using observation data, automatic weather station data, Zhanjiang Doppler Radar data and FY4A satellite high resolution visible cloud images. The results show that this strong tornado occurred near the coastal zone in the low latitude area, with a path length of about 16 km. It experienced a complex process of “three times on 〖JP2〗land and two times on sea”, lasting for about 36 minutes. The 〖JP〗mesoscale convective system producing tornado supercell appeared in front of the warm and low pressure trough, where the southwest air flow and southerly jet flow converged significantly in the middle and lower layers. The environmental conditions were characterized by strong vertical wind shear, low lifting condensation height, large storm relative helicity and large energy helicity. There were mesoscale convergence lines and smallscale vortex triggering convection on the ground. The tornado 〖JP2〗passed through the〖JP〗 automatic weather station of Hean Town Government of Xuwen County, which was affected by different parts of the tornado vortex. The wind direction of the tornado changed from clockwise to reverse to clockwise, and the wind force got to Grade 15. The average pressure and temperature dropped sharply by 2.6 hPa·(5 min)-1 min and 1.7 ℃·(5 min)-1, respectively. The tornado occurred in a supercell storm with positive cloudtoground lightning and high cell centroid. The hook echo and echo pendency were obviously accompanied by lowlevel strong mesocyclone and tornado vortex signature. The intensity and top height of the mesocyclone changed in inverse phases, and the three (two) peak value (valley value) of the intensity and three (two) valley value (peak value) of top height exactly corresponded to the time of the three (two) land (sea) activities of the tornado. When the tornado was on the land (sea), the mesocyclone was stronger (weaker) and the top height was lower (higher). The tornado occurred near the top of the hook echo and at the maximum 〖JP2〗TBB gradient on the windward side of mesoβ scale convective system, under the water vapor plume and during the period when the height of the bottom of the mesocyclone was lower than 500 m.
    9  Comparative Analysis of Damage Survey of Microburst in Lingui of Guangxi and Tornado in Zhanjiang of Guangdong in 2019
    CAI Kanglong YU Xiaoding LI Cailing HUANG Xianxiang YAN Lijun HE Qiurui MAI Wenqiang CHEN Zhifang
    2021, 47(2):230-241. DOI: 10.7519/j.issn.1000-0526.2021.02.009
    [Abstract](203) [HTML](209) [PDF 2.68 M](736)
    On 21 March 2019, an instantaneous maximum wind speed of 60.3 m·s-1 was recorded at 21:13 BT by national observation station in Lingui District, Guangxi. On 13 April 2019, an instantaneous maximum wind speed of 50.7 m·s-1 was recorded at 14:11 BT by observation station in He’an Town, Guangdong Province. Significant wind damages were observed at the two places. By analyzing surveillance video, drone aerial data, site survey and visiting witnesses, the following conclusions were obtained. The wind damage which occurred at Lingui National Station and its surrounding area from 21:09 BT to 21:14 BT was a EF2 microburst lasting at least 6 minutes and affecting 1.6 km×2.0 km. It belonged to microα scale microburst and contained seven microβ scale embedded. The damage area was featured with small aspect ratio, discontinuous spatial distribution and divergent wind pattern. The wind damage that occurred in Xuwen of Guangdong Province from 14:09 BT to 14:15 BT was a EF3 tornado which lasted for 7 minutes. The damage path was about 3.2 km long and 30-280 m wide. The surveillance video showed that there was a rotational wind tunnel existing shortly near the damage site. Compared with Lingui microburst, the damage area has larger aspect ratio, more continuous spatial distribution and convergent wind pattern.
    10  Cause Analysis of a Severe Downburst in Guilin
    LI Cailing CAI Kanglong HUANG Xianxiang ZHI Jiangling CHEN Zhifang MAI Wenqiang
    2021, 47(2):242-252. DOI: 10.7519/j.issn.1000-0526.2021.02.010
    [Abstract](197) [HTML](347) [PDF 2.76 M](862)
    An extreme gale event, hereinafter referred to as “3.21 Lingui gale event”, occurred in Lingui, Guangxi on 21 March 2019. Maximum gust of 60.3 m·s-1 (Grade 17) was recorded at the Lingui Station at 21:13 BT. Based on the results of the wind damage survey with video and meteorological data, this paper shows that the serious wind damage was caused by a severe microburst. Using the data from conventional meteorological observations, dense automatic weather station, radiosonde, Doppler weather radar, this paper analyzes the environmental conditions and influencing systems of the “3.21 Lingui gale event”. Results are that the “3.21 Lingui gale event” occurred under some favorable conditions such as active lowlevel warm and humid air flow, midlevel significant dry layer and strong lowlevel vertical wind shear. The event was triggered by the surface mesoscale convergence line and the southward cold front. The “3.21 Lingui gale event” was caused by the merging of two 〖JP2〗supercells into one supercell. Before the downburst occurred, the supercell developed to the most powerful stage. The maximum reflectivity core height (HGT) exceeded 6 km. There was a medium intensity of the mesocyclone accompanied by the (midaltitude radial convergence, MARC) value of 36 m·s-1. When the downbursts occurred, reflectivity factor began to weaken, the height of storm top dropped and HGT dropped. When HGT dropped sharply, the scanned volume interval dropped by 3.5 km, and the extreme gale of Grade 17 occurred. At this time, the lowlevel 0.5° elevation was observed in the highaltitude area of the cyclone, with a high radial divergence value of 27 m·s-1. The mesocyclone had the strongest wind shear strengthening, the bottom height rapidly dropped to less than 1 km, and so on. In addition, the occurrence of downburst was closely related to the dragging effect of extreme severe precipitation and hail. Usually, when the minutely rainfall is higher than 3 mm, wind force is higher than Grade 12; when the minutely rainfall is higher than 6 mm, the extreme gale of Grade 17 occurs.
    11  Analysis of the November 2020 Atmospheric Circulation and Weather
    NAN Yang RAO Xiaoqin YOU Yuan GUAN Liang
    2021, 47(2):253-260. DOI: 10.7519/j.issn.1000-0526.2021.02.011
    [Abstract](174) [HTML](279) [PDF 5.49 M](735)
    The main characteristics of the general atmospheric circulation in November 2020 are as follows. There were two polar vortex centers in the Northern Hemisphere. The circulation presented a threewave pattern in midhigh latitudes. The East Asian trough and the southern branch trough were weaker while the western Pacific subtropical high was stronger, located more westward. The monthly mean precipitation over China was 16.9 mm, which is 11 % less than normal (19.0 mm). One severe rain and snow process occurred from the 17 to 19 November, during which 〖JP2〗Enshi of Hubei Province and Dandong of Liao〖JP〗ning Province experienced severe rainstorm, and Mudanjiang, Jixi and Qitaihe of Heilongjiang Province and Tongliao and Chifeng of Inner Mongolia were hit by severe snowfall or extremely severe snowfall. The monthly mean temperature was 3.9 ℃, 1 ℃ higher than normal (2.9℃). During this month, there were four cold air processes, one of which was nationwide from the 18 to 22 November. Additionally, as the result of unfavorable diffusing condition of atmosphere, one foghaze event appeared in centralsouthern part of North China, west of Huanghuai Region, and Fenwei Plain during 10 to 17 November 2020.

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