Vol.33, NO.2, 2022

Display Method:
Refined Assessment of Wind Environment over Winter Olympic Competition Zone Based on Large Eddy Simulation
Liu Yujue, Huang Qianqian, Zhang Hanbin, Miao Shiguang
2022, 33(2): 129-141. DOI: 10.11898/1001-7313.20220201
The near-surface wind field over complex terrain is highly non-uniform due to the influence of topographical fluctuations. Therefore, it is extremely difficult to carry out high-density observational experiments and refined assessment of wind environment in these areas. In this case, high-resolution wind field data from numerical simulations is essential for the evaluation and analysis of near-surface wind environment. A refined wind environment assessment is carried out for Xiaohaituo alpine skiing field, Yanqing competition zone of Beijing Winter Olympic Games. Firstly, the weather patterns over the alpine skiing field during the winter competition periods from 2009 to 2021 (every February and March) are divided into 5 main types according to the Lamb-Jenkinson (L-J) atmospheric circulation classification scheme, and further classified into 93 secondary circulation types according to the wind directions and speed at 700 hPa. Secondly, the coupled model system of mesoscale meteorology and large eddy simulation (RMAPS-LES) developed by Beijing Institute of Urban Meteorology is used to simulate the wind field at a horizontal resolution of 37 m for typical cases under 93 weather patterns. The comparison between the simulation results and observations at 11 automatic weather stations shows that the model simulation performs reasonably well. The results show that the average deviation of 2 m temperature is less than 2℃, which perfectly meets the accuracy requirements of weather forecast service demand. Although 10 m wind speed is slightly overestimated for the whole typical cases of different weather patterns, the average deviation is within 3 m·s-1, and the average deviation of 10 m wind direction simulation is 10.43°-12.36°, which shows a good prediction skill. Finally, based on the wind field simulation results of different weather patterns, a ten-year winter wind environment assessment is carried out to provide detailed spatial distribution characteristics of the wind field, risk ranges, locations of gale, and the risk probability of exceeding the wind speed thresholds of the sport events, so as to provide technical supports for the organization, time arrangement, track design and wind hazard protection of 2022 Beijing Winter Olympic Games. The method provides an effective way for wind energy assessment and forecast over complex terrain, as well as meteorological services for wind-sensitive activities, such as outdoor mega-events over complex terrain, small-scale environmental design for large-scale architectural complex over mountain terrain, mountain fire disaster prevention and mitigation, mountain pollution forecasting and nuclear proliferation assessment.
Observation and Analysis of Microphysical Characteristics of Stratiform Clouds with Embedded Convections in Yunnan
Liu Chunwen, Guo Xueliang, Duan Wei, Ding Chong, Zhang Fan
2022, 33(2): 142-154. DOI: 10.11898/1001-7313.20220202
observation is an important mean to obtain cloud physical information, which is important for weather modification research and operation. In China, aircraft observation research on cloud microphysical characteristics is mainly carried out in the northern region, seldom in the southwestern region. Yunnan is a low-latitude plateau with complex topography and distinct weather and climate. The aircraft cloud physical detection equipment in Yunnan is put into use since 2017, and it carried domestic laser cloud particle probes, including cloud particle spectrometer probe, cloud particle imager probe, and precipitation particle imager probe.The aircraft can obtain the size and number of cloud particles and precipitation particles at different resolutions of 2-6200 μm, as well as 25-6200 μm particle images.The mixed cloud observations of cumulonimbus and stratiform clouds from Yun-12 and King Air-E350 aircraft in Yunnan during 2017-2020 are analyzed. Data of 76 flights are obtained, with the maximum flight altitude of 6946 m (ambient temperature -14℃). The cloud vertical structure is observed by descending and ascending flights. The results show that the number concentration of cloud particles is much higher than that in northern China. The average number concentration of cloud particles (2-50 μm) is 339.7 cm-3 with a maximum value of 1067.6 cm-3; the average water content is 0.181 g·m-3, and the maximum is 2.827 g·m-3; the average effective diameter of cloud particles is 11.2 μm and the maximum is 34.6 μm. The cloud particles have a negative exponential size distribution with double peaks. The first peak is located at 4 μm and the second peak is at 10 μm. The cloud particle number concentration, water content and extinction coefficient show obvious layered distribution characteristics with height, but the effective particle diameter doesn't change much.The reflectivity factor is maximum at the height of 3.4 km.In the warm cloud region, the average water content of rain drops with diameter from 200 to 1500 μm is 0.183 g·m-3 with a maximum value of 4.247 g·m-3. The average water content of rain particles in the range of 200-6000 μm is 0.406 g·m-3 with the maximum of 8.917 g·m-3.In Yunnan, the spectral width of cloud particles becomes wider with the increase of cloud water content.With the outbreak and establishment of the Southwest Summer Monsoon, the small cloud particles increase, and the large cloud particles decrease in the warm area of cloud. It is helpful to improve the efficiency of artificial precipitation enhancement by carrying out warm cloud artificial precipitation enhancement.
Fitting of Wind Shear Index in the Boundary Layer of Landfalling Typhoons Based on High Tower Observation
Chen Shenpeng, Duan Yihong, Li Qingqing
2022, 33(2): 155-166. DOI: 10.11898/1001-7313.20220203
The characteristics of wind speed variations with height in the boundary layer (especially in the near-ground layer) are crucial for the design of wind resistance coefficients of high buildings. The coast of South China is frequently impacted by typhoons, but the study of wind variation characteristics above 100 m within the typhoon boundary layer is insufficient due to the lack of direct observations. The 356 m Meteorological Gradient Observation Tower of Shenzhen can make up for data shortage, and 7 typhoons that affected Shenzhen since 2017(Typhoons Merbok, Roke, Hato, Pakhar, Mangkhut, Higos, and Lupit) are analyzed to study the variation of wind shear index based on the power exponential law. It shows the power index can well fit the wind profile below 350 m under the influence of typhoons, the wind shear index α increases with height, and the fitting accuracy is basically stable. The wind profile of the typhoon boundary layer is fitted with the wind speed data from the tower, the fitting accuracy differs for different combinations of levels, and the equal difference scheme leads to the best fitting results. For 7 typhoon cases, the mean value of 350 m wind shear index α during the impact period is 0.268, which is significantly higher than that of 0.1-0.177. The main cause is that the fitted height range is significantly larger than that of previous studies, and it is also related to the smaller sample of strong winds and rougher underlying surface. The maximum wind shear indices of different wind speed sections of the typhoons can be well fitted with power functions, which can predict the risk of extreme winds at different heights.The wind shear index before and after landing of Typhoon Roke is also analyzed. It shows that after the typhoon eye passes, α increases sharply, because the wind speed above 100 m may have increased significantly before the surface wind re-increase. Therefore, this result should be specially considered in the design of engineering wind resistance and typhoon prevention.
Retrieval and Experiments of Atmospheric Vertical Motions in Convective Precipitation Clouds
Dong Jiayang, Cui Ye, Ruan Zheng, Li Nan, Wei Ming, Li Feng
2022, 33(2): 167-179. DOI: 10.11898/1001-7313.20220204
Detecting the vertical motions of the atmosphere in convective clouds is difficult. The cost of aircraft detection is expensive, limited by maximum flight altitude, high detection risk, low frequency, etc. In recent years, remote sensing instruments are applied with the development of detection technology. Ground-based vertical pointing radar has become a reliable way to obtain atmospheric vertical motions, through which the cloud structure and dynamic characteristics of convective precipitation clouds can be obtained, and the distribution and evolution characteristics of the intensity and proportion of atmospheric vertical movement during the mature stage of convection can be monitored in detail. Based on the vertical structure detection data of precipitation clouds from ground to 15 km height by a vertical pointing radar with 5520 MHz C-band Frequency Modulation Continuous Wave (VPR-CFMCW) technology, the vertical motions in the convective precipitation cloud are retrieved, and the vertical structure of convection and evolution characteristics of vertical motions at different heights are analyzed. The VPR-CFMCW is used to carry out the atmospheric vertical motion retrieval experiments on 4 convective precipitation events at the Longmen Station in Guangdong Province during pre-monsoon from 20 April to 22 April in 2019. It is found that the updrafts of the atmosphere before convective precipitation have a positive contribution to the intensity of reflectivity and surface precipitation afterwards. The deep convection is inclined, which causes the vertical section to show a layered structure at certain moments. Convective precipitation is dominated by downdrafts of the entire level, updrafts and downdrafts of the upper-level atmosphere appear alternately, when downdrafts account for the highest proportion in the lower-level, and the updrafts account for an increased proportion above 6 km height. The intensity of atmospheric vertical motions is strong in the upper-level, as strong updrafts and downdrafts exceeding 10 m·s-1 mostly appear above 6 km height. The vertical motions vary greatly at 4-6 km height. The average downdraft speed is less than 5 m·s-1 and the average updraft speed is around 2 m·s-1 under 4 km height. The development of ground-based vertical pointing radar can improve the understanding of vertical structure evolution and dynamic characteristics of convective precipitation clouds.
Radar Characteristics of Straight-line Damaging Wind Producing Supercell Storms
Wang Yitong, Wang Xiuming, Yu Xiaoding
2022, 33(2): 180-191. DOI: 10.11898/1001-7313.20220205
Based on S-band Doppler weather radar data and damaging wind gust records, 56 damaging straight-line winds events from 2002 to 2020 above 25 m·s-1 caused by supercell storms are investigated. The relationship between Doppler weather radar echo characteristics and damaging straight-line winds caused by supercell storm is analyzed to obtain quantitative description of the structural characteristics. The results will be benefit for subjective and objective monitoring and warning of damaging straight-line winds produced by supercell storms. Superstorm is a highly organized strong convective storm with a long-life history, according to the statistical results, and it is possible to judge the potential of supercell storms that produce damaging gale by the Doppler weather radar echo structures. It shows that, in the supercell storm that produces damaging straight-line winds, the strong reflectivity echo above 60 dBZ is deep, and the average echo thickness of strong reflectivity is 5.5 km. The core height of the strong reflectivity of most supercell storms are above 6 km which indicate that the updraft in this kind of supercell storms can be very strong. The mid altitude radial convergence (MARC), the reflectivity core decline and rear inflow jet (RIJ) are important for warning of damaging straight-line winds features. The MARC is significant, the largest speed difference of the MARC is above 29 m·s-1 in most cases. The mesocyclone is mainly of medium intensity, the rotating speed of mesocyclone is 18.4 m·s-1 on average, which can extend up to the upper troposphere (7 km). The descending of supercell storm reflectivity core, the descending of mesocyclone core, the MARC which can exist for a long time with 29 m·s-1 largest radar radial speed difference and the decrease of vertically integrated liquid water content (VIL) value can be used as the warning indices of the damaging straight-line winds. Among them, the descending of supercell storm reflectivity core can give 15-minute precursor signal, the descending of mesocyclone core can give 8-minute precursor signal, the significant MARC can give 30-minute precursor signal, and the descending of VIL value can give 17-minute early warning signal of damaging winds. Based on narrow-band echo, the proportion that can be recognized as gust front of the supercell storm is low, and only a few damaging straight-line winds can be identified from the moving speed of storm or gust front characteristics. There are only 4 obvious low-level divergence velocity pairs identified in 56 cases, which indicate that most supercell storms produce asymmetric downburst because of horizontal movements.
The Hazardous Convective Storm Monitoring of Phased-array Antenna Radar at Daxing International Airport of Beijing
Zhang Xi, Huang Xingyou, Liu Xin'an, Lu Jianbing, Geng Lining, Huang Hao, Zhen Guangju
2022, 33(2): 192-204. DOI: 10.11898/1001-7313.20220206
The C-band phased-array antenna Doppler weather radar (C-PAR) with advanced working parameters can effectively monitor the hazardous aviation weather such as convective storm. To evaluate the performance of C-PAR, observations of two thunderstorm events in June of 2020 by the C-PAR and a S-band Doppler weather radar (CINRAD-SA) owned by Beijing Meteorological Bureau are compared and analyzed. In the morning of 18 June 2020, the weak echo of boundary outflow from thunderstorm is clearly detected by C-PAR, but CINRAD-SA cannot detect the weak echo until a new cell is triggered and enhanced by the boundary outflow, 24 minutes after first detection by C-PAR. A severe hailstorm is observed by C-PAR and CINRAD-SA, and the vortex signature of radial velocity is clearly observed by C-PAR, but not clearly by CINRAD-SA. The storm morphology and suspended echo due to updraft captured by C-PAR is well consistent with the thunderstorm conceptual model, but the storm vertical structure captured by CINRAD-SA is not so typical. The spatial variation of the intensity is very fine and with rich texture on the echo of C-PAR, but it is vague and coarse on that of CINRAD-SA. The three-body scattering spike and side-lobe echo of the hailstorm is easy to be captured by C-PAR, but it is hard to be recognized by CINRAD-SA. At the same time, the phased array radar uses pulse compression technology to obtain better weak echo detection capabilities. The differences of echo distribution and evolution revealed by C-PAR and CINRAD-SA verified that the C-PAR has advantages not only on temporal and spatial resolutions, but also on space coverage and sensitivity to weak echo. For small-scale weather systems like hailstorm, downburst and thunderstorm boundary outflow, the lifespan varies from tens of seconds to minutes, making it difficult to be captured by conventional radar. Therefore, as terminal weather radar, the C-PAR is more suitable to monitor small and medium-scale hazardous aviation weather. The C-PAR can capture the main structure characteristics of precipitation, reveal the initiation and development of a convective storm, and obtain better weak echo detection capabilities. With outstanding advantages, the C-PAR becomes an important and effective detection equipment for terminal aviation weather, which helps to improve aviation flight safety.
Characteristics of Raindrop Size Distribution at Anxi of Fujian
Huang Zewen, Peng Siyue, Zhang Haoran, Zheng Jiafeng, Zeng Zhengmao, Wang Yingjue
2022, 33(2): 205-217. DOI: 10.11898/1001-7313.20220207
Observation of raindrop size distribution (DSD) is significant for the understanding of precipitation physical processes and improvement of radar quantitative rainfall estimation. Based on DSD measurements from 2017 to 2020 collected in Anxi, Fujian Province, the DSD variation characteristics in different seasons and different rain types are analyzed. Subsequently, local empirical relation between radar reflectivity Z and rain rate R and that between Gamma shape parameter μ and slope parameter Λ are proposed. The DSDs observed in the local area are compared with counterparts obtained in other typical areas of China. The results show that DSDs in Anxi exhibit apparent seasonal variation. Generally, raindrops in summer can be the largest with the highest number concentration, while raindrops are the smallest in winter and the number concentration in spring is the lowest. With the increase of particle size, the seasonal variation of the number concentration of raindrops is similar to that in Taoyuan, Taiwan Province, China, while the number concentration of small raindrops is different. Compared with East China and North China, DSDs for summer stratiform precipitation in Anxi have higher concentration of small raindrops, while the concentrations of medium to large raindrops are similar to those in East China. For convective precipitation, the DSDs concentration is similar to that in North China for small raindrops while similar number concentration of medium raindrops to that in East China, while the number concentration of large raindrops is between that obtained in East China and North China. The Z-R relationship of summer stratiform precipitation is in good correspondence with the results obtained in Taoyuan. With the same Z, the R in East China is slightly larger than that in Anxi and Taoyuan; the Z-R relationship for convective precipitation in Anxi is also close to that in Taoyuan. When Z is not greater than 40 dBZ, the Z-R relationship in East China is very close to that in Anxi; when Z exceeds 40 dBZ, R in East China is significantly larger than that in Anxi and Taoyuan. When the slope parameter is larger than 2.5 mm-1, the relationship between the shape parameter μ and slope parameter Λ of the summer Gamma spectrum in Anxi is similar to that in Florida.
Extraction of Peanut Planting Area Based on Dual-temporal Remote Sensing Features of Crops
Guo Qile, Li Junling, Guo Peng
2022, 33(2): 218-230. DOI: 10.11898/1001-7313.20220208
Various high-resolution satellite remote sensing platforms and sensors have been established recently, but there are still many challenges for crop type fine classification. New methods are needed for fine classification of crop types and extraction of peanut planting area using high-resolution optical remote sensing data. Using panchromatic and multi-spectral (PMS) data of GF-1 and GF-6 in the middle and late stages of crop growth, 40 classification features are constructed from the perspective of spectrum, texture, and temporal variation of remote sensing image by means of spatio-temporal fusion and spectral mathematical transformation.15 features are selected by ReliefF-Pearson method. To compare the effects of different feature types on classification, the selected features are combined into four feature spaces, and the separability between crops in these feature spaces is measured by Jeffries-Matusita (J-M) distance. Using maximum likelihood classification, support vector machine and random forest as classifiers, crop classification tests of four feature space schemes are carried out, and different classification results are evaluated from the perspective of remote sensing classification accuracy and landscape analysis. Compared with the original image, in four feature spaces, the J-M distance between peanut and other crops is close to the saturation value of 2.0, and their separability is significantly enhanced. For all test results, the overall accuracy of crop classification is more than 78.0%, the Kappa coefficient of crop classification is more than 0.7, and the user's accuracy and producer's accuracy of peanut are both more than 79.0%. Compared with the three classifiers, Random Forest has the highest classification accuracy, and the average values of the overall accuracy and Kappa coefficient, peanut user's accuracy and producer's accuracy of its four schemes are 91.49%, 0.89, 94.45% and 93.30%, respectively. In addition, combining dual-temporal remote sensing data, texture and vegetation index features, as well as their temporal changes, can effectively improve the classification accuracy. It shows that adding the texture feature can improve the accuracy better than the vegetation index features. The landscape shape analysis of the classification results also shows that the overall crop classification and peanut, their patch shapes are close to the reality, and random forest is the best classifier. Its mean shape indices of crop landscape-level and peanut class-level are only 1.333 and 1.270, and the corresponding mean patch fractal dimension indices are only 1.127 and 1.110. An optimal dual temporal remote sensing crop classification model is proposed. Using this model, summer peanut planting area extraction and area measurement are carried out in four main peanut producing counties in Huang-Huai-Hai Region. Compared with the statistical data, the determination coefficient is 0.98 and the relative error of area calculation is ±16.25%, showing a good application prospect.
Future Projection of Rainstorm and Flood Disaster Risk in Southwest China Based on CMIP6 Models
Huang Xiaoyuan, Li Xiehui
2022, 33(2): 231-243. DOI: 10.11898/1001-7313.20220209
Under the background of global warming and frequent extreme weather and climate events, the occurrence of rainstorm and flood disasters in Southwest China continues to increase, causing great losses to social economy and people's lives and property. In order to project the characteristics of future rainstorm and flood disaster risk in Southwest China, 5 CMIP6 models and 5 extreme precipitation indices are selected to construct a risk assessment model, combined with topographic factors, socio-economic data and percentage of cultivated land area, by comprehensively considering disastrous factors and vulnerability. The rainstorm and flood disaster risks are mainly assessed for the baseline period (1995-2014), projected under three scenarios (SSP1-2.6, SSP2-4.5, SSP5-8.5) for two future periods (2021-2040, 2041-2060), and comparatively analyzed. The results show that the simulation performance of EC-Earth3 and EC-Earth3-Veg on the selected 5 extreme precipitation indices is excellent, and the performance of un-equal weighted aggregation (UEWA-5) is better than equal weighted aggregation (EWA-5). According to the prediction results, 5 extreme precipitation indices are high in western Yunnan, northeastern Guangxi, and the western margin of Sichuan Basin. Higher social vulnerability and radiation forcing lead to greater extreme precipitation index. From the baseline period to the next two periods, the extreme precipitation indices and risk of disastrous factors show an increasing trend. The high vulnerability areas are distributed in the economically and agriculturally developed regional central cities and the change of vulnerability is not obvious under different scenarios. The medium-high risk areas and high risk areas of rainstorm and flood disasters are mainly distributed in Chengdu City of Sichuan, the center of Chongqing and western Sichuan Basin, Kunming City of Yunnan, Guilin City and south-central parts of Guangxi. The medium-high risk areas and high risk areas in Southwest China increase with time from the base period to the far future, especially under the SSP2-4.5 scenario.
Possible Effects of the Difference in Atmospheric Heating Between the Tibetan Plateau and the Bay of Bengal on Spatiotemporal Evolution of Rainstorms
Chen Jinqiu, Shi Xiaohui
2022, 33(2): 244-256. DOI: 10.11898/1001-7313.20220210
Based on the climatical daily meteorological data from May to August during 1979-2019, using the methods of empirical orthogonal function (EOF) and multivariate empirical orthogonal function (MV-EOF), correlation analysis and synthetic analysis, the characteristics of the temporal and spatial evolution of atmospheric heat sources around the Tibetan Plateau (TP) and the Bay of Bengal (BOB) are investigated, and their relationships with the rainstorm in eastern China are analyzed. It's found that MV-EOF can well show the relationship between the spatial distribution characteristics of different elements and their temporal evolution.The results reflect the close relationship between the thermal condition of TP and its surrounding areas, the summer monsoon circulation, and the rainstorm in eastern China.Correspondingly, the rainstorm events occur in Southeast China and the middle and lower reaches of the Yangtze River, respectively. The spatial variation characteristics of the atmospheric heating in TP and surrounding areas show significant differences in the second and the third modes of MV-EOF, especially in the reversal of the thermal contrast between TP and BOB. The atmospheric heating in TP and BOB shows an opposite trend, which indicates that the sea-land thermal comparison between TP and BOB is likely to be one of the key factors leading to the occurrence of rainstorm events in different places in eastern China. The results of the synthetic analysis suggest a possible physical mechanism: When the atmospheric heating is weak over TP and strong over BOB, there is a strong ascending motion over BOB and its surrounding areas, which is conducive to the maintaining of South Asian high (SAH) and the northwestern Pacific subtropical high (WPSH) in southward position, and also conducive to the occurrence of cyclonic water vapor transportation circulation in Southeast China-South China Sea-Northwest Pacific. It weakens the southwesterly water vapor transportation, thus induces the continuous heavy precipitation in South China.After the increasing of the atmospheric heating over TP, the convergence and ascending motion of the lower atmosphere are strengthened, which attracts the SAH to move northward to TP, with an enhancement and eastward extension. The WPSH then lift northward, and the airflows around it convey more water vapor to West China and the middle and lower reaches of the Yangtze River, resulting in heavy precipitation. The above results show that in the climate average state, the thermal contrast change of the TP and BOB can change the atmospheric vertical circulation through modulation, affect the location and intensity of the SAH and WPSH, and then change the water vapor transportation. It has an important impact on the spatiotemporal variation of the rainstorm events in the eastern China.