Abstract
The Pearl River Delta (PRD), a tornado hotspot, forms a distinct trumpet-shaped coastline that concaves toward the South China Sea. During the summer monsoon season, low-level southwesterlies over the PRD’s sea surface tend to be turned toward the west coast, constituting a convergent wind field along with the landward-side southwesterlies, which influences regional convective weather. This two-part study explores the roles of this unique land–sea contrast of the trumpet-shaped coastline in the formation of a tornadic mesovortex within monsoonal flows in this region. Part I primarily presents observational analyses of pre-storm environments and storm evolutions. The rotating storm developed in a low-shear environment (not ideal for a supercell) under the interactions of three air masses under the influence of the land–sea contrast, monsoon, and storm cold outflows. This intersection zone (or “triple point”) is typically characterized by local enhancements of ambient vertical vorticity and convergence. Based on a rapid-scan X-band phased-array radar, finger-like echoes were recognized shortly after the gust front intruded on the triple point. Developed over the triple point, they rapidly wrapped up with a well-defined low-level mesovortex. It is thus presumed that the triple point may have played roles in the mesovortex genesis, which will be demonstrated in Part II with multiple sensitivity numerical simulations. The findings also suggest that when storms pass over the boundary intersection zone in the PRD, the expected possibility of a rotating storm occurring is relatively high, even in a low-shear environment. Improved knowledge of such environments provides additional guidance to assess the regional tornado risk.
摘要
粤港澳大湾区独特的“喇叭口”海岸下垫面, 长久以来被认为在区域**对流天气的形成和发展过程中发挥着重要作用. 基于**龙卷风历史个例统计, 该地区也是华南海岸带龙卷风暴相对集中发生的区域. 本研究以喇叭口海岸地形对夏季盛行西南季风气流的扰动为切入点, 探究大尺度季风气流与局地环流相互作用从而激发龙卷风暴的可能物理机制. 上篇首先通过南海夏季风活跃月份的长时段数值模拟, 揭示了喇叭口海岸在午后会形成有利于对流触发与升尺度发展的三种气团辐合交汇区, 即“三汇点”. 在午后海陆热力差异和下垫面粗糙度差异的影响下, **地面季风上岸气流在珠江口海面会发生水**切变并向西偏转, 与陆地盛行西南气流在珠江口西岸形成准静止的低层辐合边界. 当北侧出现风暴冷池出流时, 在珠江口会形成比辐合边界具有更**动力辐合与环境垂直涡度的三汇点. 本文以2020年6月1日在珠江口生成的一个龙卷风暴为例, 诊断研究其生成环境及精细结构演变. 距龙卷风暴仅6公里的相控阵天气雷达显示, 钩状回波和中涡旋形成于珠江口西岸准静止辐合边界与风暴冷池出流形成的三汇点, 后者在此次龙卷风暴的形成过程中可能发挥了重要作用. 高分辨率数值敏感性试验进一步证明, 三汇点区域的低层环境具有局地**辐合与**垂直涡度, 为中涡旋的形成提供了低层涡度来源, 请详见下篇. 观测结果还表明, 即使在弱切变环境下, 当对流系统经过喇叭口海岸的三汇点时, 发展形成旋转性风暴的可能性更高.
Similar content being viewed by others
References
Anderson-Frey, A. K., Y. P. Richardson, A. R. Dean, R. L. Thompson, and B. T. Smith, 2019: Characteristics of tornado events and warnings in the southeastern United States. Wea. Forecasting, 34, 1017–1034, https://doi.org/10.1175/WAFD-18-0211.1.
Atkins, N. T., K. M. Butler, K. R. Flynn, and R. M. Wakimoto, 2014: An integrated damage, visual, and radar analysis of the 2013 Moore, Oklahoma, EF5 Tornado. Bull. Amer. Meteor. Soc., 95, 144–1661, https://doi.org/10.1175/BAMS-D-14-00033.1.
Bai, L. Q., Z. Y. Meng, K. Sueki, G. X. Chen, and R. L. Zhou, 2020a: Climatology of tropical cyclone tornadoes in China from 2006 to 2018. Science China Earth Sciences, 63, 37–51, https://doi.org/10.1007/s11430-019-9391-1.
Bai, L. Q., G. X. Chen, and L. Huang, 2020b: Convection initiation in monsoon coastal areas (South China). Geophys. Res. Lett., 47, e202LGL087035, https://doi.org/10.1029/2020GL087035.
Brady, R. H., and E. J. Szoke, 1989: A case study of nonmesocyclone tornado development in northeast Colorado: Similarities to waterspout formation. Mon. Wea. Rev., 117, 843–856, https://doi.org/10.1175/1520-0493(1989)117<0843:ACSONT>2.0.CO;2.
Brooks, H. E., J. W. Lee, and J. P. Craven, 2003: The spatial distribution of severe thunderstorm and tornado environments from global reanalysis data. Atmospheric Research, 67–68, 73–94, https://doi.org/10.1016/S0169-8095(03)00045-0.
Bunkers, M. J., B. A. Klimowski, J. W. Zeitler, R. L. Thompson, and M. L. Weisman, 2000: Predicting supercell motion using a new hodograph technique. Wea. Forecasting, 15, 61–79, https://doi.org/10.1175/1520-0434(2000)015<0061:PSMUAN>2.0.CO;2.
Burgess, D., and Coauthors, 2014: 20 May 2013 Moore, Oklahoma, Tornado: Damage survey and analysis. Wea. Forecasting, 29, https://doi.org/10.1175/WAF-D-14-00039.1.
Chen, X. C., F. Q. Zhang, and K. Zhao, 2016: Diurnal variations of the land-sea breeze and its related precipitation over South China. J. Atmos. Sci., 73, 4793–4815, https://doi.org/10.1175/JAS-D-16-0106.1.
Davies-Jones, R., 1984: Streamwise vorticity: The origin of updraft rotation in supercell storms. J. Atmos. Sci., 41, 2991–3006, https://doi.org/10.1175/1520-0469(1984)041<2991:SVTOOU>2.0.CO;2.
Davies-Jones, R., 2006: Tornadogenesis in supercell storms: What we know and what we don’t know. Preprints, Symp. on the Challenges of Severe Convective Storms, Atlanta, GA, Amer. Meteor. Soc..
Du, Y., and G. X. Chen, 2019a: Climatology of low-level jets and their impact on rainfall over Southern China during the early-summer rainy season. J. Climate, 32, 8813–8833, https://doi.org/10.1175/JCLI-D-19-0306.1.
Du, Y., and G. X. Chen, 2019b: Heavy rainfall associated with double low-level jets over Southern China. Part II: Convection initiation. Mon. Wea. Rev., 147, 543–565, https://doi.org/10.1175/MWR-D-18-0102.1.
Fan, W. J., and X. D. Yu, 2015: Characteristics of spatial temporal distribution of tornadoes in China. Meteorological Monthly, 41, 793–805, https://doi.org/10.7519/j.issn.1000-0526.2015.07.001.
Flournoy, M. D., A. W. Lyza, M. A. Satrio, M. R. Diedrichsen, M. C. Coniglio, and S. Waugh, 2022: A climatology of cell mergers with supercells and their association with mesocyclone evolution. Mon. Wea. Rev., 150, 451–461, https://doi.org/10.1175/MWR-D-21-0204.1.
Hersbach, H., and Coauthors, 2020: The ERA5 global reanalysis. Quart. J. Roy. Meteor. Soc., 146, 1999–2049, https://doi.org/10.1002/qj.3803.
Hong, S. Y., and J. J. Lim, 2006: The WRF single-moment 6-class microphysics scheme (WSM6). J. Korean Meteorological Soc., 42(2), 129–151.
Houston, A. L., and R. B. Wilhelmson, 2007a: Observational analysis of the 27 May 1997 central Texas Tornadic Event. Part I: Prestorm environment and storm maintenance/propagation. Mon. Wea. Rev., 135, 701–226, https://doi.org/10.1175/MWR3300.1.
Houston, A. L., and R. B. Wilhelmson, 2007b: Observational analysis of the 27 May 1997 central Texas Tornadic Event. Part II: Tornadoes. Mon. Wea. Rev., 35, 727–735, https://doi.org/10.1175/MWR3301.1.
Houston, A. L., and R. B. Wilhelmson, 2012: The impact of airmass boundaries on the propagation of deep convection: A modeling-based study in a high-CAPE, low-shear environment. Mon. Wea. Rev., 140, 167–183, https://doi.org/10.1175/MWR-D-10-05033.1.
Kingsmill, D. E., 1995: Convection initiation associated with a sea-breeze front, a gust front, and their collision. Mon. Wea. Rev., 123, 2913–2933, https://doi.org/10.1175/1520-0493(1995)123<2913:CIAWAS>2.0.CO;2.
Lee, B. D., and R. B. Wilhelmson, 1997a: The numerical simulation of non-supercell tornadogenesis. Part I: Initiation and evolution of pretornadic misocyclone circulations along a dry outflow boundary. J. Atmos. Sci., 54, 32–60, https://doi.org/10.1175/1520-0469(1997)054<0032:TNSONS>2.0.CO;2.
Lee, B. D., and R. B. Wilhelmson, 1997b: The numerical simulation of nonsupercell tornadogenesis. Part II: Evolution of a family of tornadoes along a weak outflow boundary. J. Atmos. Sci., 54, 2387–2415, https://doi.org/10.1175/1520-0469(1997)054<2387:TNSONT>2.0.CO;2.
Lee, B. D., and R. B. Wilhelmson, 2000: The numerical simulation of nonsupercell tornadogenesis. Part III: Parameter tests investigating the role of CAPE, vortex sheet strength, and boundary layer vertical shear. J. Atmos. Sci., 57, 2246–2261, https://doi.org/10.1175/1520-0469(2000)057<2246:TNSONT>2.0.CO;2.
Markowski, P., and Y. Richardson, 2010: Mesoscale Meteorology in Midlatitudes. Wiley-Blackwell, 407 pp.
Marquis, J. N., Y. P. Richardson, and J. M. Wurman, 2007: Kinematic observations of misocyclones along boundaries during IHOP. Mon. Wea. Rev., 135, 1749–1768, https://doi.org/10.1175/MWR3367.1.
Mlawer, E. J., S. J. Taubman, P. D. Brown, M. J. Iacono, and S. A. Clough, 1997: Radiative transfer for inhomogeneous atmospheres: RRTM, a validated correlated-k model for the longwave. J. Geophys. Res.: Atmos., 102, 16 663–16 682, https://doi.org/10.1029/97JD00237.
Noh, Y., W. G. Cheon, S. Y. Hong, and S. Raasch, 2003: Improvement of the K-profile model for the planetary boundary layer based on large eddy simulation data. Bound.-Layer Meteor., 107, 401–427, https://doi.org/10.1023/A:1022146015946.
Orlanski, I., 1975: A rational subdivision of scales for atmospheric processes. Bull. Amer. Meteor. Soc., 56, 527–530, https://doi.org/10.1175/1520-0477-56.5.527.
Reed, R. J., and M. D. Albright, 1997: Frontal structure in the interior of an intense mature ocean cyclone. Wea. Forecasting, 12, 866–876, https://doi.org/10.1175/1520-0434(1997)012<0866:FSITIO>2.0.CO;2.
Rotunno, R., 1981: On the evolution of thunderstorm rotation. Mon. Wea. Rev., 109, 577–586, https://doi.org/10.1175/1520-0493(1981)109<0577:OTEOTR>2.0.CO;2.
Rotunno, R., and J. Klemp, 1985: On the rotation and propagation of simulated supercell thunderstorms. J. Atmos. Sci., 42, 271–292, https://doi.org/10.1175/1520-0493(1981)109<0577:OTEOTR>2.0.CO;2.
Schenkman, A. D., M. Xue, and A. Shapiro, 2012: Tornadogenesis in a simulated mesovortex within a mesoscale convective system. J. Atmos. Sci., 69, 3372–3390, https://doi.org/10.1175/JAS-D-12-038.1.
Schumacher, R. S., 2015: Resolution dependence of initiation and upscale growth of deep convection in convection-allowing forecasts of the 31 May–1 June 2013 supercell and MCS. Mon. Wea. Rev, 143, 4331–4354, https://doi.org/10.1175/MWR-D-15-0179.1.
Skamarock, W. C., and Coauthors, 2008: A description of the Advanced Research WRF version 3. NCAR Tech. Note NCAR/TN-475+STR, 113 pp.
Thompson, R. L., B. T. Smith, A. R. Dean, and P. T. Marsh, 2013: Spatial distributions of tornadic near-storm environments by convective mode. E-Journal of Severe Storms Meteorology, 8, 1–22, https://doi.org/10.55599/ejssm.v8i5.50.
Thompson, R. L., R. Edwards, J. A. Hart, K. L. Elmore, and P. Markowski, 2003: Close proximity soundings within super-cell environments obtained from the rapid update cycle. Wea. Forecasting, 18, 1243–1261, https://doi.org/10.1175/1520-0434(2003)018<1243:CPSWSE>2.0.CO;2.
Thompson, R. L., B. T. Smith, J. S. Grams, A. R. Dean, and C. Broyles, 2012: Convective modes for significant severe thunderstorms in the contiguous United States. Part II: Supercell and QLCS tornado environments. Wea. Forecasting, 27, 1136–1154, https://doi.org/10.1175/WAF-D-11-00116.1.
Wakimoto, R. M., and J. W. Wilson, 1989: Non-supercell Tornadoes. Mon. Wea. Rev., 117, 1113–1140, https://doi.org/10.1175/1520-0493(1989)117<1113:NST>2.0.CO;2.
Wakimoto, R. M., H. V. Murphey, E. V. Browell, and S. Ismail, 2006: The “Triple Point” on 24 May 2002 during IHOP. Part I: Airborne Doppler and LASE analyses of the frontal boundaries and convection initiation. Mon. Wea. Rev., 134, 231–250, https://doi.org/10.1175/MWR3066.1.
Wang, B., and LinHo, 2002: Rainy season of the Asian–Pacific summer monsoon. J. Climate, 15, 386–398, https://doi.org/10.1175/1520-0442(2002)015<0386:RSOTAP>2.0.CO;2.
Weckwerth, T. M., and D. B. Parsons, 2006: A review of convection initiation and motivation for IHOP_2002. Mon. Wea. Rev., 134, 5–22, https://doi.org/10.1175/MWR3067.1
Weiss, C. C., and H. B. Bluestein, 2002: Airborne pseudo-dual Doppler analysis of a dryline-outflow boundary intersection. Mon. Wea. Rev., 130, 1207–1226, https://doi.org/10.1175/1520-0493(2002)130<1207:APDDAO>2.0.CO;2.
Wurman, J., K. Kosiba, P. Robinson, and T. Marshall, 2014: The role of multiple-vortex tornado structure in causing storm researcher fatalities. Bull. Amer. Meteor. Soc., 95, 31–45, https://doi.org/10.1175/BAMS-D-13-00221.1.
Wurman, J., J. Straka, E. Rasmussen, M. Randall, and A. Zahrai, 1997: Design and deployment of a portable, pencil-beam, pulsed, 3-cm Doppler radar. J. Atmos. Oceanic Technol., 14, 1502–1512, https://doi.org/10.1175/1520-0426(1997)014<1502:DADOAP>2.0.CO;2.
Xue, M., and W. J. Martin, 2006a: A high-resolution modeling study of the 24 May 2002 dryline case during IHOP. Part I: Numerical simulation and general evolution of the dryline and convection. Mon. Wea. Rev., 134, 149–171, https://doi.org/10.1175/MWR3071.1.
Xue, M., and W. J. Martin, 2006b: A high-resolution modeling study of the 24 May 2002 dryline case during IHOP. Part II: Horizontal convective rolls and convective initiation. Mon. Wea. Rev., 134, 172–191, https://doi.org/10.1175/MWR3072.1.
Zhang, Q. H., X. Ni, and F. Q. Zhang, 2017: Decreasing trend in severe weather occurrence over China during the past 50 years. Scientific Reports, 7, 42310, https://doi.org/10.1038/srep42310.
Zhang, Y., L. Q. Bai, Z. Y. Meng, B. H. Chen, C. C. Tian, and P. L. Fu, 2021: Rapid-scan and polarimetric phased-array radar observations of a tornado in the Pearl River Estuary. Journal of Tropical Meteorology, 27, 81–86, https://doi.org/10.46267/j.1006-8775.2021.008.
Zhang, Y. J., F. Q. Zhang, D. J. Stensrud, and Z. Y. Meng, 2015: Practical predictability of the 20 May 2013 Tornadic thunder-storm event in Oklahoma: Sensitivity to synoptic timing and topographical influence. Mon. Wea. Rev., 143, 2973–2997, https://doi.org/10.1175/MWR-D-14-00394.1.
Zhou, R. L., Z. Y. Meng, and L. Q. Bai, 2022: Differences in tornado activities and key tornadic environments between China and the United States. International Journal of Climatology, 42, 367–384, https://doi.org/10.1002/joc.7248.
Acknowledgements
This study was supported by the Guangdong Major Project of Basic and Applied Basic Research (Grant No. 2020B0301030004) and the National Natural Science Foundation of China (Grant Nos. 42275006 and 42030604), the Guangdong Basic and Applied Basic Research Foundation (Grant No. 2023A1515011705), and the Science and Technology Research Project for Society of Foshan (Grant No. 2120001008761). The reanalysis data used can be accessed at the ECMWF’s website (https://cds.climate.copernicus.eu/cdsapp#!/dataset/reanalysis-era5-pressure-levels?tab=form). The radar and surface observations were provided by the Guangzhou Meteorological Observatory. The authors are grateful for the helpful reviews provided by the editors and anonymous reviewers.
Author information
Authors and Affiliations
Corresponding authors
Additional information
Article Highlights
• A convergent boundary routinely forms on the west coast of the trumpet-shaped Pearl River Delta during the summer monsoon season.
• The tornadic mesovortex develops where storm-generated cold outflows intersect with the convergent boundary along the west coast.
• The triple point formed by three air masses in the influence of the unique land–sea contrast contributes to the rotating storm development.
Rights and permissions
About this article
Cite this article
Bai, L., Yao, D., Meng, Z. et al. Influence of Irregular Coastlines on a Tornadic Mesovortex in the Pearl River Delta during the Monsoon Season. Part I: Pre-storm Environment and Storm Evolution. Adv. Atmos. Sci. 41, 1115–1131 (2024). https://doi.org/10.1007/s00376-023-3095-5
Received:
Revised:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1007/s00376-023-3095-5