CHARACTERISTICS AND CIRCULATION BACKGROUND OF SHANGHAI SUMMER SEA BREEZE FRONT AND ITS INDUCED CONVECTION
-
摘要: 基于2011—2014年6—9月多普勒雷达、加密自动站和NCEP/NCAR再分析资料,对上海地区海风锋及其触发对流的时空分布和环流背景进行统计,得出主要结论:(1)近4 a来上海夏季海风锋登陆65次,其中海风锋触发对流19次。海风锋最早于09时登陆,平均持续时间为5.2 h。海风锋触发对流时段为13—15时,对流平均维持时间为2.5 h。海风锋触发对流多出现在市区、北部郊区和浦东新区,呈现强局地性;(2)根据海风锋登陆点将海风锋分成北支、南支和双支3种类型。海风锋类型与环境风向密切相关,环境风为东北风时形成南支海风锋,环境风为偏南风和西南风时形成北支海风锋,环境风为偏西风时形成双支海风锋。南支海风锋不易触发对流,这与其出现时上海的热力条件不如北支和双支海风锋出现时有关;(3)海风锋触发对流日的环流背景为:500 hPa副热带高压强盛,上海受副高控制;中低层西南风增温、增湿,促进层结不稳定;低层925 hPa为弱西风。海风锋触发对流日的大气可降水量和K指数显著大于无对流日,但与其它对流日无明显差异。Abstract: Based on the Doppler radar, encrypted automatic stations and NCEP/NCAR reanalysis data from June to September, 2011—2014, the spatial and temporal distribution of a sea breeze front (SBF) and its induced convection were investigated. The results show that during the 4 years the summer SBF landed 65 times, while SBF-induced convection occurred 19 times. The SBF is prone to land at 0900 to 1200 (local time) withan average duration of 5.2 hours. SBF-induced convection tends to happen at 1300 to 1500 withan average duration of 2.5 hours. It has strong local characteristic, most likely to occur in the downtown areas, Pudong New District and Baoshan District. The SBF is divided into 3 categories according to its landing site: N-SBF landing from Yangtze River estuary, S-SBF landing from Hangzhou Bay and SN-SBF landing from both sides. Compared with SN and N-SBF, S-SBF is more difficult to trigger the convection because of the poor thermal conditions. Types of SBF depend largely on the direction of background wind. S-SBF occurs when background wind is northeasterly, N-SBF occurs when background wind is southerly and southwesterly, SN-SBF occurs when background wind is westerly.During the SBF-triggering convection days, Shanghai is under the control of a 500 hPa subtropical high. At 700 and 850 hPa southwesterly wind increases warm and humidity, promoting stratification instability. Westerly wind is rather weak at 925 hPa. PWV and K index are much greater at convection-induced days than convection-free days.
-
表 1 2011—2014年上海夏季海风锋日的对流和海风锋触发对流频数的空间统计
片区 行政区 对流频数 海风锋触发对流频数 市区 市区 3 3 北部 崇明、嘉定、宝山 11 5 东部 浦东新区、南汇 9 8 南部 金山、奉贤 1 1 西部 闵行、松江、青浦 2 2 合计 上海 26 19 表 2 2011—2014年夏季上海不同环境风下海风锋和对流发生频数分布
环境风向 海风锋频数 北支海风锋 南支海风锋 双支海风锋 对流 海风锋触发对流 触发率(触发对流频数/海风锋频数)/% N 3 2 1 0 1 1 33.33 NE 10 0 10 0 3 2 20.00 E 3 0 3 0 0 0 0 SE 7 6 0 1 1 1 14.29 S 11 8 1 1 8 6 54.50 SW 11 7 1 3 6 4 36.40 W 18 3 4 11 7 5 27.80 NW 2 0 3 0 0 0 0 合计 65 26 23 16 26 19 27.70 -
[1] ARRITT R W. The effect of water surface temperature on lake breezes and thermal internal boundary layers[J]. Boundary Layer Meteorol, 1987, 40(1): 101-125. [2] LEMONSU A, BASTIN S, MASSON V, et al. Vertical structure of the urban boundary layer over Marseille under sea-breeze conditions[J]. Boundary Layer Meteorol, 2006, 118(3): 477-501. [3] OHASHI Y, KIDA H. Local circulations developed in the vicinity of both coastal and inland urban areas: a numerical study with a mesoscale atmospheric model[J]. J Appl Meteorol, 1996, 41(1): 30-45. [4] PIELKE R A. A three-Dimensional numerical model of the sea breezes over south Florida[J]. Mon Wea Rev, 1974, 102(2): 115-139. [5] LYONS W A. The climatology and prediction of the Chicago Lake Breeze[J]. J Appl, 1972, 11 (12): 1259-1270. [6] 朱抱真.台湾的海陆风[J].天气月刊, 1955, 8(附刊): 1-11. [7] 于洪恩, 陈彬, 白玉荣.渤海湾西部海陆风的空间结构[J].气象学报, 1987, 45(3): 379-381. [8] 邱晓媛, 范邵佳.海陆风研究进展与我国沿海三地海陆风主要特征[J].气象, 2013, 39(2): 186-193. [9] 陶诗言.中国之暴雨[M].北京:科学出版社. 1980: 107-111. [10] 王彦, 于莉莉, 朱男男.等.渤海湾海风锋与雷暴天气[J].高原气象, 2011, 30(1): 245-251. [11] 刘运策, 庄旭东, 李献洲.珠江三角洲地区由海风锋触发形成的强对流天气过程分析[J].气象学报, 2001, 12(4): 434-441. [12] 董海鹰, 邵玲玲, 李德萍, 等.青岛奥帆赛期间海风锋触发的对流性降水特征[J].气象, 2008, 34(12): 48-53. [13] 卢焕珍, 赵玉洁, 俞小鼎, 等.雷达观测的渤海湾海陆风辐合线与自动站资料的对比分析[J].气象, 2008, 34(9): 57-64. [14] 王语卉, 苗峻峰, 蔡亲波.海南岛海风三维结构的数值模拟[J].热带气象学报, 2016, 32(1): 109-124. [15] 张振州, 蔡旭晖, 宋宇, 等.海南岛地区海陆风的统计分析和数值模拟研究[J].热带气象学报, 2014, 30(2): 270-280. [16] DARBY L S, BANTA R M, PIELKEJr R A. Comarisons between mesoscale model terrain sensitivity studies and Doppler Lidar measurements of the sea breeze at Monterey Bay[J]. Mon Wea Rev, 2002, 130(12): 2813-2838. [17] 东高红, 何群英, 刘一玮, 等.海风锋在渤海西岸局地暴雨过程中的作用[J].气象, 2011, 37(9): 1101-1107. [18] 尹东屏, 吴海英, 张备, 等.一次海风锋触发的强对流天气分析[J].高原气象, 2010, 29(5): 1262-1269. [19] 卢伟萍, 李江南, 梁维亮, 等.一次引发北部湾大暴雨过程的海风锋模拟研究[J].热带气象学报, 2012, 28(6): 945-952. [20] 梁钊明, 高守亭, 王彦渤.海湾地区碰撞型海风锋天气过程的资料诊断分析[J].气候与环境研究, 2013, 18(5): 608-616. [21] 王彦, 高守亭, 梁钊明.渤海湾海风锋触发雷暴的观测和模拟分析[J].高原气象, 2014, 33(3): 849-854. [22] 蒙伟光, 郑艳萍, 王宝民, 等.热岛与海风相互作用对珠三角午后强降水影响的观测和模拟研究[J].热带气象学报, 2014, 30(6): 1011-1026. [23] 苗曼倩, 唐有华.长江三角洲夏季海陆风与热岛环流的相互作用及城市化的影响[J].高原气象, 1998, 17(3): 280-289. [24] 李维亮, 刘洪利, 周秀骥, 等.长江三角洲城市热岛与太湖对局地环流影响的分析研究[J].中国科学(D辑), 2003, 33(2): 97-104. [25] 漆梁波, 陈春红, 刘强军.弱窄带回波在分析和预报强对流天气中的应用[J].气象学报, 2006, 64(1): 112-120.