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“05.6”华南暴雨中低纬度系统活动及相互作用
The Evolution Characteristics of Mid latitude and Low latitude Synoptic Systems During the "05.6" Heavy Rain Event in South China
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摘要: 利用NCEP/NCAR再分析资料、FY-2C卫星逐时云顶亮温资料（分辨率为0.05°×0.05°）及射出长波辐射资料（分辨率为0.5°×0.5°）、实时地面加密观测和实况探空资料等，对“05.6”华南持续性暴雨过程期间南海季风活动、副热带高压演变、冷空气影响、高低空急流耦合等进行深入分析，探讨中低纬度不同尺度系统的活动特征及相互作用。结果表明：“05.6”华南暴雨是在中纬度地区位势高度场稳定的北高南低背景下，由东亚沿岸槽和青藏高原短波系统引导中纬度冷空气与低纬度地区季风系统相互作用下产生的；南海副热带季风的活跃与100° 120°E处越赤道气流通道的消失密切相关，其两次大规模向北推进是过程开始和结束的重要标志；副热带高压较多年平均明显偏南且强度达到最强，700hPa中纬度冷空气的明显南侵对暴雨过程有重要贡献；高空急流入口区右后方与低空急流左侧由于强烈的高空辐散和非地转平衡强迫，构成一支横跨低空急流的经向次级环流，高低空急流耦合的正反馈机制是华南暴雨异常的重要原因之一。Abstract: The evolution characteristics and interaction between mid latitude and low latitude synoptic systems during "05.6" heavy rainfall process in South China is studied in detail. The monsoon activity in South China Sea, basic characteristics of sub tropical high in west Pacific, the influence of the cold air in middle latitude, and the coupling mechanism between upper level and low level jet are analyzed based on NCEP/NCAR reanalysis data with the resolution of 1°×1° and a series of observation data. FY 2C satellite data, including the brightness blackbody temperature on cloud top (TBB) data with the resolution of 0.05°×0.05° and outgoing long wave radiation (OLR) observation with the resolution of 0.5°×0.5°, surface observation for 3 hour interval, and auto weather station observation for 1 hour interval are used for model initialization and verification. The results are as follows: Under the stable background of high pressure in the north and low in the south, the "05.6" heavy rainfall is produced by the interaction between monsoon system from low latitude and mid latitude cold air driven by east coast trough and plateau short wave. During the "05.6" heavy rainfall, the sub tropical monsoon in South China Sea blocks the cross equatorial flow path and leads to the abnormal equator west wind in area of 100°-120°E. It moves northward massively for 2 times, indicating the beginning and end of this rainfall process. The strength of sub tropical high maintains very strong and the position of high ridge changes in an abnormal pattern of west advancing east retreating west stretching and north advancing during the prophase stable north jump finally. The south invading of 700 hPa cold air in westerly belt in the beginning of the process has important impacts on this event, which may be the most important feature in this process. During the "05.6", there is a ULJ (upper level jet) on left front of South China and a LLJ (low level jet) on the right. Strong aloft divergence of ULJ and the ageostrophic force in the left of LLJ forms the secondary circulation across LLJ, so the positive feedback of coupling mechanism between ULJ and LLJ may be one of the prime causes for the "05.6" heavy rain event.
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图 1 2005年6月17-25日华南暴雨过程累积降水量 (单位：mm)(a) 和500hPa平均位势高度 (等值线，单位：dagpm) 及TBB分布 (阴影区)(粗实线为槽线；带箭头实线为冷空气路径；带箭头虚线为暖空气路径)(b)
Fig. 1 The accumulated precipitation during 17-25 Jun 2005(unit:mm)(a) and averaged geopotential height of 500 hPa (isoline, unit:dagpm) with averaged TBB (shaded) in the same periond (thick solid linedenotes trough-line; solid arrow denotes cold air; dashed arrow denotes warm air)(b)
图 2 2005年6月17-25日平均赤道经向风纬向-高度剖面图 (单位：m/s)(a) 和850 hPa风矢量沿110°E的时间-经向剖面图 (b)
Fig. 2 The cross section of zone-heihgt for averaged meridional wind along equator during 17-25 Jun 2005(unit:m/s)(a) and the cross section of tim-meridian along 110°E for wind at 850 hPa (b)
图 3 2005年6月17-25日过程平均850hPa风矢量 (阴影区为偏南风分量风速≥1m/s)
Fig. 3 Wind vector of 850 hPa averaged during 17-25 Jun 2005 (shaded areas for southerly velocity no less than 1m/s)
图 4 2005年6月850hPa风速沿110°E (a) 及沿100°E (b) 随时间变化 (单位：m/s)
Fig. 4 The evolution of southwest wind in 850 hPa along 110°E (a) and 100°E (b)(unit:m/s)
图 5 2005年6月对流层低层沿105°~120°E平均温度的时间-经向剖面图 (单位：℃)(a)700hPa, (b)850hPa
Fig. 5 The cross section of time-meridian for temperature in the low troposphere averaged from 105°E to 120°E in June 2005 (unit:℃)(a)700hPa, (b)85 0hPa
图 6 2005年6月对流层中低层105°~120°E平均水平风矢量的时间-经向剖面 (等值线为偏北风；单位：m/s)(a)700 hPa, (b)850 hPa
Fig. 6 The cross section of time-meridian for wind of low troposphere averaged from 105°E to 120°E in June 2005(contour line is for the northerly wind; unit:m/s)(a)700 hPa, (b)850 hPa
图 7 2005年6月500hPa位势高度沿22.5°~27.5°N平均的时间-纬向剖面 (a) 和沿110°~130°E平均的时间-经向剖面 (b)(单位：dagpm)
Fig. 7 The cross section of time-zone for geopotential height in 500 hPa averaged from 22.5°N to 27.5°N (a) and the same of time-meridian averaged from 110°E to 130°E (b) in June 2005 (unit:dagpm)
图 8 2005年6月17-25日过程平均OLR分布 (单位：W/m2)(a) 和105°~120°E平均OLR (阴影，单位：W/m2) 和整层积分水汽通量 (矢量，单位：kg·m-1·s-1) 随时间的演变 (b)
Fig. 8 OLR distribution averaged during 17-25 Jun 2005 (unit:W/m2)(a) and the evolution of OLR averaged in 105°-120°E (shaded) with the moist water flux integrated from surface to 300 hPa (vector, unit:kg·m-1·s-1)(b) in June 2005
图 9 2005年6月18-23日平均200hPa高空急流 (风矢量，风速不低于30m/s) 与850hPa低空急流 (风矢量，风速不低于12m/s) 的水平分布 (a) 及平均纬向风 (等值线，单位：m/s) 与垂直环流 (带箭头虚线，单位：m/s) 的经向垂直分布 (b)
Fig. 9 The upper layer jet (ULJ) in 200 hPa (defined by velocity no less than 30m/s) and low layer jet (LLJ) in 850 hPa (defined by velocity no less than 12m/s) during 18-23 Jun2005(a) and the cross section of zonal wind (isoline, unit:m/s) with vertical circulation (dashed arrow, unit:m/s)(b)
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