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“6.29”淮河暴雨过程β-中尺度系统结构特征的数值模拟分析
Numerical Simulation Analysis on the Meso-β-scale Systems Structure of a Heavy Rain over the Huaihe River
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摘要: 利用中国科学院大气物理研究所LASG研制的AREM中尺度暴雨数值预报模式, 对2003年6月29—30日发生在淮河流域的一次大暴雨过程进行了数值模拟分析。结果表明:随着西太平洋副热带高压加强, 低空急流迅速向北推进, 加强了其北侧的风速梯度和气旋性切变, 使涡度场发生了强烈变化, 强正涡度柱的发展导致了低层β-中尺度低压和气旋的新生; 而对流层中高层β-中尺度高压的发展所引起的地转偏差使得β-中尺度高压附近的风场发生明显变化, 并导致β-中尺度强辐散中心强烈发展, 最终造成强烈的上升运动。强上升运动出现在低层θse强锋区的南侧。Abstract: By analyzing and numerical simulation of a heavy rain event, the physics process and spatial structure of the meso-scale convective system are revealed. Such studies help to get ideas beneficial to and then improve heavy rain forecast. A heavy rainfall occurred over the Huaihe River during 29—30 June 2003 is simulated by using AREM model which is the advanced LASG η-coordinates numerical meso-scale heavy rainfall prediction model with horizontal resolution of 37 km and 28 levels vertically. Comparison between hourly simulated results and observed development shows that the main rainfall period and the main precipitation system are successfully simulated. As indicated by the simulation results:① Though southwest low vorticity is not the direct influencing system, the shear line and low pressure trough area stretching out from the low vorticity provide favorable background condition for the development of meso-β-scale system. ② Southwest low-level jet is the main cause of this weather course. The fast movement of the axis of Southwest low-level jet stream enhances the gradient of the wind and the cyclonic shear in the north of the axis of low level jet, bringing sharp transformation of the vorticity. A strong column of positive vorticity leads to the occurrence and development of the meso-β-scale depression and cyclone at lower level near the vorticity column, whereas a meso-β-scale high pressure developes at the midhigh level of the troposphere without the assorted meso-scale anticyclone. ③ The geostrophic deflection caused by the new meso-high changes the wind field near the meso-high and produces the strong meso-β-scale divergence center around the high. It results in the development of a strong updraft combined with the powerful convergence at lower layer. ④ The strong updraft occurs near the south boundary of the strong frontal zone of θse at lower layer. Meridional vertical cell across the strong frontal zone of θse firstly originates in the boundary layer then develops upwards slowly. And a meso-β-scale cyclone comes into being circling the ascending branch. ⑤ With the development of the meso-β-scale convergence in lower layer and meso-β-scale divergence in higher layer, water vapor in low layer accumulates to the meso-β-scale system area, thereby forms a narrow vapor convergence band, which ultimately leads to the strong rainfall under the effect of strong updraft.
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Key words:
- meso-β-scale systems;
- AREM;
- heavy rain over the Huaihe River
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图 3 2003年6月29日20:00 700 hPa形势场模拟结果
(矢量线为流线; 实线为不低于16 m·s-1等风速线, 细虚线为初始时刻不低于16 m·s-1的等风速线, 间隔2 m·s-1; 粗断线为切变线, D表示低涡, LLJ表示低空急流)
图 4 模式积分5 h后850 hPa流场、高度场及积分后5~6 h的模拟降水
(矢量线为流线; 虚线为高度场, 间隔4 gpm; 阴影区为模拟的1 h降水区, 单位:mm, 间隔为10 mm)
图 5 700 hPa (a) 和850 hPa (b) 上沿118°E u分量和涡度随时间的演变
(实线、细虚线为u分量等值线, 间隔2 m·s-1; 粗断线表示西风急流中心位置随时间的演变; 阴影区为涡度场, 单位:10-5s-1)
图 6 模式积分5 h后沿118°E涡度和等风速线垂直剖面
(实线为等风速线, 间隔2 m·s-1; 阴影区为涡度场, 单位:10-5s-1, 正涡度最大中心值为50×10-5s-1)
图 7 模式积分5 h后400 hPa高度场、散度场和距平流场
(矢量线为流线; 虚线为等高线, 单位:gpm; 阴影区为散度场, 单位:10-5s-1, 辐散最大中心值为57×10-5s-1)
图 8 初始时刻 (a) 和积分5 h后 (b) 沿118 °E θse分布 (单位:K) 和垂直环流剖面
(虚线为θse, 间隔2 K; 矢量线为经向流线; 阴影区为不高于-20×10-3 hPa·s-1上升运动区, 中心最大值为-120×10-3 hPa·s-1)
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