西北太平洋环境风垂直切变和热带气旋移动对涡旋内对流非对称分布影响的特征分析

Effects of vertical wind shear and tropical cyclone motion on asymmetric distribution of convective clouds in TCs over the western North Pacific

中文关键词:  热带气旋  中尺度对流系统  非对称分布  环境风垂直切变

英文关键词:Tropical cyclones  Mesoscale convection systems  Asymmetry distribution  Environmental vertical wind shear

中文摘要:

      热带气旋（TC）预报特别是强度预报是当今大气科学研究和业务预报的重点、难点问题，TC环流内部的对流系统对气旋的结构和强度变化有着十分重要的影响。利用FY-2C/2E黑体亮温（TBB）资料和NCEP分析资料，研究了2005-2012年西北太平洋热带气旋外雨带区的对流非对称分布特征，及其与环境风垂直切变和TC移动的关系。分析发现，整层风垂直切变的方向与TBB一波非对称大值区关于方位角的分布有很好的对应关系。在弱整层风垂直切变条件下（<5 m/s），TC移动引起的非对称摩擦效应会使对流易出现在移动方向的右前象限。在中强整层风垂直切变条件下（>5 m/s），风切变成为影响对流非对称分布的主要因子，TC外螺旋雨带区的对流集中于顺风切方向及其左侧，对流偏离顺切变左侧的程度一方面受到TC内逆时针环流的影响，另一方面与风垂直切变的强度有关：对于发展阶段的TC，当风垂直切变增强时，一波非对称分布更加显著，切变越强，TC强度越大，外雨带区的对流越偏离顺风切左侧；对于消亡阶段的TC，风垂直切变的影响作用并不明显。

英文摘要:

      The FY-2 geostationary satellite black body temperature (TBB) data and NCEP global reanalysis data were used to investigate the asymmetric distribution of convective clouds (DCC) in the outer region of tropical cyclones (TCs) over the western North Pacific during 2005-2012. It is demonstrated that the environmental vertical wind shear (VWS) and TC motion are closely related to the DCC in TCs. When VWS is weak (<5 m/s), the DCC is located to the right front quadrant of the TC path in the lower troposphere due to friction-induced asymmetric boundary layer convergence. With increases in the VWS, the main zone of DCC changes from the right to the left quadrant of the TC path. This is because the VWS becomes the dominating factor leading to TC’s convection asymmetric distribution and the convection is concentrated to the left of the downshear. On one hand, how large the convections deviate from the downshear is subject to the counter-clockwise flow of TC; on the other hand, it is related to the strength of VWS. The results also show that the direction of the VWS corresponds well to the heavy TBB’s onewave asymmetry. When a TC is evolving in a strong VWS, TBB’s one wave asymmetry becomes more obvious. Meanwhile, convections in the outer spiral rainbands region tend to the left of the downshear. For a weakened TC, the effect of the VWS is not distinct compared with that for a stronger one.