【作者】 段云霞；

【导师】 邵爱梅； 邱崇践；

【作者基本信息】 兰州大学 ， 气象学， 2009， 硕士

【摘要】 利用多普勒雷达资料反演的风场及WRF中尺度模式对2006年登陆我国的台风过程“碧利斯”的结构进行了分析研究,并利用反演风场进行同化,试图改进对台风的预报。1)基于两步变分法,利用两部多普勒雷达资料反演的风场对0604号台风过程结构进行了分析研究。结果表明,该方法可以较好的反演出台风的水平、垂直风场特征,水平风场呈现有不对称性且有明显的偏心结构,流场随高度呈现出漏斗形特征,垂直风速与水平流场对应较好,台风中心有下沉气流,外围有上升气流。通过对台风物理量的分析发现,此次台风过程存在以最大风速半径随高度向外倾斜的主环流圈和低层为向中心流入,高层向外流出的次环流圈,并且利用WRF模式模拟结果检验了这次台风过程反演结果的合理性。2)利用反演的水平风场对常用的对称风场涡旋模型进行了验证,发现在最大风速圈内取Rankine模型,最大风速圈外取Chen 3模型对此次台风过程拟合较好。3)对比分析了单、双雷达资料对于此次台风过程的反演结果,将经验对称涡旋模型作为弱约束引入两步变分方法,提高了两步变分法对此次台风过程的反演能力,改进了单雷达资料反演的效果。4)利用中尺度模式WRF及其3D-Var分别直接同化径向风、间接同化径向风(同化反演风)资料,以期能够改进预报。结果显示:同化反演风对风场的调整较大,台风呈现非对称性,有明显偏心结构。对台风路径的预报表明,在预报的前9个小时,直接同化和间接同化径向风资料都能提高对台风路径的预报能力,而所有试验预报的台风中心气压都偏强,间接同化反演风的同化预报效果好于直接同化预报效果。更多还原

【Abstract】 The two-step variational method was used to analyse the 3D wind structure of typhoon Bilis by using two Doppler radars. WRF model and WRF 3D-Var were employed to estimate the effect of radar data assimilation on the forecasts of this typhoon process.Firstly, The 3D wind fields of this typhoon process was analyzed by using the two-step variational wind retrieval method. The results show that the method has ability to retrieve the wind characteristics of typhoon both in the horizontal and vertical sections. The asymmetrical structure can be obviously seen from the horizontal wind fields. The wind field is presented the funnel-shape characteristic with the increase of height. The downdraft occurred in the inner core and the updraft in the external part of the typhoon. By analyzing on the variables, it is found that there are a principal circulation in which the radius of the maximum wind speed dipped outward with the height and a secondary circulation with the inflow at the lower layers and outflow at the higher layers, then we utilize the simulation result by wrf model to test the retrieval result of this typhoon process.Subsequently, the retrieval wind fields were used to verify the common vortex models. The results show that the Rankine model fits well within the radius of the maximum tangential velocity, and the Chen 3 model fits well outside the radius of the maximum tangential velocity.Compared the retrieval wind from single radar with dual-doppler radar data, a constraint on this typhoon pattern was introduced into the cost function in the two-step variational method. It improves the retrieval ability of two-step variational method from single-Doppler radar data. The retrieved winds were consistent with that from two Doppler radar data.Finally, the radial velocities were assimilated into WRF 3D-Var system and the forecasts were performed by WRF model to test the effect of radial velocity assimilaton. Three experiments was designed: 1) No data was assimilated; 2) radial velocity was preprocessed to the size (about) model horizontal resolution and assimilated directly into 3D-Var system; 3) The retrieval winds by two-step variational method was assimilated into 3D-Var system. The results show that the wind is greatly adjusted and the horizontal wind is asymmetrical and eccentrical while assimilating retrieval wind. In the first nine-hour forecasts, radar data assimilation can improve the skill of the typhoon tracks forecasts. However, for all the experiments the forecasted central sea level pressures of this typhoon deepen than the observations. The forecasts of assimilating retrieval wind are better than assimilating radial velocity directly.更多还原