【作者】 滕华超；

【导师】 杨军；

【作者基本信息】 南京信息工程大学 ， 大气物理学与大气环境， 2011， 硕士

【摘要】 本文利用中尺度数值模式3.2、NCEP 1°×1°再分析资料、常规气象观测资料以及南京信息工程大学雾外场观测资料,对2007年12月13日至14日发生在江苏、安徽区域内的一次浓雾过程进行数值模拟研究,分析了动力条件、水汽条件、辐射冷却等在雾过程中的作用。结果表明：这次浓雾过程形成的主要原因是大气层结稳定、水汽条件充沛；地面辐射冷却是雾形成的重要触发条件。在雾形成时,贴地层形成逆温结构,随后逆温层抬升；雾顶逆温结构是雾维持、发展的重要条件；在雾维持阶段,雾层内近似为等温结构,日出后,太阳辐射作用加强、温度随高度降低,稳定层结被破坏导致雾体消散。动力条件上,雾形成前低空为辐合区,雾维持期间950 hPa以上为辐合区,低空对应为下沉气流,有助于稳定层结的建立和维持。水汽条件分析表明：在整个雾过程中,从东南方向有持续的水汽输入；雾过程中200 m高度以上雾区为水汽辐合区,消散阶段为水汽辐散；雾维持阶段地表在地气交换过程中得到热量,地面对大气具有冷却作用,雾消散阶段地表亏损热量,地面对大气具有加热作用。利用WRF为一维辐射雾模式PAFOG提供扰动场,构建了一个有30个成员的辐射雾集合预报方案。对本次雾过程进行预报效果分析,结果表明：该方案在地面能见度预报及雾层垂直结构预报方面均好于实际探空作为初始场的单一预报结果；模式启动时刻对预报结果有较大影响,由于辐射雾多发生在夜间,且模式需要一定时间达到稳定,本个例中一维模式在14:00启动预报效果最好,集合预报成员与实测能见度的标准差平均值为0.516 km,集合平均值的平均预报误差为0.287 km。更多还原

【Abstract】 A heavy fog event occurred in Anhui and Jiangsu province on 13-14 Dec.2007. In this study, a preliminary numerical simulation of this case was conducted by using the new generation Mesoscal model Weather Research and Forecast model (WRF), NCEP 1°×1°reanalysis data, routine observation data and the data from a comprehensive fog experiment carried out in Nanjing University of Information Science & Technology during the same period. The roles of dynamical factor, vapor factor and radiative cooling effect in the formation of a heavy fog were investigated by means of diagnostic analysis. The results show that the stable atmospheric stratification and abundant vapor supply led to the formation of fog. Long wave radiation cooling at the surface was of vital importance for the formation and the development of radiation fog. In fog formative stage the inversion was near surface and then got uplifted. Subsequent, the inversion layer was lifting, the existence of inversion at the top of fog layer played an important role in fog development and maintenance. The temperature profile in the fog layer changed slightly during the maintaining stage and after sunrise the inversion was destroyed since distinct solar radiation. Before fog formed, the lower layer was basically weak convergence region. There was downdraft under 950 hPa which was beneficial to the establishment and maintenance of stable stratification during fog episode. The water vapor budget for the fog was investigated based on simulated results of the WRF model. The research area was a rectangle contained Jiangsu and Anhui province, and the result showed that there was continuous water vapor import through the south and east boundary. During the fog there was convergence region of water vapor above 0.98a while divergence during the weakening period. The ground had a cooling effect on the surface layer because of receiving heat through radiation interchange, while it was reversed during the fog dissipation.An ensemble fog forecast system was designed based on WRF and a high resolution numerical 1-D model called PAFOG, initial perturbation conditions of PAFOG are obtained from the simulation of WRF. Comparison between prediction and observation was made during a typical radiation fog event that occurred in Nanjing during 13-14 December 2007. The results show the ensemble forecast system is better than single forecast. Using this method, the prediction for both visibility at surface and vertical structure of fog are better than those utilizing the model only initialized by radiosonde observation; the initial time of simulation played an important role on prediction, due to radiation fog mostly occurs at night, and the model will take some time to stabilize, the one-dimensional model started at 14:00 is the best choice, the standard deviation between ensemble member and observation is 0.417, and the absolute error of ensemble average is 0.228 km.更多还原