低空急流对海岸带大雾影响的实验与模拟研究

Fog in the coastal zone affects seriously traffic safety on coastal, ocean and aviation. In view of lack of knowledge of the fog weather phenomenon accompanied by the low-level jet (LLJ), it has great theoretical significance and application value to study quantitatively the influence to fog formation and dissipation from various factor of the water vapor transport, the dynamic and thermal effect through the low-level jet. Atmospheric boundary layer experiment data will be applied from the meteorological tower, wind profiler radar, microwave radiation meter and others in the project. And another microwave radiometer and closed eddy-covariance technique experiments are planning to join. On the basis of the statistical analysis of the relationship between fog and LLJ, using the FNL reanalysis data and mesoscale weather forecast model (WRF), researching the temporal and spatial changes of relevant physical quantities such as horizontal and vertical motion, temperature and humidity advection, and convergence and divergence accompanying with the LLJ, the project teams will explore the influence of LLJ on concentration and thickness of the fog. The numerical model considering the diurnal variation of the SST is also simulated to evaluate quantitatively the effect of water vapor transport on the fog process. Based on the multi-source data from numerical and experiment observations, source term of mechanical turbulent movement and radiation factors will be explored, and also the effect of vertical transportation of heat and momentum to local fog case. The objectives of the project are to clear the impact mechanism of low-level jet on the fog process and establish the concept model of low-level jet associated with fog weather in order to provide the better support for the coastal fog forecast.

海岸带大雾严重影响海陆空交通安全。开展低空急流对其影响的研究，定量分析低空急流在水汽输送方面对大雾过程的影响，以及动力、热力作用对大雾生消演变的影响具有十分重要的理论意义和应用意义。本申请利用气象铁塔、风廓线雷达、微波辐射计等大气边界层实验资料，辅以雾滴谱、闭路涡动相关实验观测，在统计分析大雾与低空急流相互关系和作用的基础上，应用FNL再分析资料和中尺度天气预报模式WRF，分析伴随低空急流的水平及垂直运动、温湿平流和辐合辐散等相关物理量的时空变化，以及对大雾浓度和厚度的影响。考虑海温的日变化，开展数值模拟控制实验，定量评估水汽输送对大雾过程的影响。综合数值模拟和湍流实验资料，分析湍流运动、辐射因子收支，探讨热量、动量的垂直输运在海岸带局地大雾天气生消过程中的作用。明晰低空急流对海岸带大雾过程影响机制，建立低空急流伴生大雾天气的概念模型，为海岸带大雾预报提供支撑。

项目背景:大雾对环渤海地区有严重影响，常常与污染气溶胶结合危害健康，低空急流对雾的影响需要加强认识。.主要研究内容：低空急流（LLJ）对大雾的影响及影响机制的观测研究；LLJ强度对大雾生消发展影响的数值模拟研究；定量评估LLJ携带的水汽对雾的影响。.重要结果及数据：.1）得到LLJ强度多小于14m/s，常在雾之前出现，提前一天出现的概率最大。同日且在雾之前出现时，多为西南LLJ，有利雾形成；滞后雾出现的急流，多为偏北急流，其强度与雾持续时间和强度呈负相关。当LLJ于雾前一天出现情况下，LLJ高度与后续雾持续时间有显著负相关。得到南风和强/弱北风LLJ影响雾事件的概念模型。为预报服务提供新思路。.2）南支LLJ对环渤海雾的作用受流经地形影响，山东丘陵影响环渤海较低层南部雾带和较高层北部雾带，导致渤海西海岸及中南部雾区面积增加，辽东湾及东北地区较高层雾区面积减少；长白山地形阻挡使环渤海雾带北段面积和液态水含量加大。为改进大雾数值预报模式提供思路。.3）LLJ引导的水汽输送初始场和侧边界水汽量值明显影响黄渤海雾区面积、发生地域和雾厚度差异。南支水汽输送影响渤海湾地区雾主要集中在近地面，约贡献90%以上；而对辽东湾及东北地区雾的影响集中在较高层，约贡献50%。另外，不同时刻初始场会显著影响南部水汽输送的积累，进而影响到雾区的面积，模拟时刻距离雾生成时刻越长，模拟值越接近真实情况。该成果为雾数值预报模式改进和中尺度数值预报产品的科学应用提供思路。.4）雾微物理特征分析表明，LWC并不能与雾浓度正相关单调对应，数浓度与液态水含量与能见度的负关系不同，指出VIS=F(LWC,N)方案有待改进。.5）观测实验得到天津气象铁塔80米和160米能见度和涡动相关观测，铁塔站及渤海A平台的雾滴谱观测，海上涡动相关、能见度加密、辐射观测，质控后的风廓线资料。为本项目及进一步科学研究提供基础。.