【作者】 屈凤秋；

【导师】 刘寿东； 易燕明； 黄健；

【作者基本信息】 南京信息工程大学 ， 应用气象学， 2008， 硕士

【摘要】 本文针对发生在2007年3月24～25日的一次华南沿海海雾过程,利用1°×1°的间隔6小时一次的NCEP/NCAR实时再分析资料和地面观测、边界层探测、雾滴谱观测资料,分析了此次海雾的大尺度天气背景特征、贴地层气象要素的变化特征、边界层结构特征及微物理结构特征,并利用WRF模式模拟分析了此次海雾过程海面水温的变化特征及辐射对平流冷却雾过程的影响。通过研究,得出以下主要结论。(1)此次海雾过程发生在西南低涡发展的天气背景下,持续的偏南暖湿气流的输送,为海雾的生成和发展提供了有利条件。海雾过程中相对湿度与能见度有良好的负相关关系。(2)在西南低压控制下,海雾发展阶段的边界层大气呈现弱静力稳定状态。海雾可以在弱静力稳定度条件下发展和成熟,而不以逆温或强稳定层结为必要条件,凝结冷却形成的雾顶结构与典型的雾顶结构有显著差异,凝结冷却层有明显的超绝热现象。(3)在海雾发展阶段,边界层低层有明显的夜间低空急流现象。低空急流一方面起到抑制下层雾垂直发展,使雾顶变得模糊的作用;另一方面还有可能通过动力强迫混合方式使上层空气冷却,为雾层向上发展提供有利条件。(4)充分混合的海雾出现在几乎整个边界层水汽达到饱和并出现雾顶水汽凝结、长波辐射冷却增强的条件下;充分混合的雾层厚度可达600m左右。(5)当雾顶以上风切变增强、气温上升时,可能引发雾顶上干、暖空气卷夹进入雾层,导致雾层破碎或消散;当雾顶以上风切变减弱、气温下降时,辐射冷却也可能使雾层恢复。(6)深厚的雾层能降低太阳短波辐射对雾的消散作用。太阳辐射一方面会使上层空气增温、雾滴蒸发,但增温也有助于低层空气保持稳定,使地面的雾层继续维持,直到太阳辐射增温由上至下逐渐侵蚀雾层。(7)在雾的发展阶段和充分混合阶段雾滴的数浓度和含水量变化不大。雾顶卷夹导致雾滴的数浓度变化不大,但大雾滴的数量明显减少,含水量大幅降低。海雾滴谱具有局地特征,此次华南沿海海雾的微物理参量值均低于其它地区。(8)用WRF模式模拟的此次华南沿海海雾过程的海水表面温度低于24℃;在海雾的发展阶段以及充分混合阶段,气水温差在2℃以内。(9)通过WRF模式进行去除辐射项的敏感性试验,发现日间太阳短波辐射对海雾的消散过程有很大的影响,而夜间长波辐射则影响雾层的垂直发展。更多还原

【Abstract】 The large scale synoptic background, near ground layer weather element, boundary layer structure and microphysical characteristics of a sustained sea fog event that occurred in the north part of the South China Sea on 24～25,march,2007,are analyzed by using the field observation and NCEP re-analysis data, and have a numerical study by the Weather Research Forecast Model (WRF) in the end. The following text is the main conclusions.(1) This sustained sea fog event is accompanied by southwest vortex developing southerly, and warm wet air flow continuously transport into the South China Sea both of them have advantage for the forming and developing of the sea fog. There is a good negative correlativity with relative humidity and visibility.(2) With control of southwest vortex, the aerosphere boundary layer has a feebleness static stabilization. The sea fog can develop and maturate in feebleness static stabilization, temperature inversion and strong stable stratification is not the sine qua non. There is notable difference between fog horizon forming by condensation cooling and typical fog horizon, and there is superadiabatic in condensation cooling layer.(3) In the developing phase, there is a obvious night lower tropospheric jet in the lower boundary layer. In one part, the lower tropospheric jet can choke back lower fog developing vertically, then fog horizon become illegible , and in another part, the higher aerosphere may cooling through dynamic forcing mixing, that is advantage for fog developing vertically.(4) The fully mixing fog occur in the condition of when boundary layer vapor is saturated, the fog horizon vapor condensation and long-wave radiation cooling enhanced. The fully mixing fog layer can reach the height of 600 m.(5) As there is not a strong temperature inversion layer, the fog horizon structure is different between forming form condensation and the typical one. The dry and wet air may enter into fog layer, when wind shear above fog horizon become stronger and air temperature rising, but radiation cooling also can renew fog layer. (6) The profound fog layer can reduce the dissipation effect from solar short-wave radiation. For one part, solar radiation can enhance higher aerosphere temperature and fog-drop vaporize, but air temperature increasing is also in favor of the lower air stabilization, and ground fog layer continue maintaining, until sea fog layer being gnawed from high layer to low layer by solar radiation.(7) In the developing and fully mixing phase, the number density and water content of fog-drop have an inconspicuous change, but the number of big fog-drop and water content reduce obviously, The sea fog-drops represent local features, the microphysical structure of the South China Sea is lower than other areas.(8) The sea surface temperature is under 24℃along the sea fog event, and air water temperature range is between 2℃in the developing and maturating phase.(9) Thought wiping off radiation calculate, we find that day short wave radiation have strong effect on fog dissipation and night long wave radiation have effect on fog layer developing vertically.更多还原