一次深厚浓雾过程的边界层特征和生消物理机制

2007年12月13-14日,南京出现一次厚度达600 m、持续近14 h的浓雾过程,其中强浓雾阶段维持4 h.通过系留气球边界层探测系统、涡动协方差测量系统、雾滴尺度分布和自动气象站等外场试验资料分析了此次深厚浓雾过程的边界层结构特征和生消物理机制.结果表明,此次雾过程首先由地面辐射冷却形成贴地雾层,而后因低空平流冷却形成低云.在发展阶段,伴随低云不断下伸,贴地雾层不断抬升.在贴地雾层受到地面弱冷空气平流降温影响下,雾中微物理过程迅速发展,雾滴数密度、含水量、平均直径、最大直径等微物理参数在15 min内跃增,雾体爆发性升高,最终导致地面雾和低云上下贯通形成深厚雾层,地面能见度骤降至15 m以下.雾体爆发性增强时,地面垂直动量通量和向下长波辐射通量密度增大,净辐射趋于零.整个雾过程中,由于贴地层持续弱冷平流降温和上层雾阻碍了下层雾的辐射降温,二者的共同作用使贴地强逆温结构始终维持.     

A model study of ATMOS observations and the heterogeneous loss of N2O5 by the sulphate aerosol layer

The heterogeneous removal of N₂O₅ by sulphuric acid aerosols as been invoked to explain the decline of mid-latitude ozone in the last decade. We have used a photochemical model to study measurements of odd-nitrogen made by Spacelab 3. The gas-phase photochemical model overestimates the amount of N₂O₅ present. The loss of N₂O₅ by aerosols does reduce N₂O₅, but is likely to be slower than assumed in WMO (1992). The sunset measurements at 25.5 km cannot be explained by heterogeneous loss of N₂O₅ and is more likely to be due to a faster photolysis than assumed. New absorption cross-sections of HNO₃ reduce the photolysis of HNO₃ so that the model with gas-phase chemistry only gives better agreement at 19 km, than a model including heterogeneous chemistry.