京津冀夏季雾的特征与预报

Characteristics and Forecasting of Summer Fog in the Beijing-Tianjin-Hebei Region

综合运用气象地面和高空观测资料、自动站资料、卫星云图及ERA5资料,分析了2000—2019年京津冀地区夏季雾的时空分布、边界层,以及高空地面气象要素特征,建立了夏季雾天气概念模型,并进行了典型个例分析。结果表明:京津冀大部分地区平均每年出现夏季雾1~4 d,西北部、东北部和东南部出雾时最小能见度相对偏低,张家口中部至保定西北部、保定东南部至沧州中部和衡水一带平均最小能见度可低至300 m以下;平原地区夏季雾持续日数空间差异小,普遍为1~1.4 d,山区持续时间相对较长;雾的生消有明显日变化,夜间至日出前后高发,日出后3 h内消散。夏季雾出现时通常逆温层底高、厚度薄、温差小、强度弱,地面气温日较差在7℃以上,风速为1~2.4 m·s^(-1)是有利于雾形成的重要条件,雾发生时风向以偏南风或偏北风为主。京津冀夏季雾的三种典型概念模型为高空槽后或高压脊控制下的辐射雾、高空槽前西南气流控制下的平流雾或平流辐射雾、副热带高压控制下的雨雾。

By using meteorological ground and high-resolution observation data,automatic station data,satellite imagery and ERA5 data,the temporal and spatial distribution characteristics of summer fog in the Beijing-Tianjin-Hebei Region from 2000 to 2019 are analyzed.The conceptual model of summer fog is established,and the typical cases are analyzed.The results show that there are 1-4 days of summer fog every year in most of the Beijing-Tianjin-Hebei Region.Minimum visibility tends to be relatively low when fog appears in the northwest,northeast and southeast of the region.Average minimum visibility from central Zhangjiakou to northwest Baoding,southeast Baoding to central Cangzhou and Hengshui areas can decrease to as low as 300 m.The spatial difference of duration of summer fog in plain area is small,generally 1-1.4 days,and the fog duration in mountainous area is relatively longer.The generation and dissipation of fog have obvious diurnal changes.Usually,fog occurs in high frequency in the morning before and after sunrise,and dissipates within 3 hours after sunrise.In summer,when the fog appears,the bottom height of the inversion layer is usually high,the inversion thickness is thin,the temperature difference is small and the intensity is weak.The diurnal temperature range on the ground is above 7℃,and the wind speed is 1-2.4 m·s^(-1).All these are the important conditions for the formation of fog.The wind direction is mainly southerly or northerly when fog occurs.Three typical conceptual models of summer fog in the Beijing-Tianjin-Hebei Region are radiation fog under the control of high pressure ridge,advection radiation fog under the control of southwest airflow in front of upper trough,and rain fog under the control of subtropical high pressure.