大连地区夏季大雾天气特征及诊断分析

Weather Characteristics and Diagnostic Analysis of Summer Fogs in Dalian

利用常规资料及NCEP资料对大连地区夏季大雾天气特征及物理机制进行分析。结果表明:大连大雾日数东部最多,北部最少,总体呈增长态势,2005或2006年出现峰值。南部和东部6、7月大雾日数明显偏多,其他地区无明显月份差异。大雾多出现在夜间至次日早晨。大连夏季持续大雾天气时,中高层副高呈纬向分布,偏西流场中有弱槽脊活动;低层位于副高后部槽前部,西南水汽输送场中;地面位于低值系统前部或顶部,持续较弱的偏东风或偏南风;近地面有逆温层,有弱的散度、涡度和垂直运动场,有利于水汽在近地层的输送和聚集,有利于大雾的形成和长时间维持。该研究获得大连地区夏季大雾天气气候特征及持续大雾天气的预报指标,为大连夏季大雾预报提供参考。

Based on the NCEP 1°×1° reanalysis data and the conventional observation data, the features and the physical mechanism of summer fog in Dalian were analyzed. The results showed that： the distribution of fog in Dalian presented the characteristics of most fog days in east part while least fog days in north part, and the fog days had an overall rising trend, reached a peak in 2005 or 2006. Heavy fog occurred most frequently in south and east part in June and July, but showed no monthly significant difference in the other parts. Heavy fog often took place from night to the next morning when continuous summer heavy fog occurred in Dalian, the subtropical high of the high altitude layer showed a zonal distribution, there were activities with weak slot and ridge in westerlies; the lower layer was in the front of the slot and behind subtropical high field, also in the southwest vapor transport field. Meanwhile, the ground was in the top or the forepart of low pressure field, which kept blowing weakly southerly or easterly. The existence of inversion temperature layer, weak divergency and vorticity, and the slightly vertical velocity vorticity field were favorable not only for the transportation and convergency of fog, but also for the formation and the maintenance of fog. In the study, forecast index of the climate characteristics of summer fog and the continuous fog days in Dalian was obtained, which could provide a reference for summer fog forecast in Dalian.