1954～2008年衡阳冰冻特征及变化趋势分析

The Analysis of Characteristics and Tendency about Freeze-ups in 1954～2008 in Hengyang City

利用1954～2008年衡阳8个地面气象观测站数据,对其年代际间曲线和气候趋势系数进行综合分析,结果表明:衡阳冰冻的年代际间变化经历了上世纪70年代的活跃期,50、90年代的低谷期,目前向正常方向发展。年平均出现冰冻24.5站次,冰冻多发年的出现机率有所加大,但仍处于较低水平。1月中旬～2月上旬是冰冻相对集中时段,其中1月下旬是全年出现冰冻最多旬,而该旬并非气温最低时段。形成冰冻的有利条件是日平均气温0～-1℃,小～中等降雨(雪)过程,日平均风速5.0 m/s以下。衡阳的冰冻发生存在地域性特点,自北向南逐渐减少。轻度冰冻、中等冰冻和重度冰冻各占69.3%、25.4%和5.3%。

With the data of the ground meteorological observation at 8 stations in Hengyang from 1954 to 2008, we do some research on the curve of decadal and climate tendency coefficient, and the results show that the inter-decadal variations of Hengyang freeze-ups experienced an active phase in the 1970s and declining period in 1950s and 1990s. It is in a gentle period at present. Averagely 24.5 stations report freezes every year, and the probability is increasing, but still at a low level. The freezes are relatively concentrated from the mid of January to early of February. Most are in late January, but the temperature is not the lowest in a year. The favorable conditions for freezes is when the temperature is 0— -1℃, with small to medium showers, and the daily average wind speed less than 5.0 m/s. Hengyang freezes have regional characters, and gradually decrease from the north to the south. Slight, medium and severe freezes account for 63.9%, 25.4% and 5.3% separately.