近46年大连地区初、终霜冻事件和无霜冻期变化

以不高于0℃最低气温作为霜冻指标, 利用1961—2006年大连地区3个国家级气象站逐日最低气温资料, 采用现代气候诊断分析方法, 分析了该地区初、终霜冻事件和无霜期变化的特征。结果表明:近46年来, 大连和瓦房店站均表现为初霜冻日推迟、终霜冻日提早、无霜冻期延长的变化趋势, 其中瓦房店站表现得更为显著; 庄河站的初霜冻日和终霜冻日表现出相似的变化, 但各自的变化趋势不显著, 而无霜冻期延长趋势显著; 大连境内极早初霜冻日和极晚终霜冻日发生频数分别为1~3次和1~4次, 大连最多, 瓦房店最少; 大连站的初霜冻日期存在2年和11年的显著周期, 终霜冻日期存在22年的显著周期, 庄河站的初霜冻日期和无霜冻期均存在11年左右显著周期; 异常霜冻事件大连和庄河站20世纪60年代出现的频数最多, 21世纪初最少; 而瓦房店21世纪初异常霜冻事件出现的频数最多, 20世纪80年代最少。

Characteristics of First/Last Frost Date Events and Frost free Period in Dalian Area During Recent 46 Years

Based on the frost index defined by the daily minimum air temperature ≤ 0℃, and the method of climate diagnosis, the climatic features of the first/last frost dates and frost-free period changes are analyzed with 3 national stations data of daily minimum temperatures in Dalian area from 1961 to 2006. Results show that the first frost dates are postponed, while the last frost dates occur earlier, leading to the significant lengthening of frost-free periods at both Dalian and Wafangdian stations during recent 46 years, with the change being more significant at Wafangdian station. The tendency of the first/last frost dates is statistically significant at Dalian and Wafangdian stations, but it is not for Zhuanghe station, though the increase in frost-free periods at the station can still pass the confidence test. On the other hand, the characteristics in 1960s and 1970s are that the first frost dates comes earlier, the last frost dates ends later so that the frost-free period is short at each station. There is a trend that the first frost dates come later and the last frost dates appear earlier from 1960s to 1980s. The first frost dates are the latest, the last frost dates end the earliest and the frost-free period is the longest in early 1990s at Dalian station. It is notable that, in the past 6 years, the first frost dates appear much later and the last frost dates end much earlier at Wafang-dian and Zhuanghe stations, but the dates tend to be stable near the normal values at Dalian station. The change of extreme frost dates for the study area is also analyzed. It is found that the frequency of extreme early first-frost events ranges from 1 to 3 times, with Dalian station witnessing the highest value, and Wafangdian station the lowest. The frequency of extreme late last-frost events is from 1 to 4 times, but it is also the highest at Dalian station and the lowest at Wafangdian station. In addition, the variability of first frost dates indicates 2-year and 11-year cycle and that of last frost dates bears 22-year remarkable quasi-periods at Dalian station, while the first frost dates and frost-free periods at Zhuanghe station have undergone 11-year quasi-periods during recent 46 years. The frequency of anomalous frost events is the highest in 1960s at Dalian and Zhuanghe stations, and the lowest in early 21 century, but it is the highest in early 21 century and the lowest in 1980s at Wafangdian station.