1960-2011年新疆初终霜日及无霜期的变化特征

利用1960-2011年新疆51个地面气象站逐日最低气温观测资料，运用线性趋势、距平分析、5 a滑动平均等方法，分析了初、终霜日和无霜期的基本特征及其变化趋势。结果表明：新疆初霜日推迟11 d，终霜日提前7 d，无霜期延长17 d。北疆、南疆和天山初、终霜日及无霜期与新疆整体变化趋势一致，但变化程度不同。天山地区变化最显著，其次是北疆，最后是南疆。初、终霜日的出现和无霜期的长短与地理因素和温度密切相关，随着海拔的升高，纬度的增加，初霜日提前，终霜日推迟，无霜期缩短。而随着温度的升高，初霜日逐渐推迟，终霜日逐渐提前，无霜期延长；从影响程度而言，最低气温的影响要大于平均气温和最高气温的影响。

Changes of the First Frost Dates, Last Frost Dates and Duration of Frost-free Season in Xinjiang during the Period of 1960-2011

In this paper, the first frost date, last frost date and duration of frost free season as well as their change trends were analyzed using the linear trend estimation, anomaly analysis and five year moving average based on the daily minimum temperature data observed by 51 meteorological stations in Xinjiang during the period from 1960 to 2011. The results showed that the average first frost date was postponed by 11 days, the average last frost date was moved up by 7 days, and the duration of frost free season was extended by 17 days. The first frost dates, last frost dates and durations of frost free season in north Xinjiang, south Xinjiang and the Tianshan Mountains were consistent with those in whole Xinjiang, but the change extent was not different. Their variation was the most significant in the Tianshan Mountains, and then in north Xinjiang and south Xinjiang. The first frost date, last frost date and duration of frost free season were closely related to the geographical and temperature factors. The first frost date occurred earlier, the last frost date later, and the duration of frost free season became shorter along with the increase of latitude and altitude. Along with the temperature increasing, however, the first frost date became later, the last frost date earlier, and the duration of frost free season longer. The effect of minimum temperature was higher than that of average temperature and maximum temperature.