中文摘要：

传统的度日因子模型很难分辨在结冻期土壤每日结冻和解冻的过程,而日小时积温可以区分正积温和负积温对土壤冻结过程的影响.利用北疆地区1951-2010年气象站数据和决策树算法,分析计算日小时积温及表层5cm和10cm土壤冻结状态数据及日小时积温对季节性冻土冻结现象的影响.结果表明：在北疆范围年小时正积温以每年平均160℃增长,而年小时负积温以每年平均153℃减少.季节性冻土发生冻结现象所需的临界值分布与北疆地区气候和土壤分布基本一致,但仍存在空间差异性.北疆地区5cm土壤结冻所需的日小时负积温为-50℃以下,而5cm到10cm土壤结冻所需日小时负积温的平均值差值为-15℃左右.与日最低气温和日平均气温作为土壤结冻判据相比,日小时积温临界值作为判据可获得较高的精确度.在昌吉地区和阿勒泰地区冻土的平均深度随着日小时负积温临界值的增加而减少.

英文摘要：

The traditional day degree model is hard to distinguish the freezing process and thawing process in a freezing day.However,the daily accumulative hourly temperature could reveal the impacts of accumulative positive temperature and accumulative negative temperature to freezing process,respectively.This paper attempts to analyze the relationship between daily accumulative hourly temperature and the frozen status at 5 cm and 10 cm depths on the basis of weather station＇s data from 1951 to 2010 in northern Xinjiang Region.Daily accumulative hourly temperature is the sum of 24 hourly temperatures in a day,which is calculated with Cosine pattern function in daily mean temperature,daily minimum temperature and daily maximum temperature.Decision and Regression Tree Algorithm in Clementine was used to study how the daily accumulative hourly temperature impacts the freezing process of seasonal frozen soil at the depths of 5 cm and 10 cm.It is found that annual accumulative hourly positive temperature is increasing with 160 ℃· a-1 and annual accumulative hourly negative temperature is decreasing with 153 ℃· a-1 in northern Xinjiang Region.The spatial pattern of annual accumulative hourly temperature is influenced by longitude,latitude and elevation.The threshold of seasonal frozen soil＇s spatial distribution is similar to soil type and climate spatial distribution with a little spatial difference.Daily accumulative hourly temperature represents the energy balance between atmosphere and ground.In Autumn,when daily accumulative hourly temperature reaches-50 ℃,soil at 5 cm depth begins to freeze.The freezing process at 10 cm depth will begin,when daily accumulative hourly temperature reaches-75 ℃.The threshold′s average difference between 5 cm and 10 cm depths is about-15 ℃.There are three criteria（daily minimum air temperature criterion,daily average air temperature criterion,and daily accumulative hourly temperature criterion） can judge the frozen status of soil.It is found that the daily accumulative h