关键词: 西北四省区, 开始日序, 持续时间, 季节

Abstract:

The beginning date and duration of in Shaanxi, Gansu, Ningxia, Qinghai in Northwest China were analyzed by using the statistical method based on the daily mean temperature data from 161 stations and 130 monthly circulation indexes provided by the National Climate Center during 1981-2015. The results were as follows:The beginning date sequence showed an  advanced trend for spring and summer. The beginning date sequence delayed for autumn and winter. The change amplitude  of beginning date sequence was largest in spring, and lowest in winter. The duration of winter and spring shortened. The duration of summer and autumn extended. And the change amplitude  of duration was largest in summer, and lowest in autumn. The winter duration increased with altitude. The central region of the study area in Northwest China had larger variations in the beginning date sequence and duration of four seasons. The ending of winter and beginning of spring in the next year were influenced by the pole vortex area in September. The beginning of summer was determined by the position of the Indian subtropical high ridge and the area of Asia polar vortex in April. The duration of summer and the beginning of autumn was affected by the adjustment of the sea temperature between the two regions. The duration of autumn and beginning of winter were affected by the position of east Asian trough and high pressure of Tibet in October.

Key words: four provinces (municipality)of Northwest China, beginning date sequence, duration, season