Analysis of the Climate Change Characteristics of the Twenty-Four Solar Terms in Tianjin from 1971 to 2020

Based on the daily meteorological data during 1971－2020 from 13 national meteorological stations in Tianjin, this study analyzed the variation characteristics of meteorological elements for 24 solar terms by using linear correlation analysis and t-test methods. The results show that: 1) The temperature changes during the 24 solar terms exhibited a certain asymmetry. The highest temperature occurred during Greater Heat, and the lowest during Lesser Cold. The largest diurnal temperature range was from Pure Brightness to Lesser Fullness of Grain (11.6℃), followed by the period from Autumn Equinox to Frost's Descent (10.5℃). The greatest temperature increase was from Spring Equinox to Pure Brightness (4.4℃), and the greatest temperature decrease was from Frost's Descent to Beginning of Winter (4.8℃). The average temperature of all solar terms showed an upward trend, and the most pronounced warming occurred during the spring-type solar terms (Beginning of Spring to Grain Rain). 2) Precipitation was highly concentrated in the summer, with the four solar terms from Summer Solstice to Beginning of Autumn accounting for 57.4% of the annual precipitation. There were significant differences in the interdecadal changes of precipitation. More than half of the solar terms had positive precipitation anomalies in the 1970s－1980s and the 2010s, while negative anomalies were identified in the 1990s and the 2000s. 3) Spring witnessed the highest wind speed, with the highest value at Pure Brightness. The wind speed in all solar terms showed a decreasing trend, reaching an extremely significant level (P < 0.01), with the largest decrease in spring. 4) The longest sunshine duration was at Lesser Fullness of Grain, and the shortest at Winter Solstice. Except for Spring Equinox, the sunshine duration in other solar terms showed a decreasing trend, with a more notable decrease in summer and autumn. 5) The relative humidity reached the lowest at Pure Brightness and the highest at Greater Heat, and all solar terms exhibited a decreasing trend of relative humidity. 6) The solar term variation of air pressure was opposite to that of temperature, with no significant trend of variation.