基于观测数据的全球大气冻融指数变化研究

Study on the change of global air freezing/thawing index based on observations

冻融指数是气候变化的一个重要敏感指示器,被广泛应用于冻土变化研究中。研究全球范围内冻融指数的空间分布特征与时间变化趋势,可为全球冻土环境评估、工程建设以及应对气候变化提供依据。本文基于1973—2021年覆盖全球陆地且超过14000个站点的逐日气温观测数据,计算大气冻融指数并分析其时空变化特征,探讨其与地理因子的关系。研究结果表明:近49年全球平均冻结指数为610.8℃·d,最大值为19653.3℃·d,北半球(667.9℃·d)大于南半球(152.4℃·d);全球平均融化指数为4709.6℃·d,最大值为11217.0℃·d,北半球(4444.5℃·d)小于南半球(6927.3℃·d)。空间上,近赤道等低纬地区的站点冻结指数基本为0℃·d,融化指数为0℃·d的站点仅出现在南极洲和格陵兰岛。冻融指数受纬度和海拔的双重影响,且具有明显的气候带分布特征。全球站点的冻结指数以平均6.4℃·d·a-1的速率下降,而融化指数以平均14.0℃·d·a-1的速率呈上升趋势;但在21世纪初冻融指数变化均趋于平缓。在1973—2021年间,全球范围内冻结指数平均减少了36%(净变化为-160.2℃·d),冷温带气候带下的高纬地区平均减少了68%;全球融化指数平均增加了11%(净变化为437.5℃·d),而冷温带气候带下的高纬地区平均增加了16%。冻融指数的长时间变化趋势反映了全球正在不同程度地变暖,高纬高海拔地区尤为强烈,且冷季增温趋势比暖季更大。

The freezing/thawing index is an important sensitive indicator of climate change,and also widely used in the permafrost change.The spatial-temporal variations of freezing/thawing index on a global scale can provide a basis for global permafrost environment assessment,engineering construction and climate change.Based on the daily observed temperature data from 1973 to 2021 covering the global land and more than 14000 stations,we calculate the air freezing/thawing index and analyze its spatial and temporal variation characteristics,and discuss the relationship with geographical factors.Results show that the global average freezing index is 610.8℃·d in the past 49 years,the maximum value is 19653.3℃·d,667.9℃·d in the Northern Hemisphere larger than 152.4℃·d in the Southern Hemisphere.The global average thawing index is 4709.6℃·d,the maximum value is 11217.0℃·d,and 4444.5℃·d in the Northern Hemisphere smaller than 6927.3℃·d in the Southern Hemisphere.Spatially,the freezing index in low latitude regions such as near the equator is basically 0℃·d,and a thawing index of 0℃·d only appear in Antarctica and Greenland.The freezing/thawing index is affected by both latitude and altitude,and has obvious climatic distribution characteristics.The freezing index of global stations showed a downward trend at an average rate of 6.4℃·d·a^(-1),while the thawing index showed an upward trend at an average rate of 14.0℃·d·a^(-1).However,the changes of the freezing/thawing index tended to be flat at the beginning of the 21st century.From 1973 to 2021,the freezing index decreased by an average of 36% globally(net change of -160.2℃·d),an average decrease of 68% in the high latitudes under the snow climate zone.The thawing index increased by an average of 11% globally(net change of 437.5℃·d),while an average increase of 16% in the high latitudes under the snow climate zone.The trend of the freezing/thawing index reflects that the global climate is warming with different degrees,especially in high latitudes and high altitudes,and the warming trend in the cold season is greater than that in the warm season.