The background of cold/warm advection for two interdecadal warming processes during the last century in China

During 20 century, there were two notable decadal warming processes in China that occurred before the 1940s and after the 1970s, respectively. An analysis of temperature advection associated with the atmospheric circulation is helpful for better understanding the regional warming processes. This paper firstly analyzes homogenized long-term temperature observations collected at 32 stations in China using the ensemble empirical mode decomposition (EEMD) method and reveals the geographical pattern of temperature anomalies around the 1940s. It is found that at the interdecadal timescale, cold anomalies occurred in northern North China, Northeast China and part of southern coast, while warm anomalies occurred in most of other areas in China around the 1940s. Similar results are obtained based on the CRU (Climatic Research Unit) global gridded temperature data. Secondly, the temperature advection around the same time period based on gridded temperature and sea level pressure data is calculated. The spatial corresponding coefficient between temperature anomalies at the stations and the large-scale temperature advection is as large as 0.85. In contrast, the coefficient between them during the recent warming period is 0.49. The results indicate from a novel point of view that the internal climate variability associated with the atmospheric circulation might play a more important role in the earlier warming process in China in the 1940s, but the recent warming progress after the 1970s could be more due to external thermal forcing.