Soil Temperature Controls the Month-To-Month Lead-Lag Correlations of Near-Surface Air Temperatures in the Middle and Lower Reaches of the Yangtze River Basin

The relationships between the variables at different times are crucial in climate prediction. This study explores the lead-lag correlations between monthly near-surface air temperatures, and analyzes the associated influencing factors and processes using mathematical physics equations and statistical methods, based on monthly observations and ERA5 reanalysis data spanning from 1979 to 2013. The results reveal high lead-lag correlations of near-surface air temperatures in the middle and lower reaches of the Yangtze River basin, characterized by high frequency and intensity of heatwaves. The lead-lag correlations between near-surface temperatures are mainly due to the lead-lag relationships between soil temperatures (STs). Current and accumulated net solar radiation, current latent heat flux and antecedent ST of several or many months ago are the main factors affecting the lead-lag relationships between STs. The processes associated with lead-lag correlations between STs are triggered by antecedent ST, concurrent and accumulated influence factors, respectively. The anomalies of antecedent ST can lead to the anomalies of current one by the persistence of anomaly signals in soil. The effects of accumulated or concurrent influential variables on the lead-lag correlations between STs are attributed to the signals similar to antecedent STs in these influential variables, and the signals may arise from the response of atmosphere to land or ocean forcing. Moreover, the use of reanalysis data increases the uncertainty of the results. The study reveals influential factors and possible physical processes associated with lead-lag correlations between near-surface temperatures, which is helpful for understanding lead-lag relationship between land surface and the atmosphere. Climate prediction depends on the finding of the relationships between the variables at different times. Our studies demonstrate the persistence of substantial lead-lag correlations between the monthly mean near-surface air temperatures in the middle and lower reaches of the Yangtze River basin. Within these lead-lag correlations, the relationship between soil temperatures (STs) at different time leads and lags play a crucial role. Net solar radiation, latent heat flux and antecedent ST of several or many months ago are the main factors affecting the lead-lag relationships between STs. The processes associated with the lead-lag correlations between STs are triggered by antecedent ST, concurrent and accumulated radiation and heat fluxes, respectively. At the monthly, seasonal and longer time scales, the relationships between air temperature or precipitation at different times generally depend on sea surface temperature, soil moisture, ST etc. due to their longer memory relative to atmospheric variables. The lead-lag relationship between variables is the essence of climate prediction, and this study proposes a new idea to analyze the main influencing factors and corresponding physical processes related to the lead-lag relationships between variables in the climate system, which is helpful to understand complex interactions in the climate system. There are high lead-lag correlations of the monthly mean temperatures in the middle and lower reaches of the Yangtze River basinThe lead-lag relationship between soil temperatures (STs) plays a major role in lead-lag correlation between air temperaturesThe net solar radiation is the main factor affecting the relationships between antecedent and current STs