Observed Evidence and Physical Mechanism of Preceding Soil Temperature Variability Affecting Sub-Seasonal Air Temperature in Summer Over Chinese Mainland

Soil temperature (ST)-air temperature (AT) coupling is an essential process of the heat exchange between land surface and atmosphere. However, the relationship between the antecedent ST and the subsequent AT remains uncertain. In this study, we quantify the ST-AT coupling strength via the correlation between 1-day ST and the subsequent 21-day mean AT over the summer season (June-July-August) in Chinese mainland. Daily ST for 1961–2016 (with 5,152 total days) is segmented into quartiles based on its anomalies, and then ST-AT coupling strength is quantified under different quartiles. We find that the persistence of ST anomaly is prolonged in the outer quartiles (first and fourth quartiles). Correspondingly, the ST-AT coupling strength is also relatively strong, enhancing the AT variability and predictability. Analysis of the land-surface energy budget indicates that ST anomalies in the outer quartiles amplify AT variability through enhancing the subsequent surface outcoming longwave radiation, sensible heat flux, ground heat flux, and atmosphere boundary layer height altogether. Furthermore, the ST-AT coupling strength shows regional variations, being stronger in arid regions and weaker in humid regions. The current findings highlight the important effects of preceding land thermal conditions on the sub-seasonal to seasonal AT, which may provide some grounds for improving prediction of summer climate.