Two distinct modes of North American spring temperature evolution shaped by tropical SST regimes and midlatitude circulation

Abnormal temperature fluctuations during spring can substantially impact vegetation growth, agricultural productivity, and ecosystem stability. However, the physical processes underlying year-to-year variations in the evolution of North American spring temperature anomalies remain poorly understood. Here, we apply Season-reliant Empirical Orthogonal Function (S-EOF) analysis to identify the leading modes of spring temperature evolution over North America. We focus on the first two modes here, which differ from conventional responses to winter El Niño–Southern Oscillation (ENSO) and are instead linked to distinct evolutions of tropical sea surface temperature (SST). The first mode (S-EOF1) features rapidly decaying Eastern Pacific (EP) ENSO-like SST anomalies from winter to spring and the emergence of tropical North Atlantic (TNA) SST anomalies, accompanied by a persistent north–south temperature dipole over North America. This mode is jointly influenced by the North Pacific Oscillation (NPO) and TNA-related North Atlantic circulation anomalies. In contrast, the second mode (S-EOF2) is associated with more persistent Central Pacific (CP) ENSO-like SST anomalies and the absence of TNA SST anomalies, together with evolving temperature patterns with temporal phase reversals across large parts of North America. This mode is primarily associated with the North Pacific (NP) pattern, whose influence may be further amplified by persistent CP ENSO-like SST anomalies. Dominance analysis further quantifies the relative contributions of tropical SST and midlatitude circulation patterns. These findings highlight the critical roles of ENSO decay rate and spatial structure, TNA SST variability, and their coupling with midlatitude circulation in shaping distinct spring temperature evolution patterns, with important implications for improving seasonal prediction.