The role of the intraseasonal tropical variability in the persistence of generalised frosts over south-eastern South America

This study analysed the influence of intraseasonal variability on the persistence of generalised frost (GF) events in the Pampa Húmeda, Argentina. The events were classified into three categories: no persistence (0 DP), 1-day persistence (1 DP) and 2 or more days of persistence (2 DP+). The 0-DP events were associated with short-lived synoptic systems, such as transient anticyclones and high-pressure systems, which promote temporary stability but lack dynamic support for consecutive frost days. In 1-DP events, a Rossby wave train propagating from the central Pacific Ocean to South America favoured cold air advection, with additional modulation from tropical forcing patterns linked to convective episodes in the region. The 2-DP+ events were associated with a persistent tropical forcing signal that led to the excitation of well-structured Rossby wave trains, sustaining cold air advection and stable conditions over multiple nights. Overall, the results show that short-lived frosts are driven by transient synoptic systems, whereas persistent events are more strongly linked to Rossby wave activity modulated by tropical–extratropical interactions. These findings enhance the understanding of the frost formation mechanisms in south-eastern South America and provide valuable input for improving forecasting and agricultural risk management strategies.