Optimal Proxy Indices for Annual Marine Heatwave Characteristics Using Monthly Sea Surface Temperature

Monitoring and understanding marine heatwaves (MHWs) are essential for assessing the impacts of climate change on oceans and implementing strategies to mitigate their consequences. This study examined the spatial distribution, long-term trends, and temporal variability of MHW characteristics (frequency, duration, intensity, and total number of MHW days) using four satellite-based sea surface temperature (SST) datasets from 1982 to 2021. Despite slight variations, the spatial patterns, trends, and temporal variabilities in the MHW characteristics were consistent across the observational SST datasets. Discrepancies in high-frequency variability among SST datasets may lead to differences in MHW characteristics. This study introduces new proxy indices for annual MHW characteristics, derived from the annual counts of months exceeding specified SST percentiles and the sum of positive SST anomalies beyond these thresholds. The evaluation, conducted in terms of temporal correlation and spatial root-mean-square errors, suggests superior performance in capturing the interannual variability of MHW characteristics over previously proposed proxy indices. The robustness of the new proxy indices is further assessed using an extended analysis period. These findings underscore the potential of these indices for the multi-decadal to centennial scale estimation of MHW characteristics.