Intrinsic short Marine Heatwaves from the perspective of sea surface temperature and height

Marine heatwaves (MHWs) have recently been recognized as extreme climate events considering their devastating impacts on marine ecosystems. Our study explored the spatial and temporal variability of short (duration < 10 days) and long MHWs in nine sub-regions around the Australian coastal region using the original (5-day) and an updated longer duration (10-day) criteria for MHW identification based on gap-free Sea Surface Temperature (SST) analyses from 1981 to 2020. By quantitatively investigating the contribution of ocean warming to short MHWs, we could consider most of the short events as background signals of a dynamic ocean surface over the Australian region. The application of the updated definition highlights areas that are more sensitive to local internal forcings, especially over the main flow of the East Australian Current. Furthermore, the Great Barrier Reef exhibit a larger increasing trend of MHW areas after excluding the short events. By numerically and graphically evaluating the relationship between the sea level anomaly (SLA) and SST metrics over two coastal regions of Australia, it is found that longer MHWs exhibiting two variation trends of large SLA metrics are ENSO dominant in the northwest coastal region (NW), and less ENSO-dominant but geographically-impacted in the southeast coastal region (SETS). However, it is possible that most short events in these two regions are a result of local and intrinsic variability or ocean warming of the water columns rather than the remote modulation of climate modes. Moreover, SLA over the 90^th percentile, which successfully observed a subsurface MHW event over the NW region in 2008, has the potential to help identify subsurface MHWs, although limited by application area. Further investigation into the applicability of these, or other similar, updates to the MHW definitions may be warranted, to draw a broadly applicable conclusion to benefit detection and prediction of strong sub-surface MHWs impacting commercial and environmental activities.