Role of atmospheric and oceanographic frequency variability on surface Marine Heatwaves in the Northern Humboldt Current System

Abstract

In this study, we investigated the role of atmospheric and oceanographic variability in shaping surface Marine Heatwaves (MHWs) in the Northern Humboldt Current System (NHCS) over the last two decades. Through a series of pluriannual hydrodynamic model simulations, we highlighted the importance of considering at least high-frequency atmospheric variability to accurately reproduce the observed MHW characteristics. On the contrary, when synoptic atmosphere variability is removed, the simulation results in fewer, longer, less frequent, less intense, and less severe MHWs. As a consequence, simulations forced with low-frequency data are only able to partially reproduce persistent MHWs. Additionally, using the heat balance analysis, it is shown that at the north, short-lived events are primarily driven by advective causes, while persistent events show an equal contribution between advection and heat fluxes. In the south, changes in heat fluxes are crucial in forming MHWs. During the dissipation phase of MHWs, cooling is dominated by advective processes, mainly coastal upwelling, in both coastal regions. Overall, these findings indicate a reduced dependence on high-frequency oceanic forcing and highlight the need to consider the atmospheric variability in regional downscaling of global climate model simulations to capture almost the full range of MHW events in the NHCS.