ENSO response to tropical volcanic eruptions: the role of the season

Stratospheric volcanic aerosol can have major impacts on the global climate. However, these impacts are eruption specific, as they critically depend on the characteristics of the eruption, such as magnitude, location and timing. Towards understanding these criticalities, only a handful of studies have either assessed the effects of eruptions at distinct times throughout the year or the location of eruption. To our knowledge, no study has hitherto considered the combined of the timing and location of an eruption. Here we investigate variations in the impact of volcanic eruptions linked on the timing of the eruption in relation to the seasons of the year and the location (Northern or Southern Tropical eruption), focusing on ENSO dynamics. In doing so, we use the Norwegian Earth System Model (NorESM) to perform a set of sensitivity experiments in which the tropical volcanic eruptions are set to go off at the beginning of each season. These experiments are meant to shed light on the role of the season in shaping the ENSO response to volcanic eruption, elucidating the nuanced role of volcanic forcing in modulating ENSO variability and enhancing our predictive capabilities of this influential climate phenomenon. In our contribution, we will describe first results from our experiments showing how boreal spring and summer Northern Tropical eruptions lead to El Niño-like conditions in the winter of the eruption, followed by strong La Niña conditions. On the other hand, boreal fall and winter eruptions causes a weak La Niña on the first 6-8 months, followed by El Niño conditions in the winter after the eruption. For Southern Tropical eruptions the response is muted and only fall and winter eruptions show El Niño conditions in the second winter of the eruption. To better understand the different responses, we will also interpret the model results within the framework of a simple delayed oscillator of ENSO.