Abstract: The tropical Pacific Ocean is home to Earth’ s largest source of interannual climate variability: the El Niño Southern Oscillation (ENSO). ENSO exerts profound worldwide effects and while our understanding of ENSO has significantly increased over the last three decades, its irregular behaviour and predictability continues to challenge scientists. It has long been understood that the volume of warm water in the equatorial Pacific 1-3 seasons before an El Nino event is related to the magnitude of the event peak, while the event initiation is triggered by bursts of westerly wind. Despite this knowledge, however, very little work has been carried out to understand what causes the build up of warm water in the equatorial region prior to an event. In the first part of this seminar, I will discuss the mechanisms responsible for the build up of this warm water with results suggesting that the same westerly wind events that trigger the event are at least partially responsible for the warm water build up. ENSO variability in the most recent 30-year period is currently at its highest level since the instrumental record began in the late 1800’s. In this seminar I will discuss the development of a unified paleo-climate reconstruction of past ENSO variability to put the 20th century changes of variability in the context of the past 400-years. The apparent impact of volcanic forcing on this proxy of past ENSO variability will also be discussed as we find that volcanic forcing can induce a statistically significant change in the mean state of ENSO in the year of the eruption and a doubling of the probability of an El Niño (La Niña) event occurring in the year of (three years after) the eruption. This will lead to the last component of the seminar, which will examine how explosive volcanic eruptions modulate the tropical Pacific and El Niño in a series couple general circulation model simulations.
Place: Buchanan 1930