Oceanography SeminarNovember 14, 3:00pm - 4:15pm
Mānoa Campus, MSB 100
“Dynamics and impacts of 2-year La Niña events”
Abstract: The observational record shows that about 35% of La Niña events last for two years or longer. In contrast, the majority of El Niño events quickly transition into La Niña in less than one year. Historically, the dynamics of La Niña have been considered as the mirror image of El Niño. However, the causes of this asymmetry in the duration of El Niño and La Niña are unknown. This issue is important for the prediction of drought over southern tier of the United States, where persistent La Niña conditions can lead to multi-year drought.
The first part of my talk will focus on the impact of these 2-year La Niña events on drought over North America. In particular, I will explore the physical processes responsible for the observed intensification and expansion of La Niña droughts during the second year. In the second part, I will explore the physical processes responsible for the multi-year persistence of La Niña in the Community Climate System Model version 4 (CCSM4) – a coupled climate model that simulates 2-year La Niña realistically. Using a nonlinear version of the delayed oscillator equation I will show that a nonlinearity of the delayed thermocline feedback that limits the rate at which heat content anomalies are replenished is responsible for the extended duration of La Niña. To conclude, I will discuss implications for the prediction of the termination of La Niña.
Oceanography, Mānoa Campus