CASPO

Talk Abstract:

Coastal upwelling rates are classically determined by the intensity of the upper-ocean offshore Ekman transport. But (sub-)mesoscale turbulence modulates offshore transport, hence the net upwelling rate. Eddy effects generally oppose the Ekman circulation, resulting in so-called “eddy cancellation”, a process well studied in the Southern Ocean. Here we investigate how air-sea heat/buoyancy fluxes modulate eddy cancellation in an idealized upwelling model. We run CROCO simulations with constant winds but varying heat fluxes with and without…

Talk Abstract:

Oceanic lee waves are generated when quasi-steady flows interact with rough topography at the bottom of the ocean. These internal waves provide an important sink of energy and momentum from the mean flow, especially in the Southern Ocean where they are a leading order mechanism for diapycnal mixing. Linear theory with a spectral representation of abyssal hill topography is generally used to estimate lee wave generation for use in parameterisations, and has been verified against idealised simulations. Here, we use a realistic wave resolving simulation of the Drake…

Talk Abstract:

Ocean turbulence transfers energy across scales, and is a key ingredient in shaping the ocean circulation. Conventional turbulence dynamics suggests that the kinetic energy in the ocean is transferred primarily to larger scales, via the inverse energy cascade that emerges under the influence of Earth's rotation. This raises the question of how dissipation is achieved in oceanic flows, which would necessarily require an energy transfer towards the small molecular scales. It has been argued that flows that…

Talk Abstract:

Shortwave radiative feedbacks from Southern Ocean clouds are a major source of uncertainty in climate projections. Much of this uncertainty arises from changes in cloud scattering properties and lifetimes that are caused by changes in cloud thermodynamic phase. Here we use satellite observations to infer the scattering component of the cloud-phase feedback mechanism and determine its relative importance by comparing it with an estimate of the overall temperature-driven cloud feedback. The overall feedback is dominated by an optical thinning of low-level clouds…

Talk summary:

In this seminar, I will talk about the atmospheric and oceanic drivers of two recent marine heatwaves, i.e., extreme temperature anomaly, in the Northwest Atlantic coastal ocean. In the first part, I will describe the unprecedented heatwave in 2012, during which the sea surface temperature was the highest for the past roughly 150 years of recorded observations. This event significantly disrupted marine ecosystem and commercial fishing industry. Analysis of observations and numerical modeling shows that the anomalies in atmospheric forcing…

Talk Abstract:

The dynamical pathways of subduction, by which water from the oceanic surface mixed layer makes its way into the pycnocline, are influenced by both geostrophic frontogenesis and submesoscale instabilities in the mixed layer. We explore the pathways and mechanisms for subduction using a submesoscale-resolving numerical model of a mesoscale front. We identify Lagrangian trajectories that exit the mixed layer and study the evolution of the dynamical properties during subduction from a statistical standpoint. Water parcels subduct within coherent regions along the…

Talk abstract:

Water quality issues have been a major concern in the San Diego-Tijuana region stemming in part from an inoperative wastewater treatment plant near Punta Bandera, Mexico that drains untreated sewage directly into the surf. From there, the wastewater can easily travel up the mostly straight, sandy San Diego-Tijuana coastline, carried by wave-driven currents. The goal of this project is to build a model that can predict the concentrations of wastewater along the shoreline through a tracer transport model that uses currents estimated from wave properties at a wave…

Talk Abstract:

Climate scientists like to use blackbodies and the Stefan-Boltzmann law to reason about Earth's energy balance. Since the Stefan-Boltzmann law scales as T^4, Earth's outgoing longwave radiation (OLR) should be a non-linear function of surface temperature. Observations and numerical models show, however, that Earth's OLR is essentially linear in temperature. In this talk, I will argue that careful thinking about when and why Earth's OLR is linear doesn't just help us understand a fundamental feature of Earth's climate, it also helps us resolve a number…

Talk abstract: Mixing is known to drive deep-ocean diapycnal velocity, but unknown details of near-bottom turbulence currently have us uncertain on its sign. Recent theory and inverse models have moved the discussion from energetics (“do we have enough Terawatts?”) to watermass transformation (“how does divergence of the buoyancy flux give rise to upwelling?”).  In this context, the observed bottom enhancement of ocean mixing gives divergent buoyancy flux and thus downwelling in a 1D interpretation.  The apparent paradox may be resolved by invoking zero buoyancy flux at the…