First Xiamen Spring School on Ocean Dynamics

Ocean Dynamics at Meso- and Submeso- Scales

March 12-17, 2018   Xiamen University

The Xiamen Spring School on Ocean Dynamics (Xmod) aims at introducing fundamental ocean dynamics, from the basics to the research frontiers, to graduate students and early-career scientists. The topics cover a wide range of oceanic phenomena and processes. It has a specific theme for every course. For each course, prestigious scientists who have made seminal contributions to the theme-related field are invited to deliver principal lectures. The school, held over one to two weeks, will consist of:

• Principal Lectures: introducing theme-related basics and research frontiers given by the principal lecturers
• Contributing Talks: covering broader materials presented by guest lecturers and school participants

The first Xmod will be held in the State Key Laboratory of Marine Environmental Science (MEL) of Xiamen University on March 12–17, 2018. The theme of the first Xmod is Ocean Dynamics at Meso- and Submeso- Scales. Two principal lecturers have been invited to deliver the core lectures, including

• Bo Qiu (University of Hawaii at Manoa, USA)

Basic geophysical fluid dynamics about instability theories and eddy-mean flow interaction; large to mesoscale variability and the transition to submesoscales, etc.

• Patrice Klein (LOPS-CNRS, Ifremer, France / California Institute of Technology, USA)

Submesoscale dynamics; coupling with gravity-wave motions; frontiers of submesoscale studies (e.g., observations and simulations), etc.

Ten graduate students and early-career scientists are selected as fellows of the school, for whom local accommodation and meals will be provided by MEL. Others are welcomed as guest participants. Fellows are expected to actively participate in all aspects of the school. The fellows are encouraged to publish their project-related outcome together with their supervisors (i.e., the principal or guest lecturers).

Coordinators

Zhiyu Liu () Rui Xin Huang (Co-chair, Woods Hole Oceanographic Institution) Bo Qiu (University of Hawaii) Jianping Gan (Hong Kong University of Science and Technology) Minhan Dai (Xiamen University)

Agenda

Synopsis of Patrice Klein’s Lectures

Twenty-five years of satellite altimetry have revealed that mesoscale eddies (with a size of 50-300 km) capture most of the kinetic energy in the World Ocean. For a long time, this mesoscale eddy turbulence was thought to explain most of the horizontal and vertical fluxes of any properties. Only recently, a new vision has emerged that points to the importance of another class of balanced (or geostrophic) motions with smaller scales (1 – 50 km), also called sub-mesoscales. These sub-mesoscales are now known to capture most of the vertical velocity field in the upper ocean. Their dynamical importance has led to revisit our understanding of the ocean dynamics. These lectures aim to explain this new vision and, in particular, to introduce the main dynamical properties associated with these sub-mesoscales as well as their impact on the dispersion of pollutants, biodiversity, air-sea interactions and the ocean energy route. The future observational systems (including those from space and in-situ), designed to capture these scales, will be presented as well as the next challenges our world community will have to meet.

Lecture 1:

-          Definition of sub-mesoscales: differences with mesoscale structures in terms of time scales and spatial scales.

-          Evidence of the existence of sub-mesoscale structures in the world ocean from satellite images (coherence between infrared, ocean color, SAR and glitter images) and from recent in-situ observations (gliders, …).

Lecture 2:

-          Basic dynamical properties of sub-mesoscales: role of mesoscale eddies to trigger density fronts at small scales (direct cascade). Vertical extension of sub-mesoscales. 

-          Why do sub-mesoscales capture most the vertical velocity field in the upper ocean (whereas mesoscale eddies capture most of the horizontal kinetic energy).

Lecture 3:

-          Frontogenesis and Omega equation: basic concepts and how they help to understand sub-mesoscales dynamics.

Lecture 4:

-          The Surface Quasi-Geostrophic model as a suitable and simple dynamical framework to understand the production of sub-mesoscales and their feedback onto mesoscale eddies (through the inverse kinetic energy cascade).

Lecture 5:

-          Surface Quasi-Geostrophic and 2-D turbulence: their major differences (and consequences of these differences on the dispersion of pollutants, the biodiversity, the climate system, …).

Lecture 6:

-          Mixed-layer instabilities as a major source of sub-mesoscales in winter.

-          Impact of mixed-layer instabilities on the seasonal cycle of the mesoscale eddy kinetic energy

Lecture 7:

-          A new satellite altimetry mission dedicated to the observation of sub-mesoscales: the Surface and Water Ocean Topography (SWOT): perspectives and challenges to meet (how to discriminate sub-mesoscales and internal gravity waves (IGW)). 

Lecture 8:

-          IGWs: basic differences with geostrophic (balanced) motions and in particular with sub-mesoscales. 

Lecture 9:

-          The Shallow Water model: a suitable and simple framework to understand the horizontal and vertical propagation of IGWs.

Lecture 10:

-          Mechanisms associated with mesoscale eddies that scatter and disperse large-scale IGWs leading to a continuous IGW spectrum with characteristics close to those of sub-mesoscales.

-          Some perspectives to discriminate sub-mesoscales and IGWs from satellite and in-situ observations.

Synopsis of Bo Qiu’s Lectures

The lectures intend to introduce basic concepts and dynamics regarding mesoscale ocean circulation variability, oceanic waves, instabilities, and nonlinear eddies. Rather than treating them as separate topics, the lectures strive to progressively combine them in a comprehensive way.  Through concrete examples of observations, the lectures attempt to help students to gain an appreciation as to how basic dynamic concepts can be usefully applied to understand real-ocean phenomena.

Lecture 1-2:

-          Baroclinic Rossby waves vs. mesoscale eddies, Mesoscale eddy statistics in world ocean, Eddy-induced material transport, Basics of instability analysis, Kelvin-Helmholts instability

Lecture 3-4:

-          Richardson number criterion, 2D->3D instability transition, Squire's theorem, Barotropic instability, Effect of beta & divergence, Finite-amplitude behavior of shear instability, eddy-eddy interaction

Lecture 5-6:

-          Baroclinic Instability, Wave-wave interaction, Seasonality in mesoscale variability, Interior versus mixed layer instability, Inverse energy cascade

Lecture 7-8:

-          Beta-plume, Zonal-mean flow generation as Rossby wave rectification, Resonant triad instability, Turbulent Sverdrup balance