99523 - TROPICAL AIR-SEA INTERACTION

Learning outcomes

The student will learn the main climate features of the tropical system with an emphasis on coupled atmosphere-ocean processes in the equatorial Indo-Pacific region. Theough this course the student will address the dynamics of tropical coupled processes, from the Madden-Julian Oscillation, to El Nino/Southern Oscillation, the Asian Summer Monsoon and their interaction with the overall global variability, using idealized and more complete models. At the end of the course the student will be able to assess how these phenomena can be modelled and predicted using Earth system models using deterministic and statistical methods.

Course contents

The tropics cover about 40% of the world surface and play a dominant role in the Earth’s climate system by influencing global atmospheric and oceanic circulation patterns and shaping weather systems. In this course we will introduce the fundamental processes characterizing tropical climate and dynamics on a wide range of spatial and temporal scales: from local (~km) to planetary (~10^4km) and from daily to multi-decadal.

In the first part of the course, we will begin with defining the tropics and reviewing the fundamental physical processes involved in the air-sea interaction, and therefore responsible for the exchange of heat, water, and momentum between the ocean and atmosphere. By looking at observational products, we will show that compared to the extratropics, the coupling between the ocean and atmosphere is generally stronger in the tropics, where atmospheric convection and wind stress are largely controlled by tropical SSTs.

In the second part, we will explore wave dynamics and discuss how at low-latitude waves play a crucial role in shaping tropical variability from sub-seasonal to interannual timescales. We will derive shallow water equations and then use their linearized set to derive and discuss inertia-gravity, Rossby and Kelvin waves. The dispersion relation of equatorial shallow water waves on the beta plane (Matsuno spectrum) will be also derived and discussed.

Lastly, we will explore dominant modes of ocean-atmosphere coupling in the tropics. Specifically, we will focus on intraseasonal oscillations (also known as the Madden-Julian Oscillation, MJO), the Indian Ocean Dipole mode, and the phenomenon of El Niño, which is a manifestation of Earth’s strongest climate mode on interannual timescales, namely El Niño-Southern Oscillation mode (ENSO). Several lectures will be devoted to ENSO: after exploring El Niño dynamics and theory, which is based on equatorial wave dynamics, we will discuss ENSO teleconnections and interaction with other climate modes, as well as its impacts, monitoring, and prediction methods. This part will end with a brief overview of Tropical cyclones dynamics: formation mechanisms, structure, tracking, forecasting techniques, and impacts.

This course will be characterized by a strong hands-on component of data analysis and modeling that will be developed in Python through a combination of in-class practical sessions and homework. State-of-the-art observational datasets will be used to analyze climate processes and modes, and to set up, calibrate and test low-order models of ENSO (e.g., ENSO delayed oscillator and recharge oscillator) and other tropical modes.

Readings/Bibliography

Essential of Atmospheric and Oceanic Dynamics (Geoffrey K. Vallis, 2019; Cambridge University Press)

Climate Change and Climate Modeling ( David J. Neelin, 2010; Cambridge University Press)

Atmospheric and Oceanic Fluid Dynamics ( Geoffrey K. Vallis, 2017; Cambridge University Press – 2^nd edition)

Additional notes and materials distributed by the professor.

Teaching methods

• Frontal lectures with blackboard and projector
• Practical session with Python/Jupyter Notebook
• Homework and final project

Assessment methods

Oral Exam

Office hours

See the website of Giovanni Liguori