Welcome to Week 2: the physics beneath the forecast

Welcome to Week 2.

In Week 1, you saw the ocean forecasting system as a whole – the end-to-end chain that turns observations into models, products, and services. This week, we go beneath that system to ask a more fundamental question: why does the ocean move at all?

Every forecast you will ever read rests on the physics of ocean motion. Currents, upwelling, waves, tides – none of these are random. They are the ocean’s response to a handful of forces, organised by the rotation of the Earth into patterns that repeat across the globe. Once you understand those forces and the balances between them, ocean forecast products stop being abstract maps of colour and start telling a physical story.

From system to physics

This week provides the physical foundations that the rest of the course builds on. The modelling, observation, and data assimilation topics in later weeks all assume an understanding of why the ocean behaves as it does. Our emphasis here is on physical intuition, not mathematics – the goal is to help you reason about ocean motion, not to derive equations.

What you’ll explore

The week builds up step by step, from the forces that drive the ocean to the motions they produce:

• Introduction to ocean dynamics – why the ocean moves, and the scales on which it moves
• Forces governing ocean motion – wind, pressure gradients, the Coriolis effect, and friction
• Geostrophic balance – the balanced flow behind most large-scale ocean currents
• Ekman balance and wind-driven circulation – how wind drives surface transport, upwelling, and the great ocean gyres
• Ocean waves – from waves breaking at the shore to the physics of how they travel
• Geophysical waves – the much larger, slower waves shaped by the Earth’s rotation and ocean stratification
• Tides – how the gravitational pull of the Moon and Sun sets the whole ocean oscillating

Grounded in real regions

Ocean dynamics is not abstract – it shapes the coastlines and economies of the world. Throughout the week you will meet real regional examples, many of them African: the coastal upwelling systems of the Canary and Benguela currents that sustain major fisheries, the wind-driven circulation along African coastlines, the equatorial Atlantic cold tongue, and the tides that shape navigation and coastal life. You are encouraged to connect each concept to the ocean you know.

By the end of this week

You should be able to:

• Explain the fundamental physical principles governing large-scale ocean circulation
• Describe geostrophic and Ekman balances in qualitative, physical terms
• Explain the role of tides and waves in ocean variability
• Distinguish between different ocean processes and the scales on which they act
• Relate physical ocean processes to observed ocean patterns and variability

A word on how to approach the week: some of these ideas – balanced flows, rotating waves, tidal forcing – can feel abstract at first. Don’t worry about mastering every detail. Focus on building physical intuition: a feel for which force does what, and why the ocean responds the way it does. That intuition is what will let you read and trust an ocean forecast for the rest of the course.