Professor Chris Hughes

Research Overview

My research focuses on the relationship between ocean dynamics, sea level, ocean bottom pressure, and geodesy. Geodesy is the science of measuring the Earth's shape, orientation, and gravity field, all of which are closely related to sea level. In fact, the Global Geodetic Observing System "Grand Challenge" goals for accuracy and stability are determined by the requirements of sea level science.

Sea level matters to people, not least because it can cause flooding - a good rule of thumb for the UK is that, for every 32 cm of sea level rise, the frequency of coastal floods would increase by a factor of 10, all other things being equal.

Ocean currents are closely related to sea level via geostrophic balance, which means that any current that persists for more than a few days will have an associated slope in the sea surface. Counterintuitively, this slope is at right angles to the flow: the current flows with high sea level to its right in the northern hemisphere, and to its left in the southern hemisphere (water to the right of the Gulf Stream stands more than half a metre higher than that to the left). The currents associated with the global ocean conveyor - ocean's biggest contribution to the climate system which carries warm water to the north throughout the Atlantic and helps keep Europe warm - result in the Pacific ocean being on average about 40 cm higher than the Atlantic.

This means two things:

1) We can learn about the ocean currents from measurements of sea level. Satellite altimetry (measuring sea level from space) has completely revolutionised our understanding of ocean dynamics because of this.

2) If we understand ocean currents, we can make better predictions of how ocean dynamics can affect sea level.

I am currently most interested in how the global continental slope acts to simplify the ocean circulation, and to connect (or disconnect) coastal sea level to sea level in the ocean's interior. The steep slope produces strong dynamical constraints on pressure variations along the slope, which has a profound influence on the global circulation, and on the interconnections between ocean basins.