Climate physics

If you are interested in any of the following research areas, we encourage you to contact the relevant supervisor directly. They will be happy to have a dialogue with you.

See also the DTP's Physical Climate System page for key areas covered by this stream.

Project examples:

The following projects are posted to give overseas candidates an idea of possible options. (Home/EU candidates who we ask to apply through the DTP will be encouraged to propose their own projects in liaison with supervisors during their first term in Oxford.)

Infrared remote sounding of atmospheric composition

Supervisor: Anu Dudhia (AOPP)

Over the past 10 years, fourier transform instruments, such as IASI and MIPAS, have been providing complete infrared spectra of the atmosphere containing many thousands of measurements, compared with the earlier generation of instruments which just had a few tens of wideband channels. The aim of this project is to take advantage of increasing computing power to develop new techniques for analysing this data to extract profiles of atmospheric temperature and composition.

Candidates should have a strong background in physics and mathematics, with an aptitude for programming.

Global teleconnections

Supervisor: Lesley Gray (AOPP)

Over the past decade or so it has become more and more clear that local weather and climate patterns can be systematically affected by events that occur at very large distances away. These influences may come from the other side of the world such as in the case of El Nino influencing UK and European weather, or from very high up in the atmosphere such as the influence of sudden stratospheric warmings on the severity of UK winters. These interactions, known as global teleconnections, can be multi-directional and are often non-linear. This project will examine some of the observed global teleconnection patterns that influence the Atlantic / European region in order to understand the important mechanisms and influences so that their representation in global climate models can be improved.

This project will require a strong foundation in physical sciences (physics, mathematics) and a keen interest in global climate dynamics.

Fluid dynamics of turbulent western boundary currents over sloping bottom boundaries

Supervisor: David Marshall (AOPP)

Most of our theoretical understanding of the fluid dynamics of western boundary currents, such as a the Gulf Stream and Kuroshio, is based on steady-state theory developed between the 1940s-1960s. These theoretical western boundary currents lean against a vertical lateral sidewall rather than flowing over sloping bottom topography with a bottom rather than lateral viscous boundary layer. In contrast, western boundary currents in the ocean are highly turbulent, with both mesoscale and submesoscale eddies on scales of order 10km and 1km respectively, and flow over a sloping bottom boundary with a turbulent bottom boundary layer. In this project we will revisit the fluid dynamics of western boundary currents in the highly turbulent regime over a sloping bottom boundary. Topics of particular interest include the interactions of the western boundary current with the quasi-stagnant water onshore and the fluid dynamics causing the boundary current to separate from the bottom boundary, e.g., at Cape Hatteras in the case of the Gulf Stream. The project will involve analysing existing high-resolution numerical model data from an ocean state estimate and/or forward model integrations, combined with idealised numerical calculations to isolate some of the critical fluid dynamical processes. Where possible, we will also compare our results with in-situ and remotely sensed observations.

This is a blue skies project that will suit a student with an interest in fluid dynamics, numerical modelling and with strong physical/mathematical skills. There is the option of collaborating with the European Centre for Medium Range Weather Forecasting to improve the representation of the Gulf Stream in their coupled ocean-atmosphere model

Idealized models of polar climate in warm and cold climates

Supervisor: Raymond Pierrehumbert (AOPP)

Recent research has shown that polar climate is strongly influenced by incursions of outbreaks of warm, moist air from lower latitudes. In cold climates this process affects the growth and decay of sea ice, and in warm climates such as the Eocene this determines the ability of polar continents (e.g. Antarctica) to avoid hard freezes in the winter. This project will explore idealized models of the response of polar climates to stochastic intrusions, with a particular eye to understanding the seasonal cycle, the extent of fluctuations about it, the influence of clouds and the way the seasonal cycle is affected by precessional variations in insolation.

This project requires a thorough understanding of fundamental physics, including thermodynamics, mechanics and electromagnetic radiation, as well as a facility with analysis of mathematical models. Familiarity with physical chemistry is also desirable. Hence, a first degree in Physics, Mathematics or a related discipline is required. The project involves considerable use of computational techniques, so basic familiarity with numerical analysis and familiarity with programming techniques in some computer language is required. The main programming languages used are Python and Fortran, but prior experience with these specific languages, while desirable, is not required.

Nonlinearity, climate sensitivity and bifurcations in the climate system

Supervisor: Raymond Pierrehumbert (AOPP)

Much current analysis of the problem of climate sensitivity is based on linearization of the Earth's energy balance about its pre-industrial state. However, our work has shown that the high-sensitivity "fat tail" of the distribution, which poses the greatest risk, is generically indicative of the climate system being near a bifurcation or tipping point. Analyses of climate sensitivity that ignore the presence of a nearby bifurcation risk missing important features of climate change. We are working on a variety of means to detect and explore tipping points in multiphysics model ensembles. We are also examining idealized mathematical models which have a dense set of bifurcations, so that climate is nowhere differentiable with regard to its parameters. Why is such exotic behavior not seen in general circulation models? Or is it just that we haven't looked hard enough?

What ended the boring billion?

Supervisor: Raymond Pierrehumbert (AOPP)

The “boring billion” is the period of Earth history roughly bookended at one end by the Great Oxygenation Event and Makganyene Snowball at the dawn of the Proterozoic, and the Cryogeneian glaciations of the Neoproterozoic (about 700 million years ago) at the other. During this period, there are few major carbon isotope excursions, and there is no evidence of major glaciations. The termination of this period of relative stasis is a key event in Earth history, as it was followed not long afterwards by the first multicellular life (the Ediacarans) and somewhat later the Cambrian Explosion which marks the dawn of the modern world of the Phanerozoic. The question of what terminated the Boring Billion is closely associated with the more specific question of how Snowball Earth events (global glaciations) are initiated, and involves consideration of the physical climate system as well as biogeochemistry. This project involves wide-ranging research aimed at understanding Proterozoic climate evolution, from a standpoint of climate dynamics, atmospheric chemistry and biogeochemistry. General circulation models, as well as a hierarchy of simpler process models, are all employed in the work. A typical DPhil research project in this area would not involve the problem as a whole, but rather some specific aspect such as the effect of ocean/atmosphere dynamics on the greenhouse gas threshold for global glaciation, or the nature of carbon cycle fluctuations that could draw down CO2 while being compatible with the proxy record of carbon isotope excursions.

This project requires a thorough understanding of fundamental physics, including thermodynamics, mechanics and electromagnetic radiation, as well as a facility with analysis of mathematical models. Familiarity with physical chemistry is also desirable. Hence, a first degree in Physics, Mathematics or a related discipline is required. The project involves considerable use of computational techniques, so basic familiarity with numerical analysis and familiarity with programming techniques in some computer language is required. The main programming languages used are Python and Fortran, but prior experience with these specific languages, while desirable, is not required.

Dynamical responses to climate forcing: an experimental approach

Supervisor: Peter Read (AOPP)

The radiative and thermodynamic causes of our changing climate are comparatively well understood, compared to the ways in which the dynamical circulation is likely to respond to changes in climate forcing. Numerical climate models provide one way to explore the dynamical responses to changing forcings, but suffer from deficiencies due e.g. to inadequate resolution, imperfect parameterizations of physical processes and numerical schemes, and are also hard to verify from incomplete observations of a highly complex climate system. Laboratory experiments in fluid flow provide a complementary approach that enables the exploration of the response of a real fluid to imposed forcings in experiments that can be well controlled and repeatable.

This project is intended to study the properties of circulations that juxtapose regions of deep convection (such as in the tropical atmosphere or polar oceans) and statically stable regions subject to baroclinic instability. Fluid motions in a large (1m diameter) cylindrical tank on a rotating table (representing the rotation of the Earth) are driven by heating from below and cooling from above, leading to localised deep convection and meridional overturning. This directly emulates the interaction between the convection in the polar seas, forming deep water masses and large-scale overturning e.g. in the Atlantic Ocean. The experiment may also include meridional barriers (representing continental margins) and sloping bottom boundaries, which could enable (amongst other things) the development of turbulent western boundary currents (cf Prof Marshall’s project). The principal aims of this project are to use laboratory experiments and associated numerical and theoretical models to develop and test quantitative scaling theories for predicting the dependence of the structure and transport properties of the flow on key parameters.

This project area requires an aptitude for both experimental and theoretical physics, including fluid mechanics, thermodynamics and the analysis of mathematical and numerical models. Hence, a first degree in Physics, Engineering, Mathematics or a related discipline is required.

Interactions between double-diffusion and baroclinic instability in the laboratory

Supervisor: Peter Read (AOPP)

Double-diffusion occurs when the density of a fluid depends on the concentration of two (or more) constituents whose molecular diffusivities differ significantly. It can be important on small scales e.g. in the oceans, where density depends on both temperature and salinity, leading either to layered convection (see figure) or a “fingering” instability which play an important role in small-scale mixing (on vertical scales of m or cm) and in determining the vertical density gradient. Baroclinic instability, on the other hand, is a large-scale process in a stratified, rotating fluid that is differentially heated horizontally (on horizontal scales of hundreds or thousands of km) that generates large-scale wave motion and turbulence, and is the main process forming cyclone/anticyclone weather systems in the atmosphere or coherent mesoscale eddies in the oceans. The properties of baroclinic instability depend on both the background rotation and the vertical and horizontal density gradients. Double-diffusion will therefore likely have an important influence on large-scale baroclinic instability where both occur together. This interaction has not been widely studied hitherto, but may be of importance in both the Earth’s oceans and in the atmospheres of the ice giant planets (Uranus and Neptune).

In this project, the interaction of double-diffusive processes on large-scale baroclinic flows will be studied in the laboratory, using a cylindrical tank on a rotating table with both differential heating (in the horizontal) and salt stratification (in the vertical). The experimental work will likely entail measurements of both horizontal velocity fields and buoyancy profiles in order to establish the relationships between double diffusion and equilibrated baroclinic waves and turbulence. The experiments will be complemented by theoretical work and numerical models in which double-diffusive effects may be parameterised.

This project is a fundamental investigation of processes relevant to oceans and atmosphere circulations, and requires a strong first degree in either Physics, Mathematics or Engineering.

Nonlinear dynamics of the Quasi-Biennial Oscillation in laboratory and theoretical models.

Supervisor: Peter Read (AOPP)

The Quasi-Biennial Oscillation (QBO) dominates the climate of the tropical stratosphere, influencing the long range transport of momentum, heat and chemical constituents. It is also thought to play an important role in influencing the predictability of various features, such as the Madden-Julian Oscillation (MJO) and other phenomena in the troposphere. So understanding what determines its variability in space and time is important for a range of problems in seasonal climate prediction. Although the basic nonlinear wave-driven mechanisms that drive the QBO are reasonably well understood, its detailed variability is complex, chaotic and much less well understood. The phenomenon is notoriously difficult to capture realistically in global climate models. The likely impact of future global climate change on the QBO is also quite controversial and uncertain.

In this project, we propose to study a number of mechanisms that might influence the behavior of the QBO, using a combination of numerical models and a laboratory analogue of the QBO, in which factors such as the wave forcing and other parameters and feedbacks can be closely controlled and varied. In the laboratory experiment, internal waves are launched into a salt-stratified fluid in an annular channel by oscillating flexible membranes in the bottom of the tank. Each segment of the membrane in the new experiment can be separately controlled by computer (a uniquely novel aspect) to enable varying spectra of internal waves to be excited and for the amplitude of the waves to be varied in time (thereby emulating the seasonal cycle and other modulations). The response of the fluid to this forcing in the form of time varying velocity fields will then be measured by optical particle imaging techniques, while conductivity probes will measure the stratification. The experiments will be complemented by a series of numerical model simulations (a) to achieve direct numerical simulation of some of the laboratory flows themselves for comparison with and validation against experimental measurements, and (b) to explore idealized simulations of QBO-like phenomena in global atmospheric circulation models. The numerical models will make use of Met Office codes such as ENDGAME to maximize opportunities to transfer benefits of this research directly to Met Office researchers.

This is a blue skies project that will suit a student with an interest in fluid dynamics, numerical modelling and with strong physical/mathematical skills. The project will involve collaboration with the Department of Engineering Science on experimental aspects, and with the Met Office on numerical modeling (for which additional funding may be available).

Machine Learning and Climate Response.

Supervisor: Laure Zanna (AOPP)

Our climate models are based on approximations of our governing equations. These approximations lead to errors in dynamical estimates of the climate response to forcing. Statistical have long been used to interpret and forecast several aspects of the climate system. However new advances in data science can help combine more efficiently dynamical and statistical models. Machine learning is now a ubiquitous technique and methodology in many fields, including big data, environment, engineering, robotics etc. Here, I propose a new method to use deep learning to combine dynamical and statistical model of climate. The focus will be on the climate response to carbon emissions - both globally and locally. The student will be involved with the state of the art methods from machine learning, and linking such methods to dynamics in order to understand and predict parts of the climate system.

This project requires a first degree in Physics, Mathematics or a related discipline. The project will suit a student with an interest in fundamental understanding of geophysical fluid dynamics and climate physics. The student should have some interest in combining theory and numerical modeling, including the analysis of idealized and complex model output.

A theory for the ocean’s role in transient climate change.

Supervisor: Laure Zanna (AOPP)

The ocean circulation is key in setting the storage and transport of heat and carbon in the climate system. Therefore the ocean plays a critical role in determining the magnitude and timescales of the climate response to external forcing, including anthropogenic greenhouse gases. Most of the theories considering the role of the ocean circulation in climate are developed for the equilibrium state. Yet, the ocean dynamics and the climate response are far from equilibrium. In this project, the student will formulate a theory for the role of the ocean under transient climate change. The project will tackle the processes setting the response of the ocean (circulation, heat uptake and sea level) to atmospheric forcing and subsequent feedback onto the atmospheric temperature. The student will be investigating dynamical and thermodynamical processes in the ocean and atmosphere, with a focus on high-latitudes, using a hierarchy of numerical models.

This project requires a first degree in Physics, Mathematics or a related discipline. The project will suit a student with an interest in fundamental understanding of geophysical fluid dynamics and climate physics. The student should have some interest in combining theory and numerical modeling, including the analysis of idealized and complex model output.