PhD projects
Update January 2012:
We are delighted to announce the PhD Topics that will be available for start in October 2012. Some of these projects already have guaranteed funding (indicated below). A selection of the remainder will be funded via research council studentships (last year we had 8 of these). The decision as to which projects and students will be funded will be made following our visit and interview day on 29/2/2012. Eligible applicants should apply as soon as possible, and no later than 15/2/12 if they wish to be considered for an invitation to this interview day. For further information on applying please see (link to http://www.met.reading.ac.uk/pg-research/pgrapplications.html) or email phdinfo@met.reading.ac.uk
Radiative forcing, climate change and the global water cycle
Supervisors: Richard Allan and Keith Shine
Imbalances between the amount of sunlight absorbed by the planet and thermal emission back to space (or radiative forcing) cause climate change. Many different mechanisms can drive climate change (for example changes in concentrations of greenhouse gases and soot particles, solar variability etc). Recently, calculations using climate models have indicated that subtleties in the precise nature of these mechanisms can impact on how the global water cycle responds. A better understanding of this is required, as changes in precipitation and evaporation are of utmost importance for climate impacts on society. In this project, the key questions to address are: how do the different drivers of climate change determine changes in global precipitation? Using this knowledge, can we reproduce past changes in precipitation and interpret correctly projected future changes in the global water cycle? To tackle these questions, the student will acquire the skills to run a state-of-the-art radiative transfer model and apply this to idealized radiative-convective simulations and other models. The precipitation response to each radiative forcing agent will be quantified. These results will then be utilized in attributing past changes in precipitation, using observations, and to interpret the range of future projections in the global water cycle made by the latest generation of coupled climate models.
Project Description (PDF)Projected changes in extreme European rainfall due to North Atlantic storms
Supervisors: Len Shaffrey, Sue Gray
One of the key questions posed by the insurance industry is whether the occurrence of recent UK floods (for example the 2005 Carlisle flood, the 2007 summer flood events and the 2009 Cockermouth flood) is evidence of the impact of climate change on extreme precipitation and flooding risk. This project will address two questions: i) are recent flooding events in the United Kingdom unprecedented? and ii) how do climate models project that extreme precipitation and extratropical cyclones will change over North Western Europe and the United Kingdom? The PhD student will address the first question using data from the recently available 20th Century Reanalysis, a global dataset of atmospheric variables spanning 1871 to present. The second question will be addressed using the latest climate model projections which will be used to inform the next report from the International Panel on Climate Change, the leading international body for the assessment of climate change. The studentship is jointly funded by the University of Reading and Lloyds Banking Group.
Transport and Dispersion of Pollutants in the Environment
Supervisor: Dr Helen Dacre
Local air quality is strongly influenced by the ability of meteorological processes to mix pollution away from sources at the Earth’s surface and ventilate it into the free troposphere. For example, during blocking episodes pollution accumulates within the boundary layer and photochemical transformation can result in ozone production and photochemical smog with consequent impacts on air quality and human health. Studies estimate that there were 400-800 premature deaths in the UK during August 2003 associated with elevated ozone and PM10 concentrations. Once ventilated from the boundary layer into the free troposphere increased wind speed, reduced mixing and cooler temperatures mean that many pollutants are longer-lived and can be transported further without dilution. This transforms a local air quality problem into a regional or even a global problem. The distribution of pollutants on these different spatial scales is connected through their dependence on meteorological processes that can ventilate pollutants from the boundary layer. However, model intercomparison studies show a surprising degree of difference in the simulated distribution of pollutants in the atmosphere on both local and global scales. These differences are largely attributed to differences in the representation of vertical transport in the different models. The lack of sufficient and detailed observations has made model evaluation difficult and impeded improvements in the representation of vertical transport. Recently however, a unique dataset of high-resolution vertical profiles of radon has been made. These vertical radon measurements provide valuable quantitative information regarding mixing and exchange processes in the atmospheric boundary layer under a range of conditions. This project aims to utilise new radon profiles to quantify boundary layer mixing processes, evaluate chemistry transport models and thus develop improved representation of vertical transport processes in regional and global climate models.
Comparison of weather-balloon observations of turbulence and clouds with model predictions
Supervisors: Giles Harrison, Paul Williams
Atmospheric turbulence and convective clouds are common and important features of the terrestrial atmosphere, but in severe weather they can present a dangerous hazard to aircraft. Clear-air turbulence alone costs airlines about $100,000,000 each year and causes hundreds of injuries to passengers. Turbulence is potentially predictable using numerical atmospheric models, by applying various diagnostics to identify the destabilised regions that are particularly susceptible. New radiosonde sensors have been developed recently at Reading, which can detect the turbulence and cloud encountered during routine weather balloon flights. New turbulence diagnostics have also been developed recently at Reading. In this project, weather balloons carrying the new instrumentation will be launched regularly from a UK site, to create an unprecedented data set of measurements of atmospheric turbulence and cloud properties. As well as analysis of the measurements obtained, the project will also compare the positions of turbulence and clouds measured by the new sensors with theoretical predictions, in order to test and refine the models.
Predictability of the opening of Arctic sea routes
(Funding guaranteed NERC – UK students- fees and living costs, EU students – fees only)Supervisors: Dr. Ed Hawkins, Prof. Keith Haines, Dr. Dan Hodson
A project studentship is available to examine the predictability of the opening of the Arctic sea routes - an important aspect of Arctic climate which is of particular importance to industry and decision makers. Arctic sea routes are important to such stakeholders for several reasons: (i) passage of ships on shorter routes between the Atlantic and Pacific, (ii) access to reserves of minerals, oil etc., and (iii) the potential for conflict over access to, and ownership of, the sea routes. Although the main focus of the studentship will be on examining the potential for predictions of the opening of Arctic sea routes on seasonal to inter-annual timescales, it will be essential to consider longer term climate projections as well. This project will form part of a larger Arctic research programme funded by NERC.
Factors controlling hurricane intensity in high-resolution atmospheric models
Supervisors: Chris Holloway and Pier Luigi Vidale
Tropical cyclones can cause
devastating loss of human life and property. Although forecasts of
tropical cyclone locations have improved greatly over the last 20
years, forecasts of their strength have shown relatively little
improvement. Meanwhile, weather and climate models have steadily
increased their horizontal resolution, allowing for the direct
simulation of smaller-scale features such as rain bands,
tightly-wrapped wind fields, and in some cases even individual
columns of rising air. The key question for this project is: what
physical processes are most important for the realistic simulation of
tropical cyclone intensity? To address this question, the student
will utilize state-of-the-art computer models at several different
resolutions to simulate and analyse case studies of actual tropical
cyclones as well as more idealised cases and longer global climate
runs.
Project Description (PDF)
Speeding up the calculation of physics in climate models
Supervisor: Bryan Lawrence
Simulations of climate can take a long time - months to years of real time - and not only is it boring to wait for the output, it's an expensive business! Future computers are not going to have faster processors - so speeding up simulations will depend on better algorithms which either scale across more processors better, or which have been coded more efficiently. The trouble with more efficient code is that it's often harder to understand and verify and even harder to evolve as the scientific understanding improves. The key question that this project will address is: What prospect is there for using "domain specific languages" in climate models to hide efficient computational code from the modellers - allowing climate models to be both faster and easier to modify. The student taking on this project will start with some simple physics code (e.g. a piece of the radiation library) and abstract out the key scientific principles before trying to provide some faster underlying code and putting it back in a climate model. There is some prior art so it wouldn't be starting from scratch, and the work is likely to be done with partners both in the UK and elsewhere.
Synchronisation in data assimilation
Supervisor: Peter Jan van Leeuwen
Numerical weather prediction is unthinkable without data assimilation. Data assimilation is a tool to combine information from the numerical weather prediction model with atmospheric observations. Present-day data assimilation methods are all based on linearisations, while the data-assimilation problem is becoming more and more nonlinear due to increasing resolution and more complex observations. Operational centres like the Met Office and ECMWF are very keen on moving into the nonlinear regime. In this project we will explore an exciting new way of looking at the problem. The model and the real atmosphere are seen as two separately evolving systems, and information flows from the real atmosphere to the model through the observations. So the observations couple the two systems, and try to 'synchronise' the model to the real atmosphere. Formulated in this way, we can explore ideas from synchronisation theory, and no restrictions on nonlinearity come into play. Starting with simple atmospheric models, like the Lorentz models and a 2-D model of the atmosphere, we will explore the possibilities of this approach. Especially, huge progress is expected when this approach is combined with the extremely efficient particle filters we are developing for much more complex models of the atmosphere. The emphasis can be changed to the ocean if the student has strong interest in that area.
Optimal assimilation of retrievals from hyperspectral infra-red satellite sounders
Supervisors Dr S. Migliorini and Dr J. Eyre (Met Office)
Satellite measurements provide an essential source of information to operational meteorological centres, which rely on these data to provide useful weather predictions to the public. A major difficulty with remotely-sensed observations is that their resolution is usually not high enough to constrain all the components of the state that is evolved by the atmospheric model. This has led operational centres to compare model forecasts and measurements in observation space, with the aim of finding better initial conditions that fit the available observations, a process called data assimilation. Although this strategy has been very successful, it has also significantly increased the complexity of the assimilation process, particularly when high-spectral-resolution (denoted as hyperspectral) sensors are considered. This proposed PhD project is focused on exploring the theoretical and practical implications of recent advances in our understanding of the satellite remote sensing inverse problem, which show that alternatives to current radiance assimilation methodologies are possible. This research is of significant practical importance, and will benefit from the collaboration of the Met Office, which we hope will sponsor the project.
A new approach to space weather forecasting: Initialising solar wind simulations using data from the STEREO Heliospheric Imagers.
Supervisors: Matt Owens and Chris Davis
“Space weather” can have numerous detrimental effects on both ground- and space-based technologies, bringing it under the auspices of NERC’s Natural Hazards program. One means of working towards the forecast and, ultimately mitigation, of such effects is to provide scientific input to the Met Office during the current development of its own space weather forecasting system. Space-weather forecasting has followed a similar development arc to its more mature weather counterpart, and is currently in the process of transitioning from empirical schemes to physics-based numerical simulations of the whole system. Models dealing with the heliospheric portion of the system, such as the Enlil code used by the Met Office, are able to accurately propagate the near-Sun solar wind out to Earth orbit. However, the biggest obstacle to space-weather forecasting is correctly inferring the solar wind properties at the inner boundary of the heliosphere. This is currently done through time-stationary models and weak empirical correlations. We instead propose to use direct measurements of the required solar wind parameters using new data from the Heliospheric Imager instruments aboard the twin STEREO spacecraft. They have been shown to be able to track solar wind from the Sun to Earth. We have performed a preliminary test of tracking many solar wind streams within a small data set and demonstrated that such a technique is able to differentiate between fast and slow-speed streams and provide an estimate of their location. It shows a great deal of promise as a means to significantly improve space-weather forecasting. The proposed project can be split into two key components. Firstly, the development of a robust methodology for characterising the near-Sun solar wind structure using Heliospheric Imager data. Secondly, using the scheme as input to the Enlil solar wind model, so as to test its feasibility as a space-weather forecast tool.
Role of composition anomalies on ocean/climate interactions
Supervisors: Remi Tailleux and Maarten Ambaum
Owing to their large thermal inertia, the oceans are expected to exert a strong control on the future global warming trend and any superimposed decadal variability. The degree of confidence one should place in the ability of current numerical ocean models to simulate decadal variability is largely unknown, however, because of the lack of observations with sufficient temporal and spatial resolutions to validate them. To increase our confidence in numerical ocean models, it is essential to ensure that they are based on physical assumptions. One such assumption for the past decades have been to assume that it is a good approximation to assume that density depends on the total amount of dissolved salts with a reference composition. It is now recognized, however, that this is only approximately valid in the Atlantic ocean, but not elsewhere. The issue is important, because it is density that mainly determines ocean currents, so that it is crucial to ensure that it is computed as
accurately as possible. The main purpose of this PhD will be to investigate ways to test the importance of chemical composition anomalies (relative to reference composition) on the ocean/climate interactions by implementing new ways to relate density to such composition anomalies that have recently been suggested by a UNESCO recommendation.
What are the physical processes controlling the existence of a bistable overturning circulation and climate?
Supervisors: Remi Tailleux and Robin Smith
On the basis of a hierarchy of ocean models of various complexity, itis widely thought that the ocean meridional overturning circulation (MOC) could possess at least two stable equilibria: an '`on'' state associated with a significant amount of poleward ocean heat transport (corresponding to current climate conditions), and an ``off'' state associated with very weak MOC and heat transport which could be associated with significant colder climate conditions in the northern hemisphere. The question of MOC stability is associated with abrupt climate changes that are known to have occurred in the past, and is also relevant for our future climate, as the heat and freshwater cycles that help drive the modern MOC are disrupted. The existence of MOC bistability has, however, not yet been demonstrated in reality or in the most realistic complex global coupled climate models. A key issue, therefore, is to understand whether MOC bistability could occur in the real world, or whether it is an artefact seen only in some models, arising from oversimplifying the physics of ocean/climate
interactions. To make progress, a physical understanding of the processes responsible for the existence of bistability is needed. The purpose of this PhD will be to explore a number of avenues to
investigate the physical processes that are key for the existence of a bistable MOC and climate, and which are required to evaluate the probability of abrupt climate change in the future.
Multi-resolution Modelling of the Global Atmosphere
Supervisor: Dr Hilary Weller, John Methven and Markus Gross
Operational weather forecasting models use nested grids in order to achieve more accurate, high resolution forecasts over an area of interest. However the forecasts can have spurious weather features near the boundary of the nested region. This project will test alternative approaches such as gradual refinement and unstructured refinement using simplified equations of motion for the atmosphere. The results will provide guidance for the design of the next Met-Office weather and climate forecasting model. The student will receive training and support to use and develop an existing C++ simulation package.
New tools for the evaluation of convective scale ensemble systems
Supervisors: Giovanni Leoncini, Stefano Migliorini, Robert Plant
At forecast lead times of one or two days, major large-scale weather patterns are generally very well predicted. By contrast, important small-scale features, such as severe thunderstorms, remain very difficult to capture in numerical simulations, limiting our ability to produce timely and reliable flood forecasts. In recent work at Reading and elsewhere, high-resolution models have been developed that are now starting to become valuable forecasting tools. However, because of the chaotic nature of the atmosphere, a single numerical simulation does not necessarily well represent what will happen, but is only a best estimate of what might happen given the information currently available. The uncertainty in a simulation can be assessed by running a number of slightly different simulations, known as an ensemble. There are many open questions about how to construct and how to analyze of an ensemble of high-resolution simulations. This project aims to develop a proper understanding of the meteorological processes and feedbacks that determine the behaviour of high-resolution ensemble systems at the convective scale, and to establish appropriate methods for assessing ensemble performance in relation to observations.
On the origin of jet streams and vertical stratification
Supervisors: Maarten Ambaum and Remi Tailleux
Jet streams are major elongated regions of directed strong winds in the atmosphere, or flows in the oceans. The atmospheric jet stream at our latitudes is responsible for setting up the large-scale environment in which local weather develops. An anomalous location of this jet stream is responsible for droughts, frosts, and other severe weather. The relative mildness of the climate at our latitudes is the combined result of the atmospheric jet and the gulf stream, the oceanic analogue of a jet stream. The origin of the jet streams on our planet but also on the gas giants in our solar system is found in the complicated interplay between small-scale turbulence and emerging large-scale properties of the flow. But there are still major problems left to resolve. For example, we still don't know what sets the number of jet streams on a particular planet and how strong those jet streams are. In this project we will use idealized numerical experiments as well as theoretical developments (mainly associated with re-arrangement theory) to further our understanding on the formation of jet streams. We hope to be able to develop re-arrangement theory to such an extent that we can predict key properties of the emerging jets from the global properties of the flow. Because there are subtle and intriguing links between this system and that of thermally driven vertical convection (leading to clouds in the atmosphere, and the meridional overturning circulation in the ocean) we will also explore the latter system and whether rearrangement theory can tell us something about vertical convection and the resulting vertical stratification.
The generation of downwind rainbands by mountains
Supervisors: Suzanne Gray (Univ. Reading), David Schultz (Univ. Manchester), Dan Kirshbaum (McGill University)
Flash floods are acute hazards with long-term social-economic consequences and it is essential that they be accurately understood and predicted. Recent devastating flash flood events include the Boscastle flood of 2004 and the Cockermouth flood of 2009. Two of the three principal mechanisms behind UK flash-flooding events are convective storms and orographic rainfall (the other being frontal systems). Although convection and orography may act independently to produce extreme rainfall, they are often closely linked over the complex UK terrain. The mechanical ascent upstream, over, and downwind of steep terrain and the thermally-driven ascent due to elevated heating lead to storms in convectively unstable airflow. Because orography is fixed in space, these storms may anchor to specific terrain features and focus their rainfall over preferred areas leading to bands of rainfall (termed rainbands). In particular, quasi-stationary rainbands, locked to the terrain, are a manifestation of orographic convection that greatly increases flood risks because they focus heavy rainfall over specific regions.
In this project we will investigate the mechanisms that lead to the formation of rainbands downwind of mountains. We will use an idealised version of the operational Met Office weather forecast model to explore potential mechanisms, exploiting the control afforded by idealised simulations.
Quantifying and fingerprinting the processes of ocean heat uptake during climate change
Supervisors: Jonathan Gregory, Nathaelle Bouttes, Matt Palmer, Peter Stott
During the 20th century the global-mean climate has become warmer, and much greater warming is projected during the 21st century due to emissions of greenhouse gases. The ocean imparts thermal inertia to the climate system; if the ocean had a negligible heat capacity, the rate of warming would be about 50% greater. The rate of warming at the surface is substantially influenced by the efficiency of vertical heat transport within the ocean, whereby heat is removed from the surface to the deeper layers. State-of-the-art global climate models exhibit a considerable range of results for this efficiency. This leads to substantial uncertainty in the expected rate of global warming, and in the rate of global-mean sea-level rise due to thermal expansion of sea water, which is the largest contribution to projected sea-level rise (it is more important than mass loss by glaciers).
Owing to the many impacts of climate change and sea level rise, it is important that we reduce these uncertainties. One way to do this is by comparison of ocean temperature changes observed and simulated for the last few decades. This comparison is the subject of the proposed PhD project.
By means of physically motivated analyses and application of statistical "fingerprinting" techniques, we hope to constrain the processes of ocean heat uptake and thus the projections. Such techniques have successfully and extensively been used to attribute aspects of surface climate change to particular forcings (such as greenhouse gases and volcanic eruptions), but less previous work has been done on ocean climate change and very little on processes of ocean heat uptake, so there are several possible approaches we could follow.
Using polarization measurements to evaluate GCMs and light scattering models of cirrus
Supervisors: Christine Chiu, Anthony Baran (Met Office) and Keith Shine
Recent studies have revealed a shocking model-to-model discrepancy in cloud ice content among the general circulation model (GCM) simulations contributed to the IPCC report, which highlights our insufficient knowledge of ice clouds. This leads to errors in both weather and climate predictions, because ice clouds not only strongly couple with weather systems via synoptic motions and deep convections, but also strongly influence global climate via their radiative impact. This project aims to fill such critical knowledge gap and reduce prediction errors using polarization measurements that are severely under-utilised.
This project includes two parts. Firstly, the project involves climate model evaluations in ice clouds using global polarization measurements from PARASOL (Polarization and Anisotropy of Reflectances for Atmospheric Sciences coupled with Observations from Lidar). Secondly, a new optimal method will be developed to globally estimate cirrus cloud properties by synergizing satellite observations from PARASOL, Caliop (lidar) and MODIS (a visible and infrared imager). Specifically, the student will:
- Retrieve global distributions of ice water content for semi-transparent cirrus (through collaboration with the University of Lille, France)
- Develop a new metric that can be used to evaluate GCM prediction in cloud phase, altitude, temperature, and corresponding shortwave flux
- Develop a new parameterization for the Met Office suite of models by exploring the linkage between cirrus ice crystal randomization, relative humidity, temperature and ice water content
Results from this project are expected to incorporate into the Met Office suite of models, and will greatly help reduce uncertainty in cirrus predictions for the climate model community.
Simulation in the terra incognita
Supervisor: Bob Plant
As computer resources continue to increase, weather forecast and climate models continue to be run at finer and finer resolutions, capturing more and more detail and helping them to become more and more accurate. Which is a good thing. Only there is starting to become a but to all of this. As the resolution gets finer, the scales at which forecast models operate are starting to approach the scales associated with turbulent motions near to the earth's surface. The current ways of handling those motions break down and fundamentally new modelling approaches become necessary. What are those approaches? Well, we don't really know: that's why it's called the "terra incognita" or sometimes the "grey zone". The models are getting there soon, and they will have to do something, so we'd better start figuring out what.