Abstracts are not currently available in GtR for all funded research. This is normally because the abstract was not required at the time of proposal submission, but may be because it included sensitive information such as personal details.

The invention of the laser in the early 1960s led to experiments where high power (> million Watts) infra-red and visible pulsed lasers were focused onto solid targets in order to produce hot (> 0.5 million degrees Kelvin) plasmas. In almost 50 years of study, the physics of the laser interaction, the physics of the expanding plume and many important applications have been elucidated in some detail. When focussed onto solid targets, visible/infra-red lasers do not penetrate to the solid for most of the pulse duration, but are absorbed in the expanding plasma plume at densities 100- 1000 times smaller than the solid density. Dropping the laser wavelength into the extreme ultra-violet (EUV), however, enables the laser to penetrate into the solid and to create plasma directly at the solid density. Initial modelling studies that have been undertaken by the PI show that the interaction of EUV laser radiation with most solid targets will cause a rapid drop in opacity (so that the target 'bleaches'). Initially an attenuation length for the EUV photon energy is bleached and then another attenuation length, so that a 'bleaching wave' propagates through the solid target on a sub-nanosecond timescale. A much more massive amount of target material is effectively ablated than can occur with infra-red or visible radiation of the same pulse energy and focal spot diameter. Little modelling work has been undertaken to elucidate understanding of EUV laser-produced plasmas because of the lack of sufficiently energetic (> 10 microJoules) laboratory EUV lasers for experiments. However, reliable capillary discharge lasers operating at wavelength 46.9 nm (photon energy 26.4 eV) producing up to 1 milliJoule/pulse and peak powers of a million Watts have been developed at the Colorado State University (CSU). We propose to develop simulation models to interpret emission spectra and mass spectrometer results from EUV laser produced plasmas. We will test spectrometer diagnostics using the University of York high power infra-red laser and in collaboration with CSU make spectral and mass spectrometer measurements for comparison to the simulation models. A new class of laser-produced plasma will be studied with potential impact in the study of warm dense matter, laser cutting and ablation and solid material lithography with relevance to the $70B p.a. revenue industry associated with the manufacture of microelectromechanical systems (MEMS).

Climate change and air pollution are two of the biggest challenges facing humanity today. Ozone and particulate matter are pollutants that are particularly harmful to human health. Recent studies have suggested that in the UK alone they cause 50,000 extra deaths and result in a financial burden of £8-22 billion per year. Both ozone and particulate matter also play an important role in climate change. Ozone absorbs infra-red radiation resulting in a warming of the climate. Particles scatter and absorb incoming solar radiation and alter the properties of clouds. This results in complex interactions with the Earth's climate, with some types of aerosol pollution warming climate whereas others cool climate. Future air quality depends both on changes to emissions of pollutants and to changes in climate. Furthermore, a warming climate can result in worsened air pollution, which in turn can drive additional warming, meaning that complex feedbacks are possible between air pollution and climate. To help understand these complex interactions and feedbacks scientists have developed Earth System Models that include a description of the important physical and biogeochemical processes. These models are increasingly being used by policy makers to make predictions about future air quality and climate and to guide policy decisions. It is therefore important that the models are rigorously tested. This testing involves using detailed observations of atmospheric composition that have been made over the past few decades at locations around the world. Most model evaluation to date has involved testing whether the models simulate current average concentrations of atmospheric pollutants. Whilst this is a useful and necessary first step in model evaluation it does not test whether the model accurately simulates the change in concentration of a pollutant under changing emissions or changing climate. For example, does the model capture the real-world change in concentrations of a pollutant given a particular change in emission or under a future climate change scenario? This is particularly important as these predictions under-pin policy recommendations for air quality abatement. In this project we will synthesis long-term (multi-decadal) observations of ozone and particulate matter and their atmospheric precursors. We will use these observations to explore trends and variability that have been observed over the past few decades. We will then develop a model-observation framework that can be used to evaluate how well models simulate observed variability and trends. We will test state-of-the-art Earth System Models using existing model output from model intercomparison exercises. Finally, we will explore the model processes that are driving simulated variability and trends. Our results will inform the scientific community as to the fidelity of Earth System Models. This project will help improve our models and give us more confidence in our predictions.

Arctic climate is warming much faster than that of the world as a whole. Global models show the general trend of enhanced warming, but generally fail to reproduce the observed dramatic reduction in sea ice. This results in part from significant biases in the surface energy budget. The largest source of uncertainty in the energy budget results from problems in the representation of low level clouds and the resulting solar and infra-red radiation fluxes at the surface, and of turbulent heat fluxes within the near-surface atmosphere. The model biases are greatest under the extreme conditions of strong forcing by warm air intrusions - regional events where warm, humid air is transported in over sea ice, cooling close to the surface to form shallow, stably stratified layers within which fog and cloud form. The shallow layers and steep vertical gradients of temperature, humidity, and turbulence are difficult for global models to resolve. Their evolution with increasing time over the sea ice, as the vertical thermodynamic profiles, cloud liquid and ice water contents, and turbulent structure change, depends strongly on small scale processes that must be parameterized within the models. Existing parameterizations are based on measurements at lower latitudes, and fail to adequately represent polar conditions. The resulting model biases can be 100s of W/m2 during warm air intrusions. ARTofMELT is the first observational study focussed on warm air intrusions. Support for an international project, proposed by our partners at Stockholm University, has been approved by the Swedish Polar Research Secretariat, and a research cruise is scheduled for spring 2023 on the Swedish icebreaker Oden. This provides a unique opportunity to make the measurements needed to provide new understanding of the processes controlling air mass modification during these events, and develop new parameterizations for global models appropriate to polar environments. Building on several previous collaborative projects we will work as a single team with our partners in Stockholm to instrument Oden for extensive in situ and remote sensing measurements of the lower atmosphere, clouds, and the components of the surface energy budget. Directed by dedicated forecasts made at ECMWF, Oden will be positioned to sample warm air intrusions entering the Arctic from the Atlantic or Eurasian sectors. We anticipate sampling 3-5 events during the cruise, and use the observations from outside the event periods as a baseline to evaluate the impact of warm air intrusions on lower-atmosphere structure, clouds, and the surface energy budget. Other participants will assess the response of sea ice to the atmospheric forcing.

Clouds containing a mixture of ice and water (mixed-phase clouds) are likely to change in response to climate change. It is expected that warming will cause an increase in the amount of water and a decrease in the amount of ice in these clouds. Because water droplets reflect more solar radiation than ice crystals (and cause less precipitation), the clouds are expected to become brighter, thereby causing a cooling effect (or negative feedback) on the climate system at mid- to high-latitudes. The magnitude of the cloud-phase feedback is very uncertain. If the feedback is strong then global temperatures will increase more slowly in future, but if it is weak then temperatures will increase more rapidly. It was recently shown that adjusting the ratio of ice and water in a climate model to match satellite observations could increase Earth's equilibrium climate sensitivity (warming with a doubling of CO2) by 1.5 degrees; hence, Earth may warm faster than thought. The feedback process is further complicated by the fact that the special particles, ice nucleating particles (INPs), which trigger ice production, may be more abundant in a warmer world where INP sources, such as glacial valleys, will be covered in ice and snow for less time. Increased INP concentrations would mean more ice in clouds and lead to a positive feedback. These two opposing feedbacks contribute to what we refer to as the cloud-phase feedback. This proposal will improve our understanding of how ice particles form in clouds and how this affects the cloud-phase feedback. Ice formation is the key process that controls this feedback. The problem can be broken down into two parts: First, we will address the open questions related to the chain of processes that link initial ice formation to the reflectivity of the clouds and how the reflectivity will change with warming. We have designed an aircraft campaign targeted at conditions of most relevance to the cloud feedback problem: moderately cold clouds that will be most sensitive to changes in temperature, and where high INP concentrations are likely to influence large regions of the N Atlantic. These cold-air outbreaks clouds provide an ideal meteorological situation for studying the formation and evolution of the kinds of shallow mixed-phase clouds which are important for cloud feedbacks. Second, we will address the paucity of knowledge on the sources, distribution and seasonal cycles of INPs at the mid- to high-latitudes. Our strategy is to use measurements to identify sources of INPs and use this information to inform the inclusion of mid- to high-latitude sources in our global model of INPs. We will perform new long-term measurements through a whole year and ship borne measurements through the key source regions in the Arctic. We have built a substantial network of Partners who will contribute INP data across the northern and southern mid- to high-latitudes which will allow us to expand our study to the globe. The new knowledge on cloud processes and INP will be used to improve the representation of mixed-phase clouds in the Met Office weather and climate model. The model will be run at very high spatial resolution so that the individual clouds in the cold-air outbreaks can be simulated. The model will be tested and improved by comparing it to our measurements as well as against satellite observations. We will then extend this study to contrasting cases from the Southern Ocean and the other side of the Atlantic. We anticipate the new knowledge will lead to a greatly improved representation of these climatically critical clouds. We will then perform a sensitivity analysis on selected cases in order to test how these cloud systems will respond to climate change. Finally, we will use the new knowledge to develop a plan for improving how mixed-phase clouds are treated in global climate models so that this work can be carried out in a follow-on project.