The North Atlantic Ocean plays a pivotal role in the global carbon cycle, by storing carbon released into the atmosphere when fossil fuels are burned, and by supporting the sinking flux of organic matter. Our understanding of how horizontal oceanic fluxes in the subtropics contribute to these processes is largely based on shipboard expeditions which occur every 5 years at 24N. Sampling at that interval is insufficient to resolve and understand the role that horizontal transfers play in regulating these processes. Detailed time-series of physical properties at 26.5N from moored instruments suggest that variability in these fluxes will be occurring on a range of timescales. Once this variability is measured, it is almost inevitable that we will modify our understanding of the role the North Atlantic subtropical gyre plays in the global carbon cycle. In this proposal we will address these issues by deploying new chemical sensors and samplers across the Atlantic at 26.5N. We will use the data they provide to calculate time-series of fluxes of nutrient and inorganic carbon, including carbon released to the atmosphere by mans activities, across 26.5N. We will adopt a hierarchical approach, successively using existing observations, then new oxygen observations and ultimately direct observations of the carbon and nutrients in order to identify the added value each successive stage of our programme provides. We will interpret our direct flux calculations as contributions to the North Atlantic budget in conjunction with other observations and models, to assess how oceanic fluxes control the strength and variability of the role the North Atlantic plays in the global carbon cycle.

The climate of the Arctic is changing faster than that almost anywhere else on Earth, warming at a rate of twice the global average. This warming is accompanied by a rapid melting of the sea ice - 2007 saw a record minimum in summer ice extent, and the years since have seen the 2nd and 3rd lowest summer ice extents on record - and a thinning of the ice that remains from year to year. The strong warming in the Arctic is due to several positive feedback processes, including a sea-ice albedo feedback (warmer conditions melt ice, lowering the average reflectivity of the mixed ice/ocean surface and thus absorbing more solar radiation, leading to increased ice melt and further lowering of the albedo) and several cloud feedbacks. Over most of the globe low clouds act to cool the surface since they reflect sunlight; over the arctic the highly reflective ice surface reduces the significance of cloud reflectivity, and the absorption of infrared radiation by cloud water droplets becomes the dominant effect - this acts to trap heat below cloud, warming the surface. Although climate models generally show a strong greenhouse warming effect in the Arctic, they also disagree with each other more in the Arctic than anywhere else, producing a wider range of possible future climate conditions. The models also tend not to be able to reproduce current Arctic climate conditions very accurately. This large uncertainty in models of the Arctic climate results primarily from poor representation of physical processes within the models, and some unique and particularly challenging conditions. The largest single source of uncertainty is the representation of clouds. The models use simple representations of cloud properties that were developed from observations in mid latitude or tropical cloud systems - very different conditions from those that exist in the Arctic. This project will make airborne in situ measurements of cloud microphysical properties, the vertical structure of the boundary layer and aerosol properties, and the fluxes of solar and infra red radiation above, below, and within cloud. It will also measure the production rates and properties of aerosol at the surface and their variability with season and extent of sea ice cover. These measurements will be used, along with a range of numerical models of aerosol and cloud processes, and atmospheric dynamics to evaluate the interactions between sea ice extent, aerosol production and cloud properties. New and improved descriptions of these processes suitable for use within climate models will be developed, tested, and implemented within the MetOffice climate model HadGEM. The ability of the current MetOffice models to reproduce the observed Arctic cloud and boundary layer properties will be tested, and the impact of the new parameterization schemes evaluated. Finally we will undertake a series of climate simulations to examine how future climate will evolve, and the feedbacks between warming of the Arctic, melting of sea ice, production of aerosol, and the properties of clouds evaluated.

This proposal will develop new methodology for summarising the spatial information obtained from analysing multiple time series of spatial trajectories. The project will involve adapting recent methodology by the applicants for the analysis of single time series trajectories, to develop the coherent analysis of multiple trajectories observed in a given spatial region. From these advances, summaries of regional spatial structure will be proposed, as well as methods for assessing the uncertainty inherent to such summaries. In particular, as a testbed, such will be implemented for regional sets of oceanographic observations from the Global Drifter Program, which contributes to providing deeper understanding of ocean circulation and its impact on climate change. The main scope of this proposal is therefore to test the feasibility of aggregate statistical analysis of the spatial information contained in multiple sets of trajectory observations. It is an ambitious research project which, if successful, would open the door to a wide set of applications such as ecology, oceanography and traffic management.

Depletion of stratospheric ozone allows larger doses of harmful solar ultraviolet (UV) radiation to reach the surface leading to increases in skin cancer and cataracts in humans and other impacts, such as crop damage. Ozone also affects the Earth's radiation balance and, in particular, ozone depletion in the lower stratosphere (LS) exerts an important climate forcing. While most long-lived ozone-depleting substances (ODSs, e.g. chlorofluorocarbons, CFCs) are now controlled by the United Nations Montreal Protocol and their abundances are slowly declining, there remains significant uncertainty surrounding the rate of ozone layer recovery. Although signs of recovery have been detected in the upper stratosphere and the Antarctic, this is not the case for the lower stratosphere at middle and low latitudes. In fact, contrary to expectations, ozone in this extrapolar lower stratosphere has continued to decrease (by up to 5% since 1998). The reason(s) for this are not known, but suggested causes include changes in atmospheric dynamics or the increasing abundance of short-lived reactive iodine and chlorine species. We will investigate the causes of this ongoing depletion using comprehensive modelling studies and new targeted observations of the short-lived chlorine substances in the lower stratosphere. While the Montreal Protocol has controlled the production of long-lived ODSs, this is not the case for halogenated very short-lived substances (VSLS, lifetimes <6 months), based on the belief that they would not be abundant or persistent enough to have an impact. Recent observations suggest otherwise, with notable increases in the atmospheric abundance of several gases (CH2Cl2, CHCl3), due largely to growth in emissions from Asia. A major US aircraft campaign based in Japan in summer 2021 will provide important new information on how these emissions of short-lived species reach the stratosphere via the Asian Summer Monsoon (ASM). UEA will supplement the ACCLIP campaign by making targeted surface observations in Taiwan and Malaysia which will help to constrain chlorine emissions. The observations will be combined with detailed and comprehensive 3-D modelling studies at Leeds and Lancaster, who have world-leading expertise and tools for the study of atmospheric chlorine and iodine. The modelling will use an off-line chemical transport model (CTM), ideal for interpreting observations, and a coupled chemistry-climate model (CCM) which is needed to study chemical-dynamical feedbacks and for future projections. Novel observations on how gases are affected by gravitational separation will be used to test the modelled descriptions of variations in atmospheric circulation. The CTM will also be used in an 'inverse' mode to trace back the observations of anthropogenic VSLS to their geographical source regions. The models will be used to quantify the flux of short-lived chlorine and iodine species to the stratosphere and to determine their impact on lower stratospheric ozone trends. The impact of dynamical variability will be quantified using the CTM and the drivers of this determined using the CCM. The model results will be analysed using the same statistical models used to derive the decreasing trend in ozone from observations, including the Dynamical Linear Model (DLM). Overall, the results of the model experiments will be synthesised into an understanding of the ongoing decrease in lower stratospheric ozone. This information will then be used to make improved future projections of how ozone will evolve, which will feed through to the policy-making process (Montreal Protocol) with the collaboration of expert partners. The results of the project will provide important information for future international assessments e.g. WMO/UNEP and IPCC reports.

The Arctic is a region of extreme sensitivity to climate change. Observations show its temperature to be increasing at twice the rate of the rest of the world. Models suggest this strong response will continue; however they also show a greater uncertainty here than for anywhere else in the world. The combination of rapid change and high uncertainty make improving predictive capability in the Arctic a matter of urgency. The strong climate response to increasing climate forcing by greenhouse gases is believed to be a result of several important feedback processes; for example the ice-albedo feedback, and several cloud-related feedbacks. Arctic stratus cloud is both extensive and long lived during the summer months. Their impact on the surface radiative budget, and hence on total energy budget, differs from that elsewhere in the world: sea ice and low clouds have very similar albedo, so that over ice the cloud has little impact on the solar radiation budget at the surface, and longwave (infra red) processes tend to dominate. Unlike anywhere else in the world, low cloud acts to warm the surface rather than cool it. The radiative properties of the clouds themselves also differ from lower latitudes because of different droplet size distributions. The Arctic has the lowest aerosol concentrations of anywhere on earth; a result of high deposition due to extensive cloud and fog, the great distance from strong continental aerosol sources, and the sea ice, which minimises marine sources. Aerosol provide the nuclei upon which cloud droplets form, so the low numbers mean the clouds have a smaller number of drops, which are consequently larger than typically found in mid-latitude stratus. The different drop-size distribution means Arctic stratus has different radiative properties than mid-latitude stratus: one of the reasons models represent their effects poorly. Small changes to cloud properties, whether from changes in aerosol availability, thermodynamic structure, or turbulent processes, can have a significant impact on their radiative properties. Small-scale processes must be parameterised in a simple form within climate models; these parameterisations must be based on measurement. Most measurements used have been from mid-latitudes or the tropics; thus the parameterizations derived from them are not necessarily appropriate for Arctic conditions. The difficulty and expense of making measurements in the Arctic has meant there are very few available against which to test the existing parameterisations or with which to develop new, more appropriate ones. The ASCOS field campaign achieved one of the most extensive and wide-ranging sets of measurements ever made in the central Arctic, and is intended to address the questions of what controls the properties of Arctic cloud. This proposal will use the unique ASCOS data set to study the interactions between the surface and the cloud that control the exchange of heat, water, and aerosol; and also the exchanges across cloud top with air from the free troposphere. It will study both the fundamental processes and examine how well they are represented within climate models, identify where parameterisations are failing, and propose alternative approaches more appropriate to the Arctic. The study will draw upon detailed in-situ and remote sensing measurements of lower-atmosphere structure, turbulent mixing, aerosol properties, cloud properties, and radiative fluxes to study the fundamental processes. These will be combined with large eddy simulation modelling to provide deeper insight into the 3-dimensional interactions, and allow perturbation experiments to be undertaken to study the relative importance of different parameters. Finally, the Met Office Unified Model will be used to study how parameterisations of these processes perform, and to discover weaknesses or failings within them. Ultimately this work will lead to improved parameterizations and more accurate predictions of future climate.