Lu et al. (2008) have shown that there is a robust relationship between solar wind dynamic pressure and the winds and temperatures in the northern polar winter stratosphere and troposphere. These wind and temperature variations are indicative of the Northern Annular Mode of climate oscillation which largely determines the predominant winter weather pattern across Europe. The signature of solar wind dynamic pressure in the lower atmosphere data is stronger and statistically more robust than those associated with either the QBO or the 11-yr solar cycle, and the timescales suggest that the most likely link is a dynamical one. Clilverd et al. (2006) predicted that solar cycle number 24, which is just beginning, would be unusually low. This has since been circumstantially supported by recent observations which show that the current solar minimum is the lowest for 200 years, that the onset of cycle 24 has been delayed, and that the solar wind dynamic pressure is ~20% lower than the previous cycle, the weakest it has been during the era of in-situ spacecraft measurements. Taken together this evidence that we are currently entering an era of low solar wind dynamic pressure, and the evidence that solar wind dynamic pressure is related to the NAM imply that, between 2012 and 2017 (the next solar maximum), we are likely to see drier winter weather with fewer storms in the UK and Scandinavia together with wetter weather in Southern Europe. However, while the statistical evidence for a relationship between the solar wind dynamic pressure and the NAM is very strong (>99%), a physical connection is not understood. The aim of the proposed research is to substantiate whether a physical connection exists by exploring, using both observations and models, just how the solar wind dynamic pressure can connect to the stratosphere in the polar regions, and hence how it can be strongly correlated with the Northern Annular Mode.

Volatile organic compounds (VOCs) in the marine environment and the atmospheric oxidative capacity over the ocean are critical but poorly understood components of the Earth System. There are tens of thousands of different VOC species in air, and they react with the hydroxyl radical (OH) and determine the reactivity of the atmosphere - often referred to as the oxidative capacity (the ability for air to cleanse itself). The oxidative capacity is key for climate through OH oxidation of methane and for air quality (e.g. via formation of ozone). Yet ~1/4 of the observed total OH reactivity over the ocean remains unexplained. VOCs are also precursors to secondary organic aerosol (SOA), which have the potential to enable particle growth to cloud condensation nuclei (CCN). Over the ocean and far away from anthropogenic sources where aerosol concentrations are typically low, clouds are far more sensitive to changes in aerosol than over land, highlighting the essential need to understand marine VOCs. Yet to date, the number of intensive VOC studies over land outnumbers studies over the ocean by orders of magnitude. The ocean contains a vast number of VOCs. Beyond a few well-studied gases, the inventory of these sea-air emissions is in its infancy due to the paucity of measurements. Compared to recent observations, models consistently underpredict the marine atmospheric concentrations of many VOCs, the total oxidative capacity, and marine SOA, strongly suggesting poorly constrained or unidentified oceanic emissions of VOCs. The highly uncertain VOC fluxes take the forms of "known unknowns" and "unknown unknowns". For the known unknowns, some VOCs are thought to be produced by marine biota or by photochemistry in seawater, but their oceanic emissions are poorly quantified. For the unknown unknowns, there are VOC fluxes or production pathways that we currently have little clue about, including light- or ozone-driven production from the sea surface. The sources and cycling of SOA over the background ocean are also poorly understood. While sea spray tends to dominate marine aerosol mass, SOA can be an important source of submicron particles and affect the abundance of CCN and so cloud droplets. In this project, we will combine a) intensive and comprehensive field measurements using novel instrumentation, b) innovative laboratory studies of physicochemical/biological processes, and c) state-of-the- art modeling on multiple scales to paint an unprecedented, holistic picture of reactive carbon and OH cycling in the background marine atmosphere. Constrained by atmospheric observations of total OH reactivity and total organic carbon mass, we will substantially improve flux estimates of established VOCs, identify new VOC emission sources, and evaluate their atmospheric impact. The fundamental questions we will address are: 1) Which VOCs exchange between the ocean and the atmosphere and what are their fluxes? 2) What are the physicochemical/biological processes that determine these fluxes? 3) What are the impacts of these marine VOCs on oxidative capacity, aerosol, clouds, and climate? COCO-VOC will achieve a step-change in understanding of VOC and OH cycling in the background environment, thereby constraining the sensitivities of VOCs, aerosol, and the global atmospheric oxidative capacity to changes in anthropogenic and natural emissions. This work will enable more accurate predictions of chemistry and climate in the past, present, and future. The new understanding will also offer insight into potential natural climate feedback processes caused by climate- driven changes in ocean-atmosphere VOC fluxes.

Tropical forests are one of the most important and diverse ecosystems on Earth; they act as a vast store for living carbon and, in doing so they help mitigate climate change by lowering atmospheric levels of the greenhouse gas carbon dioxide. However, in recent years, research has revealed an increase in the rate of tropic tree mortality, with the consequence that the strength of the carbon sink provided by tropical forests is reducing. It is therefore vital that we understand why tropical trees die and how this might change with climate change. This project will provide the very first assessment of the number of trees that are killed by lightning in tropical forests. We know that lightning can, and does, kill large trees. We also know that lightning strikes are most powerful and frequent in the tropics. Our estimates indicate that lightning strikes could affect trees containing over 1 % of the tropical forest biomass every year. If all these trees died it would indicate that lightning was a major controlling factor of tropical tree mortality rates. Worryingly, research has predicted that the rates of lightning strikes will increase significantly with climate change. Based on the most recent climate model simulations, lightning could increase by as much as 22 % to 60 % by 2100; Such an increase in lightning could substantially increase tree mortality, altering forest dynamics, and reducing the efficacy of tropical forests as a carbon store. Despite the potential significance of lightning induced tree mortality, very little is actually known about this process. This lack of knowledge arises from the simple fact that it is impossible to predict exactly when and where lightning will strike. This uncertainty makes the effects of lightning extremely hard to observe. An added complication is that trees damaged by lightning may not show any external signs of damage, making it impossible to attribute their death to lightning solely on the basis of visual observations. We propose to address the knowledge gap about lightning induced tree mortality with a revolutionary approach to observing lightning strikes on trees. To study the impacts of lightning on trees we have selected two high biomass tropical forest sites located in regions of high lightning activity in Nigeria and Cameroon. Unlike past studies that relied on visual observations, we will, for the first time, deploy sensors on 20,000 trees to provide an unambiguous record of lightning strikes over a 4 year period. We have adapted a sensor commonly used by electrical engineers to monitor electrical current and lightning strikes (called the Rogowski Coil) to make it inexpensive and easy to deploy in the field in large numbers. We have successfully tested our new version of this sensor in Cardiff University's unique lightning laboratory. By tracking a large cohort of trees we will be able to capture a large number of lightning strikes on trees and study these individuals to work out what happens following a lightning strike. We will use this information to determine which trees are struck by lightning, what happens to surrounding trees, how many trees are killed by lightning and how the carbon storage of the forest is affected. We will combine this information with environmental modelling to determine how lightning damages trees and induces mortality. Finally, we will estimate the tropical loss of biomass due to lightning strikes, and predict how biomass loss will be influenced by climate change. This research will be the very first systematic study on the rates of lightning induced tree mortality in the tropics. This information is vital to our understanding of the terrestrial carbon cycle and its continuing efficacy as a carbon sink. Therefore, this research is a priority for making informed global policy decisions on climate change mitigation.

This project will advance our ability to quantify the influence of phosphorus limitation and temperature on plant tissue respiration. The carbon balance of an organism and of an ecosystem is strongly dependent on the balance between photosynthesis and respiration. Globally, respiration on land is at present very slightly smaller than photosynthesis, meaning that terrestrial ecosystems are thought to be a 'sink' for atmospheric carbon dioxide, slowing the continual rise in carbon dioxide concentration in the atmosphere. A large fraction of the total respiration from land is thought to come from trees, so understanding what determines plant respiration is central to understanding how the terrestrial component of the Earth system works. However, despite its importance, only a limited amount of data are available to help us quantify plant respiration over large regions of the world. For example, although we know that the most important nutrients for plant growth (nitrogen and phosphorus) limit plant metabolism, we have almost no information on how phosphorus deficiency limits plant respiration, and hence the carbon balance. We also know only a little about how plant respiration responds to temperature: currently our global models of terrestrial ecosystems make large assumptions about this that may be wrong. When we consider that: (i) 30% of the global land surface may be phosphorus-deficient; (ii) the global phosphorus supply may seriously decline in under 100 years; and (iii) global climatic warming is likely to increase plant respiration this century (but by how much we don't know), there is clearly a strong and urgent need to address this issue. We will make measurements of respiration on a wide range of plant species. We will first use controlled-environment chambers to control the supply of nutrients to plants. We will then couple this with field measurements made in selected forested regions where phosphorus and nitrogen are differentially limiting, in order to compare the data from our experimental work to real ecosystems. The choice of our fieldsites in tropical South America and New Zealand makes use of existing knowledge about likely phosphorus limitations and will allow us to also address the issue of how biodiversity affects the phosphorus-respiration relationship. Finally we will analyse our data to enable us to incorporate our findings into mathematical models used to calculate how the land surface and our climate interact. Our project will enable us: (i) to quantify how phosphorus deficiency affects respiration; (ii) to quantify the influence of phosphorus deficiency on the temperature dependence of plant respiration. We will be able to link our results to existing work on the relationship between plant tissue metabolism and nitrogen concentration, and to incorporate the results into site-specific and global modelling frameworks. The project is highly cost efficient to NERC, making use of international facilities and project partner time supplied at zero cost to this project. This work will also link directly into existing research programmes funded by NERC of which the project investigators are already a part. The project will fill a signficant gap in our understanding of global ecology and the functioning of the Earth system.

A major explosive volcanic eruption in Chile has occurred at volcan Calbuco. This volcano has been quiet for over 40 years, and showed no sign that it was about to erupt until just a few hours beforehand. This eruption created a spectacular plume, which sent ash and gases high into the atmosphere, disrupting air transport and causing misery on the ground. In the three days after the eruption, volcanic ash fell across a wide area of central South America, across areas that include ancient native forests; cities, towns and villages; and farms, both on land and at sea. We plan to carry out field work across areas of Chile and Argentina where ash fell, working with local scientists to measure how much ash fell out during the eruption; and to work out what the effects of the eruption are both in the weeks after the eruption, and in the longer term. Although this is a major eruption, much of the deposits will soon become buried within the soil; blown away by winds, or washed away by rain, so we will need to work quickly to find the ash where it fell. Since ash fell out across an area where many millions of people live, we should be able to work out how much the deposits have changed in the days and weeks since eruption, by locating photographs posted across social media at the time. One of the things that we hope to learn from this eruption is to work out how to help people cope better when ash falls out across their cities and farms, and to use this information to help plan for future events.