Antarctica is changing. In February 2022, sea ice around Antarctica reached the lowest area that has been observed since satellite records began in 1979. This marks the first time that the area of sea ice ice has been observed to shrink below 2 million square kilometres. Compared to the average minimum, the 2022 February minimum is missing an area of sea ice that is about three and a half times the size of the UK. Directly following on from the sea ice minimum, in March 2022 record air temperatures were recorded across much of East Antarctica, with some meteorological stations observing temperatures 40C warmer than normal. These unprecedented conditions were associated with a very intense 'atmospheric river', a narrow corridor of warm water vapour, bringing warm air and moisture to the high Antarctic Plateau. We do not know whether these extreme regional climatic events are just 'one offs', and highly unlikely to occur again, or whether they are an indication of how Antarctic climate will develop in the future. These recent extreme weather events and conditions in Antarctica have prompted fresh concern about how climate change in this remote region will impact Earth. The protection of coastlines around the world from the future rise in sea level from Antarctica requires a better understanding of how the weather of Antarctica will evolve over the coming century. Any loss of Antarctic ice mass as a result of weather changes may raise the sea level around the globe. SURFEIT will thus investigate how changing snow and radiation, or surface fluxes, over the coming century will affect Antarctic snow and ice. The international SURFEIT team will: (i) improve how polar clouds are represented in our climate models; (ii) use pre-existing, and new, observations alongside climate model output to help improve our understanding of changes in snowfall over Antarctica; (iii) ensure we can accurately predict small-scale and extreme-event weather changes; and (iv) improve how we link our earth and ice system model components together, so that we can make better predictions of when Antarctic ice may fracture, and so raise global sea level. Our work on improving snowfall and ice predictions will help us answer our overarching question 'How will changes in Antarctic surface fluxes impact global sea-level to 2100 and beyond?'

The greenhouse gases carbon dioxide (CO2) and methane (CH4) are by far the biggest contributors to recent and ongoing climate change. Of all the known greenhouse gases (excluding water vapour), CO2 and CH4 have the highest concentrations in the atmosphere and they are rising rapidly. CO2 is particularly problematic because there is so much of it (about 200 times more than CH4) and because once emitted to the atmosphere, much of it will stay there for several hundred years. Whereas, by comparison, CH4 has a lifetime in the atmosphere of about a decade, but it is a much more potent greenhouse gas than CO2 - that is, for equal amounts of CO2 and CH4 in the atmosphere, CH4 will trap heat radiation about 70 times more effectively than CO2 (over a 20-year time period). With the ratification of the Paris Agreement, the world has committed to avoiding dangerous climate change and the most obvious way to do this is by reducing emissions of CO2 and CH4. How will we know if emission mitigation policies are effective? Which nations or regions are meeting their emissions reduction targets? How will natural CO2 and CH4 fluxes respond to extreme weather events? And which aspects of the carbon cycle remain unsolved? For example, despite decades of study, scientists are still not sure why CH4 emissions are currently rising. To answer these questions we need to be able to measure and quantify CO2 and CH4 emissions and concentrations, and have the ability to separately quantify natural and manmade sources. Our current abilities to do so are severely limited, especially for CH4, which has a diverse array of natural and manmade sources. If we cannot determine the effectiveness of mitigation policies, then our ability to predict climate change impacts will be compromised by large uncertainties. 'Polyisotopologues' are one very promising new tool for distinguishing between different source emissions. The chemical elements that make up CO2 and CH4 molecules (carbon (C), oxygen (O) and hydrogen (H)) can have different masses, called isotopes. Different sources can have different isotopic 'fingerprints' or 'signatures' (because source reaction processes may favour a lighter or heavier molecule), thus measuring isotopic signatures is a useful way to gain insight into sources. Isotopic measurements have been made routinely for several decades; whereas the state-of-the-art technology developed in this project would allow us to measure molecules with more than one rare isotope. For example, most C has a relative atomic mass of 12 and H a mass of 1. The rarer isotopes of C and H have masses of 13 and 2, respectively. Isotopologues of CH4, which are measured routinely, include 12CH4, 13CH4 and 12CH3D (where 'D' represents the heavy H atom with mass 2). Whereas polyisotopologues of CH4 include 13CH3D and 12CH2D2 - these are far more challenging to measure, yet could provide invaluable insight into source emissions and sinks. POLYGRAM (POLYisotopologues of GReenhouse gases: Analysis and Modelling) will push the frontiers for both CO2 and CH4 polyisotopologue measurement capability using the latest advances in laser spectroscopic analysis and very high-resolution isotope ratio mass spectrometry. In addition to these challenging technological developments, we will establish a small global atmospheric sampling network to examine latitudinal and longitudinal variations in polyisotopologues, which will help us to constrain overall global budgets of CO2 and CH4. We will carry out field campaigns to determine polyisotopologue source signatures, for example, of CH4 from wetlands, cattle and landfills, and of CO2 from plant photosynthesis and respiration, and from fossil fuel burning. We will conduct laboratory experiments to estimate the reaction rates for CH4 isotopologues when they are oxidised and destroyed in the atmosphere. Finally, we will carry out atmospheric transport modelling for both gases to better interpret and understand the measurements.

By modifying the amount of solar radiation absorbed at the land surface, bright snow and dark forests have strong influences on weather and climate; either a decrease in snow cover or an increase in forest cover, which shades underlying snow, increases the absorption of radiation and warms the overlying air. Computer models for weather forecasting and climate prediction thus have to take these effects into account by calculating the changing mass of snow on the ground and interactions of radiation with forest canopies. Such models generally have coarse resolutions ranging from kilometres to hundreds of kilometres. Forest cover cannot be expected to be continuous over such large distances; instead, northern landscapes are mosaics of evergreen and deciduous forests, clearings, bogs and lakes. Snow can be removed from open areas by wind, shaded by surrounding vegetation or sublimated from forest canopies without ever reaching the ground, and these processes which influence patterns of snow cover depend on the size of the openings, the structure of the vegetation and weather conditions. Snow itself influences patterns of vegetation cover by supplying water, insulating plants and soil from cold winter temperatures and storing nutrients. The aim of this project is to develop better methods for representing interactions between snow, vegetation and the atmosphere in models that, for practical applications, cannot resolve important scales in the patterns of these interactions. We will gather information on distributions of snow, vegetation and radiation during two field experiments at sites in the arctic: one in Sweden and the other in Finland. These sites have been chosen because they have long records of weather and snow conditions, easy access, good maps of vegetation cover from satellites and aircraft and landscapes ranging from sparse deciduous forests to dense coniferous forests that are typical of much larger areas. Using 28 radiometers, and moving them several times during the course of each experiment, will allow us to measure the highly variable patterns of radiation at the snow surface in forests. Information from the field experiments will be used in developing and testing a range of models. To reach the scales of interest, we will begin with a model that explicitly resolves individual trees and work up through models with progressively coarser resolutions, testing the models at each stage against each other and in comparison with observations. The ultimate objective is a model that will be better able to make use of landscape information in predicting the absorption of radiation at the surface and the accumulation and melt of snow. We will work in close consultation with project partners at climate modelling and forecasting centres to ensure that our activities are directed towards outcomes that will meet their requirements.

Recent research has suggested that energetic particles entering the Earth's atmosphere at the poles can lead to 5-10 K changes in the surface tempertaures in polar regions during the wintertime. This is thought to be as a result of chemical changes driven by energetic particles enering the Earth's atmosphere at high altitudes (50-90 km) affecting the radiation balance of the atmosphere as a whole. However the exact nature of the particles is unknown, and further analysis/confirmation of the effect on surface temperature variability is limited by this knowledge gap. We propose to fill this knowledge gap by deploying low-powered narrow band radio receivers south of the Antarctic Peninsula in order to monitor energetic particle precipitation coming from the radiation belts that surround the Earth. Only then will the study of the impact of the particles in driving atmospheric chemical changes be possible with any degree of certainty. Being able to site our experiments in the Antarctic is critical because: 1) the geomagnetic latitudes of the sites chosen for this project are associated with processes occuring at the heart of the outer radiation belt - allowing us to determine the maximum radiation belt particle influence on the atmosphere; 2) the effect of energetic particle precipitation on the experimental radiowave observations that we will make is enhanced over thick ice-sheet regions - this condition only occurs south of the Antarctic Peninsula at the geomagentic latitudes that are needed to make the best observations; 3) the region south of the Antarctic Peninsula is where most of the particle precipitation from the outer radiation belt will occur, because of the influence of the nearby South Atlantic Magnetic Anomaly in knocking the energetic particles out of their orbits and into the atmosphere. The data collected, analysed and interpreted by the project partners brought together by this proposal, will allow us to model the chemical changes in the Antarctic atmosphere due to energetic particle precipitation. As a result we will be able to determine the impact of complex radiation belt processes on the global atmosphere. Our Investigation of the effects on polar surface temperatures is part of international efforts to understand climate variability and the links to the upper atmosphere (e.g. the NERC Science Themes, the Climate and Weather of the Sun-Earth System programme, phase II, and the International Living with a Star programme - ILWS) . Our proposal is also timely in that there will be extensive supporting measurements made during the lifetime of our proposal by x-ray balloons funded by NASA, and by new NASA and CSA radiation belt satellites, all supported by the ILWS programme. Extensive collaboration between this proposal and the balloon/satellite mission scientific teams has been initiated and will continue throughout the project lifetime.

The aim of this proof-of-concept study is to determine the feasibility of new remote sensing observations that will capture, for the first time, detailed changes in the chemistry of the Earth's stratosphere, mesosphere, and lower thermosphere on short timescales that cannot be measured using other techniques. Such observations would address major gaps in our understanding of the links between solar variability & space weather, atmospheric chemistry, and the global climate system. The importance of the areas targeted by this project are highlighted by the Intergovernmental Panel on Climate Change Fifth Assessment Report (IPCC AR5) which states the need to 'assess climate change impact on - and the role of the mesosphere in radiative forcing of the atmosphere'. Ozone and hydroxyl radical (OH) are important trace gases in the middle and upper atmosphere that respond strongly to solar forcing and, at high latitudes, geomagnetic activity associated with space weather. Energetic particles from space are guided by the Earth's magnetic field into the atmosphere at high latitudes. Important questions about this energetic particle precipitation remain unresolved. These include what are the key chemical changes in the middle and upper atmosphere and how are these changes are coupled to the atmospheric layers below? Following geomagnetic storms, energetic electron precipitation (EEP) into the polar middle atmosphere causes ionisation reactions that generate odd nitrogen and odd hydrogen species, in particular OH. These reactive chemicals take part in both short-duration and long-term catalytic destruction of ozone that modifies the radiative and thermal structure of the atmosphere, affecting temperatures down to the Earth's surface. EEP occurs very frequently and potentially has a more significant impact on the atmosphere than the impulsive but highly sporadic and well-studied effects of powerful solar proton storms. It has been difficult to estimate the effect of EEP on the atmosphere because of the challenge of making measurements of rapidly-evolving atmospheric chemical composition, in particular ozone and OH, at altitudes of 20-100 km. Commercial satellite TV broadcasting is possible due to remarkable advances in microwave electronics, enabling weak signals transmitted over 36,000 km from geostationary orbit to be received by inexpensive rooftop dishes. We propose incorporating the highly-sensitive Ku-band satellite receiver technology in ground-based microwave radiometers to measure ozone and OH. The microwave spectrum of the atmosphere contains information about ozone from an emission line at 11.072 GHz and from OH at 13.44 GHz. Ku-band microwave radiometry will allow precise, quantitative characterisation of these atmospheric signals using the sensitive heterodyne detection technique combined with high-resolution radiofrequency analysis. We will use computer-based algorithms to investigate how ten-fold improvements in receiver sensitivity will allow detailed measurements of the spatial and temporal distributions of ozone and OH. The proposed instruments would be robust, semi-autonomous, and operate continuously making observations that are highly applicable to studies of EEP, atmospheric dynamics, planetary scale circulation, chemical transport, and the representation of these processes in global climate models, ultimately leading to advances in numerical weather prediction. They would provide a low cost, reliable alternative to increasingly sparse satellite measurements, extending long-term data records and also providing "ground truth" data for calibrating and validating scientific satellite data. The work is relevant to three NERC research subjects (Atmospheric physics and chemistry; Climate and climate change; Tools, technology & methods) and will build UK expertise in microwave remote sensing and atmospheric information retrieval.