The dynamics of the atmosphere and oceans at mid-latitudes is well described by focusing on the slow, large-scale motion, in nearly hydrostatic and geostrophic balance. However, fast small-scale motion in the form of gravity waves and associated instabilities plays a crucial role in a number of processes (such as momentum transport, turbulence, vertical mixing, and dissipation), which impact on large-scale circulations, middle-atmospheric circulation and ocean thermohaline circulation in particular. The mechanisms of generation of the fast, unbalanced motion have therefore received a great deal of attention in recent years. However, the so-called spontaneous-generation mechanisms, whereby the evolving hydrostatically and geostrophically balanced motion directly excites unbalanced motion, remain poorly understood, in spite of their importance. One difficutly is that these mechanisms are only efficient when the balanced motion evolves sufficiently rapidly, and that such a rapid evolution is rather atypical in the bulk of the atmosphere and oceans. Near horizontal boundaries, however, a rapid evolution is typical. By horizontal boundaries, we refer not only to the ocean surface and solid earth, but also to the tropopause, which plays a similar role. Not coincidentally, these are precisely the regions where strong unbalanced activity is observed. These also are regions where unbalanced motion has crucial consequences, the effect of turbulence on airplanes being the most obvious, if not the most important. The proposed research will examine how the generation of unbalanced motion at horizontal boundaries takes place. This will be done by analysing simple models which isolate the key feature of the boundary dynamics that is reponsible for unbalanced-motion generation, namely the formation of very active structures in the surface temperature, with both small spatial scales and short temporal scales. This feature has been well demonstrated in the context of the (balanced) surface quasi-geostrophic model, but its impact on unbalanced motion remains to be described. The proposed research will carry out this task for the first time. It will consider not only situations of frontal collapse but also the more complex cascade of small-scale instabilities which characterise surface evolution and leads to a form of turbulence. The aim is to relate the characteristics of the unbalanced motion to those of the surface fields with, as ultimate goal, the parameterisation of its impact on mixing and dissipation.

EUREC4A-UK is a programme of observational and modelling research which aims to study the detailed aerosol and cloud processes in the life cycle of shallow trade cumulus clouds and the two-way interactions between the cloud processes and the large-scale dynamics. The different responses of these clouds to warming in global climate models (GCM) explain most of the inter-model differences, yet the physics of these responses remains poorly constrained. The programme is focussed on the participation of UK scientists and the BAS Twin Otter aircraft in EUREC4A (Elucidating the Role of Clouds-Circulation Coupling in Climate). EUREC4A is a coordinated international campaign that aims to address the current lack of understanding of the processes controlling the response of trade-wind cumulus clouds to changing environmental conditions in a warmer climate. The goal of EUREC4A is to examine the interplay between the clouds, atmospheric circulations and climate sensitivity. EUREC4A-UK will make a unique and self- contained contribution to the international programme by: (i) providing observational facilities which are needed as part of the coordinated field campaign; (ii) conducting and leading the analysis of the aerosols, cloud microphysics and boundary-layer processes in the life cycle of shallow trade cumulus clouds; (iii) placing the analysis in the context of the EUREC4A problems by modelling the two-way interactions between the cloud processes and the large-scale dynamics; and (iv) applying the results by testing the new convection scheme in the UM and using the improved model to determine the dominant processes controlling the cloud fields. International partners will complement the re- search with a focus on observing and modelling the macrophysical properties and the environment of trade-cumulus clouds in order to determine: (i) what controls the convective mass flux, mesoscale organization and depth of shallow-cumulus clouds; (ii) how the trade-cumulus cloud fraction varies with turbulence, convective mixing and large-scale circulations; and (iii) the impact this variation has on atmospheric radiation. The radiative properties of the trade-wind cumulus clouds that are ubiquitous over the tropical oceans have a major influence on the Earth's radiation budget. The response to global warming of these clouds is therefore critical for global mean cloud feedbacks. It is the differing response to warming that explains most of the spread of climate sensitivity in climate models. Hence, a better understanding is required of the mechanisms that control the low-level cloud fraction. The urgency of the research is made clear by the fact that the World Climate Research Programme endorses the EUREC4A field project which supports the Grand Challenge on Clouds, Circulation and Climate Sensitivity. There is a clear need for EUREC4A-UK because the aerosol, cloud and precipitation processes influence the macrophysical properties of the clouds in different environments. For example, the vertical distribution of rain can affect the concentration and size of cloud drops in the upper detrainment layers, which influ- ences cloud radiative properties. The intensity of rain and evaporation of raindrops influences the strength of gust fronts and hence secondary cloud-production. However, model calculations of the rate of production of rain and hence the quantity of rain are uncertain due to the complex interactions of aerosols, entrainment, turbulence and giant cloud condensation nuclei (GCCN). These processes depend on the environment conditions, controlled by the large-scale dynamics. Equally, the aerosol- cloud-precipitation processes can influence the larger-scale dynamics, for example through radiative transfer. Indeed there are many interactions between processes on a range of scales that need to be understood and represented in models.

The importance of the greenhouse gases CO2 and CH4 for climate is well established. There is broad scientific consensus that human activities are the main driver for increasing concentrations of these greenhouse gases (GHGs), particularly over the past century. Based on accurate surface measurements we know that approximately 45% of the CO2 emitted by human activities remain in the atmosphere. The net balance is apparently being taken up by global oceans, terrestrial vegetation and soils. However, there are substantial uncertainties associated with the nature, location and strength of these natural components of the carbon cycle. The Amazon region is one of the largest forested regions in the world, representing the largest reservoir of above ground organic carbon. Amazonia is not only subject to changes in climate but also to rapid environmental change due to fast population growth and economic development causing extensive deforestation and urbanisation. Such external drivers can lead to further shifts in the carbon balance resulting in release of carbon stored in the biomass and soil to the atmosphere, with implications for accelerating the growth of atmospheric GHG concentrations and climate change. Despite its important role for the global carbon cycle, current understanding of the Amazonian, and more broadly the tropical, carbon cycle is poorly constrained by observations. These knowledge gaps result in large uncertainties in the fate of the Amazonian carbon budget under a warming climate, and consequently hamper any predictive skill of carbon-climate models. Since 2009, the Amazon region has been the focus of major UK and Brazilian research projects that aim at improving our knowledge of the Amazonian carbon cycle using detailed, but localized aircraft observations of CO2 and CH4 at a number of sites. These measurements are a great advance but they remain highly localized in space and time. Space-borne measurements have the ability to fill these observational gaps by providing observations with dense spatial and temporal coverage in regions poorly sampled by surface networks. It is essential, however, that such space-based observations are properly tied to the World Meteorological Organization (WMO) reference standard to ensure acceptance of space-based datasets by the carbon cycle community and to prevent misleading results on regional carbon budgets. The central aim of this proposal is to link the in-situ measurements with remotely sensed satellite data to establish an integrated Amazonian Carbon Observatory where satellite data complements the in situ data by filling the gaps between the in situ sites and by extending the coverage over the whole Amazon region. Satellite observations of GHGs are now available from a dedicated instrument on board the Japanese GOSAT satellite and results look very promising. However, satellite retrievals over the Amazon (and the Tropics) are intrinsically difficult and the accuracy of such GHG retrievals has not been established for this region which is a major obstacle for the exploitation of space-based data to constrain carbon fluxes over the Amazon. We propose to establish a network of Brazilian and UK researchers to bridge the gap between in-situ and remote sensing observations and communities and to evaluate the feasibility of remote sensing of GHG concentrations for the purpose of GHG flux monitoring over Amazonia to improve our understanding of the Amazonian carbon cycle and to increase our ability for observing tropical carbon fluxes. The proposed network will bring together world-class expertise to address highly relevant and timely scientific questions that will advance our understanding of the carbon cycle of the Amazon. It will strongly strengthen and expand UK and Brazilian relationships and it will help further strengthen the leading role of UK researchers in many areas relevant to this proposal.

The atmosphere changes on time scales from seconds (or less) through to years. An example of the former are leaves swirling about the ground within a dust-devil, while an example of the latter is the quasibiennial oscillation (QBO) which occurs over the equator high up in the stratosphere. The QBO is seen as a slow meander of winds: from easterly to westerly to easterly over a time scale of about 2.5 years. This 'oscillation' is quite regular and so therefore is predictable out from months through to years. These winds have also been linked with weather events in the high latitude stratosphere during winter, and also with weather regimes in the North Atlantic and Europe. It is this combination of potential predictability and the association with weather which can affect people, businesses and ultimately economies which makes knowing more about these stratospheric winds desirable. However, it has been difficult to get this phenomenon reproduced in global climate models. We know that to get these winds in models one needs a good deal of (vertical) resolution. Perhaps better than 600-800m vertical resolution is needed. In most GCMs with a QBO this is the case, but why? We also know that there needs to be waves sloshing about, either ones that can be 'seen' in the models, or wave effects which are inferred by parameterisations. Get the right mix of waves and you can get a QBO. Get the wrong mix and you don't. Again we do not know entirely why. Furthermore, we also know convection bubbling up over the tropics and the slow migration of air upwards and out to the poles also has a big impact of resolving the QBO. All of these factors need to be constrained in some way to get a QBO. The trouble is that these factors are invariably different in different climate models. It is for this reason that getting a regular QBO in a climate model is so hard. This project is interested in exploring the sensitivity of the QBO to changes in resolution, diffusion and physics processes in lots of climate models and in reanalyses (models used with observations). To achieve this, we are seeking to bring together all the main modelling centres around the world and all the main researchers interested in the QBO to explore more robust ways of modelling this phenomena and looking for commonalities and differences in reanalyses. We hope that by doing this, we may get more modelling centres interested and thereby improve the number of models which can reproduce the QBO. We also hope that we can get a better understanding of those impacts seen in the North-Atlantic and around Europe and these may affect our seasonal predictions. The primary objective of QBOnet is to facilitate major advances in our understanding and modelling of the QBO by galvanizing international collaboration amongst researchers that are actively working on the QBO. Secondary objectives include: (1) Establish the methods and experiments required to most efficiently compare dominant processes involved in maintaining the QBO in different models and how they are modified by resolution, numerical representation and physics parameterisation. (2) Facilitate (1) by way of targeted visits by the PI and researchers with project partners and through a 3-4 day Workshop (3) Setup and promote a shared computing resource for both the QBOi and S-RIP QBO projects on the JASMIN facility