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Sea surface temperature (SST) is characterized by abundant warm and cold structures that influence the overlying atmospheric boundary layer dynamics through two different mechanisms. First, turbulence and large eddies in the lower troposphere are affected by atmospheric stability, which can be modified by local SST, resulting in enhanced vertical mixing and larger surface winds over warmer waters. Second, the thermodynamic adjustment of air density to the underlying SST structures and the subsequent changes in atmospheric pressure drive secondary circulations. This paper aims to disentangle the effects of these processes and explore the environmental conditions that favor them. Two main environmental variables are considered: the large-scale air–sea temperature difference (proxy for stability) and wind speed. Using 5 years of daily reanalyses data, we investigate the 10-m wind response to SST structures. Based on linear regression between wind divergence and SST derivatives, we show that both mechanisms operate over a large spectrum of conditions. Ten-meter wind divergence is strongly impacted by the local SST via its effect on vertical mixing for midwind regimes in slightly unstable to near-neutral conditions, whereas the secondary circulation is important in two distinct regimes: low wind speed with a slightly unstable air column and high background wind speed with a very unstable air column. The first regime is explained by the prolonged Lagrangian time that the air parcel stays over an SST structure while the second one is related to strong heat fluxes at the air–sea interface, which greatly modify the marine atmospheric boundary layer properties. Location and frequency of the environmentally favorable conditions are discussed, as well as the response in low-cloud cover and rainfall. Significance Statement The main objective of this study is to explore the wind response to thermal structures at the sea surface under different environmental conditions using the latest atmospheric reanalysis. Recent literature suggests that fine-scale air–sea interactions affect a large spectrum of atmospheric dynamics, from seasonal to weather-type regimes. It is thus important to characterize the atmospheric response to ocean surface variability. Our findings describe the environmental conditions for which the two main physical processes through which the atmosphere responds to sea surface temperature structures are active the most and can guide the development of high-resolution observing missions and campaigns in specific geographical locations and seasons to retrieve data that can be used to improve parameterization in models.

Even though winter land–sea thermal contrast (LSC) is expected to undergo a strong weakening in the future warmer climate, its effects have been poorly investigated. Here we run a set of idealized winter simulations featuring reduced LSC in the Northern Hemisphere (NH) extratropics, or in individual extratropical sectors of the NH (Atlantic and Pacific), using an intermediate-complexity atmospheric general circulation model. Reduced LSC is obtained by imposing a warming of surface land temperatures in East Asia and North America. For similar warming intensities over the two regions, the response of the model to East Asia forcing is significantly stronger and dominates the response to the sum of the two forcing patterns. We find that the LSC reduction causes a weakening and poleward shift of the midlatitude jet streams, and a strong interference with zonal wavenumbers 1 and 2. In particular, East Asian warming reduces the amplitude of waves 1 and 2, producing a strengthening of the stratospheric vortex, while a weaker vortex due to a moderate amplification of wave 1 is detected when warming North America. Eventually, stratospheric signals propagate downward in the troposphere affecting the midlatitude winter NH even remotely from the forcing. In this work we pinpoint some mechanisms by which weakened winter LSC influences the NH extratropical circulation: the results may become useful to interpret the response to long-term projections displaying reduced LSC along with other climate change forcing patterns.

Wind Induced Surface Heat Exchange (WISHE) mechanism is considered very important for tropical cyclone intensification in a large part of the scientific literature([1], [2], [3] ): heat flux from the ocean increase with increasing wind speed, building up a positive feedback on the intensification.Simple WISHE-based models of tropical intensification predict that tropical cyclones intensify up to a steady state at the Potential Intensity (PI), obtained from the balance of heat supply rate from the ocean and dissipation rate in the boundary layer and dependent on boundary conditions only ([1]). The main problem of such models is the fact that they typically drastically simplify the convective motion within the cyclone, assuming a troposphere neutral to moist convection. ([4]).In our work we tested these predictions in idealized numerical experiments performed using the non-hydrostatic, high-resolution model System for Atmospheric Modelling (SAM). The results showed a significantly different intensity evolution, with the cyclone undergoing a oscillation in surface wind speed with peak intensity significantly lower than the PI. This intensity evolution was related to that of the environmental conditions along the whole air column: convective heating exports latent and sensible heat in the middle-upper troposphere, increasing environmental air buoyancy and so reducing CAPE. Radiative heating from the clouds further stabilizes the upper troposphere, weakening convection and thus cyclone intensity. After the intensity decay phase the upper level air surrounding the cyclone cools down through radiation emission: entrainment of cold air by the cyclone itself rebuilts CAPE and triggers a new intensification. Despite this work showed some limits in the predictivity of WISHE theory, WISHE feedback itself was proved to be fundamental for tropical cyclone intensification with a sensitivity numerical experiment. [1] K. Emanuel et al., “Tropical cyclones,” Annual review of earth and planetary sciences, vol. 31,no. 1, pp. 75–104, 2003[2] K. A. Emanuel, “An Air-Sea Interaction Theory for Tropical Cyclones. Part I: Steady-StateMaintenance.,” Journal of Atmospheric Sciences, vol. 43, pp. 585–605, Mar. 1986.[3] C. J. Muller and D. M. Romps, “Acceleration of tropical cyclogenesis by self-aggregationfeedbacks,” Proceedings of the National Academy of Sciences, vol. 115, no. 12, pp. 2930–2935, 2018.[4] K. A. Emanuel, “The behavior of a simple hurricane model using a convective scheme basedon subcloud-layer entropy equilibrium,” Journal of Atmospheric Sciences, vol. 52, no. 22,pp. 3960 – 3968, 1995.

Central Asia orography sets important features of the winter climate over East Asia and the Pacific. By deflecting the mid-latitude jet polewards it contributes to the formation of the Siberian High and, on the lee side, to the advection of dry cold continental air over the East Asian coast and the Pacific Ocean, where atmospheric instability and cyclogenesis thrive. While the mechanical forcing by the orography is assessed by a number of modelling studies, it is still not clear how near-surface temperature over the two most prominent orographic barriers of the Central Asian continent, namely the Tibetan and Mongolian plateaux, influences the winter climate downstream. Moreover, a well known issue of state-of-the art climate models is a cold land temperature bias over the Tibetan Plateau related with the difficulty in modelling land processes and land–atmosphere interaction over complex orography. Here we take advantage of the large spread in representing near surface temperature over the Central Asia plateaux among climate models taking part in the Coupled Model Inter-comparison Project, Phase 6 (CMIP6) to study how temperatures over these regions impact the atmospheric circulation. Based on composites of the CMIP6 models' climatologies showing a cold bias over the Tibetan Plateau, we find that negative temperature anomalies over Asian orography intensify the East Asia winter monsoon and, by enhancing the low-level baroclinicity in the region of the East China Sea, reinforce the southern flank of the Pacific jet. The results of the CMIP6 composite analysis are supported by the response of an intermediate-complexity atmospheric model to a similar pattern of cold surface temperatures over the Central Asia plateaux; we also distinguish the relative influence of the Tibetan and the Mongolian Plateau surface conditions. Thereby, based on the intensification of the East Asia winter monsoon in models characterised by a cold land temperature (bias) over Central Asia plateaux, we prospect that advances in the modelling of the land energy budget over this region may improve the simulation of the mean climate over the Asia/Pacific sector, together with the reliability of climate projections and the performance of shorter term forecasts.

Many cyclone detection and tracking methods (CDTMs) have been developed in the past to study the climatology of extratropical cyclones. However, all CDTMs have different approaches in defining and tracking cyclone centers. This naturally leads to cyclone track climatologies of inconsistent physical characteristics. More than that, it is typical for CDTMs to produce a non-negligible amount of bogus tracks which can be perceived as “false positives”, or more generally as CDTM artifacts, i.e. tracks of weak atmospheric features that do not correspond to large or mesoscale vortices. Lack of consensus in CDTM outputs and the inclusion of significant amounts of bogus tracks therein, has long prohibited the production of a commonly accepted reference dataset of extratropical cyclone tracks. Such a dataset could allow comparable results on the analysis of storm track climatologies and could also contribute to the evaluation and improvement of CDTMs. To cover this gap, we present a new methodological approach that combines overlapping tracks from different CDTMs and produces composite tracks that concentrate the agreement of more than one CDTM. In this study we apply this methodology to the outputs of 10 well-established CDTMs which were originally applied to ERA5 reanalysis in the 42-year period of 1979–2020. We tested the sensitivity of our results to the spatio-temporal criteria that identify overlapping cyclone tracks, and for benchmarking reasons, we produced five reference datasets of subjectively tracked cyclones. Results show that climatological numbers of composite tracks are substantially lower than the ones of individual CDTM, while benchmarking scores remain high (i.e. counting the number of subjectively tracked cyclones captured by the composite tracks). This suggests that our method is able to filter out a large portion of bogus tracks. Indeed, our results show that composite tracks tend to describe more intense and longer-lasting cyclones with more distinguished early, mature and decay stages than the cyclone tracks produced by individual CDTMs. Ranking the composite tracks according to their confidence level (defined by the number of contributing CDTMs), it is shown that the higher the confidence level, the more intense and long-lasting cyclones are produced. Given the advantage of our methodology in producing cyclone tracks with physically meaningful, distinctive life stages and including a minimum number of bogus tracks, we propose composite tracks as reference datasets for climatological research in the Mediterranean. The supplementary material provides the composite Mediterranean tracks for all confidence levels and in the conclusion we discuss their adequate use for scientific research and applications.

EUREC4A-OA is a large international project, connecting experts of ocean and atmosphere observations and modelling to enhance the understanding of key ocean and air-sea processes at the and to improve the skill of forecasts and future projections.The core of EUREC4A-OA has been a one-month (Jan/Feb 2020) field study in the western tropical North Atlantic Ocean where high-resolution, synchronized observational data have been collected using cutting-edge technology on ships, airplanes and autonomous vehicles. EUREC4A-OA investigates heat, momentum, water and CO2 transport within the ocean and exchanges across the air/sea interface using innovative high-resolution ocean observations and a hierarchy of numerical simulations. EUREC4A-OA focuses on ocean dynamics at the small-scale (0.1–100 km) and related atmospheric boundary layer processes. EUREC4A-OA is centered on the tropics where the primary external time scale affecting air-sea exchange is the diurnal cycle. However, the internal ocean and atmosphere dynamics convolute the diurnal, synoptic, seasonal and longer time scales to climate variability.The talk will present some of the results we obtained so far from the observations collected during the field experiment and from numerical simulations. The analyses carried out revealed with unprecedented detail the particular characteristics of the ocean small-scale dynamics, enlightening that such scales are also very active in the tropical regions and not only over the mid and higher latitudes ocean. Observations and models also unveil that the ocean small scales is important in contributing to the exchanges of heat, freshwater and CO2 between the ocean and the atmosphere. Moreover, the evaluation of the intensity of the coupling between the ocean and the atmosphere assessed from data and high-resolution simulations show that they are very important and intimately linked with the 3D structure of the small-scale ocean dynamics. The project has also provided preliminary results in terms of parametrization of different processes influencing the ocean and atmosphere exchanges that have been uncovered by the EUREC4A-OA field experiment. Notably a better representation of the small-scale freshwater patches due to precipitation has been introduced in the French Earth-System model that improves the overall simulations of air-sea interactions and clouds. A similar parametrization is now been introduced to take into account these physical processes in air-sea fluxes of CO2.

Centennial-scale variability of the Atlantic Meridional Overturning Circulation (AMOC) in the absence of external forcing has been identified in several climate models, but proposed mechanisms differ considerably. Therefore, better understanding of processes governing AMOC variability at these timescales is needed. Here, we analyze numerical simulations with PlaSim–LSG, an Earth System Model Intermediate Complexity (EMIC), which exhibit strong multicentennial oscillations of AMOC strength under constant pre-industrial boundary conditions. We identify a novel mechanism in which these oscillations are driven by salinity anomalies from the Arctic Ocean, which can be attributed to changes in high-latitude precipitation. We further corroborate our findings by conducting a set of millennial-length sensitivity experiments, and we interpret the mechanism by formulating a three-box model which qualitatively reproduces regular oscillations of the AMOC. While PlaSim–LSG lacks complexity compared to state-of-the-art models, our results reveal that precipitation minus evaporation (P-E) change in the Arctic is a physically plausible driver of centennial-scale AMOC variability. We discuss how this mechanism might be most relevant in climate states warmer than the present-day, raising questions about the state-dependence of multicentennial AMOC variability.

Long-term projections of the future climate display a robust reduction of winter land-sea thermal contrast in the Northern Hemisphere (NH), caused by a faster warming of the cold continents compared to the warm oceans. The reduction is expected to be strong in the extratropics, a region where the thermal contrast is relevant for maintaining the strong baroclinicity near the western coasts of the continents and for shaping the NH jets and large-scale stationary waves.In this work idealised perpetual-winter experiments characterised by a reduced land-sea thermal contrast are compared to control simulations featuring a thermal contrast similar to that observed in present-day climate. We use an intermediate-complexity AGCM with prescribed sea-surface and land temperatures. Warm temperature anomalies in East Asia and/or North America set a reduced thermal contrast in the whole NH or in individual NH sectors. We find that the Pacific-sector land-sea thermal contrast is by far more important than the Atlantic one for the large-scale mid-latitude circulation, as it impacts strongly the jet streams and the stationary planetary waves. While the local effects are coherent with the changes in baroclinicity brought by the surface forcing, the remote effects seem to be mediated by the response of the thermal and orographic components of the stationary waves. Based on the idealised-modelling results it is possible to hypothesise how the projected change in winter land-sea thermal contrast influences climate scenarios for the end of the XXI century. This factor has been rarely considered as a possible source of dynamical changes for the mid-latitude winter season.

It is timely within the Anthropocene era, more than ever before, to search for a non-anthropocentric mode of reasoning, and consequently designing. The PhotoSynthetica Consortium, established in 2018 and including London-based ecoLogicStudio, the Urban Morphogenesis Lab (Bartlett School of Architecture, University College London) and the Synthetic Landscape Lab (University of Innsbruck, Austria), has therefore been pursuing architecture as a research-based practice, exploring the interdependence of digital and biological intelligence in design by working directly with non-human living organisms. The research focuses on the diagrammatic capacity of these organisms in the process of growing and becoming part of complex bio-digital architectures. A key remit is training architects’ sensibility at recognising patterns of reasoning across disciplines, materialities and technological regimes, thus expanding the practice’s repertoire of aesthetic qualities. Recent developments in evolutionary psychology demonstrate that the human sense of beauty and pleasure is part of a co-evolutionary system of mind and surrounding environment. In these terms, human senses of beauty and pleasure have evolved as selection mechanisms. Cultivating and enhancing them compensate and integrate the functions of logical thinking to gain a systemic view on the planet Earth and the dramatic changes it is currently undergoing. This article seeks to illustrate, through a series of recent research projects, how a renewed appreciation of beauty in architecture has evolved into an operational tool to design and measure its actual ecological intelligence.

In the Northern-Hemisphere mid latitudes the winter land-sea thermal contrast is expected to decrease with increasing CO2 in the atmosphere, due to a faster warming of the continents with respect to the oceans. Moreover, the reduction of the winter thermal contrast is basin dependent, as it is influenced by regional warming patterns specific of the Atlantic and Pacific sectors, e.g. by the North-Atlantic Warming Hole.In this work we run a set of idealised perpetual-winter numerical experiments made with the simplified atmospheric circulation model SPEEDY where the extratropical land-sea thermal contrast is reduced by means of warm temperature anomalies over the continents. The reduction of the thermal contrast is performed first over the whole Northern Hemisphere, then over individual basins - Atlantic and Pacific - by warming, in turn, the land temperature of East Asia and North America. The impact of the reduced winter contrast on the mid-latitude tropospheric circulation is analysed with a focus on stationary planetary waves, the jet streams and the associated storm tracks. From the individual-basin approach we find that the Pacific land-sea thermal contrast is particularly important for the shape and amplitude of the stationary planetary waves and that it affects the whole Northern-Hemisphere circulation, reaching the North Atlantic storm track and jet. The role of the stratospheric pathway in the tropospheric response to reduced thermal contrast is also investigated, and shows nearly opposite features with respect to reduced Atlantic or reduced Pacific thermal contrast.

Climate change has a strong impact on the environment in mountain areas, especially since mountain ecosystems depend on climatic conditions that vary with altitude. In recent years, it has become clear that warming strongly depends on elevation. In this study, we examine projected climate change in the Greater Alpine Region using the Weather Research Forecasting (WRF) model. Historical 30-year simulations (1979-2008) and climate change projections (2039-2068) were performed at high spatial resolution (4 km grid spacing) and with initial and boundary conditions provided by the global EC-Earth model. A focus on the altitudinal dependence of historical and future ETCCDI Climate Change indices is presented here: the results indicate that both temperature and precipitation are affected by climate change with an altitude dependence changing seasonally. Physical mechanism at the base of those differences are discussed.

Aerosols play a crucial role in climate through different feedback mechanisms, affecting radiation, clouds, and air column stability. This study focuses on the altitude dependence of the cloud-mediated indirect effects of aerosols in the Great Alpine Region (GAR), an area characterized by high pollution levels from anthropic activities in the Po Valley and a complex orography with some of the highest mountains in Europe. Using a regional atmospheric model, 5-year-long convective-permitting sensitivity experiments have been run with different surface aerosol fluxes. The results show that seasonal mean cloud cover, temperature, and precipitations are affected by the aerosol concentrations in the air column and that the response to pollution is both elevation- and season-dependent. The overall cloud cover increase with aerosol levels leads to either surface cooling or warming depending on the surface albedo (snow covered or not). Furthermore, different types of clouds have a different response: while the lifetime of low-pressure-system clouds and orographic clouds is generally increased at high levels of aerosols, convective clouds (typical of the summer season) can decrease at high levels of pollution due to the reduction in strong updrafts associated with an increased air column stability.

Thermal structures at the sea surface are known to affect the overlying atmospheric dynamics over various spatio-temporal scales, from hourly and sub-kilometric to annual and O(1,000 km). The relevant mechanisms at play are generally identified by means of correlation coefficients (in space or time) or by linear regression analysis using appropriate couples of variables. For fine spatial scales, where sea surface temperature (SST) gradients get stronger, the advection might disrupt these correlations and, thus, mask the action of such mechanisms, just because of the chosen metrics. For example, at the oceanic sub-mesoscale, around 1–10 km and hourly time scales, the standard metrics used to identify the pressure adjustment mechanism (that involves the Laplacian of sea surface temperature, SST, and the wind divergence) may suffer from this issue, even for weak wind conditions. By exploiting high-resolution realistic numerical simulations with ad hoc SST forcing fields, we introduce some new metrics to evaluate the action of the pressure adjustment atmospheric response to the surface oceanic thermal structures. It is found that the most skillful metrics is based on the wind divergence and the SST second spatial derivative evaluated in the across direction of a locally defined background wind field.

Aerosols play a crucial role in climate through different feedback mechanisms, affecting radiation, clouds and air column stability. This study focuses on the altitude-dependence of the cloud mediated indirect effects of aerosols in the Great Alpine Region (GAR), an area characterised by high pollution levels from anthropic activities in the Po Valley and a complex orography with the highest mountains in Europe. Using a regional atmospheric model, 5-years long convective-permitting sensitivity experiments have been run with different surface aerosol fluxes. The results show that seasonal mean cloud cover, temperature, and precipitations are affected by the aerosol concentrations in the air column, and that the response to pollution is both elevation and season dependent. The overall cloud cover increase with aerosol levels leads to either surface cooling or warming depending on the surface albedo (snow covered or not). Furthermore, different types of clouds have a different sensitivity to aerosols: while the lifetime of low pressure system clouds and orographic clouds is generally increased at high levels of aerosols, convective clouds (typical of the summer season) can actually decrease at high levels of pollution, due to the reduction of strong updrafts.

Thermal structures at the sea surface are known to affect the overlying atmospheric dynamics over various spatio-temporal scales, from hourly and sub-kilometric to annual and O(1000 km). The releva...

Using 25years of ERA5 reanalysis data, this study shows that wind divergence is partially driven by small-scale sea surface temperature (SST) patterns via their effect on the boundary layer stability. Moreover, strong warm-to-cold fronts (the upper quartile) are associated with a mean increase of cloud cover of 10%±5% and a mean increase in the probability of a rain event of 15%±6%, with respect to the average values. The cloud and rainfall dependence on SST fronts is more pronounced in Fall, probably due to the stronger SST gradients present at the end of the summer season.

Sea Surface Temperature (SST) is known to affect the marine atmospheric boundary layer (MABL) at scales smaller than O(1000 km) via different mechanisms. In particular, the oceanic thermal forcing induces modification in the wind speed, its divergence and its curl by the action of the Downward Momentum Mixing (DMM) mechanism and the Pressure Adjustment (PA) one. By analyzing 25 years of observations of surface wind speed and SST in the Mediterranean, it is found that the probability of observing surface wind convergence is significantly higher over a thermal oceanic front crossed from the warm to the cold side, in agreement with the DMM mechanism. Physically, this is due to a deceleration of the surface wind over the cold side of the SST front because of the increased atmospheric stability over the cold water. The strongest response in terms of surface convergence is found when atmospheric fronts (already characterized by strong surface convergence) cross SST gradients from the warm to the cold side.Using 25 years of ERA5 reanalysis data, it is also found that the wind divergence variability within the MABL (until about 925 hPa) is partially driven by mesoscale SST patterns via their effect on the boundary layer stability. This results in a cloud cover and rainfall response: when a wind blows from warm-to-cold (cold-to-warm) ocean patterns, a converging (diverging) cell is enhanced, increasing (decreasing) low-cloud cover and favouring rainfall. Specifically, strong warm-to-cold fronts (the upper 25th percentile) are associated with a mean increase of cloud cover of 10±5% and a mean increase in the probability of a rain event of 15±6%, with respect to the average values. The cloud and rainfall dependence on SST fronts is more pronounced in fall than in the rest of the year, probably due to the stronger SST gradients present at the end of the summer season. The effects on cloud cover, in particular, are a preferential way through which mesoscale SST structures can impact the radiation budget and, thus, the Earth climate.

Around the Maldives, it was found that the interaction between currents and the steep bathymetry is responsible for a local cooling of about 0.2°C in the Archipelago during the warmest season, with respect to the surrounding waters. The reduced SST is probably linked to the Island Mass Effect: the enhanced productivity around small islands discovered in the sixties and documented worldwide. Despite its effects on marine productivity, the exact description of the physical processes behind the local cooling and nutrient input that enhances productivity is still unclear. From the analysis of SST variations and net primary productivity (NPP) around small islands and archipelagos, two kinds of signals can be identified, depending on the altitude and dimension of the islands. Around islands with considerable elevation and greatest diameters, cold/warm anomalies, most likely corresponding to upwelling/downwelling zones, emerge. Warmer areas don’t appear around smaller islands that usually display only a local cooling. Several oceanic and atmospheric processes might be involved. The case of the Maldives has been analyzed in detail using CROCO and a particle tracking model: Ariane. More than one process might coexist in generating the described patterns, the prevailing one varying along the year and depending on the strength and direction of the incoming flow. Near the Maldives, the frictional break of the currents in the presence of shallow bathymetry produces a strong vertical shear in the flow that favors vertical mixing and produces a nearly symmetric cooling around the islands. A different mechanism dominates the cooling pattern when the currents are particularly intense, such as during the monsoons: intense zonal currents cross the Archipelago and give rise to intense wakes with large horizontal shear; strong upwelling originates in the lees, creating an asymmetric temperature signal (larger cooling in the lee of the islands) and obfuscating the effects of the enhanced vertical mixing.

Long term projections of the Northern Hemisphere winter climate show an overall increase of surface temperatures that is particularly amplified at Arctic latitudes. On top of this, projections agree in predicting a faster temperature increase on land than on sea surface, therefore a reduced winter land-sea contrast in the mid latitudes. Despite the robustness of this feature in climate projections, the response of the atmospheric system to a strongly reduced winter land-sea contrast has been scarcely investigated. Here, we study how it affects the low and high frequency variability in the extratropics using a simplified GCM, with a focus on the Atlantic and Pacific jets. Moreover, different sea surface temperatures are applied to the North Atlantic and North Pacific basins in order to simulate the presence of a differential warming, as in the well-known scenario of a North-Atlantic warming hole.

Mountains play a key role for humanity providing freshwater for the areas downstream. The amount of precipitation at a given location is significantly affected by orography. Since changes of rainfall are expected in the changing climate, understanding how orographic precipitation responds to global warming and to anthropogenic forcing is becoming particularly pressing. To better understand the physical processes at play, in this study we investigate the indirect effects of aerosols on precipitation using the Weather Research Forecasting (WRF) Model: sentivity experiments are run with different numbers of water-friendly and ice-friendly aerosols in the atmospheric boundary layer. 5-years long simulations at high spatial resolution (4Km) have been run in the Great Alpine Region, where orographic lifting plays an important role and precipitation has a large spatial variability due to the complex orography. Results indicate that the indirect effects of aerosols modify cloudiness and precipitation in different ways among the flatlands (Po Valley) and the mountain areas. Physical mechanism at the base of those differences are discussed.

International audience; Using a combination of multi-directional SAR and TIR measurements, the Harmony Earth Explorer 10 mission candidate will provide high resolution simultaneous measurements of surface stress, surface currents SST and wave spectra over oceans, 3-D deformation vectors over solid Earth, and time-series of surface elevation changes over volcanic areas and land ice masses. This will serve a series of science objectives aimed at better understating multi-scale processed and feedbacks in the Earth System.

The North Atlantic Oscillation (NAO) and the Arctic Oscillation (AO) are climate variability modes significantly affecting temperature and precipitation variability in the mid-latitudes of the Northern hemisphere. In this study, we use both reanalysis data and model historical and warmer climate simulations to show that the relation between the two oscillations may change dramatically in a different climate. In the current climate, these two climate modes are highly correlated, as they are both strongly influenced by downward propagation of stratospheric anomalies into the troposphere. When considering a warmer climate scenario (RCP8.5 in the XXIII century), the correlation between NAO and AO drops significantly, revealing that they become two separate modes of variability. The stratosphere remains an important precursor for NAO, while the AO consistently precede stratospheric anomalies. The analysis suggests that these changes are owed to land-sea thermal contrast intensification in the Pacific region, which becomes more favorable for storm variability.

Air and sea interact on a wide range of scales, shaping climate and influencing weather. The direct effect of sea surface temperature (SST) structures on the extratropical atmosphere at the daily time-scale is generally masked by the large variability associated with atmospheric dynamics. With 25 years of daily SST and surface wind observational products, obtained with data from buoys, satellite and atmospheric analysis in the Mediterranean, we show that strong surface wind convergence preferentially occurs when the air encounters a cold SST front. The mechanism responsible for the influence of ocean fronts on surface winds is rooted in the thermal disequilibrium that emerges at the air–sea interface, where cold water enhances the stability of the boundary layer, decoupling surface winds from the stronger winds aloft. Surface convergence drives upward motion which, under appropriate conditions, favours cloud formation. Thus, these results suggest that weather forecast models need to properly represent the small-scale ocean thermal structures, which could affect rainfall. © 2020 Royal Meteorological Society

The importance of the upper ocean thermal vertical structure (mixed-layer depth and stratification) in the control of the precipitation during a heavy-rain-producing mesoscale convective system is investigated by means of numerical simulations. In particular, the fully compressible, nonhydrostatic Euler equations for the atmosphere and the hydrostatic Boussinesq equations for the ocean are numerically integrated to study the effect of the ocean-atmosphere coupling both with realistic initial and boundary conditions and with simpler, analytical vertical temperature profile forcing. It is found that the action of the winds associated with the synoptic system, in which the heavy precipitation event is embedded, can entrain deep and cold water in the oceanic mixed layer, generating surface cooling. In the case of a shallow mixed layer and strongly stratified water column, this decrease in sea surface temperature can significantly reduce the air column instability and, thus, the total amount of precipitation produced.

The mechanisms controlling the influence of the sea surface temperature (SST) structure on the surface winds are studied by means of numerical simulations run with a nonhydrostatic fully compressible state-of-the-art numerical model in a realistic midlatitudes setup, leading to the 9 October 2014 Genoa heavy rainfall event. Starting from a simulation with high-resolution submesoscale eddy-permitting SST field, the surface temperature boundary conditions are changed to enhance, reduce, or smooth the SST gradient. It is found that the marine atmospheric boundary layer responds to the submesoscale SST forcing structures over time scales of the order of hours. In particular, through the downward momentum mixing mechanism, the presence of SST horizontal gradients impacts the spatial structure of the surface wind convergence, which can displace the convective heavy rain bands that develop over the sea.

Artificial landscapes whose human use has expired pose a major reprogramming challenge. The Solana Open Aviary, a transformation of former salt marshes into an enormous openair ornithological park, shows how cutting-edge technology can be used to address biopolitical, operational and tectonic concerns in such situations. Claudia Pasquero and Marco Poletto – cofounders of the project-leading London practice ecoLogicStudio – explain.