Abstract. Atmospheric gravity waves (GWs) play an important role in atmospheric dynamics but accurately representing them in general circulation models (GCMs) is challenging. This is especially true for orographic GWs generated by wind flow over small mountainous islands in the Southern Ocean. Currently, these islands lie in the “grey zone” of global model resolution, where they are neither fully resolved nor fully parameterised. It is expected that as GCMs approach the spatial resolution of current high-resolution local-area models, small-island GW sources may be resolved without the need for parameterisations. But how realistic are the resolved GWs in these high-resolution simulations compared to observations? Here, we test a high-resolution (1.5 km horizontal grid, 118 vertical levels) local-area configuration of the Met Office Unified Model over the mountainous island of South Georgia (54∘ S, 36∘ W), running without GW parameterisations. The island's orography is well resolved in the model, and real-time boundary conditions are used for two time periods during July 2013 and June–July 2015. We compare simulated GWs in the model to coincident 3-D satellite observations from the Atmospheric Infrared Sounder (AIRS) on board Aqua. By carefully sampling the model using the AIRS resolution and measurement footprints (denoted as model sampled as AIRS hereafter), we present the first like-for-like comparison of simulated and observed 3-D GW amplitudes, wavelengths and directional GW momentum flux (GWMF) over the island using a 3-D S-transform method. We find that the timing, magnitude and direction of simulated GWMF over South Georgia are in good general agreement with observations, once the AIRS sampling and resolution are applied to the model. Area-averaged zonal GWMF during these 2 months is westward at around 5.3 and 5.6 mPa in AIRS and model sampled as AIRS datasets respectively, but values directly over the island can exceed 50 mPa. However, up to 35 % of the total GWMF in AIRS is actually found upwind of the island compared to only 17 % in the model sampled as AIRS, suggesting that non-orographic GWs observed by AIRS may be underestimated in our model configuration. Meridional GWMF results show a small northward bias (∼20 %) in the model sampled as AIRS that may correspond to a southward wind bias compared to coincident radiosonde measurements. Finally, we present one example of large-amplitude (T′≈15–20 K at 45 km altitude) GWs at short horizontal wavelengths (λH≈30–40 km) directly over the island in AIRS measurements that show excellent agreement with the model sampled as AIRS. This suggests that orographic GWs in the full-resolution model with T′≈45 K and λH≈30–40 km can occur in reality. Our study demonstrates that not only can high-resolution local-area models simulate realistic stratospheric GWs over small mountainous islands but the application of satellite sampling and resolution to these models can also be a highly effective method for their validation.

Two techniques are presented for characterisation of cloud-feeding coherent boundary-layer structures through analysis of large-eddy simulations of shallow cumulus clouds, contrasting conditions with and without ambient shear. The first technique is a generalisation of the two-point correlation function, where the correlation length-scale as well as the orientation can be extracted.The second technique identifies individual coherent structures and decomposes their vertical transport by the shape, size, and orientation of these objects. The bulk-correlation technique is shown to capture the elongation and orientation of coherence by ambient wind, but is unable to characterise individual coherent structures. Using the object-based approach, it is found that the individual structures dominating the vertical flux are plume-like in character (extending from the surface into cloud) rather than thermal-like, show small width/thickness asymmetry, and rise near-vertically in the absence of ambient wind. The planar stretching and tilting of boundary-layer structures caused by the introduction of ambient shear is also quantified, demonstrating the general applicability of the techniques for future study of other boundary-layer patterns.

We measured airborne exposures to the biological insecticide Bacillus thuringiensis var. kurstaki (Btk) during an aerial spray program to eradicate gypsy moths on the west coast of Canada. We aimed to determine whether staying indoors during spraying reduced exposures, to determine the rate of temporal decay of airborne concentrations, and to determine whether drift occurred outside the spray zone. During spraying, the average culturable airborne Btk concentration measured outdoors within the spray zone was 739 colony-forming units (CFU)/m3 of air. Outdoor air concentrations decreased over time, quickly in an initial phase with a half time of 3.3 hr, and then more slowly over the following 9 days, with an overall half-time of about 2.4 days. Inside residences during spraying, average concentrations were initially 2-5 times lower than outdoors, but at 5-6 hr after spraying began, indoor concentrations exceeded those outdoors, with an average of 244 CFU/m3 vs. 77 CFU/m3 outdoors, suggesting that the initial benefits of remaining indoors during spraying may not persist as outside air moves indoors with normal daily activities. There was drift of culturable Btk throughout a 125- to 1,000-meter band outside the spray zone where measurements were made, a consequence of the fine aerosol sizes that remained airborne (count median diameters of 4.3 to 7.2 microm). Btk concentrations outside the spray zone were related to wind speed and direction, but not to distance from the spray zone.

A food-waste initiative was conducted at two university canteens in the UK and India to examine food-waste attitudes and opportunities for food-waste reduction. Interventions were carried out to reduce food waste in both canteens. In the Indian canteen, postintervention data also included COVID-19-related changes, such as a change from self-service to table service, as well as reduced menu choices and an improved estimation of the number of students requiring meals. Surveys and focus groups were conducted with students to better understand their food-waste-related attitudes, while interviews were carried out with university staff to better understand food-waste management. The study in the UK university canteen found that introducing table cards, posters, and signs led to food-waste reductions of 13%. Meanwhile, the study in the Indian university canteen found that the interventions and COVID-19 impacts led to food-waste reductions of 50%. Concerning food-waste-related differences between the UK and India, culture and food preferences were key reasons for food waste in India, with 40.5% more participants in India stating that they wasted food because the ‘food didn’t taste good’. Students in India were more concerned about social issues and food poverty related to food waste, with around 9% more participants stating that the ‘food could be used by others’. Meanwhile, students in the UK were more bothered by the economic and environmental impacts of food waste, with around 31% more participants stating food waste is ‘a waste of money’, and is ‘bad for the environment’ when compared to India. Key opportunities for both countries included adopting food-sharing initiatives, informed menu choices, and meal planning, as well as student-led engagement projects.

Wind is a fundamental driver of the distribution and energy expenditure of birds at sea. Wind can also influence mortality at the nest. Yet airflows have never been fully integrated into models of breeding habitat selection. We use computational fluid dynamics to provide the first assessment of whether and how airflows predict the distribution of seabird colonies, taking common guillemots (Uria aalge) breeding on Skomer island as our study system. We reveal that air pressure predicts occupancy, demonstrating the importance of exposure (rather than wind speed) in habitat selection. Our simple model with pressure and slope correctly identified 80% of the largest colonies and 93% of avoided sites. While previous approaches have not predicted space use in novel sites, our model predicted 73% of the largest colonies on a neighbouring island. This suggests generality in the mechanisms linking airflows and breeding distributions, and highlights a novel route by which seabirds may be affected by global change.