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Despite extensive research on attainment grouping, the impact of attainment grouping on pupil attainment remains poorly understood and contested. This paper presents evidence from a study conducted with 2944 12–13 year olds, from 76 schools in England, who were allocated to between-class attainment groups (‘setting’) in English and mathematics over the first 2 years of secondary schooling. After controlling for prior attainment, pupils in the top set performed significantly better than pupils in the middle and bottom sets in both English and mathematics. The findings indicate a widening gap in attainment, especially in the case of English. Findings, especially in the case of mathematics, provide more evidence of a relative benefit for pupils placed in top sets than a relative detriment for those in bottom sets. Education Endowment Foundation (EEF)

Wellbeing declines during adolescence, for which the reasons are unclear. This analysis explored associations between wellbeing and multiple lifestyle, socioeconomic and school-level factors in young people. Data were collected as part of the Wellbeing in School (WiSe) survey of adolescent school children in Northern Ireland at age 13–14 years (N = 1618; 49% female) and 15–16 years (N = 1558; 50.5% female). Wellbeing was assessed using the short-form Warwick-Edinburgh Mental Wellbeing Scale (sWEMWBS), where scores declined between time one (13–14 years) and time two (15–16 years) in both sexes and were significantly lower in females at both timepoints. Multilevel, multivariate modelling was therefore undertaken separately for males and females with sWEMWBS scores as the dependent variable. Physical activity, family affluence, fruit and vegetable intake, social media use, sleep duration, school factors (size and type) and religion were independent variables. More frequent physical activity in both sexes at both timepoints was associated with higher sWEMWBS scores. In females, higher sWEMWBS scores were associated with less social media use at time one (and marginally at time two), greater family affluence at time two, and being Catholic at both timepoints. In males, higher sWEMWBS scores were associated with more frequent fruit and vegetable intake at time one. Mental wellbeing was unrelated to sleep duration or school factors in either sex, at both time points. Efforts to maximize mental wellbeing in adolescents should promote engagement in physical activity and implement sex-specific interventions.

Earlier chapters of this work have described procedures and protocols that are applicable to most chambers, this chapter has a slightly different focus; we predominantly consider multiphase processes where the applications are on phase transfer of chemical species rather than chemical reactions and the processes are generally occurring in highly specialized chambers. Three areas are described. Firstly, cloud formation processes; here, precise control of physical and thermodynamic properties is required to generate reproducible results. The second area examined is the air/sea interface, looking at the formation of aerosols from nonanoic acid as a surfactant with humic acid as a photosensitizer. The final apparatus described is the Roland von Glasow sea-ice chamber where a detailed protocol for the reproducible formation of sea-ice is given along with an outlook of future work. The systems studied in all three sections are characterized by difficulties in making detailed in situ observations in the real world, either due to the transitory nature of systems or the practical difficulties in accessing the systems. While these specialized simulation chambers may not perfectly reproduce conditions in the real world, the chambers do provide more facile opportunities for making extended and reproducible measurements to investigate fundamental physical and chemical processes, at significantly lower costs.

We provide the first dedicated laboratory study of collisions of supercooled water drops with ice particles as a secondary ice production mechanism. We experimentally investigated collisions of supercooled water drops (∼ 5 mm in diameter) with ice particles of a similar size (∼ 6 mm in diameter) placed on a glass slide at temperatures >-12 ∘C. Our results showed that secondary drops were generated during both the spreading and retraction phase of the supercooled water drop impact. The secondary drops generated during the spreading phase were emitted too fast to quantify. However, quantification of the secondary drops generated during the retraction phase with diameters >0.1 mm showed that 5–10 secondary drops formed per collision, with approximately 30 % of the secondary drops freezing over a temperature range between −4 and −12 ∘C. Our results suggest that this secondary ice production mechanism may be significant for ice formation in atmospheric clouds containing large supercooled drops and ice particles.

There is wide ranging research that uses innovative methods to seek the views of children in out-of-home care. In the area of education, this group of children increasingly participate in research that involves various educational interventions (including book-gifting, tutoring, paired reading), that are designed to improve their educational attainment and achievements. Despite the overall growth in research evidence, there remains an absence of widely reported research on children’s views of the educational interventions that they are involved in and secondly, an absence of more reflective contributions that outline the methodological opportunities and challenges involved. This paper makes a contribution to both areas by reporting both the findings of and critical reflections on the use of an innovative method, the Talking Album, to gather the views of young children, aged 7–9 years old, regarding a reading intervention they were involved in, known as the Reading Together programme. The methodological approach is outlined. Informed by the basic principles underpinning children’s rights as set out in the UNCRC, key learning on the selection, introduction, and support of such methods/tools is reflected upon. From the findings and reflections, recommendations for future research that concerns interventions with children are made.

In a national and international context where there is a concern about the effectiveness of social care services for children and families to address chronic, enduring social problems and where there are finite resources available, the concept of social innovation in social work policy and practice to address need in new ways is receiving increased attention. Whilst an attractive term, social innovation in child and family services is not without its challenges in terms of conceptualisation, operationalisation, implementation and evidencing impact. This article reports on the development and evaluation of the Early Intervention Support Service (EISS), a newly designed family support service in Northern Ireland set up as part of a government-supported innovation and transformation programme that aims to deliver a voluntary, targeted, flexible and time-limited service to families experiencing emergent problems. Using the EISS as a case study, the challenges, benefits in terms of addressing policy imperatives and future direction of social innovation in social work practice are reflected upon.

This article provides an overview of selected ongoing international efforts that have been inspired by Edward Zigler's vision to improve programs and policies for young children and families in the United States. The efforts presented are in close alignment with three strategies articulated by Edward Zigler: (a) conduct research that will inform policy advocacy; (b) design, implement, and revise quality early childhood development (ECD) programs; and (c) invest in building the next generation of scholars and advocates in child development. The intergenerational legacy left by Edward Zigler has had an impact on young children not only in the United States, but also across the globe. More needs to be done. We need to work together with a full commitment to ensure the optimal development of each child.

The impact of self-fulfilling prophecy in education, and of attainment grouping on pupil self-perception, remain topics of longstanding debate, with important consequences for social in/justice. Focusing on self-confidence, this article draws on survey responses from 9,059 12-13 year olds who were tracked by subject (‘setting’). They provided survey responses when placed in ‘ability’ sets at the start of their secondary schooling, and again late the following year; enabling analysis of impact over time. After controlling for prior attainment, the gap in general self-confidence between students in the top and bottom sets for mathematics is shown to widen over time, and high set students’ self-confidence in English had also grown significantly; although there was not further widening in the cases of self-confidence in mathematics or in general self-confidence between students in the top and bottom sets for English. Implications of these findings for interventions directed at addressing educational disadvantage are discussed. © 2020, © 2020 Informa UK Limited, trading as Taylor & Francis Group.

Compact Space-Bandwidth Angular Spectrum Method (CSW-ASM) is introduced for a high resolution reconstruction of digital in-line holograms with spherical wave illumination solving the distortion issue observed when using an ASM with planar reconstruction wave approach.

The terminal velocity (Vt) of ice hydrometeors is of high importance to atmospheric modeling. Vt is governed by the physical characteristics of a hydrometeor, including mass and projected area, as well as environmental conditions. When liquid hydrometeors coalesce to form larger hydrometeors, the resulting hydrometeor can readily be characterized by its spherical or near-spherical shape. For ice hydrometeors, it is more complicated because of the variability of ice shapes possible in the atmosphere as well as the inherent randomness in the aggregation process, which leads to highly variable characteristics. The abundance of atmospheric processes affecting ice particle dimensional characteristics creates potential for highly variable Vt for ice particles that are predicted or measured to be of the “same size.” In this article we explore the variability of ice hydrometeor Vt both theoretically and through the use of experimental observations. Theoretically, the variability in Vt is investigated by analyzing the microphysical characteristics of randomly aggregated hexagonal shapes. The modeled dimensional characteristics are then compared to aircraft probe measurements to constrain the variability in atmospheric ice hydrometeor Vt. Results show that the spread in Vt can be represented with Gaussian distributions relative to a mean. Variability expressed as the full width at half maximum of the normalized Gaussian probability distribution function is around 20%, with somewhat higher values associated with larger particle sizes and warmer temperatures. Field campaigns where mostly convective clouds were sampled displayed low variability, while Arctic and midlatitude winter campaigns showed broader Vt spectra.

This work presents new laboratory data investigating collisions between supercooled drops and ice particles as a source of secondary ice particles in natural clouds. Furthermore we present numerical model simulations to put the laboratory measurements into context.Secondary ice particles form during the breakup of freezing drops due to so-called “spherical freezing” (or Mode 1), where an ice shell forms around the freezing drop. This process has been studied and observed for drops in free-fall in laboratory experiments since the 1960s, and also more recently by Lauber et al. (2018) with a high-speed camera. Aircraft field measurements (Lawson et al. 2015) and lab data (Kolomeychuk et al. 1975) suggest that such a process is dependent on the size of drops, with larger drops being more effective at producing secondary ice. Collision induced break-up of rain drops has been well studied with pioneering investigations in the mid-1980s, and numerous modelling studies showing that it is responsible for observed trimodal rain drop size distributions in the atmosphere, which can be well approximated by an exponential distribution. In mixed-phase clouds we know that rain-drops can collide with more massive ice particles. This, depending on the type of collision, may lead to the break-up of the supercooled drop (e.g. as hinted by Latham and Warwicker, 1980), potentially stimulating secondary ice formation (Phillips et al. 2018 - non-spherical, Mode 2). There is a dearth of laboratory data investigating this mechanism. This mechanism is the focus of the presentation.Here we present the results of recent experiments where we make use of the University of Manchester (UoM) cold room facility. The UoM cold room facility consists of 3 stacked cold rooms that can be cooled to temperatures below -55 degC. A new facility has been built to study secondary ice production via Mode 2 fragmentation. We generate supercooled drops at the top of the cold rooms and allow them to interact with different ice surfaces near the bottom. This interaction is filmed with a new camera setup.Our latest results will be presented at the conference.ReferencesKolomeychuk, R. J., D. C. McKay, and J. V. Iribarne. 1975. “The Fragmentation and Electrification of Freezing Drops.” Journal of the Atmospheric Sciences 32 (5): 974–79. https://doi.org/10.1175/1520-0469(1975)0322.0.CO;2.Latham, J., and R. Warwicker. 1980. “Charge Transfer Accompanying the Splashing of Supercooled Raindrops on Hailstones.” Quarterly Journal of the Royal Meteorological Society 106 (449): 559–68. https://doi.org/10.1002/qj.49710644912.Lauber, Annika, Alexei Kiselev, Thomas Pander, Patricia Handmann, and Thomas Leisner. 2018. “Secondary Ice Formation during Freezing of Levitated Droplets.” Journal of the Atmospheric Sciences 75 (8): 2815–26. https://doi.org/10.1175/JAS-D-18-0052.1.Lawson, R. Paul, Sarah Woods, and Hugh Morrison. 2015. “The Microphysics of Ice and Precipitation Development in Tropical Cumulus Clouds.” Journal of the Atmospheric Sciences 72 (6): 2429–45. https://doi.org/10.1175/JAS-D-14-0274.1.

Young people choose energy-dense, nutrient-poor diets, yet understanding of potential determinants is limited. Associations between food choices, mental wellbeing, health-related quality of life (HRQoL) and family affluence were explored to identify targets for intervention to promote dietary health and wellbeing in young people. Adolescents were recruited via post-primary schools in the UK and surveyed at two time-points when aged 13-14 years and 15-16 years. The questionnaire enquired about mental wellbeing using the Short Warwick-Edinburgh Mental Wellbeing Scale, HRQoL using the KIDSCREEN-10, socio-economic status using the Family Affluence Scale and food choice by Food Frequency Questionnaire (FFQ). With missing and anomalous cases excluded, the sample comprised 1208 cases. Factor analysis on the FFQ indicated five food choice factors: 'Junk Food'; 'Meat'; 'Healthy Protein'; 'Fruit/Vegetables'; 'Bread/Dairy'. Multivariate regression analysis indicated that frequent consumption of Junk Food was associated with being male and lower mental wellbeing. Frequent Meat intake was associated with being male and with lower HRQoL. Frequent choice of Bread/Dairy foods was more common among males and associated with higher wellbeing and greater affluence. Those who consumed Fruit/Vegetables frequently were more likely to be female, have higher HRQoL, higher mental wellbeing, and greater family affluence. These direct associations endured between time points. The dietary factors were not mutually exclusive. Those who frequently chose Junk Food were less likely to choose Fruit/Vegetables. Frequent choice of Meat was associated with more frequent choice of Junk Food and Healthy Protein. Intervention to improve dietary and psychological health in young people should target males, those in less affluent households, seek to reduce consumption of 'junk' food, and increase fruit and vegetable intake.

Millions of children worldwide will not reach their potential in terms of education and development. However, it is widely known that investment in high-quality early childhood development (ECD) pays rich dividends throughout the lifespan of an individual, impacting their own lives, families, and communities in a positive way. Further evidence points to the importance of ECD in delivering the United Nations’ Sustainable Development Goals (SDGs). The multi-sectoral, integrated provision of ECD services is ideally placed to facilitate holistic positive change and enhance social cohesion in some of the most inequitable and vulnerable contexts. The LINKS project brings together an international network of researchers, who work in strategic partnership with United Nations Children’s Fund (UNICEF) and Early Years the Organisation for Young Children in Northern Ireland to support the development, implementation, and evaluation of ECD programs in low- and middle-income countries impacted by divisions and conflict. The project is designed to contribute to the international evidence base on ECD for social cohesion and sustaining peace to make a real difference in the lives of children, caregivers, and communities.

The aerosol–radiation–meteorology feedback loop is the process by which aerosols interact with solar radiation to influence boundary layer meteorology. Through this feedback, aerosols cause cooling of the surface, resulting in reduced buoyant turbulence, enhanced atmospheric stratification and suppressed boundary layer growth. These changes in meteorology result in the accumulation of aerosols in a shallow boundary layer, which can enhance the extent of aerosol–radiation interactions. The feedback effect is thought to be important during periods of high aerosol concentrations, for example, during urban haze. However, direct quantification and isolation of the factors and processes affecting the feedback loop have thus far been limited to observations and low-resolution modelling studies. The coupled large-eddy simulation (LES)–aerosol model, the University of California, Los Angeles large-eddy simulation – Sectional Aerosol Scheme for Large Scale Applications (UCLALES-SALSA), allows for direct interpretation on the sensitivity of boundary layer dynamics to aerosol perturbations. In this work, UCLALES-SALSA has for the first time been explicitly set up to model the urban environment, including addition of an anthropogenic heat flux and treatment of heat storage terms, to examine the sensitivity of meteorology to the newly coupled aerosol–radiation scheme. We find that (a) sensitivity of boundary layer dynamics in the model to initial meteorological conditions is extremely high, (b) simulations with high aerosol loading (220 µg m−3) compared to low aerosol loading (55 µg m−3) cause overall surface cooling and a reduction in sensible heat flux, turbulent kinetic energy and planetary boundary layer height for all 3 d examined, and (c) initial meteorological conditions impact the vertical distribution of aerosols throughout the day.

Prior research suggests that where pupils are 'tracked', better qualified, more experienced teachers tend to be deployed to higher attainment groups, at the expense of pupils in lower tracks. This is especially pertinent from a social justice perspective, given consistent findings in the UK that pupils from socially-disadvantaged backgrounds are over-represented in low attainment groups. This article draws on data from 380 teachers, drawn from 126 secondary schools in England, and interviews with 118 Year 7 students, to examine whether these findings from prior research in the US and elsewhere extend to the case of England in the present day. Findings show some evidence of these inequitable tendencies: those teachers highly qualified in their taught subject were less likely to be allocated to low sets. We also examine whether an intervention designed to encourage more equitable distribution had any impact on practice, and find tentative evidence that deployment in intervention schools had been impacted in relation to teacher subject qualifications. Pupils believed that teachers of higher sets had higher expectations and standards of behaviour, whereas those for low sets were seen to be unhelpfully indulgent, indicating a need for research attention to pedagogy and tracking. Findings are analysed from a social justice perspective, with interest in the consequences of inequitable distribution of teachers for the reproduction of social inequality.

A new parameterisation for the cloud droplet activation of multiple aerosol modes is presented that includes the effects of the co-condensation of semi-volatile organic compounds (SVOCs). The novel work comes from the dynamic condensation parameterisation that approximates the partitioning of the SVOCs into the condensed phase at cloud base. The dynamic condensation parameterisation differs from equilibrium absorptive partitioning theory by calculating time-dependent condensed masses that depend on the updraft velocity. Additionally, more mass is placed on smaller particles than at equilibrium, which is in better agreement with parcel model simulations. All of the SVOCs with saturation concentrations below 1×10−3 µg m−3 are assumed to partition into the condensed phase at cloud base, defined as 100 % relative humidity, and the dynamic condensation parameterisation is used to distribute this mass between the different aerosol modes. An existing cloud droplet activation scheme is then applied to the aerosol particles at cloud base with modified size distributions and chemical composition to account for the additional mass of the SVOCs. Parcel model simulations have been performed to test the parameterisation with a range of aerosol size distributions, composition, and updrafts. The results show excellent agreement between the parameterisation and the parcel model and the inclusion of the SVOCs does not degrade the performance of the underlying cloud droplet activation scheme.

Background: The use of randomised controlled trials (RCTs) in education has increased significantly over the last 15 years. However, their use has also been subject to sustained and rather trenchant criticism from significant sections of the education research community. Key criticisms have included the claims that: it is not possible to undertake RCTs in education; RCTs are blunt research designs that ignore context and experience; RCTs tend to generate simplistic universal laws of ‘cause and effect’; and that they are inherently descriptive and contribute little to theory.\ud \ud Purpose: This article seeks to assess the above four criticisms of RCTs by considering the actual evidence in relation to the use of RCTs in education in practice.\ud \ud Design and methods: The article is based upon a systematic review that has sought to identify and describe all RCTs conducted in educational settings and including a focus on educational outcomes between 1980 and 2016. The search is limited to articles and reports published in English.\ud \ud Results: The systematic review found a total of 1017 unique RCTs that have been completed and reported between 1980 and 2016. Just over three quarters of these have been produced over the last 10 years, reflecting the significant increase in the use of RCTs in recent years. Overall, just over half of all RCTs identified were conducted in North America and a little under a third in Europe. The RCTs cover a wide range of educational settings and focus on an equally wide range of educational interventions and outcomes. The findings not only disprove the claim that it is not possible to do RCTs in education but also provide some supporting evidence to challenge the other three key criticisms outlined earlier.\ud \ud Conclusions: While providing evidence to counter the four criticisms outlined earlier, the article suggests that there remains significant progress to be made. The article concludes by outlining some key challenges for researchers undertaking RCTs in education.

We present a novel method of exploring the effect of uncertainties in aerosol properties on cloud droplet number using existing cloud droplet activation parameterisations. Aerosol properties of a single involatile particle mode are randomly sampled within an uncertainty range and resulting maximum supersaturations and critical diameters calculated using the cloud droplet activation scheme. Hygroscopicity parameters are subsequently derived and the values of the mean and uncertainty are found to be comparable to experimental observations. A recently proposed cloud droplet activation scheme that includes the effects of co-condensation of semi-volatile organic compounds onto a single lognormal mode of involatile particles is also considered. In addition to the uncertainties associated with the involatile particles, concentrations, volatility distributions and chemical composition of the semi-volatile organic compounds are randomly sampled and hygroscopicity parameters are derived using the cloud droplet activation scheme. The inclusion of semi-volatile organic compounds is found to have a significant effect on the hygroscopicity and contributes a large uncertainty. For non-volatile particles that are effective cloud condensation nuclei, the co-condensation of semi-volatile organic compounds reduces their actual hygroscopicity by approximately 25 %. A new concept of an effective hygroscopicity parameter is introduced that can computationally efficiently simulate the effect of semi-volatile organic compounds on cloud droplet number concentration without direct modelling of the organic compounds. These effective hygroscopicities can be as much as a factor of two higher than those of the non-volatile particles onto which the volatile organic compounds condense.

The natural variability of gastric pH or gastric acid reducing medications can result in lower and more variable clinical pharmacokinetics for basic compounds in patient populations. Progressing alternative salt forms with improved solubility and dissolution properties can minimise this concern. This manuscript outlines a nonclinical approach comprising multiple biopharmaceutical, in vitro and physiologically based pharmacokinetic model (PBPK) modelling studies to enable selection of an alternative salt form for danirixin (DNX, GSK1325756), a pharmaceutical agent being developed for chronic obstructive pulmonary disease (COPD). The hydrobromide salt of DNX was identified as having superior biopharmaceutical properties compared to the free base (FB) form in clinical development and the impact of switching to the hydrobromide salt (HBr) was predicted by integrating the nonclinical data in a PBPK model (using GastroPlus™) to enable simulation of clinical drug exposure with FB and HBr salts in the absence and presence of a gastric acid reducing comedication (omeprazole, a proton pump inhibitor (PPI)). Subsequent investigation of DNX pharmacokinetics in a Phase 1 clinical study comparing FB with HBr salt forms confirmed that DNX HBr had reduced the variability of drug exposure and that exposure was not affected by PPI co-administration with DNX HBr. This case study therefore adds to the surprisingly few examples of a more soluble salt of a weak base translating to an improvement in human pharmacokinetics and illustrates a clear clinical benefit of salt selection during drug development.

Computational models of cloud formation typically use homogeneous nucleation to predict the ice nucleated in supercooled water. However, the existence of ultra-viscous organic aerosol in the upper troposphere has offered alternative ice nucleation pathways, which have been observed in laboratory studies. The possible effects of aerosol viscosity on cloud microphysical properties have traditionally been interpreted from simple model simulations of an individual aerosol particle based on equilibration timescales. In this study, to gain insight into the formation of ice in an ensemble of ultra-viscous aerosol particles, we have developed the first cloud parcel model with bin microphysics to simulate condensed phase diffusion through each individual aerosol particle. Our findings demonstrate, for the first time, the complex relationship between the rate of ice formation and the viscosity of secondary organic aerosol, driven by two competing effects – which cannot be explained using existing modelling approaches. The first is inhibition of homogeneous ice nucleation below 200 K, due to restricted particle growth and low water volume. The second occurs at temperatures between 200 and 220 K, where water molecules are slightly more mobile, and a layer of water condenses on the outside of the particle, causing an increase in the number of frozen aerosol particles. Our new model provides a basis to better understand and simulate ice cloud formation on a larger scale, addressing a major source of uncertainty in climate modelling through the representation of microphysical cloud processes.

Numerous turbofan power-loss events have occurred in high altitude locations in the presence of ice crystals. It is theorized that ice crystals enter the engine core, partially melt in the compressor and then accrete onto stator blade surfaces. This may lead to engine rollback, or shed induced blade damage, surge and/or flameout. The first generation of ice crystal icing predictive models use a single flow field where there is no accretion to calculate particle trajectories and accretion growth rates. Recent work completed at the University of Oxford has created an algorithm to automatically detect the edge of accretion from experimental video data. Using these accretion profiles, numerical simulations were carried out at discrete points in time using a manual meshing process. That work showed that flow field changes caused by a changing accretion profile had significant effects on the collection efficiency of impinging particles, ultimately affecting the mass of accreted ice and its shape. This paper discusses the development of the ICICLE numerical ice crystal icing code to include a fully automated two-way coupling between the accretion profile and flow field solution, to account for these effects. The numerical strategy; geometry redefinition, mesh update and flow field solution are discussed, followed by a comparison to experimental ice accretion of a simple 2D geometry and model predictions with and without flow field updating. The results showed that significant changes in leading edge accretion profiles were numerically predicted when the only the geometry was updated. Further changes then occurred when the flowfield was also updated.

Drawing upon data gathered from 9301 Year 7 students (12–13 years old) from 46 secondary schools in England, this study represents the first larger‐scale attempt to compare their actual set allocations in maths with the counterfactual position where their allocation to sets is based solely on their prior attainment at the end of primary school [using their Key Stage 2 (KS2) fine‐grained scores in maths]. Through such an analysis, the study found that nearly a third of students (31.2%) had been misallocated to lower or higher sets than their KS2 results would have warranted. Beyond this, school setting practices were found to exacerbate differences in set allocation in relation to gender and ethnicity, but not socioeconomic background. The odds of girls being misallocated to lower sets in maths than their prior attainment would warrant was found to be 1.5 times higher than that for boys. Similarly, the odds of Black students being misallocated to lower sets was 2.4 times higher than for White students, whilst the odds of Asian students being misallocated to lower maths sets was 1.7 times higher than for White students. The article concludes by reflecting on the significant role that setting by attainment in secondary school can play in exacerbating already established patterns of educational inequalities in gender and ethnicity.

Network science approaches can enhance global and national coordinated efforts to prevent and manage non-communicable diseases, say Ruth Hunter and colleagues

In-situ studies of low temperature cirrus clouds have found unexpectedly low ice crystal numbers and consistently high supersaturations, which suggest that our understanding of the freezing mechanisms under these conditions are incomplete. Computational models typically use homogeneous nucleation to predict the ice nucleated in supercooled water. However, the existence of ultra-viscous organic aerosol in the upper troposphere has offered alternative ice nucleation pathways, which have been observed in laboratory studies. The possible effects of aerosol viscosity on cloud micro-physical properties have traditionally been interpreted from simple model simulations of an individual aerosol particle based on equilibration timescales. In this study, to gain insight into the formation of ice in low temperature cirrus clouds, we have developed the first cloud parcel model with bin micro-physics to simulate condensed phase diffusion through each individual aerosol particle. Our findings demonstrate, for the first time, the complex relationship between the rate of ice formation and the viscosity of secondary organic aerosol, driven by two competing effects – which cannot be explained using existing modelling approaches. The first is inhibition of homogeneous ice nucleation below 200 K, due to restricted particle growth and low water volume. The second occurs at temperatures between 200 K and 220 K, where water molecules are slightly more mobile and a layer of water condenses on the outside of the particle, causing an increase in the number of frozen aerosol particles. Our new model provides a basis to better understand and simulate cirrus cloud formation on a larger scale, addressing a major source of uncertainty in climate modelling through the representation of cloud processes.

Microscopic droplet riming events on an ice surface have been observed using high speed video. Observations included greater propensity for droplet spreading at temperatures higher than − 15 °C on flatter ice surfaces, and subsequently, the formation of growing rime spires into the flow, allowing glancing droplet collisions and more spherical freezing of smaller droplets. Insight into differences between laboratory observations of the Hallett-Mossop process is offered, relating to the nature of droplet spreading associated with the structure of the rimer surface prior to impact. Observations of a difference between air speed and resulting droplet impact speed on an ice surface may affect interpretations of riming laboratory studies, and may explain recent observations of a high secondary ice production rate in supercooled layer clouds.