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"Mitchell, David"
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Constraining a Radiative Transfer Model with Satellite Retrievals: Contrasts between cirrus formed via homogeneous and heterogeneous freezing and their implications for cirrus cloud thinning
The efficacy of the climate intervention method known as cirrus cloud thinning (CCT) is difficult to evaluate in climate models, largely due to uncertainties governing the relative contributions of homogeneous and heterogeneous ice nucleation. Here we take a different approach by employing recent satellite retrievals from the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) which provide estimates of the fraction of cirrus clouds dominated by homogeneous and heterogeneous ice nucleation and their associated physical properties. We employ a radiative transfer model (RTM) to quantify the cloud radiative effect for homogeneous and heterogeneous cirrus clouds at the top of atmosphere (TOA), Earth's surface, and within the atmosphere. The RTM experiments are initialized using cirrus microphysical profiles derived from CALIPSO retrievals for cirrus clouds dominated by homogeneous and heterogeneous ice nucleation across different regions (Arctic, Antarctic, and midlatitude) and surface types (ocean and land). We define two bounds: the lower bound assumes a full microphysical transition from the observed composition of homogeneous- and heterogeneous-dominated cirrus to only heterogeneous cirrus and production of new cirrus. The upper bound assumes production of new cirrus and that the atmospheric dynamics enables homogeneous freezing nucleation to occur regardless of the concentration of ice nucleating particles. Based on these bounds, we estimate an instantaneous surface effect ranging from −0.5 to +0.6 W m−2 and a TOA effect from −0.9 to +1.1 W m−2, respectively, showing the possibility of both cooling and warming. Recommendations are provided to improve the treatment of cirrus clouds in climate models.
Journal Article
Cloud atlas : a novel
Recounts the connected stories of people from the past and the distant future, from a nineteenth-century notary and an investigative journalist in the 1970s to a young man who searches for meaning in a post-apocalyptic world.
Book
Chemolithotrophic processes in the bacterial communities on the surface of mineral-enriched biochars
Biochar and mineral-enriched biochar (MEB) have been used as soil amendments to improve soil fertility, sequester carbon and mitigate greenhouse gas emissions. Such beneficial outcomes could be partially mediated by soil bacteria, however little is known about how they directly interact with biochar or MEB. We therefore analyzed the diversity and functions of bacterial communities on the surfaces of one biochar and two different MEBs after a 140-day incubation in soil. The results show that the biochar and the MEBs harbor distinct bacterial communities to the bulk soil. Communities on biochar and MEBs were dominated by a novel Gammaproteobacterium. Genome reconstruction combined with electron microscopy and high-resolution elemental analysis revealed that the bacterium generates energy from the oxidation of iron that is present on the surface. Two other bacteria belonging to the genus
Thiobacillus
and a novel group within the
Oxalbacteraceae
were enriched only on the MEBs and they had the genetic capacity for thiosulfate oxidation. All three surface-enriched bacteria also had the capacity to fix carbon dioxide, either in a potentially strictly autotrophic or mixotrophic manner. Our results show the dominance of chemolithotrophic processes on the surface of biochar and MEB that can contribute to carbon sequestration in soil.
Journal Article
Inclusive education is a multi-faceted concept
With the impetus of the UN Convention on the Rights of People with Disabilities, inclusive education is an idea whose time has arrived around the world. Its scope goes far beyond learners with disabilities and has now been extended to cover all learners with special educational needs, whatever their origins. It also extends beyond the mere placement of such learners in regular classes to include consideration of multiple facets of education. The present paper examines a model of inclusive education that, in addition to placement, embraces vision, curriculum, assessment, teaching, acceptance, access, support, resources and leadership. For each of these facets, criteria are specified and indicators are suggested. (DIPF/Orig.).
Journal Article
Propulsive nanomachines: the convergent evolution of archaella, flagella and cilia
ABSTRACT
Echoing the repeated convergent evolution of flight and vision in large eukaryotes, propulsive swimming motility has evolved independently in microbes in each of the three domains of life. Filamentous appendages – archaella in Archaea, flagella in Bacteria and cilia in Eukaryotes – wave, whip or rotate to propel microbes, overcoming diffusion and enabling colonization of new environments. The implementations of the three propulsive nanomachines are distinct, however: archaella and flagella rotate, while cilia beat or wave; flagella and cilia assemble at their tips, while archaella assemble at their base; archaella and cilia use ATP for motility, while flagella use ion-motive force. These underlying differences reflect the tinkering required to evolve a molecular machine, in which pre-existing machines in the appropriate contexts were iteratively co-opted for new functions and whose origins are reflected in their resultant mechanisms. Contemporary homologies suggest that archaella evolved from a non-rotary pilus, flagella from a non-rotary appendage or secretion system, and cilia from a passive sensory structure. Here, we review the structure, assembly, mechanism and homologies of the three distinct solutions as a foundation to better understand how propulsive nanomachines evolved three times independently and to highlight principles of molecular evolution.
This review contrasts the mechanism and evolution of the superficially similar – yet entirely unrelated – “flagella\" in microbes from all three domains of life: archaeal archaella, bacterial flagella and eukaryotic cilia.
Journal Article
Advances in CALIPSO (IIR) cirrus cloud property retrievals – Part 2: Global estimates of the fraction of cirrus clouds affected by homogeneous ice nucleation
Cirrus clouds can form through two ice nucleation pathways (homo- and heterogeneous ice nucleation; henceforth hom and het, respectively) that result in very different cloud physical and radiative properties. While important to the climate system, they are poorly understood due to lack of knowledge on the relative roles of hom and het. This study differs from earlier relevant studies by estimating the relative radiative contribution of hom-affected cirrus clouds. Here, we employ new global retrievals (described in Part 1: Mitchell et al., 2025; henceforth M2025) of cirrus cloud ice particle number concentration, effective diameter (De), ice water content (IWC), shortwave extinction coefficient (αext), optical depth (τ) and cloud radiative temperature based on Imaging Infrared Radiometer (IIR) and Cloud and Aerosol Lidar with Orthogonal Polarization (CALIOP) co-located observations onboard Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO). Transition from het dominated to hom-affected regimes are identified using αext and De. Over oceans outside the tropics in winter, the zonal fraction of hom-affected cirrus generally ranges between 20 % and 35 %, with comparable contributions from in situ and warm base cirrus. Using τ distributions to establish a proxy for net cloud radiative effect (CRE), the τ-weighted fraction for hom-affected cirrus over oceans outside the tropics during winter was > 50 %, indicating that hom cirrus play an important role in climate. Using these retrievals (including those relating to the cloud geometric thickness), a conceptual model of cirrus cloud characterization is proposed.
Journal Article