A review of high impact weather for aviation meteorology

This review paper summarizes current knowledge available for aviation operations related to meteorology and provides suggestions for necessary improvements in the measurement and prediction of weather-related parameters, new physical methods for numerical weather predictions (NWP), and next-generation integrated systems. Severe weather can disrupt aviation operations on the ground or in-flight. The most important parameters related to aviation meteorology are wind and turbulence, fog visibility, aerosol/ash loading, ceiling, rain and snow amount and rates, icing, ice microphysical parameters, convection and precipitation intensity, microbursts, hail, and lightning. Measurements of these parameters are functions of sensor response times and measurement thresholds in extreme weather conditions. In addition to these, airport environments can also play an important role leading to intensification of extreme weather conditions or high impact weather events, e.g., anthropogenic ice fog. To observe meteorological parameters, new remote sensing platforms, namely wind LIDAR, sodars, radars, and geostationary satellites, and in situ instruments at the surface and in the atmosphere, as well as aircraft and Unmanned Aerial Vehicles mounted sensors, are becoming more common. At smaller time and space scales (e.g., < 1 km), meteorological forecasts from NWP models need to be continuously improved for accurate physical parameterizations. Aviation weather forecasts also need to be developed to provide detailed information that represents both deterministic and statistical approaches. In this review, we present available resources and issues for aviation meteorology and evaluate them for required improvements related to measurements, nowcasting, forecasting, and climate change, and emphasize future challenges

Growth and Characterization of BeO Thin Films Grown by Atomic Layer Deposition Using H2O and O3 as Oxygen Sources

Growth characteristics and properties of BeO films grown by atomic layer deposition (ALD) are investigated. ALD chemistries between dimethylberyllium and two different oxygen sources, H2O and O3, are governed by different reaction mechanisms, resulting in different film properties. At growth temperatures ranging from 150 to 300 ??C, the properties of the BeO films grown using H2O are temperature-independent. In contrast, the BeO films grown using O3 at low temperatures (&lt;200 ??C) show high concentrations of carbon and hydrogen, possibly owing to the incomplete removal of the ligands of the precursor, leading to a low film density. This correlates with the evolution of the rough surface and the microstructure composed of few nanometer-sized grains. The low-quality BeO films grown using O3 at low temperatures (&lt;200 ??C) show a decreased band gap (Eg: 7.7-7.9 eV) and dielectric constant (??r: 5.6-6.7). Above 250 ??C, these properties recovered to the levels (Eg ??? 9.4 eV and ??r ??? 8.1) of the BeO films grown using H2O, which show high values of Eg ??? 9.1-9.4 eV and ??r ??? 8. Collectively, these findings demonstrate that the O3-ALD process requires relatively more thermal energy than H2O-ALD does, to produce high-quality BeO films

Domain epitaxy of crystalline BeO films on GaN and ZnO substrates

We demonstrated the growth of wurtzite-crystalline beryllium oxide (BeO) thin films on GaN and ZnO substrates using atomic layer deposition (ALD). Single-crystalline BeO were epitaxially grown on GaN. Despite the inherently large lattice mismatch of BeO and GaN atoms, the 6/5 and 7/6 domain-matched structures dramatically reduced the residual strain in BeO thin films. On the other hand, the lattice mismatch of BeO and ZnO was not effectively accommodated in the mixed domains. X-ray diffraction (XRD) confirmed the in-plane crystallization of BeO-on-substrates in the (002){102}(BeO)||(002){102}(Sub) orientation and relaxation degrees of 20.8% (GaN), 100% (ZnO). The theoretical critical thicknesses of BeO for strain relaxation were 2.2 m (GaN) and 1.6 nm (ZnO), calculated using a total film energy model. Transmission electron microscopy (TEM) and Fourier-filtered imaging supported the bonding configuration and crystallinity of wurtzite BeO thin films on GaN and ZnO substrates

Crystal Properties of Atomic-Layer Deposited Beryllium Oxide on Crystal and Amorphous Substrates

We present the crystal properties of beryllium oxide (BeO) films on Si (100), GaN (001), and amorphous SiO2 substrates grown by atomic-layer deposition (ALD). Because of the strong bonding interactions intrinsic to beryllium, BeO thin films have been grown in crystalline phases regardless of the substrate type. Transmission electron microscopy revealed crystallized BeO films with small interfacial layers. The epitaxial relationships and domain-matching configurations were confirmed by crystal simulation. Using x-ray diffraction analyses, ALD BeO films with thicknesses of 50 nm showed wurtzite (002) crystal phases for all substrates studied. Raman spectroscopy confirmed that the crystallinity of the BeO film grown on GaN was superior to that on Si and SiO2 substrates. Atomic force microscopy and water contact angle goniometry measurements indicated that the BeO film grown on GaN in a planar mode was due to its low film energy

Atomic-Layer Deposition of Single-Crystalline BeO Epitaxially Grown on GaN Substrates

We have grown a single-crystal beryllium oxide (BeO) thin film on a gallium nitride (GaN) substrate by atomic-layer deposition (ALD) for the first time. BeO has a higher thermal conductivity, bandgap energy, and dielectric constant than SiO2. As an electrical insulator, diamond is the only material on earth whose thermal conductivity exceeds that of BeO. Despite these advantages, there is no chemical-vapor-deposition technique for BeO-thin-film deposition, and thus, it is not used in nanoscale-semiconductor-device processing. In this study, the BeO thin films grown on a GaN substrate with a single crystal showed excellent interface and thermal stability. Transmission electron microscopy showed clear diffraction patterns, and the Raman shifts associated with soft phonon modes verified the high thermal conductivity. The X-ray scan confirmed the out-of-plane single-crystal growth direction and the in-plane, 6-fold, symmetrical wurtzite structure. Single-crystalline BeO was grown on GaN despite the large lattice mismatch, which suggested a model that accommodated the strain of hexagonal-on-hexagonal epitaxy with 5/6 and 6/7 domain matching. BeO has a good dielectric constant and good thermal conductivity, bandgap energy, and single-crystal characteristics, so it is suitable for the gate dielectric of power semiconductor devices. The capacitance-voltage (C-V) results of BeO on a GaN-metal-oxide semiconductor exhibited low frequency dispersion, hysteresis, and interface-defect density

Long-term cloud condensation nuclei number concentration, particle number size distribution and chemical composition measurements at regionally representative observatories

Aerosol-cloud interactions (ACI) constitute the single largest uncertainty in anthropogenic radiative forcing. To reduce the uncertainties and gain more confidence in the simulation of ACI, models need to be evaluated against observations, in particular against measurements of cloud condensation nuclei (CCN). Here we present a data set - ready to be used for model validation - of long-term observations of CCN number concentrations, particle number size distributions and chemical composition from 12 sites on 3 continents. Studied environments include coastal background, rural background, alpine sites, remote forests and an urban surrounding. Expectedly, CCN characteristics are highly variable across site categories. However, they also vary within them, most strongly in the coastal background group, where CCN number concentrations can vary by up to a factor of 30 within one season. In terms of particle activation behaviour, most continental stations exhibit very similar activation ratios (relative to particles > 20 nm) across the range of 0.1 to 1.0% supersaturation. At the coastal sites the transition from particles being CCN inactive to becoming CCN active occurs over a wider range of the supersaturation spectrum. Several stations show strong seasonal cycles of CCN number concentrations and particle number size distributions, e. g. at Barrow (Arctic haze in spring), at the alpine stations (stronger influence of polluted boundary layer air masses in summer), the rain forest (wet and dry season) or Finokalia (wildfire influence in autumn). The rural background and urban sites exhibit relatively little variability throughout the year, while short-term variability can be high especially at the urban site. The average hygroscopicity parameter, kappa, calculated from the chemical composition of submicron particles was highest at the coastal site of Mace Head (0.6) and lowest at the rain forest station ATTO (0.2-0.3). We performed closure studies based on kappa-Kohler theory to predict CCN number concentrations. The ratio of predicted to measured CCN concentrations is between 0.87 and 1.4 for five different types of kappa. The temporal variability is also well captured, with Pearson correlation coefficients exceeding 0.87. Information on CCN number concentrations at many locations is important to better characterise ACI and their radiative forcing. But long-term comprehensive aerosol particle characterisations are labour intensive and costly. Hence, we recommend operating "migrating-CCNCs" to conduct collocated CCN number concentration and particle number size distribution measurements at individual locations throughout one year at least to derive a seasonally resolved hygroscopicity parameter. This way, CCN number concentrations can only be calculated based on continued particle number size distribution information and greater spatial coverage of longterm measurements can be achieved.Peer reviewe

Piezo1-Regulated Mechanotransduction Controls Flow-Activated Lymphatic Expansion

BackgroundMutations in PIEZO1 (Piezo type mechanosensitive ion channel component 1) cause human lymphatic malformations. We have previously uncovered an ORAI1 (ORAI calcium release-activated calcium modulator 1)-mediated mechanotransduction pathway that triggers lymphatic sprouting through Notch downregulation in response to fluid flow. However, the identity of its upstream mechanosensor remains unknown. This study aimed to identify and characterize the molecular sensor that translates the flow-mediated external signal to the Orai1-regulated lymphatic expansion.MethodsVarious mutant mouse models, cellular, biochemical, and molecular biology tools, and a mouse tail lymphedema model were employed to elucidate the role of Piezo1 in flow-induced lymphatic growth and regeneration.ResultsPiezo1 was found to be abundantly expressed in lymphatic endothelial cells. Piezo1 knockdown in cultured lymphatic endothelial cells inhibited the laminar flow-induced calcium influx and abrogated the flow-mediated regulation of the Orai1 downstream genes, such as KLF2 (Krüppel-like factor 2), DTX1 (Deltex E3 ubiquitin ligase 1), DTX3L (Deltex E3 ubiquitin ligase 3L,) and NOTCH1 (Notch receptor 1), which are involved in lymphatic sprouting. Conversely, stimulation of Piezo1 activated the Orai1-regulated mechanotransduction in the absence of fluid flow. Piezo1-mediated mechanotransduction was significantly blocked by Orai1 inhibition, establishing the epistatic relationship between Piezo1 and Orai1. Lymphatic-specific conditional Piezo1 knockout largely phenocopied sprouting defects shown in Orai1- or Klf2- knockout lymphatics during embryo development. Postnatal deletion of Piezo1 induced lymphatic regression in adults. Ectopic Dtx3L expression rescued the lymphatic defects caused by Piezo1 knockout, affirming that the Piezo1 promotes lymphatic sprouting through Notch downregulation. Consistently, transgenic Piezo1 expression or pharmacological Piezo1 activation enhanced lymphatic sprouting. Finally, we assessed a potential therapeutic value of Piezo1 activation in lymphatic regeneration and found that a Piezo1 agonist, Yoda1, effectively suppressed postsurgical lymphedema development.ConclusionsPiezo1 is an upstream mechanosensor for the lymphatic mechanotransduction pathway and regulates lymphatic growth in response to external physical stimuli. Piezo1 activation presents a novel therapeutic opportunity for preventing postsurgical lymphedema. The Piezo1-regulated lymphangiogenesis mechanism offers a molecular basis for Piezo1-associated lymphatic malformation in humans