Additive Manufacturing (AM) using stereolithography (SLA) was applied to produce engine O-rings using two different flexible polymer printing materials, Flex 80A and Elastic 50A. Print orientation of the O-ring in the SLA 3D printer is important, with the horizontal configuration most commonly providing for the smoothest final O-ring printed surface due to the lack of printing support tabs required. AM printing tabs lead to O-ring ‘marks’ (non-smooth surfaces) that were evaluated using the Society of Automotive Engineers SAE AS871B standard. It was seen that numerous printing approaches produced ‘marks’ that were larger than acceptable, which shows that these studied AM processes can not replace traditional methods of O-ring manufacture. However, further evaluation was pursued to explore possible remote emergency usage of these O-rings. Printed O-rings were next tested-soaked in engine related fluids in order to characterize O-ring swelling behavior. Volume swelling was greatest with acetone (100% plus increase) for both the stock O-rings tested and moderately less so with the 3D printed O-rings. Flex 80A printing material swelling was moderately less than using Elastic 50A printing material. Swell testing using motor oil and engine fuels showed significantly less swelling with volume change increases on the order of ten to fifteen percent. Pressure vessel and engine-based testing was also performed with the printed O-rings demonstrating good performance (no leaks) under operation, suggesting that shorter term emergency-based operation using these AM printed O-rings may be acceptable.

This work explored the effect of military jet (JP-5) and diesel (F-76) fuels, surrogate mixtures, and pure compounds on the swelling and tensile strength of additively-manufactured (AM) acrylate O-rings and commerciallyproduced acrylate, nitrile, and Ford Motorcraft O-rings. The composition of the fuel was determined using twodimensional gas chromatography (GC x GC) and the uptake of the organic compounds from surrogate mixtures into the AM O-rings was determined using gas chromatography. Exposure of the O-rings to various organic mixtures for 7 days produced volume changes that ranged from -3 to 155% for AM O-rings, 0 to 130% for commercial acylate O-rings, 1 to 260% for Buna-N O-rings, and -4 to 3% for Ford Motorcraft O-rings. The greatest swellings were found for the aromatic compounds followed by the cycloalkanes. JP-5 and F-76 fuels caused the AM O-rings to swell by 15.2 and 11.6%, respectively. A jet fuel surrogate containing 10% dodecane, 51% isocetane, 15% butylbenzene and 24% butylcyclohexane produced a similar swell (14.9%) to that of the JP5, which contained 10.9% aromatics, 5.6% cycloaromatics, and 25% cycloalkanes. Diesel fuel surrogates containing 1-methylnapthalene produced much higher swells in the AM polymers (greater than 22%) than did the diesel fuel, illustrating that while this component may be good for enabling diesel surrogates to emulate the physical and combustion properties of diesel fuel, it also comes with increased swelling. Tensile strengths of the swollen O-rings were reduced by as much 90%. Evaporation of the fuels and components from the O-rings for more than 3 weeks returned most of the O-rings to their original size and tensile strength, suggesting that the short-term exposure did not adversely affect the O-rings.

Research aircraft measurements of detailed microphysical properties of mid-latitude cirrus, mid-latitude anvil and tropical anvil clouds are discussed. A cloud particle imager (CPI) and standard optical probes are used to generate composite particle size distributions, ice water content, effective radius, extinction coefficient and particle habit in 13 mid-latitude cirrus clouds. Over 250,000 ice particles are classified by crystal habit. The measurements show that the predominant crystal type by number in anvils is small spheroidal particles, occurring in concentrations from 0.1 to 5 cm. In cirrus, the predominant crystal type, weighted by mass is the bullet rosette. Cirrus microphysical properties are compared with mid-latitude and tropical anvils, which are found to have one to two orders of magnitude higher concentrations of ice crystals. Bullet rosettes are rare in anvils. Chains of small ice particles, aggregates and complex crystals are common in mid-latitude anvils, but far less-common in tropical anvils. The difference may be a function of the higher electric fields in mid-latitude anvils, which may also lead to the formation of chains of small ice particles.

The atmospheric boundary layer (ABL) height (zi) over complex, forested terrain is estimated based on the power spectra and the integral length scale of cross-stream winds obtained from a three-axis sonic anemometer during the two summers of the BEARPEX (Biosphere Effects on Aerosol and Photochemistry) Experiment. The zi values estimated with this technique show very good agreement with observations obtained from balloon tether sondes (2007) and rawinsondes (2009) under unstable conditions (z/L < 0) at the coniferous forest in the California Sierra Nevada. On the other hand, the low frequency behavior of the streamwise upslope winds did not exhibit significant variations and was therefore not useful in predicting boundary layer height. The behavior of the nocturnal boundary layer height (h) with respect to the power spectra of the v-wind component and temperature under stable conditions (z/L > 0) is also presented. The nocturnal boundary layer height is found to be fairly well predicted by a recent interpolation formula proposed by Zilitinkevich et al. (2007), although it was observed to only vary from 60–80 m during the 2009 experiment in which it was measured. Finally, significant directional wind shear was observed during both day and night soundings. The winds were found to be consistently backing from the prevailing west-southwesterlies within the ABL (the anabatic cross-valley circulation) to southerlies in a layer ~1–2 km thick just above the ABL before veering to the prevailing westerlies further aloft. This shear pattern is shown to be consistent with the forcing of a thermal wind driven by the regional temperature gradient directed east-southeast in the lower troposphere.

The spacing of cloud droplets observed along an approximately horizontal line through a cloud may be analyzed using a variety of techniques to reveal structure on small scales, sometimes called clustering, if such structure exists. A number of techniques have been applied and others have been suggested but not yet rigorously defined and applied. In this paper techniques are studied and evaluated using synthetic droplet spacing data. For the type of small-scale structure (clustering) modeled in this study, the most promising analysis approach is to use a combination of the power spectrum and the fishing statistic. Standard deviations and confidence intervals are determined for the power spectrum, the pair correlation function, and a modified fishing statistic. The clustering index and the volume-averaged pair correlation are shown to be less usefully normalized forms of the fishing statistic.

Data from the new two-dimensional stereo (2D-S) probe are used to evaluate drop size distributions in rain shafts observed during the Rain in Shallow Cumulus over the Ocean (RICO) experiment. The 2D-S takes images of both precipitation drops and cloud droplets with 10-mm resolution. These are the first reported measurements of rain to include sizes smaller than 100 mm. The primary result is that there are almost no hydrometeors smaller than about 100 mm in these rain shafts. The measured low concentration of small hydrometeors implies that their rate of production is slow relative to their removal rate. Algorithms for removing the spurious effects of splashing precipitation and noisy photodiodes on 2D probes are also described.

Aircraft in situ observations of precipitation during the Rain in Cumulus over the Ocean (RICO) field project are used to study and parameterize the effects of precipitation on cloud probes. Specifically, the effects of precipitation on the Forward Scattering Spectrometer Probe, the King cloud liquid water hot-wire probe, and the particle volume monitor are parameterized as linear functions of the precipitation water content.

The size, shape and concentration of ice particles in tropical anvil cirrus and in situ cirrus clouds have a significant impact on cloud radiative forcing, and hence on global climate change. Data collected in tropical anvil and cirrus clouds with a 2D‐S probe, an optical imaging probe with improved response characteristics and the ability to remove shattered artifacts, are analyzed and discussed. The data were collected with NASA DC‐8 and WB‐57F research aircraft near Costa Rica during the 2007 Tropical Composition, Cloud and Climate Coupling (TC4) field project, and with the DC‐8 near Cape Verde during the 2006 NASA African Monsoon Multidisciplinary Analyses (NAMMA) campaign. Data were collected in convective turrets, anvils still attached to convection, aged anvils detached from convection and cirrus formed in situ. Unusually strong maritime convection was encountered, with peak updrafts of 20 m s −1 , ice water contents exceeding 2 g m −3 and total particle concentrations exceeding 10 cm −3 at 12.2 km. Ice water contents in the anvils declined outward from the center of convection, decreasing to <0.1 g m −3 in aged anvil cirrus. The data show that microphysical and radiative properties of both tropical anvils and cirrus are most strongly influenced by ice particles in the size range from about 100 to 400 μ m. This is contrary to several previous investigations that have suggested that ice particles less than about 50 μ m control radiative properties in anvils and cirrus. The 2D‐S particle area and mass size distributions, plus information on particle shape, are input into an optical properties routine that computes cloud extinction, asymmetry parameter and single scattering albedo. These optical properties are then input into two‐stream radiative code to compute radiative heating profiles within the various cloud types. The results produce short‐ and long‐wave heating/cooling vertical profiles in these tropical clouds. A simple parameterization based on 2D‐S measurements is derived from the particle mass size distribution that yields an area size distribution. The parameterized area size distribution can then be used in large‐scale numerical simulations that include radiative transfer packages.

Radar observations of small cumulus clouds are compared to predictions of radar measurements based on in situ measurements and the theory of radar back-scatter. At the wavelengths used, both Rayleigh and Bragg scatter can be important in small cumulus. A theoretical derivation of radar back-scatter from small cumulus clouds, in which both terms are succinctly derived using a common mathematical model, is presented.For the earliest stages of cumulus clouds, the predictions of Bragg scatter, based on in situ measurements of water-vapour fluctuations, are in close agreement with radar-measured Bragg scatter. This suggests that the theory is adequate and our interpretations of the radar observations are correct. These interpretations include identifying regions where entrainment and mixing are ongoing, identifying adiabatic cores, and estimating the Kolmogorov microscale of turbulence.As the small cumulus develop and enter the early collision and coalescence stages, another source of Bragg scatter can become significant. It is argued, via observations, that the additional Bragg scatter comes from anomalous liquid-water fluctuations. These liquid-water fluctuations are called 'anomalous' because they exceed what would result if liquid water mixed as a passive scalar. The Bragg scatter caused by liquid water may reach effective values of 5-10 dBZ, for a 3 cm-wavelength (X-band) radar, and thus confounds attempts to derive Rayleigh-scatter values below this level using a dual-wavelength (X- and S-band) radar system. Copyright (C) 2007 Royal Meteorological Society.

Abstract In early February 2001 (during the austral summer), over 900 000 digital images of ice crystals were recorded at the South Pole using two ground-based cloud particle imagers (CPIs). Of these, 721 572 crystals >50 μm were classified into crystal habits. When sorted by number, 30% of the crystals were rosette shaped (mixed-habit rosettes, platelike polycrystals, and rosette shapes with side planes), 45% were diamond dust (columns, thick plates, and plates), and 25% were irregular. When sorted by area, rosette shapes comprised 50%, diamond dust 30% and irregular 20%. By mass, the percentages were 57% rosette shapes, 23% diamond dust, and 20% irregular. Particle size distributions as a function of maximum dimension and equivalent radius are compared with previous studies. Particles are generally found to be slightly larger than previous austral wintertime studies. In 2002, a polar nephelometer (PN) that measures scattering phase function was incorporated with one of the CPIs. Correlated measurements ...

The microphysical properties of wave clouds based on data collected during 17 missions flown by a Learjet research aircraft are presented and discussed. This extensive dataset expands upon previous aircraft studies of wave clouds and introduces some new findings. While most aspects of the observations are consistent with basic cloud physics, some aspects remain difficult to interpret. Most notable among these are ice nucleation and aspects of the dynamical structure of wave clouds. A new hypothesis to explain the ice nucleation behavior is presented. The average and standard deviation of bulk microphysical parameters are presented for various locations within the wave clouds. Using digital imagery from a cloud particle imager (CPI), the shapes of ice particles are studied and crystal habits are classified. For certain categories—rosette shapes, columns, and irregular shapes—power-law parameterizations of particle area from particle length are presented. Polycrystals with rosette shapes dominate the ice mass while small spheroidal and irregularly shaped crystals dominate the ice number concentration. The concept and difficulties of using wave clouds as natural cloud physics laboratories are discussed and evaluated. A study of the riming threshold size of columns is in good agreement with the results of previous studies, showing that column width is the predominate factor in determining riming threshold. The first reported studies of the riming threshold size of rosette shapes and the threshold size for side-plane growth are presented.

The design, laboratory calibrations, and flight tests of a new optical imaging instrument, the twodimensional stereo (2D-S) probe, are presented. Two orthogonal laser beams cross in the middle of the sample volume. Custom, high-speed, 128-photodiode linear arrays and electronics produce shadowgraph images with true 10-mu m pixel resolution at aircraft speeds up to 250 m s(-1). An overlap region is defined by the two laser beams, improving the sample volume boundaries and sizing of small (< similar to 100 mu m) particles, compared to conventional optical array probes. The stereo views of particles in the overlap region can also improve determination of three-dimensional properties of some particles.Data collected by three research aircraft are examined and discussed. The 2D-S sees fine details of ice crystals and small water drops coexisting in mixed-phase cloud. Measurements in warm cumuli collected by the NCAR C-130 during the Rain in Cumulus over the Ocean (RICO) project provide a test bed to compare the 2D-S with 2D cloud (2D-C) and 260X probes. The 2D-S sees thousands of cloud drops 100 m s(-1) by the 2D-C and 260X probes are probably (erroneously) generated from out-of-focus particles. Development of the 2D-S is in its infancy, and much work needs to be done to quantify its performance and generate software to analyze data.

In Part I of this two-part series, a new relationship for ice particle mass M was derived based on an expanded dataset of photographed ice particles and melted drops. The new relationship resulted in a reduction of nearly 50% in the rms error in M. In this paper, new relationships for computing particle mass and ice water content from 2D particle imagery are compared with other relationships previously used in the literature. Comparison of the old and new relationships, when applied to data collected in natural clouds, shows that results using the old relationships differ from the new relationships by up to a factor of 3, depending on particle size and shape. One of the new relationships can be applied to existing (archived) datasets of two-dimensional images, provided that the number of occulted pixels in each image (i.e., projected area) is available.