Cloudy Parts Research Articles

Increasing Resolution and Resolving Convection Improve the Simulation of Cloud‐Radiative Effects Over the North Atlantic

AbstractClouds interact with atmospheric radiation and substantially modify the Earth's energy budget. Cloud formation processes occur over a vast range of spatial and temporal scales, which make their thorough numerical representation challenging. Therefore, the impact of parameter choices for simulations of cloud‐radiative effects is assessed in the current study. Numerical experiments are carried out using the ICOsahedral Nonhydrostatic (ICON) model with varying grid spacings between 2.5 and 80 km and with different subgrid‐scale parameterization approaches. Simulations are performed over the North Atlantic with either one‐moment or two‐moment microphysics and with convection being parameterized or explicitly resolved by grid‐scale dynamics. Simulated cloud‐radiative effects are compared to products derived from Meteosat measurements. Furthermore, a sophisticated cloud classification algorithm is applied to understand the differences and dependencies of simulated and observed cloud‐radiative effects. The cloud classification algorithm developed for the satellite observations is also applied to the simulation output based on synthetic infrared brightness temperatures, a novel approach that is not impacted by changing insolation and guarantees a consistent and fair comparison. It is found that flux biases originate equally from clear‐sky and cloudy parts of the radiation field. Simulated cloud amounts and cloud‐radiative effects are dominated by marine, shallow clouds, and their behavior is highly resolution dependent. Bias compensation between shortwave and longwave flux biases, seen in the coarser simulations, is significantly diminished for higher resolutions. Based on the analysis results, it is argued that cloud‐microphysical and cloud‐radiative properties have to be adjusted to further improve agreement with observed cloud‐radiative effects.

Errors induced by the neglect of polarization in radiance calculations for three-dimensional cloudy atmospheres

Remote sensing instruments observe radiation being scattered and absorbed by molecules, aerosol particles, cloud droplets and ice crystals. In order to interpret and accurately model such observations, the vector radiative transfer equation needs to be solved, because scattering polarizes the initially unpolarized incoming solar radiation. A widely used approximation in radiative transfer theory is the neglect of polarization which allows to greatly simplify the radiative transfer equation.It is well known that the error caused by multiple Rayleigh scattering can be larger than 10%, depending on wavelength and sun-observer geometry (Mishchenko et al., 1994 [1]). For homogeneous plane-parallel layers of liquid cloud droplets the error is comparatively small (below 1%) (Hansen, 1971 [2]). Therefore, in radiative transfer modelling for cloud remote sensing polarization is mostly neglected. However, in reality clouds are not plane-parallel layers of water droplets but complex three-dimensional (3D) structures and observations of clouds usually include pixels consisting of clear and cloudy parts. In this study we revisit the question of the magnitude of the error due to the neglect of polarization in radiative transfer theory for a realistic 3D cloudy atmosphere.We apply the Monte Carlo radiative transfer model MYSTIC with and without neglecting polarization and compare the results. At a phase angle of 90° and 400 nm wavelength we find the maximum overestimation error of about 8% for complete clear-sky conditions. The error is reduced to about 6% in clear-sky regions surrounded by clouds due to scattering from clouds into the clear regions. Within the clouds the error is up to 4% with the highest values in cloud shadows. In backscattering direction the radiance is underestimated by about 5% in clear regions between clouds. For other sun-observer geometries, the error ranges between the two extremes. The error decreases with wavelength and in the absorption bands.

Different insulin concentrations in resuspended vs. unsuspended NPH insulin: Practical aspects of subcutaneous injection in patients with diabetes

AimsThis study measured the insulin concentration (Ins[C]) of NPH insulin in vials and cartridges from different companies after either resuspension (R+) or not (R−; in the clear/cloudy phases of unsuspended NPH). MethodsMeasurements included Ins[C] in NPH(R+) and in the clear/cloudy phases of NPH(R−), and the time needed to resuspend NPH and time for NPH(R+) to separate again into clear/cloudy parts. ResultsIn vials of NPH(R+) (assumed to be 100%), Ins[C] in the clear phase of NPH(R−) was<1%, but 230±41% and 234±54% in the cloudy phases of Novo Nordisk and Eli Lilly NPH, respectively. Likewise, in pen cartridges, Ins[C] in the clear phase of NPH(R−) was<1%, but 182±33%, 204±22% and 229±62% in the cloudy phases of Novo, Lilly and Sanofi NPH. Time needed to resuspend NPH (spent in tipping) in vials was brief with both Novo (5±1s) and Lilly NPH (6±1s), but longer with all pen cartridges (50±8s, 40±6s and 30±4s from Novo, Lilly and Sanofi, respectively; P=0.022). Time required for 50% separation into cloudy and clear parts of NPH was longer with Novo (60±7min) vs. Lilly (18±3min) in vials (P=0.021), and affected by temperature, but not by the different diameter sizes of the vials. With pen cartridges, separation into clear and cloudy parts was significantly faster than in vials (P<0.01). ConclusionIns[C] in NPH preparations varies depending on their resuspension or not. Thus, subcutaneous injection of the same number of units of NPH in patients with diabetes may deliver different amounts of insulin depending on its prior NPH resuspension.

Experimental and first-principles IR characterization of quercetin adsorbed on a silica surface

A combined experimental–theoretical study of quercetin adsorbed on a silica surface has been carried out in order to investigate the specific nature of their interaction. By means of an accurate hybrid functional PBE-D* approach, inclusive of dispersion interactions through the empirical D* Grimme’s term, the energetics of various configurations has been evaluated. IR spectra of the most probable ones, determined on the basis of thermodynamics considerations, have been simulated and compared to ad hoc measured spectra. A detailed classification of the peaks is proposed which sheds light onto some cloudy parts of the experimental IR spectra assignments. The most notable feature of our results is the extended and enhanced hydrogen-bonds network which is formed throughout the surface-molecule aggregate, thanks to the molecule acting as a bridge among the hydrogen bonds already present on the pristine silica surface.

Transect method for Antarctic cloud property retrieval using AVHRR data

For studies of Antarctic climate change, the Advanced Very High Resolution Radiometer (AVHRR) offers a time series spanning more than two decades, with numerous overpasses per day from converging polar orbits, and with radiometrically calibrated thermal infrared channels. However, over the Antarctic Plateau, standard multispectral application of AVHRR data for cloud optical property retrieval with individual pixels is problematic due to poor scene contrasts and measurement uncertainties. We present a method that takes advantage of rapid changes in radiances at well-defined cloud boundaries. We examine a transect of AVHRR-measured radiances in the three thermal infrared channels across a boundary between cloudy and cloud-free parts of the image. Using scatter diagrams, made from the data along this transect, of the brightness temperature differences between channels 3 and 4, and channels 4 and 5, it is possible to fit families of radiative transfer solutions to the data to estimate cloud effective temperature, thermodynamic phase, and effective particle radius. The major approximation with this method is that along such a transect, cloud water path has considerable spatial variability, while effective radius, phase, and cloud temperature have much less variability. To illustrate this method, two AVHRR images centred about the South Pole are analysed. The two images are chosen based on their differing contrasts in brightness temperature between clear and cloud-filled pixels, to demonstrate that our method can work with varying cloud top heights. In one image the data are consistent with radiative transfer simulations using ice cloud. In the other, the data are inconsistent with ice cloud and are well simulated with supercooled liquid water cloud at 241.5 K. This method therefore has potential for climatological investigation of the radiatively important phase transition in the extremely cold and pristine Antarctic environment.

A statistical approach to the life cycle analysis of cumulus clouds selected in a virtual reality environment

In this study, a new method is developed to investigate the entire life cycle of shallow cumuli in large eddy simulations. Although trained observers have no problem in distinguishing the different life stages of a cloud, this process proves difficult to automate, because cloud‐splitting and cloud‐merging events complicate the distinction between a single system divided in several cloudy parts and two independent systems that collided. Because the human perception is well equipped to capture and to make sense of these time‐dependent three‐dimensional features, a combination of automated constraints and human inspection in a three‐dimensional virtual reality environment is used to select clouds that are exemplary in their behavior throughout their entire life span. Three specific cases (ARM, BOMEX, and BOMEX without large‐scale forcings) are analyzed in this way, and the considerable number of selected clouds warrants reliable statistics of cloud properties conditioned on the phase in their life cycle. The most dominant feature in this statistical life cycle analysis is the pulsating growth that is present throughout the entire lifetime of the cloud, independent of the case and of the large‐scale forcings. The pulses are a self‐sustained phenomenon, driven by a balance between buoyancy and horizontal convergence of dry air. The convective inhibition just above the cloud base plays a crucial role as a barrier for the cloud to overcome in its infancy stage, and as a buffer region later on, ensuring a steady supply of buoyancy into the cloud.

Striped‐pattern deterioration and morphological analysis of injection molding comprising polypropylene/ethylene–α‐olefin rubber blends. II. Influence of heating

AbstractUnique deterioration with a striped pattern caused by thermal heating is reported for injection molding comprising polypropylene/ethylene–α‐olefin rubber blends. This stripe is due to the formation of glossy and cloudy parts in alternation approximately perpendicular to the flow direction of the molten resin. On the surface of the cloudy part, a number of micro‐objects appear. They have a dome shape about 10 μm in diameter and 2 μm height. Some experimental evidence indicates that the objects are composed of the rubber contained in the blends. On the other hand, only a few objects appear in the glossy region after heating. This is the reason that the stripe with the micro‐objects (migrating rubber to the surface) is examined in terms of a higher order structure of injection molding with laser scanning microscopy, wide‐angle X‐ray scattering, and microhardness (Martens hardness). Consequently, we have concluded that this thermally deteriorated stripe depends on periodic changes in the crystallinity along the flow direction. The evidence indicates that a snakelike flow occurs during the injection process of the molding. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008

A description of cloud production by non‐uniformly distributed processes

AbstractPrognostic cloud‐fraction and condensate equations, for the case in which a source injects condensate‐laden, saturated air into a volume, are derived by considering the response of a general distribution of thermodynamic variables within the volume. These prognostic equations are compared with those derived by assuming that condensate is added uniformly to both clear and cloudy parts of the region. For non‐uniform forcing, the local condensate mixing ratio associated with the condensate source is important in controlling the rate of change of cloud fraction and in‐cloud condensate. For the case of a convective condensate source, the cloud‐fraction equation is contrasted with previously derived alternatives. Lastly, the validity of a prognostic equation for cloud fraction is discussed in the light of a different approach in which the moments of a distribution of thermodynamic variables are specified from prognostic equations and used to calculate cloud fraction and condensate diagnostically. © Crown copyright, 2003. Royal Meteorological Society

A diagnostic model of turbulent transport in a cumulus cloud layer

Results are presented from a mixed-layer model which has been used to diagnose the average turbulent flux profiles in cumulus-capped boundary-layers. The model makes use of separate mixed layer models for the clear and cloudy parts of the broken cloud layer. It is shown, by comparison with aircraft observations, that the model can be applied to estimate the area-averaged flux profiles under conditions in which the clouds penetrate the capping inversion. It is also shown that a small but significant part of the vertical transport results from the displacement of air from above the inversion around the growing clouds.

Parameterization of the Condensation Process in Small Nonprecipitating Cumuli

Measurements of the droplet size distribution collected in a field of small nonprecipitating cumuli are analyzed. It appears that despite the high variability of the measured droplet concentration, the droplet spectral shape at given levels is almost invariable. An original method, based on the coincidence effects in the droplet counter, is used to show that most of the low concentration samples are in fact heterogeneous and that the actual droplet concentration in the cloudy parts of these samples is comparable to the concentration in regions of the cloud which are uniform. Observed spectra are much broader than provided by adiabatic lifting. The frequency distribution of the spectral shapes is compared to the results of a one-dimensional cloud model for various values of the entrainment rate. The limitations of the previous models are discussed and the inhomogeneous mixing formulation of Baker et al. is then modified to allow nucleus activation in the entrained air before its fine scale mixing with the cloudy droplets. Finally the proposed scheme is simplified to derive a parameterization of the broad spectra. The range of spectral shapes reproduced at any level by the parameterization is in agreement with their observed frequency distribution.

Surface temperature sensitivities from cloud cover variations in the Hummel-Kuhn radiative-convective model with three different cloud approximations

In modeling the thermal structure of the atmosphere, the role of clouds is critically important. Clouds modify the solar flux distribution throughout the atmosphere, radiate significantly in the infrared, and provide large thermal reservoirs because of the large latent heat of water. In the best current radiative convective one-dimensional models the global atmosphere is modeled as the sum of clear and cloudy sky parts weighted by a fractional cloud cover. In considering the cloudy sky part, previous models have treated the clouds as input and characterized them simply in terms of their altitudes, thicknesses, and optical properties. This report compares the surface temperature sensitivities to variations in cloud cover for three cloud approximations: (1) a single effective fixed cloud with a mean water vapor profile, (2) a floating clouds approximation in which cloud altitudes and thicknesses are calculated and a mean water vapor profile is used and (3) a fully interactive formulation in which cloud altitudes and thicknesses are calculated and separate clear and cloudy water vapor profiles are used. In all three approximations the cloud cover amount, A c , is an input. The fully interactive approximation is shown to reduce the sensitivity of surface temperature to cloud cover variations from ?4.7 times 10 -2 K/(1% A c ) for the single effective approximation to ?3.6 times 10 -2 K/(1% A c ). This reveals that when the model allows the clouds and water vapor to interact, calculated surface temperature changes caused by changing the amount of clouds are less than previous studies indicate. DOI: 10.1111/j.2153-3490.1981.tb01769.x

Carbon content of magnesium oxide single crystals grown by the arc fusion method

The carbon content of nominally high purity (99.9% and 99.99%) MgO single crystals was determined by means of the nuclear reaction 12C(d,p) 13C and compared with carbon determinations by combustion in streaming O 2 at 900°C. The average carbon content is 0.3% by weight or 10,000 ppm. Cloudy parts of 99.99% MgO crystals gave values up to 0.9%. The carbon seems to be present in the MgO in form of elemental carbon, probably atomic.