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Water Path (water + path)
Selected AbstractsCrystal structures of isomaltase from Saccharomyces cerevisiae and in complex with its competitive inhibitor maltoseFEBS JOURNAL, Issue 20 2010Keizo Yamamoto The structures of isomaltase from Saccharomyces cerevisiae and in complex with maltose were determined at resolutions of 1.30 and 1.60 Å, respectively. Isomaltase contains three domains, namely, A, B, and C. Domain A consists of the (,/,)8 -barrel common to glycoside hydrolase family 13. However, the folding of domain C is rarely seen in other glycoside hydrolase family 13 enzymes. An electron density corresponding to a nonreducing end glucose residue was observed in the active site of isomaltase in complex with maltose; however, only incomplete density was observed for the reducing end. The active site pocket contains two water chains. One water chain is a water path from the bottom of the pocket to the surface of the protein, and may act as a water drain during substrate binding. The other water chain, which consists of six water molecules, is located near the catalytic residues Glu277 and Asp352. These water molecules may act as a reservoir that provides water for subsequent hydrolytic events. The best substrate for oligo-1,6-glucosidase is isomaltotriose; other, longer-chain, oligosaccharides are also good substrates. However, isomaltase shows the highest activity towards isomaltose and very little activity towards longer oligosaccharides. This is because the entrance to the active site pocket of isomaltose is severely narrowed by Tyr158, His280, and loop 310,315, and because the isomaltase pocket is shallower than that of other oligo-1,6-glucosidases. These features of the isomaltase active site pocket prevent isomalto-oligosaccharides from binding to the active site effectively. [source] Discriminating raining from non-raining cloud areas at mid-latitudes using meteosat second generation SEVIRI night-time dataMETEOROLOGICAL APPLICATIONS, Issue 2 2008B. Thies Abstract A new method for the delineation of precipitation during night-time using multispectral satellite data is proposed. The approach is not only applicable to the detection of mainly convective precipitation by means of the commonly used relation between infrared cloud-top temperature and rainfall probability but enables also the detection of stratiform precipitation (e.g. in connection with mid-latitude frontal systems). The presented scheme is based on the conceptual model that precipitating clouds are characterized by a combination of particles large enough to fall, an adequate vertical extension [both represented by the cloud water path (CWP)], and the existence of ice particles in the upper part of the cloud. As no operational retrieval exists for Meteosat Second Generation (MSG) to compute the CWP during night-time, suitable combinations of brightness temperature differences (,T) between the thermal bands of Meteosat Second Generation-Spinning Enhanced Visible and InfraRed Imager (MSG SEVIRI, ,T3.9,10.8, ,T3.9,7.3, ,T8.7,10.8, ,T10.8,12.1) are used to infer implicit information about the CWP and to compute a rainfall confidence level. ,T8.7,10.8 and ,T10.8,12.1 are particularly considered to supply information about the cloud phase. Rain area delineation is realized by using a minimum threshold of the rainfall confidence. To obtain a statistical transfer function between the rainfall confidence and the channel differences, the value combination of the channel differences is compared with ground-based radar data. The retrieval is validated against independent radar data not used for deriving the transfer function and shows an encouraging performance as well as clear improvements compared to existing optical retrieval techniques using only IR thresholds for cloud-top temperature. Copyright © 2008 Royal Meteorological Society [source] Modelling advection and diffusion of water isotopologues in leavesPLANT CELL & ENVIRONMENT, Issue 8 2007MATTHIAS CUNTZ ABSTRACT We described advection and diffusion of water isotopologues in leaves in the non-steady state, applied specifically to amphistomatous leaves. This explains the isotopic enrichment of leaf water from the xylem to the mesophyll, and we showed how it relates to earlier models of leaf water enrichment in non-steady state. The effective length or tortuosity factor of isotopologue movement in leaves is unknown and, therefore, is a fitted parameter in the model. We compared the advection,diffusion model to previously published data sets for Lupinus angustifolius and Eucalyptus globulus. Night-time stomatal conductance was not measured in either data set and is therefore another fitted parameter. The model compared very well with the observations of bulk mesophyll water during the whole diel cycle. It compared well with the enrichment at the evaporative sites during the day but showed some deviations at night for E. globulus. It became clear from our analysis that night-time stomatal conductance should be measured in the future and that the temperature dependence of the tracer diffusivities should be accounted for. However, varying mesophyll water volume did not seem critical for obtaining a good prediction of leaf water enrichment, at least in our data sets. In addition, observations of single diurnal cycles do not seem to constrain the effective length that relates to the tortuosity of the water path in the mesophyll. Finally, we showed when simpler models of leaf water enrichment were suitable for applications of leaf water isotopes once weighted with the appropriate gas exchange flux. We showed that taking an unsuitable leaf water enrichment model could lead to large biases when cumulated over only 1 day. [source] Intercomparison of model simulations of mixed-phase clouds observed during the ARM Mixed-Phase Arctic Cloud Experiment.THE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 641 2009II: Multilayer cloud Abstract Results are presented from an intercomparison of single-column and cloud-resolving model simulations of a deep, multilayered, mixed-phase cloud system observed during the Atmospheric Radiation Measurement (ARM) Mixed-Phase Arctic Cloud Experiment. This cloud system was associated with strong surface turbulent sensible and latent heat fluxes as cold air flowed over the open Arctic Ocean, combined with a low pressure system that supplied moisture at mid-levels. The simulations, performed by 13 single-column and 4 cloud-resolving models, generally overestimate liquid water path and strongly underestimate ice water path, although there is a large spread among models. This finding is in contrast with results for the single-layer, low-level mixed-phase stratocumulus case in Part I, as well as previous studies of shallow mixed-phase Arctic clouds, that showed an underprediction of liquid water path. These results suggest important differences in the ability of models to simulate deeper Arctic mixed-phase clouds versus the shallow, single-layered mixed-phase clouds in Part I. The observed liquid-ice mass ratios were much smaller than in Part I, despite the similarity of cloud temperatures. Thus, models employing microphysics schemes with temperature-based partitioning of cloud liquid and ice masses are not able to produce results consistent with observations for both cases. Models with more sophisticated, two-moment treatment of cloud microphysics produce a somewhat smaller liquid water path closer to observations. Cloud-resolving models tend to produce a larger cloud fraction than single-column models. The liquid water path and cloud fraction have a large impact on the cloud radiative forcing at the surface, which is dominated by long-wave flux. Copyright © 2009 Royal Meteorological Society [source] Representation of 3D heterogeneous cloud fields using copulas: Theory for water cloudsTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 636 2008Peter M. Norris Abstract It is shown that a general representation of GCM column cloud fraction within probability density function (PDF)-based statistical cloud parametrizations can be obtained using statistical functions called copulas that encapsulate the dependence structure of rank statistics in a multivariate system. Using this theory, a new Gaussian copula formulation of GCM cloud overlap is obtained. The copula approach provides complete flexibility in the choice of the marginal PDF of each layer's moisture and temperature, and, compared with earlier approaches, including the ,generalized overlap' approach, allows a far more general specification of the correlation between any pair of layers. It also allows easy addition of new layer variables, such as temperature, into the modelled grid-column statistics. As a preliminary test of this formulation, its ability to statistically describe a cloud-resolving model simulation of a complex multi-layer case-study, including both large-scale and convective clouds, is examined. The Gaussian copula cloud fraction is found to be significantly less biased than other common cloud overlap methods for this case-study. Estimates of several nonlinear quantities are also improved with the Gaussian copula model: the variance of condensed water path and the fluxes of solar and thermal radiation at atmospheric column boundaries. This first paper, though limited to the simpler case of water clouds, addresses subgrid-scale variability in both moisture and temperature. This work is envisaged as a first step towards developing a generalized statistical framework for GCM cloud parametrization and for assimilating statistical information from high-resolution satellite observations into GCMs and global analyses. Copyright © 2008 Royal Meteorological Society [source] A concept for a satellite mission to measure cloud ice water path, ice particle size, and cloud altitude,THE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue S2 2007S. A. Buehler Abstract A passive satellite radiometer operating at submillimetre wavelengths can measure cloud ice water path (IWP), ice particle size, and cloud altitude. The paper first discusses the scientific background for such measurements. Formal scientific mission requirements are derived, based on this background and earlier assessments. The paper then presents a comprehensive prototype instrument and mission concept, and demonstrates that it meets the requirements. The instrument is a conically scanning 12-channel radiometer with channels between 183 and 664 GHz, proposed to fly in tandem with one of the Metop satellites. It can measure IWP with a relative accuracy of approximately 20% and a detection threshold of approximately 2 g m,2. The median mass equivalent sphere diameter of the ice particles can be measured with an accuracy of approximately 30 µm, and the median IWP cloud altitude can be measured with an accuracy of approximately 300 m. All the above accuracies are median absolute error values; root mean square error values are approximately twice as high, due to rare outliers. Copyright © 2007 Royal Meteorological Society [source] A modelling study of aerosol impacts on cloud microphysics and radiative propertiesTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 623 2007Chao-Tzuen Cheng Abstract A warm cloud microphysical parameterization was incorporated into a regional model to study the sensitivity to aerosols of cloud-radiative properties and precipitation. Assuming a trimodal lognormal aerosol size distribution, the aerosol numbers were explicitly calculated from prognostic aerosol masses, considering advection, diffusion, and cloud and raindrop activation/deactivation processes. Clean continental, average continental and urban aerosols, each with different modal parameters, were used to serve as condensation nuclei (CCN) of cloud- and raindrops, whose activations depended on supersaturation and aerosol composition. Consistent with other studies, simulations conducted for a warm cloud system indicate that more aerosols result in more cloud water and more, but smaller, cloud drops, yielding increases in cloud albedo and decreases in surface precipitation. For example, the cloud drop effective radius decreased from ,9 µm for clean continental aerosols to ,5 and ,2 µm, respectively, for average continental and urban aerosols, resulting in an increase in the respective cloud water path by ,10% and ,35% and cloud albedo by ,6% and ,12%. On the other hand, the accumulated precipitation decreased from 2.2 mm for clean continental aerosols to 1.9 and 1.2 mm, respectively, for average continental and urban aerosols. The presence of giant nuclei increased both the cloud drop effective radius and the precipitation, while the use of volumetric cloud drop radius tended to result in larger estimated cloud solar radiative forcing than the use of effective cloud drop radius. Copyright © 2007 Royal Meteorological Society [source] The effect of overlying absorbing aerosol layers on remote sensing retrievals of cloud effective radius and cloud optical depthTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 598 2004Jim M. Haywood Abstract Two types of partially absorbing aerosol are included in calculations that are based on intensive aircraft observations: biomass burning aerosol characterized during the Southern AFricAn Regional science Initiative (SAFARI 2000) and mineral dust aerosol characterized during the SaHAran Dust Experiment (SHADE). Measurements during SAFARI 2000 reveal that the biomass burning aerosol layer is advected over the South Atlantic ocean at elevated altitudes above the marine boundary layer which is capped by semi-permanent stratocumulus cloud sheets. Similarly, the mineral dust is measured at elevated altitudes during SHADE resulting in transport above cloud for distances of several thousands of kilometres. We perform theoretical calculations of the effect of these partially absorbing aerosol layers on satellite retrievals of cloud effective radius and cloud optical depth, and show that, in these cases, retrievals of cloud optical depth or liquid water path are likely to be subject to systematic low biases. The theoretical calculations suggest that the cloud effective radius may be subject to a significant low bias for Moderate resolution Imaging Spectrometer (MODIS) retrievals that rely on the 0.86 and 1.63 µm radiance pair for an overlying aerosol layer of either biomass burning aerosol or mineral dust. Conversely, the cloud effective radius may be subject to a significant high bias for Advanced Very High Resolution Radiometer or MODIS retrievals that rely on the 0.63 and 3.7 µm radiance pair for an overlying aerosol layer of mineral dust. Analysis of 1 km resolution MODIS data for the SAFARI 2000 period suggests that the effective radius derived from the 0.86 and 1.63 µm radiance pair is, indeed, subject to a low bias in the presence of overlying biomass burning aerosol. These results show the difficulties associated with remote sensing retrievals, which must be kept in mind when attempting to assess any potential indirect effect. © Crown copyright 2004. [source] | ||||||||||