COSMO Model Research Articles

A quantum chemical investigation of the electronic structure of thionine

We have examined the electronic and molecular structure of 3,7-diaminophenothiazin-5-ium dye (thionine) in the electronic ground state and in the lowest excited states. The electronic structure was calculated using a combination of density functional theory and multi-reference configuration interaction (DFT/MRCI). Equilibrium geometries were optimized employing (time-dependent) density functional theory (B3LYP functional) combined with the TZVP basis set. Solvent effects were estimated using the COSMO model and micro-hydration with up to five explicit water molecules. Our calculated electronic energies are in good agreement with experimental data. We find the lowest excited singlet and triplet states at the ground state geometry to be of π→π* (S(1), S(2), T(1), T(2)) and n→π* (S(3), T(3)) character. This order changes when the molecular structure in the electronically excited states is relaxed. Geometry relaxation has almost no effect on the energy of the S(1) and T(1) states (~0.02 eV). The relaxation effects on the energies of S(2) and T(2) are moderate (0.14-0.20 eV). The very small emission energy results in a very low fluorescence rate. While we were not able to locate the energetic minimum of the S(3) state, we found a non-planar minimum for the T(3) state with an energy which is very close to the energy of the S(1) minimum in the gas phase (0.04 eV above). When hydration effects are taken into account, the n→π* states S(3) and T(3) are strongly blueshifted (0.33 and 0.46 eV), while the π→π* states are only slightly affected (<0.06 eV).

A regional climate model study of the impact of tectonic and orbital forcing on African precipitation and vegetation

The development of the East African Rift System (EARS) caused by tectonic forcing during the past 20million years is believed to influence the regional climate in Africa. However, changes in the Earth's orbital parameters also have an influence on climate on these timescales. To analyze the influence of both tectonic and orbital forcing, we applied the non-hydrostatic regional climate model COSMO-CLM (COSMO model in Climate Mode, CCLM). The regional simulations are driven by different global simulations performed with the coupled ocean–atmosphere general circulation model ECHO-G. To analyze the impact of tectonic forcing a different topography representing a possible past stage of the development of the EARS is applied in the model. The results indicate that tectonic forcing has a strong impact on precipitation in Africa caused by circulation changes. To analyze the impact of orbital forcing, which means the impact of changing insolation patterns, we chose configurations of the Earth's orbit that result in significantly different patterns of insolation. One example is the orbital configuration of the last interglacial at 125,000years before present, when the seasonality of insolation in the Northern Hemisphere was greatly enhanced, whereas in the Southern Hemisphere it was substantially weakened compared to preindustrial conditions. The simulation of this time slice shows a strong impact of orbital forcing on precipitation in large parts of Africa, caused by altered moisture transport. The application of a biome model helps in analyzing the impact of the two forcing factors on vegetation for a more direct comparison with proxy data.

Low-energy conformers of pamidronate and their intramolecular hydrogen bonds: a DFT and QTAIM study

Extensive DFT and ab initio calculations were performed to characterize the conformational space of pamidronate, a typical pharmaceutical for bone diseases. Mono-, di- and tri-protic states of molecule, relevant for physiological pH range, were investigated for both canonical and zwitterionic tautomers. Semiempirical PM6 method were used for prescreening of the single bond rotamers followed by geometry optimizations at the B3LYP/6-31++G(d,p) and B3LYP/6-311++G(d,p) levels. For numerous identified low energy conformers the final electronic energies were determined at the MP2/6-311++G(2df,2p) level and corrected for thermal effects at B3LYP level. Solvation effects were also considered via the COSMO and C-PCM implicit models. Reasonable agreement was found between bond lengths and angle values in comparison with X-ray crystal structures. Relative equilibrium populations of different conformers were determined from molecular partition functions and the role of electronic, vibrational and rotational degrees of freedom on the stability of conformers were analyzed. For no level of theory is a zwitterionic structure stable in the gas-phase while solvation makes them available depending on the protonation state. Geometrically identified intramolecular hydrogen bonds were analyzed by QTAIM approach. All conformers exhibit strong inter-phosphonate hydrogen bonds and in most of them the alkyl-amine side chain is folded on the P-C-P backbone for further hydrogen bond formation.

A multivariate statistical analysis of the QSAR of 2-(substituted phenyl)indan-1,3-diones with hypolipidemic activity

Electronic descriptors obtained from AM1 molecular orbital calculations were employed, along with the empirical parameters log P and π, in a multivariate statistical analysis of the quantitative structure-activity relationships (QSAR) in a group of sixteen 2-(substituted phenyl)indan- 1,3-diones possessing hypolipidemic activities. AM1 descriptors were obtained both for the isolated molecule model and, to simulate the solvent effect, for the COSMO model (conductor-like screening model) in our QSAR analysis. From sixteen studied derivatives, three were excluded from the set of molecules used in the model building stage in order to serve as a test set. In general, the results obtained from this test set validated our quantitative models, which were based on linear regressions and principal component analysis (PCA). From these results, new derivatives were predicted to be more potent hypolipidemic agents than the indan-1,3-diones for which experimental activities were determined. For instance, our results suggest that 2-(ortho-hydroxy-phenyl)indan-1,3-dione is a potential candidate for new experimental screening studies for reducing serum cholesterol and triglyceride levels.

A unified energy footprint for simulation software

The focus in High-Performance Computing increasingly turns to energy efficiency. Therefore the pure concentration on floating point operations and runtime performance is no longer sufficient. In terms of hardware, this change of paradigm has already taken place: The GREEN500 list as counterpart to the runtime performance oriented TOP500 list has been established. The new metrics take runtime and energy consumption into account. Nevertheless, all these developments consider hardware only—still an inadequate situation to face the challenges of Energy-Efficient Exascale Computing. The necessity of optimizing simulation software with respect to power and energy draft demands for detailed profiling of the power consumption during the calculations and a norm quantifying the respective efficiency. In this paper we propose a unified energy footprint for simulation software that enables a fast comparison between different models, implementations and hardware configurations, respectively. By way of example we provide the footprints for the tomographic reconstruction code PyHST optimized for CPU and GPU operation as well as the operational numerical weather prediction model COSMO. We then discuss the power and energy profiles and investigate the effects of scaling with respect to hardware resources and simulation parameters.

A Time-Dependent Density Functional Study of a Non-Aromatic [1.1.1.1.1]-Pentaphyrin and Its Lutetium Complex

The molecular structures and absorption electronic spectra of two novel phototoxic pentapyrrolic expanded porphyrins (a isopentaphyrin derivative and its lutetium complex) have been studied at the density functional level and its time-dependent extension (TDDFT). The geometries were optimized with three different exchange-correlation functionals (PBE0, B3LYP, and ωB97XD) and the SV(P) basis set plus the pseudopotential method for the complex. With respect to the porphyrin, the structure of [1.1.1.1.1]-pentaphyrin and its lutetium complex are predicted much distorted due to the lack of conjugation. The lowest excitation energy band (experimental at 814 nm) for the free-base isopentaphyrin is well predicted by the ωB97XD at 772 nm. The possible photodynamic reaction mechanisms (types I and II) were studied through the calculation of the electron affinity and ionization potentials in solvent, using the COSMO model.

Assessment of the impact of the meteorological meso-scale circulation on air quality in arid subtropical region

In this paper, COSMO numerical weather prediction model is used to simulate land-sea breeze circulation in the north coast of Oman and to analyze the variability of the PBL depth. Typical summer day 1st August 2009 and winter day 1st January 2009 were simulated and verified by surface observations. The COSMO model was initialized using the German global model which runs as 40km resolution and 40 vertical layers. The simulations show differences in the onset, strength, and inland penetration of the sea breeze. The high sea-land thermal contrast in the summer season induces earlier onset and progression of the sea breeze with larger horizontal and vertical extents. The summer and winter inland penetration is simulated around 150 and 65km, respectively. The PBL depth was defined from the verticals profiles of the turbulence kinetic energy (TKE). The simulated PBL height varied at 1,600m in summer and 700m in the winter case. These results are in general in good agreement with the simulations of the National Centers for Environmental Prediction Global Data Assimilation System (NCEP-GDAS) model. The dispersive ability of the atmosphere was tested through the vertical mixing coefficient (VMC) generated by NCEP-GDAS simulations. The VMC during the summer simulated case is approximately four times larger than the respective one during the winter case. Consequently, during the advection of winter sea breeze, a shallow dome less than 100m is shaped and forms an obstacle to the air-pollutant dispersion.

Study of Specific Ion–Amino Acid Interactions through the Use of Local Correlation Methods

Specific ion effects, related to the hydration of ions and ion-solute interactions, play a fundamental part in many processes in chemistry and biology. Although intensively studied since the seminal studies of Franz Hofmeister and co-workers, their molecular origin has only recently started to be unveiled. In this work, we have investigated the interaction between halide anions and a selected set of amino acid residues in an attempt to identify the forces behind ion specificity. Two-dimensional potential energy surfaces have been calculated with the use of local second order Møller-Plesset perturbation theory (LMP2), coupled with the COSMO model to describe solvent effects. The results show in great detail the impact of dispersion interactions, in particular for the heavier anions (Br(-) and I(-)). The obtained potential energy surfaces also hint at a greater mobility of iodide in the vicinity of a residue, which correlates well with its placing in the Hofmeister series.

Comparison of dynamical cores for NWP models: comparison of COSMO and Dune

We present a range of numerical tests comparing the dynamical cores of the operationally used numerical weather prediction (NWP) model COSMO and the university code Dune, focusing on their efficiency and accuracy for solving benchmark test cases for NWP. The dynamical core of COSMO is based on a finite difference method whereas the Dune core is based on a Discontinuous Galerkin method. Both dynamical cores are briefly introduced stating possible advantages and pitfalls of the different approaches. Their efficiency and effectiveness is investigated, based on three numerical test cases, which require solving the compressible viscous and non-viscous Euler equations. The test cases include the density current (Straka et al. in Int J Numer Methods Fluids 17:1–22, 1993), the inertia gravity (Skamarock and Klemp in Mon Weather Rev 122:2623–2630, 1994), and the linear hydrostatic mountain waves of (Bonaventura in J Comput Phys 158:186–213, 2000).

Disaggregation of screen-level variables in a numerical weather prediction model with an explicit simulation of subgrid-scale land-surface heterogeneity

The earth’s surface is characterized by small-scale heterogeneity attributable to variability in land cover, soil characteristics and orography. In atmospheric models, this small-scale variability can be partially accounted for by the so-called mosaic approach, i.e., by computing the land-surface processes on a grid with an explicit higher horizontal resolution than the atmosphere. The mosaic approach does, however, not account for the subgrid-scale variability in the screen-level atmospheric parameters, part of which might be related to land-surface heterogeneity itself. In this study, simulations with the numerical weather prediction model COSMO are shown, employing the mosaic approach together with a spatial disaggregation of the atmospheric forcing by the screen-level variables to the subgrid-scale. The atmospheric model is run with a 2.8 km horizontal grid resolution while the land surface processes are computed on a 400-m horizontal grid. The disaggregation of the driving atmospheric variables at screen-level is achieved by a three-step statistical downscaling with rules learnt from high-resolution fully coupled COSMO simulations, where both, atmosphere and surface, were simulated on a 400-m grid. The steps encompass spline interpolation of the grid scale variables, conditional regression based on the high-resolution runs, and an optional stochastic noise generator which restores the variability of the downscaled variables. Simulations for a number of case studies have been carried out, with or without mosaic surface representation and with or without atmospheric disaggregation, and evaluated with respect to the surface state variables and the turbulent surface exchange fluxes of sensible and latent heat. The results are compared with the high-resolution fully coupled COSMO simulations. The results clearly demonstrate the high importance of accounting for subgrid-scale surface heterogeneity. It is shown that the atmospheric disaggregation leads to clear additional improvements in the structures of the two-dimensional surface state variable fields, but to only marginally impacts on the simulation of the turbulent surface exchange fluxes. A detailed analysis of these results identifies strongly correlated errors in atmospheric and surface variables in the mosaic approach as the main reason for the latter. The effects of these errors largely cancel out in the flux parameterization, and thus explain the comparably good results for the fluxes in the mosaic approach without atmospheric disaggregation despite inferior performance for the surface state variables themselves. Inserting noise in the disaggregation scheme leads to a deterioration of the results.

The isotopic composition of precipitation from a winter storm – a case study with the limited-area model COSMO&amp;lt;sub&amp;gt;iso&amp;lt;/sub&amp;gt;

Abstract. Stable water isotopes are valuable tracers of the atmospheric water cycle, and potentially provide useful information also on weather-related processes. In order to further explore this potential, the water isotopes H218O and HDO are incorporated into the limited-area model COSMO. In a first case study, the new COSMOiso model is used for simulating a winter storm event in January 1986 over the eastern United States associated with intense frontal precipitation. The modelled isotope ratios in precipitation and water vapour are compared to spatially distributed δ18O observations. COSMOiso very accurately reproduces the statistical distribution of δ18O in precipitation, and also the synoptic-scale spatial pattern and temporal evolution agree well with the measurements. Perpendicular to the front that triggers most of the rainfall during the event, the model simulates a gradient in the isotopic composition of the precipitation, with high δ18O values in the warm air and lower values in the cold sector behind the front. This spatial pattern is created through an interplay of large scale air mass advection, removal of heavy isotopes by precipitation at the front and microphysical interactions between rain drops and water vapour beneath the cloud base. This investigation illustrates the usefulness of high resolution, event-based model simulations for understanding the complex processes that cause synoptic-scale variability of the isotopic composition of atmospheric waters. In future research, this will be particularly beneficial in combination with laser spectrometric isotope observations with high temporal resolution.

The 1-way on-line coupled atmospheric chemistry model system MECO(n) – Part 3: Meteorological evaluation of the on-line coupled system

Abstract. Three detailed meteorological case studies are conducted with the global and regional atmospheric chemistry model system ECHAM5/MESSy(→COSMO/MESSy)n, shortly named MECO(n). The aim of this article is to assess the general performance of the on-line coupling of the regional model COSMO to the global model ECHAM5. The cases are characterised by intense weather systems in Central Europe: a cold front passage in March 2010, a convective frontal event in July 2007, and the high impact winter storm "Kyrill" in January 2007. Simulations are performed with the new on-line-coupled model system and compared to classical, off-line COSMO hindcast simulations driven by ECMWF analyses. Precipitation observations from rain gauges and ECMWF analysis fields are used as reference, and both qualitative and quantitative measures are used to characterise the quality of the various simulations. It is shown that, not surprisingly, simulations with a shorter lead time generally produce more accurate simulations. Irrespective of lead time, the accuracy of the on-line and off-line COSMO simulations are comparable for the three cases. This result indicates that the new global and regional model system MECO(n) is able to simulate key mid-latitude weather systems, including cyclones, fronts, and convective precipitation, as accurately as present-day state-of-the-art regional weather prediction models in standard off-line configuration. Therefore, MECO(n) will be applied to simulate atmospheric chemistry exploring the model's full capabilities during meteorologically challenging conditions.

The 1-way on-line coupled atmospheric chemistry model system MECO(n) – Part 2: On-line coupling with the Multi-Model-Driver (MMD)

Abstract. A new, highly flexible model system for the seamless dynamical down-scaling of meteorological and chemical processes from the global to the meso-γ scale is presented. A global model and a cascade of an arbitrary number of limited-area model instances run concurrently in the same parallel environment, in which the coarser grained instances provide the boundary data for the finer grained instances. Thus, disk-space intensive and time consuming intermediate and pre-processing steps are entirely avoided and the time interpolation errors of common off-line nesting approaches are minimised. More specifically, the regional model COSMO of the German Weather Service (DWD) is nested on-line into the atmospheric general circulation model ECHAM5 within the Modular Earth Submodel System (MESSy) framework. ECHAM5 and COSMO have previously been equipped with the MESSy infrastructure, implying that the same process formulations (MESSy submodels) are available for both models. This guarantees the highest degree of achievable consistency, between both, the meteorological and chemical conditions at the domain boundaries of the nested limited-area model, and between the process formulations on all scales. The on-line nesting of the different models is established by a client-server approach with the newly developed Multi-Model-Driver (MMD), an additional component of the MESSy infrastructure. With MMD an arbitrary number of model instances can be run concurrently within the same message passing interface (MPI) environment, the respective coarser model (either global or regional) is the server for the nested finer (regional) client model, i.e. it provides the data required to calculate the initial and boundary fields to the client model. On-line nesting means that the coupled (client-server) models exchange their data via the computer memory, in contrast to the data exchange via files on disk in common off-line nesting approaches. MMD consists of a library (Fortran95 and some parts in C) which is based on the MPI standard and two new MESSy submodels, MMDSERV and MMDCLNT (both Fortran95) for the server and client models, respectively. MMDCLNT contains a further sub-submodel, INT2COSMO, for the interpolation of the coarse grid data provided by the server models (either ECHAM5/MESSy or COSMO/MESSy) to the grid of the respective client model (COSMO/MESSy). INT2COSMO is based on the off-line pre-processing tool INT2LM provided by the DWD. The new achievements allow the setup of model cascades for zooming (down-scaling) from the global scale to the lower edge of the meso-γ scale (&amp;amp;approx;1 km) with a very high degree of consistency between the different models and between the chemical and meteorological boundary conditions.

Aerosol-cloud-precipitation effects over Germany as simulated by a convective-scale numerical weather prediction model

Abstract. Possible aerosol-cloud-precipitation effects over Germany are investigated using the COSMO model in a convection-permitting configuration close to the operational COSMO-DE. Aerosol effects on clouds and precipitation are modeled by using an advanced two-moment microphysical parameterization taking into account aerosol assumptions for cloud condensation nuclei (CCN) as well as ice nuclei (IN). Simulations of three summer seasons have been performed with various aerosol assumptions, and are analysed regarding surface precipitation, cloud properties, and the indirect aerosol effect on near-surface temperature. We find that the CCN and IN assumptions have a strong effect on cloud properties, like condensate amounts of cloud water, snow and rain as well as on the glaciation of the clouds, but the effects on surface precipitation are – when averaged over space and time – small. This robustness can only be understood by the combined action of microphysical and dynamical processes. On one hand, this shows that clouds can be interpreted as a buffered system where significant changes to environmental parameters, like aerosols, have little effect on the resulting surface precipitation. On the other hand, this buffering is not active for the radiative effects of clouds, and the changes in cloud properties due to aerosol perturbations may have a significant effect on radiation and near-surface temperature.

Influence of microphysical processes on the potential vorticity development in a warm conveyor belt: a case‐study with the limited‐area model COSMO

AbstractThe potential vorticity (PV) in warm conveyor belts (WCBs) is strongly influenced by the latent heating associated with the various microphysical processes occurring during the formation of clouds. The first‐order effect is that PV increases below the level of maximum diabatic heating and decreases above. Thus, the WCB reaches the upper troposphere with low PV values and has the potential to influence the large‐scale dynamics. In order to quantify the influence of different microphysical processes on the diabatic heating rates (DHRs) and associated PV development during the ascent, a Lagrangian analysis is used and applied to a regional model simulation of a selected WCB event. First, the individual DHRs caused by the various microphysical processes are calculated with the COSMO model. Then, the DHRs and the associated changes in PV are evaluated along the WCB trajectories. The relative role of the different microphysical processes is quantified for the latent heating and the diabatic PV modification, for which the gradient of the latent heating and the absolute vorticity are crucially important. It is shown that condensation of vapour and depositional growth of snow each contribute ∼10 K to the total latent heating. However, the diabatic PV modification due to condensation is stronger since it occurs close to the cold frontal low‐level maximum of the z‐component of the absolute vorticity, ηz, whereas a similar heating rate gradient caused by depositional growth of snow modifies the PV much less since it occurs in a region with much weaker ηz. This highlights the importance of ηz for determining the PV modification due to a certain diabatic heating rate. Furthermore, cooling processes like the evaporation of rain, also co‐occurring with high ηz near the surface cold front, have the potential to strongly modify the PV below the WCB. Copyright © 2011 Royal Meteorological Society

Regime-dependent evaluation of accumulated precipitation in COSMO

Regime-dependent evaluation is a relatively new approach to assess model performance. It consists of classifying the model biases according to a discrete number of regimes and evaluating model output within each regime. In this paper, the regimes are firstly defined by the large-scale atmospheric circulation, based on the objective Jenkinson-Collison classification technique which distinguishes synoptic patterns by strength, direction and vorticity of the geostrophic flow. Eight directional and two vorticity circulation regimes (circulation types) are specified. In this way, it is possible to quantify the model performance for cases with for example westerly winds only, or with cyclonic circulation only. A second regime classification is based on temperature, which allows for detection of temperature-dependent model performance. Modelled accumulated precipitation (mm/6 h) is evaluated with rain gauges for the years 2007 and 2008. Two variants of the COSMO model are evaluated: a fine-resolution version (2.8 km, COSMO-DE) and a coarse-resolution version (7 km, COSMO-EU). In COSMO-EU, a windward/leeward effect becomes visible since circulation is related to dominant wind direction, hence to windward and lee side of orography. In COSMO-DE, no circulation dependent but a height-related bias is identified and further explored, making use of temperature-dependent evaluation which unveils a positive model bias related to solid precipitation.

Theoretical and spectroscopic studies on the conformational equilibrium of 9-oxabispidines in solution

Abstract The conformational behavior of N,N-dimethyl-9-oxabispidine and four 2-endo-substituted 9-oxabispidines (3,7-diaza-9-oxabicyclo[3.3.1]nonanes) in solution was investigated by theoretical and spectroscopic methods. The electronic energies of all conformers were calculated on the B3LYP/TZVP level of theory and solvent effects were taken into account by the continuum solvent model COSMO. Only two conformers, the double chair form A1 (both N–R exo) and the boat–chair form B2 (Nchair–R exo, Nboat–R endo), were of energetic relevance (ΔE ⩽ 18.2 kJ mol−1), with the former one strongly dominating (A1:B2 ⩾ 98:2 at room temperature), independent of the existence or nature of the 2-endo-substituent. Compared to the corresponding bispidines, the dominance of the double chair conformers A1 was more pronounced in the 9-oxabispidines, presumably due to stronger N,O-repulsions in their boat–chair conformers B2. 1H NMR studies on 21 2-endo-substituted 9-oxabispidines, using the 3J coupling constants of the exo-methylene protons with the neighboring bridgehead protons as conformational probes, gave no evidence on a noticeable population of the boat–chair conformers B in solution, which is good agreement with the calculations. In addition, the experimentally determined proton shifts of two 2-endo-substituted 9-oxabispidines matched excellently with those calculated for their double chair conformers A1.

Application of an adaptive radiative transfer scheme in a mesoscale numerical weather prediction model

AbstractThe computational burden of radiative transfer parametrization is considerable, and hence operational atmospheric models use various sampling, coarsening and interpolation techniques to reduce this load; this, however, introduces new errors. An adaptive radiative transfer scheme takes advantage of the spatial and temporal correlations in the optical characteristics of the atmosphere to make the parametrization computationally more efficient. The adaptive scheme employed here generalizes the accurate radiation computations made in a fraction of the spatial and temporal space to the rest of the field. In this study, a previously developed scheme has been extended to atmospheric heating rates and implemented in the numerical weather prediction model COSMO. The performance of the adaptive scheme is compared with the performance of the currently operational COSMO‐DE radiation configuration, in which radiation computations are performed quarter‐hourly on 2 × 2 averaged atmospheric columns. The reference for both schemes is a set of frequent radiation computations for the full grid. We show that the adaptive scheme is able to reduce the sampling errors in the radiation surface fluxes by 15–25% and to conserve the spatial variability, in contrast to the operational scheme. Deviations in the heating‐rate profiles are reduced for larger averaging scales. Physical relationships between the radiative quantities and cloud water or rain rates are better captured. We demonstrate that these improvements also lead to improvements with respect to the dynamical development of the model simulation, showing a smaller divergence from the reference model run. Copyright © 2011 Royal Meteorological Society

Estimation of Hansen solubility parameters using multivariate nonlinear QSPR modeling with COSMO screening charge density moments

New QSPR multivariate nonlinear models based on artificial neural network (ANN) were developed for the prediction of the components of the three-dimensional Hansen solubility parameters (HSPs) using COSMO-RS sigma-moments as molecular descriptors. The sigma-moments are obtained from high quality quantum chemical calculations using the continuum solvation model COSMO and a subsequent statistical decomposition of the resulting polarization charge densities. The models for HSPs were built on a training/validation data set of 128 compounds having a broad diversity of chemical characters (alkanes, alkenes, aromatics, haloalkanes, nitroalkanes, amines, amides, alcohols, ketones, ethers, esters, acids, ion-pairs: amine/acid associates, ionic liquids). The prediction power of the correlation equation models for HSPs was validated on a test set of 17 compounds with various functional groups and polarity, among them drug-like molecules, organic salts, solvents and ion-pairs. It was established that COSMO sigma-moments can be used as excellent independent variables in nonlinear structure–property relationships using ANN approaches. The resulting optimal multivariate nonlinear QSPR models involve the five basic sigma-moments having defined physical meaning and possess superior predictive ability for dispersion, polar and hydrogen bonding HSPs components, with test set correlation coefficients R 2 d = 0.85, R 2 p = 0.91, R 2 h = 0.92 and mean absolute errors of Δ δ d = 1.37 MPa 1/2, Δ δ p = 1.85 MPa 1/2 and Δ δ h = 2.58 MPa 1/2.

Evaluation of the COSMO-SC turbulence scheme in a shear-driven stable boundary layer

The performance of the COSMOsingle column turbulence scheme (a TKE scheme with a 1.5 order turbulence closure at the hierarchy level 2.5 following Mellor and Yamada) is investigated in the framework of the first GABLS intercomparison case. This is an idealized shear-driven stable boundary layer case with no advection. Overall the COSMO model performs reasonably well compared to the other participating models and the reference Large Eddy Simulations. However, the modification of some model parameters, together with the prescribed high vertical resolution, reveals a problem of numerical stability in the turbulence scheme: for the investigated shear-driven stable boundary layer the vertical diffusivities show unrealistic oscillations. This model deficiency, which has previously been described in literature, is explored in quite substantial detail and possible solutions are evaluated. It is found that under the given conditions the numerical description of the vertical wind gradients is crucial for the stability of the turbulence scheme. It is shown that for the determination of vertical gradients information from grid points beyond the immediately neighboring model levels must be incorporated – as it is common practice in the treatment of horizontal gradients – in order to obtain a numerically stable turbulence scheme. As a first approach vertical wind gradients are filtered using a 5-point filter prior to the evaluation of the stability functions. This approach yields to the overall best performance among all those tested and found in literature. The simulations additionally show that the use of a too high minimum diffusion coefficient (which is introduced in the model in order to avoid too low mixing) leads to losing important structures of the planetary boundary layer, such as the low level jet or a near-surface temperature inversion