Similarity Relations for C_{T}^2 in the Unstable Atmospheric Surface Layer: Dependence on Regression Approach,Observation Height and Stability Range

A great variety of similarity functions for the structure parameter of temperature ( \(C_{T}^2\) ) have been proposed in the literature. They differ in the way they were derived from the data and in the characteristics of the dataset used for their derivation (surface type, observation level, stability range). In this study, we use one single dataset (CASES-99 experiment) and investigate the impact on the similarity functions of applying various regression approaches, and measuring at different heights and within different stability ranges. We limit ourselves to similarity functions under unstable conditions, and evaluate only the most common shape that describes the relation with two coefficients ( \(f\left( z/L\right) =c_{1} \left( 1-c_{2} {z}/{L}\right) ^{-2/3}\) , where \(z\) is the height, and \(L\) is the Obukhov length and a measure of the stability, and \(c_{1}\) and \(c_{2}\) are the regression coefficients). The results show that applying various regression approaches has an impact on the regression coefficients \(c_{1}\) and \(c_{2}\) . Thus studies should always specify the regression approach when presenting similarity relations. We suggest use of an orthogonal distance regression method such that uncertainties in \(-z/L\) are also taken into account, to apply this to the logarithmic transformation of both dimensionless groups, and to use a weighted dataset such that unreliable data points have a smaller influence on the fit. Dividing the dataset into eight height ( \(z\) ) and eight stability ( \(-{1/L}\)  classes) classes, we show that the observation height and the stability range has an impact on the coefficients too. This implies that variations in \(c_{1}\) and \(c_{2}\) found in the literature may result from variations in the height and stability ranges among the datasets. Furthermore, application of the coefficients on a dataset obtained at a different height or within a different stability range has to be made with care. Finally, the variation in the coefficients between the classes indicates that the Monin–Obukhov similarity function for \(C_{T}^2\) is not sufficiently described by the two-coefficient function used here.     

Towards a data assimilation system for morphodynamic modeling: bathymetric data assimilation for wave property estimation

Data assimilation is mainly concerned with the proper management of uncertainties. The main objective of the present work is to implement and analyze a data assimilation technique capable of assimilating bathymetric data into a coupled flow, wave, and morphodynamic model. For the case presented here, wave significant height, wave direction of incidence, and wave peak period are being optimized based on bathymetric data taken from a twin experiment. An adjoint-free variational scheme is used. In this approach, a linear reduced order model (ROM) is constructed as an approximation of the full model. The ROM is an autoregressive model of order 1 (AR1) that preserves the parametrization. Since the ROM is linear, the construction of its adjoint is straightforward, making the implementation of 4D variational data assimilation effortless. The scheme is able to update the morphodynamic model satisfactorily despite the fact that the model shows nonlinear behavior even for very small perturbations of all three parameters. The size and direction of the perturbations necessary for constructing the ROM have a significant impact on the performance of the technique.     

Birkhoff's normalization

Birkhoff's normalizing canonical transformation at an equilibrium of elliptic type with no internal resonance can be built explicitly and recursively, without partial inversions or substitutions, by means of Lie transforms.Invariant sections and ordinary families of periodic orbits for truncated normalized systems are analyzed in detail.     

Economic Commission for Europe inventory of transboundary ground water in Europe

In Europe, a long history of cooperation over transboundary rivers--most notably the Rhine and Danube rivers--exists. To help foster cooperation and communication vis-à-vis transboundary ground water, the United Nations Economic Commission for Europe (UNECE), as part of its ground water program, conducted a survey on transboundary aquifers in Europe. The survey produced 25 responses from 37 countries and identified 89 transboundary aquifers. Respondents reported on the degree of ground water use within their own boundaries, transboundary aspects (agreements, joint commissions, etc.) of ground water, and transboundary aquifers themselves. The inventory proved useful, but a number of problems were identified: different map scales and symbols, difficulty in identifying transboundary aquifers, inconsistent labeling of aquifers, and data discrepancies. The UNECE ground water program also drafted guidelines for monitoring and assessment of transboundary ground water. These guidelines are not legally binding but have been adopted by 25 countries, deal mainly with monitoring and assessment, and are being implemented through a number of pilot projects. Other organizations-the United Nations Scientific, Educational and Cultural Organization, the Food and Agriculture Organization, the International Association of Hydrogeologists, and the European Union--are all supporting the investigation of transboundary aquifers in an effort to facilitate data sharing and coordinated management of these valuable resources.     

The first height measurements of the negative ion composition of the stratosphere

For the first time, height profiles of the stratospheric negative ion composition are presented. The results are from two nights of balloon borne mass spectrometers and cover an altitude range from 23.8 to 38.9 km. Below approx. 30km, NO^?₃ · mHNO₃ ions are dominant. These are replaced by HSO₄^? · nH₂SO₄ · oHNO₃ ions above this height. There are indications that the most abundant ions above 32 km have masses greater than 280 atomic mass units (amu), the instruments' mass range. The fractional ion count rates as a function of altitude are presented and their significance for neutral trace gas analysis and ion sampling is discussed.     

A comparison of wind-tunnel experiments and numerical simulations of neutral and stratified flow over a hill

A comparison is made of numerical and experimental results for flow over two-dimensional hills in both neutral and stably stratified flow. The numerical simulations are carried out using a range of one-and-a-half order and second-order closure schemes. The performance of the various turbulence schemes in predicting both the mean and turbulent quantities over the hill is assessed by comparing the results with new wind-tunnel measurements. The wind-tunnel experiments include both neutral and stably stratified flow over two different hills with different slopes, one of which is steep enough to induce flow separation. The dataset includes measurements of the mean and turbulent parts of the flow using laser Doppler anemometry. Pressure measurements are also made across the surface of the hill. These features make the dataset an excellent test of the model performance. In general second-order turbulence schemes provide the best agreement with the experimental data, however, they can be numerically unstable for steep hills. Some modifications can be made to the standard one-and-a-half order closure scheme, which results in improved performance at a fraction of the computation cost of the second-order schemes.     

Analysing Product-Specific Behaviour to Support Process Dependent Updates in a Dynamic Spatial Updating Model

A scale‐independent database that allows derived maps to be dynamically updated from a centrally maintained data source is an appealing alternative to traditional map revision techniques, which by today's standards are costly and inefficient. This paper presents a dynamic spatial updating model that supports automated updating of non‐standard maps in a scale‐independent database‐centric map production environment. Maps derived from the database are not separate data sets, but rather active views of the database. Each derived map is displayed in a unique way by implementing cartographic operations at the map level. While the operations applied require user involvement for strategic cartographic decisions, and algorithmic initiation and control, the technique allows geographic data to be processed cartographically without affecting the geometric integrity of the database. Each time a derived map is opened it retrieves the spatial data (and updates) from the database and applies the unique cartographic representation methods that persist on the individual derived maps. Database updates are automatically triggered to cartographic products, as process dependent updates, according to their individual product‐specific behaviour. This paper investigates product‐specific behaviour (product multiplicities) and the cartographic processing requirements to support dynamic spatial updating techniques in an object‐oriented map publishing environment. These techniques are implemented in an off‐the‐shelf software environment using ArcGIS.     

Granta MIST

The magnetosphere, ionosphere and solar–terrestrial physics community gathered at Selwyn College, University of Cambridge, for three days between Tuesday 5 April and Thursday 7 April 2005. Neil Arnold and Andrew Lyons report.