Deriving characteristic parameters of the convective boundary layer from sodar measurements of the vertical velocity variance

This paper deals with the derivation of the convective mixing height and the characteristic convective velocity w _* from profiles of _w measured by sodar. The parameters were obtained by fitting an analytical profile to the observed data. Results were compared with values obtained by the meteorological preprocessor of a dispersion model and from noon radiosoundings. In addition, a Monte Carlo method was applied to study the influence of measurement errors. It turned out that it is inherently difficult to determine the depth of deep mixed layers from sodar measurements with a limited range, although the determination of w _* should be possible. However, a significant underestimation of _w , and thus w _*, was found, which is probably due to disproportional sampling of updrafts and downdrafts.     

Inter-annual and seasonal variations in the air–sea CO2 balance in the central Baltic Sea and the Kattegat

We estimated the net annual air–sea exchange of carbon dioxide (CO₂) using monitoring data from the East Gotland Sea, Bornholm Sea, and Kattegat for the 1993–2009 period. Wind speed and the sea surface partial pressure of CO₂ (pCO₂^w), calculated from pH, total alkalinity, temperature, and salinity, were used for the flux calculations. We demonstrate that regions in the central Baltic Sea and the Kattegat alternate between being sinks (−) and sources (+) of CO₂ within the −4.2 to +5.2 mol m⁻² yr⁻¹ range. On average, for the 1994–2008 period, the East Gotland Sea was a source of CO₂ (1.64 mol m⁻² yr⁻¹), the Bornholm Sea was a source (2.34 mol m⁻² yr⁻¹), and the Kattegat was a sink (−1.16 mol m⁻² yr⁻¹). Large inter-annual and regional variations in the air–sea balance were observed. We used two parameterizations for the gas transfer velocity (k) and the choice varied the air–sea exchange by a factor of two. Inter-annual variations in pCO₂^w between summers were controlled by the maximum concentration of phosphate in winter. Inter-annual variations in the CO₂ flux and gas transfer velocity were larger between winters than between summers. This indicates that the inter-annual variability in the total flux was controlled by winter conditions. The large differences between the central Baltic Sea and Kattegat were considered to depend partly on the differences in the mixed layer depth.     

Effects of nonlinear model response on allocation of streamflow depletion: exemplified by the case of Beaver Creek,USA

Anomalies found when apportioning responsibility for streamflow depletion are examined. The anomalies arise when responsibility is assigned to the two states that contribute to depletion of Beaver Creek in the Republican River Basin in the United States. The apportioning procedure for this basin presumes that the sum of streamflow depletions, computed by comparing simulation model runs with and without groundwater pumping from individual states, approximates the streamflow depletion when both states are pumping. In the case study presented here, this presumed superposition fails dramatically. The stream drying and aquifer-storage depletion, as represented in the simulation model used for allocation, are examined in detail to understand the hydrologic and numerical basis for the severe nonlinear response. Users of apportioning procedures that rely on superposition should be aware of the presence and likely magnitude of nonlinear responses in modeling tools.     

Monotone nonlinear finite-volume method for challenging grids

This article presents a new positivity-preserving finite-volume scheme with a nonlinear two-point flux approximation, which uses optimization techniques for the face stencil calculation. The gradient is reconstructed using harmonic averaging points with the constraint that the sum of the coefficients included in the face stencils must be positive. We compare the proposed scheme to a nonlinear two-point scheme available in literature and a few linear schemes. Using two test cases, taken from the FVCA6 benchmarks, the accuracy of the scheme is investigated. Furthermore, it is shown that the scheme is linearity-preserving on highly complex corner-point grids. Moreover, a two-phase flow problem on the Norne formation, a geological formation in the Norwegian Sea, is simulated. It is demonstrated that the proposed scheme is consistent in contrast to the linear Two-Point Flux Approximation scheme, which is industry standard for simulating subsurface flow on corner-point grids.     

A review on missing hydrological data processing

Like almost all fields of science, hydrology has benefited to a large extent from the tremendous improvements in scientific instruments that are able to collect long-time data series and an increase in available computational power and storage capabilities over the last decades. Many model applications and statistical analyses (e.g., extreme value analysis) are based on these time series. Consequently, the quality and the completeness of these time series are essential. Preprocessing of raw data sets by filling data gaps is thus a necessary procedure. Several interpolation techniques with different complexity are available ranging from rather simple to extremely challenging approaches. In this paper, various imputation methods available to the hydrological researchers are reviewed with regard to their suitability for filling gaps in the context of solving hydrological questions. The methodological approaches include arithmetic mean imputation, principal component analysis, regression-based methods and multiple imputation methods. In particular, autoregressive conditional heteroscedasticity (ARCH) models which originate from finance and econometrics will be discussed regarding their applicability to data series characterized by non-constant volatility and heteroscedasticity in hydrological contexts. The review shows that methodological advances driven by other fields of research bear relevance for a more intensive use of these methods in hydrology. Up to now, the hydrological community has paid little attention to the imputation ability of time series models in general and ARCH models in particular.     

Devensian Late-glacial and early Flandrian environmental history of the Vale of Pickering,Yorkshire, England

Pollen, sedimentological and charcoal particle analyses are presented from Devensian Late-glacial and early- to mid-Flandrian deposits from a former lake in the Vale of Pickering, Yorkshire. The combined analytical methods provide evidence for a short-lived climatic deterioration towards the end of the Late-glacial Interstadial, followed by a brief recovery prior to the Loch Lomond Stadial. This deterioration may be correlated with one of the ‘pre-Younger Dryas’ cooling periods identified not only in other pollen sequences from Britain and Europe, but from such diverse sources as Foraminifera from the Norwegian Sea and electrical conductivity measurements from the Greenland ice sheet. Loss-on-ignition and magnetic susceptibility data suggest that the Loch Lomond Stadial was characterised by an initial prolonged temperature decline, followed by a sudden more severe downturn resulting in particularly intense solifluction. Radiocarbon accelerator dating of the early Flandrian marl deposits illustrates the problem of age determination in calcareous lakes, and an estimate of the magnitude of ‘hard water error’ is obtained. The local population expansion of Alnus glutinosa is dated to 7640 ± 85 yr BP, but there is possible evidence for a Late-glacial presence of the tree, the significance of which is discussed in relation to other sites in east Yorkshire. © 1996 John Wiley & Sons, Ltd.     

A formulation for diagnostic anomaly models

It is shown that the anomaly model governing the difference between two integrations of the equations of motion can be written in a form that is formally linear in the anomalies, by choosing the basic state to be the mean of the results of the two integrations.