C.—W. M. O.—O. M. M.

Abstract

The intrusion of seawater in a tidal river is treated as a diffusion problem, characterized by a coefficient of longitudinal diffusivity.

In order to analyse the longitudinal diffusivity, a mathematical model is set up, consisting of two bodies of water, either one besides the other or one on top of the other. The two bodies are assumed to move relatively to each other, as a secondary effect of the tidal flow. It is moreover assumed that there is turbulent exchange of salt between the bodies.

It is demonstrated that the diffusion of salt into the river is greatest for an optimum value of the coefficient of exchange between the two bodies.

Exchange weaker or stronger than this optimum both diminish the salt intrusion.

The theory is applied to the Rotterdam Waterway, for which estimates of the exchange are made. Estimation of the reduction of the turbulence by stratification and hence of the vertical exchange, shows that the observed strong intrusion is explainable.

Intensified vertical mixing, for instance as provoked by compressed air, need not always result in less intrusion, and hence should be considered carefully.     

The Influence of the Prandtl Number on the Style of Vigorous Thermal Convection

The effect of the Prandtl number on convection in a planar three-dimensional geometry is investigated in this study. We have employed a numerical scheme to integrate the governing equations. Differently from previous studies we have chosen stress-free boundaries. Experiments have been performed at a Rayleigh number of Ra = 10 6 for Prandtl numbers (Pr) ranging from 0.025 to 100. We have further conducted one experiment in the limiting case of infinite Prandtl number. Despite the differences in the geometry and the boundary conditions, as compared to other studies, we find a similar transition in the dynamics of the flow when the Prandtl number is increased. While the velocity and the temperature structure show diffusive character at low Pr, sharp thermal boundary layers form at high Pr. The heat transport efficiency increases with Pr until a transition value is reached, from there on Nu behaves almost asymptotically. The transition can not be caused by a change in hierarchies between velocity and thermal boundary layers, as suggested in other studies. Due to the stress-free boundaries, a velocity boundary layer does not exist. We observe that the toroidal part of the flow is strong at low Pr and looses its strength with increasing Pr, thus it is likely to be responsible for the transition. In a further chapter we demonstrate that due to the neglect of the toroidal part in two-dimensional calculations at low Pr results are obtained which are misleading, even in a qualitative sense. Infinite Pr results from 2D calculations closely resemble the dynamics of fully 3D flows.     

Application of the soil and water assessment tool model on the Lower Porsuk Stream Watershed

Watershed models that combine hydrology and water quality are being widely used in integrated watershed management for the determination of best water management practices. In this study, the hydrology of the Lower Porsuk Stream Watershed in Turkey has been modelled with the Soil and Water Assessment Tool to determine optimal water management strategies. The calibration and the validation process have been accomplished using data from two monitoring stations. The model has been run for the 1978–2009 period, and while the 1998–2004 period has been used for calibration, the validation has spanned the whole period. The SWATCup calibration and uncertainty program has been used for this purpose. No significant differences have been detected among different iteration numbers in the calibration period. The monthly Nash–Sutcliffe and R² performance indicators for the upstream Esenkara station have been 0.74 and 0.88, respectively, for the calibration period, and 0.87 and 0.87, respectively, for the validation period. The Kiranharmani station, which is located close to the watershed outlet, has shown values of 0.59 and 0.72, respectively, for the calibration period, and 0.44 and 0.56, respectively, for the validation period. There are uncertainties in the abstracted irrigation and groundwater quantities that have reflected in the results in the Kiranharmani station, which is more affected as it lies downstream of the irrigation areas. The effects of different irrigation practices on the flow regime have been also investigated. A scenario has been implemented in which drip irrigation wholly replaces conventional furrow and sprinkler irrigation. The scenario has shown increases in stream flows by 87% for the whole year. The adoption of more efficient irrigation practices thus results in reducing the water stress induced by irrigation demands. With this study, a modelling framework has been founded to aid water management applications in the Lower Porsuk Stream Watershed by generating scenarios for best management practices. Copyright © 2012 John Wiley & Sons, Ltd.     

Seasonality of the submesoscale dynamics in the Gulf Stream region

Frontogenesis and frontal instabilities in the mixed layer are known to be important processes in the formation of submesoscale features. We study the seasonality of such processes in the Gulf Stream (GS) region. To approach this problem, a realistic simulation with the Hybrid Coordinate Ocean Model is integrated for 18 months at two horizontal resolutions: a high-resolution (1/48°) simulation able to resolve part of the submesoscale regime and the full range of mesoscale dynamics, and a coarser resolution (1/12°) case, in which submesoscales are not resolved. Results provide an insight into submesoscale dynamics in the complex GS region. A clear seasonal cycle is observed, with submesoscale features mostly present during winter. The submesoscale field is quantitatively characterized in terms of deviation from geostrophy and 2D dynamics. The limiting and controlling factor in the occurrence of submesoscales appears to be the depth of the mixed layer, which controls the reservoir of available potential energy available at the mesoscale fronts that are present most of the year. Atmospheric forcings are the main energy source behind submesoscale formation, but mostly indirectly through mixed layer deepening. The mixed layer instability scaling suggested in the (Fox-Kemper et al., J Phys Oceanogr 38:1145–1165, 2008) parametrization appears to hold, indicating that the parametrization is appropriate even in this complex and mesoscale dominated area.     

Periodic behavior of solar flare index during solar cycles 20 and 21

Short-term periodicities of solar activity were studied with the flare index by using Discrete Fourier Transform for the time interval 1966–1986. Two noticeable periodicities (18.5 and 5 months) have been found. The existence of these periodicities comparing with the early findings is discussed.     

Distribution of LDE flares on the Sun during solar cycles 20 and 21

We have studied the latitude and longitude (northern and southern hemispheric) distributions based on 2277 LDE flares observed during the period from 1966 to 1986. We have found that there exist active zones, in which the LDE flare occurrence rate is much higher. Latitudinal belts between 11–20° and longitudinal belts around 80–100° are the most prolific places to produce LDE flares. During cycles 20 and 21 these active zones produced 36% of the total number of LDE flares by occupying only 6% area of the Sun.     

In situ measurements of heating parameters in the auroral ionosphere

Four sounding rocket payloads were launched in early 1977 to measure heating parameters in the auroral oval. Geophysical conditions were different for the four flights: auroral arc substorm main phase diffuse aurora, and auroral arc with negative bay. The conductivity tensor and the heating rates of particle and Joule heating are determined. The heating rates range in the order of a few tens of mWm^?2. These magnitudes accord with those determined with the aid of backscatter facilities and other sounding rocket observations.     

A search for the solar Sr 87 content and the solar Rb/Sr ratio

Some energy levels of Sr 87 shows hyperfine splitting which broadens strontium lines in the solar spectrum. By analysis of two faint photospheric Sr i lines of Multiplet No. 3 an upper limit of the relative Sr 87 content (Sr 87/Sr) of 1/4 has been found. The terrestrial value is 0.07–0.075.The solar abundance of strontium found from the two lines is log _Sr = 2.90 in the log _H = 12.00 scale. Using the solar rubidium abundance recently determined by the author (Hauge, 1972), one obtains _Rb/ _Sr = 0.5±0.1. This value is larger than found even in chondrites showing high rubidium content.     

Peculiar solar flares and plages of possible interest for the study of electric quadrupole lines of NaI and Mgii

Attention is drawn to flare-like plages showing the resonance lines of Nai and Mgii as strong emission lines. Spectra of such objects may prove of interest for the study of electric quadrupole lines of the type 3² S-n ²D.Paper dedicated to Professor Hannes Alfvén on the occasion of his 80th birthday, 30 May 1988.     

Space-time Interpolation by Combining Air Pollution and Meteorologic Variables

In this paper, a technique is proposed in order to study triple time series. It combines the variable of interest, sulfur dioxide (SO₂) with two related meteorological variables. Hence, three variables measured at the same time points are jointly analyzed. Instead of using classical multiple time series analysis, it is suggested to consider the measurements of the two meteorological variables as coordinates of a two-dimensional space and the simultaneous observation of the third variable (associated SO₂ concentrations) at each pair of coordinates. Subsequently, well-known optimum interpolation is used for predicting the SO₂ concentrations on the basis of six meteorological variables. All the variables of the study are measured at the same times (all days in 2000) around the city of Istanbul, Turkey. The triple diagrams, in the form of contour maps, help to answer various questions concerning the SO₂ concentration variability with respect to meteorological variables. The same diagrams also provide a basis for the prediction of SO₂ concentrations. It is shown that the relative prediction error is less than 10%, which is acceptable for the practical studies.