Beljaars et al. (1987) developed a model for neutrally stratified boundary-layer flow over roughness changes and topography. It has been discovered that a constant parameter, , was missing in the algebraic-stress closure equations of their paper. This omission also occurred in the MSFD model code but only affects the Askervein Hill shear-stress results for the E-- turbulence closure in Beljaars et al. It also changes the stress results of Karpik (1988), but not his conclusions regarding the robustness of his improved numerical scheme. The present paper demonstrates the effect of the omission of the parameter, , and tests the sensitivity of the model to variations in its value. The new results are compared with the data and model results of Zeman and Jensen (1987). 相似文献
This paper investigates the kinetics of biogenic silica dissolution in seawater, through batch dissolution, where the reaction
is observed as the increase in dissolved silicic acid concentration with time. It utilises new data from dissolution of the
marine diatom Cyclotella cryptica, and the freshwater diatom C. meneghiniana, as well as literature results. The sum of exponentials form:
, is hypothesised as the most general rate equation, with the single exponential form occurring in a minority of cases. The
consistency of this behaviour with a near-exponential decay of surface area with time, an appropriate mathematical integration,
and surface heterogeneity, is discussed. (Serious errors in some existing integrations are identified.) The rate of dissolution
at constant surface area is shown to decrease non-linearly as the ambient concentration of silicic acid increases. A fractional
order with respect to silicic acid in the back reaction, close to 0.5, leads to a mechanism in which an intermediate is formed
from the surface and an, as yet, unidentified molecule, probably water. Good preliminary fits are found between the model
and literature results found using entirely different methods. A parallel treatment of hydrogen ion dependency is suggested.
The likely distortion of full reaction curves from exponential behaviour imposed by the back reaction, is considered in detail. 相似文献
This paper presents results of a trial of a Pisces HF radar system aimed at assessing its use as a component of a wave-monitoring network being installed around the coasts of England and Wales. The radar system has been operating since December 2003 and the trial continued to June 2005. The data have been processed in near-real time and displayed on a website. Radar measurements of the directional spectrum and derived parameters are compared with those measured with a directional waverider and with products from the Met Office, United Kingdom, operational wave model. Radar measurements of currents and winds are also compared with Met Office model products and, in the case of winds, with the QuikSCAT scatterometer. Statistics on data availability and accuracy are presented. The results demonstrate that useful availability and accuracy in wave and wind parameters are obtained above a waveheight threshold of 2 m and at ranges up to 120 km at the radar operating frequencies (7-10 MHz) used. Waveheight measurements above about 1 m can be made with reasonable accuracy (e.g., mean difference of 2.5% during January-February 2004). Period and direction parameters in low seas are often contaminated by noise in the radar signal. The comparisons provide some evidence of wave model limitations in offshore wind and swell conditions 相似文献
The possibility of observing satellites with the very long baseline interferometry (VLBI) technique has been discussed for several years in the geodetic community, with observations of either existing satellites of the global navigation satellite systems or of satellites dedicated to realise a space tie. Such observations were carried out using the Australian telescopes in Hobart and Ceduna which, for the first time, integrated all the necessary steps: planning the observations (automated scheduling), correlation of the data and the generation of a series of time delay observables suitable for a subsequent geodetic analysis. We report on the development of new and the adaptation of existing routines for observing and data processing, focusing on technology development. The aim was to use methods that are routinely used in geodetic VLBI. A series of test experiments of up to six hours duration was performed, allowing to improve the observations from session to session and revealing new problems still to be solved. The newly developed procedures and programs now enable more observations. Further development assumed, this bears the prospect of being directly applied to the observation of dedicated space-tie satellites. 相似文献
Since 1993 it is known that there is a good correlation between the scintillation in the solar irradiance and solar image quality (Seykora, 1993). This effect is now being used in a number of experiments to evaluate solar image quality and to measure site seeing. In this paper we explore further the calibration of this scintillation (I) in terms of the Fried parameter (r0) taking into account variations in the refractive index structure constant C
N2
with height (h), zenith distance () dependence and the effects of wind velocities. A variant in the scintillometer setup is proposed which decreases sharply the dependance on C
N2
, , and the wind velocities. It uses an array of scintillometers. The same array can be used to measure theC
N2
profile with height. Some preliminary results of the calibration of current NSO site survey measurements are presented. 相似文献
Cesium and Strontium concentrations were analyzed in eight pedogenetic soil profiles developed on different rocks from a semiarid
mediterranean region: La Mancha (Central Spain). Concentration activities of 137Cs and 90Sr, as for some soil properties, were also measured. The results are presented in this document: Cs concentrations range between
0.4 and 18.3 mg kg−1 and Sr varies widely between 11.0 and 3,384 mg kg−1. Therefore, it is clear that there is a broad range of concentrations and there are also values significantly higher than
the average values stated by several authors. Concentrations of long-life artificial radionuclides (137Cs, 90Sr) were determined in some of the same soils. The activity concentration mean values (Bq kg−1) were ranging between 0.82 and 21.76 for 137Cs and 90Sr variations range between 6.73 and 0.35. There were no significant correlations between radionuclides and stable trace elements.
The data indicate that the soils do not show significant radioactivity of these elements and therefore they do not pose a
danger. By the same token, no risk of contamination by this activity was detected. Finally, spatial patterns seem to be affected
by the soil type and some soil properties. 相似文献