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Organized spatial distribution of plants (plant zonation) in salt marshes has been linked to the soil aeration condition in the rhizosphere through simplistic tidal inundation parameters. Here, a soil saturation index (ratio of saturation period to tidal period at a soil depth) is introduced to describe the soil aeration condition. This new index captures the effects of not only the tidal inundation period and frequency but also the flow dynamics of groundwater in the marsh soil. One‐dimensional numerical models based on saturated flow with the Boussinesq approximations and a two‐dimensional variably saturated flow model were developed to explore the behaviour of this new soil aeration variable under the influence of spring‐neap tides. Simulations revealed two characteristic zones of soil aeration across the salt marsh: a relatively well aerated near‐creek zone and a poorly aerated interior zone. In the near‐creek zone, soils undergo periodic wetting and drying as the groundwater table fluctuates throughout the spring‐neap cycle. In the interior, the soil remains largely water saturated except for neap tide periods when limited drainage occurs. Although such a change of soil aeration condition has been observed in previous numerical simulations, the soil saturation index provides a clear delineation of the zones that are separated by an ‘inflexion point’ on the averaged index curve. The results show how the saturation index represents the effects of soil properties, tidal parameters and marsh platform elevation on marsh soil aeration. Simulations of these combined effects have not been possible with traditional tidal inundation parameters. The saturation index can be easily derived using relatively simple models based on five non‐dimensional variables. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
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Gualtiero Badin Jörn Behrens Christian Franzke Jens Rademacher 《地球物理与天体物理流体动力学》2019,113(5-6):425-427
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V. V. Alpatov V. I. Badin I. A. Grebnev M. G. Deminov D. S. Faermak 《Geomagnetism and Aeronomy》2012,52(6):793-796
The results of a theoretical analysis of the radial distribution of electron temperature T e in the area of heating of the lower ionosphere by intense shortwave radiation are presented. It was established that effective radius r eff of heating at a certain height may differ significantly from the characteristic radius of illumination of the ionosphere (a) by radiation at this height. At the boundary of the heating area (r = r eff ), the characteristic radial scale of T e changes is less than the corresponding scale of changes in the squared amplitude of the radiation electric field, and it is almost independent of the amplitude value; i.e., the formation of a relatively strong T e gradient at such a boundary is a common feature of heating of the lower ionosphere by intense shortwave radiation. 相似文献
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V. I. Badin 《Geomagnetism and Aeronomy》2011,51(2):178-186
A method for detecting discrete equidistant spectra in high-latitude magnetic observations is proposed. The method finds approximate
solutions of the classical Schuster problem, which finds a hidden periodicity in observations with considerable noise. The
usage of difference signals makes it possible to increase the latitudinal resolution of the magnetometric diagnostics. The
equidistant spectra of two different types have been detected based on the proposed method. The spectra of the first type
are interpreted as frequencies of coupled compressional-transverse magnetohydrodyncompressionalamic oscillations in the magnetospheric
cavity. The origin of the second type of spectra can be related to a rotating source, i.e., a small-scale vortex of magnetospheric
convection. Such an interpretation takes into consideration the Doppler frequency shift caused by entrainment of the ionospheric
neutral gas by magnetospheric convection. The results confirm the conclusion that discrete auroral frequencies are stable
under disturbed conditions. 相似文献
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Geomagnetism and Aeronomy - A new foE model for the auroral region is constructed; the model is based on an analysis of the models of auroral electron precipitations, the boundaries of the discrete... 相似文献
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G. Badin 《地球物理与天体物理流体动力学》2013,107(5):526-540
The surface quasi-geostrophic approximation is re-written in an oceanic context using the two-dimensional semi-geostrophic approximation. The new formulation allows to take into account the presence of out-of-balance flow features at scales comparable to or smaller than the Rossby radius of deformation and for small bulk Richardson numbers. Analytical solutions show that, while the surface quasi-geostrophic approximation tends to underestimate the buoyancy anomaly, the inclusion of finite Rossby number allows for larger values of the buoyancy anomaly at depth. The projection of the surface semi-geostrophic solution on the first baroclinic modes is calculated. The result of the projection is a functional form that decreases with the values of the Rossby number and toward smaller scales. Solutions for constant and exponential profile for the background potential vorticity are compared. Results of the comparison show that, in agreement with the results found for balanced flows, even for large Rossby number the exponential profile for the background potential vorticity retains smaller values for the buoyancy anomaly at depth than the solution found using a constant potential vorticity profile. 相似文献
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Low-permeability layer (LPL), formed by natural deposit or artificial reclamation and commonly found below the intertidal zone of coastal groundwater system, can retard the ingress of seawater and contaminants, and shorten the travel time of the land-sourced contaminant to the marine environment compared with a homogenous sandy coastal aquifer. However, there is limited understanding on how an intertidal LPL, a condition occurred in a coastal aquifer at Moreton Bay, Australia, influences the groundwater and contaminant transport across the shallow beach aquifer system. We characterized the aquifer hydrological parameters, monitored the in situ groundwater heads, and constructed a 2-D numerical model to analyses the cross-shore hydrological processes in this stratified system. The calibrated model suggests that in the lower aquifer, the inland-source fresh groundwater flowed horizontally towards the sea, upwelled along the freshwater–saltwater interface, and exited the aquifer at the shore below the LPL. Whereas in the upper aquifer, the tidally driven seawater circulation formed a barrier that prevented fresh groundwater from horizontal transport and discharge to the beach above the LPL, thereby directing its leakage to the lower aquifer. A contaminant represented by a conservative tracer was ‘released’ the upper aquifer in the model and results showed that the spreading extent of the contaminant plume, the maximum rate of contaminant discharge to the ocean, and its plume length decreased compared with a simulation case in a homogenous sandy aquifer. Sensitivity analysis was also conducted to investigate the characteristics of the LPL, including its continuity and hydraulic conductivity, which were found to vary along the beach at Moreton Bay. The result shows that with a lower hydraulic conductivity and continuous layer of LPL reduced the groundwater exchange and contaminant transport between upper and lower aquifer. The findings from the combined field and modelling investigations on the impact of an intertidal LPL on coastal aquifer systems highlight its significant implications to alter the groundwater and mass transport across the land–ocean interface. 相似文献
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V. I. Badin 《Geomagnetism and Aeronomy》2016,56(1):87-94
Maps for standard deviations of the drift velocity of E layer ionosphere electrons in the radar field of vision were constructed with the aid of narrowband and low-pass filtering based on STARE Doppler data. In these maps, narrowband filtering reveals the geometric configurations of the excitation of particular ultralow-frequency (ULF) oscillations. Such a configuration indicates nonresonant origins of these oscillations. Low-pass filtering of the Doppler data revealed specific absorption of background ULF signals; this absorption is attributed to the resonance of magnetic field lines. Quantitative estimates for minimum frequencies of the resonant ULF absorption occurring in the eigenfrequency continuum of magnetic field lines were found. 相似文献