Quantifying peakflow attenuation/amplification in a karst river using the diffusive wave model with lateral flow

The aim of this paper is to quantify peakflow attenuation and/or amplification in a river, investigating lateral flow from the intermediate catchment during floods. This is a challenge for the study of the hydrological response of permeable/intermittent streams, and our contribution refers to a modelling framework based on the inverse problem for the diffusive wave model applied in a karst catchment. Knowing the upstream and downstream hydrographs on a reach between two stations, we can model the lateral one, given information on the hydrological processes involved in the intermediate catchment. The model is applied to 33 flood events in the karst reach of the Iton River in French Normandy where peakflow attenuation is observed. The monitored zone consists of a succession of losing and gaining reaches controlled by strong surface‐water/groundwater (SW/GW) interactions. Our results show that despite a high baseflow increase in the reach, peakflow is attenuated. Model application shows that the intensity of lateral outflow for the flood component is linked to upstream discharge. A combination of river loss and overbank flow for highest floods is proposed for explaining the relationships. Our approach differentiates the role of outflow (river loss and overbank flow) and that of wave diffusion on peakflow attenuation. Based on several sets of model parameterization, diffusion is the main attenuation process for most cases, despite high river losses of up to several m³/s (half of peakflow for some parameterization strategies). Finally, this framework gives new insight into the SW/GW interactions during floods in karst basins, and more globally in basins characterized by disconnected river‐aquifer systems.     

Stochastic modelling of a diffusive wave for flood propagation using the random walk particle tracking method in a hypothetical city

Deterministic numerical schemes have been widely used for the solution of the diffusive wave (DW) equation, however, these schemes are computationally costly and suffer instability issues. This paper presents a stochastic random walk particle tracking (RWPT) method to solve such an equation for a dam‐break flow problem. Three different wave duration scenarios are presented for simulations of the DW for flood flows in a hypothetical city. The hypothetical city is represented by a domain of size 2,000 m by 500 m in x and y directions, respectively. The domain is divided into 25 m by 25 m cells. A dam is located at the upstream of the hypothetical city. Each scenario has a distinct propagation pattern after the dam is breached. Analysed and presented are 18 different simulations, which are composed of three different building configurations, two different bed slopes, and three different shapes of hydrographs. In this method, the flood volume is divided into a large number of particles where each particle carries a fixed amount of the flood volume. These particles undergo convective and diffusive movements, and their superposition represents propagation of the DW in the flow domain. The solution algorithm of the RWPT‐based equations is used to compute flood inundation depths in the hypothetical city. Comparison is drawn among the simulated results from three different shapes of the inflow hydrographs. The proposed stochastic method has two major advantages over traditional deterministic schemes: (a) greater efficiency, thus lesser computational costs, and (b) no instability issues.     

Nonlinear baroclinic equilibration at finite supercriticality

The nonlinear equilibration of finite amplitude baroclinic waves in Phillips two-layer model is investigated at finite supercriticality. The aims are to quantify the robustness and relevance of the nonlinear theory of Warn, Gauthier and Pedlosky (WGP) for the evolution of the developing baroclinic wave, and to assess the tightness of pseudomomentum and improved pseudoenergy bounds for disturbance amplitude and energy. A high-resolution numerical model is used to perform a parameter sweep in (β,?W)-space, where β is the inverse criticality of the initial flow, and W is the ratio of the channel width to the (internal) Rossby radius. At low supercriticalities, the main predictions of WGP are found to be accurate at short times, but at long times the fully nonlinear results are found to diverge from WGP's solution. The mechanism for equilibration involves the elimination of the lower layer potential vorticity (PV) gradient, but as the supercriticality increases this is achieved by the roll-up of a train of opposite-signed vortices, rather than by coarse-grain PV homogenization as in WGP. Peak wave amplitudes are typically ≈90% of the maximum attainable under the pseudomomentum bound. New formulae are given for the pseudoenergy bound on disturbance energy which, unlike the WGP solution and the pseudomomentum bound, have non-trivial dependence on W. A detailed assessment is made of the extent to which these bounds are attained.     

Isotopic fractionation induced by a surface effect influences the estimation of the hydrological process of topsoil

Isotopic heterogeneity in soil water has hindered the application of isotope compositions (δ¹⁸O and δ²H) in soil water dynamics. This heterogeneity has been suggested to be caused by soil properties such as organic matter (OM) and clay content. However, this is yet to be verified in field soil. We sampled the organic layer (O-horizon soil) with highly decomposed organic material and the A-horizon soil in western Sichuan, China, and equilibrated these samples with vapour created by unconfined labelling water. The relationship between soil properties and isotopic fractionation (ε_T/U) between unconfined water and the total soil water was used to determine the line-conditioned excess (lc-excess) and source rain of A-horizon field soil by removing the influence of confined water. Equilibration experiments demonstrated a significant isotopic difference between the ε_T/U levels in the A-horizon and O-horizon soils, indicating that OM plays an important role in isotopic fractionation. In field samples, the lc-excess of the unconfined A-horizon water was, on an average, 2.5‰ higher than that of bulk soil water. The average offsets between the annual rain and the estimated source rain of soil water decreased by 5.0 and 0.5‰ for hydrogen and oxygen after removing the influence of confined water. Isotopic heterogeneity should not be ignored while examining the evaporation of soil water, soil source rain, and hence the recent ‘two water worlds’ hypothesis, which is especially true for cases in which the soils contain high levels of OM.     

Shock acceleration of solar cosmic rays

We investigated the acceleration of solar cosmic rays (SCRs) by the shock waves produced by coronal mass ejections. We performed detailed numerical calculations of the SCR spectra produced during the shock propagation in the solar corona in terms of a model based on the diffusive transport equation using a realistic set of physical parameters for the corona. The resulting SCR energy spectrum N(ε) ∝ ε^?γ exp [? (ε/ε_max)^α] is shown to include a power-law portion with an index γ?2 that ends with an exponential tail with α ? 2.5 ? β, where β is the spectral index of the background Alfvén turbulence. The maximum SCR energy lies within the range ε_max = 1–300 MeV, depending on the shock velocity. Because of the steep spectrum of the SCRs, their backreaction on the shock structure is negligible. The decrease in the Alfvén Mach number of the shock due to the increase in the Alfvén velocity with heliocentric distance r causes the efficient SCR acceleration to terminate when the shock reaches a distance of r = 2–3R_⊙. Since the diffusive SCR propagation in this case is faster than the shock expansion, SCR particles intensively escape from the shock vicinity. A comparison of the calculated SCR fluxes expected near the Earth’s orbit with available experimental data indicates that the theory satisfactorily explains all of the main observed features.     

On hydromagnetic instabilities and the mean electromotive force in a non-uniformly stratified Earth’s core affected by viscosity

Linear magnetoconvection in a model of a non-uniformly stratified horizontal rotating fluid layer with a toroidal magnetic field is investigated for no-slip and finitely electrically conductive boundaries and with very thin stably stratified upper sublayer. The basic parabolic temperature profile is determined by the temperature difference between the boundaries and by the homogeneous heat source distribution in the layer. This results in a density pattern, in which a stably stratified upper sublayer is present. The developed diffusive perturbations (modes) are strongly affected by the complicated coupling of viscous, thermal and magnetic diffusive processes. The calculations were performed for various values of Roberts number (q ≪ 1 and q = O(1)). The mean electromotive force produced by the developed hydromagnetic instabilities is investigated to find the modes, which can be appropriate for creating the α-effect. It was found that the azimuthal part of the EMF is dominant for westward modes when the Elsasser number Λ ≲ O(1).     

基于遗传算法的扩散波洪水演算参数的确定方法

大量的理论分析和实际洪水演算表明,扩散波方法是一种既具有足够精度又相对简单的一类洪水演算方法。以线性扩散波方程在自由下边界条件下的解析解为例,利用遗传算法来确定扩散波方程的参数。遗传算法和一般的优化算法不同,它具有全局寻优能力,一般能得到问题的最优解或准最优解,是一类优秀的非线性函数优化方法。实例计算结果表明,采用遗传算法所得到的参数精度较高,可以类推到其它水文模型的参数率定中去。     

NaCl不饱和的海水体系卤水—矿物平衡研究

本文用实验的方法研究了Ｋ，Ｎａ，Ｍｇ，Ｃｌ，ＳＯ４－Ｈ２Ｏ体系在ＮａＣｌ不饱和条件下的卤水－矿物平衡关系，并与该体系对ＮａＣｌ饱和的相图作了对比。研究成果有利于更深入地探讨盐类矿床的形成和演化，对钾盐生产工艺的制订亦有重要指导作用。本文对四川盆地富钾卤水的成因作了合理的解释。     

Chemical Indicator of Spinel During Partial Melting and Subsolidus Equilibration of Mantle Peridotite:Experimental Study and Application to Natural Rocks

Systematic experimental studies on partial melting and subsolidus equilibration of three reconstituted spinel-peridotites have been carried out at temperatures ranging from 1000 to 1380℃ and pressures of 1.0 and 1.5 GPa. The results shows (1) during partial melting, Mg# [=Mg/(Mg+Fe)]and Cr# [=Cr/(Cr-Al)]of spinel increase with an increase in degrees of melting) (2) during subsolidus equilibration, with increasing temperatures, Mg# of spinel increases but Cr# of spinel remains almost unchanged in dunite and increases slightly in Iherzolite and harzburgite. The negative and quasi-linear Mg# -Cr# correlation of spinel represents an isotherm of total non-equilibrium. The same results have been obtained by means of mathematical modelling. It is also proved by Mg# -Cr# correlation of spinel in natural peridotites. As a result of the spinel subsolidus equilibration, only variation of Cr# of spinel is limited, and then Cr# of spinel can be used to estimate the relative degree of melting undergone by host rocks