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41.
An improved diagnostic stratocumulus scheme based on estimated inversion strength and its performance in GAMIL2 总被引:1,自引:0,他引:1
Based on satellite data and the estimated inversion strength (EIS) derived by Wood et al. (2006), a feasible and uncomplicated stratocumulus scheme is proposed, referred to as EIS scheme. It improves simulation of cloud radiative forcing (CRF) in the Grid-point Atmospheric Model of IAP/LASG version 2 (GAMIL2.0) model. When compared with the original lower troposphere stability (LTS) scheme, the EIS scheme reproduces more reasonable climatology distributions of clouds and CRF. The parameterization partly corrects CRF underestimation at mid and high latitudes and overestimation in the convective region. Such improvements are achieved by neglecting the effect of free-tropospheric stratification changes that follow a cooler moist adiabat at middle and high latitude, thereby improving simulated cloudiness. The EIS scheme also improves simulation of the CRF interannual variability. The positive net CRF and negative stratiform anomaly in the East Asian and western North Pacific monsoon regions (EAWNPMR) are well simulated. The EIS scheme is more sensitive to sea surface temperature anomalies (SSTA) than the LTS. Therefore, under the effect of a warmer SSTA in the EAWNPMR, the EIS generates a stronger negative stratiform response, which reduces radiative heating in the low and mid troposphere, in turn producing strong subsidence and negative anomalies of both moisture and cloudiness. Consequent decreases in cloud reflection and shading effects ultimately improve simulation of incoming surface shortwave radiative fluxes and CRF. Because of the stronger subsidence, a stronger anomalous anticyclone over the Philippines Sea is simulated by the EIS run, which leads to a better positive precipitation anomaly in eastern China during ENSO winter. 相似文献
42.
Optimization models play an important role in long-term hydroelectric resources planning. The effectiveness of an optimization
model, however, depends on its capability of dealing with uncertainties. This study presents a multistage interval-stochastic
programming model for long-term hydropower planning, in which uncertainties are reflected as randomness and intervals. The
model is developed based on interval programming technique and recourse-based multistage stochastic programming and using
the expected value of long-term hydroelectric profit as the objective function. A solution method of the developed model is
also presented, which is based on a decomposition method by partitioning the multistage interval-stochastic program into two-stage
stochastic programming sub-problems in each scenario-tree node. A hypothetical case study is used to demonstrate the developed
model and its solution method. Modeling results demonstrates the computationally effectiveness of the solution method and
reveal the applicability of the developed model for long term planning of hydroelectric resources. 相似文献
43.
Tae-Woong Kim Hosung Ahn 《Stochastic Environmental Research and Risk Assessment (SERRA)》2009,23(3):367-376
Missing data in daily rainfall records are very common in water engineering practice. However, they must be replaced by proper
estimates to be reliably used in hydrologic models. Presented herein is an effort to develop a new spatial daily rainfall
model that is specifically intended to fill in gaps in a daily rainfall dataset. The proposed model is different from a convectional
daily rainfall generation scheme in that it takes advantage of concurrent measurements at the nearby sites to increase the
accuracy of estimation. The model is based on a two-step approach to handle the occurrence and the amount of daily rainfalls
separately. This study tested four neural network classifiers for a rainfall occurrence processor, and two regression techniques
for a rainfall amount processor. The test results revealed that a probabilistic neural network approach is preferred for determining
the occurrence of daily rainfalls, and a stepwise regression with a log-transformation is recommended for estimating daily
rainfall amounts. 相似文献
44.
45.
Interaction of a river plume with coastal upwelling in the northeastern South China Sea 总被引:5,自引:0,他引:5
Observational and modeling studies were conducted to investigate the Pearl River plume and its interaction with the southwesterly driven upwelling circulation in the northern South China Sea during the summer. After exiting the Pearl River Estuary, the discharged freshwater generates a nearly stationary bulge of freshwater near the entrance of the estuary. Forced by the wind-driven coastal upwelling current, the freshwater in the outer part of the bulge flows downstream at the speed of the current and forms a widening and deepening buoyant plume over the shelf. The plume axis gradually shifts offshore of the current maximum as a result of currents induced by the contrasting density at the nose of plume and by the intensified Ekman drift in the plume. In this plume–current system, the fraction of the discharged freshwater volume accumulated in the bulge reaches a steady state and the volume of newly discharged freshwater is transported downstream by the upwelling current. Enhancement of stratification by the plume thins the surface frictional layer and enhances the cross-shelf circulation in the upper water column such that the surface Ekman current and compensating flow beneath the plume are amplified while the shoaling of the deeper dense water in the upwelling region changes minimally. The pressure gradient generated between the buoyant plume and ambient seawater accelerates the wind-driven current along the inshore edge of the plume but retards it along the offshore edge. Along the plume, downward momentum advection is strong near the highly nonlinear source region and a weaker upward momentum advection occurs in the far field over the shelf. Typically, the plume is shaped by the current over the shelf while the current itself is adjusting to a new dynamic balance invoked by the plume-induced changes of vertical viscosity and the horizontal pressure gradient. The spatial variation of this new balance leads to a coherent change in the cross-isobath transport in the upper water column during upwelling. 相似文献
46.
The Changjiang diluted water (CDW) around Jeju Island between 2002 and 2006 in response to external forcings, such as wind, tidal forcing and low river discharge, is studied using a three-dimensional model. The model results suggest that wind largely determines spatial differences of CDW and the freshwater export toward Jeju Island between two years. In 2006, when northwestward wind blows during mid June to mid August, the wind-induced Ekman flow causes a broad northeastward extension of CDW and carries a significant amount of freshwater northeastward Jeju Island in August. On the other hand, in 2002 northward wind during mid July to early August drives the CDW to the southwest of Jeju Island, and thereafter the CDW is mainly advected northeastward along the Cheju Current during mid August when the wind becomes weak. Therefore, the amount of freshwater around Jeju Island increases in September, not in August. The response to tidal forcing shows that tide-induced vertical mixing tends to enhance a meander of CDW around Changjiang Bank and shift the CDW flowing into the Yellow Sea southeastward toward Jeju Island. As a result, the amount of freshwater toward Jeju Island becomes larger than that in no-tides case. The summer low river discharge as a flood control scenario has little influence on the spatial behavior of CDW around Jeju Island although the discharge contributes to the amount of freshwater around Jeju Island. 相似文献
47.
In this work we develop a new multiscale procedure to compute numerically the statistical moments of the stochastic variables which govern single phase flow in heterogeneous porous media. The technique explores the properties of the log-normally distributed hydraulic conductivity, characterized by power-law or exponential covariances, which shows invariance in its statistical structure upon a simultaneous change of the scale of observation and strength of heterogeneity. We construct a family of equivalent stochastic hydrodynamic variables satisfying the same flow equations at different scales and strengths of heterogeneity or correlation lengths. Within the new procedure the governing equations are solved in a scaled geology and the numerical results are mapped onto the original medium at coarser scales by a straightforward rescaling. The new procedure is implemented numerically within the Monte Carlo algorithm and also in conjunction with the discretization of the low-order effective equations derived from perturbation analysis. Numerical results obtained by the finite element method show the accuracy of the new procedure to approximated the two first moments of the pressure and velocity along with its potential in reducing drastically the computational cost involved in the numerical modeling of both power-law and exponential covariance functions. 相似文献
48.
This paper describes a stochastic analysis of steady state flow in a bounded, partially saturated heterogeneous porous medium subject to distributed infiltration. The presence of boundary conditions leads to non-uniformity in the mean unsaturated flow, which in turn causes non-stationarity in the statistics of velocity fields. Motivated by this, our aim is to investigate the impact of boundary conditions on the behavior of field-scale unsaturated flow. Within the framework of spectral theory based on Fourier–Stieltjes representations for the perturbed quantities, the general expressions for the pressure head variance, variance of log unsaturated hydraulic conductivity and variance of the specific discharge are presented in the wave number domain. Closed-form expressions are developed for the simplified case of statistical isotropy of the log hydraulic conductivity field with a constant soil pore-size distribution parameter. These expressions allow us to investigate the impact of the boundary conditions, namely the vertical infiltration from the soil surface and a prescribed pressure head at a certain depth below the soil surface. It is found that the boundary conditions are critical in predicting uncertainty in bounded unsaturated flow. Our analytical expression for the pressure head variance in a one-dimensional, heterogeneous flow domain, developed using a nonstationary spectral representation approach [Li S-G, McLaughlin D. A nonstationary spectral method for solving stochastic groundwater problems: unconditional analysis. Water Resour Res 1991;27(7):1589–605; Li S-G, McLaughlin D. Using the nonstationary spectral method to analyze flow through heterogeneous trending media. Water Resour Res 1995; 31(3):541–51], is precisely equivalent to the published result of Lu et al. [Lu Z, Zhang D. Analytical solutions to steady state unsaturated flow in layered, randomly heterogeneous soils via Kirchhoff transformation. Adv Water Resour 2004;27:775–84]. 相似文献
49.
The status of tropical glaciers is enormously important to our understanding of past, present, and future climate change,
yet lack of continuous quantitative records of alpine glacier extent on the highest mountains of tropical East Africa prior
to the 20th century has left the timing and drivers of recent glacier recession in the region equivocal. Here we investigate
recent changes (the last 150–700 years) in lacustrine sedimentation, glacier extent, and biogeochemical processes in the Rwenzori
Mountains (Uganda- Democratic Republic of Congo) by comparing sedimentological (organic and siliciclastic component determined
by loss-on-ignition; LOI) and organic geochemical profiles (carbon and nitrogen abundance, ratio, and isotopic composition
of sedimentary organic matter) from lakes occupying presently glaciated catchments against similar profiles from lakes located
in catchments lacking glaciers. The siliciclastic content of sediments in the ‘glacial lakes’ significantly decreases towards
the present, whereas ‘non-glacial lakes’ generally show weak trends in their siliciclastic content over time, demonstrating
that changes in the siliciclastic content of glacial lake sediments primarily record fluctuations in glacier extent. Radiometric
dating of our sediment cores indicates that prior to their late 19th-century recession Rwenzori glaciers stood at expanded
‘Little Ice Age’ positions for several centuries under a regionally dry climate regime, and that recession was underway by
1870 AD, during a regionally wet episode. These findings suggest that the influence of late 19th century reductions in precipitation
in triggering Rwenzori glacier recession is weaker than previously thought. Our organic geochemical data indicate that glacier
retreat has significantly affected carbon cycling in Afroalpine lakes, but trends in aquatic ecosystem functioning are variable
among lakes and require more detailed analysis. 相似文献
50.
The effect of transient eddy on interannual meridional displacement of summer East Asian subtropical jet 总被引:3,自引:0,他引:3
Using ERA-40 reanalysis daily data for the period 1958-2002,this study investigated the effect of transient eddy(TE) on the interannual meridional displacement of summer East Asian subtropical jet(EASJ) by conducting a detailed dynamical diagnosis.The summer EASJ axis features a significant interannual coherent meridional displacement.Associated with such a meridional displacement,the TE vorticity forcing anomalies are characterized by a meridional dipole pattern asymmetric about the climatological EASJ axis.The TE vorticity forcing anomalies yield barotropic zonal wind tendencies with a phase meridionally leading the zonal wind anomalies,suggesting that they act to reinforce further meridional displacement of the EASJ and favor a positive feedback in the TE and time-mean flow interaction.However,The TE thermal forcing anomalies induce baroclinic zonal wind tendencies that reduce the vertical shear of zonal wind and atmospheric baroclinicity and eventually suppress the TE activity,favoring a negative feedback in the TE and time-mean flow interaction.Although the two types of TE forcing tend to have opposite feedback roles,the TE vorticity forcing appears to be dominant in the TE effect on the time-mean flow. 相似文献