Eastward Dlc
Anthony
The Craney Island Dredged Material Management Area (CIDMMA) was authorized by the River and Harbor Act of 1946 and constructed from 1956-1958. The Federally-owned facility is operated by USACE and is used by private interests, local municipalities, Federal and Commonwealth of Virginia government agencies for the disposal of dredged material from Norfolk Harbor and its adjacent waterways, including the Elizabeth and Nansemond Rivers.
Originally designed for a 20 year life span, USACE has been studying ways to extend the life of CIDMMA since the 1970s. In 1997 the U.S. House of Representatives Committee on Transportation and Infrastructure authorized Norfolk District to prepare a Feasibility Study to determine the feasibility of expanding Craney Island into the east, and to consider rapid filling of the new dredge material site to provide an area for a new marine terminal. The Feasibility Study, concluded in 2006, determined that the existing CIDMMA would reach capacity in 2025 and the VPA would run out of cargo handling capacity in 2011. The objectives of the study were then focused on providing a solution that could address both of these capacity shortfalls. In accordance with the National Environmental Policy Act (NEPA), USACE evaluated all reasonable alternatives to avoid and minimize impacts to the environment.
The Corps evaluated a total of 51 alternatives for dredged material placement and a total of 25 port alternatives for container handling capacity. An eastward expansion emerged as the best solution to increase the capacity of CIDMMA for dredged material and also provide an area to construct the fourth marine terminal. The final Feasibility Study recommended an eastward expansion, with a future project planned to strengthen the western dikes. The Feasibility Study and Environmental Impact Statement (EIS) were approved by the Chief of Engineers of the Army Corps of Engineers, Lt. Gen. Carl A. Stock, in October of 2006.
Contracts for the 522-acre expansion project will be bid in phases to match project funding. The initial eastward expansion construction contract, which includes construction of the containment cell cross dikes will be advertised in summer 2010 and awarded in early fall 2010. Additional contracts bid in 2010 include the first environmental mitigation project and Naval pipeline relocation. Main dike construction, completion of the cross dikes, and additional mitigation projects will be bid over the course of the next several years. The undertaking will generate $6 billion in National Economic Development (NED) benefits over the 50-year life of the project.
Most early theories that aimed to explain the existence and properties of the MJO treated it as some form of atmospheric equatorial Kelvin wave, modified by interaction of moist convection with the larger-scale flow. In recent years, it has become clear that convectively coupled Kelvin waves do exist, but that the MJO occupies a distinctly different region of the spectrum (Wheeler and Kiladis 1999). It has also been realized that moisture plays a greater role than it did in the early theories. MJO simulation in particular is improved when convection is made more sensitive to environmental moisture (e.g., Tokioka et al. 1988; Wang and Schlesinger 1999; Maloney and Hartmann 2001; Benedict and Randall 2009; Hannah and Maloney 2011; Kim et al. 2012). Studies with limited-domain cloud-resolving models have shown that, at least under mean conditions of large-scale ascent and relatively frequent deep convection, moisture contains most of the memory in the atmosphere that can regulate convection on time scales longer than a few days (Tulich and Mapes 2010; Kuang 2010).
The idea has emerged that the MJO is a moisture mode. We gave our own definition of this term in a previous study (Sobel and Maloney 2012, hereafter SM12), in which we also proposed a particular very simple model of a moisture mode with the aim of capturing the essential features of the MJO. That model did not appear to be particularly successful. The only linear unstable modes were westward propagating. A nonlinear mode also discussed in SM12 differed substantially in structure from the MJO, having a shocklike jump in moisture at the leading edge of an active phase, whereas the actual MJO has a gradual buildup. Here, we consider extensions to this model to incorporate additional processes that have been hypothesized to be important to the MJO, and which one might expect to cause eastward propagation. These processes include advection of a mean zonal moisture gradient by perturbation zonal winds, modulation of synoptic-scale transient eddy drying by the MJO-scale zonal wind, and frictional convergence.
Another potentially relevant linear process is zonal MSE advection in the presence of a background eastward MSE gradient, which would contribute a term of the form to the right-hand sides of (2) and (8), and thus a contribution to D in (10). A gradient of the right sign to give moistening in easterly anomalies is present in the Indian Ocean basin, where the drier air over the western Indian Ocean transitions to a moister regime as one moves eastward toward the Maritime Continent. Hsu and Li (2012) argue that this mechanism is important to MJO development in the Indian Ocean.
We have presented a brief analysis of a simple linear moisture-mode model. This is a modification of that in Sobel and Maloney (2012), including a simple representation of processes that have been proposed as contributing to eastward propagation of the MJO: modulation of synoptic-eddy drying by the MJO-scale zonal winds, advection of a mean zonal moisture gradient, and frictional convergence. All of these are crudely parameterized as sources of moist static energy that are proportional to minus the low-level zonal wind perturbation. Our primary conclusions are as follows:
In order for eastward propagation of moisture modes to occur in this model, the other processes causing moistening in low-level easterlies must be stronger than the drying associated with suppression of surface fluxes in perturbation easterlies.
Absent any scale-selective damping, the growth rates of eastward-propagating unstable modes are maximized at the largest and smallest spatial scales in the system. There is a minimum in between at synoptic scales (precisely those where the maximum occurred in SM12).
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The lateral expansion of the southeastern Tibetan Plateau causes devastating earthquakes, but is poorly understood. In particular, the links between regional variations in surface motion1,2,3 and the deeper structure of the plateau are unclear. The plateau may deform either by movement of rigid crustal blocks along large strike-slip faults4,5, by continuous deformation6,7, or by the eastward flow of a channel of viscous crustal rocks8,9. However, the importance of crustal channel flow was questioned in the wake of the 2008 Wenchuan earthquake10,11,12. Controversies about the style of deformation have persisted, in part because geophysical probes have insufficient resolution to link structures in the deep crust to the observed surface deformation. Here we use seismic data recorded with an array of about 300 seismographs in western Sichuan, China, to image the structure of the eastern Tibetan Plateau with unprecedented clarity. We identify zones of weak rocks in the deep crust that thicken eastwards towards the Yangtze Craton, which we interpret as crustal flow channels. We also identify stark contrasts in the structure and rheology of the crust across large faults. Combined with geodetic data, the inferred crustal heterogeneity indicates that plateau expansion is accommodated by a combination of local crustal flow and strain partitioning across deep faults. We conclude that rigid block motion and crustal flow are therefore not irreconcilable modes of crustal deformation.
In the version of this Letter originally published online, the author Jiu Hui Chen was affiliated with the incorrect institution. The correct affiliation is the State Key Laboratory of Earthquake Dynamics, Institute of Geology, CEA, Beijing 100029, China. This has been corrected in all versions of the Letter.
Q.Y.L and R.D.v.d.H. wrote the paper. All authors discussed the interpretations and commented on the manuscript. Y.L., H.J.Y. and H.H. conducted ambient noise data analyses. J.H.C., B.G., S.H.Q., J.W. and S.C.L. conducted field work and teleseismic data analyses.
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