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Western Boundaries (western + boundary)

Distribution by Scientific Domains

Earth and Environmental Science	100%

Selected Abstracts

Climate of the seasonal cycle in the North Pacific and the North Atlantic oceans

INTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 4 2001
Igor M. Yashayaev
Abstract Time series of monthly sea-surface temperature (SST), air temperature (AT) and sea level pressure (SLP) were constructed from merged releases of the Comprehensive Ocean-Atmosphere Data Set (COADS). The time series were decomposed into seasonal and non-seasonal (short and long-term) components. The contribution of the seasonal cycle to the total variance of SST and AT exceeds 80% in the mid and in some high latitude locations and reaches its peak (>95%) in the centres of subtropical gyres. In most cases, a combination of annual and semiannual harmonics accounts for more than 95% of the seasonal variability. Amplitudes of SST and AT annual cycles are highest near the western boundaries of the oceans; annual phases of SST and AT increase toward the eastern tropical oceans, revealing a southeastern propagation of the annual cycle over the Northern Hemisphere oceans. The annual cycle of AT leads that of SST by 1,3 weeks. The largest phase differences are observed in the regions of western boundary currents in the North Pacific and the North Atlantic oceans. This is consistent with spatial patterns of integral air,sea heat fluxes. Annual phases of SST increase along the Gulf Stream and the Kuroshio Current. This points to the importance of signal transport by the major ocean currents. The lowest annual amplitudes of SLP are observed along the equator (0°,10°N) in both oceans. There are three distinct areas of high annual amplitudes of SLP in the North Pacific Ocean: Asian, Aleutian and Californian. Unlike the North Pacific, only one such area exists in the North Atlantic centred to the west of Iceland. A remarkable feature in the climate of the North Pacific is a maximum of semiannual SLP amplitudes, centred near 40°N and 170°W. It is also an absolute maximum in the entire Northern Hemisphere. Analysis of phases of harmonics of SLP seasonal cycle has revealed the trajectories of propagation of the annual and semiannual cycles. Analysis of semiannual to annual amplitudes ratio has revealed the regions of semiannual cycle dominance. Copyright © 2001 Royal Meteorological Society [source]

Tectonic Constraints on the Transformation of Paleozoic Framework of Uplift and Depression in the Ordos Area

ACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 6 2006
WANG Qingfei
Abstract: During the Paleozoic, the Ordos area in the western North China Plate was located at the intersecting position of microplates and controlled by their interaction. The structural framework in the Ordos area, which underwent transformations in the Ordovician, the Carboniferous and the Permian respectively, was dominated by the alternation of uplift and depression. The transformations of structural framework are utilized as the clues to investigate the microplates' interacting type and its response in the Ordos area. According to the regional structural evolution, the Ordos area is simplified into an isopachous, isotropic and elastic shell model, and under proposed various boundary conditions, three series of numerical simulations corresponding to the three structural transformations are carried out to determine the detailed tectonic constraints. Numerical simulations reveal that the structure of the uplift and depression, which is similar to the actual pattern, develops only under one special boundary condition in each of the three series, indicating that the structural framework responds to the unique tectonic background. The simulation results show that in the Early Paleozoic, the L-shaped paleouplift formed nearby the southwestern corner of the Ordos area because the intensity of the compressions in the southern and western boundaries resulting from the ocean-continent collisions was similar. In the Late Paleozoic, it evolved into continent-continent (or arc-continent) interaction in the southern and northern boundaries; in the preliminary stage of the interaction, since the interface between the North China Plate and the plates on the south and north was narrow, the relative acting force was little and the regional western boundary immobile, and the structural framework in the basin was characterized by the N-S trending slender-waist,shaped uplift; as the interface between the plates expanded gradually, the extrusive force in the southern and northern boundaries of the North China Plate increased, resulting in the paleogeographic divisions showing E-W trending, and, the western boundary of the basin was extruded westward due to the intense compression inducing the local NE trending of paleogeographic division in the central area. The simulation results further reflect that the symmetry of the uplift-depression pattern is restricted by that of the boundary conditions, suggesting that the Paleozoic structural transformations of the Ordos area under boundary constraints accord with the universal physical symmetrical principle. [source]

Seismogenic Structure around the Epicenter of the May 12, 2008 Wenchuan Earthquake from Micro-seismic Tomography

ACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 4 2009
Meijian AN
Abstract: A three-dimensional local-scale P -velocity model down to 25 km depth around the main shock epicenter region was constructed using 83821 event-to-receiver seismic rays from 5856 aftershocks recorded by a newly deployed temporary seismic network. Checkerboard tests show that our tomographic model has lateral and vertical resolution of ,2 km. The high-resolution P -velocity model revealed interesting structures in the seismogenic layer: (1) The Guanxian-Anxian fault, Yingxiu-Beichuan fault and Wenchuan-Maoxian fault of the Longmen Shan fault zone are well delineated by sharp upper crustal velocity changes; (2) The Pengguan massif has generally higher velocity than its surrounding areas, and may extend down to at least ,10 km from the surface; (3) A sharp lateral velocity variation beneath the Wenchuan-Maoxian fault may indicate that the Pengguan massif's western boundary and/or the Wenchuan-Maoxian fault is vertical, and the hypocenter of the Wenchuan earthquake possibly located at the conjunction point of the NW dipping Yingxiu-Beichuan and Guanxian-Anxian faults, and vertical Wenchuan-Maoxian fault; (4) Vicinity along the Yingxiu-Beichuan fault is characterized by very low velocity and low seismicity at shallow depths, possibly due to high content of porosity and fractures; (5) Two blocks of low-velocity anomaly are respe tively imaged in the hanging wall and foot wall of the Guanxian-Anxian fault with a ,7 km offset with ,5 km vertical component. [source]