摘要:

Drought is a complex phenomenon that can be defined from several perspectives [Wilhite and Glantz,1987]. The common characteristic and central idea of these perspectives is the straightforward notion of a water deficit. Complexity arises because of the need to specify the part of the hydrologic cycle experiencing the deficit and the associated time period. For example, a long‐term deficit in deep groundwater storage can occur simultaneously with a short‐term surplus of root zone soil water.Figure 1 [Changnon,1987] illustrates how the definitions of drought are related to specific components of the hydrologic cycle. The dashed lines indicate the delayed translation of two hypothetical precipitation deficits with respect to runoff, soil moisture, streamflow and groundwater. From this perspective, precipitation can be considered as the carrier of the drought signal, and hydrological processes are among the final indicators that reveal the presence of drought [Hare,1987;Klemes,19

ISSN:0002-8606    

DOI:10.1029/89EO00305

年代:1989

数据来源: WILEY

摘要:

After six years of planning and preparation, U.S. ocean scientists are poised to begin putting instruments into the water for the World Ocean Circulation Experiment (WOCE), the 40‐nation study of the global ocean that gets underway in 1990.The world ocean has a profound influence on long‐term climate changes, but relatively little is known about the general circulation of the ocean, how it varies, and why. The goal of WOCE is to describe and understand the ocean circulation and its relationship to climate change over periods of decades and lon

ISSN:0002-8606    

DOI:10.1029/89EO00307

年代:1989

数据来源: WILEY

摘要:

The extreme sensitivity of the atmosphere to human intervention is demonstrated by new evidence of the rapidly expanding role of chlorofluorocarbons in greenhouse warming.A new study indicates that CFCs, present in just a few parts per billion in the atmosphere, are responsible for fully a quarter of greenhouse warming over the last decade, more than previously estimated. Projections suggest that if CFC production had not declined after 1974 the compounds would today be the largest single trace gas cause of climate change, responsible for nearly as much eventual warming as carbon dioxide, methane, and nitrous oxide combined.

ISSN:0002-8606    

DOI:10.1029/89EO00309

年代:1989

数据来源: WILEY

摘要:

During the last decade, physicists and applied mathematicians have made substantial headway in understanding the dynamics of complex nonlinear systems. Progress has been possible due to the development of several new tools, including the renormalization group approach, phase portraits, and scaling methods (fractals). At the same time, mathematical geophysicists interested in earthquakes have begun to utilize these same concepts to generate models of faults and fractures.In order to bring these scientific communities together, it was decided to convene the workshop, Physics of Earthquake Faults: Deterministic or Chaotic?, held February 12–15, at the Asilomar conference center near Monterey, Calif. Thirty‐six Earth scientists met with 15 physicists and applied mathematicians to discuss how recent advances in nonlinear systems might be applied to better understand earthquakes. Funding was provided by the Geodynamics Branch of the National Aeronautics and Space Administration, the National Science Foundation, and the Office of Basic Energy Sciences of the U.S. Department of Energy. Organizational and logistical support were provided by the U.S. Geological Sur

ISSN:0002-8606    

DOI:10.1029/89EO00311

年代:1989

数据来源: WILEY

摘要:

The Gulf Coast province provides an array of scientific dilemmas ranging from the origin of the gulf itself to the causes and effects of long‐lasting circulation of hot, deep waters throughout the thick sedimentary section. The nature of the underlying crust and superjacent sediments and their contained waters; the precise timing of rifting; depositional history and diagenesis of the sedimentary sequence; fluid dynamics; geochemistry; hydrocarbon generation and migration; thermal history, including unusually high thermal gradient; and the fluid pressure regime in the deep sedimentary section are too poorly understood to permit quantitative analysis of processes that are of enormous scientific and practical importance. The area centered on DeWitt and Victoria counties, Texas, on the southeastern extension of the San Marcos arch, is probably the best location for a deep borehole to investigate these important phenomena and problems. The arch extends southeastward from exposed Grenville‐age basement rocks of the Llano uplift and separates the deep South Texas and Houston embayment salt basins. Seaward of the Llano uplift, highly deformed and slightly metamorphosed rocks of the Ouachita‐Marathon orogen have been intersected beneath Cretaceous sediments. The inferred edge of continental crust underlies an extensive Lower Cretaceous reef trend southeast of known Ouachita orogen rocks. Rapid thickening of Tertiary and possibly of Cretaceous sediments southeast of the shelf edge, together with geophysical indications of a relatively shallow Moho, suggests that “transitional continental crust” underlies sediments basinward of the inferred edge of continental crust. This transitional crust, the ultimate objective for a proposed deep well, could be rifted Grenville basement, buried rocks of the Ouachita trend, an island arc related to the Ouachita trend, or exotic continental basement related to a proto‐South American continent. To achieve optimum results to guarantee adequate basement penetration, a borehole should be designed to penetrate a relatively thin succession of lower Mesozoic synrift, graben‐fill sediments seaward of the shelf edge. Because of expected high temperatures and pressures, new technologies will need to be developed to successfully drill and

ISSN:0002-8606    

DOI:10.1029/EO070i040p00885-03

年代:1989

数据来源: WILEY

摘要:

NASA's Earth Observation System (EOS) is planned as the prime source of remotely sensed geophysical data for at least a decade. SinceEOSis expected to be submitted as a new start in the NASA budget for Fiscal Year 1991, it is appropriate that AGU adopt a formal position on the program. To do this, a panel has been formed by President Don Anderson to draft an AGU position for Council approval. The panel will report by January 1990. It will focus on scientific as opposed to management aspcets in keeping with AGU's expertise.

ISSN:0002-8606    

DOI:10.1029/89EO00312

年代:1989

数据来源: WILEY