摘要:

As a spacecraft observes the setting or rising of the Sun or a star behind the limb of a planet, the absorption spectrum of the upper atmosphere can be observed as a function of height. This powerful method can give the composition and the vertical distribution of individual gases, from which temperatures can be derived. This review describes the technique and methods of data reduction. Early experiments on the Earth's atmosphere (many from sounding rockets) are briefly summarized; many of them were compromised by the need to use instruments not designed for the purpose. Emphasis is placed on observations of the other planets, by ultraviolet spectrometers able to look at the Sun as well as stars. Mariner 10 set tight upper limits on the atmosphere of Mercury (and also found tiny quantities of H and He). The Voyager instruments defined the upper atmospheres of all four Jovian planets, as well as the satellites Titan and Triton. The potential for future measurements is at least as rich as the history, especially by use of instruments and platforms optimized for the purpose.

ISSN:8755-1209    

DOI:10.1029/RG028i002p00117

年代:1990

数据来源: WILEY

摘要:

The influence of clouds on the radiation field is reviewed from the point of view of their representation in climate models. Such models are expected to include, in the very near future, condensed water as an additional prognostic variable. We examine how simple parameterizations based on the liquid water content can realistically simulate the radiation field. We focus on the extended low‐level clouds for which numerous results of simultaneous radiation and microphysics measurements are available. Particular attention is given to the shortwave absorption in cloud layers because theoretically calculated absorptances are generally weaker than those observed. The problem of the broken field is approached in terms of a relationship between the actual cloud cover and the equivalent cloud cover which gives the same irradiances but using the plane‐parallel formal

ISSN:8755-1209    

DOI:10.1029/RG028i002p00145

年代:1990

数据来源: WILEY

摘要:

In over 30 years of paleomagnetic research, the available paleomagnetic pole determinations from North America and Europe have become much more abundant and, especially, more reliable. While it was still possible in the mid 1960s to conclude that the scatter in paleomagnetic poles made tests of continental reconstructions dubious and inconclusive at best, the data base now allows a much better resolution. For this study, paleomagnetic poles from the stable interiors of North America and Europe have been compiled with a quality index (0 ≤Q≥ 7) based on seven reliability criteria, with the purpose to test continental reconstruction parameters for closing the North Atlantic Ocean. An appropriate geographic and temporal data selection (withQ≥ 3) allows a direct comparison of mean paleopoles for the entire interval of Ordovician through Early Jurassic with various Europe‐North America continental reconstructions published by Bullard and colleagues, Herron and colleagues, Le Pichon and colleagues, Sclater and colleagues, Srivastava and Tapscott, Savostin and colleagues, and Rowley and Lottes. The European set of mean paleopoles compares most favorably with those of North America in the fit of Bullard and colleagues. Using the best fit reconstruction, a common apparent polar wander path has been constructed for Europe and North America, which can serve as a reference path for analysis of displaced terrane motions. I conclude from this study that for the continents bordering the North Atlantic the paleopole data base has become fairly robust, that tight fits such as those by Bullard and colleagues are in superior agreement with the paleomagnetic data, and that the combined paleomagnetic North America‐Europe data set is apparently not affected by significant long‐term, nonzonal, nondi

ISSN:8755-1209    

DOI:10.1029/RG028i002p00167

年代:1990

数据来源: WILEY

摘要:

A clear identification of the movement of water through soils is of central importance to the characterization of surface water acidification. One currently popular view is that the chemical composition of stream water is a function of the mixing of varying volumes of water deriving from different parts of the catchment, all with their own individual chemical “signatures.” The development of models describing this process, and their use for predictive purposes, is a controversial issue. Some would shun the use of models altogether; others would insist on their development based rigorously on the laws of physics; and yet others would accept the aggregation and approximation of simpler conceptual models. As such, this controversy is common to many of the disciplines of geophysics. The paper explores in detail the problem of how a uniquely best set of values for the coefficients of simple conceptual models can be estimated from field observations. In particular, we investigate the role of tracer observations in reducing the uncertainty (and hence ambiguity) associated with the model's constituent hypotheses about hydrological mechanisms. Results from one of the field sites of the (U.K.) Royal Society’s Surface Water Acidification Programme show that even simple conceptual models can lead to quite different interpretations of the dominant flow paths in a catchment. The skill of predicting future behavior will lie therefore in locating this almost inevitable ambiguity and in seeking to make predictive statements that are minimally sensitive

ISSN:8755-1209    

DOI:10.1029/RG028i002p00207

年代:1990

数据来源: WILEY

摘要:

In 1985 and 1986, six spacecraft encountered two comets and obtained a wealth of new data about the plasma processes at work in the interaction of an active comet with the solar wind. This paper summarizes those data and their interpretations. The interaction process starts millions of kilometers from the nucleus where the solar wind first picks up cometary ions. The cometary ions not only slow down the wind but also create disturbances which are ultimately responsible for the surprisingly high fluxes of energetic particles detected at comets. After passing through a structure that is arguably called a bow shock, the plasma continues to slow down as it accretes more cometary ions. The deceleration of the wind causes the interplanetary magnetic field to pile up and drape around the comet's ionosphere, as predicted by Alfvén in 1957. It is this draped field that defines the geometry of a comet's plasma tail. At Halley the Giotto spacecraft detected a well‐defined boundary separating the mixture of solar wind and cometary plasmas and the interplanetary magnetic field from the field‐free, nearly pure cometary plasma in the inner coma. Other unexpected features in the inner coma were a flux of fast “granddaughter” ions and high densities of negative ions. For all the comet encounters, the region between the bow shock and the field‐free cavity was distinguished by several sudden changes in the properties of the plasma; the natures and causes of these features are subjects of inte

ISSN:8755-1209    

DOI:10.1029/RG028i002p00231

年代:1990

数据来源: WILEY

ISSN:8755-1209    

DOI:10.1029/RG028i002p00253

年代:1990

数据来源: WILEY