摘要:

The concept of the auroral oval was proposed independently by Feldstein and by Khorosheva in the early 1960's, and it has since been widely used as a reference frame for the organization of high‐latitude optical, particle, and ionospheric data. More recently, different structural regions associated with the oval have been distinguished, and these have been identified with different magnetospheric regions by different workers. The net result is an inconsistent set of nomenclature and relationships. The literature of this development is reviewed in detail, and an interpretation and terminology that is consistent, in the opinion of the authors at least, are proposed. It is hoped that this proposal will serve as a useful basis for further discussion on the ordering of auroral phenomena in relation to the magnetospher

ISSN:8755-1209    

DOI:10.1029/RG023i003p00217

年代:1985

数据来源: WILEY

摘要:

A large variety of objects in chondritic meteorites formed as a result of impact melting: shock veins, metal‐troilite mixtures, metal and sulfide nodules, melt pockets, vugs, agglutinates, glassy and crystalline spherules, and numerous types of melt‐rock clasts. The type of object produced in an impact event is related to the interaction of the shock waves with the particular target rock. Impact melting has also affected large portions of several chondrite breccias; many of these contain vugs and patches of silicate glass. Some workers have suggested that various iron meteorites (including groups IAB, IIICD, and IIE as well as several ungrouped irons) were formed from individual impact melt pools in chondritic regoliths. The Eagle Station Trio pallasites and several ungrouped meteorites (Bencubbin, Weatherford, Enon, Acapulco and Allan Hills A77081) may have formed from impact‐melted chondritic material. It is also possible that the parent magmas of ureilites were derived from impact‐melted metal‐rich carbonaceous chondrite

ISSN:8755-1209    

DOI:10.1029/RG023i003p00277

年代:1985

数据来源: WILEY

摘要:

Least squares collocation in physical geodesy is now a standard technique for estimating gravity‐related quantities from discrete observations in a limited region. It is an optimal method because estimation errors due to measurement noise and the discreteness and finite extent of observations are minimized. However, for large observation sets, the computational problem of collocation (i.e., the problem of solving a large, possibly ill‐conditioned, linear system of equations) is also well known and is very clearly illustrated with airborne gravity gradiometry. Natural alternatives to rigorous least squares collocation are therefore examined and are categorized as being either nonoptimal, suboptimal, or virtually optimal. All choices of estimation method are directed at reducing the computational requirements with an awareness of the desired estimation accuracy. An example of a nonoptimal procedure is the use of integral formulas of the Stokes or Vening‐Meinesz type; suboptimal estimation is exemplified by frequency domain collocation; and a case of virtual optimality is the approximate collocation estimator obtained with a few iterations of the conjugate gradient method used to invert the autocovariance m

ISSN:8755-1209    

DOI:10.1029/RG023i003p00301

年代:1985

数据来源: WILEY