Pressure comparison method in magnetopause shape calculation: Under uniform outside pressure

A numerical method called the pressure comparison method is proposed for the theoretical magnetopause shape calculation and tested in an assumed situation in which the external plasma pressure is constant and homogeneous over the magnetopause. The results are consistent with that of previous researchers.     

Water Vapor Variability in the Tropical Western Pacific from 20-year Radiosonde Data

The 20-year (1976-1995) daily radiosonde data at 17 stations in the tropical western Pacific was ana lyzed. The analysis shows that the atmosphere is more humid in a warmer climate on seasonal, inter-annual and long-term (20-year) time scales, implying a positive water vapor feedback. The vertical structure of the long-term trends in relative humidity (RH) is distinct from that on short-term (seasonal and inter-annual) time scales, suggesting that observed water vapor changes on short time scales could not be considered as a surrogate of long-term climate change. The increasing trend of RH (3%-5%/decade) in the upper troposphere is stronger than that in the lower troposphere (1%-2% / decade). Such vertical structure would amplify positive water vapor feedback in comparison to the common assumption of constant RH changes vertically. The empirical orthogonal function (EOF) analysis of vertical structure of RH variations shows distinct features of the vertical structure of the first three EOFs. The first three EOFs are optimal for repre sentation of water vapor profiles and provide some hints on physical mechanisms responsible for observed humidity variability. Vaisala radiosondes were used at nine stations, and VIZ radiosondes used at other eight stations. The Vaisala data are corrected for temperature-dependence error using the correction scheme developed by NCAR / ATD and Vaisala. The comparison of Vaisala and VIZ data shows that the VIZ-measured RHs after October 1993 have a moist bias of ～ 10% at RHs ＜ 20%. During 1976-1995, several changes in cluding both instruments and reporting practice have been made at Vaisala stations and introduce errors to long-term RH variations.     

Exoplanets

George Cole reviews the properties and significance of the planetary systems discovered around stars other than our Sun.
There has been speculation for centuries that planets might exist around stars other than our Sun. Might they form planetary systems like our solar system? Will life be found elsewhere one day? Planets were, in fact, discovered orbiting a pulsar in 1991 but, more interestingly, companions were found to stars like our Sun four years later. More stars with companions are continually being discovered and some 50 systems are known at the present time. Can some of these orbiting bodies be planets and what might they be made of? Is there a pattern in the systems being found? How do they compare with the solar system? Can they sustain living material? This article attempts to throw light on these questions.     

Early physical conditions of the planets and satellites

An understanding of the origin of the Solar System is proving hard to achieve and there is still no finally accepted account. A wider range of reliable data, and especially for the outer Solar System, has become available over the last decade due to the use of space vehicles, and particularly the two Voyager probes which are now passing out of the Solar System. The planetary and satellite systems can, therefore, be viewed now more nearly as a whole than previously and consequences for the theory of the origin of the System should follow. The subject is here reviewed again but emphasis is placed on the relative planetology of the whole System. The only reliable data available to us are associated with the System as it is now and this will be the starting point for our discussion.     

The petrology, phase relations and tectonic setting of basalts from the taupo volcanic zone, New Zealand and the Kermadec Island arc - havre trough, SW Pacific

Volcanism in the Taupo Volcanic Zone (TVZ) and the Kermadec arc-Havre Trough (KAHT) is related to westward subduction of the Pacific Plate beneath the Indo-Australian Plate. The tectonic setting of the TVZ is continental whereas in KAHT it is oceanic and in these two settings the relative volumes of basalt differ markedly. In TVZ, basalts form a minor proportion (< 1%) of a dominant rhyolite (97%)-andesite association while in KAHT, basalts and basaltic andesites are the major rock types. Neither the convergence rate between the Pacific and Indo-Australian Plates nor the extension rates in the back-arc region or the dip of the Pacific Plate Wadati-Benioff zone differ appreciably between the oceanic and continental segments. The distance between the volcanic front and the axis of the back-arc basin decreases from the Kermadec arc to TVZ and the distance between trench and volcanic front increases from around 200 km in the Kermadec arc to 280 km in TVZ. These factors may prove significant in determining the extent to which arc and backarc volcanism in subduction settings are coupled.All basalts from the Kermadec arc are porphyritic (up to 60% phenocrysts) with assemblages generally dominated by plagioclase but with olivine, clinopyroxene and orthopyroxene. A single dredge sample from the Havre Trough back arc contains olivine and plagioclase microphenocrysts in glassy pillow rind and is mildly alkaline (< 1% normative nepheline) contrasting with the tholeiitic nature of the other basalts. Basalts from the TVZ contain phenocryst assemblages of olivine + plagioclase ± clinopyroxene; orthopyroxene phenocrysts occur only in the most evolved basalts and basaltic andesites from both TVZ and the Kermadec Arc.Sparsely porphyritic primitive compositions (Mg/(Mg+Fe²) > 70) are high in Al₂O₃ (>16.5%), and project in the olivine volume of the basalt tetrahedron. They contain olivine (Fo₈₇) phenocrysts and plagioclase (> An₆₀) microphenocrysts. These magmas have ratios of CaO/Al₂O₃, A1₂O₃/TiO₂ and CaO/TiO₂ in the range of MORB and MORB picrites and can evolve to the low-pressure MORB cotectic by crystallisation of olivine±plagiociase. Such rocks may be the parents of other magmas whose evolutionary pathways are complicated by interaction of crystal fractionation, crystal accumulation and mixing processes and the filtering action of crust of variable density and thickness. The interplay of these processes likely accounts for the scatter of data about the cotectic. More evolved rocks from both TVZ and KAHT contain clinopyroxene and orthopyroxene phenocrysts and their compositions merge with basaltic andesites and andesites. Stepwise least-squares modelling using phenocryst assemblages in proportions observed in the rocks suggest that crystal fractionation and accumulation processes can account for much of the diversity observed in the major-element compositions of all lavas.We conclude that the parental basaltic magmas for volcanism in the TVZ and KAHT segments are similar thereby implying grossly similar source mineralogy. We attribute the diversity to secondary processes influencing liquids as they ascended through complex plumbing systems in the sub arc mantle and cross.     

A quantitative comparison between acoustic sounder returns and the direct measurement of atmospheric temperature fluctuations

Results are presented which show that reasonably accurate estimates of the atmospheric temperature structure paparmeter C _T ² can be derived from the returns of a monostatic acoustic sounder in both stable and convective atmospheric conditions.