Comments about the direct perturbations of Venus and Mars on the Moon's motion     

D. Standaert 《Celestial Mechanics and Dynamical Astronomy》1982,26(1):113-119

In a previous paper (Standaert, 1980) we have described an algorithm to compute the direct perturbation of the planets on the Moon's motion. A short summary of this algorithm is presented in Section 2 of this paper. Our first results permit us to present some complements and comments about these computations.The algorithm is based upon the Lie transform method and is implemented using Chapront's ELP as solution of the main problem with the partial derivatives of Henrard's Semi-Analytical Lunar Ephemeris (SALE), and Bretagnon's mean Keplerian orbit.An analysis of truncation errors in intermediate results is presented including the resonance effects. The final accuracy of the solution is intended to be about 0.0005 for terms of period up to 2000 yr in the case of Venus and up to 5000 yr in the case of Mars.The effects of second-order terms in the masses are investigated. Only those depending upon the second derivatives of the mean motions are found to be significant to the given accuracy and are included.Proceedings of the Conference on Analytical Methods and Ephemerides: Theory and Observations of the Moon and Planets. Facultés universitaires Notre Dame de la Paix, Namur, Belgium, 28–31 July, 1980.  相似文献   

Periodicities in sea-level changes at Stockholm     

R. P. Kane  D. Gobbi 《Climatic change》1992,21(1):77-85

The annual mean sea-level time series for Stockholm (Sweden) for 1825–1984 (160 data points) had a large long-term negative (almost linear, only slightly quadratic) trend. After correcting for the same, the detrended series was subjected to maximum entropy spectral analysis (MESA). Choosing selected periodicities for further multiple regression analysis, series for the first 80 yr (1825–1904) showed periodicities at T = 2.40, 5.0, 6.1, 13.5, 14.8 and 32 yr, significant at a 2 level. The three largest peaks (italicized) had amplitudes of approximately (2.5–3.0) ± 0.8 cm. The latter 80 yr (1905–1984) showed significant periodicities at T= 2.05, 2.7, 3.0, 3.6, 4.4, 5.5, 6.3, 7.7, 9.8, 20.5 and 33 yr. The three largest peaks (italicized) had amplitudes of approximately (2.0–2.5) ± 0.7 cm. The whole period of 160 yr (1825–1984) showed significant periodicities at T = 2.05, 2.9, 3.2, 4.5, 4.9, 5.6, 6.4, 7.8, 11.0, 13.7, 14.8, 29 and 43 yr. The three largest peaks (italicized) had amplitudes of approximately (1.6–1.9) ± 0.6 cm. All these significant peaks explained a variance of only about 30% or less, indicating a large random component of approximately 70%. Peaks at T = 11 yr (sunspot cycle) or T = 18.6 yr (lunar nodal term) were either absent or very weak. Most of the other peaks were transient (present in the first 80 yr or the latter 80 yr) except an uncertain quasibiennial oscillation (QBO) (T = 2–3 yr) and T = 5–6 yr and T 30 yr, which seemed to be persistent throughout the whole period. Some periodicities seem to resemble those seen in the Southern Oscillation (SO) index.  相似文献   

The front of 8 October 1987 — Predictions of three mesoscale models     

Dr. H. Volkert  Dipl.-Met. M. Kurz  Dipl.-Met. D. Majewski  Dr. T. Prenosil  Dr. A. Tafferner 《Meteorology and Atmospheric Physics》1992,48(1-4):179-191

Summary The forntal passage of 8 October 1987, which was extensively sampled during the first intense observation period of the German Front Experiment, is simulated by aid of three mesoscale models. The results are intercompared and held against the manually and objectively analysed observations of the meso and meso- scales, respectively. The orographic impact is studied by comparing model runs with full and cut-off Alps. Implications regarding similar efforts in the future conclude the paper.With 11 Figures  相似文献   

Fossil-pollen evidence for abrupt climate changes during the past 18 000 years in eastern North America     

Eric C Grimm  George L Jacobson Jr 《Climate Dynamics》1992,6(3-4):179-184

A quantitative measure of the rate at which fossil-pollen abundances changed over the last 18 000 years at 18 sites spread across eastern North America distinguishes local from regionally synchronous changes. Abrupt regional changes occurred at most sites in late-glacial time (at 13700, 12 300, and 10000 radiocarbon yr BP) and during the last 1000 years. The record of abrupt late-glacial vegetation changes in eastern North America correlates well with abrupt global changes in ice-sheet volume, mountain snow-lines, North Atlantic deep-water production, atmospheric CO₂, and atmospheric dust, although the palynological signal varies from site to site. Changes in vegetation during most of the Holocene, although locally significant, were not regionally synchronous. The analysis reveals non-alpine evidence for Neoglacial/Little Ice Age climate change during the last 1000 years, which was the only time during the Holocene when climate change was of sufficient magnitude to cause a synchronous vegetational response throughout the subcontinent. During the two millennia preceding this widespread synchronous change, the rate of change at all sites was low and the average rate of change was the lowest of the Holocene.Contribution to Clima Locarno Past and Present Climate Dynamics; Conference September 1990, Swiss Academy of Sciences — National Climate Program  相似文献   

The role of sediments in the phosphorus cycle in Lake Lugano. I. Geochemical approach     

D. Span  J. Dominik  M. A. Lazzaretti  J. -P. Vernet 《Aquatic Sciences - Research Across Boundaries》1992,54(3-4):277-284

The bottom sediment from three coring stations in Lake Lugano (Lago di Lugano) show major differences in their role in the P-cycles related to their geochemistry and characteristics of sedimentation. In the northern basin, the deepest sediment may be considered practically inactive, due to a permanently reduced condition at the sediment-water interface. In the southern basin, the sediments are active with respect to P-recycling with strong seasonal variations. One of the sites (Figino) behaves as a sink for P due to a high iron content and an important rate of detrital sedimentation.  相似文献   

Time resolved simulation of lightning by lip     

Jebens DS  Lakkaraju HS  McKay CP  Borucki WJ 《Geophysical research letters》1992,19(3):273-276

In this letter, we report results of time resolved spectra of lightning simulation in air by laser-induced plasma (LIP). The measured electron temperatures varied from (1.7 +/- 0.1)X10(4) K at 600 ns to (1.2 +/- 0.1)X10(4)K at 4 microseconds after the ignition of the plasma. Electron densities in the plasma varied from (7.0 +/- 1.4)X10(17)/cm3 to (9.0 +/- 1.8)X10(16)/cm3 for the above times. We also present, for the first time, a comparison of state variables for LIP and natural lightning. We find that immediately following the ignition both natural lightning and LIP reach temperatures in excess of 16,000K and relax to ambient pressure with different rates. They are expected to approach 2000 - 4000 K temperature range, which is important to chemical synthesis, in an asymptotically similar fashion.  相似文献   

Periodicities in the time series of annual minimum temperatures for the United States Gulf Coast region     

R. P. Kane  D. Gobbi 《Pure and Applied Geophysics》1992,138(2):323-333

The minimum winter temperature series for the United States Gulf Coast for 1799–1988 (190 values) was subjected to Maximum Entropy Spectral Analysis. Significant periodicities in the QBO region (T-2–3 years) and atT=3.7, 4.5, 5.5, 6.5, 7.5, 12.9, 15.5 and 22 years were detected. Some of these were present in the first half only (1799–1893) while others in the latter half only (1894–1988), indicating a transient nature. Also, more than 50% of the variance was random. Many of the significant periodicities are seen in other geophysical parameters. Some may be harmonics of the 11-year sunspot cycle and the 22-year Hale magnetic sunspot cycle.  相似文献   

The influence of amphibole fractionation on the evolution of calc-alkaline andesite and dacite tephra from the central Aleutians,Alaska   总被引：3，自引：1，他引：2  

Jay D. Romick  Suzanne Mahlburg Kay  Robert W. Kay 《Contributions to Mineralogy and Petrology》1992,112(1):101-118

Petrologic studies of tephra from Kanaga, Adak, and Great Sitkin Islands indicate that amphibole fractionation and magma mixing are important processes controlling the composition of calc-alkaline andesite and dacite magmas in the central Aleutians. Amphibole is ubiquitous in tephra from Kanaga and Adak Islands, whereas it is present only in a basaltic-andesite pumice from Great Sitkin. Dacitic tephra from Great Sitkin do not contain amphibole. Hornblende dacite tephra contain HB+PLAG+OX±OPX±CPX phenocrysts with simple zoning patterns, suggesting that the dacites evolved in isolated magma chambers. Andesitic tephra from Adak contain two pyroxene and hornbelende populations, and reversely zoned plagioclase, indicating a more complex history involving mixing and fractional crystallization. Mass balance calculations suggest that the andesitic tephra may represent the complements of amphibole-bearing cumulate xenoliths, both formed during the evolution of high-Al basalts. The presence of amphibole in andesitic and dacitic tephra implies that Aleutian cale-alkaline magmas evolve in the mid to lower crust under hydrous (>4 wt.% H₂O) and oxidizing (Ni–NiO) conditions. Amphibole-bearing andesites and pyroxene-bearing dacites from Great Sitkin indicates fractionation at several levels within the arc crust. Despite its absence in many calc-alkaline andesite and dacite lavas, open system behavior involving amphibole fractionation can explain the trace element characteristies of lavas found on Adak Island. Neither open nor closed system fractionation involving a pyroxene-bearing assemblage is capable of explaining the trace element concentrations or ratios found in the Adak suite. We envision a scenario where amphibole was initially a liquidus phase in many calc-alkaline magmas, but was later replaced by pyroxenes as the magmas rose to shallow levels within the crust. The mineral assemblage in these evolved lavas reflects shallow level equilibration of the magma, whereas the trace element chemistry provides evidence for a earlier, amphibole-bearing, mineral assemblage.  相似文献   

The energetics of interaction between oxygen vacancies in sillimanite: A model for the mullite structure     

S. Padlewski  V. Heine  G. D. Price 《Physics and Chemistry of Minerals》1992,19(3):196-202

A microscopic model is introduced to discuss the modulated structure of mullite. The oxygen vacancies of this aluminosilicate are known to play a central role. In particular, a single vacancy strongly orders its surrounding Al/Si tetrahedral sites. It is shown in this work that if two oxygen vacancies approach too closely to one another, their Al/Si dressing overlap. This situation results in repulsive interaction. The field of interaction between the vacancies is estimated with the use of an atomistic computer simulation. We use a Bragg-Williams type of theory to dicuss the ordering pattern of the vacancies. Due to frustration between the two dominant repulsive interactions, our model predicts a modulated phase transition in agreement with observation.  相似文献   

Phase Relations of an Armalcolite-Phlogopite Lamproite from Smoky Butte, Montana: Applications to Lamproite Genesis   总被引：1，自引：0，他引：1  

EDGAR  A. D.; CHARBONNEAU  H. E.; MITCHELL  R. H. 《Journal of Petrology》1992,33(3):505-520

Suprasolidus phase relations at pressures from 8 to 30 kb andtemperatures from 950 to 1380C have been determined experimentallyfor a glassy armalcolite–phlogopite lamproite from thechilled margin of a medium–grained lamproite from SmokyButte, Montana: The armalcolite-phlogopite lamproite has microphenocrystsof olivine in a groundmass of phlogopite, sanidine, armalcolite,clinopyroxene, chromite, priderite, apatite, and abundant glass.The lamproite is SiO₂-rich and has high F/H₂O relative to lamproitesthat have been investigated in previous experimental studies.Our data show that with decreasing temperature from the liquidusat pressures above 12 kb, melt coexists successively with:olivine; orthopyroxene + clinopyroxene; orthopyroxene + clinopyroxene+ phlogopite; clinopyroxene +phlogopite; and clinopyroxene +orthopyroxene + K-richterite. Below 12 kb, the assemblage successionis: olivine; olivine + clinopyroxene; olivine + clinopyroxene+ phlogopite; and olivine +clinopyroxene + phlogopite + armalcolite.The main difference from the natural paragenesis is that therock does not contain any orthopyroxene—a feature thatis rather remarkable inasmuch as it has 16% normative hypersthene—andthe rock differs also in that it contains sanidine and priderite.In the experiments, sanidine is observed only as ghostlike domainsin some of the glass and appears to have formed during quenching. The solid phases crystallized experimentally are generally compositionallysimilar to the minerals in the rock. These similarities andthe experimental phase relations support the concept of a rapidinitial magma ascent with only a small temperature drop andcrystallization of olivine, but not of orthopyroxene. At lowerpressures, less than 12 kb, it appears that the magma ascendedmore slowly with a larger temperature drop suggested by thesimilarity of the experimentally determined sequence of assemblagesto the paragenesis of the rock. No quasi-invariant multiphase-saturation point was found suchas might be indicative of pressure and temperature conditionsfor formation of the lamproite magma by eutectic-type partialmelting of a mantle source. The occurrence of olivine, orthopyroxene,and clinopyroxene near the liquidus, and the high proportionof normative hypersthene in the melt suggest that lherzoliteor harzburgite was probable in the magma source rock. The highSiO₂ and MgO contents of the Smoky Butte lamproites may indicatethat orthopyroxene was a source mineral even though it did notcrystallize under near-surface conditions. The curve definingthe appearance of phlogopite appears at progressively lowertemperatures from the liquidus as pressure increases, so itwould appear that either phlogopite was not the mantle K-reservoir,or it was entirely consumed during the partial melting process.The composition of the near-liquidus glass in the experimentsis likely to be the composition of the bulk rock less the verysmall amounts of olivine + clinopyroxene + orthopyroxene crystallizedwithin a few degrees below the liquidus. From the inferred compositionof this glass, anhydrous phlogopite is a potential mineral.The principal variable that determines whether phlogopite crystallizesas a near-liquidus mineral is F/H₂O; low values of this ratiopromote the presence of phlogopite as a near-liquidus mineralwhereas high values deter its crystallization. The common practiceof adding H₂O but not F in experiments to compensate for degassingmay obscure the role of phlogopite in the evolution of lamproitemagmas.  相似文献