Climate spectra and detecting climate change   总被引：6，自引：0，他引：6  

Peter Bloomfield  Douglas Nychka 《Climatic change》1992,21(3):275-287

Part of the debate over possible climate changes centers on the possibility that the changes observed over the previous century are natural in origin. This raises the question of how large a change could be expected as a result of natural variability. If the climate measurement of interest is modelled as a stationary (or related) Gaussian time series, this question can be answered in terms of (a) the way in which change is estimated, and (b) the spectrum of the time series. These computations are illustrated for 128 years of global temperature data using some simple measures of change and for a variety of possible temperature spectra. The results highlight the time scales on which it is important to know the magnitude of natural variability. The uncertainties in estimates of trend are most sensitive to fluctuations in the temperature series with periods from approximately 50 to 500 years. For some of the temperature spectra, it was found that the standard error of the least squares trend estimate was 3 times the standard error derived under the naïve assumption that the temperature series was uncorrelated. The observed trend differs from zero by more than 3 times the largest of the calculated standard errors, however, and is therefore highly significant.  相似文献   

Origin,Bulk Chemical Composition And Physical Structure Of The Galilean Satellites Of Jupiter: A Post-Galileo Analysis     

Prentice  A. J. R. 《Earth, Moon, and Planets》1999,87(1):11-55

The origin of Jupiter and the Galilean satellite system is examinedin the light of the new data that has been obtained by the NASA Galileo Project. In particular, special attention is given to a theory of satellite origin which was put forward at the start of the Galileo Mission and on the basis of which several predictions have now been proven successful (Prentice, 1996a–c). These predictions concern the chemical composition of Jupiter's atmosphere and the physical structure of the satellites. According to the proposed theory of satellite origin, each of the Galilean satellites formed by chemical condensation and gravitational accumulation of solid grains within a concentricfamily of orbiting gas rings. These rings were cast off equatorially by the rotating proto-Jovian cloud (PJC) which contracted gravitationally to form Jupiter some 4 billion years ago. The PJC formed from the gas and grains left over from the gas ring that had been shed at Jupiter's orbit by the contracting proto-solar cloud (PSC). Supersonic turbulentconvection provides the means for shedding discrete gas rings.The temperatures T_n of the system of gas rings shed by the PSCand PJC vary with their respective mean orbital radii R_n (n = 0, 1, 2, Ϊ ) according as T_n ∝ R_n ^-0.9. If the planet Mercury condenses at 1640 K, so accounting for the high density ofthat planet via a process of chemical fractionation between iron and silicates, then T_n at Jupiter's orbit is 158 K. Only 35% of the water vapour condenses out. Thus fractionation between rock and ice, together with an enhancement in the abundance of solids relative to gas which takes place through gravitational sedimentation of solids onto the mean orbit of the gas ring, ensures nearly equal proportions of rock and ice in each of Ganymede and Callisto. Io and Europa condense above the H₂O ice point and consist solely of hydrated rock (h-rock). The Ganymedan condensate consists of h-rock and H₂O ice. For Callisto, NH₃ ice makes up ∼5% of the condensate mass next to h-rock (∼50%) and H₂O ice (∼45%). Detailed thermal and structural models for each of Europa, Ganymedeand Callisto are constructed on the basis of the above initial bulk chemicalcompositions. For Europa (E), a predicted 2-zone model consisting of a dehydrated rock core of mass 0.912M_E and a 150 km thick frozen mantle of salty H₂O yields a moment-of-inertiacoefficient which matches the Galileo Orbiter gravity measurement. For Ganymede (G), a 3-zone model possessing an inner core of solid FeS and mass ∼0.116M_G, and an outer H₂O ice mantle of mass ∼0.502M_G is needed to explain the gravity data.Ganymede's native magnetic field was formed by thermoremanent magnetization of Fe₃O₄. A new Callisto (C) model is proposed consisting of a core of mass 0.826M_C containing a uniform mixture of h-rock (60% by mass) and H₂O and NH₃ ices, and capped by a mantle of pure ice. This model may have the capacity to yield a thin layer of liquid NH₃ċ2H₂O at the core boundary, in line with Galileo's discovery of an induced magnetic field This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Kelvin-Helmholtz instability of two viscous superposed rotating and conducting fluids     

Vijay Mehta  P. K. Bhatia 《Astrophysics and Space Science》1988,141(1):151-158

Kelvin-Helmholtz instability of the interface separating two viscous rotating-conducting fluids has been studied in the presence of finite ion-Larmor radius (FLR) effects. Emloying the normal mode technique, the solutions have been obtained when the fluids are assumed to be permeated by a uniform horizontal magnetic field. For the case of two highly viscous fluids, the dispersion relation has been derived and solved numerically. It is found that the streaming velocity has a stabilizing influence on the potentially unstable arrangement of the fluids. The viscosity and FLR effects are also found to have a stabilizing influence while the Coriolis forces have a destabilizing influence on the system.  相似文献   

Extensions of linear discriminant analysis for statistical classification of remotely sensed satellite imagery     

Paul Switzer 《Mathematical Geology》1980,12(4):367-376

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Reviews     

R. H. Wimble  J. E. Robinson  R. A. Reyment  F. Demirmen  D. F. Merriam 《Mathematical Geology》1976,8(5):589-596

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When are relative variograms useful in geostatistics?     

Noel Cressie 《Mathematical Geology》1985,17(7):693-702

The relative variogram has been employed as a tool for correcting a simple kind of nonstationarity, namely that in which local variance is proportional to local mean squared. In the past, this has been linked in a vague way to the lognormal distribution, although if {Z_t; t D}is strongly stationary and normal over a domain D,then clearly {exp (Z_t); t D}will stillbe stationary, but lognormal. The appropriate link is made in this article through a universal transformation principle. More general situations are considered, leading to the use of a scaled variogram.  相似文献   

Stratigraphic analysis and the asymptotic distribution of the coefficient of cross-association     

Miloslav Nosal  Jan Vrbik 《Mathematical Geology》1982,14(1):11-36

The asymptotic distribution of the coefficient of cross-association between two sequences of nominal data is investigated under the assumption of independent random sampling from a multinomial distribution slightly modified to suit geological applications. This modification is due to merging consecutive strata of the same rock type into one lithological unit, and can be described by a simple Markov chain. A distinction is made between the case in which the theoretical frequencies are known, and the situation where these have to be estimated from the observed data.  相似文献   

"A stream depletion field experiment," by Bruce Hunt,Julian Weir,and Bente Clausen,March-April 2001 issue,v. 39, no.2: 283-289     

Kollet SJ  Zlotnik VA 《Ground water》2002,40(4):448-449

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Mode Mixing by a Shallow Sunspot     

Barnes  G.  Cally  P.S. 《Solar physics》2000,193(1-2):373-382

Sunspots are strong absorbers of f and p modes. A possible absorption mechanism is direct conversion to slow magnetoacoustic waves. Calculations based on vertical magnetic field models show that this works well for f modes, but is inadequate for p modes. Using a very simple shallow spot model, in which the effects of the magnetic field are accounted for solely by a surface condition, we investigate the possibility that p modes first scatter into f modes inside the spot, which are then more susceptible to conversion to slow modes. We find that the coupling between an incident p mode and the internal f mode is unlikely to be strong enough to account for the observed absorption, but that the incident modes do couple strongly to the acoustic jacket in some cases, leading to a region immediately around the sunspot where a significant fraction of the surface velocity is due to the jacket modes.  相似文献   

Observations of the Polar Magnetic Fields During the Polarity Reversals of Cycle 22     

Snodgrass  H.B.  Kress  J.M.  Wilson  P.R. 《Solar physics》2000,191(1):1-19

The Mount Wilson synoptic magnetic data for the period September 1987 through March 1996 are completely revised and used to provide polar plots of the solar magnetic fields for both hemispheres. This period, from Carrington rotations 1793 to 1906, covers the reversals of the polar magnetic fields in cycle 22. Comparison of our plots with the presently available H filtergrams for this period shows that the polarity boundaries are consistent in these two data sets where they overlap. The Mount Wilson plots show that the polar field reversals involve a complex sequence of events. Although the details differ slightly, the basic patterns are similar in each hemisphere. First the old polarity becomes isolated at the pole, then shortly thereafter, the isolation is broken, and the polar field includes unipolar regions of both polarities. The old polarity then reclaims the polar region, but when the isolation of this field is established for a second time, it declines in both area and strength. We take the reversal to be complete when the old polarity field is no longer observed in the Mount Wilson plots. With this criterion we find that the polar field reversal is completed in the north by CR 1836, i.e., by December 1990, and in the south by CR 1853, i.e., March 1992.  相似文献