ISSN:8755-1209    

DOI:10.1029/RG022i003p00237

年代:1984

数据来源: WILEY

摘要:

The ∼ 200‐year periodicity in the time variations of atmospheric radiocarbon is shown to extend over the entire 8500‐year La Jolla record and appears to be associated with a longer period between about 1500 and 2000 years via amplitude, frequency, or phase modulation, or some combination of these; but the statistical certainty of the source and form of the modulation is hampered by the low signal/noise ratio of the two periods. Autocorrelations of the La Jolla sequence show that the record violates even weak stationarity; although the 200‐year period is well ordered in time, the appearance of other periods may be more sporadic. Significant cross correlation between the very long period and the modulation envelope about the neighborhood of the 200‐year line suggests an identity between the two manifestations of the long period, and modulation by a nonlinearity satisfying the rule that it have at least one nonvanishing derivative of odd order andn>2. Commensurate segments of the La Jolla, Belfast, and Groningen radiocarbon records confirm the existence between 3900 B.C. and 3200 B.C. of other periods, particularly 150 and 300 years. A likely source of these periodic changes in the radiocarbon record is the sun because the source of the variations is time dependence of the cosmic ray flux on the atmosphere. Further evidence is the recently reported correlation of radiocarbon and bristlecone pine growth ring variations and the lack of observational evidence to support the very large change in the earth's main field required for a geomagnetic explanation, especially of the ∼200‐year period. If it can be confirmed that the sun is the source, the very long periods suggest as one possibility that the core of the sun is the ultimate source, though multiple convective zone dynamo eigenmodes are an equally conjectural possibility. An alternate source for the longer period is pressure variations of the local arm of the galaxy, but this model i

ISSN:8755-1209    

DOI:10.1029/RG022i003p00239

年代:1984

数据来源: WILEY

摘要:

The purpose of this paper is to review the definition, to outline advantages and disadvantages, and to present both solved and unsolved problems of homomorphic deconvolution. The advantages of homomorphic deconvolution are that it does not require the assumptions of a minimum‐phase wavelet and of a white random reflection coefficient series. Recognized disadvantages of the method have been difficulties in unwrapping the phase, in dealing with band‐limited signals, and in handling mixed‐phase reflection coefficient series. These difficulties may be overcome by using an “adaptive numerical integration algorithm,” frequency transformations, and exponential weighting of the signal, respectively. Two unresolved problems in homomorphic deconvolution are deciding the cutoff quefrencies in liftering convolutional components and eliminating the effect of additive noise. No theoretical means of recovering one convolutional component of an arbitrary real seismogram which is not contaminated by the other component has been discovered. Additive noise plays an important role in homomorphic deconvolution, so that it is unreliable when the spectral amplitudes of the signal are very small over certain frequency bands in signals of relatively small signal‐to

ISSN:8755-1209    

DOI:10.1029/RG022i003p00255

年代:1984

数据来源: WILEY

摘要:

A review is given of the accumulating evidence that ion acceleration and heating at low altitudes play an important role in the dynamics and chemistry of the topside ionosphere and the outflow of plasma into the magnetosphere. Published fluid and kinetic descriptions of the topside ionosphere and ion exosphere provide the macroscopic context in which relevant observations are discussed. Though such models have for the most part been descriptions of regions without the strong magnetic field‐aligned currents associated with ion acceleration, the observations suggest possible means of extending the models. The incorporation of transverse acceleration at low altitudes is particularly suggested, and the effects of such heating on ion chemistry are explored using a simple continuity model. One result is that the known response of the neutral atmosphere to solar activity, in the presence of transverse ion heating near 1000 km altitude, implies H+escape at solar minimum and O+escape at solar maximum. Increasing interest in the modeling of extreme conditions associated with high levels of geomagnetic activity and auroral processes, together with increasing availability of very low energy plasma observations, provides opportunities for fruitful interactions between theory and observatio

ISSN:8755-1209    

DOI:10.1029/RG022i003p00264

年代:1984

数据来源: WILEY

摘要:

This paper provides a review of recent advances in our understanding of gravity wave saturation in the middle atmosphere. A brief discussion of those studies leading to the identification of gravity wave effects and their role in middle atmosphere dynamics is presented first. This is followed by a simple development of the linear saturation theory to illustrate the principal effects. Recent extensions to the linear saturation theory, including quasi‐linear, nonlinear, and transient effects, are then described. Those studies addressing the role of gravity wave saturation in the mean circulation of the middle atmosphere are also discussed. Finally, observations of gravity wave motions, distribution, and variability and those measurements specifically addressing gravity wave saturation are reviewe

ISSN:8755-1209    

DOI:10.1029/RG022i003p00275

年代:1984

数据来源: WILEY