摘要:

The sea‐level record over an 8‐year period at the Biological Station, Bermuda, has been analyzed in an attempt to deduce the complete physics of sea‐level variations in the frequency band of 1 cycle per 8 years to 0.5 cycles per hour. The admittance of the linear tidal lines was calculated, and, on the basis of certain assumptions about a linear system, the Hilbert transform relation between real and imaginary parts of the admittance function was used to deduce the function between diurnal and semidiurnal tides. The North Atlantic appears to be resonant with a period of 14.8 hours having aQexceeding 3.3. An overtone of the resonance is also possibly present. An examination of the overtides in the record indicates that the hydrodynamical regime plus measuring system is highly linear. The spectra of observed atmospheric pressure, temperature, and winds were calculated, and the transfer functions between atmospheric narrow‐band processes (tides) and the continuum with sea level were computed. The tidal constituentS2is about 10 per cent radiational in nature. The continuum of sea level is found to be dominated by pressure in an inverted barometer sense for periods shorter than a year. At longer periods, the winds appear to dominate, but low‐frequency sea‐level power rises more rapidly than any other weather variable, so that the sea‐level spectrum essentially decouples from the atmosphere. The effect of atmospheric temperature is found to be negligible. A comparison between temperature measured in the main thermocline and the sea‐level record yielded no coherence in any part of the spectrum. Approximately 0.1 cm of the semidiurnal tide is attributed to motion of the sea surface by the baroclinic tide. Otherwise, the rest of the internal wave spectrum can be ignored. The Panulirus hydrographic station sequence shows coherence between dynamic heights and the residual (nonweather) sea‐level record for periods between 6 months and a year. At very low frequencies, the dynamic height spectrum tapers off, indicating that the lowest‐frequency energy in the sea‐level record is probably in barotropic motions. Examination of the coherence between the sea‐level record and another record made nearby on Bermuda indicates that the tide‐gage record used in this study is representative of sea‐level motion over a scale of a few miles. Approximately 87 per cent of the total sea‐level variance is explicitly accounted for. The remainder of the energy is in errors of the analy

ISSN:8755-1209    

DOI:10.1029/RG010i001p00001

年代:1972

数据来源: WILEY

摘要:

Numerical simulation of turbulent flow is of practical importance in geophysics and is useful as a test of turbulence theory. From a basic scale analysis of turbulent flow it is shown that complete simulation is only practicable for two‐dimensional or marginally turbulent three‐dimensional flows. Some examples of such simulations are described. A more useful approach for practical applications is to directly simulate the larger scales of motion and only consider the small unresolved scales with respect to their gross statistical interactions with the larger scales. A variable eddy viscosity model has proved useful for this purpose, although better approximations can be devised. Methods of discretization and numerical integration are discussed, and it is proposed that Galerkin methods are preferred when feasible in order to avoid truncation and aliasing err

ISSN:8755-1209    

DOI:10.1029/RG010i001p00051

年代:1972

数据来源: WILEY

摘要:

For 45 years, men have measured and studied echoes from the distant surface of the earth, obtained with high‐frequency signals (3 to 30 MHz) that travel to and from the scatterers via ionospheric refraction. During the last five years, much progress has been made in the understanding of this ‘sky‐wave backscatter.’ An explanation of the various interacting phenomena is presented, as is a review of the current state of knowledge reflecting recent advances in observational methods and analytic techniques. New narrow‐beam antennas, coupled with signal modulations that permit fine resolution in time delay, are beginning to yield information concerning the character of the scatterers, which now can be separately discerned. These narrow beams also permit study of polarization fading from small regions, and this shows promise as a means for learning the distant sea state. Doppler shifts of a fraction of a hertz on signals of tens of megahertz are separable, permitting isolation of sea returns from ground returns by virtue of the Doppler effect resulting from sea‐wave speed; this also suggests a potential sea‐monitoring principle. New modulation equipment permits short‐wave broadcast stations to make sky‐wave backscatter soundings with existing transmitters as an adjunct to normal operations, so that area coverage can be observed in real time. Despite these advances, there is little practical application of sky‐wave backscatter as a means of environmental monitoring. This lack is attributed to the large remaining gaps in our understanding of the echoes and our inability to interpret the forms of data that can be acquired with equipment of reasonable cost. It is still not possible to calculate ionospheric structure from an observation of sky‐wave backscatter although it is the opinion of many workers that this should be feasible. It is now at least possible to carry out the reverse process, calculating sky‐wave backscatter from an assumed ionosphere of much complexity. Study of such synthetic data is yielding additional insight into the causes of diverse forms of observ

ISSN:8755-1209    

DOI:10.1029/RG010i001p00073

年代:1972

数据来源: WILEY

摘要:

The mechanisms by which substorms are generated are still a subject of considerable controversy. A brief review of the historical development of some of the concepts of substorm generation, and the relative merits of these concepts, are discussed against the background of the large number of observational data now available. Polar magnetic substorms are generated through the intensification of the ionospheric current in a localized region of the westward electrojet. At this time field‐aligned currents flow, linking the ionospheric electrojet and magnetospheric current systems near the inner edge of the plasma sheet. It is now apparent that the north‐south component of the interplanetary magnetic field regulates the flow of energy from the interplanetary medium into the magnetosphere. The magnetotail acts as a temporary storage reservoir for this energy, which is eventually released in substorms. Convection is the physical mechanism that dominates in the distribution of energy in the nightside magnetosphere. The over‐all picture presented suggests that substorms are a drastic mechanism by which energy stored in the nightside magnetosphere is dissi

ISSN:8755-1209    

DOI:10.1029/RG010i001p00157

年代:1972

数据来源: WILEY

摘要:

This review is intended to cover the principal developments that have occurred within the last six years in the paleomagnetic study of marine sediments. Recent work utilizing the reflecting‐light microscope indicates that detrital high‐temperature Fe‐Ti oxides are probably responsible for most of the magnetic remanence in marine sediments. These minerals possess a spectrum of coercivities that makes it necessary to use alternating‐field—demagnetization techniques to isolate stable components. It is possible to use the standard magnetic stratigraphy for the last 4 m.y. of earth history derived from terrestrial lavas. Using the ages of the magnetic boundaries from this time scale it is possible by extrapolation and interpolation to better determine the ages of the major events. The ages of these events in increasing age are Jaramillo, 0.87 to 0.92 m.y.; Olduvai, 1.71 to 1.86 m.y.; Kaena, 2.82 to 2.90 m.y.; Mammoth, 3.0 to 3.085 m.y.; Cochiti, 3.72 to 3.82 m.y.; Nunivak, 3.97 to 4.14 m.y.; ‘c’ event of the Gilbert series, 4.33 to 4.65 m.y. Through the use of long cores from the central Pacific and through correlation using fossil datums, it has been possible to extend the magnetic stratigraphy back to the upper middle Miocene to magnetic epoch 5. It is concluded that very short magnetic events are probably short‐term excursions of the field and not true magnetic events. It is shown that the field of the earth averages to an axial‐dipole field within a period of 27,000 years and that the field over the last two million years has acted as a geocentric axial dipole. The evidence shows that when reversals of the dipole occur, the values of the reversed inclination are not significantly different from the normal values. The use of magnetic stratigraphy in marine geology has opened up a new era in study of sedimentary processes and evolution of

ISSN:8755-1209    

DOI:10.1029/RG010i001p00213

年代:1972

数据来源: WILEY

摘要:

The discrete general linear inverse problem reduces to a set ofmequations innunknowns. There is generally no unique solution, but we can findklinear combinations of parameters for which restraints are determined. The parameter combinations are given by the eigenvectors of the coefficient matrix. The numberkis determined by the ratio of the standard deviations of the observations to the allowable standard deviations in the resulting solution. Various linear combinations of the eigenvectors can be used to determine parameter resolution and information distribution among the observations. Thus we can determine where information comes from among the observations and exactly how it constrains the set of possible models. The application of such analyses to surface‐wave and free‐oscillation observations indicates that (1) phase, group, and amplitude observations for any particular mode provide basically the same type of information about the model; (2) observations of overtones can enhance the resolution considerably; (3) the degree of resolution has generally been overestimated for many model determinations made from surface waves; and (4) computation of parameter and information resolution is such a simple extension of any inversion procedure based on perturbation parameters that such inversion studies are incomplete without considering resolut

ISSN:8755-1209    

DOI:10.1029/RG010i001p00251

年代:1972

数据来源: WILEY

摘要:

The theory of the flow of water at the base of a glacier is reviewed and extended. A detailed analysis is made of flow through Röthlisberger channels. (Röthlisberger channels are channels at the base of a glacier that are incised upward into the ice mass.) It is shown that, in general, a pressure gradient drives water melted from the bottom surface of a glacier away from Röthlisberger channels. Thus these channels are not good collectors of the water produced at the bottom surface of a glacier or ice sheet. If Nye channels exist (Nye channels are incised downward into the bedrock of a glacier bed), they should be important in the discharge of water at the base of a glacier. Nye tributary channels are expected to be spaced over several hundred meters apart. The analysis indicates that sheet flow is the main mechanism by which water melted from the bottom ice surface flows out of a glacier or ice sheet. The sheet flow described in this paper is a modification of that considered in our earlier papers. The thickness of the present sheets is not roughly uniform, but rather squeezes to negligible values at high‐pressure zones, where ice moves over the upstream side of obstacles and irregularities in the bed. The pressure of the water in the sheets is lower than the ice overburden pressure. The difference between the pressure in the sheets and the ice overburden pressure is estimated with the aid of the recent major refinements to glacier sliding theory made by J. F. Nye and by B. Kamb. (L. Lliboutry made the original suggestion that the pressure of the water at the base of a glacier is smaller than the ice overburden pressure.) Analysis indicates that a single Röthlisberger channel runs down the center of a glacier over a major fraction of its length. Pressure gradients, produced by the concave shape of the transverse bed profile, exist that drive water in the sheet toward this channel. However, in the upper parts of a glacier, this channel may take the form of a thick water layer of finite br

ISSN:8755-1209    

DOI:10.1029/RG010i001p00287

年代:1972

数据来源: WILEY

摘要:

A procedure is given for calculating the evolution of a sedimentary basin underlain by a phase‐change boundary that is in isostatic equilibrium. The equation of motion of the water depthw(t) as a function of the water depth and as a function of the sedimentation rateds/dtis wherel(t) is the lag of the phase boundary behind the transient equilibrium position. Numerically precise integrals of this equation are given for different time regimes by use of certain approximations for the temperature field that determinedl/dt. Solutions are demonstrated that are attenuated, explosive, or near periodic, depending on the physical parameters used. The results clearly show the possibility of depositing very thick sedimentary sections and the existence of self‐sustained oscillations (above and below sea level) for a sedimentary basin of this t

ISSN:8755-1209    

DOI:10.1029/RG010i001p00335

年代:1972

数据来源: WILEY

摘要:

Recent developments have shed new light on the composition of the upper Venus clouds. An analysis of the Mariner 5 occultation data has led to improved temperature and pressure profiles. When these are combined with transit data, it is concluded that there is an optically thin cloud layer with a top at 81‐km altitude where the temperature and pressure are, respectively, 175°K and 3 mb. The inclusion of temperatures derived from the near‐infrared CO2bands leads to the postulate of a second cloud deck with a top at 61‐km altitude, whereT= 260°K andP= 240 mb. Additional important constraints on cloud models are imposed by the measured abundances of HCl and H2O, by the polarization data, and by the reflection and emission spectra. It is concluded that the leading candidate for the uppermost clouds is liquid drops of HCl‐H2O, that there is no recommended candidate for the second cloud deck, and that H2O ice is at most a minor component of these clou

ISSN:8755-1209    

DOI:10.1029/RG010i001p00369

年代:1972

数据来源: WILEY

摘要:

Since the original study of PCA riometer measurements, solar energetic particles have been increasingly employed as test particles in the magnetosphere. The characteristics of the access of these particles to the magnetosphere are studied to determine if substantial connection exists between the earth’s dipole field and the solar‐generated interplanetary field. Satellite measurements over the polar caps indicate strong north pole‐south pole proton flux asymmetries that may be related to existing interplanetary particle anisotropies. High‐latitude measurements indicate significant pseudo‐trapping of the solar fluxes on closed magnetospheric field lines. Particle flux comparisons between satellites in interplanetary space and within the magnetosphere suggest that the particle access point is probably not greater than 1000RE(earth radii) behind the earth in the ma

ISSN:8755-1209    

DOI:10.1029/RG010i001p00379

年代:1972

数据来源: WILEY