摘要:

AbstractRecent work on the magnetohydrodynamics of the liquid core of the Earth and on the interaction between core motions and the overlying solid mantle has yielded a number of novel results. A new type of magneto‐hydrodynamic wave has been discovered through an attempt to explain the geomagnetic secular variation; the nature of the horizontal stresses at the core‐mantle interface that are implied by the ‘decade’ fluctuations in the length of the day has been elucidated; and evidence pointing to a previously unsuspected correlation between the Earth's gravitational and magnetic fields has been found. Global‐scale undulations in level of the core‐mantle interface that are so shallow (a kilometre or so) as to be unresolvable by contemporary seismological techniques are strongly implied by some of th

ISSN:0035-9009    

DOI:10.1002/qj.49709641002

出版商:John Wiley&Sons, Ltd    

年代:1970

数据来源: WILEY

摘要:

AbstractThe intensity and spectrum of temperature fluctuations recorded at a height of 2 m over flat grassland in stable conditions are examined. Thr results show a demarcation between two distinct régimes, ‘ turbulent ’ for Ri less than a critical value of about 0.2 and ‘ quiet ’ for larger Ri.The magnitude of the temperature fluctuations, scaled relative tozδz, is comparatively large in the turbulent régime, decreases as Ri increases towards the critical value, and remains small in the quiet régime. The temperature, while always of a typically turbulent character in the turbulent régime, is of variable behaviour in the quiet régime ‐ intermittently quiescent with occasional isolated smooth pulses (usually negative), or wave‐like with assorted frequencies, or turbulent.In the turbulent régime, the spectrum approximates to the − 5/3 power form for normalized frequenciesnz/Ugreater than 0.6. In the quiet régime, the form of the spectrum varies unpredictably from on

ISSN:0035-9009    

DOI:10.1002/qj.49709641003

出版商:John Wiley&Sons, Ltd    

年代:1970

数据来源: WILEY

摘要:

AbstractAn objective method is described for obtaining an estimate of the wind‐speed values within the interior of a region when only the streamline field for the region and the wind‐speed values along the boundary are given. The method has been developed and tested for possible use in data‐scarce areas where conventional wind analyses can not be made, but where wind‐direction fields might be derived with reasonable accuracy and detail from satellite cloud photographs. The basic approach consists of computing the wind speeds within the interior of the region by stepping downwind along the streamlines from the known wind‐speed values at the inflow boundary. Divergence is assumed to be constant along each streamline and is determined in a manner such that successive computational cycles minimize the differences between the computed and known wind speeds at the outflow boundary. The testing was conducted using known wind‐velocity fields over the United States and also ATS‐3 cloud‐motion data over the Caribbean. The computed wind‐speed fields were found to be in reasonably good agreement with the actual

ISSN:0035-9009    

DOI:10.1002/qj.49709641004

出版商:John Wiley&Sons, Ltd    

年代:1970

数据来源: WILEY

摘要:

AbstractThe time series of 500 mb heights and 1,000‐500 mb thickness at a network of points over the Northern Hemisphere are filtered in a way which extracts those disturbances with periods in the range 15 to 60 days. Such disturbances are shown to have a maximum amplitude in latitudes 60 to 70 degrees north and be strongly influenced geographically. They are closely linked to the phenomenon of blockin

ISSN:0035-9009    

DOI:10.1002/qj.49709641005

出版商:John Wiley&Sons, Ltd    

年代:1970

数据来源: WILEY

摘要:

AbstractDifferent terms in the equations describing the balance of kinetic energy and available potential energy in the so‐called stationary disturbances or standing waves (deviation of the atmosphere's time‐mean flow from axial symmetry) are evaluated approximately by using the observational statistics of the atmospheric flow. Because many simplifications and assumptions have been necessary in order to get estimates of certain terms, the results only give a rough first‐estimate picture about the maintenance of the stationary disturbances.The results indicate that in winter the stationary disturbances are typically baroclinic waves, which get available potential energy from the temperature distribution of the zonally‐averaged mean flow and partly convert it into kinetic energy to offset the destructive effect on the latter by small‐scale turbulent friction, large‐scale transient motions and conversion into zonally‐averaged mean motion. The most important ‘ external ’ forcing seems, from the energy point of view, to be the stationary heat sources and sinks, which in winter destroy the available potential energy of the stationary disturbances; the effect of mountains in the energy balance of the standing waves seems to be relatively minute and actually smaller than the kinematic and thermal effects of large‐scale transient flow systems.In summer the stationary disturbances appear to form a thermally‐driven system, where the frictional loss of kinetic energy is compensated for by a conversion from the available potential energy, which in turn is maintained by generation du

ISSN:0035-9009    

DOI:10.1002/qj.49709641006

出版商:John Wiley&Sons, Ltd    

年代:1970

数据来源: WILEY

摘要:

AbstractSix months of records of the hemispheric fluxFof long‐wave radiation at Aspendale, Victoria, are analysed. A day‐time correction to Swinbank's formula for the radiation from clear skies is established, and this correction is probably applicable also to other more accurate formulae which include a term dependent on screen level humidity. It varies with time of day and season, but is of the order of − 3 mW cm−2on summer afternoons. The correction is applied to all‐weather data, and at Aspendale the average long‐wave radiation at the ground due to clouds is found to be 0.6 mW cm−2/tenth of cloud cover. The mean value ofFunder cloudy skies is sensibly constant throughout the day, and is not greatly influenced by the diurnal variation of scree

ISSN:0035-9009    

DOI:10.1002/qj.49709641007

出版商:John Wiley&Sons, Ltd    

年代:1970

数据来源: WILEY

摘要:

AbstractThe present state of the art of retrieving the atmospheric temperature profile from remote measurements is briefly described, and methods based on maximum probability and minimum variance criteria are discussed. A maximum probability method is derived for the case of a cloudy atmosphere and synthetic examples of its use are given. The method is numerically fast and is capable of being generalized to incorporate other kinds of information. Such extra information might be for example surface temperature, cloud estimates from television pictures or forecast profiles.

ISSN:0035-9009    

DOI:10.1002/qj.49709641008

出版商:John Wiley&Sons, Ltd    

年代:1970

数据来源: WILEY

摘要:

AbstractIn this theoretical paper, Eady's linear model of baroclinic instability of a zonal basic flow of an inviscid non‐conducting Boussinesq fluid in quasi‐geostrophic motion is extended by consideration of non‐linearity. The method of normal mode cascade is used to find the non‐linear development of a slightly unstable linear disturbance. Amplitude vacillations are found, similar to some observed in experiments on a differentially‐heated rotating annulus. Interactions of the zonal flow and non‐linear waves are described analytically and related to instability of the westerlies in mi

ISSN:0035-9009    

DOI:10.1002/qj.49709641009

出版商:John Wiley&Sons, Ltd    

年代:1970

数据来源: WILEY

摘要:

AbstractThe dynamics of disturbances on a theoretically derived Intertropical Convergence Zone (ITCZ) are studied.Radiative cooling over a hemisphere is parameterized by a Newtonian cooling law, relative to a radiative equilibrium temperature which decreases from Equator to Pole. Release of latent heat of condensation in the Tropics is treated as a function of convergence in the planetary boundary layer.The zonally symmetric field of motion which evolves in response to these sources of energy shows a concentrated region of rising motion near, but not at, the Equator. The associated low‐level wind field possesses a strong cyclonic shear.Asymmetric perturbations periodic in longitude are introduced by means of truncated Fourier series. The wavelengths are chosen to correspond to maximum instability in the ITCZ, and as such are too small to permit baroclinic instability in middle latitudes. In this way, the stability of the low latitude flow is examined while excluding middle latitude perturbations.The low‐level wind field in the vicinity of the ITCZ is found to be barotropically unstable, the wavelength of maximum growth rate being about 2,000 km. The correspondinge‐folding time is found to be of the order of two days, depending on the frictional and heating coefficients.The perturbations are allowed to grow to finite amplitude. In the initial stages of growth, the Reynolds stresses supply most of the perturbation energy. At the mature stage, the energy is provided mainly by direct conversion of condensationally produced eddy available potential energy. Further growth is then limited by frictional dissipation of kinetic energy.The mean flow is in turn influenced by the disturbance through the mechanisms of Reynolds stresses, eddy conduction and the modification of the mean flow condensational heating through boundary‐layer pumping. The influence is seen on the mean temperature and zonal wind fields, and may extent to latitudes poleward of where the perturbation amplitudein situhas decreased to zero.A framework is thus provided for viewing tropical disturbances as an integral component of the general circulation of the atm

ISSN:0035-9009    

DOI:10.1002/qj.49709641010

出版商:John Wiley&Sons, Ltd    

年代:1970

数据来源: WILEY

摘要:

AbstractThis paper corrects Hall's work in the light of more complete experiments which have established that a thermal is merely a special case of a buoyant puff. The general theory, presented here, applies to any isolated buoyant or non‐buoyant puff in shearing surroundings of uniform potential density.This theory is then applied to the case of constant mass deficit and constant wind shear, and solutions are obtained in the form of algebraic equations and simple definite integrals. When these solutions are evaluated numerically, using experimentally determined constants, it is found that the ratio of the coefficients of vertical transport of momentum and heat attributable to the puff lies in the range 0.27 σ to 0.7 σ approximately, where σ is the (small) proportion of the area of the horizontal plane through any height which is occupied by puffs. Also, realistic variation of the angle of spread of puffs is found to produce a very considerable effect on the depth of the convective layer. Only narrow puffs rise

ISSN:0035-9009    

DOI:10.1002/qj.49709641011

出版商:John Wiley&Sons, Ltd    

年代:1970

数据来源: WILEY