摘要:

AbstractIt is suggested that the high albedo of a desert contributes to a net radiative heat loss relative to its surroundings and that the resultant horizontal temperature gradients induce a frictionally controlled circulation which imports heat aloft and maintains thermal equilibrium through sinking motion and adiabatic compression. In the subtropics this sinking motion is superimposed on the descending branch of the mean Hadley circulation but is more intense. Thus the desert feeds back upon itself in an important manner.If one takes into account the biosphere, this feedback mechanism could conceivably lead to instabilities or metastabilities in desert border regions. It is argued that a reduction of vegetation, with consequent increase in albedo, in the Sahel region at the southern margin of the Sahara would cause sinking motion, additional drying, and would therefore perpetuate the arid conditions. Numerical integrations with the general circulation model of NASA's Goddard Institute for Space Studies appear to substantiate this hypothesis. Increasing the albedo north of the ITCZ from 14% to 35% had the effect of shifting the ITCZ several degrees of latitude south and decreasing the rainfall in the Sahel about 40% during the rainy season.

ISSN:0035-9009    

DOI:10.1002/qj.49710142802

出版商:John Wiley&Sons, Ltd    

年代:1975

数据来源: WILEY

摘要:

AbstractA technique which yields quantitative measurements of the opacity of accreted ice deposits is described. This consists of determining the attenuation of a light beam as it passes through a thin section of the deposit, using a photovoltaic cell as the detector. The transmittance of the deposits is related to the air bubble concentration, and the technique provides a useful supplementary method for analysing the air bubble structures of hailstones.

ISSN:0035-9009    

DOI:10.1002/qj.49710142803

出版商:John Wiley&Sons, Ltd    

年代:1975

数据来源: WILEY

摘要:

AbstractStudies have been made of the crystallographic orientation of 100μm‐radius supercooled droplets frozen on ice substrates whose c‐axis orientations varied from 0 to 90° to the surface normal. For a given droplet temperature and substrate orientation, there is a critical substrate temperature below which a frozen droplet has a high (>0·8) probability of having an orientation which differs from that of the substrate. Above this critical substrate temperature there is a small (<0·2) residual probability of reorientation which is dependent on the droplet temperature and substrate orientation but independent of the substrate temperature.The lengths and maximum widths of ice crystals in accreted ice deposits have also been determined. In the dry growth regime there is a general decrease in the mean length from ∼ 8 to 0·25mm, and in the mean maximum width from ∼ 1 to 0·2mm, as the ambient temperature decreases from − 5 to − 30°C. At ambient temperatures above − 15°C there is no dependence of the crystal dimensions on the temperature of the deposit. At ambient temperatures below this value, the crystal dimensions vary with deposit temperature in a manner consistent with the individual droplet studies. Consequently, measurements of the crystal dimensions in hailstone layers may give useful indications of th

ISSN:0035-9009    

DOI:10.1002/qj.49710142804

出版商:John Wiley&Sons, Ltd    

年代:1975

数据来源: WILEY

摘要:

AbstractThe stratospheric water vapour altitude profile has been derived from a measurement of the attenuation of solar infrared radiation at 2·61μ using a rocket‐borne sensor. The solar zenith angle during the flight, which was made from Woomera in April 1970, was 98°. The water vapour to air mixing ratio obtained was in the range 0·5 to 2μg/g in the lower stratosphere, with an upper limit of 4μg/g

ISSN:0035-9009    

DOI:10.1002/qj.49710142805

出版商:John Wiley&Sons, Ltd    

年代:1975

数据来源: WILEY

摘要:

AbstractMeasurements were made of the electric charge acquired by drops of mean radius of about 750μm, in the presence of a vertical electric fieldE, the value of which could be varied from 4·5 to 27kV/m. It was found that the average charge acquired by the water drop as a consequence of the inductive process increased from 0·1fC to about 0·25fC as the electric field strength increased from 5kV/m to about 15kV/m, but there‐after decreased with increasing values of electric field.This work suggests that the collisions between polarized rain‐drops and cloud droplets in natural clouds could give rise, very effectively, to the production of electric fields of about 30kV/m; but that significantly larger fields could not be produced since all collisions in the higher fields would result in permanent coal

ISSN:0035-9009    

DOI:10.1002/qj.49710142806

出版商:John Wiley&Sons, Ltd    

年代:1975

数据来源: WILEY

摘要:

AbstractOf all the models of turbulent motion that are based on a random‐walk technique, the simplest are ones which simulate individual particle trajectories. The accuracies of two such models are assessed by applying them to low‐level diffusion in the atmosphere. It is found that one based on a Markov‐Chain principle predicts particle concentrations over short and medium ranges which are consistent with observation. Calculations are extended to include dispersion in unstable conditions, and by postulating the dependence of several important turbulence parameters onz/L, it is possible to derive a physically realistic

ISSN:0035-9009    

DOI:10.1002/qj.49710142807

出版商:John Wiley&Sons, Ltd    

年代:1975

数据来源: WILEY

摘要:

AbstractUsing measurements from two instruments on the Nimbus 4 satellite comparisons between ozone concentration and temperature have been made at levels near 1mb during an occasion of stratospheric warming. High correlation exists between ozone concentration and temperature. Good agreement has been found with a photochemical model which incorporates ‘classical’ oxygen photochemistry together with reactions involving

ISSN:0035-9009    

DOI:10.1002/qj.49710142808

出版商:John Wiley&Sons, Ltd    

年代:1975

数据来源: WILEY

摘要:

AbstractLee waves in the lower stratosphere are estimated by a consideration of natural wave ‘modes’ which have complex wavenumber and hence decay with distance in the downstream direction. For simple two layer troposphere‐stratosphere models the ‘leaky modes’ can be evaluated explicitly and compared with computed waves. When there is a layer of neutral stability in the upper troposphere the natural complex wave‐numbers are responsible for some quasi‐resona

ISSN:0035-9009    

DOI:10.1002/qj.49710142809

出版商:John Wiley&Sons, Ltd    

年代:1975

数据来源: WILEY

摘要:

AbstractThis article investigates an eigenvector technique for predicting monthly surface pressure anomalies over a network of grid points covering most of the Northern Hemisphere from the previous months' surface pressure anomalies. Eigenvector analyses on archival monthly surface pressure anomalies enabled the anomalies to be represented by natural components whose coefficients were used as predictors in linear regression models for estimating the next month's surface pressure anomaly at each of the grid points.The results show that most of the predictive value was provided by about the first ten natural components accounting for the highest proportion of monthly surface pressure variance. They gave weak, but significant, predictions even after allowing for long period climatic trends, and for persistence of surface pressure anomalies from one month to the next.Further investigation was carried out to discover the nature of the relationships, and these results are also presented.

ISSN:0035-9009    

DOI:10.1002/qj.49710142810

出版商:John Wiley&Sons, Ltd    

年代:1975

数据来源: WILEY

摘要:

AbstractThe effects of ambient wind shearUoon the evolution of an isolated three‐dimensional convective cloud are studied. Sixteen cases are considered which differ from one another both in the value ofU′0in the initial value of the energy of atmospheric instability per unit height of the unstable layer,E0. It is found that convective clouds may be grouped into two types, ‘weak’ and ‘strong’: ifE0/H<0−65 × 102cm s−2then convection is ‘weak’; ifE00−65 × 10−2cm s−2then convection is ‘strong’. For ‘weak’ convective clouds there is a critical value of shear,U′0cr|U′0|

ISSN:0035-9009    

DOI:10.1002/qj.49710142811

出版商:John Wiley&Sons, Ltd    

年代:1975

数据来源: WILEY