ISSN:0035-9009    

DOI:10.1002/qj.49710343502

出版商:John Wiley&Sons, Ltd    

年代:1977

数据来源: WILEY

摘要:

AbstractThe sensitivity of a tropical model to soil moisture content has been investigated using a simplified version of the UK Meteorological Office 11‐layer model. the model area represented a zonally‐symmetric version of West Africa. the results of one experiment (D) with a desert in the same latitudes as the Sahara were compared with those of another experiment (W) in which the desert was replaced by moist land. the initial fields contained an idealized easterly wave which developed during the experiments to form depressions whose movement, structure and associated rainfall were strongly influenced by the dryness of the underlying surface. the energetics of these disturbances were analysed and two distinct mechanisms for maintaining their eddy kinetic energy are proposed, depending on the soil moisture.Results from W suggest that once the land was moist it maintained itself in this state for at least several weeks. In D, however, the initial aridity north of 14°N was sustained, suggesting that ground dryness alone can cause deserts to persist. an analysis of observed rainfall data for the northern Sahel provides much stronger evidence for the persistence of rainfall anomalies from year to year than do similar analyses for the southern Sahel. the possibility that soil moisture anomalies could contribute to this persistence is briefly discu

ISSN:0035-9009    

DOI:10.1002/qj.49710343503

出版商:John Wiley&Sons, Ltd    

年代:1977

数据来源: WILEY

摘要:

AbstractThe advance inland of the sea‐breeze past Lasham, 45 km from the south coast of England, has been measured over a period of twelve years. In this time 76 sea‐breeze fronts passed Lasham, 36 passed Reading and 12 reached Harwell, 85km from the coast. the rate of advance from Lasham to Harwell in calm or light offshore winds was close to 3 ms−1, and the latter station was passed after sunset at a mean time of 2105 GMT. With onshore winds fronts only appear 30 or 40 km inland, and some fronts may be modified by effects due to the east coast. In some cases detailed measurements were made using pilot balloons, an instrumented motor‐glider and radar. the fronts were shown to have raised heads about twice the depth of the following flow and within the heads dry patches occur. Variable secondary flows are inferred and comparison with water‐tank models shows that several dynamical features in the tank and in the atmosphere are similar. Measurements support the picture of the development of the front during the day as a gravity current, and theoretical rates of advance are deduced. the observed acceleration of the front in the late afternoon is explained in terms of the increased temperature contrast at the front due to the decrease in solar heating of the sea‐air. Shortly before sunset, a sea‐breeze vortex may be detached from the rest of the flow. In a case study, it is shown that friction at the upper surface is at least five times that at the ground, and heat and humidity budgets are given for the de

ISSN:0035-9009    

DOI:10.1002/qj.49710343504

出版商:John Wiley&Sons, Ltd    

年代:1977

数据来源: WILEY

摘要:

AbstractDeparture characteristics of the large‐scale circulation are studied in relation to extreme drought and flood years in northeastern Brazil identified from a collective of long‐term rainfall stations and series of river discharge. Ship observations during 1911–72 compiled with a one degree square resolution and extending between 30°N and 30°S from the African coast to the eastern Pacific form a major observational basis.The rainy season of northeastern Brazil is narrowly centred around March/April and is related to the southernmost seasonal migration of a lower‐tropospheric confluence axis over the adjacent eastern tropical Atlantic. the ‘Sěcas’ of Ceará province are characterized by an equatorward expansion of the South Atlantic, and a poleward retraction of the North Atlantic, high ‐ associated with a northward displacement of the enclosed near‐equatorial trough of low pressure. Concurrently, the zonally oriented bands of maximum cloudiness and precipitation frequency stay farther north, the North Atlantic trades weaken, and the South Atlantic trades become stronger than in the long‐term mean. the sea surface temperature pattern during a deficient rainy season in northeast Brazil is characterized by positive departures in a broad band across the North Atlantic and in the eastern Pacific, and anomalously cold waters in most of the South and equatorial Atlantic. During abundant rainy seasons in northeast Brazil, departure patterns are approximately inverse to those typical of drought years.A strong negative linkage exists between northeast Brazil rainfall and sea surface temperature along the Ecuador/Peru coast. This seems to be caused by inverse long‐term pressure variations over the eastern South Pacific and South Atlantic oceans, which in turn may be part of large‐scale mass adjustments of the Southern Oscillation type.Development of the equatorward expansions of the North and South Atlantic highs, pre‐season precipitation in northeast Brazil and the Guayanas, and location of the cloudiness and precipitation belts over the adjacent western tropical Atlantic, are among the more promising predictors for seasonal foreshadowing of extreme rainy season be

ISSN:0035-9009    

DOI:10.1002/qj.49710343505

出版商:John Wiley&Sons, Ltd    

年代:1977

数据来源: WILEY

摘要:

AbstractGreen's parameterization of the latitudinal flux of zonal momentum by large‐scale eddies is investigated. In a steady‐state, β‐plane model of the zonal mean troposphere a simple basis for estimating transfer coefficients (eddy diffusivities) leads to a satisfactory representation of this large‐scale momentum flux, as indicated by the surface zonal flow. the simple basis appears inappropriate for systems in which the β‐effect is not dominant. In a spherical polar, quasi‐geostrophic model of the zonal mean troposphere an adaptation of the method leads to less satisfactory results. It is clear that the spatial variation of the transfer coefficients is more important than in the β‐plane case; and a more precise way of estimating this variation is desirable. Barotropic/baroclinic stability analyses seem likely to provide the most reliable basis, but their use would amount to an essentially different parameterization technique: less elaborate methods

ISSN:0035-9009    

DOI:10.1002/qj.49710343506

出版商:John Wiley&Sons, Ltd    

年代:1977

数据来源: WILEY

摘要:

AbstractAnalysis of profiles measured over irrigated cotton in the Sudan Gezira showed that the crop boundary layer remained stable throughout most of the day. The shape of wind profiles measured within the canopy suggested that momentum was absorbed mostly in the upper layers of the canopy, with the lower regions remaining isolated from the microclimate above. A similarity analysis based on dynamic scaling factors yielded a generalized wind profile from which momentum diffusivities and mixing lengths were calculated. The analysis showed that aerodynamic features of the upper layers of the canopy were characterized by the friction velocity and the height of the zero‐plane displacemen

ISSN:0035-9009    

DOI:10.1002/qj.49710343507

出版商:John Wiley&Sons, Ltd    

年代:1977

数据来源: WILEY

摘要:

AbstractThe separate effects of fluid inertia and friction at the lower boundary on the flow of a rotating, stably stratified, incompressible fluid over a three‐dimensional shallow isolated obstacle are investigated.Analytic solutions of the perturbation equations are obtained as a power series expansion in the Rossby number, and some examples are presented. Possible meteorological applications to the flow over the Alps are discusse

ISSN:0035-9009    

DOI:10.1002/qj.49710343508

出版商:John Wiley&Sons, Ltd    

年代:1977

数据来源: WILEY

摘要:

AbstractSatellite and aircraft data indicate an approximate 0–64 probability that the intensity of a typhoon will have increased during the 24 hours prior to the time when a plume of middle and high cloud streaming from the centre of the storm towards the northeast is first seen on satellite photograp

ISSN:0035-9009    

DOI:10.1002/qj.49710343509

出版商:John Wiley&Sons, Ltd    

年代:1977

数据来源: WILEY

摘要:

AbstractFrequent and detailed upper air observations at Laverton (38°S) for 30 days during September/October 1966 are analysed to determine the local horizontal eddy flux of heat and the mean horizontal potential temperature gradient. Components in the meridional and zonal directions are studied, but a more meaningful relation emerges when the vector eddy flux is considered in relation to the vector temperature gradient. the angle, δ, between these two vectors, and the down‐gradient and cross‐gradient exchange coefficients,KandR, are derived. A 3‐tiered structure between the surface and 30 km emerges, with down‐gradient flux (Kpositive) in most of the troposphere and mid‐stratosphere, and counter‐gradient flux (Knegative) in the lower stratosphere. the cross‐gradient flux is in the direction of the thermal wind (Rpositive) at nearly all heights except in the lowest layers and between 20 and 24 km. δ exhibits a fairly steady and systematic change throughout the height range analysed (2–28 km). Computations using standard upper air observations at selected Australian stations for 1970 show a mean annual pattern which is remarkably coherent with latitude (10–55°) and height (0–22km), except in the tropical troposphere. Typical derived mid‐latitude values for 1970 are:\documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{*{20}c} {} & {K(10^9 {\rm cm}^{\rm 2} {\rm s}^{{\rm ‐ 1}})} & {R(10^9 {\rm cm}^{\rm 2} {\rm s}^{{\rm ‐ 1}} } & {\delta ^0 } \\ {{\rm Lowerstratosphere}} & {{\rm ‐ 10}} & {{\rm 10}} & {{\rm 45}} \\ {{\rm Uppertroposphere}} & {{\rm 10}} & {{\rm 20}} & {{\rm 116}} \\ {{\rm Lower troposphere}} & {{\rm 20}} & {{\rm ‐ 10}} & {{\rm 206}} \\ \end{array} $$ \end{document}Only part of the vertical variation in the lowest layers can be accounted for by surf

ISSN:0035-9009    

DOI:10.1002/qj.49710343510

出版商:John Wiley&Sons, Ltd    

年代:1977

数据来源: WILEY

摘要:

AbstractA simple model is used to give a closed expression for the distribution of intensity in the parhelia, in terms of elementary functions of position on the celestial sphere. Some numerical values are given in the form of intensity contour maps. the frequently observed appearance of the parhelia ‘on the slant’ for large elevations is explained. Brief remarks are made on the under‐parhelia and the arcs of L

ISSN:0035-9009    

DOI:10.1002/qj.49710343511

出版商:John Wiley&Sons, Ltd    

年代:1977

数据来源: WILEY