摘要:

AbstractBuoyant convection in the wind‐mixed layer of the ocean provides a source of turbulent kinetic energy that is restricted to a layer whose depth,C, is equal to, or less than,H, the depth of the mixed layer. At nightC = H, and convection contributes significantly to deepening the mixed layer by turbulent entrainment. During most of the day, when the rate of heat input by the Sun exceeds the rate of surface heat loss by evaporation, conduction and long wave radiation,C

ISSN:0035-9009    

DOI:10.1002/qj.49710644902

出版商:John Wiley&Sons, Ltd    

年代:1980

数据来源: WILEY

摘要:

AbstractFor the atmosphere below approximately 60 km the dynamical behaviour of the zonal mean circulation model described by Harwood and Pyle (1975, 1977) is discussed in detail and compared with observations. The major features of the observed extra‐tropical circulation are reproduced by the model, although the principal jets are overestimated. Equatorial temperatures are representative but horizontal temperature gradients are too large, in keeping with the excess wind speed.The roles played in forcing the mean meridional circulation by the diabatic heating and the eddy fluxes of angular momentum and heat are considered.The temperature structure of the summer stratopause is discussed in detail; the model results indicate that this region is in radiative equilibrium to a good approximation.The model has been used to investigate stratospheric ozone and in this paper the sensitivity of the ozone distribution to a number of the model variables is discussed. Reasonable changes in the specified eddy diffusion coefficients and momentum fluxes can alter the total ozone column by around 10%. For small changes (∼ a few tenths K d−1) in the radiative heating of the lower stratosphere even larger changes in the ozone amount are found in the model. The net radiative heating in the lower stratosphere is difficult to calculate. The implication of these sensitivity experiments for pollution perturbation calculations is stressed. Unless all feedback processes are included calculations of pollution‐induced changes in ozone of around 10% must be regarded with

ISSN:0035-9009    

DOI:10.1002/qj.49710644903

出版商:John Wiley&Sons, Ltd    

年代:1980

数据来源: WILEY

摘要:

AbstractThe transport of reactive trace gases by stationary planetary scale waves has been investigated with the aid of Matsuno's stationary planetary wave model (1970) and the linear eddy equation derived from the tracer continuity equation. It is shown that, for stationary fluxes, K‐theory fields, as introduced by Reed and German (1965), may be defined. These become matrix fields when photochemical coupling effects are considered. The eddy flux of a particular trace gas is related to the gradients of the mean concentrations of the other chemically coupled trace gases, as well as to the gradients of its own mean concentration. In the special case of a chemically inert tracer our treatment indicatesKyy=Kxx= 0 andKyx= –Kxyin contradiction to the results obtained by Reed and German (1965) but in agreement with recent results of Clark and Rogers (1978) and Matsuno (1980). The consequences of photochemical coupling effects for eddy fluxes are investigated quantitatively for two simple chemical schemes involving the pairs O3and NOx, and NO and NO2. These effects are shown to be significant especially for NO and NO2whose photochemical time‐constants are short. Furthermore, even in regions of the atmosphere where coupling effects become small, such as the lower stratosphere for O3and NOx, the uncoupled K‐fields are quite different for various species indicating a source of error in current 1‐ and 2‐dimensional photochemical models. The relative importance of dynamical and chemical contributions to the uncoupled K‐fields is dependent on the characteristic time‐scales for photochemical and zonal advection processes. The relation of our work to a Lagrangian description of the transport proce

ISSN:0035-9009    

DOI:10.1002/qj.49710644904

出版商:John Wiley&Sons, Ltd    

年代:1980

数据来源: WILEY

摘要:

AbstractA simple analytic model is constructed to elucidate some basic features of the response of the tropical atmosphere to diabatic heating. In particular, there is considerable east‐west asymmetry which can be illustrated by solutions for heating concentrated in an area of finite extent. This is of more than academic interest because heating in practice tends to be concentrated in specific areas. For instance, a model with heating symmetric about the equator at Indonesian longitudes produces low‐level easterly flow over the Pacific through propagation of Kelvin waves into the region. It also produces low‐level westerly inflow over the Indian Ocean (but in a smaller region) because planetary waves propagate there. In the heating region itself the low‐level flow is away from the equator as required by the vorticity equation. The return flow toward the equator is farther west because of planetary wave propagation, and so cyclonic flow is obtained around lows which form on the western margins of the heating zone. Another model solution with the heating displaced north of the equator provides a flow similar to the monsoon circulation of July and a simple model solution can also be found for heating concentrated along an inter‐tropical converg

ISSN:0035-9009    

DOI:10.1002/qj.49710644905

出版商:John Wiley&Sons, Ltd    

年代:1980

数据来源: WILEY

摘要:

AbstractObservational and numerical model data have indicated the crucial role of the downdraught in the motion, structure and regeneration of severe storms. This paper considers downdraught dynamics in two dimensions, using both a numerical and an analytical model. In the numerical model the downdraught is produced and maintained by a constant heat sink. The adjustment of an ambient inflow, and the resultant downdraught and potential regeneration of storm cells, is simulated.To elucidate physical principles, steady analytical models are also described in which a simple parametrization of downdraught thermodynamics is used. Two distinct types of individual draught dynamics, labelled symmetric and jump, have been identified allowing a qualitative description of six dynamically consistent updraughts and downdraughts. In particular, a cold symmetric downdraught and a cold jumptype updraught are analysed, the former having negative, the latter positive outflow shear. These analytical solutions agree well with steady states developed by the numerical model.The numerical model is also used to describe the propagation of downstream and upstream gust fronts, and these results are in good agreement with atmospheric and tank data.

ISSN:0035-9009    

DOI:10.1002/qj.49710644906

出版商:John Wiley&Sons, Ltd    

年代:1980

数据来源: WILEY

摘要:

AbstractConsideration is given to the leading edge of a well‐defined flow of dense air without significant condensation, such as occurs at a thunderstorm outflow or a sea‐breeze front. Explanation of the front is proposed in terms of a gravity (density) current formed by the denser air. Observations of such flows are related both to laboratory gravity current heads in which head, tail and calm wind conditions are simulated and to a simple, theoretical gravity current model based primarily on a momentum balance. Good agreement is found between the atmosphere, laboratory and analytical results.The mean flow in the gravity current behind the head is greater than the velocity of the head, a result of mixing between the two fluids. This mixing nearly all occurs at the leading edge of the current. The excess height of the head of the gravity current is interpreted as the mixing region at the leading edge, and this mixed fluid lays down a stable layer above the following gravity current. In the laboratory the effect of a headwind is to flatten the profile of the raised head at the front and to reduce its rate of advance by about three‐fifths of the value of the opposing

ISSN:0035-9009    

DOI:10.1002/qj.49710644907

出版商:John Wiley&Sons, Ltd    

年代:1980

数据来源: WILEY

摘要:

AbstractThe diurnal variation of mass divergence and vertical velocity is documented for tropical summertime oceanic weather systems in the Western Pacific, Western Atlantic and the GATE region. It is shown that it is large and has the same basic character in all regions.Gray and Jacobson (1977) proposed that the diurnal variation of mass convergence is a result of diurnal differences in the net radiative and convective heating rates in the thick cirrus‐shield covered weather systems and their surrounding clear areas. Fingerhut (1978) has developed a numerical model which appears to substantiate this hypothesis. A comparison of observations with results from his model reveals that a simple radiation‐condensation model simulates most of the observed diurnal variations of convergence. The hypothesis is that radiational forcing is one of the major contributors to the maintenance and modulation of tropical weather syst

ISSN:0035-9009    

DOI:10.1002/qj.49710644908

出版商:John Wiley&Sons, Ltd    

年代:1980

数据来源: WILEY

摘要:

AbstractComposited summertime deep cumulus convective weather systems are investigated over three tropical oceans. The occurrence and intensity of the convection are governed by various large‐scale forcing mechanisms, such as ITCZ convergence, easterly waves, and differences in diabatic heating between the disturbance and its clear or mostly cloud‐free surrounding region. Vertical profiles of divergence and vertical velocity for the weather systems are analysed from the point of view of trying to establish the relative importance of each large scale control on convection.The dominant forcing in the Western Pacific and the GATE region is ITCZ convergence, with important secondary roles being played by differential radiative‐convective heating, easterly waves and convective feedback. In the Western Atlantic trade wind region there is no contribution from ITCZ convergence; the vertical motion of a typical weather system is consequently much weaker than in the other regions.In all three regions the contribution to vertical velocity from frictional convergence is shown to be quite small.A large diurnal modulation of convection is observed. In the GATE region a diurnal variation is documented for the low‐level convergence into the ITCZ. A physical mechanism is proposed to explain this phenomenon.It is shown that the actual observed vertical motion of the summer‐time tropical oceanic weather systems comes from a combination of forcing mechanisms and does not result from any individual large‐scale control acting by itself. It is important that any idealized picture of tropical weather systems be broad and flexible enough to account for the large regional and multi‐scale forcing mechanism differences which exist. A simple ‘easterly wave’ or ‘ITCZ’ model of organized tropical con

ISSN:0035-9009    

DOI:10.1002/qj.49710644909

出版商:John Wiley&Sons, Ltd    

年代:1980

数据来源: WILEY

摘要:

AbstractA model to estimate the duration of condensed water on the surface of cocoa pods after sunrise is modified to use readily available meteorological data. Changes in wind speed, air temperature and humidity with height and time in a cocoa plantation are presented. Pod temperature and the amount of condensation calculated from the maximum and minimum temperatures and humidity at 0900h agree well with measured values. The effects on pod wetness of changing pod size, short‐wave radiation and wind speed are investigate

ISSN:0035-9009    

DOI:10.1002/qj.49710644910

出版商:John Wiley&Sons, Ltd    

年代:1980

数据来源: WILEY

摘要:

AbstractThe diurnal variation of the average albedo, during 1970, over a tropical dry evergreen forest and a nearby clearing was investigated. The study is based on a most comprehensive set of solar radiation data in Southeast Asia. A strong dependence of the albedo on the zenith angle is evident. This dependence is subdued during cloudy days. The average midday albedo for the winter monsoon season is 10.6 for the forest and 13.4 for the clearing; for the summer monsoon it is 12.0 for the forest and 14.6 for the clearing. Generally, results show great uniformity. The largest standard deviations are 0.05 with a more representative value in the range 0.01–0.0

ISSN:0035-9009    

DOI:10.1002/qj.49710644911

出版商:John Wiley&Sons, Ltd    

年代:1980

数据来源: WILEY