ISSN:0035-9009    

DOI:10.1002/qj.49710544302

出版商:John Wiley&Sons, Ltd    

年代:1979

数据来源: WILEY

ISSN:0035-9009    

DOI:10.1002/qj.49710544303

出版商:John Wiley&Sons, Ltd    

年代:1979

数据来源: WILEY

摘要:

AbstractThe description of the evaporation of rainfall intercepted by forests in terms of a regression of evaporation loss on incident rainfall is discussed and some of the assumptions implicit in that method are re‐examined. The two major factors which control the evaporation of intercepted rainfall are identified. These are: (i) the amount of time that the canopy spends saturated during rainfall and the evaporation rate applicable under these conditions; and (ii) the canopy saturation capacity and the number of times this store is emptied, by drying out after the cessation of rainfall. A model is then constructed which is conceptually similar to the Rutter model, but which replaces that model's numerical approach with an analysis by storm events. The evaporation from a saturated canopy during rainfall is estimated from the Penman‐Monteith equation; the evaporation after rain has ceased, the effect of small storms insufficient to saturate the canopy, wetting‐up the canopy and evaporation from the trunks are added as separate terms. The model has been tested against data from Thetford Forest in East Anglia, with satisfactory agreement between observation and estimation. It is suggested that the model may be capable of making useful estimates of the evaporation of intercepted rainfall, solely from rainfall measure

ISSN:0035-9009    

DOI:10.1002/qj.49710544304

出版商:John Wiley&Sons, Ltd    

年代:1979

数据来源: WILEY

摘要:

AbstractIn this paper we use data from radars and raingauges in England, Wales and southern Ireland to study the motion and changes in intensity of mesoscale precipitation areas (MPAs) some tens of kilometres across as they traversed two regions of high land and an intervening stretch of sea. The MPAs studied were associated with an area of middle‐level potential instability within a windy and moist wintertime warm sector, a situation known to produce major orographic effects. Despite the very large modulation of the rainfall intensity by orography, it was found that most of the MPAs could be tracked for 6h over a distance of 600 km, all the way from the west coast of Ireland to southern England. The implications of this are discussed with regard to the use of radar and satellite data in short‐period forecast

ISSN:0035-9009    

DOI:10.1002/qj.49710544305

出版商:John Wiley&Sons, Ltd    

年代:1979

数据来源: WILEY

摘要:

AbstractThe unusual atmospheric behaviour observed at middle and high latitudes during the winter of 1976/77 is discussed in both synoptic and dynamical terms, using routine, objectively analysed data. During this period the growth of large amplitude, planetary‐scale waves in the troposphere resulted in a marked wave growth in the stratosphere. A qualitative discussion of the interaction between these waves and the zonal flow is followed by referring to the temporal evolution of the relevant terms in the zonally averaged momentum and heat equations. It is shown that the export of momentum from high latitudes by the waves was crucial in effecting a zonal wind reversal in both troposphere and stratosphere. The importance of this mechanism during the period of study indicates the need for a revision of the currently favoured dynamical model of the stratospheric sudden warmin

ISSN:0035-9009    

DOI:10.1002/qj.49710544306

出版商:John Wiley&Sons, Ltd    

年代:1979

数据来源: WILEY

摘要:

AbstractThe way in which equatorial sea surface temperature (s.s.t.) anomalies may interact with the atmosphere is discussed. A simple model is developed to simulate this air‐sea interaction in the Australian region. It is shown that the model can correctly simulate many interesting aspects of the observed statistical behaviour of the ocean‐atmosphere system, including the seasonal variation in persistence of pressure anomalies, the seasonal variation in pressurev. s.s.t correlation, a biennial oscillation in the atmosphere and ocean, and certain lag correlations between pressure, temperature and rainfall. It is concluded that the air‐sea interaction simulated by the model is an important control on the behaviour of the atmosphere and

ISSN:0035-9009    

DOI:10.1002/qj.49710544307

出版商:John Wiley&Sons, Ltd    

年代:1979

数据来源: WILEY

摘要:

AbstractThe structure and dynamics of tornadoes and the mechanisms leading to their formation are explored in the context of an axi‐symmetric numerical model of a tornado cyclone. The paper extends a recent study of tornadogenesis by the authors to include explicit representation of moisture effects.The calculations show that the distribution of buoyancy in the updraught of a severe ‘supercell’ thunderstorm can account for the generation and maintenance of an intense tornado when the level of rotation in the storm is within the observed range of values. The simulated vortex extends to high levels in the cloud but maximum swirling velocities occur within the lowest kilometre or two above the ground in concordance with recent Doppler radar observations.For a fixed vertical distribution of ambient temperature and moisture, the vortex strength is sensitive to the imposed circulation: if the latter is too small, the cloud updraught rotates weakly but there is no evidence of a vortex or a funnel cloud; if it is too strong, a vortex and its associated funnel cloud may form but terminate aloft. This explains why only a few apparently suitable thunderstorms spawn damaging tornadoes.The effects of surface friction on vortex strength and structure are studied in some detail and the results suggest that the terminating inflow layer at the ground may have a less important control on the vortex dynamics than has hitherto been sup

ISSN:0035-9009    

DOI:10.1002/qj.49710544308

出版商:John Wiley&Sons, Ltd    

年代:1979

数据来源: WILEY

摘要:

AbstractTwo‐dimensional numerical integrations of the Navier‐Stokes equations for flow of an Ekman layer ove a ridge on a range of length scales corresponding to large Rossby numbers are presented. The results are compared, where appropriate, with numerical solutions of the triple deck equations of boundary layer flow For steady flow agreement is good and, as predicted by triple deck theory, the net change intotalforce or the domain is small for homogeneous flow. An increase in force arises either through gravity wave radiation when triple deck predictions agree well, or when the ridge is sufficiently steep to give eddy shedd

ISSN:0035-9009    

DOI:10.1002/qj.49710544309

出版商:John Wiley&Sons, Ltd    

年代:1979

数据来源: WILEY

摘要:

AbstractAn ‘almost trivial’ climate system of geometrical dimension zero is analysed. It consists of the global energy storage which is balanced by the globally averaged net radiation (solar input minus infrared emission) with ice‐albedo and greenhouse feedbacks included. This nonlinear and time‐dependent climate system is formulated as a gradient system of a potential. It can be analysed without explicit time integration according to catastrophe theory, so that the resilience of the system, due to changes of the external parameters and due to variations of the state variable, can be determined. For the ice‐albedo or the greenhouse feedback alone, two equilibrium solutions appear: the stable ones are attractors, characterizing the present day interglacial; the unstable ones define a lower or an upper bound, respectively, for temperature changes to be absorbed by the systems. Beyond thresholds of external parameters (fold catastrophes) no equilibria exist, so that the systems attain the states of ‘deep freeze’ and ‘desert heat’, respectively. The two feedbacks combined lead to three equilibria, the stable interglacial being bounded by two unstable solutions, beyond which initial temperature values tend towards the ‘deep freeze’ or ‘desert heat’. External parameter changes can lead to structural instability occurring at fold lines, which meet at the cusp catastrophe. Outside the fold and cusp catastrophes only unstable equilibria appear, from which initial temperature values tend towards ‘desert heat

ISSN:0035-9009    

DOI:10.1002/qj.49710544310

出版商:John Wiley&Sons, Ltd    

年代:1979

数据来源: WILEY

摘要:

AbstractSeveral gaseous pollutants show marked diurnal variations, with daily maxima and nightly minima of concentration. The nocturnal decrease is held to be due to deposition at the ground, with isolation of the lowest layers of the atmosphere from the air above by the nocturnal inversion. In the morning, deep mixing is re‐established and brings material down to the surface from higher layers. Ozone exhibits this behaviour clearly and is convenient to study as an example, but it has been suggested by some authors that changes in the rates of gas‐phase reactions that produce and destroy ozone are responsible for the daily cycle of concentration. We have studied the destruction of ozone at the surface and conclude that this process can probably explain the nocturnal decline of concentration near the ground.Deposition rates for ozone were deduced from profiles of concentration, windspeed and temperature measured over grassland in southern England. The mean deposition velocity was 0.58cms−1by day and 0.29cms−1by night. The aerodynamic and surface components of resistance both increased at night, but the behaviour of the surface resistance was not consistent with stomatal control.Observations of the nocturnal decrease of ozone concentration at the same site are reported. A computer simulation of the behaviour of ozone, with a description of the nocturnal boundary layer due to Wyngaard, duplicated the major features observed, and a procedure for predicting the height of the mixed layer and the rate of decline of ozone concentration at the ground gave good agreement with observations on many occasions.The nocturnal behaviour has important consequences for the measurement of mean concentrations in the atmosphere, and for long‐range transport. Observation of the daily cycle of concentration may indicate the likely importance of the surface sink for m

ISSN:0035-9009    

DOI:10.1002/qj.49710544311

出版商:John Wiley&Sons, Ltd    

年代:1979

数据来源: WILEY