ISSN:0035-9009    

DOI:10.1002/qj.49711649502

出版商:John Wiley&Sons, Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractThe formation of major northern hemisphere blockings during January 1979 is studied in numerical simulations of the global atomosphere with a sea surface temperature (s.s.t.) field updated with observations during the model integration. Both the standard 4 × 5 degrees latitude‐longitude and high‐resolution 2 × 2.5 degrees versions of the Goddard Laboratory for Atmospheres general circulation models (GCMs) are employed. the s.s.t. field is provided by a blend analysis ofin situand satellite‐retrieved data.The simulations by the high‐resolution GCM with a realistic s.s.t. field of the ocean surface are shown to be capable of producing two successive realistic major blockings in the Pacific and Atlantic through a one‐month period. the skill in predicting the blocking formation as obtained in the simulations is due to improved skill in forecasting of ultralong waves. Although the results are encouraging, only one initial state is involved in this series of simulations; therefore, the results should not be generalized yet at this stage of in

ISSN:0035-9009    

DOI:10.1002/qj.49711649503

出版商:John Wiley&Sons, Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractComputational aspects of methods used to simulate the transport of water vapour in a global atmospheric general circulation model are examined. A set of properties useful in characterizing numerical methods for modelling atmospheric transport are identified. Spectral and semi‐Lagrangian methods, which are very different in terms of these desired properties are compared.The extent to which the schemes do not satisfy certain properties of the continuous equations provides a measure of one component of the error of the solution. For the spectral scheme, negative specific humiditiesqindicate such an error component. Conventional semi‐Lagrangian schemes are also susceptible to generating negative values. In addition, they are not inherently conservative. Shape‐preserving semi‐Lagrangian methods do not generate negative values, but still are non‐conservative. the degree to which the advection process does not conserve mass provides a measure of another error associated with the numerical solution. the negative error is shown to be large for the spectral transport scheme, measured either locally or globally. Measured globally, the semi‐Lagrangian transport schemes' conservation errors are equally large. Locally, the correction of this error can be made very much smaller, relative to physical processes in the model.The study highlights the computational problems which still exist within the better numerical methods used to simulate the transport of water vapour, and demonstrates the care with which one must apply computational constraints to the solution. the spectral and semi‐Lagrangian transport schemes produce very different climatologies in model simulations. A comparison of these climatologies will app

ISSN:0035-9009    

DOI:10.1002/qj.49711649504

出版商:John Wiley&Sons, Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractObservations of travelling waves in the ozone measurements made by the Solar Backscatter Ultraviolet (SBUV) instrument on board the Nimbus‐7 satellite are presented. In one month's data for January 1979 evidence for a westward travelling 5‐day wave and an equatorially trapped eastward travelling Kelvin wave of 7‐day period is found. These modes arise through the coupling of ozone with the temperature perturbation field: their structure depends on the mean zonal wind, the mean zonal ozone and the photochemistry of ozone. It is shown that the structure of these waves can be described reasonably well by a simple theory involving only the latitudinal variation of the important physical processes. the waves are shown to reach highest amplitudes in the transition region between about 3 mb and 1 mb and it is speculated that they may contribute to the transport of ozone by wave interaction in the stratosphere. Some data are also presented showing wave‐induced effects on the temperature dependence of ozone in the strat

ISSN:0035-9009    

DOI:10.1002/qj.49711649505

出版商:John Wiley&Sons, Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractCurrent theories of stellar evolution imply that the solar luminosity was 25‐30% less than at present during early phases of the Earth's history. the response of the global annual climate to changes of the solar input is examined using the maximum entropy production (MEP) principle and a zonal energy balance model including ice‐albedo feedback. It is shown that this formulation reproduces satisfactorily the present meridional heat flux and latitudinal temperature distributions. It is found that the model predicts that the efficiency of the meridional heat transport decreases for low values of the solar constant. Consequently, if the solar irradiance is lowered, a progressive development of the polar caps and a decrease of the global surface temperature are obtained without major irreversibility in the system. A comparison with a similar model including diffusive heat transport formalism shows that the value of the critical solar luminosity causing a global glaciation is decreased when the meridional heat fluxes are determined by the MEP princi

ISSN:0035-9009    

DOI:10.1002/qj.49711649506

出版商:John Wiley&Sons, Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractThe time‐height variability of the lower marine atmosphere during the eastwards propagation of coastal lows around the coast of southern Africa is presented. These coastal lows are shallow, mesoscale disturbances that are trapped vertically by a strong subsidence inversion and horizontally, through Coriolis effects, against the steep escarpment that fringes the subcontinent. Prior to the event, warm offshore flow descending off this escarpment at about the inversion level provides an input of buoyancy which, together with the cyclonic vorticity acquired during the descent, acts to generate a coastal low rather than a high.Analysis of the data shows that coastal lows are characterized by a marked lowering of the inversion level, a switch in the direction of the winds below the inversion and a drop in the near‐surface temperature, which are all consistent with the hypothesis that the coastal low is an internal Kelvin wave propagating in the marine layer. Good agreement between the observed propagation speed of the coastal low and the theoretical phase speed of such a wave reinforces this hypothesis.A model of the vertical buoyancy advection into the marine atmosphere that results from the warm offshore flow is presented. It is illustrated that an internal Kelvin wave, in the form of a coastal low, results from this buoyancy advection.Comparisons are made between coastal‐low dynamics and those characteristics of other mesoscale, coastally‐trapped disturbances which propagate in the marine layers of California and south‐eastern

ISSN:0035-9009    

DOI:10.1002/qj.49711649507

出版商:John Wiley&Sons, Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractA study defining the occurrence, structure and evolution of “maritime continent” island thunderstorms over Bathurst and Melville Islands near Darwin, Australia is presented. Satellite data for the November‐December pre‐monsoon transition season show unambiguous records of island thunderstorms on at least 65% of days over the period 1978‐1986. Storms develop most commonly between 1230LST and 1530LST and radar data indicate a mean lifetime of 2.5 h. Non‐occurrence was found on only 7% of the days examined and was associated with a return to dry flow typical of the early transition season with middle level subsidence or suppressed conditions in the wake of previous convective activity.Environmental sounding data indicated that these “maritime continent” thunderstorms develop in a regime with moderateCAPE, low to moderate shear and high moisture. the dynamic regime is characteristic of multicellular storms. Examination of the evolution of the storms indicates the existence of a typical lifecycle but with considerable variability in detail. Initially, the lifecycle is consistent with the multicellular storm concept, but the developing storms tend to aggregate to form one or more mesoscale systems which in turn may develop into propagating squall lines in the mature stage. the developing storms have preferred geographic regions of genesis and intensification over the islands; and while motion of the storms is variable, it is generally consistent with the mean surface‐to‐700mb pre

ISSN:0035-9009    

DOI:10.1002/qj.49711649508

出版商:John Wiley&Sons, Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractAircraft measurements of radiative fluxes over the North Sea during a heavy straw‐burning pollution episode are presented and compared with results from a radiative transfer model.The model uses aerosol properties derived from aircraft and satellite measurements, and acceptable agreement with the measured fluxes is obtained.High levels of aerosol concentration are described, with correspondingly large radiative effects. Boundary layer heating rates of 3K day−1are measured, and rates of 5‐10K day−1in regions of higher aerosol loading are i

ISSN:0035-9009    

DOI:10.1002/qj.49711649509

出版商:John Wiley&Sons, Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractA model designed to predict the enhancement of rainfall and the wet deposition of aerosol in complex terrain has been extended and compared with field data. the results of five separate field studies performed over an extensive region of complex terrain in northern England are presented and compared with the model predictions. It is found that the main features of the data are predicted by the model in widely varying conditions but the full details of a particular case‐study cannot be reproduced quantitatively owing to the complexities of the meteorology over the extended distances and collection periods.The main physical processes controlling the deposition pattern have been established and it is concluded that a simple model of the seeder‐feeder process is able to give reasonable descriptions of deposition patterns in complex terrain both for individual episodes and for longer‐period ave

ISSN:0035-9009    

DOI:10.1002/qj.49711649510

出版商:John Wiley&Sons, Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractA heat‐flux scheme, based on the assumption of a constant relative humidity and air‐sea temperature difference, is tested for the tropical oceans. It is compared with heat fluxes over the Pacific Ocean, determined by empirical formulae and maritime observations, both for long‐term monthly‐mean fluxes and for interannual variations in heat fluxes over the equatorial Pacific Ocean.It is shown that the differences in latent heat flux between values obtained by the scheme and those calculated from maritime observations are generally no greater than the uncertainty in the bulk aerodynamic method. the method is also shown to be successful in reproducing the interannual variation in surface heat loss in the eastern Pacific Ocean, though the variability is less than that obtained from maritime observations in the coastal upwelling zone adjacent to South America.Finally, the sensitivity of the heat‐flux scheme to sea surface temperature, for wind speeds typical over the tropical Pacific Ocean, is compared to other schemes. It is shown that the sensitivity coefficient is a function of both wind speed and sea surface temperature, and has values in the range 2‐16 W m−2K−1for the

ISSN:0035-9009    

DOI:10.1002/qj.49711649511

出版商:John Wiley&Sons, Ltd    

年代:1990

数据来源: WILEY