摘要:

AbstractThe two main principles underlying the use of isentropic maps of potential vorticity to represent dynamical processes in the atmosphere are reviewed, including the extension of those principles to take the lower boundary condition into account. the first is the familiar Lagrangian conservation principle, for potential vorticity (PV) and potential temperature, which holds approximately when advective processes dominate frictional and diabatic ones. the second is the principle of ‘invertibility’ of the PV distribution, which holds whether or not diabatic and frictional processes are important. the invertibility principle states that if the total mass under each isentropic surface is specified, then a knowledge of the global distribution of PV on each isentropic surface and of potential temperature at the lower boundary (which within certain limitations can be considered to be part of the PV distribution) is sufficient to deduce, diagnostically, all the other dynamical fields, such as winds, temperatures, geopotential heights, static stabilities, and vertical velocities, under a suitable balance condition. the statement that vertical velocities can be deduced is related to the well‐known omega equation principle, and depends on having sufficient information about diabatic and frictional processes. Quasi‐geostrophic, semigeostrophic, and ‘nonlinear normal mode initialization’ realizations of the balance condition are discussed. an important constraint on the mass‐weighted integral of PV over a material volume and on its possible diabatic and frictional change is noted.Some basic examples are given, both from operational weather analyses and from idealized theoretical models, to illustrate the insights that can be gained from this approach and to indicate its relation to classical synoptic and air‐mass concepts. Included are discussions of (a) the structure, origin and persistence of cutoff cyclones and blocking anticyclones, (b) the physical mechanisms of Rossby wave propagation, baroclinic instability, and barotropic instability, and (c) the spatially and temporally nonuniform way in which such waves and instabilities may become strongly nonlinear, as in an occluding cyclone or in the formation of an upper air shear line. Connections with principles derived from synoptic experience are indicated, such as the ‘PVA rule’ concerning positive vorticity advection on upper air charts, and the role of disturbances of upper air origin, in combination with low‐level warm advection, in triggering latent heat release to produce explosive cyclonic development. In all cases it is found that time sequences of isentropic potential vorticity and surface potential temperature charts—which succinctly summarize the combined effects of vorticity advection, thermal advection, and vertical motion without requiring explicit knowledge of the vertical motion field—lead to a very clear and complete picture of the dynamics. This picture is remarkably simple in many cases of real meteorological interest. It involves, in principle, no sacrifices in quantitative accuracy beyond what is inherent in theconceptof balance, as used for instance in the initialization of nu

ISSN:0035-9009    

DOI:10.1002/qj.49711147002

出版商:John Wiley&Sons, Ltd    

年代:1985

数据来源: WILEY

摘要:

AbstractResults from four pairs of 50‐day wintertime integrations of the Meteorological Office's 5‐level general circulation model, with warm and cold sea surface temperature (s.s.t.) anomalies of about 3 K in the northwest Atlantic, are described. Difference fields between the warm and cold integrations are statistically significant at the 1% level with positive geopotential height over the central north Atlantic, and weaker negative height over Europe. the storm track over the Atlantic is displaced from its normal position. Results from four further pairs of integrations with halved s.s.t. anomalies are also described. the response is approximately linear, with systematic differences in 500 mb geopotential height over the Atlantic, parts of which are just significant at the 10% level with half the full s.s.t. anomaly. Overall, however, the model's response is weaker than could be obtained with tropical s.s.t. anomalies of the same magnitude.Results from the model integrations are compared with results from an observational study of the relationship between wintertime s.s.t. in the north‐west Atlantic, and mean sea level pressure and 500mb height. Two independent 30‐year periods were chosen for study, thus minimizing the influence of long‐term trends in s.s.t. Over the Atlantic and Europe the model results compared well with the observations. With s.s.t. data lagging the atmosphere by one month, the observational study appears to show that the s.s.t. anomalies are initially forced by perturbations in the atmospheric circulation. With s.s.t. data leading the atmosphere by one month results show that atmospheric and s.s.t. anomalies are most persistent in the period October to December. Throughout the winter these lagged relationships are much weaker and not statistically significant.Diagnostics ofE‐vector divergence from the GCM experiments are used to suggest that anomalous baroclinic wave activity over the Atlantic is important as a momentum forcing for the anomalous time‐mean flow pattern. On the other hand, the role of thermal forcing, provided by anomalous diabatic heating and transient eddy heat flux convergence, may be important. to substantiate this statement, a simple linear steadystate two‐layer model of the response to extratropical thermal forcing is described. With a suitable basic state flow, and a mid tropospheric heat source (given mainly by the transient eddy heat flux convergence), the response is shown to be equivalent barotropic with a downstream ridge and ascent over the thermal source.Conversely, results from an ocean mixed layer model are discussed which suggest that warm s.s.t. anomalies could be maintained by a positive surface pressure perturbation positioned downstream of the anomaly, through anomalous northward advection of warm ocean water by Ekman drift currents. This northward advection would balance the sensible and latent heat loss into the atmosphere over the s.s.t. anomaly. Hence it is possible that some positive ocean‐atmosphere feedback may account for the persistence of such atmospheric and

ISSN:0035-9009    

DOI:10.1002/qj.49711147003

出版商:John Wiley&Sons, Ltd    

年代:1985

数据来源: WILEY

摘要:

AbstractUsing analyses made during the First GARP Global Experiment (FGGE), a study has been made of the angular momentum budget of the atmosphere. the time evolution of atmospheric angular momentum has been compared with the calculated torques acting upon it. This comparison has shown for the first time that the mountain torque is the main contributor to the short‐term variation in the global atmospheric angular momentum. the variation of the torques as functions of latitude has also been compared with the total torque implied by the meridional transport of angular momentum by the atmosphere. the torques calculated agree qualitatively with the angular momentum transport, but there are some significant differences in magnitude; some possible reasons for these differences are discussed in the light of results from a general circulation model and from a second set of analyses made during the FGG

ISSN:0035-9009    

DOI:10.1002/qj.49711147004

出版商:John Wiley&Sons, Ltd    

年代:1985

数据来源: WILEY

摘要:

AbstractData from the LIMS and SAMS instruments on Nimbus 7 are used to derive zonal‐mean OH fields from 85°N to 64°s for November 1978 to May 1979. Two methods are used. One relies on the establishment of a photochemical steady state between NO2and HNO3. In the second method OH is calculated from its sources and sinks. There is substantially good agreement between the two methods. Areas of discrepancy can be explained. Indeed, some differences should be expected if present photochemical theory is corr

ISSN:0035-9009    

DOI:10.1002/qj.49711147005

出版商:John Wiley&Sons, Ltd    

年代:1985

数据来源: WILEY

摘要:

AbstractOzone photochemistry over Antarctica in summer has been examined using a 1‐D model. With diffusive transport alone, the predicted ozone decay rates from the December (summer) solstice to the March (autumn) equinox were found greatly to exceed observed rates. In order to obtain broad agreement between calculated and observed ozone amounts, it was necessary to include the effects of a slow downward mean velocity. the velocities used, a few tens of metres per day, are compatible with a Lagrangian mean circulation pattern derived from thermodynamic considerations and from GCMs.The rates of change of ozone amounts computed for 75°S decrease abruptly following the change from continuous to interrupted photolysis when the sun first sets (in mid‐February) after the long polar day of midsummer. In the polar day regime, N2O5concentrations are depressed strongly, and CIONO2concentrations moderately, relative to those in regions subjected to diurnal interruption of photolysis. the effects on the diurnal variations of ozone and other minor constituents are descr

ISSN:0035-9009    

DOI:10.1002/qj.49711147006

出版商:John Wiley&Sons, Ltd    

年代:1985

数据来源: WILEY

摘要:

AbstractIt is shown that photochemical acceleration of the thermal relaxation rate in the stratosphere may be expressed as a matrix multiplication between a square matrix, which may be calculated for quite general conditions, and a vector representing the deviation of temperature from an equilibrium profile. Such a matrix is presented and its form discussed. Use of this matrix allows for temperature perturbations of any vertical scale and thus provides an accurate, as well as fast, method for calculating photochemical acceleration suitable for use in numerical models of stratospheric dynamics. the inclusion of the ozone 9.6 m̈m band into the heating rate calculations is shown to reduce the photochemical relaxation rate in the upper stratosphere

ISSN:0035-9009    

DOI:10.1002/qj.49711147007

出版商:John Wiley&Sons, Ltd    

年代:1985

数据来源: WILEY

摘要:

AbstractThis paper discusses the relationship between certain well‐posedness results for the equations of motion and simple phenomenological arguments pertaining to the predictability of the flow fields. the barotropic and quasi‐geostrophic equations have been shown to be well‐posed under certain conditions. From this, it has been inferred that Lorenz's conjecture of finite predictability time for any scale of initial error is false. Such an inference is justified in the error energy may be made small by confining the error to small scales of motion. It is shown that this may be achieved, given finite bounds on the vorticity. It is also shown that there is no contradiction between essentially Kolmogorovian phenomenological arguments and the well‐posedness of the equations, since the conditions uder wich a finite predictability time is predicted by the former are those then phenomenological trubulence arguments and rigorous existence proofs imply that the predictability time of a barotropic fluid may be made as long as we wish if the initial error scale can be made small enough. Both sets of arguments also imply that enstrophy dissipation tends to zero as viscosity tends to zero. For a three‐dimensional fluid phenomenology implies a finite predictability time, and non‐zero energy dissipation as viscosity tends to zero, implying the ill‐posendness of the three‐dimensional

ISSN:0035-9009    

DOI:10.1002/qj.49711147008

出版商:John Wiley&Sons, Ltd    

年代:1985

数据来源: WILEY

摘要:

AbstractThe influence of mechanical forcing on the formation of a mesoscale vortex which occurred over the eastern flank of the Qinghai‐Tibetan Plateau (QTP) is investigated by running a series of numerical experiments. Different orography schemes are tested. It is shown that there are three branches of air flow converging towards the vortex: the northerlies associated with the middle latitude westerly currents, the southerlies with the lowlevel monsoon jet, and the easterlies with the west Pacific subtropical high. These flows are very sensitive to mechanical forcing and play very important roles in the formation and location of the vortex.The model with either the mean or the envelope orography is shown to be capable of predicting the formation of the vortex and the associated torrential rain. However, its location is not predicted precisely. A modified orography, simulating the ‘step’ structure of the eastern flank of the QTP, is then used in an attempt to improve the prediction. Results from this experiment suggest that the weakening of some of the steep slopes of the large‐scale orography in a numerical model, due to excessive smoothing of mountain height and expanding of mountain area, is responsible for the inaccuracy in the forecast of such synoptic systems. Therefore further improvements in the orography scheme are di

ISSN:0035-9009    

DOI:10.1002/qj.49711147009

出版商:John Wiley&Sons, Ltd    

年代:1985

数据来源: WILEY

摘要:

AbstractA considerable international effort is being made to improve all aspects of the physical processes represented in numerical models of climate. This particular paper is concerned with one of those aspects, namely the manner in which soil hydrology is included in such models and how it affects climate. For this purpose a 1‐dimensional radiative‐convective model has been coupled with various soil hydrology formulations. This simple approach has the combined advantages of permitting a self‐consistent energetic evaluation of the impact of the moisture content of the soil, and of providing a very economical means for investigating the model's response to perturbations in selected variables. Three soil hydrology parametrizations suitable for use in climatic models were compared, and their individual characteristics illustrated. A method devised by J. W. Deardorff was judged to be superior and was therefore used in the subsequent experiments. These experiments were designed to clarify the role of soil moisture and its variability on the model's surface temperature and surface heat fluxes. the approach adopted permitted individual responses to be followed in great detail, and highlighted the potential role of the model for assisting in the design and subsequent analysis of appropriate experiments using climatic models. Importantly, the results illustrate the limitations of current formulations for surface hydrology used in climatic models, and the need for better parametrizations to be deve

ISSN:0035-9009    

DOI:10.1002/qj.49711147010

出版商:John Wiley&Sons, Ltd    

年代:1985

数据来源: WILEY

摘要:

AbstractThree operational shallow water wave models are intercompared for two artificial experiments and verified for a severe storm hindcast, with the objectives of further understanding the effects of the parametrization of shallow water wave processes in numerical models.The models used are the HYPAS (Max‐Planck Institute) and GONO (KNMI) coupled‐hybrid models, and the BMO (Meteorological Office) coupled‐discrete model which are all briefly described. In the first case, depth‐dependent fetch‐limited wave growth in a steady wind is examined. In the second case a steady onshore wind is specified over an idealized constant slope coastal shelf, and the stationary wave spectra at various depths are intercompared. For the third case the wind fields for the North Sea storms of 18‐26 November 1981 were accurately reconstructed and used by each model in its operational configuration to produce a wave hindcast for this period.In case 1 the GONO and BMO models exhibit similar behaviour in the evolution of energy and peak frequency, whereas HYPAS displays less depth attenuation and little variation in peak frequency. In case 2 the energy values at different shelf depths are approximately as predicted in case 1 for HYPAS though rather higher for BMO and GONO. However, GONO and HYPAS show little change in peak frequency with depth here whereas BMO wave spectra become double‐peaked with a wind‐sea peak migrating to higher frequencies in shallower waters. In case 3, the hindcasts, all models produce qualitatively similar results. the time series of wave height and period agree well with measurements, BMO and HYPAS predicting correct energy levels except at storm peaks and GONO generally overpredicting both at lower energy levels and in a duration‐limited strong wind case. the r.m.s. error in wave height at the southern shallow water verification site is 0.5 m for all models, and varies between 0.9 m (GONO) and 1.5m (HYPAS) at the northern deep water site. Some wave spectra are presented and the directional relaxation of wind‐sea in each model is illustrated.The results of cases 1 and 2 are readily explained by the formulation of shallow water processes adopted in each model, but it is difficult to isolate and identify these mechanisms in the measured or modelied spectra from the hindcast. It is suggested that future studies involving detailed verification and intercomparison of wave models should be confined to more carefully designed wave‐measuring experiments so that less ambiguous

ISSN:0035-9009    

DOI:10.1002/qj.49711147011

出版商:John Wiley&Sons, Ltd    

年代:1985

数据来源: WILEY