ISSN:0035-9009    

DOI:10.1002/qj.49710745402

出版商:John Wiley&Sons, Ltd    

年代:1981

数据来源: WILEY

摘要:

AbstractObservations are presented of the effects of topography on thermally driven baroclinic flows in a rotating annulus. It is observed that the transition from baroclinically stable to unstable flows is stabilized in the presence of small amplitude topography. However, when baroclinic waves are present they are of shorter wavelength and larger amplitude than those in flows driven by similar temperature differences in the absence of topographic forcing. Non‐linear interactions between stationary forced and drifting baroclinic waves may result in the appearance of significant amounts of energy in drifting waves which are not harmonics of the dominant baroclinic wave.A local linear analysis is used to explain the observations of the effects of topography on the onset of baroclinic instability. Despite the limitations of this analysis which arise due to the similarity of the wavelengths of the baroclinic and forced waves the quantitative predictions of the analysis are in reasonable agreement with the observation

ISSN:0035-9009    

DOI:10.1002/qj.49710745403

出版商:John Wiley&Sons, Ltd    

年代:1981

数据来源: WILEY

摘要:

AbstractUsing the data obtained at the Boulder Atmospheric Observatory (BAO), we have analysed a gravity wave‐turbulence event, which occurred on 18 September 1978. A 300m tower was equipped with various sensors at eight different levels and provided information on the vertical structure of the disturbance to an unprecedented degree. These data were complemented by measurements from a nearby microbarograph network which allowed us to determine the period and horizontal wavelength of the disturbance. It was the rather accurate determination of the period of the gravity wave and its near monochromaticity that made possible the utilization of the phase average operator in separating the periodic and turbulent components of the field variables. In this paper, we concentrate on describing the wave field and on comparing it with a linear model, deferring to a second paper the discussion of the effect of the periodic disturbance on the coexisting turbulence. We show that a linear model adequately describes the observed parameters (period and horizontal wavelength) and the vertical structure of the fluctuations in the temperature and horizontal and vertical velocity component

ISSN:0035-9009    

DOI:10.1002/qj.49710745404

出版商:John Wiley&Sons, Ltd    

年代:1981

数据来源: WILEY

摘要:

AbstractAn atmospheric internal gravity wave was measured over a two‐hour period by a microbarograph array and a series of fast response wind and temperature sensors deployed along a 300m tower. the particularly monochromatic nature of the pressure signal at the ground enabled an explicit separation of the velocity field into mean, wave, and turbulent components. Large wave‐frequency fluctuations were observed in the turbulent Reynolds stresses. Their significance is discussed at length with special regard to their role in the budget of wave kinetic energy. It is shown that the quadrature relationship which they maintain with the components of wave‐shear, limits their effectiveness in reducing the wave amplitude. Analysis of the important time scales in the budget of turbulent kinetic energy reveals that the energy containing eddies have time scales longer than the wave period, and consequently the turbulence cannot remain in equilibrium with large, wave‐frequency fluctuations in shear production. the result is a boundary layer which never attains a true equilibriu

ISSN:0035-9009    

DOI:10.1002/qj.49710745405

出版商:John Wiley&Sons, Ltd    

年代:1981

数据来源: WILEY

摘要:

AbstractObservations of neutral flow around an isolated island are presented. the island has a fairly smooth shape with slopes of about 30° and a horizontal section which is roughly elliptical with axis ratio 1.5. the flow field 4 m above the surface shows a speed‐up around the sides and over the summit, with reverse flow on the lee slope. Measurements with an instrumented aircraft, of the mean flow in the wake of the island reveal a single very powerful trailing vortex, with axis close to the upstream wind direction. There are indications that the single vortex was a consequence of the asymmetry caused by the island's elliptical shape. Measurements of fluctuating quantities with a tethered balloon system show marked changes in the components of the turbulence energy in the flow around the side of the hi

ISSN:0035-9009    

DOI:10.1002/qj.49710745406

出版商:John Wiley&Sons, Ltd    

年代:1981

数据来源: WILEY

摘要:

AbstractThe turbulence and microphysical structures of small cumulus clouds have been studied in some detail using three turbulence probes and a droplet spectrometer attached to the tethering cable of a large (1300 m3) balloon. the airflow in and around clouds showed some evidence for a ‘P‐shaped’ circulation in the vertical plane and rotation in the horizontal plane. Power spectra of the vertical component of air motion both in and out of cloud and in the mixed layer below cloud base are described and contrasted. Mean turbulence characteristics (i.e. averaged over a few hours) strongly resemble those from the upper regions of the clear convective boundary layer but in the vicinity of clouds the turbulence field is considerably altered. Observations of the cloud droplet field near cloud top and the rate of dissipation of turbulent kinetic energy provide evidence that the entrainment and mixing of dry air proceed essentially inhomogene

ISSN:0035-9009    

DOI:10.1002/qj.49710745407

出版商:John Wiley&Sons, Ltd    

年代:1981

数据来源: WILEY

摘要:

AbstractThe assumption of steady two‐dimensional flow imposes constraints on the motion of a layer of cold air propagating through a body of warm air. Some general properties, such as the propagation speed of the front, can be deduced from consideration of the equations of motion away from the frontal region. Thus the differences between anafronts and katafronts are discusse

ISSN:0035-9009    

DOI:10.1002/qj.49710745408

出版商:John Wiley&Sons, Ltd    

年代:1981

数据来源: WILEY

摘要:

AbstractA band‐pass filter transparent to fluctuations in the 2£5‐6 day period range is applied to a set of twice‐daily analyses covering the 1979 (FGGE year) winter of the Southern Hemisphere. Fields analysed include MSL pressure, 500mb height, 300mb wind, and the meridional heat flux due to transient eddies at 850mb. Variance maxima in these filtered fields indicate regions of high cyclonic activity, with favoured cyclolysis areas in the vicinity of the Antarctic coastline also showing up in the MSL pressure statistics. Using these results, supplemented by data on the distribution of cyclogenesis, we are able to identify the major depression tracks. In this analysis, extensive use is made of studies relating satellite‐observed cloud vortices to the various stages of cyclonic development. In general, it appears there was significantly more activity in the eastern hemisphere than in the western during the 1979 winter.By evaluating the terms in the time‐averaged zonal momentum equation (using the unfiltered data set), it is possible to assess the role of transient eddies in the maintenance of the time‐mean zonal flow. This analysis shows that Coriolis acceleration associated with poleward time‐mean ageostrophic flow at the tropopause level dominates the forcing of the jet centred around 25°S, but that convergence of eddy momentum flux maintains the higher latitude jet around 50°S. However, a significant contribution to the latter jet comes from poleward ageostrophic flow

ISSN:0035-9009    

DOI:10.1002/qj.49710745409

出版商:John Wiley&Sons, Ltd    

年代:1981

数据来源: WILEY

摘要:

AbstractAn analysis is presented of the large‐scale mean state kinematic properties of the wind field based on observed rawinsonde data taken over western Africa and the eastern Atlantic during Phases I, II, and III of GATE. Variables presented are wind direction and speed, zonal wind component, temporal standard deviation of the zonal wind component, verticalp‐velocity and relative vorticity. Wind direction and speed and temporal standard deviation of zonal wind were subjectively analysed at the surface, 850mb, 700mb, 500mb, 400mb, 300mb, 250mb, 200mb, 150mb and 100mb. Grid point data were extracted from analyzed charts at increments of 2° latitude and longitude and used to compute vertical motion and vorticity. Resultant analyses are examined to determine kinematic properties common to all three phases of GATE, trends in these properties from one phase to the next, and differences between properties over western Africa (land) and the eastern Atlantic (water). Features of the mean state are compared with results obtained by other investigators for such phenomena as large‐scale westward propagating wave disturbances, low‐level cyclonic vortices, satellite‐derived precipitation and cloud clusters associated with sq

ISSN:0035-9009    

DOI:10.1002/qj.49710745410

出版商:John Wiley&Sons, Ltd    

年代:1981

数据来源: WILEY

摘要:

AbstractThree different numerical models are used to simulate the surge generated by the 1977 Andhra cyclone. In each of these we simulate the effect of three days of wind‐stress forcing before landfall of the cyclone at the Andhra Pradesh coast. the analysis area in the first model includes the entire Bay of Bengal north of 6°N and utilizes a curvilinear boundary treatment to represent the coastlines. the second model is a coastal zone model extending along the east coast of India, again utilizing a curvilinear treatment of the coastline. In the third model, which again covers the entire Bay of Bengal, the coastlines are represented by a conventional stepwise procedure. Using available data on the Andhra cyclone as a guide in representing the effect of wind‐stress forcing in our models, we compare the predicted rise in the sea‐surface elevation obtained from each of these with estimates based on reports received from Andhra Pradesh after the disastrous flooding in that region. Each of the three models produces a qualitatively similar surge response. the slight quantitative differences are explained in terms of the different boundary treatments. the predicted peak surface elevation above mean sea‐level compares well with the estimated 5 m reported along part of the Andhra Pradesh coast south of Masu

ISSN:0035-9009    

DOI:10.1002/qj.49710745411

出版商:John Wiley&Sons, Ltd    

年代:1981

数据来源: WILEY