ISSN:0035-9009    

DOI:10.1002/qj.49710745202

出版商:John Wiley&Sons, Ltd    

年代:1981

数据来源: WILEY

摘要:

AbstractAn attempt is made to understand the long‐term balance of the total relative angular momentum M of an inviscid barotropic fluid forced by orography. the problem is treated by integrating the barotropic potential vorticity equation with the β‐plane approximation, and on the sphere, using spectral methods. First, a highly truncated system containing only the superrotational flow and one wave component is studied by analytical means. A fairly complete understanding of the behaviour and the climatic mean value of M is achieved. Then, less truncated systems with up to five zonal wave‐numbers are investigated by numerical integrations. It turns out that a climatic mean value can be ascribed to M if the integration is carried out for several weeks or more. It is demonstrated that this long‐term mean value can be estimated reasonably weil on the basis of the study of the highly truncated system. A possible application of these results to more realistic fluid systems is s

ISSN:0035-9009    

DOI:10.1002/qj.49710745203

出版商:John Wiley&Sons, Ltd    

年代:1981

数据来源: WILEY

摘要:

AbstractGill (1977) has interpreted the coastal lows of southern Africa as atmospheric coastal Kelvin waves. the lows are trapped horizontally next to the steep slopes of the Great Central Plateau by Coriolis forces and vertically by a low‐level inversion. This hypothesis is tested and extended using two linear models.A barotropic primitive‐equation analysis on an equatorial beta‐plane models the generation of these waves. an impermeable eastern boundary is included to reflect the blocking of the low‐level flow below the coastal inversion by the orography. Results of the linear analysis suggest that the formation of the coastal lows may be explained in terms of the scattering of eastward‐propagating synoptic‐scale disturbances at the meridional boundary. the boundary response is structurally similar to a Kelvin wave. At the frequencies of interest, no zonally propagating Rossby waves are excited. Further, in contrast to the case of a western boundary, the equatorial response is negligible.A two‐layer, f‐plane model enables the dynamics of the layer of fluid below the interior inversion to be incorporated. At the period of the synoptic forcing (six days), the boundary response is a maximum along the escarpment and decays exponentially from it. the e‐folding distance is slightly less than the appropriate Rossby radius of deformation. These results, together with observations, suggest that the coastal low and its companion low over the interior may be interpreted as forced internal double Kelvin waves.The possible application of these results to foehn (chinook) winds and lee cyclogen

ISSN:0035-9009    

DOI:10.1002/qj.49710745204

出版商:John Wiley&Sons, Ltd    

年代:1981

数据来源: WILEY

摘要:

AbstractVarious mechanisms which lead to nocturnal accelerations and formation of the low‐level jet are examined by analysing Wangara data. the stress field is inferred from the wind field and equations of motion. the evolution of the stress divergence, during the evening transition from daytime mixed layer flow to nocturnal boundary layer flow, is found to increase the ageostrophic flow and subsequent nocturnal accelerations by roughly a factor of two. During this transition the stress divergence in the lowest few hundred metres increases due to the fact that the influence of decreasing boundary layer depth exceeds the effect of decreasing surface stress. This leads to temporary deceleration and rotation of the low‐level wind vector towards low pressure and thus increases the ageostrophic flow.Diurnal variation of the geostrophic wind is also found to significantly strengthen the nocturnal flow. This diurnal variation is apparently due to heating and cooling over terrain which slopes gently upward, east of the location of the Wangara experim

ISSN:0035-9009    

DOI:10.1002/qj.49710745205

出版商:John Wiley&Sons, Ltd    

年代:1981

数据来源: WILEY

摘要:

AbstractThe formula for the cross‐section for scattering of sound in a turbulent flow, upon which SODAR meteorology relies, is derived from a simplified, physically appealing argumen

ISSN:0035-9009    

DOI:10.1002/qj.49710745206

出版商:John Wiley&Sons, Ltd    

年代:1981

数据来源: WILEY

摘要:

AbstractA case study is presented showing the kinematic structure of a train of large‐amplitude billows associated with a strongly sheared layer of high static stability in the upper troposphere. the observations were obtained using a high‐power microwave Doppler radar with a range resolution of 30 m. A beamwidth resolution almost as good as this was achieved at the ranges of interest using a 25 m paraboloid aerial. the resulting detailed measurements revealed the kinematic structure of secondary billows of wavelength 350m growing on the back of primary billows of wavelength 4.2km. the secondary billows were regions of moderate turbulence, the outer scale of which was small compared with the radar resoluton. Streamers of cirrus ice particles were present in the region of interest and these served as tracers showing how the billows perturbed the flow over a considerable depth above and below the primary bill

ISSN:0035-9009    

DOI:10.1002/qj.49710745207

出版商:John Wiley&Sons, Ltd    

年代:1981

数据来源: WILEY

摘要:

AbstractProfiles of the upward and downward solar and infrared flux densities and of the downward beam radiance at 11 μm are reported for six cirrus cloud decks over Socorro, New Mexico. the data are used to derive empirical relations between vertical ice‐water path (obtained from simultaneously measured particlesize distributions) and solar absorptance, solar albedo, broad‐band infrared flux emittance and the 11μm beam emittance. As a guide, for ice‐water paths of about 75 gm−2where the infrared emittances are approaching unity, the solar albedo is about 0.4, the solar absorptance is of the order of 0.15 and the geometrical thicknesses are between 1.5 and 2.5 km. Within an individual cloud there is little variation of particle size distribution with height, but the geometrically thicker clouds favour large particles. No icecrystal shape information is available, but the observed relation between albedo and emittance suggests that theoretical treatment of cirrus ice particles as ‘cylinders’ is better than treatment as ‘equi

ISSN:0035-9009    

DOI:10.1002/qj.49710745208

出版商:John Wiley&Sons, Ltd    

年代:1981

数据来源: WILEY

摘要:

AbstractA field study of the microphysical properties of a radiation fog was conducted in Meppen, West Germany, on 17 February 1978. It is described and interpreted in terms of the prevailing meteorological conditions.Pronounced periodic fluctuations in liquid water content (intervals ∼70s) were observed at times in the radiation fog. It is suggested that these were a result of convective motions in the form of Bénard cells. the drop size distributions were broad, containing drops of radii up to 25 μm. Calculations indicate that these larger drops cannot be produced by radiative cooling from the fog top. It is argued that these large drops may have been produced either by large supersaturation fluctuations near the fog top, resulting from downwards entrainment of warmer moister air, or by convective motions causing a fraction of the larger drops to make several excursions to the radiative cooling region near the fog top. the radiation fog was observed to clear when cloud was advected over the site. It is suggested that this was due mainly to eddy diffusion and gravitational sedimentation of drops to ground, after radiative cooling from the fog top had been severely curtailed by the cloud la

ISSN:0035-9009    

DOI:10.1002/qj.49710745209

出版商:John Wiley&Sons, Ltd    

年代:1981

数据来源: WILEY

摘要:

AbstractA multilayer crop model is used to simulate the interception and evaporation of rainfall as well as transpiration loss for a pine canopy. A considerable improvement, in terms of physical realism, over the Rutter (Rutteret al.1971) model appears to have been achieved and the results generally agree with experimental work. Simulation runs on synthetic meteorological data indicate that the Rutter model substantially underestimates the interception loss from low intensity rainstorms. the multilayer pine model, MANTA, is run with a year's data and the results compared with those from an equivalent unilayer pine and also a grass model. the results show that MANTA predicts a 20% increase in interception loss over the Rutter model estimate and that over the year the interception loss from grass is one quarter of that from pine.

ISSN:0035-9009    

DOI:10.1002/qj.49710745210

出版商:John Wiley&Sons, Ltd    

年代:1981

数据来源: WILEY

摘要:

AbstractThe analysis of records, for the period 1962‐1975, reveals that the wave height observations exhibit a seasonal variation in both the average value and the standard deviation. Examination of the seasonally adjusted wave heights indicates that these values may be approximately described by first order autoregressive time series models. the validity of these models is checked using statistical tests, comparing short‐term forecasts of wave heights with actual observations and by simulating observations and examining the frequency and duration of storms and calm periods. Methods of improving the models for wave height are exami

ISSN:0035-9009    

DOI:10.1002/qj.49710745211

出版商:John Wiley&Sons, Ltd    

年代:1981

数据来源: WILEY