摘要:

AbstractA numerical procedure is described for determining, in a barotropic model, the horizontal wind (V) from the field of geopotential height, based on the approximation d2V/dt2= 0. The technique used to solve the resultant simultaneous equations is outlined and some of the problems which were encountered in their solution are also mentioned. The approximation permits the evaluation of the geopotential height tendency and a comparison is made between barotropic forecasts based on this condition and on conventional barotropic and baroclinic numerical integrations.

ISSN:0035-9009    

DOI:10.1002/qj.49709640702

出版商:John Wiley&Sons, Ltd    

年代:1970

数据来源: WILEY

摘要:

AbstractAn observational study of the temperature profile over grass, snow and bare soil surfaces in strong stability is presented. It was found that in nearly calm, clear conditions the minimum temperature occurred 1 to 50 cm above the surface. The height and intensity of the minimum is strongly correlated with wind speed, surface roughness and stability. A discussion of existing hypotheses suggests that the most likely explanation for the phenomenon should involve both turbulence and infra‐red flux divergenc

ISSN:0035-9009    

DOI:10.1002/qj.49709640703

出版商:John Wiley&Sons, Ltd    

年代:1970

数据来源: WILEY

摘要:

AbstractCalculations of the transfer of kinetic energy from the troposphere to the stratosphere by means of the pressure‐interaction term are carried out for the mid‐winter stratospheric warming of 1967‐1968. This term is computed in the wave number domain for the 100 mb level by means of the Eliassen and Palm (1960) approximation. There appears to be a distinct correlation between the stratospheric kinetic energy per wave number at the 10 mb level and the energy transfer by that wave number at the 100‐mb level. A comparison of the magnitude of the energy flux for 1963 versus that for this later warming suggests that this term is of the same order as the remaining terms in the kinetic energy equation calculated by Perry (1967). Results obtained using this approximation appear to give good agreement with those obtained by direct calculation of the vertical velocit

ISSN:0035-9009    

DOI:10.1002/qj.49709640704

出版商:John Wiley&Sons, Ltd    

年代:1970

数据来源: WILEY

摘要:

AbstractOn the basis of total ozone, Umkehr data and ozone soundings with Mast‐Brewer sondes at Aspendale, it is shown that the systematic effect of selectivity in the days on which Umkehr observations are made may be as large as 10 to 35 per cent of the annual mean content of layers 2 and 3. This selectivity effect varies with time, and is reasonably explained in terms of a correlation between ozone content in the lower stratosphere and cloudiness. Caution with regard to the use of Umkehr‐derived mean ozone distributions in climatological studies is therefore urged, and the need for further research is pointed out. The statistical limitations of mean distributions derived from ozone‐sonde flights are also discussed, with particular reference to quasi‐periodic inf

ISSN:0035-9009    

DOI:10.1002/qj.49709640705

出版商:John Wiley&Sons, Ltd    

年代:1970

数据来源: WILEY

摘要:

AbstractTwo case studies are presented of the detailed structure of frontal zones with strong vertical shear. Temperature structure has been obtained from sequential radiosonde ascents. Wind structure, including the fields of horizontal divergence and deformation, has been obtained on scales of 1 to 10 km by means of Doppler radar techniques. The results are consistent with the frontal zones being at least partly controlled by shearing instability, in so far as there was a balance between a wind field tending to diminish the Richardson number (Ri) and shearing instability tending to impose a lower limit to Ri. One of the main factors tending to diminish Ri was stretching deformation in a direction normal to the local shear vector. A typical rate of decrease of Ri which this would have produced in the absence of shearing instability was 10−4s−1. The Richardson number itself within the frontal zones was mainly between 0.2 and 0.4 when averaged vertically over 200 m and horizontally over circles of diameter 10 km; however, Ri diminished to about half of these values locally on horizontal scales of about 1 km. As a result shearing instability is thought to have led to turbulent breakdown in only isolated patches rather than in a sustained fashion over the entire depth of the frontal zo

ISSN:0035-9009    

DOI:10.1002/qj.49709640706

出版商:John Wiley&Sons, Ltd    

年代:1970

数据来源: WILEY

摘要:

AbstractCertain theoretical features of high altitude lee waves for some simple two‐dimensional models are described. It is shown that some of these allow an intense local radiation of lee waves in a nearly vertical beam into the high stratosphere (similar to the leakage upwards of short radio waves in a familiar electromagnetic theory). Some associated quasi‐resonance phenomena are no

ISSN:0035-9009    

DOI:10.1002/qj.49709640707

出版商:John Wiley&Sons, Ltd    

年代:1970

数据来源: WILEY

摘要:

AbstractThe diabatic mean profile forms in the surface layer are studied, by applying analysis methods having high resolving power to data from O'Neill, U.S.A. (heights up to 6.4 m) and from Kerang and Hay, Australia (heights mostly up to 16 m).It is found, concordantly from the O'Neill and Australian data, that the log‐linear law is valid for z/L values between — 0.03 and + 1, which includes a small range of unstable and a surprisingly wide range of stable conditions. For all quantities studied (wind, potential temperature, and specific humidity), it is concluded that the Monin‐Obukhov coefficient α is near 4.5 in unstable and 5.2 in stable conditions, within a standard error of about 10 per cent. The ratios KH/KMand KW/KMevidently remain constant, equal to unity, over the whole of the log‐linear range (and somewhat beyond).In stable conditions, the log‐linear law implies that Ri approaches a critical value α−1, approximately 0.2, as z/L → ∞. However, at z/L a second régime sets in, in which the profiles are only quasi‐determinate, approximating, on the average, a simple logarithmic form (gradients proportional to z−1); this régime covers the range approximately 1

ISSN:0035-9009    

DOI:10.1002/qj.49709640708

出版商:John Wiley&Sons, Ltd    

年代:1970

数据来源: WILEY

摘要:

AbstractWinds and temperatures in the boundary layer measured during two Australian expeditions are analysed according to the similarity scheme, with the use of four stability classifications.Under conditions of deep convection there is a minimum potential temperature and a maximum velocity component in the direction of the surface wind, at a height of about 0.12 u*/f. In the very stable cases, the temperature gradient follows rather closely a z−2law for a considerable height range from 0.08 u*/f upwards. An expression closely fitting the mean data in stable conditions is suggested for the vertical temperature structure at all levels in the boundary layer.Wind data processed in this way show, for all four stability classes, a rudimentary Ekman spiral. With deep convection the spiral is found to be reversed in sense, but the flow in the convecting layer is down the gradient of pressure. If the convective limit lies broadly within the Ekman layer, a spiral of the expected sense is found. The upper limit of the Ekman layer (as defined by the ‘spiral’) is found to lie at a height of 0.17 to 0.24 (increasing with stability) in units of u*/f. Stress and heat‐flux are apparently considerable above this level, with sub‐geostrophic wind, when deep convection is occurring.Approximations to the universal distributions of stress, eddy coefficients, mixing length and rate of degradation of mean flow kinetic energy are computed for the various stabilities. The mixing length in unstable conditions increases almost as height up to a level of about 0.08 u*/f, and then decreases, but in general appears not to vanish in stable layers above the boundary layer. In the unstable boundary layer with deep convection, the eddy transfer coefficient for heat exceeds that for momentum up to 0.12 u*/f, where it becomes infinite, and is negative at higher levels. In stable conditions the transfer coefficients for a small sample of soundings were estimated to be closely similar.The universal functions of stability, A, B and C, which enable one to compute free atmosphere wind vector and temperature, given surface conditions, have been evaluated with moderate success, although B, which essentially describes the change of wind direction with height, exhibits excessive variability. A method is suggested for computing horizontal advection in the boundary layer when this is to be ‘parameterized’ in mathematical models.The drag coefficient, in terms of free atmosphere wind, has almost a 50‐fold range, due to stability variation only. Most of the variation occurs relatively close to neutral, so warning against too ready an assumption of neutrality in practical applications.It is suggested that, for modelling purposes, it is preferable to adopt boundary layer formulations which are not too sensitive to departures from ideal conditions, and eddy coefficients, perhaps based on mixing lengths, may well provide the best approach curr

ISSN:0035-9009    

DOI:10.1002/qj.49709640709

出版商:John Wiley&Sons, Ltd    

年代:1970

数据来源: WILEY

摘要:

AbstractThe differential equation for cup and vane anemometers, developed earlier (Ramachandran 1969) is checked by comparing the computed overestimations of mean values in sinusoidally fluctuating winds with the experimental results of Deacon (1951). The equation predicts an overestimation of low frequency components in winds containing more than one sinusoidal component.Results from direct measurements are compared with those obtained from compensated data, using an approximate compensation technique.The logarithmic power spectra obtained from compensated data show peaked shapes arising out of the removal of the nonlinear overestimation of response at the low frequencies.

ISSN:0035-9009    

DOI:10.1002/qj.49709640710

出版商:John Wiley&Sons, Ltd    

年代:1970

数据来源: WILEY

摘要:

AbstractThe best eigenvector representations of Northern Hemispheric fields of the height of the 1,000 mb surface and the 1,000‐500 mb thickness are compared with those previously found for the 500 mb surface. It is shown that the use of the first 50 eigenvectors of the 500 mb fields, for all three types of field, produces a representation which is only marginally inferior to that obtainable by using three different sets of eigenvector

ISSN:0035-9009    

DOI:10.1002/qj.49709640711

出版商:John Wiley&Sons, Ltd    

年代:1970

数据来源: WILEY