摘要:

AbstractTemporal spectra and cross‐spectra of the three turbulent wind components for meso‐synoptic scales at 250 m vertical intervals in the planetary boundary layer are presented. The data were derived from hourly simultaneous balloon ascents from a 5‐point grid at Hay, New South Wales, Australia (lat. 34 ½S), during the Wangara expedition. The spectra indicate a meso‐scale gap foru(eastward component of wind) andv(northward component). The computedw‐spectra suggest that no marked gap is present. For periods less than 1 day theu‐andv‐spectra, with a correction applied for high frequency noise, fall off approximately asn−2·6, wherenis the frequency, and this result appears to be invariant with height within and just above the planetary boundary layer. The correctedw‐spectra exhibitn−1dependency in this frequency range. Theuv, uw, andvwcospectra also show only small contributions on the meso‐scale (periods less than a day) compared to the synoptic scale, indicating that meso‐scale motions may not have to be explicitly modelled in atmospheric general circulation models. An inertial peak is found foruandvbut thew‐spectra show a diurnal peak. The phase angles showed thatuandvwere in approximate quadrature at the inertial frequency, demonstrating the existence of the inertial cycle. Tests for horizontally two‐dimensional isotropy indicated that the turbulence did

ISSN:0035-9009    

DOI:10.1002/qj.49709941912

出版商:John Wiley&Sons, Ltd    

年代:1973

数据来源: WILEY

摘要:

AbstractHourly energy budgets measured in Thetford Forest, Norfolk, are analysed for seven fine days in months from May to September.Values found for the Bowen ratio β ranging from near 1 to 4 or more, are used to show that the bulk physiological resistance rSTof the forest exhibits a consistent diurnal trend, from near 1·2 s cm−1in the forenoon (once the trees are dry) to as much as 4 s cm−1by late afternoon ‐ consistent with independent biological measurements (Robins, personal communication). In contrast, the forest's bulk aerodynamic resistance r generally lies between 0·05 and 0·10 s cm−1. The ratio rST/ralone, of order 20:1, is shown to imply that transpiration from the forest must occur at rates much less dependent, primarily, on net radiation,Rn, than on ambient vapour pressure deficit (v.p.d.), (provided that the latter is not too small, i.e. ≮ 1 mb per 100 W m−2ofRn, say); and also that the evaporation of intercepted rainfall from the trees must occur at about 5 times the corresponding transpiration rate under the same meteorological conditions. In addition, because lighter winds during fine weather tend to favour larger v.p.d's the observed decrease in transpiration rate with increasing wind speed is much larger than that expected from the accompanying decrease in r alone.Other conclusions are (i) that the storage associated with a 1° C change in air temperature per hour, within the canopy, is 18 W m−2, which is not always negligible, as it is for short vegetation; and (ii) that values derived for the dimensionless excess resistance parameter,B−1, although remarkably small, 2 to 3 foru* ∼ 0·75 m s−1, are commensurate with other bulk aerodynamic resistances in the system: accordingly, the easily‐derived surface resistance parameter,rs, (Monteith 1965; Thom 1972) provides an estimate ofrSTfor the forest wit

ISSN:0035-9009    

DOI:10.1002/qj.49709941913

出版商:John Wiley&Sons, Ltd    

年代:1973

数据来源: WILEY

摘要:

AbstractSwinbank's recent claim that Mildner's so‐called Leipzig wind profile data for the atmospheric boundary layer support the hypothesis that the shearing stress vector and the wind vector are parallel, is critically examined and compared with the conflicting classical hypothesis that stress and velocity shear are parallel as previously applied by Lettau. The geostrophic wind direction, known only imprecisely from Mildner's measurements, is allowed to vary in order to produce best‐fit profiles consistent with each hypothesis and generally accepted ‘boundary’ conditions. The degree of fit (theory to measurements) is roughly ten times better in the classical case than in Swinbank's case, the former showing a r.m.s. angular difference between the stress and shear vectors in the lowest 800 m of

ISSN:0035-9009    

DOI:10.1002/qj.49709941914

出版商:John Wiley&Sons, Ltd    

年代:1973

数据来源: WILEY

摘要:

AbstractThis paper discusses the thermodynamic transports of heat, liquid water and (briefly) water vapour by non‐precipitating cumulus convection. It is shown that because of the irreversible mixing between cloud and environment, there is a downward transport of enthalphy in the cumulus layer. A lapse‐rate adjustment model relates stratification to the life‐cycle of a model cloud parcel. A sub‐cloud layer model specifies the lower boundary of the lapse‐rate model, and the convective transports through cloud‐base. Budget equations together with the lapse‐rate model, and its time dependent boundary conditions, predict the time development of the cumulus layer, and show the dependence on large‐scale mean vertical motion, cloud‐base variations, and the surface s

ISSN:0035-9009    

DOI:10.1002/qj.49709941915

出版商:John Wiley&Sons, Ltd    

年代:1973

数据来源: WILEY

摘要:

AbstractIn the extreme seasons the winter hemisphere Hadley cell dominates the entire zonally averaged mean meridional circulation by extending well into the summer hemisphere, and the summer hemisphere Hadley cell practically disappears. The hypothesis that this apparent disappearance is due to the process of zonal averaging, and that a summer hemisphere Hadley cell does exist when the averaging is restricted to the longitudes not occupied by the Asiatic monsoon, is tested. Using data for 1957–1964 covering the months June‐August, it is found that the summer hemisphere Hadley cell was indeed present over the longitudes 160°E‐0–30°E, or two thirds of the Tropics. It is argued that some of the most interesting features of the meridional circulation and their associated transport processes are obscured by the zonal averagin

ISSN:0035-9009    

DOI:10.1002/qj.49709941916

出版商:John Wiley&Sons, Ltd    

年代:1973

数据来源: WILEY

ISSN:0035-9009    

DOI:10.1002/qj.49709941917

出版商:John Wiley&Sons, Ltd    

年代:1973

数据来源: WILEY

ISSN:0035-9009    

DOI:10.1002/qj.49709941918

出版商:John Wiley&Sons, Ltd    

年代:1973

数据来源: WILEY

ISSN:0035-9009    

DOI:10.1002/qj.49709941919

出版商:John Wiley&Sons, Ltd    

年代:1973

数据来源: WILEY

ISSN:0035-9009    

DOI:10.1002/qj.49709941920

出版商:John Wiley&Sons, Ltd    

年代:1973

数据来源: WILEY

ISSN:0035-9009    

DOI:10.1002/qj.49709941923

出版商:John Wiley&Sons, Ltd    

年代:1973

数据来源: WILEY