ISSN:0035-9009    

DOI:10.1002/qj.49709339802

出版商:John Wiley&Sons, Ltd    

年代:1967

数据来源: WILEY

摘要:

AbstractExisting theory of the stability of a stably stratified fluid containing a strong vertical shear suggests that unstable waves may develop when the curvature of the velocity profile changes sign and the Richardson number is somewhere less than 1/4. Some observations are described which show the properties of atmospheric billow clouds formed in travelling amplifying waves (transverse to the shear vector), on occasions when these conditions appear to be met. Static instability seems to arise in parts of the wave‐pattern where layers are inverted, and to cause a convective overturning, which may halt the wave development. The most pronounced waves occur in the upper troposphere in association with jet streams, in layers of strong wind shear which are usually dry. They probably only rarely produce clouds, and may more frequently be responsible for the clear‐air turbulence encountered by aircraft. The associated relative air velocities occur over a range of scales: up to about 1 km in the convective regions, and up to the several km associated with the billow wave‐lengths, with magnitudes of up to 10 m sec−1

ISSN:0035-9009    

DOI:10.1002/qj.49709339803

出版商:John Wiley&Sons, Ltd    

年代:1967

数据来源: WILEY

摘要:

AbstractPressure fluctuations due to an explosive point‐source in an atmosphere containing steady winds may be described in terms of a fundamental mode of long period followed by modes of the acoustic and gravity type, with relative amplitudes, group speeds and periods dependent upon winds. Far‐field ground‐pressure contributions of various modes are presented for a particular model atmosphere. Inverse dispersion and the Airy phase are found to be important features of the dispersion. A study is made of barograms in the light of new results obtained. Some previously unexplained features of barograms are seen to be attributable to

ISSN:0035-9009    

DOI:10.1002/qj.49709339804

出版商:John Wiley&Sons, Ltd    

年代:1967

数据来源: WILEY

摘要:

AbstractDrops which freeze in isolation or by accretion on an ice particle are found to be single or polycrystalline depending on the drop supercooling and the particle temperature. Subsequent growth from the vapour depends on the number and orientation of these crystals. The airflow around the particle, characterized by the Reynolds Number, Re, is important in the initial accretion process. The particle falls steadily for small Re, but oscillates and eventually tumbles as Re approaches 500. The deformation of accreted drops depends both on the dendrite freezing velocity through the liquid compared with the impact velocity and on the drop impact kinetic energy compared with its surface energy. Viscous dissipation becomes important as the deformation, defined as the ratio of the base radius of the deformed drop to its height, exceeds 10. Deformations of about 10 have been measured for 40 μ radius supercooled drops impacting on an ice surface at 13.5 m sec−1. The heat economy of a freezing accreted drop is dominated by a collecting particle which is large compared with the drop, when complete freezing takes place from the contact area outwards. Symmetrical freezing, from top and bottom of the drop, only occurs for surface temperature approaching 0°C, or when the drop accretes on a narrow spike, when there is a possibility of drop shatter and separation of electric charge. Drops accreting on particles growing spongily may interact first with a liquid layer whose thickness may be of the same order as the drop size and produce splash droplets even at large supercoolings for critical values of layer thickness. Opacity is related to bubble size. Opaque ice forms when the particle is growing spongily or dry, with transparent ice forming when the growth is just wet. Just spongy growth at low temperatures is associated with small crystals and opaque

ISSN:0035-9009    

DOI:10.1002/qj.49709339805

出版商:John Wiley&Sons, Ltd    

年代:1967

数据来源: WILEY

摘要:

AbstractMeasurements made of the charges acquired by water drops and smooth ice spheres suspended in electric fields and exposed to streams of positive ions only, negative ions only, and ions of both signs present in equal and unequal concentrations were found to be in excellent quantitative agreement with the equations of Whipple and Chalmers. Electrical masking was probably responsible for the slightly increased charging obtained when the experiments were repeated with ice spheres of irregular surface structure. The charges acquired by drops falling through ion streams in electric fields are explicable in terms of the Wilson process.

ISSN:0035-9009    

DOI:10.1002/qj.49709339806

出版商:John Wiley&Sons, Ltd    

年代:1967

数据来源: WILEY

摘要:

AbstractConstant volume balloon (tetroon) flights made over New York City at heights of about 300 metres during June of 1965 are analysed. The transponder‐equipped tetroons were tracked to distances exceeding 100 km by means of the wsr‐57 weather radar located in Central Manhattan. On non‐sea breeze days the tetroons tend to move towards low pressure with an angle of 35 degrees, and to move with about two‐thirds of the geostrophic wind speed. There is a correlation of 0.73 between lapse rate and tetroon‐derived r.m.s. vertical velocity, and of 0.43 between lapse rate and Lagrangian period of vertical oscillation. Tetroon‐derived vertical velocities are also used to obtain estimates of the mean Reynolds stress (1.3 dynes cm−2at flight level) and the downwind variation of vertical diffusion over

ISSN:0035-9009    

DOI:10.1002/qj.49709339807

出版商:John Wiley&Sons, Ltd    

年代:1967

数据来源: WILEY

摘要:

AbstractA description is presented of the experimental techniques used on four micrometeorological expeditions. The instrumentation was designed to provide half‐hourly mean values of wind speed, temperature and humidity at a number of levels up to 16 metres, and of the vertical fluxes of heat, water vapour, net radiation and sensible heat into the ground. The observational material is to be published separately.Analysis of the observations, all for the unstable case, shows close similarity between the turbulent transfer processes for heat and water vapour over the whole range of stability represented by the measurements. Both are more strongly influenced by instability than the exchange of momentum, the difference in behaviour becoming more marked with increasing instability. It is suggested that the similarity between heat and water vapour transfer is due to a correlation between the temperature and specific humidity of the air which originates at the evaporating surfac

ISSN:0035-9009    

DOI:10.1002/qj.49709339808

出版商:John Wiley&Sons, Ltd    

年代:1967

数据来源: WILEY

摘要:

AbstractMicro‐meteorological data acquired during five expeditions to carefully chosen sites are analysed to determine the flux‐gradient relation for the transfer of heat and water vapour in the lower atmosphere. The analysis takes the form of a direct assessment of the Monin‐Obukhov universal functions φHand φW. Data for φHwere available from all five expeditions, and for φWfrom two of these.It was found that φH= φWover the whole of thez/Lrange available, indicating an identity in mechanism for the turbulent transport of heat and water vapour over a freely evaporating surface. Over the range 0.02<|z/L|0.2, φHwas found to vary as |z/L|−1/2. Insufficient data limited the value of the corresponding analysis for φWExcellent agreement was found between the φHand φWdata, and φ‐curves assessed from a previous shape‐function analysis (Swinbank and Dyer 1967). The empirical relation φ = (1–15z/L)−0·55agrees with the experimental values of φHand φWover the whole of the |z/L| range to within a few pe

ISSN:0035-9009    

DOI:10.1002/qj.49709339809

出版商:John Wiley&Sons, Ltd    

年代:1967

数据来源: WILEY

摘要:

AbstractTheoretical and experimental data on the travel and deposition of small particles in the atmosphere are used to calculate the cross‐pollination between neighbouring plots of sugar beet grown for seed.If two 20 acre plots are situated at a distance apart of 1,000 m the number of pollen grains falling on one plot which come from the other is about 4 × 10−3of the number which come from the plot itself. The effect of varying the size and separation of the plots is calculated, and a very approximate estimate of the contribution from background sources of pollen is given.The calculations are made for average meteorological conditions. In moderately unstable conditions the proportion of cross‐pollination between plots is likely to be reduced by about 25 pe

ISSN:0035-9009    

DOI:10.1002/qj.49709339810

出版商:John Wiley&Sons, Ltd    

年代:1967

数据来源: WILEY

摘要:

AbstractA recent paper by Starr and Mason (1966) described experimental determinations of the collection efficiencies of water drops and of simulated snow crystals for small, roughly spherical particles in the form of spores and pollen grains. Using these data and additional information obtained from observations on the impaction of particles on sticky spheres in a wind tunnel, calculations are presented for the rates at which particles of these sizes would be removed from the atmosphere by impaction on raindrops and snow crystals as a function of precipitation intensity. The raindrop scavenging results are compared with those of earlier computations by Chamberlain (1953) who used the theoretically derived values of collection efficiency by Langmuir (1948) and applied an intuitive equation suggested by Langmuir to interpolate between viscous and potential flow solutions for the collection efficiency.

ISSN:0035-9009    

DOI:10.1002/qj.49709339811

出版商:John Wiley&Sons, Ltd    

年代:1967

数据来源: WILEY