摘要:

AbstractThe model is described and the results of three integrations presented. Its main novel features are the inclusion of non‐hydrostatic terms in a pressure co‐ordinate system, and the treatment of flow through the lateral boundaries. The results of the integrations, one with an ambient vertical wind shear and two without, indicate that the cloud dynamics is quite sensitive to assumptions made regarding the cloud microphysics, particularly at the stage when the downdraught is produ

ISSN:0035-9009    

DOI:10.1002/qj.49710042402

出版商:John Wiley&Sons, Ltd    

年代:1974

数据来源: WILEY

摘要:

AbstractA primitive equation system using pressure as the vertical coordinate has been derived, and this system has been applied to modelling both deep and shallow convetion. It has been demostrated that this system, including suitable boundary conditions, filters out the acoustic mode entirely. There exist certain advantage due to having gridpoints at constant pressure.

ISSN:0035-9009    

DOI:10.1002/qj.49710042403

出版商:John Wiley&Sons, Ltd    

年代:1974

数据来源: WILEY

摘要:

AbstractIn contradiction to earlier work it has been found that substantial corona currents can be initiated from ice surfaces over a wide range of conditions. Measurements have been made of the critical fields required to initiate corona from ice particles a few millimetres in length suspended in a uniform electric field. The variables included size, shape, purity, orientation and the surface features of the particles, their initial charge, pressure and temperature. Currents of about 0.1 μA at onset were obtained and the details of the forms of discharge and associated currents were determined as a function of applied field. A particularly interesting finding was that substantial corona currents were obtained only at temperatures higher than −18°C. A semi‐quantitative explanation of these results is given in terms of the surface conductivity of ice. The characteristics of the streamers observed have been related to the Dawson‐Winn model as extended by Phelps. In view of these new results it is suggested that the role of corona from ice hydrometeors in a thunderstorm is of much greater importance than has previously been realized, particularly in connection with the initiation of lightning and the enhancement of ionic conductivity; the onset fields for corona emission from ice in the central regions of thunderclouds are probably in the range 400 to 5

ISSN:0035-9009    

DOI:10.1002/qj.49710042404

出版商:John Wiley&Sons, Ltd    

年代:1974

数据来源: WILEY

摘要:

AbstractCalculations have been made, on the basis of the ionic balance equations derived by Phillips (1967), of the electrical conductivity of clouds in the presence, and in the absence, of secondary ion production resulting from corona.In weakly electrified clouds ‐ no corona ‐ the immobilization of ions on cloud droplets resulting from diffusional capture results in a reduced ionic concentration and conductivity. The normalized conductivityλthe ratio of the in‐cloud value to the clear‐air value at the same altitudeZwas calculated for three different cloud types (cumulus congestus, strato‐cumulus and fog) as a function ofZ, liquid water contentL, droplet chargeQand field strengthE.λwas found to be very sensitive to variations inLandE, but only slightly affected by changes inZ,Qand the manner in which the charge is distributed over the size‐spectrum. For example, whenE= Oλpossessed the values 0.034 and 0.17 in a cumulus congestus cloud forL= 0.5 gm/m3and 0.1 gm/m3respectively, whereas whenE= 90 kV/mλwas 1.5 times; 10−3and 7.6 times; 10−3respectively for the same two values ofL.The experimental measurements of corona onset fields and currents from ice hydrometeors,Ecandicrespectively, made by Griffiths and Latham (1974) were used to calculate the normalized conductivity within strongly electrified clouds. Corona from ice provides a copious supply of positive and negative ions which causesλto increase from between 10−3and 10−4to greater than 1 whenEcis achieved. The value ofλonce corona is initiated depends onLand the concentration of corona sites,J. In this situation altitudeZplays an important role becauseEcdecreases quite rapidly with decreasing pressure. For example, with a typical distribution of temperature and pressure within a thundercloud, corona will be initiated from hailstones atEc= 720 kV/m ifZ= 2.5 km (0° C) and 540 kV/m at 5.5 km (‐18° C); the corresponding values ofEcfor snowflakes are 540 and 390 kV/m respectively. At 2.5 km is slightly higher than and lower than 10 respectively, asLis increased from 1 to 5 gm/m3withJ= 1 m−3.It is concluded that the introduction of an ionic leakage current into calculations of field growth within thunderclouds is unnecessary, and that the distribution of electric field is crucial in determining whether corona, once initiated, will trigger lightning or merely

ISSN:0035-9009    

DOI:10.1002/qj.49710042405

出版商:John Wiley&Sons, Ltd    

年代:1974

数据来源: WILEY

摘要:

AbstractMeasurements have been made of the values of electric fieldEc, required to produce electrical corona from a pair of water drops, of radiiR= 2.7 mm andr= 0.65 mm colliding with a relative velocity of 5.8 ms−1. For central collisions the larger drop went into the ‘bag‐mode’ while for more glancing collisions a liquid filament, typically several timesRin length, was drawn out between the separating drops, and eventually collapsed. The values ofEcdecreased with increasing values ofL‐ the length of the combined drop‐pair in the direction of the field at the moment of separation ‐ which itself increased as the collisions became less central.Ecranged from about 500 kV/m for head‐on collisions to about 250 kV/m for glancing collisions producing the longest filaments. Only a small number of corona pulses ‐ each carrying about 10−10‐ accompanied each collision producing a discharge.Subsidiary experiments with model drops reinforced the conclusion that corona resulted initially from a point on the drop surface which had been disrupted by mechanical or electrical forces.Calculations indicate that the emission of positive corona from colliding raindrops can readily occur in thunderclouds, and thereby possibly trigger lightning, in fields below about 350 kV/m; a value considerably lower than that resulting from any other natural triggering p

ISSN:0035-9009    

DOI:10.1002/qj.49710042406

出版商:John Wiley&Sons, Ltd    

年代:1974

数据来源: WILEY

摘要:

AbstractTo help understand the observed variability of zonal wind, the amplitude and phase of five component waves are displayed on height‐latitude sections, 20 to 65 km, 80° N to 70° S using rawinsonde and meteorological rocket data for twelve years. Among the new features are the polar semiannual wave in the Southern Hemisphere, matching that in the Northern Hemisphere. The tropic semiannual wave seems displaced south of the Equator. A terannual wave with 20 m s−1amplitude is possibly related to the square wave properties of the annual insolational heating at high latitudes. Both the annual and terannual waves appear to have minima north of the Eq

ISSN:0035-9009    

DOI:10.1002/qj.49710042407

出版商:John Wiley&Sons, Ltd    

年代:1974

数据来源: WILEY

摘要:

AbstractTemporal and longitudinal variations in mean meridional wind are estimated from GHOST and EOLE constant level balloon flights at 100 and 200 mb in south temperate latitudes during the period 1966/72. At these latitudes there is evidence of about a 0.3 m s−1poleward flow in winter‐spring and equatorward flow in summer‐autumn, with the oscillation at 100 mb preceding that at 200 mb by 1 to 2 months. This annual oscillation may reflect a direct circulation between summer and winter hemispheres. At 200 mb in south temperate latitudes there is also evidence for about a 0.1 m s−1poleward flow during the west wind phase, and equatorward flow during the east wind phase, of the quasi‐biennial zonal wind oscillation in the low tropical stratosphere. The significance of this relation has not yet been ascertained. The overall mean equatorward drift of 0.04 m s−1points up the existence of the Ferrel Cell in the long‐term average. A breakdown of the data by longitude shows that the annual variation in zonal‐average meridional wind is due to large seasonal variations in meridional wind over the

ISSN:0035-9009    

DOI:10.1002/qj.49710042408

出版商:John Wiley&Sons, Ltd    

年代:1974

数据来源: WILEY

摘要:

AbstractUsing data obtained from a probe mounted on the flying cable of a tethered kite balloon, this paper presents a fairly comprehensive description of the structure of a ‘hummocky’ subsidence inversion and the associated air motions, including the formation and breakdown of billows at the crests of the hummocks. Below the inversion, the transfer of warm air downwards was detected and the rate at which this occurred estimated using the model proposed by Readingset al.(1973). This estimate is shown to be in good agreement with that derived from some radio‐sonde ascents. The fluxes of potential heat downwards at the inversion and upwards at the ground are estimated and their ratio is shown to be about

ISSN:0035-9009    

DOI:10.1002/qj.49710042409

出版商:John Wiley&Sons, Ltd    

年代:1974

数据来源: WILEY

摘要:

AbstractAn objective method of predicting the category of 15‐day and monthly rainfall and mean temperatures in terms of terciles and quintiles over England and Wales is developed. The method selects those areas in the Northern Hemisphere where anomalies on 500 mb monthly mean charts preceding warm months have been significantly different from the anomalies in the same areas preceding cold months at the same time of year. For this purpose data over the period 1945‐72 have been used and Welch's test has been applied to assess the significance of the difference between the two means.Having found the areas which have been significantly different before warm and cold months, the anomalies at all grid points within these areas are added for each year of the data, taking due account of sign, and the years then ranked in terms of the total anomalies. The result is a list with most of the cold years at the top, the average ones in the middle and the warm ones at the bottom. If the same procedure is carried out on current data and the current month included in the ranking, a forecast of the probable temperature category can be made.A similar procedure is used for rainfall, and for both elements on the 15‐day time scale. A test involving some 250 forecasts over a period of a year shows excellent re

ISSN:0035-9009    

DOI:10.1002/qj.49710042410

出版商:John Wiley&Sons, Ltd    

年代:1974

数据来源: WILEY

摘要:

AbstractTrends and periodicities in the annual rainfall of 31 meteorological sub‐divisions of India based on data for over 60 years have been examined by various latest techniques like Mann‐Kendall rank method, low‐pass filter and power spectrum analysis. It is seen that the frequency distribution of annual rainfall for the period of 1901 to 1960 is not normally distributed in some sub‐divisions of the country. Positive trend is noticed over central India and the adjoining parts of the peninsula and also over two smaller areas in north‐west and north‐east India. Only over some parts of eastern India there is negative trend. Increase in mean rainfall for 30 years shows a gradient from the west coast to the interior parts of the country with a maximum over the west coast.The spectral analysis of the annual rainfall of these sub‐divisions shows a significant cycle of range 8.5 to 12.0 years which is mainly seen in and around the arid and semi‐arid regions of Rajasthan, some central parts of India and extreme south peninsula. A cycle of 2.0 to 3.5 years is also observed over large parts of the country mainly over north‐west India, central parts of peninsula and some parts o

ISSN:0035-9009    

DOI:10.1002/qj.49710042411

出版商:John Wiley&Sons, Ltd    

年代:1974

数据来源: WILEY