摘要:

AbstractData from the Nimbus 5 selective chopper radiometer have been used to study certain features of the dynamics and energetics of the January‐February 1973 sudden warming. Daily values of the energetics of the upper stratosphere during a sudden warming have been calculated. Analyses of the rates of change of temperature and geopotential wave amplitude give no support to the suggestion that the disturbance suffers a time lag with increasing height. Maximum rate of warming is shown to descend from the upper stratosphere. Interaction between travelling and quasi‐stationary waves did not appear to be important in the development of the warming. Two main results arise from an analysis of the latitudinal distributions of the energetics. Firstly there is good evidence to suggest that the amplification of the temperature wave between 10 and 2mb results from a transfer of eddy potential energy from the 50–10mb layer, and not from the lower stratosphere or troposphere below 50mb. However, energy propagation above 2mb is initiated by a large increase in energy flux through the 50mb level. Secondly, despite considerable uncertainty in the kinetic energy budgets, it appears that eddy kinetic energy increases in high latitudes as a result of convergence of the vertical energy flux but increases in middle latitudes as a result of barotropic conversion from the zonal flow. The westerly zonal flow is decelerated in mid‐latitudes and initially accelerated in high latitudes by divergence and convergence of large poleward eddy momentum transport. Eventually the effect of the induced mean meridional circulation leads to easterly acceleration in high as well as middle latitudes. Some strong resemblances are found in the numerically simulated zonal flow changes of some model warmings which show a meridional lag in the onset of easterly accel

ISSN:0035-9009    

DOI:10.1002/qj.49710544312

出版商:John Wiley&Sons, Ltd    

年代:1979

数据来源: WILEY

摘要:

AbstractDew forms on cocoa pods after sunrise when the dew‐point temperature of air in the canopy rises faster than the surface temperature of the pods. Exchanges of heat and water vapour are estimated by treating a pod as an isothermal body with homogeneous thermal properties. Two treatments of this simple model are discussed. First, the heat balance equation is simplified to a form which allows the environmental limits for condensation to be derived explicitly. Second, the equation is solved numerically to find the duration and mean depth of wetness as a function of environmental variables. Consistent with observation, the thermal lag of the pod is about 1 to 3K; condensation to a depth of 10 to μm occurs when air at sunrise is almost saturated and windspeed is light.Condensation on cocoa pods is likely to be significant in the spread of Black Pod, a serious fungal disea

ISSN:0035-9009    

DOI:10.1002/qj.49710544313

出版商:John Wiley&Sons, Ltd    

年代:1979

数据来源: WILEY

摘要:

AbstractAircraft traverses were made from north to south across Venezuela during the rainy season of 1972 to determine whether a convectively active equatorial low pressure trough occurred and, if so, its structure, average properties and mechanics. The trough could indeed be located regularly near latitudes 5−7°N flying along the Orinoco River. Near cloud base (920mb) there was a wind shift from east to west and from north to south components. Farther south, winds from southeast were encountered. The low troposphere was warm with a maximum equivalent potential temperature at the axis. At 700mb neither the warm layer nor any wind shift could be found. The structure closely resembled that of the equatorial trough observed in the Garp Atlantic Tropical Experiment of 1974.The traverses largely indicated negative correlation between thermodynamic energy, mainly controlled by water vapour, and buoyancy, given by virtual temperature, on mesoscale distances of 30–50km. Occasional ‘hot tower’ penetrations were encountered. Surface air reached cloud base undiluted. Absolute vorticity was highest at cloud base just north of and at the trough, decreasing sharply to near zero to its south, just where heaviest convection was concentrated. Here also the largest vertical shear of the zonal wind component was located, again in agreement with GATE. The pressure‐height field was calculated from the wind data and indeed yielded a minimum value at the trough axis. To the north, the zonal wind increased with height though temperature decreased northwards. Calculations on the balance of forces with frictional retardation and on the origin of the low‐level warm layer give indications of the mechanics of the structure; the latter appears to be suggestive of a widely applicable equatorial

ISSN:0035-9009    

DOI:10.1002/qj.49710544314

出版商:John Wiley&Sons, Ltd    

年代:1979

数据来源: WILEY

摘要:

AbstractData from the 1973 Minnesota atmospheric boundary layer experiment are used to investigate details of the turbulence kinetic energy budget in convective conditions. Surface layer results are presented in nondimensional form and compared with conclusions from earlier Kansas data. Above the surface layer the terms are nondimensionalized using mixed layer similarity length and velocity scales and compared with indications from other recent experiments.

ISSN:0035-9009    

DOI:10.1002/qj.49710544315

出版商:John Wiley&Sons, Ltd    

年代:1979

数据来源: WILEY

摘要:

AbstractRadiance measurements derived from the Nimbus 5 selective chopper radiometer during the two years 1973–1974 are utilized to produce estimates of the global stratospheric temperature structure. Results are presented as polar stereographic maps of equivalent temperature for various of the instrument channels, and as meridional cross‐sections. Seasonal, monthly and daily averages, as well as monthly and daily averages of zonal wavenumbers one and two in temperature, are analysed. Monthly mean zonal winds are also computed, using the radiance data together with conventional 200mb height fields.The seasonal analysis confirms that the southern hemisphere experiences greater extremes of temperature than does the northern. In the monthly analysis considerable differences in temperature and zonal wind are found between the two hemispheres. Maximum wavenumber‐one amplitudes are generally found in regions of weak westerly winds. Wavenumber‐two amplitudes are usually less than half those of wave‐number one. A peak in the wavenumber‐two amplitude at the equator during January 1974 suggests that cross‐equatorial wave propagation occurs. Daily variations of zonal mean temperatures show that equatorial coolings occur at times of sudden warmings in the winter hemisphere and the daily variations of wavenumbers one and two reveal the more regular nature of wave activity in the southern hemisphere compared to the northe

ISSN:0035-9009    

DOI:10.1002/qj.49710544316

出版商:John Wiley&Sons, Ltd    

年代:1979

数据来源: WILEY

摘要:

AbstractZonal winds in the stratosphere for a period of 20 years have been analysed at nine stations between 7°S and 66°S centred on the longitude of eastern Australia. The amplitude, period and phase of the third (‘quasi‐biennial’) cycle are determined. Although a coherent pattern emerges in the variation of period with latitude and height it is concluded that, at least in the tropics, the representative period is 832 days (27.35 months). The well‐known maximum in amplitude of this third cycle in the tropics decreases to a minimum at about 30°S but increases again polewards, reaching a maximum at about 50°S at the highest levels of observation (6mb). The phase of the cycle ‘leads’ at high levels and low latitudes and also at the height and latitude of the polar night jet. Below these maxima there is a downward propagation of the cycle but little phase variation with height exists in middle latitudes. For the tropics, the variation with latitude of amplitude and phase is consistent with lateral diffusion of a forced equatorial cycle, with eddy diffusion coefficients of 1 × 109cm2s−1at 80mb, decreasing to 3

ISSN:0035-9009    

DOI:10.1002/qj.49710544317

出版商:John Wiley&Sons, Ltd    

年代:1979

数据来源: WILEY

摘要:

AbstractAbsorption of the direct solar beam was measured using an instrument based on the spectrophone. The method is described and results obtained from filtered and unfiltered air samples are presented. This enabled the aerosol's contribution to the absorption to be determined. Comparison of this absorption was made with the local visibility: with a visibility of 10km the heating rates observed were typically 0.2K day−1, increasing to 0.5K day−1when smoke made a major contribution to the aero

ISSN:0035-9009    

DOI:10.1002/qj.49710544318

出版商:John Wiley&Sons, Ltd    

年代:1979

数据来源: WILEY

摘要:

AbstractIntense electric fields beneath thunderstorms produce electrical discharges (coronae) at the tips of trees, bushes and other sharp objects attached to the surface of the earth. We find typical corona current densities of about 1 nA m−2in an 8 kV m−1field at the ground. The ions released into the air limit the magnitude of the field at the ground to about 10kV m−1. Our measurements beneath thunderstorms with a balloon‐borne electric field meter show that the magnitude of the field a hundred metres above the ground is several times larger than at the ground; in one case the field 300 metres above ground was 6 times that at the ground. The substantial thickness of the space charge layer and the speed with which it vanishes when the electric field strength declines imply that the charge carriers have substantial velocities (0.4m s−1) either because their mobilities are high or because they are carried by air motions.Coronae also influence the time behaviour of the electric field at the ground. The field at the ground often changes very rapidly after a lightning flash. The rate of change decreases as the field approaches the value it had prior to the flash. In contrast, the field a hundred metres above the ground, which is often above most of the influence of space charge produced by coronae, increases more uniformly (linearly) during the time interval between lightning flashes. This behaviour is similar to that of the field farther aloft in the interior of the cloud. Our numerical simulations of the shapes of recovery curves indicate that the corona current density is more accurately described by a cubic function than by a quadratic function of the electric field strength at the ground.Despite strong influences of coronae, three properties of the field at the ground accurately reflect what happens above the space charge layer. First, the rapid changes in electric field during a lightning flash are not usually affected by corona space charge. Second, when the field at the ground is nearly constant it usually has the same polarity as the field above the space charge layer. And third, when the field strength at the ground is nearly zero, and when certain other conditions are met, the time rate of change of the field at the ground is the same as that above the space cha

ISSN:0035-9009    

DOI:10.1002/qj.49710544319

出版商:John Wiley&Sons, Ltd    

年代:1979

数据来源: WILEY

ISSN:0035-9009    

DOI:10.1002/qj.49710544320

出版商:John Wiley&Sons, Ltd    

年代:1979

数据来源: WILEY

ISSN:0035-9009    

DOI:10.1002/qj.49710544321

出版商:John Wiley&Sons, Ltd    

年代:1979

数据来源: WILEY