摘要:

AbstractA numerical model is developed for the simulation of surges generated by a tropical cyclone in the Bay of Bengal. The analysis area extends from approximately 11°N to 22°N and, in the northeastern sector of the Bay, includes a representation of the Ganges‐Brahmaputra‐Meghna river system in Bangladesh. The extent of the analysis area allows three days of the surge‐generating capacity of a cyclone originating in the southern Indian Ocean to be recorded before landfall at the Bangladesh coast. The incorporation of the river system permits a potentially deep inland penetration of surges originating in the Bay. The model is non‐linear and this allows a determination of the interactive effect between surge and the astronomical tide. Numerical experiments are described that relate to the change in surge response resulting from a change in the cyclone track during the 24 hours preceding landfall. An account is given of the interaction between surge and tide in the Bay and the riv

ISSN:0035-9009    

DOI:10.1002/qj.49710644702

出版商:John Wiley&Sons, Ltd    

年代:1980

数据来源: WILEY

摘要:

AbstractThe radiance distribution predicted by classical physical models of the sunpillar is calculated. It is shown that the loci of constant tip angle calculated by Stuchtey differ from loci of constant radiance only as a result of variation of the reflection coefficient with arc distance from the source. At least at low source elevations, crystals oscillating about a horizontal equilibrium position are more efficient as pillar producers than those rotating about horizontal C6 axes, but there is no conclusive evidence that the latter never produce pillars. It is shown that the variation of the cross‐sectional area of the incident beam has important effects, such as production of a minimum radiance at the source. Neglect of this factor by recent workers casts doubt on some of their conclusions.No evidence is found to suggest that the classical models need replacement: tentative suggestions are made that diffraction, transfer effects, and modes other than external reflection in crystals rotating about horizontal C6 axes may enhance the formation of pillars at higher source elevation

ISSN:0035-9009    

DOI:10.1002/qj.49710644703

出版商:John Wiley&Sons, Ltd    

年代:1980

数据来源: WILEY

摘要:

AbstractMeasurements obtained with research aircraft in clouds associated with various types of mesoscale rainbands in extratropical cyclones have been examined together with radar data and other detailed measurements. The analyses have yielded information on the structure and microphysical characteristics of the clouds and the nature of the vertical air motions in the clouds associated with each type of mesoscale rainband, and schematic models of the different mesoscale rainbands have been constructed.In clouds accompanying warm frontal rainbands, ice particles formed above the warm front, probably in shallow convective cells, and fell into the stable air mass below, where they grew by aggregation and helped glaciate stratiform clouds.Warm sector rainbands resembled squall lines. A younger, convectively active rainband occurred just ahead of an older, less convectively active one. The younger rainband contained both cloud liquid water and ice particles, and ice particles were growing by riming. The older rainband was nearly glaciated, with ice particles growing by aggregation.Narrow cold frontal rainbands were located along the convergence lines at the advancing edges of cold frontal zones. Each was associated with a convective updraught, 1 to 5 km wide and 1 to 3ms−1in magnitude, and a similarly narrow downdraught. The core of the updraught contained young, developing cloud, with much higher cloud liquid water content and lower ice particle concentration than in its immediate surroundings. Ice particles grew by aggregation and were heavily rimed. Wide cold frontal rainbands (several tens of kilometres in width) occurred when lifting above a cold front was enhanced to several tens of centimetres per second. Clouds in this region consisted of supercooled water and ice and contained embedded convective elements. Below the cold front, high concentrations of ice particles grew by aggregation.Prefrontal surges of cool and dry air occurred above the warm front and ahead of the cold front in occluded cyclones. A surge rainband, resembling a wide cold frontal rainband, occurred at the leading edge of the surge and was followed by a field of convective elements. These elements, sometimes arranged in lines, were in various stages of development.Postfrontal rainbands were lines of convective clouds located well behind a cold front. They may have been associated with secondary fronts and sometimes appeared to behave as organized convective system

ISSN:0035-9009    

DOI:10.1002/qj.49710644704

出版商:John Wiley&Sons, Ltd    

年代:1980

数据来源: WILEY

摘要:

AbstractThe angular distribution of diffuse radiation was measured from May 1976 to May 1977 with a set of purpose‐built actinometers. Radiance distributions for 98 overcast hours were fitted well by an expression similar to the conventional function for a ‘standard overcast sky’ (SOC). However, values of the coefficientbaveraged 1.23, significantly smaller than for the SOC (b= 2). Expressions for the interception of diffuse irradiance by sloping planes are disc

ISSN:0035-9009    

DOI:10.1002/qj.49710644705

出版商:John Wiley&Sons, Ltd    

年代:1980

数据来源: WILEY

摘要:

AbstractA study is made of the horizontal variations of eddy momentum and heat fluxes induced by long planetary waves in a linear two‐layer quasi‐geostrophic spherical model. A wide range of basic flows, consisting of upper‐layer, pure baroclinic or pure barotropic long waves together with solid‐body rotation or either of two zonal jet profiles, characteristic of the troposphere, are considered. The superposition of long planetary waves on otherwise zonal flow profiles has an effect on the eddy fluxes which is profound but is highly variable, depending on the basic flow. It is found, however, that for all profiles involving basic upper‐layer or baroclinic waves, the horizontal structure of both momentum and heat fluxes may be understood in terms of a generalization of Phillips's criterion for incipient instability. For these profiles, the regions of preferential development of baroclinic eddies are also found to be related to the general stability criterion. When barotropic planetary waves are present in the basic flows, the structure of the eddy fluxes is more complicated, reflecting the strong zonal wavenumber coupling in the disturbance stream

ISSN:0035-9009    

DOI:10.1002/qj.49710644706

出版商:John Wiley&Sons, Ltd    

年代:1980

数据来源: WILEY

摘要:

AbstractWhen the atmospheric turbulent flux of a minor constituent such as CO2 (or of water vapour as a special case) is measured by either the eddy covariance or the mean gradient technique, account may need to be taken of variations of the constituent's density due to the presence of a flux of heat and/or water vapour. In this paper the basic relationships are discussed in the context of vertical transfer in the lower atmosphere, and the required corrections to the measured flux are derived.If the measurement involves sensing of the fluctuations or mean gradient of the constituent'smixing ratiorelative to the dry air component, then no correction is required; while with sensing of the constituent'sspecific mass contentrelative to the total moist air, a correction arising from the water vapour flux only is required. Correspondingly, if in mean gradient measurements the constituent'sdensityis measured in air from different heights which has been pre‐dried and brought to a common temperature, then again no correction is required; while if the original (moist) air itself is brought to a common temperature, then only a correction arising from the water vapour flux is required.If the constituent'sdensityfluctuations or mean gradients are measured directly in the airin situ, then corrections arising from both heat and water vapour fluxes are required.These corrections will often be very important. That due to the heat flux is about five times as great as that due to an equal latent heat (water vapour) flux. In CO2 flux measurements the magnitude of the correction will commonly exceed that of the flux itself. The correction to measurements of water vapour flux will often be only a few per cent but will sometimes exceed 10 per cen

ISSN:0035-9009    

DOI:10.1002/qj.49710644707

出版商:John Wiley&Sons, Ltd    

年代:1980

数据来源: WILEY

摘要:

AbstractMeasurements have been made, under neutral conditions, of the turbulent wind structure on a 100m tower at the crest of a hill of heighth= 170m. A local velocity maximum, or ‘jet’, was observed at abouth/5, below which the ratio of increase in wind speed to the upwind value at the same height was 1.07, and almost independent of height near the surface.The r.m.s. turbulence components σw σv and σw were also approximately doubled near the surface, but whereas σu and σv both decreased with height, the surface increase in σw extended over the entire height of measurement. Reynolds stress was almost uniform above the ‘jet’, but increased sharply towards the surface, to 3–5 times the upwind value. Departures from neutrality affected the profile shape and the magnitude of turbulence fluctuations very markedly.Although the size of hill lay outside the range of validity of an analytical theory of Jackson and Hunt, their expressions for velocity and horizontal pressure gradient were in good agreement with the observations. Numerical theories by Frost, Harper and Fichtl and by Taylor, for hills of different shape, but similar slope to the experimental hill, also produced values of surface stress and velocity increase of the mag

ISSN:0035-9009    

DOI:10.1002/qj.49710644708

出版商:John Wiley&Sons, Ltd    

年代:1980

数据来源: WILEY

摘要:

AbstractA column model coupling photochemistry and radiative transfer has been used to examine the relationship between carbon dioxide and ozone amounts in the stratosphere in a chlorine‐free atmosphere. The annually averaged ozone column density increases by about 10% as the CO2 volume mixing ratio is increased from 250 to 700ppmv. These increases result from cooling of the upper stratosphere by up to 20 K over this range. The phase of the seasonal variation of ozone in the upper stratosphere is correctly reproduced, with the annual maximum occurring at the time of minimum temperature rather than at the time of maximum insolatio

ISSN:0035-9009    

DOI:10.1002/qj.49710644709

出版商:John Wiley&Sons, Ltd    

年代:1980

数据来源: WILEY

摘要:

AbstractIt is shown that the inclusion of a chlorine chemistry mechanism, necessitated by present abundances of methyl chloride and carbon tetrachloride, reduces the modelled natural stratospheric ozone above about 25 km by 20 to 40% compared with part I, resulting in substantial agreement with observations. The effects of simultaneous increases in the atmospheric mixing ratios of carbon dioxide and chlorofluoromethanes (CFMs) are investigated. It is found that there is alleviation of the CFM‐induced ozone reductions attributable to increased CO2, and that the effects of the two perturbations upon ozone column density are not quite linearly additive. The net effect on ozone column density consists of larger percentage decreases in the upper stratosphere almost compensated by smaller percentage increases in the lower stratosphere, where most of the ozone is residen

ISSN:0035-9009    

DOI:10.1002/qj.49710644710

出版商:John Wiley&Sons, Ltd    

年代:1980

数据来源: WILEY

摘要:

AbstractFlights through the central regions of thunderstorms were made over New Mexico on 6 and 15 August 1977 with the ONR/NMIMT Schweitzer aeroplane which carried equipment designed to measure all three components of the electric field, and the charge,Q, and diameter,d, of individual precipitation elements. On the earlier day, information was also obtained with: a rain‐gauge network surrounding Langmuir Laboratory; a 3 cm radar; an acoustic system for locating lightning channels; a ground‐based field‐change meter.The first cell on 6 August produced precipitation at the ground but no lightning. Vertical fields,Ex, of up to about 50kVm−1and precipitation charge densities ρ of up to −0.5 C km−3were recorded within the cloud. The second cell, which grew as the first one decayed, produced 7 lightning strokes in 9 minutes during which time the radar revealed vigorous vertical growth in a narrow zone containing precipitation.Thunder reconstructions showed the acoustic sources for the first flash of this cell to be very near the top of the cloud at an altitude of 10 km a.s.1. The subsequent flashes produced acoustic signals from progressively lower in the cloud. When the radar echo reached its maximum height lightning activity ceased.Exvalues of up to about 50kVm−1and pp values of down to −1 Ckm−3were measured. ρp was consistently negative, individual charges being less than ±40 pC.Qvalues were within the inductive limit for a thundercloud at breakdown but no systematic relation betweenQanddwas found.Six penetrations were made through the thundercloud of 15 August, which produced only two lightning strokes. TheExrecords were indicative of a (±) dipole located near the cloud top, at around –13°C. Fields of up to about 100kVm−1and ρp values (positive and negative) of around 5Ckm−3were measured.Qvalues of up to ±250 pC were recorded, with charges around ±50 pC being commonly found. No systematic Q‐drelation was revealed, and smaller precipitation particles frequently carried charges (positive or negative) in excess of the inductive limit.On both days estimated precipitation rates were of order 10mmh−1and on most occasions the pilot reported precipitation particles to be either

ISSN:0035-9009    

DOI:10.1002/qj.49710644711

出版商:John Wiley&Sons, Ltd    

年代:1980

数据来源: WILEY