ISSN:0035-9009    

DOI:10.1002/qj.49708436202

出版商:John Wiley&Sons, Ltd    

年代:1958

数据来源: WILEY

摘要:

AbstractCombined absorption and emission spectra have been recorded in the atmospheric window from 770 to 1,250 cm−1both in London and in the relatively clean air of Ascot, Berks. The absorption spectra have been partially analysed in terms of selective and continuous extinction. The continuous extinction outweighs the selective in both Ascot and London. There is good agreement between the observed selective absorption and existing theoretical and laboratory data upon gases known to be present in the atmosphere.The opacity of the continuum shows an increase towards low frequency, and it is much greater in London than in Ascot; in both places it is positively correlated with water vapour. The average effective emission temperature of the continuum is not significantly different from that of water vapour.The only hypothesis which seems to fit all the observations is that in London the continuum extinction is largely caused by aerosol extinction while in Ascot this is only of minor importance. This requires that the extinction at Ascot be caused by wings of distant lines; this old suggestion of Elsasser is re‐examined and found to be plausible.Attention is drawn to the important contribution which the continuum can make to the heat balance of the atmosphere below 2

ISSN:0035-9009    

DOI:10.1002/qj.49708436203

出版商:John Wiley&Sons, Ltd    

年代:1958

数据来源: WILEY

摘要:

AbstractFlying swarms have been observed to vary in vertical extent from a few metres to several thousand metres, with the spacing of the locusts in them ranging from more than 10 locusts/m3down to the order of 0·001/m3. Some characteristic effects seen, from ground and air, are described in qualitative terms.Two well‐documented records of flying locusts in numbers at some 2,000 m above ground were both associated with lapse rates close to the dry adiabatic, from the ground up to at least the level of these locusts. On two other occasions detailed observations of vertical temperature distribution have been made in the immediate vicinity of large swarms flying up to 1,100–1,700 m above ground, and in both these cases the topmost locusts were within 150 m of the upper limit of superadiabatic or adiabatic lapse rates from the surface. Comparable observations on a swarm in which all flying locusts were below 6 m demonstrated isothermal conditions, with the air temperature at 50 m within 1/2°F of that at the surface.All adequately‐documented records of swarm displacement so far available have been directly down‐wind, at ground speeds which for the larger swarms studied have approximated to the speed of the corresponding wind. The smaller swarms, most of them less than 10 km2in extent, have shown lower flying heights, relative to the corresponding vertical extent of dry adiabatic lapse rates, together with ground speeds which were also low, in relation to the wind speeds concerned and to the corresponding performance of the larger swarms.There is some evidence of an association between rain and low flying heights; and consideration of heat exchange at the ground surface indicates that the energy normally available for convection, in the arid regions frequented by swarms, is likely to be drastically reduced after rain.Quantitative evidence on the strength and distribution of the vertical components of air movement likely to be encountered by flying locusts has been provided by pilot‐balloon and accelerometer data. Twin‐theodolite pilot‐balloon observations in central Somalia have shown that during much of the day some 10 per cent of uniformly‐distributed locusts in flight at about 20 m at any one time could be expected to experience up‐currents exceeding their gliding sinking‐speed. Gust‐spectra recorded by aircraft accelerometer within and around high‐flying swarms have demonstrated up‐gusts, exceeding a value equivalent to the sinking‐speed of a gliding locust, at about fifty points per km2among the higher‐flying locusts at any one time.The possible use of locusts as indicators of air movements is discussed, with a summary of the evidence available on the contributions made by the active behaviour of the locusts themselves to the effects observed. Attention is directed to the importance of gregarious behaviour in the continued cohesion of individual swarms, observed over many days and hundreds of kilometres, despite the disruptive effects both of atmospheric turbulence and of the apparently random orientation of the flying locusts themselves. The order of magnitude of these potentially disruptive effects is estimated for a particular case, and shown to be large compared with the variations actually observed in th

ISSN:0035-9009    

DOI:10.1002/qj.49708436204

出版商:John Wiley&Sons, Ltd    

年代:1958

数据来源: WILEY

摘要:

AbstractDuring the midwinter months the general airflow over N. Greenland is southwesterly, but near the surface of the ice sheet, which is cooled by radiation in the polar night, katabatic winds flow from the higher parts of the ice sheet towards the coast. At sheltered places on or near the coast pools of cold stagnant air collect in fine weather when the pressure gradient is weak.Analysis of the 700 mb charts for two midwinter seasons shows that breaks in the predominantly fine weather were caused by depressions and their associated fronts which crossed the inland ice. There were about 15 disturbances per month which affected N. Greenland, but only a few of these caused precipitation. Most of the fronts were weak and the snowfall slight. During the first period of two midwinter months under consideration the only considerable fall of snow occurred when a deep depression remained almost stationary over S. Greenland for three days and drew moist air from the N. Atlantic over N. Greenland. The onset of the strong northwesterly wind on the coast after a period of calm is generally associated with the passage of a cold front.There is normally an inversion in the lowest layers above the ice sheet and the air temperature on the inland ice varies with the wind speed and the air mass. It is estimated that the temperature difference between the bottom and top of the inversion varies from around 0°C in overcast conditions with a strong wind to around 25°C in clear and calm conditions. Warm air is sometimes carried in the southwesterly circulation over the inland ice : the highest temperature measured on the ice sheet in the midwinter months was −18°C in a warm sector, and the lowest was −66°C in fine and almost calm weather. On the coast the onset of the northwesterly wind is marked by a sudden rise of temperature and fall of humidity : when the wind falls to calm the temperature falls rapidly at first, but within 24 hours reaches a value from which it differs little during the period of several days before the next onset of the northwesterly wind.There is a fairly close relationship between the height and intensity of drift snow, the wind speed and the visibility. Snow does not begin to drift until the wind speed reaches 10 kt; the snow drift is moderate with a visibility of about 2 km when the wind speed is 17 kt and is heavy with a visibility of about 200 m when the wind speed is 27 kt. After a spell of fine weather over N. Greenland drift snow was absent on the inland ice even with a wind speed of 21 kt. Drift snow was observed in the coastal area only after a fall of snow.A comparison of the mean pressures and precipitation totals for the midwinter months under review with mean charts and mean monthly precipitation totals for other stations in the area for different years suggests that the two Januarys studied were normal months, but the two Decembers were a

ISSN:0035-9009    

DOI:10.1002/qj.49708436205

出版商:John Wiley&Sons, Ltd    

年代:1958

数据来源: WILEY

摘要:

AbstractExploratory flights through fronts beneath the jet stream confirm that a narrow frontal zone some 30 to 50 mi wide with sharp boundaries is often present at the 500 mb level. On other occasions the temperature changes are more diffuse. The air in and near the frontal zone is usually very dry and must have undergone subsidence.Dynamic considerations suggest that the very strong temperature gradient of the frontal zone at 500 mb arises from the differential subsidence of air on the cold side of the jet stream which leads to a tilting of the isentropic surfaces.

ISSN:0035-9009    

DOI:10.1002/qj.49708436206

出版商:John Wiley&Sons, Ltd    

年代:1958

数据来源: WILEY

摘要:

AbstractThis is the continuation of a previous paper (Q.J.,83, 1957) in which the structure of the steady rotating‐dishpan experiment was described. The present article begins with a calculation of the heat balance and a determination of the mechanisms that transport heat from heat to cold source. Of particular interest is the question whether the heat transport is effected by quasi‐geostrophic horizontal or by non‐geostrophic vertical circulations. Calculations were performed in the conventional polar coordinate system and also in a curvilinear coordinate system following the jet‐stream axis. In polar coordinates the heat transport is accomplished largely by horizontal circulations, and in the curvilinear coordinate system by an ageostrophic vertical mass circulation. Thus the ‘mechanism’ of heat transfer that is found depends largely on the framework of reference in which calculations are made.When the vertical circulations are averaged with respect to longitude in the two coordinate systems, a three‐cell structure with direct equatorial and polar branches and an indirect middle‐latitude branch is found in polar coordinates. In contrast, the calculations yield a single direct cell for the curvilinear system.Computation of the transport of absolute angular momentum in the two coordinate systems produces corresponding results.Calculations of kinetic and potential energy balance were performed in curvilinear coordinates. Production of kinetic energy by the mass circulation far exceeds actual net generation of kinetic energy, so that ‘eddies’ with respect to the jet‐stream axis convert kinetic energy to work done across the boundaries of the volume considered. Similarly, the potential energy release is achieved by means of the mass circulation while the eddies store potential energy poleward of the jet‐stream axis.An attempt was made to determine whether the velocity distribution near the top surface, especially the jet‐stream core, could be derived using only the mass circulation and the theorem of conservation of potential vorticity. The result showed that the velocity profile on the anticyclonic side of the jet stream is well reproduced by the calculation, but that the computed jet‐stream axis is situated far poleward of the observed position and that the computed strength of the jet centre exceeds the actual strength by 50 per cent.In conclusion, the result of the computations shows that at least two, and possibly a much greater number of general circulation ‘mechanisms’ can be found, depending upon the reference frame chosen. Mathematically, these solutions are all equally correct and yield the same total transports. From the physical viewpoint, the general circulation is represented as a simple heat engine in the curvilinear coordinate system. Considering the energy balance, the solution indicates that the kinetic energy of the general circulation is produced and maintained by the largest cell, the single direct circulation extending from heat to cold source, and that this kinetic energy is then converted to kinetic

ISSN:0035-9009    

DOI:10.1002/qj.49708436207

出版商:John Wiley&Sons, Ltd    

年代:1958

数据来源: WILEY

摘要:

AbstractThe convective flow and temperature distribution above a horizontal heated surface in air have been examined by optical methods. Attention has been given both to the open system and to enclosed air layers. The observations show the existence close to the surface of a mode of convection similar to the cellular convective motion previously noted in shallow enclosed layers. This motion is found to be present both in the open system and in the lower part of an enclosed layer of wide separation, i.e., large Rayleigh number.The mean temperature profile in this region has been found for a range of surface temperatures and the results show that the logarithm of the mean absolute temperature (T) varies as the power (−1/2) of the height (Z) above the heated surface. This measured distribution has been compared with theoretical predictions in particular that of the Priestley similarity theory, which properly refers to convection above an infinite surface and in which the postulated conditions will apply more exactly in higher layers. Nevertheless the measured temperature profile in the surface region is of the form predicted by the Priestley theory with the experimental value (−1/2) in place of the theoretical (−1/3) as the power of the heigh

ISSN:0035-9009    

DOI:10.1002/qj.49708436208

出版商:John Wiley&Sons, Ltd    

年代:1958

数据来源: WILEY

摘要:

AbstractA numerical study of the effect of mountain shape on two‐dimensional lee‐wave flow shows that asymmetrical ridges are slightly more favourable than symmetrical profiles for the formation of lee waves, especially for short wavelengths. A technique is suggested for determining the lee wavelength when only part of the lee‐wave flow is obser

ISSN:0035-9009    

DOI:10.1002/qj.49708436209

出版商:John Wiley&Sons, Ltd    

年代:1958

数据来源: WILEY

摘要:

AbstractSome recent observations together with data from earlier expeditions (Court 1942, Schumacher 1955 and others) suggest that the annual variation of temperature in the stratosphere over the Antarctic is characteristically asymmetric with a steep rise of temperature in the spring. This is probably not general over the Arctic. The tropopause over the Antarctic is significantly higher than over the Arctic in their respective winters and the variability of temperature in the lower stratosphere appears to be considerably less in the same season over the Antarctic than over the Arctic.

ISSN:0035-9009    

DOI:10.1002/qj.49708436210

出版商:John Wiley&Sons, Ltd    

年代:1958

数据来源: WILEY

摘要:

AbstractThe possibility that radar echoes from atmospheric inhomogeneities are the explanation of echoes received in conditions which make it certain they are not received from precipitation elements (‘angel’ echoes) is examined quantitatively. It is shown that such an explanation is theoretically possible but that the required refractive index changes are large, involving changes of a few mb in vapour pressure and/or a few degrees C in temperature in a distance of about 25 cm. Reflection of the main or side‐lobe energy at a limited quasi‐horizontal surface is shown to give the most likely meteorological explanation, but the inability to measure changes of refractive index in the free atmosphere to the required accuracy prevents positive confi

ISSN:0035-9009    

DOI:10.1002/qj.49708436211

出版商:John Wiley&Sons, Ltd    

年代:1958

数据来源: WILEY