摘要:

AbstractA global analysis is made of upper stratospheric circulations with the aid of Nimbus 5 and Tiros N satellite observations in order to make a comparison of characteristics between the northern hemisphere (NH) and the southern hemisphere (SH).It is shown that the reversal of north‐south gradient of the zonal mean temperature at the stratopause level is always observed in higher latitudes of the SH winter, while the temperature gradient of the NH winter is variable because of the occurrence of sudden warmings. Consequently, due to the thermal wind relation, the polar night westerlies of the SH stratosphere are generally stronger than those of the NH stratosphere. In association with this difference, the activity of transient planetary waves of wavenumber 2 is striking in the SH, in contrast to the predominance of steady waves in the NH.Finally, the interrelation between the zonal mean field and planetary waves in the upper stratosphere is briefly discusse

ISSN:0035-9009    

DOI:10.1002/qj.49710946102

出版商:John Wiley&Sons, Ltd    

年代:1983

数据来源: WILEY

摘要:

AbstractA linearized, steady‐state, 15–level numerical model is used to study the stationary planetary wave response of the stratosphere to thermal and orographic forcing in the troposphere. Zonally symmetric basic states representative of northern hemisphere winter and summer conditions are used. Solutions for each zonal wave‐number are considered separately. Eliassen‐Palm cross‐sections are used as a diagnostic of wave propagation.First, several simple thermal and orographic forcing distributions are used in the winter basic state. The response in the stratosphere is sensitive to changes in the zonal wind but its structure is insensitive to the forcing mechanism and to the dissipation used in the model. For representative northern hemisphere thermal and orographic forcing, solutions in winter agree well with observations except for wavenumber one, which has too small an amplitude and an incorrect structure.The solutions for wavenumbers one and two in the troposphere have small differences from those obtained using a similar 5–level model described by us earlier. For higher wavenumbers, the 15–level and 5–level solutions in the troposphere converge, as these waves are trapped in the troposphere.For the summer basic state, the planetary wave response has large amplitude in the troposphere only. It is necessary to use vorticity forcing in the upper troposphere to give a solution with a phase variation similar to that obs

ISSN:0035-9009    

DOI:10.1002/qj.49710946103

出版商:John Wiley&Sons, Ltd    

年代:1983

数据来源: WILEY

摘要:

AbstractMost papers dealing with numerical simulation of the zonally averaged atmospheric circulation start with the solar heat input as an external source that drives the circulation. In this paper, the reverse way will be followed. First, the meridional structure of the wave modes with zonal wavenumber m = 0 within the atmospheric waveguide is determined from tidal theory. Then the height structure of these modes is calculated numerically applying a heat source configuration per mode by trial and error such that the observed global zonal wind and temperature fields between 0 and 100km can be reproduced reasonably well.Observations during solstice and equinox conditions outside the equatorial regions can be grossly simulated by the four wave modes of lowest degree. These wave modes are driven by two heat sources, one centred near 3 km, the other near 50 km altitude. The symmetric component of the lower atmospheric heat source is strongly enhanced when compared with the expected direct solar heat input into the atmosphere, indicating the dominant influence of latent heat in redistributing solar energy. The antisymmetric component of the middle atmospheric heat source is enhanced by a factor of more than two when compared with direct solar heating. Here, dissipated energy of planetary waves may be the origin of the additional source. The absence of that source leads to wind and temperature changes within the middle atmosphere which strongly resemble the situation during a minor stratospheric warming.

ISSN:0035-9009    

DOI:10.1002/qj.49710946104

出版商:John Wiley&Sons, Ltd    

年代:1983

数据来源: WILEY

摘要:

AbstractPositive and negative anomalies in the initial soil moisture over central Europe were introduced in turn into integrations of a global model of the July atmosphere. The results show that by modifying the partitioning of the turbulent fluxes such anomalies can have major effects on the modelled rainfall, humidity and temperature during the following 50 days over the anomaly area and that the anomalies can propagate into adjacent land areas. Similar results were obtained with a lower‐resolution version of the model.The effects on rainfall were already important on day 3 of the integration over the anomaly area and on day 6 over parts of Scandinavia outside the anomaly area.The experiment was repeated with a version of the model in which the prevailing flow over Europe was less weak with increased moist westerly flow from the Atlantic. In this case the dry anomaly persisted for only about 20 days before it became too weak to affect the evaporation significantl

ISSN:0035-9009    

DOI:10.1002/qj.49710946105

出版商:John Wiley&Sons, Ltd    

年代:1983

数据来源: WILEY

摘要:

AbstractA three‐dimensional, time‐dependent, anelastic model is employed to simulate the evolution of nonlinear internal waves which are forced by stratified flow over isolated topography. Both two‐dimensional and three‐dimensional flows are considered. In the former case the discussion focusses upon the development of the wave field induced by a uniform mean flow with constant stability. The full three‐dimensional model is employed to study the nonlinear development of atmospheric ‘ship‐waves’ which have recently been observed in satellite photographs to the lee of oceanic islands in the Norwegian and Barents seas. The model is able to reproduce the characteristics of the observed wave patterns rather nicely when it is initialized with vertical profiles of wind and stability obtained through upper air ascents from stations located on the islands themselves. Detailed comparisons of the output of the nonlinear model with the results of three‐dimensional linear steady state theory are also provided. As is found to be the case in two‐dimensional analyses, linear theory may considerably underestimate the forced wave amplitude for symmetric top

ISSN:0035-9009    

DOI:10.1002/qj.49710946106

出版商:John Wiley&Sons, Ltd    

年代:1983

数据来源: WILEY

摘要:

AbstractA planned project to generate hydroelectric power by carrying Mediterranean water into the Dead Sea has stimulated a preliminary numerical model study of the regional meteorological patterns and the evaluation of some possible local climatic modifications. Predicted mesoscale meteorological patterns associated with two frequent synoptic conditions over the region are presented. Emphasis has been focussed on illustrating and studying two general aspects of the thermal circulations generated by a lake which is confined between mountains (LMC): the effect of external flows on the LMC structure and the effects of lake water temperature on the LMC intensity.

ISSN:0035-9009    

DOI:10.1002/qj.49710946107

出版商:John Wiley&Sons, Ltd    

年代:1983

数据来源: WILEY

摘要:

AbstractA semi‐geostrophic deformation model of a front studied by B. J. Hoskins and F. P. Bretherton is studied further. It is shown that a unique solution of the Lagrangian conservation laws governing the motion can still be constructed after the front has formed. This solution shows that separate upper and lower fronts propagate into the fluid, and are separated by a region where only smooth variations occur. Finite difference solutions of the primitive equations are also given which converge to a front with the correct mean slope and maximum long‐front velocity but without the correct variation in slope through the depth of the fl

ISSN:0035-9009    

DOI:10.1002/qj.49710946108

出版商:John Wiley&Sons, Ltd    

年代:1983

数据来源: WILEY

摘要:

AbstractOrographic enhancement of rain via the ‘feeder‐seeder’ mechanism has been calculated using a stratified airflow model. The effect of wind drift on precipitation has been included. Comparisons have been made using potential flow models both in two and in three dimensions and in the model of M. J. Bader and W. T. Roach.For high windspeeds (≥ 15ms−1), when large enhancements occur, the potential flow treatment is sufficient. Inclusion of stratification does not significantly affect the total washout, although in the case of long hills (half‐length ≥ 10km) the precipitation maximum is moved upwind. For long hills the results are also in close agreement with the model of Bader and Roach. Over shorter hills both wind drift and non‐hydrostatic effects are important. Wind drift decreases both maximum and total enhancements. The Bader and Roach airflow formulation is inaccurate since it overestimates streamline displacements over the hill. Three‐dimensional effects are small except over

ISSN:0035-9009    

DOI:10.1002/qj.49710946109

出版商:John Wiley&Sons, Ltd    

年代:1983

数据来源: WILEY

摘要:

AbstractSeveral sources of error have been identified in measuring rainfall by radar. In this paper we discuss these sources of error as they affect the calibration of a radar system using raingauge data. Present calibration techniques are considered, and the need for procedures based upon a knowledge of the structure of precipitation systems is noted. Finally, a new procedure is described, and its performance assessed for a number of cases of frontal and convective rainfall.

ISSN:0035-9009    

DOI:10.1002/qj.49710946110

出版商:John Wiley&Sons, Ltd    

年代:1983

数据来源: WILEY

摘要:

AbstractA laboratory investigation of electric charge transfer during the impact of vapour‐grown ice crystals and supercooled water droplets upon a simulated soft‐hailstone target has shown that the magnitude of the charge transferred to the riming surface when crystals separate from it is a function of temperature, crystal dimension, relative velocity, liquid water content, and impurity content of the water droplets and hence the impurity content of the riming target. The sign of the charge transfer depends on temperature, liquid water content and droplet and rime impurity content.In the absence of crystals, no charge transfer was detected during riming. In the absence of supercooled water droplets, crystals impacting at 10ms1on an evaporating rime target produced a small negative charge on the rime of less than − 0.25fC per separating crystal. When the target surface grew by vapour diffusion it gained a small positive charge during such interactions. Much larger charges and completely different charge transfer behaviour was noted during riming. The target became positively charged at high liquid water contents and temperatures above a critical value, but negatively charged at lower temperatures or with lower liquid water contents. The critical sign reversal temperature at a liquid water content of 1 gm−3was about − 20°C. At − 10°C with a liquid water content of 2gm−3, a 125 μm crystal impacting at 3ms−1charged the target by +101C upon separation. The charge transfer increased sharply with impact speed and crystal size. Warming the positively charging rime to cause it to evaporate failed to reverse the sign of the charge transfer. Experiments with impurities showed that the sign reversal temperature increased if the droplets contained contaminants at concentrations found in cloud water.It is suggested that there are two distinct charge transfer processes during crystal interactions with an ice target, the dominant one requiring the presence of supercooled water droplets. Careful control and knowledge of the microphysical properties of the clouds used in these experimental simulations has permitted an examination of charge transfer under many of the conditions used in previous studies. The results provide an understanding of the differences and a reconciliation between some of the previously disparate findings in terms of the two distinct charg

ISSN:0035-9009    

DOI:10.1002/qj.49710946111

出版商:John Wiley&Sons, Ltd    

年代:1983

数据来源: WILEY