ISSN:0035-9009    

DOI:10.1002/qj.49710945902

出版商:John Wiley&Sons, Ltd    

年代:1983

数据来源: WILEY

摘要:

AbstractThis review substantially updates the earlier review by Pittock (1978) in the light of more than 100 papers published in the last few years. Note is made of an encouraging trend towards the study of physical mechanisms, as well as important new evidence on the short, intermediate, and longer time‐scales which must be taken into account. Notable amongst these are increasing doubts and controversy surrounding the claimed effects of solar magnetic field sector boundary crossings, new studies and ideas concerning correlations on the decadal time‐scales, and the availability of long series of proxy data on solar activity and climatic fluctuations on a thousand‐year time‐scale. The review concludes with a discussion of the controversy over solar variability, weather and climate as an example of scientific decision‐making in the face of inadequate data and other uncertainties, with reference to the statistical ideas of Type I and Type II errors and Weinberg's concept of a ‘republic of tra

ISSN:0035-9009    

DOI:10.1002/qj.49710945903

出版商:John Wiley&Sons, Ltd    

年代:1983

数据来源: WILEY

摘要:

AbstractData from the orbiter infrared radiometer (OIR) of the Pioneer Venus mission have allowed the global structure of the middle atmosphere of Venus to be studied in detail for the first time. Between 4 December 1978 and 14 February 1979 this instrument made over 300 000 soundings in ten spectral channels, covering most of the northern and some of the southern hemisphere in the altitude range 65–100 km (100–0·01 mb). Preliminary analyses indicate that mean atmospheric structure in this region is strongly dependent on latitude and local time of day, although day‐to‐day variations are seen. This paper presents the mean temperature field and cloud top structure retrieved from the data of five OIR channels averaged in a solar‐fixed coordinate system. The retrieval scheme and the derivation of the weighting functions that characterize the vertical response of each channel are also described.The middle atmosphere can be divided into two distinct regions separated by a low‐latitude temperature minimum of less than 170K at 95km in the retrieved zonal‐mean temperature field. Below 95km, day‐night temperature contrasts are small but above 70km pole‐equator contrasts are positive reaching a maximum of 20–25 K at 85km. Fourier analysis shows that within 45° of the equator the longitudinal variation of temperature is dominated by wavenumber‐2 tidal structure with a phase that moves eastwards with increasing altitude. Above 95km, the pole‐equator temperature gradient is reversed, day‐night contrasts become appreciable and wavenumber‐1 longitudinal structure dominates. At equatorial latitudes mean cloud optical depth at 11·5 μn is unity at 100mb (66·5 km), and the cloud top has a scale height of 0·85 times the atmospheric value. The cloud top falls slowly with increasing latitude and has a wavenumber‐1 longitudinal dependence of £20mb (£1 km), with the highest cloud found just before the evening terminator. Retrievals are insensitive to cloud structure in the polar regions, but it is clear that the cool collar that surrounds the warm polar region is not a high‐cloud feature. It is in fact a deep temperature inversion in which temperatures can be more than 30 K less t

ISSN:0035-9009    

DOI:10.1002/qj.49710945904

出版商:John Wiley&Sons, Ltd    

年代:1983

数据来源: WILEY

摘要:

AbstractA numerical forecast model based on use of a hybrid vertical coordinate which is terrain‐following at low levels but which tends continuously to a pressure coordinate at upper levels is introduced. Results from this model are first presented for 10‐day forecasts (extending up to 10mb) of the major stratospheric circulation changes which occurred during the winter of 1979. A considerable degree of success is illustrated, not only in predicting a major wavenumber‐two warming up to 10 days ahead, but also in the forecasting of a preceding development of wavenumber one and a subsequent decay of the wavenumber two perturbation. Diagnosis using Eliassen‐Palm cross‐sections confirms previous observational diagnoses and aids understanding of the performance of the forecast model. Computations of the meridional gradient of zonal‐mean potential vorticity are also discussed.The sensitivity of tropospheric forecasts to stratospheric resolution and the choice of vertical coordinate is also examined. These forecasts are in fact characterized by a marked insensitivity to such aspects. Thus lowering the top forecast level from 10mb to 50mb has little effect on objective forecast scores averaged over the extratropical troposphere of the Northern Hemisphere, although planetary‐wave structures in high latitudes are affected to a small degree. The hybrid coordinate gives results similar to those obtained using the usual sigma coordinate, but such differences as are found tend to favour the use of the hybrid representation. Idealized analyses of the stability of the semi‐implicit time scheme for hybrid coordinates are confir

ISSN:0035-9009    

DOI:10.1002/qj.49710945905

出版商:John Wiley&Sons, Ltd    

年代:1983

数据来源: WILEY

摘要:

AbstractThe seasonal response of an atmospheric general circulation model to changes in atmospheric carbon dioxide concentrations and sea surface temperatures is discussed. The model has five layers and a quasi‐uniform 330km horizontal grid. Sea surface temperatures, sea ice extents, and zonally mean cloud amounts are prescribed from climatology, so that feedbacks between these variables and the rest of the model are ignored. Soil moisture, snow depth and boundary layer height are modelled explicitly, and both diurnal and seasonal variations of solar zenith angle are included. Two experiments are carried out, and compared with a three‐year control integration. In each case, the model's response varies with season and location. In the first experiment the effect of increasing atmospheric carbon dioxide concentrations with prescribed present day sea surface temperatures is examined. The model's troposphere becomes warmer, thereby increasing the low level static stability over the ocean and reducing evaporation and precipitation. The warming is larger over land than over the oceans. In summer, this results in an increase in precipitation along the eastern coasts of continents. In the second experiment, the sea surface temperatures are increased by 2 K and the carbon dioxide concentration is doubled. The land surface temperature rises by 3 K. Evaporation increases markedly over the oceans. Precipitation increases in the main regions of atmospheric convergence and decreases in some regions of the subtropics. The magnitude of the model's response is shown to be reasonably consistent with that found in other three‐dimensional climate m

ISSN:0035-9009    

DOI:10.1002/qj.49710945906

出版商:John Wiley&Sons, Ltd    

年代:1983

数据来源: WILEY

摘要:

AbstractTwenty‐four years data of zonal mean sea surface temperature (SST) were assembled to examine the seasonal and nonseasonal variations of SST. Outside the tropics, annual and semi‐annual variations of SST dominate, accounting for over 90% of the variance. In the tropics, the nonseasonal variation of SST is dominated by low‐frequency variations with periods longer than 3 years in the Pacific. Variations with periods of 24–32 months account for more than 10% of the variance in the tropical Atlantic from 25 £N to 10 £S and in the equatorial Pacific from 0–10 £S. An empirical orthogonal function (EOF) analysis showed that the major global pattern of zonal mean SST variations is dominated by variations in the equatorial eastern Pacific which precede zonal mean SST variations elsewhere. The time series of this EOF is found to be correlated with an index of the Southern Oscillation. The maximum correlation coefficient is −0£61, with the index leading by 2 months. Finally, the relation between SST and tropical tropospheric temperature (TTT) is examined. SST variations in the Atlantic and in the Indian Ocean are almost contemporary with variations in TTT. Possible explanations for the 1–2 seasons lead time between SST and TTT as found in earlier stud

ISSN:0035-9009    

DOI:10.1002/qj.49710945907

出版商:John Wiley&Sons, Ltd    

年代:1983

数据来源: WILEY

摘要:

AbstractSatellite observations of outgoing terrestrial infrared (IR) radiation as a function of latitude exhibit a minimum near the equator 20–40 Wm−2smaller than peaks in the subtropics. We attempt to dissect the causes of the dip through calculations with a spectrally‐detailed multi‐level radiative transfer model. Roughly one third of the dip can be attributed to the latitudinal variation of atmospheric water vapour; the remainder apparently is due to latitudinal variations in cloud amount and (especially) cloud‐top height. However, inclusion of clouds as given by published climatologies enhances the clear‐sky dip only slightly. Thus, about one half of the dip is essentially unexplained. We suspect the explanation is that near‐equatorial cirrus and cumulonimbus heights are too low in the cloud climatology, emphasizing the need for a better cloud climatology.Since tropospheric humidity variations have a strong effect on clear‐sky outgoing IR, empirical studies which correlate cloud with IR variations may overestimate the effect of clouds on outgoing IR if cloud amount is correlated with relative humidity.The effect of humidity variations on outgoing IR suggests that a measure of tropospheric humidity be incorporated explicitly in the parametrization of outgoing IR for simple

ISSN:0035-9009    

DOI:10.1002/qj.49710945908

出版商:John Wiley&Sons, Ltd    

年代:1983

数据来源: WILEY

摘要:

AbstractAngular momentum budget equations are developed for Eulerian and Lagrangian cylindrical coordinate systems centred on a tropical cyclone. All non‐friction terms are reduced to boundary transports and the effects of cyclone motion in the Eulerian coordinate system are isolated. A number of intensifying and weakening composite northwest Pacific cyclones are used to illustrate the physical role and relative importance of each process in the maintenance or destruction of tropical cyclones at various intensity stage

ISSN:0035-9009    

DOI:10.1002/qj.49710945909

出版商:John Wiley&Sons, Ltd    

年代:1983

数据来源: WILEY

摘要:

AbstractA three‐dimensional numerical model is developed for the simulation of storm surges generated by tropical cyclones off the east coast of India. Experiments are performed using wind‐stress forcing data representative of the 1977 Andhra cyclone and the results are compared with earlier simulations using a depth‐averaged model. The three‐dimensional model incorporates a turbulence energy closure scheme and is fairly sophisticated in comparison with the depth‐averaged approach. Even with the apparently more refined treatment of the frictional processes, there is no substantial difference between simulations performed with the t

ISSN:0035-9009    

DOI:10.1002/qj.49710945910

出版商:John Wiley&Sons, Ltd    

年代:1983

数据来源: WILEY

摘要:

AbstractA mesoscale analysis of the snowstorm of 8–9 January 1982 has been carried out using data from the U.K. weather radar network, the geostationary satellite Meteosat and other more conventional sources. More than 60cm of snow accumulated over S.E. Wales and neighbouring parts of England in association with an intense frontal zone. Much of the snow occurred during a period when synoptic forcing and orographic modulation were essentially steady. The depth of cloud and moist air was not great in the region of heavy snowfall in south Wales, but an orographically enhanced circulation on the mesoscale nevertheless led to efficient growth of precipitation through the seeder‐feeder mechanism. The seeder cloud was generated within a shallow current of air which ascended above the front and which originated from low levels, probably mostly from the boundary layer, on the warm side of the front. Precipitation was initiated within this current repeatedly along a well‐defined and remarkably stationary line just upwind of the south Wales coast. As the rising current travelled inland towards the E.N.E., convective generating cells embedded in it produced precipitation particles which fell into the underlying cold easterly flow. Considerable growth occurred as these particles descended through orographically enhanced feeder cloud, much of the growth occurring in the lowest kilometre

ISSN:0035-9009    

DOI:10.1002/qj.49710945911

出版商:John Wiley&Sons, Ltd    

年代:1983

数据来源: WILEY