摘要:

AbstractThe change of mean monthly rainfall, expressed as a percentage of mean annual rainfall, is described for the region south of 17°S during the course of summer. The areas with most rapidly increasing rainfall during monthly intervals are found to follow an almost circular path, starting out along the east coast and the adjacent interior in September and then being successively displaced to Zimbabwe, northern Botswana and northern South West Africa/Namibia, central and southern South West Africa/Namibia and ending in the central Cape Province in March. Several features of the atmospheric circulation and humidity are suggested and described as being partly responsible for the changing rainfall distribution

ISSN:0196-1748    

DOI:10.1002/joc.3370060602

出版商:John Wiley&Sons, Ltd.    

年代:1986

数据来源: WILEY

摘要:

AbstractVarious attempts to define chinooks from commonly observed surface weather phenomena have met with limited success. It is now apparent that many of the features normally considered unique to chinooks in southern Alberta are shared with other weather types. A new study found that there were statistically significant differences between both the means and variances of weather variables measured in chinooks and non‐chinooks in only one of eight variables considered. The means differed significantly in three parameters whereas the variances differed in four. But the significance attained by the difference in variance was always higher than attained in the mean, indicating that discrimination between the two weather types was more strongly expressed in the range of conditions experienced than in the mean condition. Collectively the variables were able to separate chinooks from non‐chinooks in all but one of the events stud

ISSN:0196-1748    

DOI:10.1002/joc.3370060603

出版商:John Wiley&Sons, Ltd.    

年代:1986

数据来源: WILEY

摘要:

AbstractMarked intraseasonal variations in the intensity of the south‐west U.S. summer precipitation singularity (the ‘Monsoon’) are identified for the years 1980–1982 from a previously developed satellite cloud climatology. These ‘bursts’ and ‘breaks’ are examined synoptically by compositing sea level pressure and 500 mb height data. Both types of events are controlled by the upper‐level flow. This typically involves, for bursts, the intrusion into subtropical latitudes of a trough in the westerlies with attendant cold air advection. In conjunction with intense surface heating, this produces widespread atmospheric destabilization over the South‐west. Monsoon breaks are characterized by enhanced ridging of the Bermuda and North Pacific subtropical anticyclones with associated subsidence over southern Arizona/California. Between‐year differences in these composite patterns are identified, and it is suggested that wetter summers may be characterized by larger within‐season variations in 500 mb heights and isobaric curvature compared with drier summers. Several 500 mb synoptic types associated with burst events are determined subjectively, and composite patterns are derived. These indicate that bursts occasionally occur with anticyclonic conditions aloft, but thelatitudeof the ridge seems critical in determining the extent of moist air penetration from the south.Twice‐daily aerological soundings at five stations in the South‐west and northern Mexico are also used to determine the thermodynamic characteristics of bursts and breaks and the dominant source of monsoon moisture. Monsoon bursts in Arizona are evidently a combination of moisture from the Gulf of Mexico, transported on a light south‐easterly flow, and more rapid lower‐level ‘surges’ originating in the Gulf of California. Moisture from the latter source is transported rapidly into the Great Basin on a low‐level wind‐speed maximum of marked directional constancy. This study has implications for longer‐term summer rainfall‐synoptic circul

ISSN:0196-1748    

DOI:10.1002/joc.3370060604

出版商:John Wiley&Sons, Ltd.    

年代:1986

数据来源: WILEY

摘要:

AbstractIn earlier studies the authors have established that monsoon rainfall up to the time scale of at least 5 days is dependent on its past value. In this study we examine the dependence in daily rainfall for 12 stations spread all over India, and in daily rainfall of 10 meteorological regions during the summer monsoon; (i) by analysing the rainfall as a stochastic point process by fitting Markov chains of orders 1 to 4 to the station data and (ii) by fitting autoregressive and autoregressive moving average models to the spatially averaged data. The significant conclusion is that the Markov chain of order 3 fits the runs of wet and dry spells better than chains of lower order, and that the autoregressive model of order 1 fits the spatially averaged rainfall amounts satisfactorily as compared to the higher order autoregressive or ARMA models.Examination of rainfall intensities during spells of various lengths has revealed that the rain intensity is greater during spells of 2 or 3 days than on isolated days. The rain intensity is greater on the days lying in the middle of a wet spell than on isolated days or on the first and the last days of a longer wet spell.

ISSN:0196-1748    

DOI:10.1002/joc.3370060605

出版商:John Wiley&Sons, Ltd.    

年代:1986

数据来源: WILEY

摘要:

AbstractTo assess the impact on the global atmospheric circulation of zonally‐varying sea surface temperature (SST), a general circulation model experiment has been run in which this variation has been removed for a January climate simulation. This results in an adjustment of the atmospheric parameters on a global scale, and particularly in the tropics. Surface pressure increases and rainfall decreases in the Australian‐Indonesian region and rainfall increases in the east Pacific and over Peru. Large changes occur in the Walker‐type circulations along the equator. Even though the mean meridional SST gradient is left unchanged in the experiment, the modelled Hadley cells are, perhaps surprisingly, weakened and the reduction in condensational heating leads to an equatorial troposphere which is cooler than the control run by up to 1°C. Outside the tropics the model response is predominantly barotropic. Our experiment demonstrates the fundamental role of the longitudinal variation of SST in determining the location of the subtropical highs in the Southern Hemisphere.The observation that the SST ‘anomaly’ distribution used is similar in some respects to that observed during an El Niño (particularly the 1982–1983 event) led us to compare the model response to anomalies observed during that time. The change in the Walker circulation and the shift in the surface pressure and rainfall distributions bore considerable similarity to those observed. However, the weakening of the Hadley cells and the cooling of the tropical troposphere were rather different to what actually occurred. Our results suggest that regions of forcing other than, or taken in conjunction with, that in the ‘key region’ in the east Pacific can influenc

ISSN:0196-1748    

DOI:10.1002/joc.3370060606

出版商:John Wiley&Sons, Ltd.    

年代:1986

数据来源: WILEY

摘要:

AbstractIn climate research it is important to have access to reliable data which are free from artificial trends or changes. One way of checking the reliability of a climate series is to compare it with surrounding stations. This is the idea behind all tests of the relative homogeneity. Here we will present a simple homogeneity test and apply it to a precipitation data set from south‐western Sweden. More precisely we will apply it to ratios between station values and some reference values. The reference value is a form of a mean value from surrounding stations. It is found valuable to include short and incomplete series in the reference value. The test can be used as an instrument for quality control as far as the mean level of, for instance, precipitation is concerned. In practice it should be used along with the available station history. Several non‐homogeneities are present in these series and probably reflect a serious source of uncertainty in studies of climatic trends and climatic change all over the world. The significant breaks varied from 5 to 25 per cent for this data set. An example illustrates the importance of using relevant climatic normals that refer to the present measurement conditions in constructing maps of anomal

ISSN:0196-1748    

DOI:10.1002/joc.3370060607

出版商:John Wiley&Sons, Ltd.    

年代:1986

数据来源: WILEY

ISSN:0196-1748    

DOI:10.1002/joc.3370060608

出版商:John Wiley&Sons, Ltd.    

年代:1986

数据来源: WILEY

ISSN:0196-1748    

DOI:10.1002/joc.3370060609

出版商:John Wiley&Sons, Ltd.    

年代:1986

数据来源: WILEY

ISSN:0196-1748    

DOI:10.1002/joc.3370060610

出版商:John Wiley&Sons, Ltd.    

年代:1986

数据来源: WILEY

ISSN:0196-1748    

DOI:10.1002/joc.3370060601

出版商:John Wiley&Sons, Ltd.    

年代:1986

数据来源: WILEY