摘要:

AbstractA synoptic mechanism is proposed for a long‐known, but synoptically little‐studied, tropical influence on northern Victorian rainfall during the winter half‐year, based on results from a 12 winter (June‐September) climatology covering the period 1971–82. It is shown that heavy precipitation events in northern Victoria commonly result from ‘interactions’ between cloud masses originating at low latitudes within the Australian region, and high amplitude frontal troughs moving within the midlatitude westerly flow. Most of the precipitation falls ahead of surface cold fronts, within moist northerly airstreams. The low latitude cloud masses involved may originate in several ways, but most commonly take the form of so‐called ‘northwest cloudbands’ originating over the tropical Indian Ocean northwest of Australia.‘Interacting’ frontal systems contribute some 50 per cent of northern Victoria's winter precipitation, but the presence of a relatively modest topographical barrier across the centre of the State substantially reduces their contribution to total rainfall in southern and southeastern Victoria. A distinction is made between these ‘interacting’ (or I) fronts, and ‘non‐interacting’ (NI) fronts: although I fronts occur less frequently than NI fronts, they produce considerably heavier rainfall. Analysis of the moisture content of prefrontal airmasses reveals that the airmasses ahead of I fronts are generally much moister than those ahead of NI fronts, and that the heavier I frontal rainfall is largely attributable to this moisture. An investigation is also made of moisture‐rainfall relationships for cold lows, also a significant source o

ISSN:0196-1748    

DOI:10.1002/joc.3370080502

出版商:John Wiley&Sons, Ltd.    

年代:1988

数据来源: WILEY

摘要:

AbstractIn an earlier paper examining relationships between monthly rainfall, raindays and mean daily rainfall intensity in the tropics, two Australian stations showed a consistent pattern of deviations from the worldwide regression equations. Using data from some 50 stations, this present paper demonstrates that this pattern applies generally over northern Australia. Rainfall is much more concentrated, with fewer raindays and higher mean daily intensities, than would be predicted from monthly totals and the worldwide tropical regressions. This marked concentration will have varied implications for hydrology, soil erosion and agriculture. The importance of tropical cyclones and other closed low pressure systems over northern Australia provides a reasonable explanation of the deviations, with support from some other tropical regions. However, a simple distinction between tropical cyclonic and non‐cyclonic areas is inadequate to explain patterns on a worldwide basi

ISSN:0196-1748    

DOI:10.1002/joc.3370080503

出版商:John Wiley&Sons, Ltd.    

年代:1988

数据来源: WILEY

摘要:

AbstractThe severe drought conditions observed during 1983 over a large extent of tropical lands were associated with the 1982–1983 El Niño event. In contrast, above normal rainfall was observed over these areas during 1984. The tropical circulations have been examined for these two contrasting years. The intensity and location of the rising and sinking motions were consistent with the rainfall anomalies and also with the outgoing longwave radiation anomalies. It was found that the north‐south migration of the tropical trough played an important role in modulating the tropical rainfall during these two years. In the context of the currently acceptable theoretical notions of the tropical circulation, some of the observed characteristics could be explained in terms of an atmospheric response to tropical heat sources. The results suggest that seasonal changes were involved in the 1982–1983 El Niño c

ISSN:0196-1748    

DOI:10.1002/joc.3370080504

出版商:John Wiley&Sons, Ltd.    

年代:1988

数据来源: WILEY

摘要:

AbstractA rainfall anomaly time series for the Short Rains (September to December) on the Kenyan Coast (KCS) is derived for the period 1901–84. On the year‐to‐year time scale a high degree of association can be seen between high/low extremes of a Southern Oscillation Index and negative/positive anomalies in the KCS series.The SOI‐rainfall relationship is investigated seasonally with KCS lagging the SOI series by one, two and three seasons. A decay of the correlation with increasing lag can be seen. When the time series is divided into 1901–42 and 1943–84 the relationships are stronger in the more recent period. Some forecasting skill does seem possible using the June to August (JJA) SOI to predict the September‐December rains. While the 1901–42 period shows a skill not much improved from using a simple climatological forecast, the 1943–84 period shows a much stronger relationship. Possible reasons are discussed for the disparity between the two time periods, also evident in results from others parts of Africa and Asia. There may well have been a change in some underlying climate mechanism between the early decades of this century and the mo

ISSN:0196-1748    

DOI:10.1002/joc.3370080505

出版商:John Wiley&Sons, Ltd.    

年代:1988

数据来源: WILEY

摘要:

AbstractIn this study, the fields of northern hemispheric 700 mb height tendency from January to April and from March to April are examined for the period 1950–1984 in relation to Indian monsoon (June to September) rainfall. The height tendency from January to April at three locations (near Pacific high and near Siberian high at sea level, and over southwest U.S.A) and from March to April at one location (about 50° of longitude west of sea level Aleutian low) are found to be significantly related to the Indian monsoon rainfall. These four variables are generally not inter‐related amongst themselves, and are not significantly related to the April 500 mb ridge, the tendency of the Southern Oscillation Index (SOI), and the eastern equatorial Pacific sea surface temperature tendency from DJF to MAM season.The best amongst the height tendency variables is the height tendency from January to April near sea level Pacific high. This variable is not as good as the tendency of SOI; however, when used in conjunction with April 500 mb ridge and the tendency of SOI, it makes a highly significant contribution to the explained variance and improves the forecasts for independent years as judged by different measures of assessment. This height tendency thus makes a useful additional predictor for the Indian monsoon rainfall.The mechanism of the influence of the development of the Pacific high on the Indian monsoon rainfall is not clear. It is, however, possible that the linkage between the development of the Pacific high and the Indian monsoon rainfall is through linkage of the Pacific high with the development of the summer season trough of low pressure over the Indian sub‐continent. This, however, needs to be invest

ISSN:0196-1748    

DOI:10.1002/joc.3370080506

出版商:John Wiley&Sons, Ltd.    

年代:1988

数据来源: WILEY

摘要:

AbstractThe effect of local sea surface temperature changes on frequency shifts in the 40–50 day oscillation is examined using seasonal means. Data were stratified into ENSO (El Niño‐Southern Oscillation) and non‐ENSO years and a significant difference found. In non‐ENSO years, a seasonal shift was noted at some sites. Seasonal frequency means were described qualitatively in terms of sea surface temperatures and changes in zonal circulati

ISSN:0196-1748    

DOI:10.1002/joc.3370080507

出版商:John Wiley&Sons, Ltd.    

年代:1988

数据来源: WILEY

摘要:

AbstractIt is important to be aware of systematic errors when using data from ship observations to infer climatic changes. The development of our understanding of systematic errors in sea and air temperatures and cloudiness is reviewed. Many reasons for suspecting similar errors in wind data are noted. Wind data for the tropical Pacific for 1920–1979 are then analysed. Trends to stronger trade winds in both the north and south Pacific, and also large anomalies in the winds in these areas during the Second World War, are found in the data. Quantitative comparisons are made with the associated pressure gradients, and qualitative comparisons with rainfall at Pacific island stations. These series provide no support for the suggestion that the wind changes were rea

ISSN:0196-1748    

DOI:10.1002/joc.3370080508

出版商:John Wiley&Sons, Ltd.    

年代:1988

数据来源: WILEY

摘要:

AbstractThe temporal characteristics of drought in Florida are compared with drought behaviour in the remainder of the southeastern United States, and are discussed in relation to previous studies by other researchers. Florida's wet/dry episodes are frequently out of phase with other south‐eastern States. Possible causes for this phenomenon are presente

ISSN:0196-1748    

DOI:10.1002/joc.3370080509

出版商:John Wiley&Sons, Ltd.    

年代:1988

数据来源: WILEY

摘要:

AbstractThe April cloud amounts recently presented by Barryet al.(1987) were significantly larger than expected. It was suggested that this discrepancy was caused by the obscuration of surface features by Arctic haze, which is believed by Barryet al.to consist of pollution aerosol transported from middle latitudes. The present note suggests that a significant portion of the surface obscuration that occurs in April is due to small ice crystals that form in the lower troposphere of high latitudes before the summer warming begins. These ice crystals appear to be a major feature of the Arctic heat regime, and should be included in cloud statistics.

ISSN:0196-1748    

DOI:10.1002/joc.3370080510

出版商:John Wiley&Sons, Ltd.    

年代:1988

数据来源: WILEY

ISSN:0196-1748    

DOI:10.1002/joc.3370080511

出版商:John Wiley&Sons, Ltd.    

年代:1988

数据来源: WILEY