摘要:

AbstractThe global and monthly distribution of the diurnal variation of outgoing longwave radiation (OLR) has been calculated by compositing estimates of the planetary OLR obtained from polar orbiting satellites at different equator crossing times. These data include NOAA and NASA polar orbiting satellites for the year 1974 through 1983, giving a total of ten different local observations per day throughout the whole data period. A Fourier analysis was then applied to calculate the phase and amplitude of the diurnal cycle on a 2.5° latitude/longitude grid for each month of the year. Assumption was implicitly made that the first harmonic alone explains most of the diurnal variation.The results are represented on maps extending from 55° south to 55° north for four different seasons from which a large seasonal variability of the diurnal harmonic primarily experienced by the mid‐latitude continents was clearly depicted. Over land areas the amplitude of the diurnal variation was large. In desert and semi‐arid areas it seem to be clearly related to surface solar heating i.e. phases of maximum OLR generally occurring near noon during summer and afternoon during winter months. Over the oceans, the amplitude is generally small even in the convectively active regions, such as the ITCZ, and the diurnal cycle appears to be modulated primarily by clouds.Finally, a ‘harmonic dial’ was constructed to examine the most dramatic features of the diurnal variation representative of such areas as the ITCZ, deserts, tropical convective clouds regions and highly variable mid‐latitude areas. Results of this study are consistent with other studies of the diurnal variability of clouds and radiation budge

ISSN:0196-1748    

DOI:10.1002/joc.3370080102

出版商:John Wiley&Sons, Ltd.    

年代:1988

数据来源: WILEY

摘要:

AbstractSignificant differences in rainfall over central South Africa are known to occur between opposite extremes in the phase of the Southern Oscillation, but details of both temporal and spatial aspects of the modulation of South African rainfall with the phase changes of the Oscillation remain to be described. Zero‐lag correlations between the Tahiti—Darwin Southern Oscillation Index and monthly and 3‐month seasonal rainfall over South Africa suggest that the rainfall—Southern Oscillation Index association is best defined in the late summer season January—March and in a north‐west to south‐east aligned zone across the central summer rainfall region of South Africa. Rainfall in this zone is directly related to the Southern Oscillation Index, increasing during high phase summers. An apparent semi‐annual cycle in the rainfall—Southern Oscillation Index correlations over central South Africa is in phase with the November and February turning points of a semi‐annual cycle in atmospheric circulation parameters over southern Africa. A plausible circulation mechanism is suggested to account for some of the spatial and temporal characteristics of the association between the Southern Oscillation and Sou

ISSN:0196-1748    

DOI:10.1002/joc.3370080103

出版商:John Wiley&Sons, Ltd.    

年代:1988

数据来源: WILEY

摘要:

AbstractTeleconnections between the Southern Oscillation and seasonal rainfall over East Africa during the period 1923–1984 were investigated using correlation methods. The results from the study indicated significant negative zero lag correlations between Southern Oscillation and seasonal rainfall over parts of East Africa during the months of October—December. Maximum correlations were concentrated along the coast and over some western parts. Peak values in the range — 0.6 were, however, centred along central and northern coastal regions.During the months of July—September significant positive zero lag correlations in the range of 0.5 were observed over some western parts. Low zero lag correlations were, however, obtained over most of the regions with the January—May and annual rainfall records. The computed lagged correlation values displayed characteristics similar to those observed from the zero lag correlations. Highest month to month persistences were again centred within October/November when significant lag correlations persisted for time lags greater than 2 months at some locations.It was, however, noted that although there were some relationships between the Southern Oscillation and seasonal rainfall over parts of East Africa, some of the extreme wet and dry episodes were not related to the Southern Os

ISSN:0196-1748    

DOI:10.1002/joc.3370080104

出版商:John Wiley&Sons, Ltd.    

年代:1988

数据来源: WILEY

摘要:

AbstractRainfall series to 1986 have been examined for North Darfur and North Kordofan. Annual and monthly series are presented and analysed. Relatively dry conditions have persisted in this region since 1966 due mainly to a decline in rainfall during July, August and September, the critical months for the annual agricultural cycle. Changes in daily rainfall magnitude and frequency are examined for these four rainy season months. It is recommended that agricultural planning and government policies be based on recent meteorological patterns.

ISSN:0196-1748    

DOI:10.1002/joc.3370080105

出版商:John Wiley&Sons, Ltd.    

年代:1988

数据来源: WILEY

摘要:

AbstractPrevious studies within a shallow valley east of the city centre of Johannesburg (South Africa) revealed the presence of some anomalies in the mesoscale, winter, nocturnal climate regime. Among them: the valley was relatively warmer during inversion nights; more than one thermal belt was discerned and valley winds dominated the early hours of the mornings. A tethered balloon and a mobile acoustic sounder were used to monitor temperature, wind and humidity profiles in the valley and vicinity, whilst ground mobile units measured temperature. Observations revealed a three layer wind system in which an elevated country breeze is sandwiched between the katabatic flow near the ground and the gradient wind aloft. The double thermal belts observed on the valley's slopes are probably due to the oscillation of the country breeze (the lower) and the meso‐scale valley inversion top (the upper one). The inversion top over the ridge lines is probably caused by the regional nocturnal inversion or an elevated inversion eroded by the urban heat island plum

ISSN:0196-1748    

DOI:10.1002/joc.3370080106

出版商:John Wiley&Sons, Ltd.    

年代:1988

数据来源: WILEY

摘要:

AbstractIt is now clear that conditions in the tropical Pacific Ocean and the overlying atmosphere can have significant associations with the seasonal—mean circulation of the mid‐latitude atmosphere, particularly in winter. Notable is a tendency for an intensification of the climatological standing wave pattern over the North Pacific and North America during the warm tropical conditions associated with El Niño/Southern Oscillation (ENSO) events. However, the actual mid‐latitutde circulation anomalies do show a great deal of variability among individual ENSO years. This paper addresses the question of whether the variability of the mid‐latitude response to ENSO events can be attributed to differences in the details of the tropical anomalies from event to event. The investigation embraced the period 1899–1982 and employed data on tropical sea surface temperatures (SSTs), tropical rainfall, and mid‐latitude atmospheric surface pressures and air temperatures.The results suggest that a major factor in determining the strength of the Northern Hemisphere extratropical response is the SST anomaly in the far western Pacific/Indonesian region. In particular, it appears that the strong extratropical teleconnections with ENSO events occur more frequently when the SST in the far western Pacific is anomalously warm (or at least not overly cold). This finding appears to be consistent with the results of at least some recent numerical experiments conducted with comprehensive general circul

ISSN:0196-1748    

DOI:10.1002/joc.3370080107

出版商:John Wiley&Sons, Ltd.    

年代:1988

数据来源: WILEY

摘要:

AbstractSuperposed‐epoch analyses show statistically significant warming and cooling of the East Tropical Pacific Ocean a few seasons after major low‐latitude and high‐latitude volcanic eruptions respectively, confirming the results of Handler (1986a). The statistical significance of the results is confirmed by a Monte Carlo sampling technique which takes account of pre‐eruption changes in the oceanic temperatures, and the results are only slightly sensitive to the selection of eruptions. Occasional sequences of extreme temperatures in the random samples underline the need for numerical modelling studies to complement the statistical investi

ISSN:0196-1748    

DOI:10.1002/joc.3370080108

出版商:John Wiley&Sons, Ltd.    

年代:1988

数据来源: WILEY

摘要:

AbstractAn apparent association between low latitude volcanic eruptions and the El Niño‐Southern Oscillation (ENSO), has been examined using a superposed epoch composite analysis of Darwin monthly mean pressure, an index of ENSO. Ten eruptions have been included in the analysis. In the composite, the date of eruption tends to be preceded by lower than average pressure at Darwin, and followed by above average pressure. A strong linear upward trend in the composite pressure anomaly starts well before the date of eruptions and continues for several months after the eruption. The analysis suggests that ENSO events are not caused by low latitude volcanic eruptions, since significant anomalies in Darwin pressure, and an upward trend in the anomalies, are observed well before the date of eruption. Low latitude eruptions tend to be preceded by the start of the sequence of events which leads to EN

ISSN:0196-1748    

DOI:10.1002/joc.3370080109

出版商:John Wiley&Sons, Ltd.    

年代:1988

数据来源: WILEY

ISSN:0196-1748    

DOI:10.1002/joc.3370080111

出版商:John Wiley&Sons, Ltd.    

年代:1988

数据来源: WILEY

ISSN:0196-1748    

DOI:10.1002/joc.3370080113

出版商:John Wiley&Sons, Ltd.    

年代:1988

数据来源: WILEY