摘要:

AbstractThe computer‐assisted classification of weather at Prague‐Clementinum used the average linkage clustering technique. Since the results of the clustering exhibit the snowballing effect, the usual methods of determining the threshold aggregation level (i.e. the level at which the clustering procedure is to be terminated) appeared to be inapplicable. A new method based on Monte Carlo simulations of the means was developed. Its key idea is the termination of the clustering procedure at different aggregation levels in different parts of the data set. This ensures that the number of resultant clusters is reasonable, while minimizing the numbers of very small clusters and unclustered days.The weather categorization resulted in 44 clusters for 14 winters in the period 1965–1978. Thirty‐one of the clusters had sizes of 5 or more days. The Monte Carlo scores, comparing the means and variances of the clusters with those of a large number of subsets chosen randomly, indicate that all the resulting clusters represent meaningful weather types.This study may provide a basis for nucleated clustering, which will enable us to deal with longer data series and to study the long‐term trends of the properties of weat

ISSN:0899-8418    

DOI:10.1002/joc.3370130802

出版商:John Wiley&Sons, Ltd.    

年代:1993

数据来源: WILEY

摘要:

AbstractThe characteristics of 30–50 day variability in the Australian summer monsoon rainfall has been investigated by using station rainfall data. In particular, the influence of the El Niño/Southern Oscillation (ENSO) phenomenon on the Australian summer monsoon rainfall is analysed. Results of the power spectrum analysis indicate statistically significant peaks in the 30–50 day band during anti‐ENSO events in the north‐central, and north and east coast regions. The spectral analysis also reveals a statistically significant peak in this band during ENSO events in the inland desert and north and east coast regions. Filtered rainfall values show an eastward propagation pattern during anti‐ENSO events, whereas ENSO events demonstrate a pattern characteristic of a standing oscillation and sometimes a westward propagation pattern. The present study also suggests some tendency for the 30–50 day oscillation to be phase‐locked to the seasonal cycle of this region. The phase‐locking phenomenon is also observed in the daily mean sea‐level pressure at Darwin, which is very clear during th

ISSN:0899-8418    

DOI:10.1002/joc.3370130803

出版商:John Wiley&Sons, Ltd.    

年代:1993

数据来源: WILEY

摘要:

AbstractMean monthly values of the zonal index of surface pressure for the zone 35°–65°N during the period 1899–1990 are studied. The extreme values – 11·5 hPa in February 1947 and 16·5 hPa in January 1978 define the range of zonal index variability. The highest annual value occurred in 1990. On average, the maximum of zonal index occurs in October (mean value 7·5 hPa), the minimum in May (2·5 hPa). Spectral variance analysis shows 2‐month, 3‐month, 6‐month, annual, quasi‐biennial, and 13·2‐year cyclicity in time series of monthly values. The quasi‐biennial and 13‐year cyclicity appear also in seasonal values of the zonal index.Instability of the zonal index spectra and autocorrelation for monthly values has been noted.The period under study is divided into three subperiods characterized by high (1899–1938 and 1972–1990) and low (1939–1971) zonal indexes.The correlation and correspondence between zonal index and air temperature changes of the Northern Hemisphere and ov

ISSN:0899-8418    

DOI:10.1002/joc.3370130804

出版商:John Wiley&Sons, Ltd.    

年代:1993

数据来源: WILEY

摘要:

AbstractThis investigation documents the relationships between anomalous North Pacific sea‐surface temperatures (SSTs) and the occurrence of growing season extended dry spells on the Canadian Prairies. Results show a significant correlation between extended dry spells and a positive SST anomaly gradient in the east‐central North Pacific. The gradient exists between an area of anomalously cold water in the east‐central North Pacific in the area 30°N–40°N latitude and 165°W‐135°W longitude, and an area of anomalously warm water along the central west coast of North America in the area 45°N–55°N latitude and 130°W‐125°W longitude. A probability model shows that the longer this positive gradient persists, the greater the probability of a major extended dry spell on

ISSN:0899-8418    

DOI:10.1002/joc.3370130805

出版商:John Wiley&Sons, Ltd.    

年代:1993

数据来源: WILEY

摘要:

AbstractThe results from a series of 3‐ to 6‐year simulations of the climatic impacts of tropical deforestation using a version of the NCAR Community Climate Model (CCM1–Oz) indicate considerable sensitivity to the specification of the vegetation and soil that replaces the tropical forest. The simulations, which encompass landscapes from forest, through grass with some trees, grass‐only, no vegetation with forest soils, to a devastated terrain, suggest that the predicted climate change depends about equally on at least three factors: (i) the global model and its large‐scale circulation sensitivity, (ii) the length of the model simulation, and (iii) the nature of the prescribed land‐use change, particularly the relative magnitudes of the changes (forested to deforested) in albedo and vegetation rough

ISSN:0899-8418    

DOI:10.1002/joc.3370130806

出版商:John Wiley&Sons, Ltd.    

年代:1993

数据来源: WILEY

摘要:

AbstractMethods are presented for estimating the effect of known site changes on temperature and rainfall measurements. Parallel cumulative sums of seasonally adjusted series from neighbouring stations are a useful exploratory tool for recognizing site‐change effects at a station that has a number of near neighbours. For temperature data, a site‐change effect can be estimated by a difference between the target station and weighted mean of neighbouring stations, comparing equal periods before and after the site change. For rainfall the method is similar, except for a logarithmic transformation. Examples are given. In the case of isolated stations, the estimation is necessarily more subjective, but a variety of graphical and analytical techniques are useful aids for deciding how to adjust for a site cha

ISSN:0899-8418    

DOI:10.1002/joc.3370130807

出版商:John Wiley&Sons, Ltd.    

年代:1993

数据来源: WILEY

摘要:

AbstractA study of the average distribution of total ozone was accomplished for the period from October 1982 to September 1983 in the area 20–50°N, 90–160°E, i.e. the entrance region of the East Asian subtropical jet stream. Total ozone data were obtained from the Total Ozone Mapping Spectrometer on the Nimbus‐7 satellite.Normally, the subtropical jet stream (STJ) marks a steep gradient in total ozone. From the monthly mean study of total ozone and wind fields at the 200 hPa surface, it was found that in winter the total ozone contours are almost parallel to the wind directions; the horizontal gradient in total ozone increases as the wind speed strengthens. In winter and spring, a sharp gradient in total ozone is found on the cyclonic side of the STJ because of the strong Hadley circulation. As the Hadley cell ceases in summer, the jet weakens and horizontal gradients in total ozone become much smaller, disappearing almost entirely by early

ISSN:0899-8418    

DOI:10.1002/joc.3370130808

出版商:John Wiley&Sons, Ltd.    

年代:1993

数据来源: WILEY

ISSN:0899-8418    

DOI:10.1002/joc.3370130809

出版商:John Wiley&Sons, Ltd.    

年代:1993

数据来源: WILEY

ISSN:0899-8418    

DOI:10.1002/joc.3370130810

出版商:John Wiley&Sons, Ltd.    

年代:1993

数据来源: WILEY

ISSN:0899-8418    

DOI:10.1002/joc.3370130801

出版商:John Wiley&Sons, Ltd.    

年代:1993

数据来源: WILEY