摘要:

AbstractCluster analysis has been applied to 9 years of daily 1000 hPa analyses for 1980–1988 over the New Zealand region. The resulting 13 synoptic groupings are characterized mainly by high‐pressure cells and pressure gradients reflecting the predominant wind directions. Low‐pressure centres are not well represented, presumably because of their smaller horizontal scale and lower frequency of occurrence.Seasonal variations in cluster frequency over this period typically differ by a factor of two. The most persistent patterns are associated with highs to the south of New Zealand, whereas the transitions between clusters show the familiar sequence of eastward‐propagating high‐pressure cells interspersed with troughs.It is anticipated that these synoptic classifications will prove helpful in interpreting inter‐annual climate fluctuations, in validating the performance of climate models for the New Zealand region and in providing improved guidance to forecasters. Their application to the analysis of daily and monthly variations in climatic elements is described in a comp

ISSN:0899-8418    

DOI:10.1002/joc.3370140702

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractThe effectiveness of the classification of daily mean sea‐level pressure patterns over New Zealand into 13 synoptic types by Kidson (1994) has been tested through their relationship with daily and monthly variations in temperature, precipitation, sunshine, and daily wind run over the period 1980–1990.The mean anomalies of these weather elements for each synoptic class often showed spatially consistent patterns, with departures falling in the second and fourth (below normal and above normal) quintiles. These were readily interpretable in terms of the effects of advection, differences in static stability, and the influence of mountain ranges on the low‐level circulation.On a monthly basis, 60 per cent of the variance in the frequencies of occurrence of the 13 synoptic types was found to be due to three significant EOFs. These formed the basis of an iterative clustering process to group the flow patterns for the 11‐year period into eight sets of monthly analogues or “regimes”, for which the composite patterns of the weather element were obtained.Overall, the results suggest that the synoptic classifications are likely to be helpful in specifying daily values of weather elements, and in interpreting the monthly departures of the New Zealand climate. They should also prove useful in validating climate model performance for the New Zealand region and in providing better detail of the regional climate changes likely to result from the greenh

ISSN:0899-8418    

DOI:10.1002/joc.3370140703

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractAn inverse relationship has been documented by previous studies between antecedent Eurasian winter snow cover (EWSC) and all‐India summer monsoon rainfall. Because both China and India are strongly influenced by the Asian monsoon system, it may be reasonable to ask whether a similar relationship exists between the EWSC and summer rainfall over China. This study seeks an answer to this question.Only a weak interannual relationship is found between the EWSC and summer rainfall over China as a whole. This weak EWSC‐rainfall linkage occurs only when the averaged rainfall over the entire country is used. By dividing the country into several geographical regions based on observed features in the interannual variability of rainfall, we find much stronger regional rainfall‐EWSC relationships. A strong in‐phase EWSC‐rainfall relationship is found in southern and northern China, whereas an inverse EWSC‐rainfall relationship appears in the western, central, and north‐eastern parts of China. Thus, EWSC may be a useful predictor for regional Chinese summer rainfall, but not for rainfall over the count

ISSN:0899-8418    

DOI:10.1002/joc.3370140704

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractUsing monthly 300 hPa height and 300–1000 hPa thickness data published by the synoptic climatology group of the Free University of Berlin, height and associated zonal flow changes were analysed for the period 1976 through to 1990. The 300 hPa heights rose most notably in the tropics, somewhat less in the lower mid‐latitudes, and they were lower in high latitudes. Via the height gradient, an increase in the zonal flow at 300 hPa can be derived for the subtropics and in upper mid‐latitudes. Using correlation analysis, relationships between tropospheric thickness anomalies in the lower latitudes—where the bulk of the most recent tropospheric warming has occurred—and changes in the 300 hPa height field elsewhere are explored. It is found that warm (cold) anomalies in the tropical troposphere are related to 300 hPa gradient increases (decreases) in the subtropics, but to gradient decreases (increases) in mid‐latitudes. Gradient increases in the mid‐latitudes moreover are generally related more closely to high‐latitude cool anomalies than to lower mid‐latitude warm anomalies or low‐lati

ISSN:0899-8418    

DOI:10.1002/joc.3370140705

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractComplex principal components analysis has been shown to be a useful tool for exhibiting propagating features in spatial‐temporal data sets. As in other applications of principal components analysis, rotation may lead to more interpretable components. Real orthogonal matrices have been used elsewhere, in combination with the varimax criterion, to find rotated solutions, but these fail to show invariance to complex scalings of the initial eigenvectors. It is shown that complex orthogonal, or unitary matrices have the desired invariance, and their use is illustrated on two examples, one synthetic and one involving sea‐level pressure d

ISSN:0899-8418    

DOI:10.1002/joc.3370140706

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractAn attempt is made to characterize the mesoscale climatological structures of the daily maximum and minimum temperature anomalies (with respect to monthly climatology) and total daily precipitation of the Emilia Romagna region of northern Italy (essentially the Po Valley) by means of multivariate statistical analysis techniques. Firstly, a definition of homogeneous seasons is attempted, based on the analysis of the month‐to‐month variability of the temporal variance of the parameters, derived from 24 years of daily data (1961–1984). This definition is then adjusted following a monthly empirical orthogonal functions (EOF) analysis of the spatial structures of variability of the same fields. Having defined “seasons” in this way, attention is concentrated on the cold season, an “sextended winter” ranging from October‐November to March‐April. Empirical orthogonal functions of both temperature anomalies and precipitation parameters are then recomputed for this extended season. Separate cluster analyses of the low‐dimensionality subspaces defined by the first three EOF coefficients (the principal components, PC) of the two parameters reveals the existence of winter weather ‘regimes’. Projections of these ‘regimes’ on geopotential height‐fields analyses in the middle (500 hPa) and low (mean sea‐level pressure) troposphere are qualitatively consistent with synoptic knowledge of the typical ‘weather types’ (grosswetterlagen) of the Mediterranean area. A comparison between the cluster analyses of temperature and precipitation shows that mutually compatible thermal and pluviometric regimes can be defined, providing a unified description of the space‐time mesoscale v

ISSN:0899-8418    

DOI:10.1002/joc.3370140707

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractA total of 42 different empirical model equations for estimating global insolation from other meteorological parameters is discussed and their predictions compared with measured values for Port Harcourt. The parameters are sunshine hours, relative humidity, temperature as well as geographical declination, latitude and altitude. It is found that a number of the models give significantly the same level of prediction. The average error in the calculated insolation being between 1.7 and 2.6 per cent (maximum deviation less than 7 per cent) when 8‐year monthly average data are used. Utilizing the individual monthly average or daily average data resulted in higher errors in the range 6–7 per cent (maximum deviation less than 33 per ce

ISSN:0899-8418    

DOI:10.1002/joc.3370140708

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

ISSN:0899-8418    

DOI:10.1002/joc.3370140710

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

ISSN:0899-8418    

DOI:10.1002/joc.3370140711

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

ISSN:0899-8418    

DOI:10.1002/joc.3370140701

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY