摘要:

AbstractMonthly Palmer Drought Severity Indices (PDSI) have been calculated for the period 1892–1991 over a 5° latitude by 5° longitude grid covering Europe and south‐west Asia from 35 °N to 70 °N and 10 °W to 60 °E. These indices are used to describe the spatial and temporal details of relative moisture variability during summer (June‐August). The full series of mean summer PDSI maps are presented. Over Europe as a whole, there has been a consistent (but statistically insignificant) increase in moisture supply throughout the period of record. The 1930s and 40s were exceptionally dry. The summer of 1947 was the driest, both in terms of average PDSI but also in terms of the spatial extent of moderate drought. However, the summer of 1921 was by far the most extreme when considering the spatial extent of severe drought conditions. Widespread drought conditions also prevailed over many regions of Europe during the 1890s. The wettest summers occurred in 1987 and 1916. The total area of Europe experiencing either severe dry or severe wet conditions has increased noteably during recent years.Nine regions of coherent summer moisture variability are objectively defined by orthogonal rotation of the principal components of the summer PDSI. The nine rotated components, which explain 60 per cent of total variability of this data set, represent moisture variability in north‐western Europe (NWEUR), the north‐west Mediterranean (NWMED), the lower Volga (LVOLG), central European Russia (CERUS), the north‐east Mediterranean (NEMED), the southern Caspian Sea (SCASP), the Pechora Basin (PECHB), the Danube Basin (DANUB), and northern Fennoscandia (NFENN). The last 3 years have been very dry in NWEUR and NWMED. The most recent summer in our analysis, 1991, was the wettest on record in both CERUS and NEMED. Preliminary spectral analyses provide little evidence for a solar‐moisture relationship in these European da

ISSN:0899-8418    

DOI:10.1002/joc.3370140502

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractInterannual variability of present‐day climate has been clearly linked to the occurrence of large‐scale sea‐surface temperature anomalies, particularly in the Pacific Ocean. Prediction of such anomalies many seasons in advance by using relatively simple, coupled oceanic‐atmospheric models provides a basis for predicting the atmospheric climate over the same period. This is achieved by inserting the sea‐surface temperature anomalies predicted by the coupled model at appropriate time intervals into a global climatic model and integrating forward in time. Prediction experiments for 1991 and 1992 have been conducted on this basis using sea‐surface temperature anomalies predicted for the Pacific Ocean. Global and regional rainfall outcomes are presented here, although the predictions are not expected to be valid for the whole globe. Detailed results are given for Australia and southern Africa, which experienced severe drought conditions in 1991 and 1992. Useful skill, with statistical significance for predictions when substantial rainfall anomalies occurred, was obtained for these regions, indicating the potential utility of the method. Considerable scope exists for improvements in the technique presented here, particularly in the global climatic model used, so that increasing accuracy should result as the technique is developed. Operational implementation of this method is essentially stra

ISSN:0899-8418    

DOI:10.1002/joc.3370140503

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractThe interannual variability of tropical cyclone (TC) movement has been found to be rather significant in certain regions of the western North Pacific. Westward and northwestward moving TCs are found to occur mostly at low latitudes and have the largest interannual variations in the region just east of the Philippines and over the northern part of the South China Sea. The area east of the Ryukyu Islands and south of Japan is identified as having the largest interannual variation of northward moving TCs.Correlations are made between the annual number of occurrences of TCs in these prescribed regions and the principal components of the monthly mean 850‐ and 500‐hPa zonal wind patterns over the western North Pacific (for the months of November of the previous year to April of the current year). Westward‐moving cyclones are found to correlate well with the 850‐hPa zonal wind patterns in January and March. Using the principal components associated with these patterns, prediction equations are then developed using the total (dependent) sample and the jackknife method (simulating an independent sample). The predictions made with both the dependent and “independent” samples are found to be very good.For north‐westward moving cyclones, no prediction equation is developed because principal components of the 850‐ and 500‐hPa zonal winds found to be significant can explain less than 30 per cent only of the total variance. However, the February 500‐hPa zonal winds correlate well with northward‐moving cyclones in the region east of the Ryukyu Islands and south of Japan. Predictions made using the principal components associated with this flow pattern for both the dependent and “independent” samples give rather good results.Because all the predictors are between January and March, they can be used operationally to predict the annual number of occurrences of TCs in the predefined regions. As TCs in these regions are likely either to move into the South China Sea or affect Japan, these results should prove useful in the seasonal prediction of TC occurre

ISSN:0899-8418    

DOI:10.1002/joc.3370140504

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractUnderstanding the potential for future climate change to affect ecosystems or agriculture in a region will depend, in part, on understanding how variable the present climate is and what its present effects are. Because the central prairie region of North America undergoes short‐term climate shifts (particularly drought), and appears sensitive to these changes, we were interested in characterizing the duration and nature of precipitation fluctuations. We used split, moving‐window dissimilarity analysis to locate transition points between periods of relatively homogeneous rainfall over the Kansas region. We identified statistically significant discontinuities in precipitation that appear to represent shifts in the regional climate during the last 115 years. All of the transitions were associated with changes in May, June, and July rainfall. Drought and drought cycles were the dominant fluctuations over decade‐long periods. Over somewhat longer periods (20–30 years) there were transitions, varying in abruptness, that may also be related to drought or perhaps larger scale climatic fluctuations. The relatively strong periodicity shown by the decadal discontinuities supports the contention that drought climates are triggered, or ended, by a cyclic phenomenon. The use of dissimilarity analysis allowed us to identify fluctuations in climate of the central North American prairie that were not previously described, and that may have been significant enough to influence natural and agricultural eco

ISSN:0899-8418    

DOI:10.1002/joc.3370140505

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractThe effects of interannual variations in El Niño‐Southern Oscillation (ENSO) upon annual, seasonal and monthly precipitation totals of San José, Costa Rica, over the period 1882–1987 are analysed using both a Southern Oscillation index (SOI) and a classification of El Niño and anti‐El Niño years. The analyses confirm the posited regional positive relationship between annual precipitation and the SOI and suggest that estimates of the probabilities of annual rainfall could be made successfully by using a mixed probability distribution that incorporates changes in both the mean and variance of precipitation under each of the three classes of El Niño activity. Strong seasonality is identified in the effects of ENSO, particularly in the months of July, August, and October, whereas the month of September seems unaffected. Monthly lead lag analyses imply that there may also be a reversal of the nature of association between the SOI and precipitation in the foll

ISSN:0899-8418    

DOI:10.1002/joc.3370140506

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractBox‐Jenkins modelling has some advantages over other techniques for the analysis of time series of climatological variables. Not only does it provide more information than other methods of anlysis, in a more elegant way, but it is also perfectly acceptable from the mathematical point of view. Other methods may not be immediately applicable because of the problem of autocorrelation in time series. The method of Box‐Jenkins univariate modelling is briefly discussed. As an example of its application to climatological time series analysis, and as an illustration of its usefulness, we examined the monthly activity of temperature inversions over Hemsby (eastern England) over a 14‐year period. The results showed that the monthly activity series, for both surface and elevated inversions, are stationary. However. the series for surface midnight inversions has a seasonal non‐stationarity of lag 12. There is a 1Zmonth seasonality for surface inversions and a weaker 6‐month seasonality for elevated inversions. The monthly activity of surface inversions exhibits less variation than the monthly activity of elevated inversions. This simply reflects the fact that the physical processes responsible for the formation of surface midnight inversions have a more regular evolution overtime than those responsible for the formation of elevated inversions. These results are in accordance with those obtained by using standard statistical t

ISSN:0899-8418    

DOI:10.1002/joc.3370140507

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractMore than 200, weekly spaced, lidar‐derived vertical profiles of aerosol concentration in the lower atmosphere (up to 1380 m above ground level) obtained during night‐time between October 1986 and August 1990 at the Indian Institute of Tropical Meteorology (IITM), Pune (18°32'N, 73°51'E, 559 m above mean sea‐level), India, have been used to study the long‐term variations in aerosol concentration in different air layers. Selected meteorological parameters for the above period at Pune have also been examined to investigate their association with the aerosol concentration. The spectral analysis of the data revealed significant periodicities in four different characteristic ranges, namely 2.5–13.5,ca.27,ca.33 and 40–48 weeks in both lidar‐derived aerosol content and meteorological parameters; the fourth range being more predominant in all the parameters. These results, together with those of cross‐correlation analysis of the data, indicate an association between the long‐term trends present in both aerosol and meteorological parame

ISSN:0899-8418    

DOI:10.1002/joc.3370140508

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

ISSN:0899-8418    

DOI:10.1002/joc.3370140501

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY