Showing papers in "International Journal of Climatology in 1983"

The spatial and temporal characteristics of northern Hemisphere surface air temperature variations

Abstract: Variations in temperature over landmasses during the present century are determined. The spatial patterns of change accompanying major warming and cooling episodes are mapped. The spatial representativeness of the Northern Hemisphere average is assessed and implications for proxy climate studies are considered. Finally, the seasonal breakdown of trends and correlations between monthly and annual data for the Arctic and Northern Hemisphere is considered.

Sub-Saharan rainfall update for 1982: continued drought

Abstract: The 1982 value of a sub-Saharan rainfall index previously published for 1941-1981 is given. This establishes that the drought which commenced in 1968 and persisted very strongly throughout the 1970s and 1980-1981 continued into 1982. which was the third driest year of the period 1968-1982, and also appears to have received substantially less rainfall than the drought years of the 1940s. Several meteorological and socioeconomic implications of this situation are discussed. The paper also provides a recomputation of the entire 1941-1982 index time series that was permitted by the forward extension of the database since the original calculation for 1941-1974.

Climate reconstruction from tree rings: Part 1, basic methodology and preliminary results for England

Abstract: Ring widths of oak trees from a network of 14 sites (13 in the British Isles and one in France) are used to reconstruct spatially averaged temperature and rainfall for England. A multiple linear regression technique is used, in which the regressors are orthogonal principal components of the ring widths. The multiple correlation coefficients are, statistically, highly significant, and the regression models' stability has been confirmed using independent data. These results demonstrate the usefulness of tree-ring widths for climate reconstruction in temperate, maritime areas.

Climatic clusters of the Indian region

Abstract: In this paper we derive climatic clusters of the Indian region using data on monthly mean profiles of the precipitation, the moisture index (defined as the ratio of precipitation and potential evapotranspiration) and of the minimum temperature. The delineation of regions over which the patterns of profiles of important climatic factors such as precipitation are similar is necessary for the determination of meteorological zones over which prediction can be made as well as for understanding the distribution of vegetation cover. The latter has been the major aim of the studies of climatic classification. In the traditional approach to this problem, the meteorological stations in the region are assigned to predetermined categories such as arid, semi-arid etc. on the basis of the values of the climatic factors (or of the bulk parameters derived therefrom) characterizing these stations. Here the variation of the climatic patterns over the Indian region has been analysed to obtain climatic clusters, which represent natural grouping of the patterns and hence of the meteorological stations at which they occur, as well as the climatic boundaries separating these clusters. This analysis is facilitated by an initial reduction of dimensionality in the description of the patterns achieved by using principal component analysis. Sixteen clusters of the mean monthly profiles of the moisture index have been obtained. It is found that there is a close correspondence between these clusters and the distribution of the vegetation types in the country.

The use of average annual rainfall to derive estimates of orographic enhancement of frontal rain over England and Wales for different wind directions

Abstract: A field of average annual enhancement, defined as the mean rainfall rate al inland sites minus the mean rate over the coast, has been derived for England and Wales. Past cases of frontal rain associated with low-level winds from the SW quadrant were analysed so as to determine the typical distribution and intensity of orographic enhancement. It is shown that these results are sensitive to wind speed and, in particular, direction. Comparison of these results suggest relationships between orographic enhancement and average annual enhancement which are used to produce estimates of the distribution of enhancement which may occur with low-level winds from other directions. These enhancement fields can he combined with radar observations of rain over the sea to produce short-period forecasts of rainfall intensity when it moves overland.

Persistence of wet and dry spells at uccle (Belgium)

Abstract: The rainfall persistence at Uccle (Belgium) is examined statistically using 75 years of daily observations. Different kinds of distributions expressing this persistence have been fitted to the sequences of dry and wet days: the geometric series, the logarithmic series, the Eggenberger-Polya distribution, the simple Markov Chain and the Markov Chain of order higher than one. Wet and dry spells are best described by a Markov Chain model of order four. Nevertheless for wet days, the Eggenberger-Polya distribution provides a good fit to the observed data. For Uccle, the rainfall persistence seems to remain constant after four consecutive days of precipitation.

Teleconnections and the siege of time

Abstract: The recent surge of interest in climate has resurrected correlation coefficients as tools for identifying ‘significant’ atmospheric teleconnections. Unfortunately, large coefficients may diminish and even change sign with time, suggesting absence of real physical relationships. Some statistical evidence supports the view that higher than normal sea surface temperatures in the central and eastern Pacific ‘cause’ less than normal rainfall in the Indian summer monsoon. However, a study of individual Augusts uncovers major exceptions and at the same time fails to confirm that Indian summer rainfall influences central and eastern Pacific rainfall or that the Southern Oscillation Index can be consistently related to conditions in either region. Around 1963-1964 the apparent relationship between the Southern Oscillation Index and Indian rainfall reversed. At about the same time other global climatic relationships changed, raising the possibility of identifying and describing a major global climatic singularity separating two distinct statistical populations.

Extreme distributions of Australian annual rainfall in relation to sea surface temperature

Abstract: Sea surface temperature (SST) measurements from 1950 to 1969 are analysed for an extensive region of the Southern Hemisphere for six years of very high and very low areal extent of above normal Australian continental rainfall. Years of extensive drought are found to be associated with a predominantly low SST persisting throughout the year over the eastern Indian Ocean and the south west Pacific in the Australasian region particularly at low latitudes; very wet years over the continent are associated with a persistently warm SST extending from the equator to mid latitudes in the same region. Although the extreme years tend to be related to extremes of a Southern Oscillation index this is not always the case. Examination of SST over the eastern Pacific for the same years indicates some evidence that its thermal anomalies are in general opposite to those in the Australasian region though this is not so in all cases. Eastern South Pacific SST data sequences for years preceding and following individual extreme rainfall years over Australia show rapid and differing changes so that their forecasting potential is very limited.

The estimation of missing climatological data

Abstract: Various methods of estimating montly means and extremes of climatological data are examined. Any generalized method is likely to be based on a correlation matrix, but the incompleteness of the data introduces problems with this approach. These are illustrated by program BMDPAM of the BMDP suite, which produces estimates inferior to those using traditional methods based on single station comparisons. Principal component analysis is considered likely to be the best statistical technique for estimating missing values among highly correlated data. The high quality correlation matrix required as input can be obtained by using a simple estimating procedure to produce a preliminary set of complete data. A simple technique devised for estimating climatological data in the U.K. was found to give results similar to those obtained from an eigenvector scheme used for quality control purposes. The accuracy of the technique is such that it is suggested that satisfactory averages could be estimated for stations with only 10 years of data, and possibly less.

The value of climate information: A decision‐analytic approach

Abstract: A decision-analytic approach to the problem of assessing the value of climate information is presented and an application of this methodology to a decision-making problem involving the use of climate information is described. First, decision analysis is discussed briefly with emphasis on its informational aspects. Then a decision-making situation is considered in which a farmer must decide which of two crops to plant in the face of uncertainty as to whether growing season precipitation will be above or below average. It is assumed that information concerning growing season precipitation is embodied in a climate forecast provided by a meteorologist and that this information constitutes the basis for the farmer's decision. Several probabilistic models for the climate forecasts are considered, including symmetric and asymmetric discrete distributions and a normal model. These models can provide reasonable descriptions of currently available climate forecasts. The analysis reveals that relatively uncertain climate information may be of value in some decision-making situations, although the value of climate forecasts with skill levels commensurate with existing seasonal forecasts does not approach the value of perfect forecasts. Nevertheless, in the situations considered, once a minimum level of skill is achieved, further improvements in the forecasts result in steadily increasing benefits. Finally, it is indicated that decision analysis is also applicable to more complex situations in which climate information may play an important role.

Rain day frequency and mean daily rainfall intensity as determinants of total rainfall over the eastern Orange free state

Abstract: Summer rainfall totals over the eastern Orange Free State are described in terms of number of days of rain and of mean rainfall per rain day. Variations in rainfall may be considered to result from frequency changes in an objectively-chosen subset of significant rain days. It is demonstrated, through the use of the equation y = αx exp (βx) (where x and y are the cumulative percentages of the number of rain days and of the rainfall respectively), that increases in mean rainfall per rain day result from an increased number of, and increased intensity of rain on, the heaviest rain days. Some implications of these findings for studies of atmospheric circulation changes and for weather modification are discussed.

Spatial and temporal aspects of the surface wind regime on the canterbury plains, New Zealand

Abstract: Seasonal and diurnal patterns produced by the interaction of synoptic scale winds and two thermo-topographic systems, the land/sea breeze and mountain/plain winds, are investigated in a spatial context. Together with gradient winds and the shallow ‘lee trough’ north-easterlies these local winds create a wind regime composed of several distinctive regional element, the boundaries of which are transitional in nature and dependent on time day and year and the strength of synoptic influences. The sea breeze maximum frequency by day in summer in coastal areas whereas katabatic flows are most frequent by night, in winter adjacent to the Alps. Banks Peninsula strongly influences the wind regime by funnelling north-easterly airflow onto the plains and possibly creating a zone of sea breeze convergence extending inland. South of Banks Peninsula the interaction of onshore wind components with north-easterly synoptic winds appears responsible for the diurnal rhythm in the synoptic wind, a phenomenon already observed north of Banks Peninsula in relation to south-westerly gradient winds. Practical and theoretical implications of the regional study are discussed.

The dynamic climatology of the Beaufort to Laptev Sea sector of the Polar Basin for the summers of 1975 and 1976

Abstract: For the summer months of 1975 and 1976, the total vertical velocity at 850 millibars is computed from a diagnostic atmospheric model as an index of synoptic activity in the Beaufort to Laptev Sea sector of the Polar Basin. The objective is to identify the major modes of synoptic activity in the region and to determine the major formative mechanisms for significant synoptic vortices. This will lead to an understanding of the dynamics involved in the evolution and maintenance of synoptic patterns in the Arctic. Cluster analysis is used to stratify the 850 mb geopotential height data into synoptic modes. The mean 850 mb total vertical velocity field for each cluster is calculated, and indices related to each of the formative mechanisms are related to these individual fields through regression analysis and pattern comparison. These mechanisms are: vorticity and thickness advection, diabatic effects of latent heat release and surface heating, and frictional and orographic influences at the surface. Explanations for the dynamics of the major regional vortices are discussed.

Frost mapping in southern Victoria: An assessment of HCMM thermal imagery

Abstract: HCMM satellite thermal imagery is used in a detailed frost assessment in an important horticultural area near Melbourne, Australia. Good general agreement is found to exist between plots based on night-time HCMM data which show surface temperature differences across the study area and frost risk maps based on terrain and land cover. However, it is concluded that the HCMM data have insufficient spatial resolution for use in local frost mapping in the study area. Improved thermal resolution will make thermal imagery from future satellites an increasingly important tool in topo-climatology. Without such improvements, local frost mapping will, in the absence of climatic network data or mobile topo-climatological surveys, continue to depend on data from thermal scanners in aircraft and on detailed assessment of terrain and land cover.

Modelling climate and the nature of climate models: A review

Abstract: A new structural framework for climate models is presented Four basic model types are discussed: general circulation models, energy balance models, one dimensional radiative convective models and two dimensional zonally averaged dynamical models The fundamental importance of three primary processes in the climate system-radiation, dynamics and surface processes-is underlined and the degree to which each of these mechanisms is incorporated in each model is highlighted

Rainfall distribution, variability and probability in plateau state, Nigeria

Abstract: The basic objective of this investigation is the determination of the spatial distribution of rainfall in Plateau State. Nigeria. The results show that the greatest amounts of rainfall are obtained in the southern and western parts of the State and on the southern and western margins of the high Plateau in particular. This pattern of rainfall distribution is explained partly by the movements and positions of the ITD (intertropical discontinuity) at various times of the year, and partly by the interplay of the direction of rainbearing south-westerly winds with the physiographic features in the State. In general, also, the rainfall amounts are higher on the highland parts of the Stale than on the lowlands. Conversely, rainfall variabilities are higher on the lowlands of the State than on the high Plateau. Furthermore, rainfall variabilities are higher at the beginning and at the cessation of rainfalls than in the middle of the rainy season. Examples of implications of high rainfall variability and low probability of receiving certain given threshold amounts of rainfall at different phenological stages of crop developments, are given. These examples serve to substantiate the need for supplementary irrigation facilities in the Slate.

Solar and net radiation in Peninsular Malaysia

Abstract: Linear regression equations relating the global solar radiation and sunshine duration are derived for a total of 14 stations in Peninsular Malaysia. Mean monthly global solar radiation values for other stations which have only sunshine data are estimated using these regression equations. The intensities of global solar radiation during different times of the day and under different meteorological conditions are discussed. Maps of mean monthly global solar radiation are presented and discussed. It is found that the distribution pattern of global solar radiation follows somewhat with that of rainfall pattern. Net radiation was estimated using empirical equations developed by Chang (1970), Davies (1967). Selirio et al. (1971) and Penman (cited by Chang, 1970). Comparison of the estimated net radiation with the limited net radiation record available shows that the Davies' formula gives the best estimates. Hence Davies' formula is used for the estimation of net radiation. Maps of estimated net radiation are similarly prepared and discussed.

The impact of weather and climate on industrial production in Great Britain

Abstract: The Index of Industrial Production (HP) is used as a measure of output from industry in Great Britain. A time-series of this Index is derived extending from January 1958 to May 1979. This is compared both with seasonal extremes of climate and with more general departures from ‘average’ conditions, to determine the influence, if any, of weather and climate on industrial production. With respect to extreme seasons, a pronounced decline in industrial production look place during the drought summers of 1975-6, and the severe winters of 1962-3 and, to a lesser extent, 1978-9. Non-climatic factors, such as industrial disputes, are unlikely 10 have contributed substantially to the shortfall. The categories of industry affected were quite different during the two types of extreme weather event: during the 1962-3 winter it was industries linked to work out-of-doors which suffered, in the 1975-6 drought it was high water requirement industries. To determine the impact of general weather conditions, three sets of step-wise multiple regression analyses are performed using a selection of climate and industrial dispute measures as the independent variables. The dependent variables are values of the January and July IIP with the trend expressing economic growth removed, and the size of the labour force in the construction industry in February. The analyses are performed both upon the full time-series and on the time-series with the extreme events removed. The results suggest that normal variations in the weather influence industrial production.

Independence of rainfalls through the rainy season and the implications for the estimation of rainfall probabilities

Abstract: A detailed study of more than 50 years of daily rainfall records from three sites in seasonally arid West Africa revealed no dependence between rainfall at different times within the rainy season. Years were grouped on the basis of the date of the start of the rains and rainfall models fitted separately to early, medium and late start groups. Any differences between the groups in subsequent rainfall pattern bordered on statistical significance and were too small to be of practical significance. Thus, the best estimates of the probabilities of rainfall events are obtained by considering all years of the rainfall record. As rainfalls at different times of the season can be assumed to be independent, it is straightforward to calculate conditional distributions, for example, the probability distribution of the length of the rains given the actual starting date. The calculation and value of using conditional distributions are discussed.

Secular variations of surface temperature and precipitation patterns over the great lakes region

Abstract: Spatial patterns of surface temperature and precipitation variability over the Great Lakes region and their changes during the past 78 years are examined using eigenvector analysis. The results show that the region is homogeneous in terms of temperature variations. The most important regional temperature trends have been very similar to the trends in the average annual temperature for the Northern Hemisphere. In the case of precipitation, however, an important boundary divides the region into a north-western and south-eastern portion. Positive precipitation anomalies occurred over the south-east during the early part of this century and again after about 1960. The north-western portion, on the other hand, experienced wet conditions during most of the intervening years.

Fluctuations in the surface temperature and surface salinity of the north-east Atlantic at frequencies of one cycle per year and below

Abstract: Time-series of monthly sea surface temperature and salinity data (1951-1974) from stations in the N.E. Atlantic were investigated by calculating cross-spectra using the method of maximum entropy analysis. This new technique has not previously been applied to climatological problems. The temperature and salinity data were also compared with surface heat-flux and evaporation time-series and wind observations. The main features of the seasonal cycle are apparent in the results, in particular, the close synchronism of the temperature cycle across the region. In addition, the results show that: variations in the seasonal flux of low salinity water led to short period anomalous salinity values, salinity and temperature anomalies tended to drift with the surface currents, and salinity and temperature changes at the lowest frequencies were caused by displacements of water masses which do not seem to have been forced locally. Fluctuations in heat-flux and evaporation contributed to variations on a timescale of about three years and it is shown that these gave rise to additional spectral peaks by interacting with the seasonal cycle.

The spatial organisation of daily rainfall in eastern New South Wales

Abstract: Product-moment correlation are used to provide an estimate of the degree of association of daily rainfalls between a number of sited in eastern New South Wales. Completely dry days are omitted from the analysis so that the coefficients obtained represent the strength of association between sites for days on which rainfall occurs. Maps showing the strength of links between sites are used to illustrate general trends in the spatial organization of daily rainfall on a monthly basis. Certain very district seasonal changes in rainfall patterns emerge, principally distinguishing the summer (December to February) from the cooler part of the year (April to October) in terms of the nature of association and the separation of discrete rainfall areas. Many of these comprise groups of two or three Bureau of Meteorology forecasting areas. More widespread rainfall associated with lager-scale atmospheric disturbance occurs in February, and in April and May, but during the April to October period the Divide is seen as a very important climate, as well as topographic, feature. At other times smaller topographic units apparently exert a control over rainfall occurrence. This is particularly true of the Hunter valley which is the center of rainfall development for a wide area in January. Sea breeze front effects are also seen as important enhancers of rainfall in the summer.

Estimation of the daily global solar irradiation at Corvallis, Oregon (U.S.A.) from the hours of bright sunshine, the daily temperature range and relative humidity

Abstract: Simple empirical relationships based on the hours of bright sunshine, the daily temperature range and relative humidity have been developed to estimate the daily global solar irradiation at Corvallis, Oregon (U.S.A.). It is observed that the greater part of the variability in the daily solar radiation income at the surface is explained by changes in the available solar energy at the top of the atmosphere in the course of the year. The relationship based on the hours of bright sunshine yields estimates of the daily global solar irradiation which compare favorably with the measured values (coefficient of determination >0-90).

Quasi‐periodic meteorological series and second‐order autoregressive processes

Abstract: Quasi-periodic behaviour in meteorological or climatological series is a widespread phenomenon; various attempts have been made to explain such behaviour in physical terms, often invoking external influences in the explanations. While it is not disputed that external influences or feedback mechanisms may have a part to play, it is argued in the present note that a substantial part of quasi-cyclic behaviour can often be explained by a simpler mechanism, namely second-order dependence of a series on its own past. The plausibility of second-order dependence is discussed, and the way in which such dependence leads to quasi-periodic behaviour is described. Data on sunspots. Baltic ice area and a zonal circulation index are used to illustrate these ideas.

A statistical method for quality control of routine temperature observations in developing countries

Abstract: A simple statistical method is outlined to evaluate and improve routine temperature observations from meteorological stations in developing countries. This quality control achieves two things. It identifies anomalous data before storage or use. It also reveals whether thermograph, minimum thermometer, maximum thermometer and dry bulb thermometer have to be checked and/or how their data must be improved to be internally consistent. In addition this statistical approach assesses differences between averaging methods. It can be concluded that with this cost-efficient method, temperature data accuracy obtained will be adequate for agricultural purposes and other climatological applications.

On the correlation between monthly and annual mean temperatures

Abstract: Excepte les mois d'hiver, la correlation entre les moyennes annuelles et mensuelles des temperatures au centre de l'Angleterre est plus elevee que si les temperatures moyennes mensuelles n'etaient pas correlees. Cette correlation croit si on prend des moyennes de decade ce qui indique que le facteur de correlation persiste sur une decade ou plus