bluuebunny/crossref_metadata_2025 huggingface dataset:
Relationships between the Southern Oscillation and the rainfall of Sri Lanka
Authors: Suppiah Ramasamy
Published: February 2007

The Southern Oscillation (SO) signals in the monthly and seasonal rainfall of Sri Lanka are studied by using statistical analyses. Correlation coefficients (CCs) between the rainfall of the first intermonsoon season (March‐April) and the seasonal Southern Oscillation Index (SOI) of August‐September‐October (ASO) and November‐December‐January (NDJ) are positive and significant. In particular, March rainfall in region A is significantly correlated with the subsequent SOI of ASO and NDJ. The CC between the rainfall of the southwest monsoon season (May‐September) and the SOI is also positive. Cumulative rainfall of the peak monsoon months (July and August) reveals a strong and positive correlation with the seasonal SOI.

The CC between the rainfall of the second intermonsoon season (October‐November) and the SOI is negative and significant. The rainfall of this season is also significantly correlated with the SOI (Tahiti‐Darwin) of May‐June‐July (MJJ). The SOI of MJJ serves as a particularly useful predictor for this seasonal rainfall. The CC between the rainfall of the northeast monsoon season (December‐February) and the SOI is also negative but weak.

Large signals appear in wind anomalies over Sri Lanka prior to El Niño/Southern Oscillation (ENSO) events. Upper level easterlies (westerlies) and weak (strong) low‐level easterlies are dominant in March before the La Niña (El Niño) years. These wind anomalies persist until the ENSO events reach maturity.

Based on the results of correlation analysis and wind anomalies, schematic models of the zonal circulation along the Equator between 60°E and 140°W are presented for La Niña and El Niño phases for northern hemispheric summer and winter seasons.
Mean seasonal and spatial variability in gauge‐corrected, global precipitation
Authors: Legates David R. , Willmott Cort J.
Published: February 2007

Using traditional land‐based gauge measurements and shipboard estimates, a global climatology of mean monthly precipitation has been developed. Data were obtained from ten existing sources, screened for coding errors, and redundant station records were removed. The edited data base contains 24,635 spatially independent terrestrial station records and 2223 oceanic grid‐point records. A procedure for correcting gauge‐induced biases is presented and used to remove systematic errors caused by wind, wetting on the interior walls of the gauge, and evaporation from the gauge. These ‘corrected’ monthly precipitation observations were then interpolated to a 0·5° of latitude by 0·5° of longitude grid using a spherically based interpolation procedure. Bias‐corrected spatial distributions of the annual mean and intraannual variance are presented along with a harmonic decomposition of the intra‐annual variance.
A search for accelerations in records of European mean sea level
Authors: Woodworth P. L.
Published: February 2007

Long records from European tide gauges have been inspected for evidence of modifications in the rate of change, or ‘accelerations’, of mean sea level (MSL). In general, no evidence was found for MSL accelerations significantly different from zero over the period 1870 to the present, although non‐zero accelerations were observed at individual stations. Changes in surface air pressure may have been responsible for an overall slightly negative acceleration observed in northern Europe. In order to extend the study to time‐scales longer than a century, data from the oldest European MSL records at Brest, Sheerness, Amsterdam and Stockholm starting in 1807, 1834, 1700 and 1774, respectively, were also investigated with the result that a positive acceleration of order 0·4 (mm year−1) per century appears to be typical of European Atlantic coast and Baltic MSL over the last few centuries. Although of interest as an indicator of past climate change, this small low‐frequency MSL acceleration is an order of magnitude less than that anticipated over the next few decades as a result of greenhouse warming. A conceptual study of possible future Newlyn (UK) tide gauge data has shown that the MSL acceleration anticipated from the global warming should be apparent in the records by the early part of the next century.
North pacific circulation anomalies, El Niñto and anomalous warmth over the North American continent in 1986–1988: Possible causes of the 1988 North American drought
Authors: Weber Gerd‐Rainer
Published: February 2007

The relationships between 300/1000 mbar thickness anomalies over the North Pacific Ocean and thickness anomalies over the adjacent North American continent are investigated on the basis of monthly anomalies for the 34‐month period January 1986 to October 1988. It is found that in 21 out of the 34 months a pattern exists that links negative anomalies over the North Pacific Ocean to positive anomalies over the North American continent. Using teleconnection analysis, it can be shown, that in spring a strong relationship exists between positive anomalies over the western half of the North American continent in mid‐latitudes and negative thickness anomalies over the North Pacific Ocean in mid‐latitudes as well as between positive anomalies over the North Pacific Ocean in tropical and subtropical latitudes. Statistically, the strongest relationships emerged between the thickness gradient departures 20°–30°N over the east‐central Pacific Ocean and positive anomalies over North America. The abnormal warmth over the North American continent in the springs of 1986, 1987, and 1988 may be explained in terms of an intensified circulation across the Pacific Ocean, which resulted in large positive thickness anomalies downstream over the North American continent. The intensification of those anomalies in the spring of 1988 is discussed as a contributing factor to the initiation of the 1988 North American drought.
some aspects of daily rainfall distribution over India during the south‐west monsoon season
Authors: Soman M. K. , Kumar K. Krishna
Published: February 2007

This paper presents the results of an analysis of the daily rainfall at 365 Indian stations for the 80‐year period, 1901–1980. The rainfall data relate to the south‐west monsoon season June to September (122 days), which accounts for the major part of the annual rainfall over most parts of the country. For each of the stations the rain‐days are arranged in ascending order of rain amount, and the association between the cumulated percentage rain amount (x) and the cumulated percentage number of rain‐days (y), designated as the normalized rainfall curve (NRC), is calculated. It has been shown in an earlier study that x and y are related by the equation x = y exp [— b(100—y)c], where b and c are empirical constants that depend on the coefficient of variation (CV) of the rainfall series. This equation has been utilized to study various parameters of the daily rainfall distribution.

The coefficient of variation of the daily rainfall series varies between 100 per cent and 230 per cent at individual stations, with nearly half the number of stations having CV values in the range 130–150 per cent. The number of days of significant rainfall (days with rainfall greater than the mean intensity per rain‐day) constitute about 30 per cent of the total number of rain‐days and account for about 75 per cent of the seasonal rainfall at almost all the stations.
Tropical‐extratropical cloudbands in the Australian region
Authors: Kuhnel Ivan
Published: February 2007

The climatology of the tropical‐extratropical cloudbands (TECBs) in the Australian region is examined, using a subdivision of the cloudband phenomena, according to their convective sources of origin. In addition to previously described parameters (e.g. amplitude of mid‐latitude troughs, cross‐equatorial flow, jet stream), the 1979–1983 TECB activity is analysed with respect to other indices, such as global pressure and sea‐surface temperature, the Southern Oscillation Index (SOI), 40–50‐day oscillation, Hadley cell circulation or cloudiness anomalies. It is shown that during a period marked by a significant decrease in the TECB activity, 5–6 months prior to the lowest value of the SOI, the TECB tends to develop in 40–50‐day intervals, whereas otherwise, its development can be associated with higher frequency (18–21 day) oscillations. Similar fluctuations have also been observed in tropical cloudiness in the TECB area of origin. On a large‐scale, the TECB activity seems to be closely linked to large‐scale pressure fluctuations in the Indian and northern Pacific Oceans.
Volcanic aerosols, El Niñmo and the Southern Oscillation
Authors: Handler Paul , Andsager Karen
Published: February 2007

In this paper some of the questions raised by Nicholls (1988) concerning the relationship of volcanic aerosols to the El NiñMo/Southern Oscillation are examined and answered. Using Monte Carlo techniques, the statistical significance of the composite sea surface temperature (SST) anomalies and the Southern Oscillation Index (SOI) are reexamined both before and after the eruption of a set of low‐latitude volcanic eruptions. Significantly warmer SST and negative SOI anomalies are found in the composites immediately following the eruption period. These significant anomalies after the composite eruption season are found not to depend on the appearance of cooler SST and positive SOI before the key season, a possibility suggested by Nicholls (1989). This result is in agreement with Parker (1988). The volcanic hypothesis states that low‐latitude volcanic aerosols are the immediate and only cause of warmer than normal SST or El NiñMo. This implies that when no low‐latitude aerosol is present the SST should be cooler than normal. Both of these aspects of the volcanic hypothesis are found to be satisfied to a very high level of statistical significance by the observed SST and SOI data.
Temporal and spatial characteristics of annual precipitation over the balkans in the twentieth century
Authors: Maheras Panagiotis , Kolyva‐Machera Fotini
Published: February 2007

A study of the annual totals of precipitation is presented for 12 stations in the Balkan area for a period of 92 years (1894–1985) The homogeneity of the precipitation series is examined, and their statistical characteristics are analysed. An abrupt climatic change is found at the station of Belgrad, and a statistically significant trend of annual precipitation is found for various periods for the stations of Kerkyra, Patras, Hvar, and Sarajevo. Persistence is only ascertained for the Belgrad station. The application of principal component analysis has yielded three groups of stations. Group A includes northern and continental stations, group B includes stations of the Ionian and Adriatic Seas, and group C includes the stations of Thessaloniki and Athens. The most important period of fluctuations covers the years 1933–1953, when a humid period is followed by a dry period. The most recent 5‐year period can be described as a very dry one.

Finally, comparison between rainfall fluctuations and types of circulation shows that the predominance of meridional circulation over the Balkans results in an increase of precipitation, whilst a zonal circulation results in a decrease of precipitation.
Characteristics of the low‐level temperature inversion along the Alaskan Arctic coast
Authors: Kahl Jonathan D.
Published: February 2007

The climatological characteristics of low‐level tropospheric temperature inversion along the Alaskan Arctic coast are examined from a 10‐year record of surface and upper‐air meteorological data at Barrow and Barter Island, Alaska. The meteorology at the two stations is found to be remarkably similar; surface‐based inversions occur nearly half of the time, but even in the winter months inversions are frequently based up to 200 m above the surface. Median inversion depths range from 250m to 850m, with median temperature differences across the inversion ranging from 2°C to 11°C. In March and April when the inversion is strongest, the lowest levels frequently erode. This indicates that the transient character of the inversion reduces its effectiveness as a barrier to vertical mixing. The inversion depth closely follows the annual cloud‐cover cycle, demonstrating that the development and maintenance of the inversion is a result of complex interactions between radiative forcing, synoptic activity, and sea‐ice dynamics.
Space–time variability of rainfall in April and October–November over East Africa during the period 1932–1983
Authors: Beltrando Gérard
Published: February 2007

The space–time variability of precipitation over East Africa during the two rainy seasons (April and October–November) is investigated using a network of 56 stations for the period 1972–1983 and 32 stations for the period 1932–1983. The analysis relies on a model of two‐mode variance with rotation, which determines homogeneous groups of stations having a common time evolution.

During April, three components represent a large part of the variance with their cores (i) near the Zanzibar channel, (ii) the Kenyan‐Tanzanian highlands and eastern Lake Victoria, and (iii) the southern part of the Tanzanian highlands. During the October–November rainy season, rainfall is more homogeneously distributed. The first component takes account of 60 per cent of the variance and encompasses a large part of the domain, except southern inland Tanzanian stations and western and northern Ugandan stations.

Spectral analysis of the time series associated with the space component reveals peaks around 5–6 years, which appears to be the major periodicity over East Africa.
Low‐latitude volcanic eruption signal in Indian surface air temperatures
Authors: Hingane L. S. , Kumar K. Rupa , Patil S. D.
Published: February 2007

The effect of major low‐latitude volcanic eruptions on the all‐India mean surface‐air temperature has been studied using data for the period 1899–1985, by using superposed epoch analysis over 36 months before and after the month of eruption. The eruptions are grouped into three categories and their effects on monthly temperatures are presented. In general, there is no evidence of persistent decrease in the mean annual temperature following the eruptions. There is, however, an abrupt and significant surface cooling over India in the first 2 months following northern hemispheric eruptions, with recurrent drops in the next 2–3 years. Southern hemispheric eruptions do not show any effect on the Indian surface temperatures.
On the annual and seasonal patterns of rainfall fluctuations in sub‐saharan West Africa
Authors: Adejuwon J. O. , Balogun E. E. , Adejuwon S. A.
Published: February 2007

Monthly rainfall data for 16 stations in Nigeria were collected for the period 1922–1985. From this, the annual, the wet season, the onset, the peak, and the retreat rainfall data were derived. The patterns of fluctuations of rainfall were analysed therefrom. The series were first examined for trends and then for periodic fluctuations. Trend analysis revealed that a majority of the series exhibit negative trends, and in some cases the trends were significant. For all the series analysed, there is the general tendency towards increasing aridity. Spectral analysis indicates prominent periods of between 2‐and 8‐year cycles. Other periodicities observed include 16‐, 18‐, and 21‐year cycles.
Autumn and winter daily precipitation areas in Wales, 1982–1983 to 1986–1987
Authors: Bonell Mike , Sumner Graham
Published: February 2007

Daily precipitation data from 121 sites for five autumn‐winter seasons (September to January, 1982–1983 to 1986–1987) have been analysed to determine discrete precipitation areas within Wales, using S‐mode principal components (PCA) and cluster analyses. Using unrotated PCA, much of the variation in daily precipitation is explained by the first five PCs, representing an accumulated variance of 75.7 per cent. The first four PCs appear to relate respectively to: altitude (60.8 per cent of the total variance explained), an exposure effect relative to north or north‐east winds (6.0 per cent), a ‘westerly exposure’ effect (4.2 per cent) and an ‘easterly exposure’ effect (2.9 per cent). The fifth PC, with high scores only over Ynys Mǒn and Gwent, could not be attributed to any particular influence. Oblique rotation produced a better simple structure, enhanced the apparent importance of exposure to wind from the main compass directions, but lessened that of altitude. Three methods of clustering PCs were subsequently tried on the Oblimin solution: centroid, median and Ward. The precipitation areas produced by each were broadly similar, and the boundaries between them often coincided with clear topographic units, influenced by exposure and shelter effects. The Ward technique yielded the areas best defined in terms of topography and exposure, and best satisfied criteria determined by the nature of the data themselves.
A method for classification of wind field patterns and its application to southern California
Authors: Green Mark C. , Myrup Leonard O. , Flocchini Robert G.
Published: February 2007

A method for classification of wind field patterns is described. The method forms groups of days having similar wind field patterns, including their diurnal variations. The expansion coefficients of the first eigenvector of an empirical orthogonal function analysis of the vector wind were used to determine if pairs of days are similar. A grouping procedure was then applied to form groups of similar days. Diurnally varying best‐fit wind fields were generated for each group of similar days, or types. The method was applied to southern California each season for a 2‐year period. Averaged mesoscale pressure and specific humidity fields were computed for each wind field pattern. Cause and effect relationships between the pressure, wind, and humidity fields in the complex topographic and meteorological setting are demonstrated.
Continentality: A basic climatic parameter re‐examined
Authors: Driscoll Dennis M. , Fong Juan M. Yee
Published: February 2007

Continentality, a basic control of climate, is difficult to quantify in terms of the factors that govern it. As a result, a chief consequence of continentality, annual range of temperature, has been used as a surrogate. Annual range, however, is determined primarily by seasonal variations in radiation receipts, and attempts at constructing continentality indexes have attempted to compensate for this variation by dividing annual range by the sine of the latitude. In so doing it has been assumed that the latitudinal variation of seasonal radiation increases monotonically with latitude. It is shown that this is not the case; thus, indexes of continentality based on this assumption are flawed.

A continentality index based not on annual range of temperature, but on residuals from the regression line of annual temperature range on latitude, is formulated. The result is a maximum of continentality in the location suggested by a qualitative look at the factors influencing it. Additional advantages to this approach are specified.
A five‐year climatology of elevated inversions at Hemsby (UK)
Authors: Milionis A. E. , Davies T. D.
Published: February 2007

Temperature inversions up to the 500‐mbar level are studied in 50‐mbar depth layers over Hemsby, in eastern England. The inversions are characterized by vertical gradients of temperature, potential temperature, dew point temperature, and depth. An inversion index, which is the product of potential temperature gradient and frequency of occurrence, is used. The zone of maximum activity for elevated inversions is 950–800 mbar, resulting from subsidence within anticyclones. A theoretical explanation of the processes is given. Inversion characteristics are essentially similar for day and night, except in the 1000–950‐mbar layer, where daytime frequency is greater. It is suggested that turbulence‐capping inversions and/or sea‐breeze effects may be the reason. The implications of elevated inversions for air pollution dispersion are discussed.
700‐HPA geopotential height anomalies from a statistical analysis of the French Hemis data set
Authors: And Sylvie Clinet , Martin Serge
Published: February 2007

The low‐frequency time variations of the Northern Hemisphere 700‐hPa heights have been investigated using the French Hemis grid‐point data set and a statistical model based upon an orthogonal rotated principal component analysis. The data consists of 389 10‐day means of geopotential height (from 1970 to 1980) distributed over an octagonal grid of 1977 points, poleward of 20°. The model summarizes the major modes of 700‐hPa height fluctuations; for each mode, it provides the corresponding spatial pattern and the associated time component.

Four seasonal analyses have been performed using 10‐day means. The major modes of the spatial anomaly structure are described in detail and are clearly identified for each season. The stability of these modes through the separate seasonal analyses is examined. The robustness of the resulting patterns is analysed through their consistency with results of other studies.
The suburban energy balance: Methodological considerations and results for a mid‐latitude west coast city under winter and spring conditions
Authors: Grimmond C. S. B.
Published: February 2007

Previous measurements of the urban energy balance primarily have been conducted in summertime. This paper reports the first extended set of winter‐spring‐time energy balance measurements for a city. The study was conducted in a suburb of Vancouver, British Columbia, from January to June 1987. It included hourly measurements of net all‐wave radiation, sensible heat flux and the Bowen ratio. The anthropogenic and storage heat fluxes were modelled. A dynamic source area model was employed to ensure the modelled parameters were consistent spatially with the measured turbulent fluxes. The winter‐spring urban energy balances observed in this study are different to those reported for summertime conditions at the same site. The fluxes for the entire period are not symmetrical about solar noon. Hence earlier interpretations possibly should be modified. Apart from this feature the spring season balances are similar to those reported for the summertime in terms of relative importance of individual fluxes. The wintertime energy balance appears to be different to that of spring and summer. The most noticeable feature is the increased importance of the latent heat flux, which on average is the largest output flux in the balance. A secondary, more expected feature, is the increased importance of anthropogenic heat flux as an input in winter.
Synoptic climatology of thermal low‐pressure systems over south‐western north America
Authors: Rowson David R. , Colucci Stephen J.
Published: February 2007

Analyses of closed‐isobar, non‐migratory, thermal low‐pressure frequencies are presented for an 11‐year period, 1974–1984, over the south‐western USA and north‐western Mexico. Average onset and breakdown dates, preferred locations, and the vertical extent of the system are presented. The effect of upper level (500 mbar) flow on the presence of the thermal low and relationships between the system and precipitation in Arizona and western Mexico also are investigated. The analyses suggest a preferred region for the formation and sustenance of the thermal low near the south‐west coast of the USA and the west coast of Mexico. Within this region exist two frequency maxima, centred over the desert regions of the American South‐west and north‐western Mexico and over the plateau highlands of the Sierra Madre Occidental. The system is most prevalent from mid‐June until mid‐September and reaches its maximum vertical extent near 700 mbar in July and early August. This variation may be attributed to the zenithal progression of the sun, although short‐term fluctuations in the strength of the system during the summer period probably are related to changes in cloud cover over the low. Specifically, precipitation in advance of 500‐mbar troughs passing to the north of the system appears to be associated with the weakening of the thermal low, suggesting a negative feedback relationship that deserves further investigation.
Rainfall changes in Africa: 1931–1960 to 1961–1990
Authors: Hulme Mike
Published: February 2007

It remains common for 1941–1970, or even 1931–1960, climatological rainfall normals to be used in applied climate studies in Africa. Often this is due simply to the easier availability of station means or rainfall maps for these periods. Such rainfall statistics, however, are unrepresentative of recent decades, especially the new World Meteorological Organization standard period, 1961–1990. In this paper two independent 30‐year rainfall climatologies for Africa are constructed from 572 quality controlled station time series of monthly rainfall. These climatologies are for the periods 1931–1960 and 1961–1990 and are constructed on a 5° grid. Differences between these two 30‐year periods are determined with respect to mean seasonal rainfall, interannual variability and rainfall seasonality. Latitudinal profiles of mean seasonal rainfall emphasize the dominance of reduced Sahelian rainfall in the rainfall changes occurring over this period. This decline in boreal summer rainfall is shown to be statistically significant using field comparison statistics. Annual time series of regional rainfall anomalies for the Sahel, East Africa and south‐western Africa are constructed; these three time series possess quite different interannual rainfall characteristics. Possible explanations for these observed rainfall changes are discussed with respect to land cover changes, global sea‐surface temperature patterns, and greenhouse gas forcing.
Precipitation events in the south‐east United States of America
Authors: Robinson Peter J. , Henderson Keith G.
Published: February 2007

A precipitation event climatology is defined as the frequency distributions of the number, duration, and precipitation amounts of individual rainfall events at an observing station. A preliminary analysis of hourly precipitation records for 27 stations in the south‐east United States of America for the 1958–1987 period indicates that the operational definition of an event is a period of continuously recorded precipitation separated from other such periods by a dry interval of 2 h or more. The choice of the 2‐h separation interval influences the climatological frequency distributions slightly, but maintains a distinction between convective and cyclonic systems. All south‐eastern stations displayed similar results, the average number of events varying from near 30 in autumn to about 40 in summer. Most events lasted less than 3 h and gave less than 0.2 in. of precipitation. The seasonal and spatial variations in results suggest close connections between the event climatology and the atmospheric circulation. Short‐duration storms suggestive of convective activity dominated in all seasons in Florida. To the north the winter maximum in durations and amounts indicated the importance of depression passage, while increased durations in all seasons over the Appalachian mountains reflected a topographic influence. A general region‐wide relationship between the number of events per season, the seasonal total precipitation, and the seasonal number of rain days was obtained, but the results varied greatly from station to station.
Validation of trends in the surface wind field over the Mozambique channel
Authors: Bigg Grant R.
Published: February 2007

The evolution of the atmospheric circulation over the Mozambique Channel over 1950–1987 is examined, using ship and land‐based pressure gradients as consistency checks on the surface wind field over the ocean. It is found that in the austral summer, when the Inter‐Tropical Convergence Zone crosses the region, the winds show little evidence of change. However, in the winter the prevailing southerly winds in the north of the channel show evidence in both pressure records and wind data of a significant strengthening.
18.6‐year luni‐solar nodal and 10–11‐year solar signals in rainfall in India
Authors: Mitra Kumares , Dutta S. N.
Published: February 2007

The 115 year (1871–1985) long, summer monsoonal rainfall data of ten macroregions (m‐r) of India have been subjected to maximum entropy spectral analysis (MESA). The results appear to indicate quasi‐periodic fluctuations in rainfall in eight and six m‐r, presumably corresponding to the 18.6–year luni‐solar nodal and 10–11‐year solar cycles respectively. The solar term in the remaining four m‐r appears to be split up into two components, as a result of spectral analysis. The filtered data, evidencing either or both of the signals in MESA, were then subjected to two band‐pass filters, centred at 19.0 and 10.5 years respectively. The derived rainfall waveforms are found to have some good phase relationships with the 18.6–year nodal and 10–11‐year solar cycles, when relatively free from meteorological disturbances. The luni‐solar rainfall waveforms in m‐r 2, 3 and 7 exhibit the phenomenon of a sudden 180° phase change in the early parts of the data series.
Interannual variability of surface climate in the Amazon basin
Authors: Marengo José A.
Published: February 2007

This empirical study examines the circulation mechanisms of anomalously wet and dry years in the Amazon basin. Data sources include surface ship observations in the tropical Atlantic, eastern Pacific, and Indian Oceans, as well as various hydrometeorological indices in Amazonia during 1951–1983. Rainfall and river water level anomalies in northern Amazonia are associated with distinct circulation patterns in the tropical Atlantic, particularly at the March–April peak of the rainy season. Thus, abundant rainfall in northern Amazonia and high Rio Negro water levels are accompanied by a strong North Atlantic high, steep meridional pressure gradient on its equatorward side, accelerated North‐east trades, and cool surface waters in the tropical North Atlantic. The intensified North‐east trades may entail enhanced boundary‐layer moisture transport from the tropical North Atlantic into the Amazon basin. This ensemble of atmospheric and oceanic anomalies is characteristic of, but not limited to, the high phase of the Southern Oscillation (defined by anomalously high/low pressure at Tahiti/Darwin).
A model‐based approach to the calculation of global warming potentials (GWP)
Authors: Rotmans J. , Den Elzen M. G. J.
Published: February 2007

The Global Warming Potential (GWP) of greenhouse gas emissions can be defined as a greenhouse pendant to the Ozone Depleting Potential (ODP). Global Warming Potentials are calculated for the most important greenhouse gases (CO2, CH4, CO, N2O, CFC‐11, CFC‐12, CFC‐13, CFC‐14, CFC‐113, CFC‐114, CFC‐115, CFC‐116, CF3Br, CCl4, CH3CCl3, and HCFC‐22) and eight potential CFC substitutes using the integrated climate assessment model IMAGE. Two different methods are presented for the calculation of GWP values using IMAGE: one that generates equivalent pulses for all greenhouse gases, and an iterative trace‐back method which calculates the different pulses required to achieve an identical global temperature increase for all greenhouse gases. In addition the influence of the emission scenario used is tested when determining GWPs; it is demonstrated that GWPs are indeed scenario‐dependent, so the choice of the underlying emission scenario is important. Finally, the GWPs calculated using these methods are compared with GWPs that have been published previously. It appears that our GWP estimates are substantially higher than the IPCC estimates, which can be explained by the fact that our carbon cycle model has a balanced global carbon budget. This results in lower projections of future atmospheric carbon dioxide compared with the IPCC projections.
The spatial organization of daily rainfall over Mallorca, Spain
Authors: Sumner Graham , Ramis Clemente , Guijarro José A.
Published: February 2007

Daily rainfall affinity areas are derived for the island of Mallorca using four years of data, and a 96 × 96 intersite correlation matrix. An initial visual impression of the nature of rainfall organization is afforded by the mapping of correlation links between sites. The Serra de Tramontana form a climatological as well as topographic barrier, producing a marked alignment in spatial rainfall occurrence in that part of the island. Elsewhere ‘core’ sites are identified, about which rainfall correlation is high for distances of up to 15 km. These centre on higher elevation locations in the Serra de Llevant and in the central area, and also the Palma and Campos coastal embayments. Use of rotated principal components and cluster analyses applied to the correlation matrices permits the division of the island into seven major rainfall areas. The uplands of the north‐west and east of the island provide clear units in terms of both exposure and altitude, and their general exposure to prevailing rain‐bearing winds appears important, whilst an urban effect due to Palma and clear sea‐breeze convergence effects near the centre of the island are also implied.
An analysis of Australian seasonal rainfall anomalies: 1950–1987. II: Temporal variability and teleconnection patterns
Authors: Drosdowsky Wasyl
Published: February 2007

A detailed examination of the variability of Australian district rainfall of seasonal time‐scales over the period 1950–1987 is described. In Part I, S‐ and T‐mode rotated principal component analysis (RPCA) was used to obtain a compressed representation of Australian district rainfall anomalies on seasonal time‐scales.

In this paper, the temporal variability of these spatial patterns is examined, and their relationship to some large‐scale circulation indices, such as the Southern Oscillation (SO) and Pittock's L index. The S‐mode components show large intercomponent correlations as a result of the rotation of the principal components, although much of this is due to a common relationship to the SO. The T‐mode components are less strongly interrelated and only the first two show large correlations with the SO. The relationship with the SO and the L index are consistent with previous studies. Spectral analysis shows that most components do not have any dominant periodicity. Two distinct biennial tendencies are identified; in the north‐east associated with the SO, and in the south‐east associated with the L index.

The large‐scale circulation anomalies associated with both the S‐ and T‐mode patterns are examined using the Comprehensive Ocean Atmosphere Data Set (COADS) and a network of rawindsonde stations over Australia and the South‐west Pacific. Three dominant teleconnection patterns are identified; the well‐known Southern Oscillation anomalies associated with the dominant T1 pattern of continental‐scale rainfall anomalies, a predominantly winter season Indonesian‐Indian Ocean pattern previously documented by Nicholls, and a spring/summer south Tasman Sea pattern. The evolution of these patterns is examined through composites, and the physical mechanisms for the initiation and maintenance of the anomaly patterns are discussed. In the latter two cases both the rainfall and SST anomalies appear to be driven by anomalies in the large‐scale mid‐latitude circulation.
Luni‐solar 18.6‐ and 10–11‐year solar cycle signals in South African rainfall
Authors: Currie Robert G.
Published: February 2007

Spectrum analysis of 59 South African rain‐gauge records yields evidence for two peaks with periods 18.2·1.4 years (57 out of 59 series covering virtually the entire country) and 10.3·0.5 years (in 37 series covering almost all except easternmost South Africa). They are identified as the luni‐solar 18.6‐year Mn and 10–11‐year solar cycle Sc signals in climate; their phases and amplitudes are non‐stationary with respect to both time and geography and, in particular, 180° phase changes in wave polarity are observed. These phase changes occurred in the early part of the century and by mid‐epochs 1964.0 and 1982.6 (mid‐epochs are dates of minimum in Mn tidal forcing) a unipolar cell of drought encompassed virtually the entire nation. Constructive interference by the Sc wave, which reached a minimum near 1981, exacerbated the droughts of mid‐epoch 1982.6 which were more severe than even those of the 1960s. The results confirm and extend in many respects those found by P. D. Tyson and his co‐workers in the 1970s.
The effect of coastline curvature on the weakening of atlantic tropical cyclones
Authors: Rogers Robert E. , Davis Robert E.
Published: February 2007

This study attempts to determine the relationship between the curvature of the coastline and the filling (increase in central pressure) of hurricanes and tropical storms by comparing both the rate of filling and the total filling for storms striking convex, concave, and linear coastlines. The USA and Mexican coastline was approximated by a subjective smoothing procedure, and the coastal curvature corresponding to each landfalling Atlantic tropical cyclone from 1900 to 1979 was measured and grouped into one of the three curvature categories. Storm‐filling rates and total amounts of filling were determined before and after landfall by computing the change in wind speed for various Saffir‐Simpson hurricane intensity categories. The averages of these variables within each strength and curvature grouping were compared in order to determine if they were statistically different. Storms were also compared in order to determine if stronger storms fill a greater total amount than weaker storms, regardless of the coastline's curvature.

Concave coasts were found to be associated with storms filling both more rapidly and by a greater amount than convex coasts for weak hurricanes and strong tropical storms, and they were associated with storms that filled by a greater amount for hurricanes of moderate strength. This most likely results from the lower water‐to‐land ratios associated with storms striking concave coasts and the reduction in latent and sensible heat fluxes from the surface. Also, stronger storms were found to fill more rapidly and by a greater total amount than weaker storms, and storms striking the East Coast generally filled more rapidly and by a greater total amount than storms striking the Gulf Coast or Florida.
Interannual variability of rainfall in the eastern horn of Africa and indicators of atmospheric circulation
Authors: Beltrando Gérard , Camberlin Pierre
Published: February 2007

Relationships between rainfall variations in the Eastern Horn of Africa, the Southern Oscillation, and the Indian Ocean temperature and pressure surface fields are studied for the period 1932–83. Rainfall data consist of stations and regional indices calculated for three selected areas experiencing quite different rainfall patterns. The results indicate significant negative correlations between northern autumn rains in Somalia and the Southern Oscillation during the same season. These rains are also negatively correlated with pressure in the Western Indian Ocean, and positively correlated in the Eastern Indian Ocean. The reverse pattern is shown with sea‐surface temperature. This agrees very well with the observations made in Kenya as far as the short rains of October‐November are concerned.

Central Ethiopia summer rains, in contrast, indicate significant positive correlations with the Southern Oscillation, at zero and 3 months lag. El Niño years often correspond to drought years in this region. Evidence of an inverse relationship between the amount of rainfall in Ethiopia during summer (especially during September) and both the pressure and sea temperature over the Indian Ocean is also given. Correlations with the Arabian Sea are particularly strong.

However, teleconnections between summer rains in Northern Ethiopia (Eritrea) and the ENSO or the Indian Ocean fields are much weaker.

These results suggest that, although summer rains over Ethiopia are said to be related to the monsoon air flow from the Congo Basin and the Atlantic Ocean, there also exist quite strong connections with the surface conditions prevailing in the Indian and Pacific Oceans.
Detection of trend or change in annual flow of Australian rivers
Authors: Chiew F. H. S. , McMahon T. A.
Published: February 2007

Changes in streamflow volumes resulting from climatic change can affect the management of water resources. However, the detection of a statistically significant trend can be difficult because of the large interannual variability and the relatively short period of instrumental record. In this paper, five statistical tests are applied to the historical annual streamflow series of 30 unregulated Australian rivers, located in protected natural catchments, in order to detect trends or changes in the means. The Student t‐statistic is also used to describe the relationship between interannual variability and the magnitude of change and length of data required to identify a statistically significant trend. The analysis indicates that, with the current data set, there is no clear evidence to suggest that the greenhouse effect is impacting on Australian streamflow volumes. The change required to identify a statistically significant change in the mean is directly proportional to the interannual variability, and less dependent on the length of data available. The interannual variability of Australian streams is twice that of Northern Hemisphere streams, therefore, a greater change is required in Australian flow volumes before a statistically significant change can be identified. The analysis of available historical records, however, indicates that statistically significant trends can be detected in the future flow volumes if the scenarios predicted by the G'CMs are realized.
Weather categorization based on the average linkage clustering technique: An application to European mid‐latitudes
Authors: Huth Radan , Nemesova Ivana , Klimperová Nina
Published: February 2007

The 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 weather types.
Variations of hemispheric zonal index since 1899 and its relationships with air temperature
Authors: Koźuchowski K. M.
Published: February 2007

Mean 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 over Europe has been also examined.
Monthly anticyclonicity and cyclonicity in the southern hemisphere; Averages for january, april, july, and october
Authors: Leighton R. M.
Published: February 2007

Geographical distribution across the Southern Hemisphere of 15‐year averages (23‐year averages in the Australian Region) of monthly anticyclonicity and cyclonicity as well as monthly anticyclone and cyclone immobility times, for the months of January, April, July and October for the years 1973–1987 (1965–1987 in the Australian Region) are presented in the form of maps.

Comparisons are made with an existing atmospheric climatology of the Southern Hemisphere by the National Climate Centre of the Bureau of Meteorology, Melbourne covering the period 1976–1990 calculated from numerical analyses and with relevant climatologies contained in the World Survey of Climatology. References are made to past works relating to the climatology of the Southern Hemisphere and synoptic features of the climatology are discussed.
Mapping temperature using kriging with external drift: Theory and an example from scotland
Authors: Hudson Gordon , Wackernagel Hans
Published: February 2007

Land suitability mapping requires information about climate, topography, and soils in relation to crop performance. Climatic data are available from recording stations which present point samples and so interpolation is needed to generate estimates for non‐sampled points. The annual temperature cycle must be interpolated differently for different land suitability projects. A common theme, however, is spatial interpolation and here we investigate the application of kriging with external drift to mapping January mean temperatures in Scotland. The spatial structure of the mean temperature is analysed using variograms computed in different directions. From these we see that January temperature is second‐order stationary in the north‐south direction. Hence the variogram exists in that direction and is taken to represent the underlying variogram. This variogram is modelled and used in universal kriging to produce point‐kriged estimates on a 5‐km square grid. These estimates do not adequately show the variation in temperature between stations and so the correlation with elevation was exploited in universal kriging with elevation as external drift. This method gives a kriged estimate for temperature that reproduces the correlation with elevation at the climate stations.