bluuebunny/crossref_metadata_2025 huggingface dataset:
Diurnally varying regional climatic simulations
Authors: Hunt B. G. , Gordon H. B.
Published: February 2007

A detailed analysis has been made of the atmospheric variability at a number of specific geographical points as simulated with a global general circulation model. The objective of this study was to assess the model's performance as regards diurnal and interdiurnal variability, but more importantly to identify critical features which should be monitored in climatic‐change experiments. Since the model contains a number of physical processes, including cloud forecasting, three independent rain‐producing mechanisms, a very responsive surface‐hydrology formulation, sea‐ice determination, etc., complex interactions among the various climatic components can occur. Results are presented for a number of longitudinal points at three selected latitudes, representative of summer, winter, and tropical conditions. One of the clearest features of the model output was the very marked longitudinal asymmetry in atmospheric forcing arising from land‐sea contrast. The vital role of the soil moisture, which depends critically on its model formulation, in determining whether this forcing is due to latent or sensible heating over the land is also demonstrated.

The unique diurnal variations which were simulated at individual geographical points suggest that systematic distortions must occur in most near‐surface processes in non‐diurnal models. The extreme sensitivity of the convective mechanisms and the consequent impact on rainfall is noted, together with its implications for experiments involving climatic change. Finally, the interdiurnal variability of the model is illustrated by a number of examples, one of which highlights the potential misrepresentation of air‐sea exchanges in models employing fixed sea‐surface temperatures.
Sahel drought: Meteorological or agricultural?
Authors: Agnew C. T.
Published: February 2007

Meteorological definitions of drought are deemed to reveal little of the effects of water deficiencies upon the inhabitants of arid regions. An agricultural definition of drought is obtained using a water‐balance model of the moisture available to millet (Pennisetum typhoides).The model accepts inputs of rainfall, potential evapotranspiration, and crop development for 5‐day periods. Values for field capacity, wilting point, bulk density, crop coefficients, and rooting depth are obtained, and changes in soil moisture, actual evapotranspiration, and drainage are computed. The resulting seasonal millet moisture deficits are mapped for ‘millet drought’ in Niger from 1967 to 1978. These maps indicate that for traditional areas of millet cultivation, ‘millet drought’ was a rare event during the 1970s, but was common and widespread in the more northerly, marginal lands.
Heavy rainfalls over East Asia
Authors: Matsumoto Jun
Published: February 2007

The mean annual and monthly frequency distribution of heavy rainfalls for the period 1971–1980 are investigated over the whole of East Asia, including Japan, China, Korea, USSR, and Hong Kong. The highest frequency region (< 10 times per year) is shown to be located along the southern coast of Japan. The second highest region (< 8 times per year) is located along the southern coast of China. The high‐frequency area advances northward over China during the summer monsoon season, in accordance with the northward advance of the ‘Mei‐yü frontal zone’. Maps of the axes of high‐frequency heavy rainfall areas (frequency per 10‐day period) and of maximum‐frequency 10‐day periods at each station, clearly reveal the intra‐seasonal shift of the heavy rainfall area during the summer monsoon season.

According to the dominant causes of heavy rainfalls, four regions are identified. The investigated area is also divided into three regions (I‐III) with respect to the annual frequency distribution of heavy rainfalls. Based on these regional divisions, the northern limit of the influence of the ‘Mei‐yü front’ is determined in terms of heavy rainfall occurrence.
Morphology of bistable 180° phase switches in 18.6‐year induced rainfall over the north‐eastern United States of America
Authors: Currie Robert G. , O'Brien Douglas P.
Published: February 2007

Using a novel data presentation technique, bistable 180° phase switches in 18.6‐year induced precipitation over the northeastern United States of America are re‐examined. It is found that bistable switching in 19‐year wavetrains occurred principally at epochs 1898–9, 1917.5, and 1954.7, although some occurred at mid‐epoch 1908–2, and at epochs 1936.1 and 1973.3 (epochs are dates of maximum in the luni‐solar 18.6‐year tide). The 180° phase switch at 1898.9 occurred along the northern Atlantic seaboard, and by epoch 1954.7 this invading ‘cell’ from the east blanketed virtually the entire region. O'Brien and Currie (1988) have provided a construct in mathematical physics which can explain how such sudden readjustments in the standing wave pattern for air pressure occur on subcontinental scales, and such adjustments are found in other climatic parameters such as air temperature and pressure. Results for seven tree‐ring chronologies in the region are also given, and are found to have serious inconsistencies both among themselves and also with respect to instrumental rain‐gauge data.
A five‐year radar climatology of convective precipitation for New Jersey
Authors: Croft Paul J. , Shulman Mark D.
Published: February 2007

A radar climatology of convective precipitation for New Jersey during the summer season (May‐September) was developed using manually digitized radar (MDR) data from four local radar sites. Convective precipitation frequencies were determined by tabulating occurrences of echo intensity levels equal to 2 or more for each of 63 grid boxes located in and around New Jersey. Convective precipitation frequencies over a 5‐year period (1978–1982) were plotted by grid box, and isopleths of duration and intensity level were constructed. The distribution of the frequency of occurrence of convective activity was examined for thunderstorm (level 3 or more) occurrence and severe thunderstorm (level 5 or more) occurrence. The highest convective frequencies occurred over south‐eastern Pennsylvania while the greatest frequency of more intense convection occurred over south‐central New Jersey. An analysis of variance (ANOVA) was performed on the data set to determine the relative variability of convective precipitation in the grid. Year‐to‐year and week‐to‐week variability was high whilst intergrid‐box variability was low. Duncan's multiple range test (DMRT) was applied to compare individual years to each other, and individual weeks to each other. When grid boxes were assigned to four climatological regions and DMRT applied, some regions were found to be significantly different from one another. No significant differences were found between grid boxes within each region. There was no interaction between grid regions and years as differences in mean convective activity between regions remained generally constant from year to year. The distribution of convective activity over New Jersey was found to be determined by local climatological factors while the total frequency from year to year was determined by the mean synoptic pattern.
Reconstruction of New Zealand summer temperatures to 1730 ad using dendroclimatic techniques
Authors: Norton D. A. , Briffa K. R. , Salinger M. J.
Published: February 2007

The first statistically calibrated and verified reconstructions of past New Zealand temperatures are presented. The reconstructions of summer (December‐March) temperature are derived from a grid of ten subalpine Nothofagus menziesii (Hook. f.) Oerst. and N. solandri (Hook. f.) Oerst. tree‐ring chronologies using dendroclimatological techniques. A regression model where climate in year i is estimated as a function of tree growth in years i−1, i and i + 1 for each chronology is used. Two reconstruction models are developed (for 1853–1915 AD and 1916–1979 AD) and account for 55 per cent and 66 per cent of the temperature variance respectively. Verification of these models accounts for 34 per cent and 42 per cent of the temperature variance over an independent time period. Analysis of the spectral properties of the reconstructions indicates that relatively short‐period variability (<30 years) is better reconstructed than is longer period variability (>60 years). The reconstructions, extending back to 1730 AD, provide statistically reliable estimates of annual to decadal temperature variations. The relative coolness of the 1780s and late 1840s and warmth of the 1750s appear to be notable features of the reconstruction. The reconstructions indicate a far more complicated sequence of palaeotemperature variations than have previously been inferred for New Zealand.
Ocean‐atmosphere interactions in low‐latitude Australasia
Authors: Allan Robert J. , Pariwono John I.
Published: February 2007

An analysis of ocean‐atmosphere interactions in low‐latitude Australasia is undertaken using simultaneous and lagged cross correlations and with reference to specific El NiñTo/Southern Oscillation (ENSO) and anti‐ENSO episodes during the period 1964–1983. Major emphasis is placed on the relative importance of wind‐stress‐sea‐surface‐temperature (SST) mechanisms and cloudiness‐radiation mechanisms, and the possible influence of SST advection, oceanic mixing, Indonesian throughflow, and low‐frequency forcings on ocean‐atmosphere couplings in the region.

The evolution of ENSO events in Australasia is usually marked by a distinct alternation from anti‐ENSO to ENSO conditions. Ocean‐atmosphere dynamics, involving primarily wind and radiative forcings, have been seen to be linked to such developments. However, SST advection and oceanic mixing are also found to play integral roles in forcing and feedback processes. Thus anti‐ENSO (ENSO) events are marked by easterly (westerly) wind‐stress anomalies in the western equatorial Pacific, southerly (northerly) wind‐stress anomalies in eastern Indonesian and eastern Coral Sea regions, +(−)SST anomalies and weak (strong) SST advection in northern Australian waters, positive (negative) cloudiness anomalies over Australasia and high (low) sea‐level anomalies at southern Philippine and northern Australian stations. There are also indications that ENSO‐like conditions can develop in Australasia with no apparent events in the wider Pacific basin. However, there seems to be no conclusive evidence for the influence of oceanic throughflow on ocean‐atmosphere interactions, and thus ENSO or anti‐ENSO phases. Nevertheless, there are indications that Indonesian throughflow is modulated by remote low‐frequency forcings that are also apparent in SST anomalies in northern Australian waters.

The potential for precursors of ENSO and anti‐ENSO events in the Australasian region is high. All of the parameters examined in this study show significant lead/lag correlations, with the strongest persistence generally centering on the Southern Hemisphere winter‐spring period.

However, further investigation of potential and suggested links with coherent precipitation patterns over the region is still required. Moreover, any future developments in our understanding of ocean–atmosphere interactions in Australasia will need to address the general problem of establishing and maintaining extensive data networks.
The influence of long‐range transport of air pollutants on summer visibility at Dublin
Authors: Leavey Maurice , Sweeney John
Published: February 2007

Photochemical air pollution has recently been identified as a European as well as North American phenomenon. This paper examines periods of visibility reduction at Dublin Airport and suggests that summer hazes are associated with long‐range transport of pollutants from continental and British sources. Back trajectory analyses of air masses during a number of episodes appear to imply that transport beneath a stable, inverted layer may occur in certain meteorological circumstances, particularly involving passage over a cool sea surface. Major donor areas are probably in the Paris Basin, Ruhr, Low Countries, the English Midlands and London area.
A contribution to the study of action centres in the North Atlantic
Authors: Sahsamanoglou H. S.
Published: February 2007

The North Atlantic High appears notably weakened from the beginning of the examined period (1873–1980) until the beginning of this century. From then until 1930, it exhibits an increased central pressure. From the beginning of the period until 1914, the North Atlantic High exhibits a significant trend of intensification and at the same time a trend of displacement to the west. From 1915 until 1963 it exhibits a trend of weakening and a trend of eastward displacement. The North Atlantic Low has not exhibited a significant trend of its central pressure, but it has shown a small trend of displacement to the west. There is generally a negative correlation between the pressures of these two centres of action and a positive correlation between latitudinal position of the centres. The meridional component of the pressure gradient created between the two action centres, appears to have low values during epochs of low frequency of westerlies and high values when the westerlies are more frequent.
The role of radiation geometry in the climate response of Mount Kenya's glaciers, part 3: The latitude effect
Authors: Kruss Phillip D. , Hastenrath Stefan
Published: February 2007

Two earlier papers in this series investigated the role of solar radiation geometry in defining the glacier climate of Mount Kenya from the references of both horizontal and sloping surfaces. The present study examines the effect of latitude through a series of model simulations for clear‐sky conditions. This study answers the question about whether sloping or horizontal surfaces are the most appropriate for climatic heat and mass budget studies of glaciers throughout the region from 0° to 60° latitude, and also investigates, in quantitative terms, the latitude‐forced changes in radiation amount reaching high mountain glaciers owing to geometry effects. While preserving mountain topography, calculations were performed successively for the Equator, 15°, 30°, 45°, and 60°N and S. For the mountain as a whole, values tend to be larger for horizontal than for sloping surfaces, except for the domains poleward of 45° latitude. The altitudinal variation of radiation is, for the true equatorial location of Mount Kenya, characterized by an overall decrease upward, for both horizontal and sloping surfaces, as a consequence of the topographic obstruction increasing from the peripheral towards the central higher portions of the mountain. The altitudinal pattern changes with latitude, such that at 60°N radiation increases towards higher elevation bands, which are better exposed when solar elevation angles are low. Similar to results for the complete mountain, for the extremely steep southward facing Diamond Glacier, radiation drops off from the Equator towards the higher latitudes of the Southern Hemisphere, with values smaller for sloping than for horizontal surfaces. In the Northern Hemisphere, by contrast, the Diamond Glacier surface is most favourably oriented for radiation around 30–45°N. The latitude effect on the mountain climate is moderate within the tropical belt, while substantially different radiation characteristics result with a shift to high latitudes. Overall it is found that the use of a horizontal reference surface is as good an approximation, and typically an even more acceptable one, at higher latitudes than at the Equator. This is not so for only the steepest of glaciers.
Mixed analog/persistence prediction of seasonal mean temperatures for the USA
Authors: Livezey Robert E. , Barnston Anthony G. , Neumeister Brian K.
Published: February 2007

The operational analog prediction system used as input to official USA seasonal temperature category forecasts was modified to produce anomaly forecasts instead of most probable class forecasts. These modified forecasts led to more conservative predictions, but were more reliable for above‐and below‐normal classes. They were subsequently combined with persistence forecasts in a variety of objective ways in the hope of producing forecasts more skilful than either input. Several versions of two basic mixing approaches, bivariate linear regression and persistence plus analog‐predicted change, were tried. All combined schemes were, overall, more skilful than either of the component schemes. Bivariate linear regression slightly outperformed persistence plus analog‐predicted trend. The former was most skilful when use of the regression forecast was limited to cases where the regression coefficient for the analog term was positive and significance tests were passed at least to a minimal extent in a cross‐validated examination of the regression equation.
Convection and rainfall over Mexico and their modulation by the Southern Oscillation
Authors: Cavazos Tereza , Hastenrath Stefan
Published: February 2007

The role of the Southern Oscillation (SO) in the interannual variability of convection and rainfall over Mexico is studied by correlation analysis of long‐term precipitation records, a satellite‐derived set of highly reflective clouds (HRC), upper‐air soundings, surface ship observations, and an SO index defined as high for anomalously high low pressure at Tahiti/Darwin.

Highly reflective clouds and rainfall have a similar annual cycle and interannual variability, except in certain regions and seasons with prevalence of stratiform cloudiness. During the boreal winter (November‐April) dry season, the low SO phase (or El NiñMo) is, in much of the country, characterized by increased precipitation associated with the enhanced influence of mid‐latitude westerlies. However, in the Isthmus of Tehuantepec, most exposed to Norte invasions, precipitation is larger in the high SO phase. During the boreal summer (May‐October) rainy season, precipitation is more abundant in the high SO phase, when the northward retraction of the North Atlantic High, weaker trades, and a northward displaced near‐equatorial trough are conducive to enhanced ascending motion over the area.
Analysis of the Kuwait city urban heat island
Authors: Nasrallah Hassan A. , Brazel Anthony J. , Balling Robert C.
Published: February 2007

Twenty‐three years of maximum and minimum air temperature data are analysed for selected stations in and near Kuwait City, Kuwait. The results of a series of statistical analyses reveal the general lack of a well‐developed heat island in this rapidly expanding urban area. This finding is in stark contrast to the identification of large heat islands in the growing arid‐land cities of North America. The similarities in the urban‐rural landscape of the Kuwait City environment and its close proximity to a large water body are suggested as explanations for the observed temporal and spatial temperature patterns.
Low‐latitude volcanic eruptions and the El Niñmo/Southern Oscillation: A reply
Authors: Nicholls N.
Published: February 2007

The Handler‐Andsager hypothesis that low‐latitude eruptions are the “only cause” of El NiñMo events is tested by examining El NiñMo events and low‐latitude eruptions case‐by‐case. This examination confirms that low‐latitude eruptions are not the only cause, or probably even a cause of El NiñMo events. The Handler‐Andsager hypothesis can, at best, account for about one quarter of the El NiñMo events of the past fifty years, and none of the strong events. There is conclusive evidence from stratospheric data that at least some El NiñMo events were not caused by low‐latitude eruptions. Some of the eruptions composited by Handler and Andsager occurred after the start of El NiñMo events and could not, therefore, be the cause of these events. The case‐by‐case examination reveals the dangers of uncritical acceptance of composites.
The CFC greenhouse potential of scenarios possible under the montreal protocol
Authors: Bach Wilfrid , Jain Atul K.
Published: February 2007

Measurement campaigns have given concrete evidence of serious ozone destruction both over the Antarctic and the Arctic regions. This has spawned international action for the protection of the ozone layer, such as the Vienna Convention in 1985 and the Montreal Protocol in 1987. Current chlorofluorocarbon (CFC) reduction plans are, however, inadequate. Therefore, a strengthening of the Protocol's provisions is intended for 1990. The urgency of the Protocol's revision gains strength by the fact that the ozone depleting CFCs have also a strong greenhouse potential, thereby contributing significantly to climatic change.

In this paper we consider five CFC production and emission scenarios (scenarios A‐E) that are possible under the Protocol's provisions, and two phase‐out scenarios by 2000 and 1996, respectively (scenarios F and G). The possible global mean surface temperature changes are calculated with the parameterized form of a one‐dimensional radiative‐convective model from 1986 to 2050 for the five CFCs (11, 12, 113, 114, and 115) controlled by the Protocol, eight additional CFCs, some of which could be used as possible substitutes, and the main greenhouse gases CO2, CH4, N2O. The key findings are as follows. Without control, in 2050 the equilibrium global mean warming due to the five CFCs could rise sixteen fold above the 1985 vulue. The present Protocol provisions would still permit two to nine times higher equilibrium temperatures than today. A phase‐out by 2000 and 1996 would, over the period of 1986–2050, result in a reduction from the present equilibrium temperature change of 9 and 18 per cent, respectively. In addition, the other CFCs (e.g. CCl4, CH3CCl3, HFC‐22) may add significantly to global warming and thus should also be controlled. The high greenhouse warming potential provides another strong motive for the necessity of a phase‐out of all ozone‐depleting CFCs.
Decadal‐scale changes of the circulation in the tropical atlantic sector associated with Sahel drought
Authors: Hastenrath Stefan
Published: February 2007

Trends in the general circulation setting during 1948–1983 accompanying the progressive aggravation of drought in sub‐Saharan Africa are investigated from ship observations over the tropical Atlantic and surface station records in western Africa.

Decadal‐scale circulation changes in the Atlantic sector include a pressure rise over the tropical North Atlantic; southward displacement of the near‐equatorial wind confluence and associated maximum cloud belt; acceleration of the north‐east trades and possibly a strengthening of the South Atlantic trades, along with increasing cloudiness in the equatorial zone; increasing cloudiness over the tropical North Atlantic and Central American seas; and cooling of surface waters in a band across the tropical North Atlantic contrasting with warming in the South Atlantic. These changes occurred in all seasons, but were most pronounced at the height of boreal summer.

Records at land stations in western Africa show that near the coasts the temperature and pressure trends are consistent with the adjacent ocean areas. In the interior of sub‐Saharan Africa, warming trends prevail in boreal summer, presumably as a direct consequence of reduced inflow of cool maritime monsoon air; the concomitant downward pressure trends at continental stations in sub‐Saharan Africa may reflect the hydrostatic effect of increasing temperature. In contrast to boreal summer, slight cooling trends and pressure rises prevail in the interior during winter.

In the course of the past four decades, the near‐equatorial wind confluence over the eastern Atlantic migrated southward by 200 km in July–August and 150 km for the rainy season as a whole. Given the steep meridional precipitation gradients across the Sahel, these circulation shifts are large enough to account for the observed downward trend in Sahel rainfall.
Regionalization and spatial estimation of ethiopian mean annual rainfall
Authors: Eklundh Lars , Pilesjö Petter
Published: February 2007

This study aims at developing methods that will lead to the generation of a reliable mean annual precipitation data base for Ethiopia. Multiple regression models have been formulated that explain the mean annual rainfall as a function of elevation and geographical location. The estimations, based on yearly values from a data set of 63 Ethiopian rainfall stations with records between 1969 and 1985, were developed for the whole country as well as for the already existing Food and Agricultural Organization (FAO) rainfall pattern regions and a new zonation derived by principal component and common factor analyses (PCA/CFA). In the PCA/CFA study, monthly rainfall values between 1968 and 1985 for 43 stations were used. The optimal zonation was derived by testing 36 different combinations resulting in different rainfall pattern regions. The alternatives tested were: correlation and covariance dispersion matrices, PCA and CFA eigentechni‐ques, unrotated and rotated (Varimax and Direct Oblimin) components/factors and number of possible significant components/factors (3, 7, and 11). Principal component analysis of covariance matrix, Varimax rotation and seven extracted components gave by far the best relationship between mean annual rainfall, elevation, and geographical location. Models explaining at least 72 per cent of the variation in rainfall were constructed for regions covering about 98 per cent of the country, which is better than models based on the FAO rainfall pattern regions (69 per cent explained variation for 81 per cent of the country) and a model for the whole country (66·5 per cent explained variation).
Principal component analysis of the Lamb Catalogue of Daily Weather Types: Part 2, seasonal frequencies and update to 1987
Authors: Briffa K. R. , Jones P. D. , Kelly P. M.
Published: February 2007

Principal component analysis is applied to seasonal weather‐type frequencies from the Lamb Catalogue of Daily Weather Types for the British Isles. Four combinations of the major weather types are identified, which represent around 70 per cent of the variance of the data set. Long‐term trends in the seasonal principal component time series are described and relationships with temperature and precipitation are identified.

It is shown that a pronounced change in the character of the synoptic circulation over the British Isles has occurred in recent decades. A decline in the frequency of westerly weather types has been compensated for by an increase in the frequency of pure cyclonic and anticyclonic types and, dependent on season, directional types. This development suggests greater variability in the atmospheric circulation and related climatic parameters. The westerly decline has not been as marked in autumn. In this season, though, there has been a notable shift towards greater southerliness at the expense of northerly weather types.
Climatological contingency probabilities of clouds
Authors: Goodman A. H. , Henderson‐Sellers A. , McGuffie K.
Published: February 2007

The ideas surrounding contingency co‐occurrence probabilities of cloud types are discussed with respect to two types of probability: firstly, that given a lower level cloud (L) there is also an upper level cloud (U), P(L ⇒ U), and secondly the probability that given an upper cloud layer there is a lower cloud layer, P(U ⇒ L). Particular emphasis is placed on the fact that analyses to date have considered the frequency of observation of co‐occurrence, not, the potentially more useful, coexistence probability. From four separate months of global surface observations the P(L ⇒ U) was calculated as a function of lower level cloud amount on a global, regional, and individual station basis for (i) stratiform and altiform and (ii) stratiform and cirriform cloud type combinations. Global patterns of P(L ⇒ U) behaviour are somewhat similar to regional patterns produced by previous work and are, on occasions, reproducible on a regional scale and, in some instances, by individual stations. Values of P(L ⇒ U) involving lower level overcasts are required in the calculation of the P(U ⇒ L) term, thus rendering climatological estimates of P(U ⇒ L) susceptible to biasing if an inappropriate value of P(L ⇒ U) for L = overcast is chosen. To demonstrate this effect, monthly global climatologies of P(U ⇒ L) were generated for several combinations of upper and lower cloud types using (i) an assumed mean value for the overcast case and (ii) a modification to the previously assumed overcast P(L ⇒ U) values, as suggested here. Comparison of these climatologies revealed differences, widely spread across the globe, of mostly within ± 10 per cent according to cloud type, but with a few larger changes in excess of 30 per cent.
Climatic classification for queensland using multivariate statistical techniques
Authors: Puvaneswaran Manickam
Published: February 2007

An array of 28 climatic variables for 113 stations in Queensland, Australia, is subjected to factor analysis and cluster analysis. The factor analytical approach elucidated three major factors, a humidity factor, a temperature factor, and a rainfall factor, from the matrix. Spatial variation of factor scores was described and linear equations were compiled using the factor loadings that are significant. By grouping these factor scores with the aid of a distance‐grouping technique, Queensland was classified into three major homogeneous climatic regions. A further 12 subclimatic regions have also been identified. These regions were compared with Koppen's classification scheme.
Drought over Zimbabwe in a regional and global context
Authors: Matarira Caxton H.
Published: February 2007

This study attempts to identify meteorological conditions that lead to dry and wet episodes over Zimbabwe. Correlation analyses are carried out between the Southern Oscillation Index and rainfall over south‐eastern central Africa. The results show significant correlation between the Southern Oscillation (SO) and seasonal rainfall over the region. The results also indicate that the SO signal is stronger over the south‐east of Zimbabwe and along the coastal areas of Mozambique. El NiñTo events seem to be associated with below normal rainfall over Zimbabwe, while cold events, which are the opposite extreme of the SO, are accompanied by above average rainfall.

Three‐month seasonal (December–February) deviations of 1000–mbar temperature, surface pressure, and the 500‐mbar geopotential height from the long‐term mean are analysed during wet and drought years. The anomaly pressure gradient force is directed towards the subcontinent during wet periods and towards the ocean area during dry episodes. A similar pattern is observed at the 500‐mbar level.

A comparison of wet and dry seasons in relation to the temperature anomaly field points to an association between warmer 1000‐mbar surface temperatures around the African subcontinent and above normal seasonal rainfall. Correlation analysis shows that a high incidence of tropical cyclones in the Mozambique Channel is associated with below normal rainfall over Zimbabwe.
Regionality and periodicity observed in rainfall variations of the baiu season over Japan
Authors: Murata Akihiko
Published: February 2007

The regionality of rainfall variations of the Baiu, a rainy season over Japan, is investigated with special reference to periodicity. Using the Varimax rotated principal component analysis (PCA), Japan is divided into eight regions based on natural‐logarithm‐transformed rainfall data of June. In order to find significant rainfall variations from a sequence of rainfall data in each region, non‐rotated PCA is applied to the rainfall data for each region. Its first component score is defined as the rainfall variation index (RVI). Four regions show statistically significant periodicities of 10, 8, 4, or 2·2 years in rainfall variations. In addition, the rainfall variations reveal a similarity in the general shapes of spectral density for each region. The temporal variations of each periodicity show non‐stationary changes. This feature is especially distinct for periodicities at 4 and 2·2 years. From the results of squared coherence, it is pointed out that these periodicities are closely related to variations of the North Pacific High and the Okhotsk High. In the discussion, the validity of the regional division proposed in the present study is confirmed in comparison with other studies. Seasonal representativity of monthly rainfall variations is also discussed.
Historical evidence for Southern Oscillation‐southern African rainfall relationships
Authors: Lindesay J. A. , Vogel C. H.
Published: February 2007

Summer rainfall over the central area of southern Africa is known to be modulated with the phase changes of the Southern Oscillation such that rainfall is above normal during high‐phase (cold event) and below normal during low‐phase (warm event) summers. This relationship holds for the period 1935–1986; the temporal stability of Southern Oscillation–southern African rainfall associations on longer time‐scales has not been tested. A documentary‐derived rainfall chronology has been developed for the southern parts of the summer rainfall area for the 100‐year period 1820–1920, enabling the extension of the rainfall record backward some 60 years before reliable meteorological records are available for the region. Comparison of the documentary series with both early Southern Oscillation chronologies and earliest southern African rainfall records suggests that the nature of the relationship between summer rainfall over the subcontinent and the Southern Oscillation has remained essentially unaltered since at least 1820.
An ice‐cover climatology for lake erie and lake superior for the winter seasons 1897–1898 to 1982–1983
Authors: Assel Aymond A.
Published: February 2007

Observations of mid‐lake Great Lakes ice cover are sparse prior to the decade of the 1960s. In an effort to provide an historical perspective of mid‐lake ice cover back to the turn of the century, daily average ice cover for Lakes Erie and Superior over 86 winters (1897–1898 to 1982–1983) was reconstructed using empirical‐statistical ice‐cover models developed in an earlier study. Long term average maximal monthly ice cover occurs in February and is 68 per cent for Lake Erie and 40 per cent for Lake Superior. Mid‐lake ice formation occurs about 1 month earlier on both lakes during severe winters. Average maximal monthly ice cover during severe and during mild winters is 95 per cent and 14 per cent for Lake Erie, 87 per cent and 17 per cent for Lake Superior. Severe winters are associated with lower 700‐mbar heights over the eastern USA compared with mild ice‐cover winters. Analysis of total winter ice cover indicates three ice cover regimes: (i) a high ice‐cover regime from the late 1890s to early 1920s; (ii) a low ice‐cover regime from the early 1920s to late 1950s; and (iii) a high ice‐cover regime from the late 1950s to the early 1980s. Ice‐cover climatologies developed during the 1960s and 1970s are not representative of ice covers in the low ice‐cover regime of the 1920s to late 1950s. Spectral analysis of the reconstructed total winter ice cover suggests interannual variations in ice cycles that correspond with the 2–3‐year interannual variation in atmospheric variables known as the quasi‐biennial oscillation.
Dust storms in the Canadian Prairies
Authors: Wheaton E. E. , Chakravarti A. K.
Published: February 2007

Although dust storms are quite frequent in the Canadian Prairies, no scientific studies of the nature of dust storms of this area exist, to the authors' knowledge. This work is a preliminary step in depicting temporal and spatial variations of dust storms in the Canadian Prairies. Dust storms occur at least once to as often as five times per year, on average, in the agricultural prairies. This frequency indicates the risk of occurrence of the various impacts of dust storms, such as serious soil erosion. Dust storm frequencies exhibit a pronounced peak in the spring and a weak secondary peak in August. The spatial pattern of dust storms indicates a low risk of occurrence in the northern agricultural prairies and the highest risk in the south central prairies. Knowledge of these patterns in space and time should facilitate the control or avoidance of such impacts of dust storms as wind erosion of soils, crop damage, air pollution, and general environmental degradation. Studies should be carried out to further investigate the relationships of climatic factors with dust storms as well as their linkages with other environmental aspects.
Spatial patterns of drought frequency and duration in the contiguous USA based on multiple drought event definitions
Authors: Soulé Peter T.
Published: February 2007

This study examines patterns of drought frequency and duration in the contiguous USA based on multiple definitions of drought events. Patterns are examined using data from the three Palmer indices: monthly moisture anomaly index (ZINX), drought severity index (PDSI), and hydrologic drought index (PHDI). The data span a 94‐year period and are spatially aggregated to the climatic division level. The stimulus for this study is the lack of systematic examination of the possibility of varying spatial patterns of drought frequency and duration among the drought types represented by these indices.

Isoline maps of mean drought frequency indicate that the index used to define a drought has a major impact on the spatial patterns. Patterns identified using the monthly moisture anomaly index are nearly inverse of those for the drought severity and hydrologic drought indices. Patterns of drought duration also vary among the indices, although previous findings of greater drought persistence in the interior regions of the USA were upheld by all three indices. Results also indicate that varying the parameters (intensity, minimum duration) of an index‐specific drought event definition has a minor impact only on the spatial patterns.
Studies of surface energy balance of sloping terrain
Authors: Oliver H. R.
Published: February 2007

Measurements of radiation and soil energy balance components were made for a complete solar season on a south and north facing slope on the edge of the Chilterns, England.

The contrasts between the two slopes are illustrated on both the diurnal and seasonal time‐scale. It is shown that a consistent relationship exists between daily solar and net radiation totals for the slopes throughout the year but that soil heat flux cannot be modelled easily. Further, it is shown that it is possible to derive a simple model of solar radiation on to a slope from measurements made on the horizontal.

Combining these conclusions points the way towards simple routine calculation of slope radiation balances for use in energy and evaporation models over undulating terrain.
Rainfall characteristics of Mainland Europe's most southerly stations
Authors: Wheeler Dennis , Martin‐Vide Javier
Published: February 2007

The rainfall in the far south of Spain is well represented by the records of Tarifa and Gibraltar, the latter being of unusual length. The complex interplay of locational and climatological elements singles out the region's climate as one of particular interest. Cyclic patterns in the record are examined, revealing evidence of periodicities of different frequencies.
Australian rainfall trends during the twentieth century
Authors: Nicholls Neville , Lavery Beth
Published: February 2007

A set of high‐quality rainfall records is used to examine rainfall trends over Australia during the twentieth century. The 191 stations used have been selected by an exhaustive search of documentation regarding instrumentation, observational practices, site relocations, and exposure. Statistical tests of the reliability of observing practices also have been applied in the selection process, as well as tests to detect inhomogeneities. The data set used is the most reliable available for monitoring rainfall trends during the twentieth century. The data have been clustered objectively into groups exhibiting similar variations in annual rainfall. A subset of 10 stations (one for each cluster) suitable for long‐term monitoring of rainfall trends is selected. The trends in annual, winter, and summer rainfall are exhibited. The study confirms trends noted in earlier studies. Summer rainfall over much of eastern Australia increased abruptly around 1950. In the south‐west of the continent most stations recorded a smoother trend to lower winter rainfall, although there is a small area with increased rainfall. The identification of these trends in this study indicates that they are not the result of unreliable observations or to doubtful compositing of stations into groups. These trends have now continued for some decades after their initial observation. It is possible, however, that the twentieth century trends simply reflect a return to conditions of the late nineteenth century, rather than a trend that could be unambiguously attributed to an enhanced ‘greenhouse effect’.
Contrasting meteorological structure of intra‐seasonal wet and dry spells in Zimbabwe
Authors: Matarira Caxton H. , Jury Mark R.
Published: February 2007

The meteorological structure of contrasting wet and dry spells in Zimbabwe, south‐east Africa is studied using European Centre for Medium Range Weather Forecasts composites. Diagnostic examination of composite synoptic‐scale features indicates that lower northerly and upper easterly flow is enhanced during wet spells, corresponding with a tropical low over Zambia and an anticyclone off the south‐east coast of Africa, respectively. Dry spells exhibit an increase in mid‐latitude cyclones off the south‐west coast of Africa and tropical cyclones near Madagascar. Mid‐tropospheric troughs are located over the east and west coasts of Africa near 25°S and serve to increase anticyclonic vorticity over Zimbabwe in dry spells. Specific humidity fields reveal that the maximum shifts southward 5° and eastward 10° in the wet spells. Cyclonic vorticity and low geopotential heights occur on two or three days in the wet spell, coincident with intense cumulus convection and high rain rates. The eddy covariances of zonal wind and specific humidity are dominated by westward (eastward) fluxes in wet (dry) spells; while poleward moisture fluxes contributed by transient eddies are largest over the south Mozambique Channel (south‐east Atlantic) in wet (dry) spells. The eddy fluxes are shifted 15–20° longitude eastward in the wet spells. The relative contribution of thermodynamic and kinematic inputs are evaluated in the mean flows and transient eddies for contrasting wet and dry spells. Much of the difference between wet and dry spells is explained by the mean flow, while the transient flux in the mid‐latitudes assumes a subordinate role.
Spatial and subseasonal patterns of the long‐term trends of Indian summer monsoon rainfall
Authors: Kumar K. Rupa , Pant G. B. , Parthasarathy B. , Sontakke N. A.
Published: February 2007

Long‐term changes in the Indian monsoon rainfall on regional and local scales have important social and economic consequences. To present a comprehensive picture of such changes, the monthly rainfall data at 306 stations, well spread over India, have been analysed over 114 years (1871–1984), for long‐term trends. The trends are quantified by linear trend for monthly as well as seasonal rainfall for each station. Some broad contiguous areas showing statistically significant trends have been identified. Areas of increasing trend in the monsoon seasonal rainfall are found along the west coast, north Andhra Pradesh and north‐west India, and those of decreasing trend over east Madhya Pradesh and adjoining areas, north‐east India and parts of Gujarat and Kerala.

The subseasonal patterns indicate that the excess or deficiency of the monsoon rainfall is more frequently realized in the later half of the season. Monsoon rainfall tends to be more concentrated in August, over the west coast and central India.
A new daily central England temperature series, 1772–1991
Authors: Parker D. E. , Legg T. P. , Folland C. K.
Published: February 2007

In 1974 Manley produced a time series of monthly average temperatures representative of central England for 1659–1973. The present paper describes how a series of homogenized daily values representative of the same region has been formed. This series starts in 1772, and is consistent with Manley's monthly average values. Between 1772 and 1876 the daily series is based on a sequence of single stations whose variance has been reduced to counter the artificial increase that results from sampling single locations. For subsequent years, the series has been produced from combinations of as few stations as can reliably represent central England in the manner defined by Manley. We have used the daily series to update Manley's published monthly series in a consistent way.

We have evaluated recent urban warming influences at the chosen stations by comparison with nearby rural stations, and have corrected the series from 1974 onwards. The corrections do not (yet) exceed 0.1°C.

We present all the monthly data from 1974, along with averages and standard deviations for 1961–1990. We also show sequences of daily central England temperature for sample years. All the daily data are available on request.
A coherence between the QBO and the amplitude of the Mauna Loa atmospheric transmission annual cycle
Authors: Dutton Ellsworth G.
Published: February 2007

The transmission of direct solar radiation through the atmosphere above Mauna Loa, Hawaii, is shown to have a quasi‐biennial cyclic component that is coherent with the well‐known tropical stratospheric quasi‐biennial oscillation (QBO). The QBO‐related signal in the 32‐year transmission record is manifested as an oscillation in the amplitude of the annual cycle. The transmission annual cycle is known to be caused by seasonal transport of Asian continental dust to and over the island of Hawaii. Variations in water vapour and ozone are eliminated as possible influences in the transmission‐QBO relationship, leaving aerosols as the source of the oscillation. The ultimate cause for the quasi‐biennial signal in the transmission record is unknown. Small but cyclic modifications to the tropospheric energy budget occur as a result of the transmission variations. The magnitude of the energy budget variations are less than those typically expected to have a significant climatic impact.
Relationship between QBOs of stratospheric winds, ENSO variability and other atmospheric parameters
Authors: Kane R. P.
Published: February 2007

The 50‐mbar tropical zonal wind has a predominent quasi‐biennial oscillation (QBO) mode of an average period of ca. 28 months, with variation in the range 21–33 months and amplitudes varying within ± 20 per cent. For the Southern Oscillation, Tahiti minus Darwin (T‐D), sea‐surface temperature (SST) and equatorial rainfall indices, QBO is not the strongest mode. Periods of 3.6 and ca. 6 years are stronger. The QBO modes for these and other parameters (e.g. surface winds and winds in upper and lower troposphere and stratospheric winter temperature at the North Pole) are very irregular, with amplitudes, phases, and sometimes even period having large changes with time. It seems that these have little relationship with the 50‐mbar zonal wind QBO and may have altogether different origins.
Establishment of a data bank from records of climatic disasters and anomalies in ancient Chinese documents
Authors: Fang Jin‐Qi
Published: February 2007

On the basis of a survey of the existing literature on unique ancient Chinese documents, a data bank of climatic calamities and anomalies during historical times for 68 regions of China has been established in numerical code. The stored climatic disaster and anomaly patterns include flood, drought, plagues of locust, hail, famine, unusually cold and warm spells, and harvests. In addition, records of floods and low water levels of the Yellow River and its major tributaries were stored under a special title. This paper provides an introduction to the data and data bank.