bluuebunny/crossref_metadata_2025 huggingface dataset:
Canyon geometry, street temperatures and urban heat island in malmö, sweden
Authors: Bärring Lars , Mattsson Jan O. , Lindqvist Sven
Published: February 2007

The paper demonstrates the relevance of sky view factor analysis in urban canyons to thermal features of the surface and air in the urban canopy layer at night. The result of the study, made in the city of Malmö (population about 230,000) in southern Sweden, indicates, among other things, that the street geometry and its regional distribution within the city area plays a fundamental role in generating the street surface temperature pattern of the city, its 'surface heat island, The paper also demonstrates a digital image processing technique of determining the sky view factor from fish‐eye lens photographs.
Seasonal changes in heat flux and heat storage forth estuary, scotland in the intertidal mudflats of the forth estuary, scotland
Authors: Harrison S. J. , Phizacklea A. P.
Published: February 2007

The surface energy balance of intertidal sediments is complex. Heat is exchanged across sediment‐atmosphere and sediment‐water interfaces at differing states of the tide. This takes place within the context of seasonal changes in the temperature of the atmospheric boundary layer, and sea and river water. Subsurface heat flux in an intertidal mudflat near Grangemouth in the Forth Estuary, Scotland, was determined over a full seasonal range of ambient conditions during 1981. Measurements of temperature and weather variables were made from a 4.3m high instrument tower. Thermal properties of the muddy sediment were determined under laboratory conditions. Heat flux in and out of a 0.1 m deep surface layer of mud was calculated. Time of high water exerts a strong control over net heat flux in a 24 hour period. This is due to variation in heat exchange across the sediment‐water interface during tidal inundation, and across the sediment‐atmosphere interface at low water. The relationship between time of high water and net heat flux during inundation follows a broadly similar form at all seasons. Season, however, determines the magnitude of heat exchanges.
Climatic clusters in a small area
Authors: Galliani G. , Filippini F.
Published: February 2007

The optimization of agricultural productivity by means of numerical weather models requires a detailed analysis of historical daily weather data in order to determine which areas best meet the climatic requirements of a particular crop. The determination of the profiles of climatic factors, in order to identify climatologically similar and closely correlated zones, provides an adequate method of transferring locally tested numerical crop‐weather models from one area to others with the same agroclimatic conditions.

This study was made on a small but meteorologically, orographically and agriculturally varied area. It is based on daily measurements of precipitation and of minimum and maximum temperatures, taken by 42 weather recording stations over the period 1961‐1977. The climatic profiles are made by analysing the spatial and temporal variability of meteorological parameters in order to select the similarity functions to be used in models of hierarchical clustering.
Relations between minimum temperature and topography in great britain
Authors: Tabony R. C.
Published: February 2007

The effects of topography on two measures of temperature, the daily minimum and the diurnal range, were investigated using the conventional network of climatological stations in the U.K. The effects of large bodies of water and buildings were minimized by restricting the analysis to data obtained from 145 inland rural sites.

Topographic influences were considered to be mainly due to the effects of ‘local’ and ‘large‐scale’ shelter. Local shelter is associated with ‘height above the valley’ and is represented by the drop in altitude within 3 km, whereas large‐scale shelter is associated with nocturnal drainage of cold air, and is represented by the average height of the terrain above the valley over a radius of 10 km. The height above the valley is the most important variable and its maximum effect on diurnal range occurs in the early autumn, when the difference in soil moisture deficit between valleys and summits reaches its maximum. Large‐scale shelter is more important in winter than in summer, and for diurnal range, for rare rather than common events. This represents the increasing importance of nocturnal air drainage with the length of the night and suitable radiating conditions. For minimum temperatures in winter, however, the maximum impact of large‐scale shelter occurs for events with a return‐period around 2 years, and which are loosely associated with cold spells lasting a day or so. More extreme temperatures are usually attained at the end of cold spells lasting several days, when continued radiational cooling over level ground can produce temperatures as low as those attained through cold air drainage.
European rainfall patterns
Authors: Vines R. G.
Published: February 2007

This analysis suggests substantial coherence of rainfall data from Northern Europe, in a region from England to eastern Germany. Within this entire area, there appears to be a long‐term fluctuation in rainfall with a period of about 16 years. Further south, from Switzerland into northern Italy, a different long‐term fluctuation of about 20‐22 years is evident, which exhibits a possible relationship with the double sunspot cycle. Both rainfall variations are out of phase with corresponding fluctuations in North America, which have been reported previously.

Other quasi‐periodic fluctuations in precipitation of 10‐12 years (medium term) and 6‐7 years (short term) are observed in the same parts of Europe. Comparisons are made between these systematic temporal rainfall variations and those similarly found in both the northern and southern hemispheres.
Cloudiness and sunshine in cracow, 1861‐1980, and its contemporary tendencies
Authors: Morawska‐horawska Maria
Published: February 2007

The averages of daytime cloudiness for each year from 1861‐1980, smoothed by taking 11‐year consecutive averages (in view of the 11‐year cycle of the sun's activity), closely resemble a sinusoid with minimum values occurring from 1903‐1906. Sunshine values, likewise smoothed, can also be compared to a sinusoid, that is a descending sinusoid. It is worth noting the coincidence of the descending tendency of both graphs in the last 25 years.

The correlations between relative sunspot numbers and cloudiness showed a positive dependence with a time‐lag of 5‐7 years, and the strongest correlation, expressed by r = 0.32 (significance level 0.001), occurs with a lag of 6 years after the maximum sunspot number.

Sunshine and relative sunspot number show a negative correlation with time‐lags of 6‐11 years, and the strongest correlations occur with a lag of 8 years after the maximum sunspot number, and are expressed by the value r = ‐0.34 (significance level 0.001).

A harmonic analysis of detrended data for various periods of time in the space of 122 years, showed two periodicities of cloudiness: 14.3 and 3.6 years respectively. The first is very close to the known periodicity of precipitation and temperature in Cracow. As regards sunshine, the significant periodicities are as follows: 22.2, 10.3 and 3.6 years, respectively. The first two seem to be associated with the 11‐year cycle of solar activity. The 3.6‐year periodicity is probably connected with the identical periodicity in cloudiness.

On the basis of the results obtained for Cracow, it cannot be ascertained whether the recorded cycle of sunshine and cloudiness is a regional phenomenon or one of wider consequence.

A decline in cloudiness over the past 25 years is connected with rapid growth of Cracow which took place in that time. This caused the drying up of the air, and a decline in cloudiness.

Despite the decline in cloudiness (at its highest at noon), there persists in Cracow a decline in sunshine which has existed since 1890 and which has steadily increased over the past 30 years. It has been caused by the industrialization of Cracow which took place after 1950, and is connected with increase in air pollution.
Rainfall analysis of the sahelian drought in the gambia
Authors: Hutchinson Peter
Published: February 2007

Using rainfall data from five stations in The Gambia, it is shown that there has been a very marked decrease in annual rainfall over the last thirty years. This decrease is thought to be due to a reduction in the number of rain‐producing synoptic situations rather than a decrease in intensity of rainfall.

Using monthly data for the five stations and decadal and daily data for one station, it is demonstrated that the characteristics of the rainfall season have varied systematically over the years. Although the length of the season is virtually unaltered there is a marked reduction of rainfall in the middle of the season, so that there is a tendency towards bimodality, which could have serious consequences for rain‐fed agriculture.
Possible association between the climatic effects of stratospheric aerosols and sea surface temperatures in the Eastern tropical Pacific Ocean
Authors: Handler Paul
Published: February 2007

Recent model calculations have suggested that the occurrence of ENSO (El Niño/Southern Oscillation) events may be related to the appearance of a stratospheric aerosol generated by volcanic eruptions. The association of sea surface temperature anomalies in the eastern tropical Pacific Ocean with the occurrence of major eruptions in investigated over the period 1866–1982. It is found that after the eruption of low latitude volcanoes (<20°) that the sea surface temperatures are significantly warmer than normal within the first nine months (>95 per cent confidence level). These results are consistent with the statistical dynamical model calculations of MacCracken and Luther (1984) for the El Chichon aerosol. A second unexpected result was that the sea surfaces temperatures are significantly cooler than normal nine to fifteen months after the eruption of a high latitude volcano (>20°). Additional data such asin situmeasurements in the stratosphere and acid concentrations in the Greenland ice core are discussed to support the observed association.
The distribution of rainfall intensity in Israel, its regional and seasonal variations and its climatological evaluation
Authors: Sharon D. , Kutiel H.
Published: February 2007

A large body of data has been used to study the distribution of instantaneous rainfall intensity in Israel and its variations in space and in time. Time resolution is ±3 minutes. Besides the direct uses that the numerical results may have for practical purposes, the results have been used here to characterize rainfall in a climatologically more meaningful way. This includes reference to the atmospheric processes and surface‐conditioned effects that influence rainfall formation, and the identification of regional and seasonal variations in these processes. Thus, it has been shown that contrary to prevalent views, orographic rainfall in Israel is characterized by low intensity, apparently resulting from a continuous advection of moist air through a zone of gradual topographically forced uplifting.

In the presentation of results, emphasis has been put also on the significance of results from the point of view of rain‐conditioned processes occurring on the earth surface, such as in hydrology, geomorphology, etc. In this context, the water yield from high intensity rainfall has been shown to reflect a high degree of concentration, both areally (through convergence in the atmosphere and run‐off processes on the ground surface) and in time (in warm seasons and in certain parts of the day). These features, as well as the relative frequency of high‐intensity rains itself, has been shown to be more pronounced in the arid Negev than in the more humid parts of the country. This explains at least in part the increased uncertainty characterizing rainfall in the arid zone.
Forecasting of monsoon performance over India
Authors: Bhalme H. N. , Jadhav S. K. , Mooley D. A. , Murty Bh. V. Ramana
Published: February 2007

The technique of screening‐regression analysis is applied to forecasting the monsoon performance (percentage rainfall departure) over India from the immediately preceding May's meteorological variables. The resulting prediction equation with five variables performed well, with a few exceptions, on independent data. The forecasting scheme shows some promise of providing a useful forecast of monsoon rainfall departures over India before the beginning of the season.
The response of a global food model to possible climate changes: A sensitivity analysis
Authors: Liverman Diana M.
Published: February 2007

This paper describes some ways in which global simulation models of relationships between envrionment, economics and population, might be used to examine the impacts of climate change on the world food system. The paper presents an analysis of the response of the International Futures Simulation model to changes in crop yields as a surrogate for climate. This sensitivity analysis provides a range of scenarios of how global and regional food systems might respond to a variety of climate changes. It also demonstrates how these models can respond in an unrealistic or unstable way to certain types of variation. The analysis provides some insight into the complex responses of actual food systems to changes in food production.
Daily totals of solar UVB radiation estimated from routine meteorological measurements
Authors: Webb A. R. , Steven M. D.
Published: February 2007

Daily totals of solar ultraviolet‐B (300–316 nm) and fullband (300–3000 nm) radiation were measured over 18 months at Sutton Bonington in the English Midlands. A relation was established between the little‐measured but biologically active UVB waveband and the routinely recorded full solar radiation. A linear relation between the ratio of energy in the two wavebands and the cosine of the zenith angle at noon enables the UVB irradiation to be estimated from the full waveband. Information about ozone amounts, either daily values or monthly means, allows the estimates to be improved.
The nature of rainfall variability in Africa South of the Equator
Authors: Nicholson Sharon E.
Published: February 2007

The spatial patterns of rainfall variability over southern and equatorial Africa are examined using a regionally averaged data set comprising approximately 700 station records. Seasonal persistence of anomalies is also considered. Typical rainfall departure patterns, or anomaly types, are derived using a linear correlation method to assess the similarity of annual departure maps for the years 1901 to 1973. Six basic types describe most of the variability in the area 0 to 35°S. These indicate a remarkable spatial coherence of anomalies, but with a strong tendency for opposition between the equatorial and subtropical latitudes. The results are given an interpretation in terms of circulation features and synoptic situations affecting southern Africa.
Change of rainfall distribution and circulation patterns over Southern Africa in summer
Authors: Taljaard J. J.
Published: February 2007

The change of mean monthly rainfall, expressed as a percentage of mean annual rainfall, is described for the region south of 17°S during the course of summer. The areas with most rapidly increasing rainfall during monthly intervals are found to follow an almost circular path, starting out along the east coast and the adjacent interior in September and then being successively displaced to Zimbabwe, northern Botswana and northern South West Africa/Namibia, central and southern South West Africa/Namibia and ending in the central Cape Province in March. Several features of the atmospheric circulation and humidity are suggested and described as being partly responsible for the changing rainfall distribution.
Analysis of persistence in daily monsoon rainfall over India
Authors: Singh S. V. , Kripalani R. H.
Published: February 2007

In earlier studies the authors have established that monsoon rainfall up to the time scale of at least 5 days is dependent on its past value. In this study we examine the dependence in daily rainfall for 12 stations spread all over India, and in daily rainfall of 10 meteorological regions during the summer monsoon; (i) by analysing the rainfall as a stochastic point process by fitting Markov chains of orders 1 to 4 to the station data and (ii) by fitting autoregressive and autoregressive moving average models to the spatially averaged data. The significant conclusion is that the Markov chain of order 3 fits the runs of wet and dry spells better than chains of lower order, and that the autoregressive model of order 1 fits the spatially averaged rainfall amounts satisfactorily as compared to the higher order autoregressive or ARMA models.

Examination of rainfall intensities during spells of various lengths has revealed that the rain intensity is greater during spells of 2 or 3 days than on isolated days. The rain intensity is greater on the days lying in the middle of a wet spell than on isolated days or on the first and the last days of a longer wet spell.
Characteristics and frequency of reversals in mean sea level pressure in the north Atlantic sector and their relationship to long‐term temperature trends
Authors: Moses T. , Kiladis G. N. , Diaz H. F. , Barry R. G.
Published: February 2007

Reversals in the usual monthly mean sea level pressure (SLP) gradient over the North Atlantic during winter—an extreme mode of the North Atlantic Oscillation—are documented back to 1867. Such events are typically associated with well‐below‐normal temperatures in north‐west Europe and above‐normal precipitation amounts in the western Mediterranean area. Also noted during these events is the tendency for above‐normal temperatures in western Greenland and below‐normal temperatures in the eastern United States.

Temporal changes in the frequency of SLP reversals relate well to trends in the strength of the zonal wind and the frequency of blocking in the north‐east Atlantic area. Part of the fluctuations in temperature in western Europe during the last century can be explained by these changes in circulation. Nevertheless, major trends in winter temperature over this period, particularly the early 20th century rise in temperature, remain when adjustments are made to account for the effects of circulation changes during reversal winters. This suggests that mechanisms other than changes in the frequency of circulation regimes also play an important role in determining hemispheric temperature trends on these time scales.
Good king wenceslas: Alternative strategies for the U.K. department of health and social security(DHSS)
Authors: Giles Brian D. , Kings John
Published: February 2007

The U.K. Department of Health and Social Security (DHSS) is required to make, to those eligible, a single payment for additional fuel costs during a period of exceptionally severe weather. Previous methods of assessing exceptionally severe weather, criticized on a number of grounds by Social Security Commissioners, resulted in parliamentary debate and frequent press attention. Work on exceptionally severe weather in winter in Birmingham is presented here for the period since November 1959. Three measures of cold—mean daily temperature, degree days and windchill—are assessed for their usefulness in identifying exceptionally severe weather as a single day occurrence and/or as runs of days, during the winter months from November to March. Recommendations are made that thresholds based on probability of occurrence be used and that windchill is the best of the three measures which could be used in future winters. It is concluded that although climatologists can provide the necessary data, probability levels and parameters, it must be Parliament and the DHSS who must define ‘period’ and ‘exceptionally severe’. In either case the final decision can only be a political one.
Low‐latitude volcanic Eruptions and their effects on Sri Lankan rainfall during the north‐east monsoon
Authors: Mukherjee B. K. , Indira K. , Dani K. K.
Published: February 2007

Recent studies have pointed out the modification of climate by aerosols released in the stratosphere by strong volcanic eruptions. The rainfall at 15 meteorological stations in Sri Lanka and the low latitude (20° N to 20° S) volcanoes, having volcanic explosivity index (VEI) 4 or more, for a period of 112 years (1869–1980), are investigated to examine the effects of the eruptions on the rainfall activity over Sri Lanka during the north‐east monsoon season (November and December). The present study has suggested deficient rainfall in 14 out of 15 Sri Lankan stations during both the first and the first two successive north‐east monsoon seasons, which followed 53 to 80 per cent of volcanic eruption years. Also 53 to 100 per cent of the stations received deficient rainfall during both the first and the first two successive north‐east monsoon seasons following 12 out of 20 volcanic eruption years. Occurrence of deficient rainfall to the north of the inter tropical convergence zone (ITCZ) over Sri Lanka after the eruptions of the low‐latitude volcanoes could be attributed to the southward shift of the ITCZ due to depletion of the solar radiation caused by the aerosols released in the stratosphere by the strong volcanic eruptions.
A multivariate classification and regionalization of west African climates
Authors: Anyadike R. N. C.
Published: February 2007

Cluster analysis is used to group into regions over West Africa, a climatic data set which had been previously reduced to four factors. The regions thus derived are more firmly climate based than is the case with previous classifications. Various degrees of generality are also achieved by the methods, ranging from five regions at the primary level to twenty regions for more detailed work. Overall, a ten‐region climatic cluster is found to be optimal for most purposes.
England and Wales precipitation: A discussion of recent changes in ariability and an update to 1985
Authors: Wigley T. M. L. , Jones P. D.
Published: February 2007

Recent changes in precipitation variability are examined for five regions of England and Wales. The only statistically significant changes that have occurred over the past 10 years have been an increase in the frequency of extreme dry summers and wet springs. The importance of large‐scale climate forcing factors, such as pressure gradients and weather types, in controlling precipitation variations is examined using simple correlation analyses. The homogenized England and Wales precipitation series is updated to 1985.
Investigation of the sensitivity of the land‐surface parameterization of the NCAR Community Climate Model in regions of tundra vegetation
Authors: Wilson M. F. , Henderson‐Sellers A. , Dickinson R. E. , Kennedy P. J.
Published: February 2007

A series of sensitivity experiments has been conducted using a version of the NCAR Community Climate Model (CCM) and a complementary zero‐dimensional land‐surface model in order to invesligate the sensitivity of the models to surface process parameterizations in northern high latitudes. The study was motivated by anomalously high surface temperatures at these latitudes in a control simulation with the CCM. The effects of perturbing the maximum vegetation cover, distribution of the roots within the active soil layer, the depth of the active soil layer, soil albedo, and of maintaining a fully saturated upper and active soil layer were explored. Little response occurred in either model when the depth of the soil or the root distribution was altered. Increasing the percentage of ground covered by vegetation increased the canopy air temperature but generally reduced soil temperatures in the zero‐dimensional model. However, in the CCM integration the surface air temperature increased over most of the region for this change. This response seems to be due to the high level of precipitation during the three‐dimensional integration and is similar to one of the zero‐dimensional computations in which a large rainfall event was prescribed on the second day of the 10 day integration. Maintaining the moisture contents of both soil layers at their capacity caused a decrease in soil temperatures at most locations in the CCM and in the zero‐dimensional model once the soil in the control began to dry out. Increasing the soil albedo also produced soil and surface air cooling in both models. All the integrations underlined the considerable sensitivity of the land‐surface parameterization scheme to the instantaneous and preceding soil moisture conditions. Reduction in surface temperatures achieved was significantly less than the original discrepancy between CCM temperatures and observations. Part of the discrepancy could be caused by unrepresentative observational data and a model bias toward high levels of net surface radiation. In addition, preliminary calculations suggest that explicit inclusion of permafrost may be necessary before a fully satisfactory representation of the tundra land‐surface climate can be achieved. This conclusion may be important for CO2‐induced climate‐change studies.
Some features of the south‐west monsoon rainfall of Cochin and Minicoy
Authors: Ananthakrishnan R. , Kajan C. K.
Published: February 2007

Several characteristics of (he south‐west monsoon rainfall of the low latitude stations of Cochin (coastal) and Minicoy (island) have been studied using the hyetograms of these stations for the ten year period 1973–1982. Both stations exhibit diurnal variations of rainfall with maximum activity in the post‐midnight hours and minimum in the afternoon hours. The amplitude of the diurnal variation increases for rain events of increasing intensities. The integrated duration of the seasonal rainfall is about 250 h at Cochin and 110 h al Minicoy. Half the total rain from heavy falls is received in a fifth of the total duration; half the total duration accounts for only a fifth of the total rain from light falls.

The association between cumulative percentage rainfall (x) and cumulative percentage rain duration (y) is found to be of the form x = ay exp (byc) where a, b and c are empirical constants. The average rain intensity varies from about I mm/h to 25 mm/h along this rainfall curve. An equation of the same form also gives a satisfactory representation of the variation of cumulative percentages of rain amount/rain‐duration/rain hours with rain events of increasing amounts.
On bistable phasing of 18‐6‐year induced drought and flood in the Nile records since AD 650
Authors: Currie Robert Guinn
Published: February 2007

A maximum entropy analysis of winter and summer flood records of the Nile from ad 622 to 1490 shows evidence for periodic lunar nodal 18′6‐year(as well as weaker 10–11 year cyclic) induced drought/flood in regions of Africa drained by this river. This supports the results of Hameed (1984) who analyzed the same records using the Fourier transform method, and of Hameed and Currie (1985) who studied the summer flood records of the modern period (ad 1690–1962) using the maximum entropy method. The nodal term exhibits bistable phasing with respect to dates or epochs of maximum in the nodal tide, a phenomenon previously found in drought/flood proxy data in South America (Currie, 1983), in India (Currie, 1984a), in North America (Currie, 1984c), in China (Currie and Fairbndge, 1985), and in precipitation data for the northeastern United States (Currie, 1987c). Evidence for the 10–11 year solar cycle term in the Nile records is also discussed. Tyson (1980,1981) found terms near 19‐ and 11‐years in South African rainfall data, with the former exhibiting a bistable switch in phase at the beginning of our century, which is in agreement with results of Hameed and Currie (1985) for the modern Nile record.
Rotation of principal components: A reply
Authors: Richman Michaf. L. B.
Published: February 2007

Jolliffe's comments raise some interesting and important points concerning both unrotated principal component analysis and rotated principal component analysis that deserve further consideration. These are examined herein, with particular attention to my original review of rotation.
Some features of the growing season precipitation fluctuations in the Interior Plains of North America
Authors: Oladipo E. Olukayode
Published: February 2007

Long‐term growing season precipitation series for the period 1931–1978 at 407 stations in the Interior Plains of North America and for a decreasing number of stations with records dating back to 1875 were subjected to various statistical analyses in order to understand their inter‐annual and long‐term variability. Only a few stations showed any sign of inhomogeneity, there being no evidence of any significant trend in the precipitation series. The higher degree of spatial variability of seasonal precipitation series over the southern Plains indicated a higher frequency of occurrence of thunderstorms in the sub‐region compared with the northern Plains and the Canadian Prairies.

The test for normality by Fisher's statistic and the Geary coefficient indicated that about 20 per cent of the precipitation series were not normally distributed. For meaningful statistical analysis, there is always the need to convert the frequency distribution of rainfall series from non‐normal to normal. Using only the square root transformation method, most of the non‐normal cases were transformed to normal.

Subperiods analysis as tested by Cramer's test indicated that, although the 1941–1970 normal was wetter than the preceding non‐overlapping 30‐year normal period, there had been no significant secular change in the growing season precipitation in the Interior Plains, at least since 1911. Analysis of the precipitation anomalies decade by decade from the 1941–1970 averages indicated that the 1940s and 1960s were generally wet, while other decades, especially the 1930s and 1950s were particularly dry. The 30‐year period 1941–1970 was probably the most anomalously wet period in the nearly 104‐year time sequence considered. On the whole, the results of the statistical analyses indicated no significant changes in some of the secular features of growing season precipitation totals in the Interior Plains.
The effect of urbanization on some characteristics of relative humidity in Ibadan
Authors: Adebayo Yinka R.
Published: February 2007

Examined in this work was the effect of urbanization on some aspects of the diurnal, seasonal and spatial patterns of relative humidity in Ibadan. Two approaches were adopted in the analyses. Firstly, a rural‐site station was used as a control, while its 20‐year (1961–1980) data were compared with those of the two urban‐located stations. Secondly, isoline maps of the spatial patterns were produced‐ In doing this, occasional, diurnal recordings were carried out at strategic locations over a period of 1 year.

The analyses show that relative humidity was lower within the city than in the rural area. The mean difference varied from 2 to 3 per cent at 0900 h to about 10 per cent at 1500 h. There was a seasonal trend in this difference. While there was virtually no difference by 0900 hand a difference of just about 5 per cent existed at 1500 hat the peak of the wet season, the situation at the height of the dry season was different. By then, whereas the relative humidity was about 3–6 per cent lower in the urban area at 0900 h, the difference was about 12–17 per cent at 1500 h. The isoline maps also reflect the diurnal and seasonal patterns, and the attenuation of relative humidity with increase in the intensity of urbanization. The analyses do not confirm there was any significant decrease in relative humidity, over time, as a result of the impact of the city‐growth.
South African rainfall, the Southern Oscillation and a Southern Hemisphere semi‐annual cycle
Authors: Lindesay J. A.
Published: February 2007

Significant differences in rainfall over central South Africa are known to occur between opposite extremes in the phase of the Southern Oscillation, but details of both temporal and spatial aspects of the modulation of South African rainfall with the phase changes of the Oscillation remain to be described. Zero‐lag correlations between the Tahiti—Darwin Southern Oscillation Index and monthly and 3‐month seasonal rainfall over South Africa suggest that the rainfall—Southern Oscillation Index association is best defined in the late summer season January—March and in a north‐west to south‐east aligned zone across the central summer rainfall region of South Africa. Rainfall in this zone is directly related to the Southern Oscillation Index, increasing during high phase summers. An apparent semi‐annual cycle in the rainfall—Southern Oscillation Index correlations over central South Africa is in phase with the November and February turning points of a semi‐annual cycle in atmospheric circulation parameters over southern Africa. A plausible circulation mechanism is suggested to account for some of the spatial and temporal characteristics of the association between the Southern Oscillation and South African rainfall.
Changing rainfall patterns in Western Sudan
Authors: Eldredge Elizabeth , Khalil Suhair El Sayeed , Nicholds Nigel , Abdalla Atif Ali , Rydjeski Denis
Published: February 2007

Rainfall series to 1986 have been examined for North Darfur and North Kordofan. Annual and monthly series are presented and analysed. Relatively dry conditions have persisted in this region since 1966 due mainly to a decline in rainfall during July, August and September, the critical months for the annual agricultural cycle. Changes in daily rainfall magnitude and frequency are examined for these four rainy season months. It is recommended that agricultural planning and government policies be based on recent meteorological patterns.
A case study of low level country breeze and inversion heights in the Johannesburg area
Authors: Goldreich Yair , Surridge Anthony D.
Published: February 2007

Previous studies within a shallow valley east of the city centre of Johannesburg (South Africa) revealed the presence of some anomalies in the mesoscale, winter, nocturnal climate regime. Among them: the valley was relatively warmer during inversion nights; more than one thermal belt was discerned and valley winds dominated the early hours of the mornings. A tethered balloon and a mobile acoustic sounder were used to monitor temperature, wind and humidity profiles in the valley and vicinity, whilst ground mobile units measured temperature. Observations revealed a three layer wind system in which an elevated country breeze is sandwiched between the katabatic flow near the ground and the gradient wind aloft. The double thermal belts observed on the valley's slopes are probably due to the oscillation of the country breeze (the lower) and the meso‐scale valley inversion top (the upper one). The inversion top over the ridge lines is probably caused by the regional nocturnal inversion or an elevated inversion eroded by the urban heat island plume.
Stratospheric aerosols and sea‐surface temperatures
Authors: Parker D. E.
Published: February 2007

Superposed‐epoch analyses show statistically significant warming and cooling of the East Tropical Pacific Ocean a few seasons after major low‐latitude and high‐latitude volcanic eruptions respectively, confirming the results of Handler (1986a). The statistical significance of the results is confirmed by a Monte Carlo sampling technique which takes account of pre‐eruption changes in the oceanic temperatures, and the results are only slightly sensitive to the selection of eruptions. Occasional sequences of extreme temperatures in the random samples underline the need for numerical modelling studies to complement the statistical investigations.
Low latitude volcanic eruptions and the El Niño‐Southern Oscillation
Authors: Nicholls Neville
Published: February 2007

An apparent association between low latitude volcanic eruptions and the El Niño‐Southern Oscillation (ENSO), has been examined using a superposed epoch composite analysis of Darwin monthly mean pressure, an index of ENSO. Ten eruptions have been included in the analysis. In the composite, the date of eruption tends to be preceded by lower than average pressure at Darwin, and followed by above average pressure. A strong linear upward trend in the composite pressure anomaly starts well before the date of eruptions and continues for several months after the eruption. The analysis suggests that ENSO events are not caused by low latitude volcanic eruptions, since significant anomalies in Darwin pressure, and an upward trend in the anomalies, are observed well before the date of eruption. Low latitude eruptions tend to be preceded by the start of the sequence of events which leads to ENSO.
Development processes for five depression systems within the Polar Basin
Authors: Ledrew Ellsworth F.
Published: February 2007

Five synoptic sequences in the Polar Basin are studied on a day by day basis. A diagnostic model is used to illustrate the relative roles of the dynamic properties of the advected air flow in comparison to mechanisms related to the characteristics of the underlying surface. It is found that the properties of the advected air flow are the major contribution to the vertical circulation associated with synoptic evolution and are a necessary condition. Latent heat release may also be a significant mechanism which supports the proposal by others that a CISK type process may contribute to further development in the Arctic. The surface sensible heat flux is not a necessary process and it may at times oppose the vertical circulation when warm air is advected into the region of development within the circulation of the depression. The surface frictional effect is a minor contribution within the central Polar Basin but is a significant process in systems migrating along the Asiatic coastline.

A feedback linkage between synoptic evolution and intensification of the baroclinicity is proposed in the Greenland region for a cold low type of vortex. A cold pool, apparently created by intense radiative cooling over Greenland, was identified in early July. There was significant advective convergence associated with the thermal gradients which contributed to synoptic development as the depression migrated around this pool. It appears that the intensification of the potential temperature gradient with the advection maintained the baroclinicity, despite warm air advection into the centre of the pool. This is an interesting feature which requires further study and confirmation.
Changes in precipitation conditions in the western mediterranean over the last century
Authors: Maheras Panagiotis
Published: February 2007

A study of precipitation variations over the western Mediterranean is given, for a period of 95 years (1891 to 1985), based on the use of Principal Component Analysis. The curves for the scores are traced and then analyzed for annual as well as seasonal precipitation. Two principal moist periods are found (1901 to 1921 and 1930 to 1941) and two principal dry periods (1922 to 1929 and 1942 to 1954). A comparison of variations in precipitation and zonal indices (ZIa) indicates that with a meridional circulation dominating over the western Mediterranean, we have an increase in precipitation; with a zonal circulation dominating we have a decrease in precipitation.
Variability of mean monthly temperatures and semi‐annual precipitation totals in Europe in relation to hemispheric circulation patterns
Authors: Kozuchowski K. , Marciniak K.
Published: February 2007

The influence of general hemispheric circulation on European temperature and precipitation was investigated. Data from the period 1901–1976 were utilized: the monthly frequencies of occurrence of W, E, C circulation pattern types according to the Wangenheim‐Girs classification, monthly values of pressure differences between 35° an 65°N (zonal index), mean temperatures of January and July at 30 stations in both the warm season (May‐October) and the cold season (November‐April) and semi‐annual precipitation totals for 21 stations in Europe. The correlation coefficients between the circulation characteristics and climate elements indicated above in Europe were calculated.

Maps of these correlation coefficients have been produced, with the areas of their statistical significance. The results show that variability of temperature, and also partly of precipitation in Europe are significantly correlated with changes of circulation pattern types. January temperature also depends on the zonal index.

If it is assumed that in future, until the end of this century, an increase of W type frequency and a decrease of C circulation pattern types will take place—it may be expected that temperature and precipitation will undergo appropriate changes in certain parts of Europe. Northern and some central areas of Europe are likely to change from continental to oceanic climate as regards temperature; precipitation is likely to increase in northern Europe.
The synoptic climatology of ablation on a New Zealand glacier
Authors: Hay J. E. , Fitzharris B. B.
Published: February 2007

Local scale ablation and energy budget measurements are reported for the Ivory glacier in the Southern Alps of New Zealand over 53 days during two consecutive summer periods. Ablation averaged 38 mm day−1, but varied from less than 10 mm day−1 to over 70 mm day−1. Radiation supplied 52% of the energy for glacier melt, with the convective fluxes contributing most of the remainder. The results are related to large scale synoptic weather patterns over the southwest Pacific region. Different synoptic situations generate distinctive energy budgets, with radiation important during southerly circulation patterns and the convective fluxes relatively more important with northerly circulation patterns. These findings are discussed in the context of the retreat of New Zealand glaciers this century and possible circulation changes.
Storm rainfall on the Njemps flats, baringo district, Kenya
Authors: Rowntree K. M.
Published: February 2007

Annual, seasonal and storm rainfall characteristics are analysed for the Njemps Flats, a semi‐arid area near Lake Baringo in the Kenya Rift Valley. Storm rainfall is analysed in terms of intensity, timing, duration and total storm depth. Storms characteristically occur in the early evening, with one storm of around 2 h making up the daily rainfall totals. High intensity rainfall seldom persists longer than 30 min. The maximum 30 min intensity recorded was 80 mm/h, the maximum 60 min intensity was 75 mm/h. An analysis of annual and monthly recurrence intervals of storm depth indicate that for a 1 in 10 year recurrence interval, June, July and April suffer the heaviest falls, whereas for a 1 in 2 year recurrence interval the months with the heaviest storms become August, July and April. The significance of this to erosion potential and runoff harvesting are discussed.
An index of sea ice variations in the Nordic seas
Authors: Sear C. B.
Published: February 2007

Twentieth century sea ice data from the Nordic Seas (the Atlantic Sector of the Arctic) are examined using a simple index of variations in sea ice extent. The index measures overall sea ice extent variations in the Nordic Seas between 1901 and 1977. Variations in the marginal ice zone during the melt season are shown to reflect regional air temperature changes. Reduction of the index data using principal component analysis highlights sub‐regional heterogeneity in melt season sea ice extent variations. An important spatial pattern of variation is one in which sea ice extent in the Barents Sea varies out of phase with that in the central Greenland Sea. This alternating pattern has a quasi‐periodicity of around three years. Time series analyses of other sea ice records indicate significant quasi‐periodicities in the region of between 3 and 4 years and 2.5 years. Three years may be a key time scale of variation in the Atlantic Sector of the Arctic seasonal sea ice zone.
Reginalization of daily rainfall in Kenya by means of common factor analysis
Authors: Bärring Lars
Published: February 2007

Daily rainfall data from 73 stations distributed throughout Kenya were subjected to maximum likelihood factor analysis. Data for the period January 1971 to December 1985 were used. A brief analysis of data quality and representativity and the problem of missing data are included. The data were transformed by natural logarithms. Scree and LEV plots together with the Kendall/North criterion for eigenvalue separation indicated break points at 5, 11 and 15 factors. The 11‐factor model was judged as being the most parsimonious, for both statistical and climatological reasons. It explained 38 per cent of the total variance.

The general features of the regionalization are found to be reasonably consistent with other studies. The major regions (the coast, the Highlands, the Lake Victoria area, and the dry northern/eastern areas) appear in this regionalization but are divided into several subregions. It can be concluded that this subdivision is partly linked to physiographical regions and orographic influence. In addition, possible links to regional circulation patterns are discussed.
Climatic changes in and around the Rajasthan desert during the 20th century
Authors: Pant G. B. , Hingane L. S.
Published: February 2007

Rainfall and temperature data during the period 1901–1982 are studied for the northwest Indian region consisting of the meteorological subdivisions of Punjab, Haryana, west Rajasthan, east Rajasthan and west Madhya Pradesh. The results indicate a decreasing trend in the mean annual surface air temperature, which is mainly contributed by the south‐west monsoon season (June through September), The mean annual and south‐west monsoon season rainfall series over most parts of the region indicate a conspicuous increasing trend. The increasing trend is significantly marked for the subdivisions constituting the peripheral areas of the Rajasthan desert. These trends in rainfall and temperature are examined in relation to the changing land use pattern of the region due to extensive irrigation. Earlier findings of Winstanley (1973) reporting a decreasing trend in rainfall are found to be unacceptable due to the unrealistic assumptions of his study.
El Niño and its effect on precipitation in Arizona and Western New Mexico
Authors: Andrade Edward R. , Sellers William D.
Published: February 2007

This paper focuses primarily on the effect of El Niño on seasonal and annual precipitation at 26 locations in Arizona and western New Mexico for an 86‐year period from 1900 to 1985. Following Rasmusson (1984), each year is classified as either a non‐El Niño year (51) or an El Niño year (35), with the El Niños designated as being very weak (4), weak (8), moderate (12), or strong (11). Using the Mann‐Whitney U‐test for the 19 stations in Arizona, we find that, in the spring (March‐May) and in the autumn (September‐November), there is a positive relationship between precipitation in Arizona and both moderate and strong El Niños.

These results are verified by correlating seasonal and annual precipitation for the complete 26‐station network with the pressure difference between Tahiti and Darwin. Plausible physical explanations for these results are given.