bluuebunny/crossref_metadata_2025 huggingface dataset:
The annual and seasonal distribution of fronts over central‐southern Europe and the Mediterranean
Authors: Flocas A. A.
Published: February 2007

An analysis of the frequency of occurrence of fronts over central‐southern Europe and the Mediterranean was carried out based on daily synoptic charts for the nine year period from 1971 to 1979. Tables and charts are presented showing the annual and seasonal frontal frequencies over the area, and the variation of average frequency of fronts with latitude and longitude is demonstrated. The distribution of the frequency of fronts fits in with generally accepted models of hemisphere circulation. An interesting feature is the relative importance of each type of front to the seasonal patterns which emerge. Cold fronts contribute strongly in all seasons with frequencies of approximately 1 in every 10 days in spring, summer and autumn and of 1 each week in winter.
Northern Hemisphere extratropical cyclone activity for four mid‐season months
Authors: Whittaker L. M. , Horn L. H.
Published: February 2007

Cyclone frequency, cyclogenesis and the primary and secondary tracks followed by extratropical cyclones within the Northern Hemisphere are examined for the four mid‐season months: January, April, July and October. The data for these four months were compiled from several sources for the period 1958–1977. Cyclogenesis was defined as the point of origin of a cyclone provided it maintained a closed isobar for 24 hours. Cyclone frequency was determined from the number of occurrences of an extratropical cyclone passing through a 5° latitude‐longitude grid box. Analyses of the grid values of cyclone frequency reveal relative maxima which define the cyclone tracks. The tracks are partitioned into primary and secondary tracks depending on the size of the relative maxima of cyclone frequency.

Cyclogenesis is concentrated in the lee of major mountain ranges and along the east coasts of Asia and North America, with cyclogenesis in coastal North America found nearer the coastline than in the Asian area. A major cyclogenetic region also exists in the Gulf of Genoa‐Northern Italy region of the Mediterranean Sea, but here cyclogenesis is confined to the cooler seasons. As expected the areas of most frequent cyclogenesis shift poleward during the warmer months. Similarly, cyclone frequency exhibits a poleward displacement during the warmer months. It is also noted that whereas winter (January) is characterized by a significantly greater cyclone frequency over the ocean than over land, summer (July) finds the frequency over the continent about as large as over the oceans. Similarly there are significant poleward displacements of cyclone tracks in summer, but the displacement is in no way uniform over the hemisphere. These results can be compared with earlier hemispheric studies of cyclone activity.
On the cause of ‘fram’ type seasonal change in diurnal amplitude of air temperature in polar regions
Authors: Ohmura Atsumu
Published: February 2007

The cause of Fram' type seasonal trend of diurnal amplitude of air temperature is investigated from the viewpoint of the surface energy balance. First, the cause of diurnal amplitude of the surface temperature is examined. Then, the effect of the atmosphere between the surface and the screen‐level on the amplitude of air temperature is evaluated.

The data of the energy balance used in this work were collected at the base camp of the Axel Heiberg Island Expedition (79°25′N, 90°45′W, 200 m) in the Queen Elizabeth Islands, N.W.T., Canada. This site shows a typical ‘Fram’ type trend of diurnal amplitude with annual maximum in April, the summer minimum in June and a secondary peak in August.

The April maximum is due to extremely slow sublimation and heat conduclion in the subsurface. The decrease in the amplitude during the later dry snow period in May and early June is due to a gradual increase in sublimation which is induced by the temperature increase. During the melt in June, the diurnal amplitude of the surface temperature is effectively reduced owing to the diurnal change of the latent heat of fusion. After the snow melt, the diurnal amplitude of absorbed global radiation is tripled compared with April. The temperature amplitude remains small, however, owing to the rapid increase in the diurnal amplitudes of energy sinks. The cause of the slight recovery of the diurnal temperature amplitude in August is the decrease in the sensible heat flux.

Throughout the entire period, the result of the heat exchange is reflected in a larger temperature variation under lower temperature due to the Stefan‐Boltzmann law. This effect contributes to a larger diurnal amplitude in spring.
Autoregressive modelling of the tropical stratospheric quasi‐biennial oscillation
Authors: Koscielny Albert J. , Duchon Claude E.
Published: February 2007

Autoregressive time series models are used to make forecasts of stratospheric zonal wind and temperature at Kwajalein Island near the equator in the northern Pacific Ocean. The tropical stratosphere is dominated by the quasi‐biennial oscillation (QBO). Because the QBO has a varying period, an autoregressive model is more appropriate than a mixture of sinusoids. The data for 11 levels are efficiently represented by principal components, and univariate and multivariate autoregression models are fitted to six of the principal components. The autoregressive models are used for estimation of variance density spectra and for forecasting. The multivariate model is found to perform better in both detecting and forecasting the quasi‐biennial oscillation than either univariate models of the principal components or autoregressive models of the data set itself.
Influence of evaporation in semi‐arid regions on the July circulation: A numerical study
Authors: Sud Y. C. , Fennessy M. J.
Published: February 2007

In this study, two 47‐day simulations were made with the general circulation model of the Goddard Laboratory for Atmospheric Sciences starting from the observed initial conditions for 15 June (00Z) 1979 as produced by NMC analysis. In the first simulation, the soil moisture was normally initialized and then allowed to vary by the model generated surface water balance. In the second simulation, the evaporation was prescribed and maintained zero in four chosen semi‐arid regions: the Sahel, the Thar Desert border in the Indian subcontinent, the Great Plains in North America and north‐east Brazil in South America. Elsewhere the soil moisture was calculated as in the first simulation. The two runs were identical in all other respects.

The local climatology simulated by the GCM was analysed in the four anomaly regions. The mean July precipitation increased slightly in the Great Plains and Sahel regions, while it increased substantially (∼70 per cent) in the Thar Desert border region. However, in the north‐east Brazil region it decreased slightly. Relative thermal lows were created in each region, along with enhanced rising motion. There was also an increase in the mean monthly diabatic heating in all four regions. An analysis of the vertical structure of the moisture convergence field revealed that there was an increase in the low level moisture convergence in all of the anomaly regions. This compensated for the local moisture deficit created by the lack of evaporation.

These results are based on one set of simulations representing the month of July. Further simulations would be required in order to evaluate their statistical significance.
The north‐west Australian cloud band: Climatology, characteristics and factors associated with development
Authors: Tapp R. G. , Barrell S. L.
Published: February 2007

The broad characteristics of the North‐west Australian Cloud Band, frequently observed across the Australian continent, are outlined. The cloud in the Band is most frequently first apparent within approximately 5° latitude and 17° longitude of 12DS 100°E, and may extend from there for several thousand kilometres, typically towards the east‐south‐east. It is found to be most in evidence during the winter months. Various atmospheric features associated with the development of the Cloud Band are discussed.
A system for predicting the onset of the north Australian wet‐season
Authors: Nicholls N.
Published: February 2007

An index is defined for the date of onset of the north Australian wet‐season, based on rainfalls observed at ten stations across tropical Australia. The index is shown to be reasonably representative of wet‐season onset throughout the area of interest. Some suggestion of bimodality is found in the frequency distribution of onset dates. An operationally feasible method for predicting the probability that the wet‐season will commence late is presented, building on earlier published work which has established the feasibility of prediction of seasonal rainfall near the date of onset of the wet. The forecast method uses the linear logistic equation and Darwin pressures observed in months prior to the onset to make predictions. Acceptable forecasts can be issued four months prior to onset. Two examples of the use of the method are provided.
Weather‐type classification by factor analysis in the Thessaloniki area
Authors: Maheras Panagiotis
Published: February 2007

In an attempt to study weather and climatological conditions in the Thessaloniki area during the winter period, a weather‐type classification is proposed according to principles first adopted by Russian authors. The methods of factorial analysis are used for this weather‐type classification. A study of the monthly and yearly frequencies of good, unpleasant, cloudy or overcast weather allows us to better understand the area's ‘atmospheric quality’ affecting man's life in it.
The effect of weather map scale on the results of A synoptic climatology
Authors: Yarnal Brent
Published: February 2007

The results of an objective synoptic climatology of glacier mass balance in south‐western Canada are affected by the scale and degree of generality of the synoptic patterns used. Two scales of 500 mb daily weather maps are compared. Statistical analysis shows little direct relationship between the two scales: the smaller, high wave number patterns vary randomly within the more general flow of the larger circulation patterns. However, further analysis suggests that the smaller synoptic patterns control glacier mass balance in coastal British Columbia. Glacier accumulation in the Canadian Rockies is more closely related to larger‐scale atmospheric flow.
Tendency prediction of precipitation and inundation in July in the Sichuan Basin, China
Authors: Ju‐Ying Chen
Published: February 2007

In July 1981, there occurred a comparatively severe flood and inundation in the Sichuan Basin. Before its occurrence, certain precursory phenomena appeared in the May 500 mb circulation field. The Western Pacific subtropical high apparently strengthened and extended westward, the mid‐latitudinal zonal circulation weakened, whereas the meridional circulation strengthened. At the same time, the astronomical background suggested a rainy period. All these precursory features unanimously indicated the probability of heavy precipitation and a tendency for flooding and inundation in July‐August, but especially in July, in the Basin. In this paper analysis and discussion emphasize the astronomical factors, the circulation factors and the prediction instrumentation which resulted in a successful prediction.
Air temperature variations in Greece. Part 1. Persistence, trend, and fluctuations
Authors: Giles B. D. , Flocas A. A.
Published: February 2007

This paper considers annual and seasonal variations of temperatures at three stations in Greece with at least 80 years of records. The extent and nature of non‐random changes, such as persistence, trend and fluctuations, are investigated. There is statistical evidence of both Markov linear and non‐linear persistence in the data depending on stations and season. The trend analysis showed little of significance, probably because of the time periods chosen. The data were subjected to a ‘lowpass filter’ of a Gaussian type and the series of fluctuations which resulted are discussed. Finally the data for all three stations were combined and filtered in order to show changes that have occurred in the Greek region during the twentieth century.
The Southern Oscillation, sea‐surface‐temperature, and interannual fluctuations in Australian tropical cyclone activity
Authors: Nicholls N.
Published: February 2007

The relationship between interannual variations of the number of tropical cyclones observed in the Australian region during a cyclone season and the Southern Oscillation (SO) has been explored. Strong, significant, stable correlations were found between the SO and cyclone numbers. Years with relatively many tropical cyclones were preceded by high North Australian SST, low east Pacific SST and low Darwin pressure. Such years also tended to be followed by the reverse pattern. The study confirms an earlier suggestion (Nicholls, 1979a) that Australian tropical cyclone activity is predictable some months prior to the start of the cyclone season. The observed correlations may result from feedback between the atmosphere and the ocean.
Rainfall over the southern slopes of the Himalayas and the adjoining plains during ‘breaks’ in the monsoon
Authors: Dhar O. N. , Soman M. K. , Mulye S. S.
Published: February 2007

During ‘breaks’ in the south‐west (or summer) monsoon there is a general cessation of rainfall activity over most of the Indian area, but this activity increases over the southern slopes of the Himalayas and its adjoining plains. In this study, rainfall distribution during the ‘break’ monsoon situations has been studied, over the southern slopes of the Sikkim, Nepal and Uttar Pradesh Himalayas (i.e. from longitude 78°E to 89°E) and their adjoining plains. Rainfall distributions during the major ‘break’ situations which occurred during the principal monsoon months of July and August of the period from 1957 to 1969 were studied. This study has shown that, on a ‘break’ day, positive percentage departures of rainfall as high as 100 to 300 per cent have occurred at stations located in the outer Himalayas and the adjoining plains of north Bengal, east and central Nepal, Bihar and east Uttar Pradesh. However, the width of this heavy rain‐belt is maximum over the hills and plains of south‐eastern Nepal and the adjoining plains of north Bihar. This study has also shown that on a ‘break’ day there is a decrease of rainfall activity over the Himalayas west of longitude 80°E. Decrease of rainfall also takes place along a narrow belt immediately to the south of the great Himalayan range to the east of longitude 80cE outside Sikkim. Over the adjoining Gangetic plains, an increase in rainfall is noticed even to the south of the Ganga river in Bihar and its neighbourhood. Thus, owing to the increase in rainfall activity during ‘break’ monsoon situations in the catchments of Himalayan rivers located in Sikkim and Nepal, a peculiar situation arises which is responsible for causing floods in the downstream plains which experience almost drought conditions.
A comparative study of hailstorms in Switzerland, Canada and South Africa
Authors: Admirat Pierre , Goyer Guy G. , Wojtiw Lubomir , Carte Ernest A. , Roos Danie , Lozowki Edward P.
Published: February 2007

A comparison of 5 to 20 years of qualitative and quantitative observations of hailfalls and hailstorms by three of the most active hail research groups in the world, shows very similar characteristics in a number of aspects of the hail phenomenon. The main similarities are that (a) the frequency of hailstorms decreases with increasing intensity, (b) the characteristics of hailstones (maximum size, number density) and hailswaths (length, surface area, energy) increase with increasing hailstorm intensity (i.e. lifetime, volume), (c) the single and multi‐cellular type storms are most frequent, whereas the supercell is rare, (d) the hail flux is not constant but pulsating, (e) the spatial structure of large hailswath is not uniform but contains ‘hailcores’ and (f) the post embryonic trajectories of common hailstones are often simple and similar.

A number of differences are also observed between some of the regions, the main ones being (a) the upper limit of intensity of the more severe storms, (b) the succession and scale of cells in the storm development and (c) the percentage of various embryo types.

A major conclusion of this comparative study is that the severe hailstorms, which cause most of the damage, are exceptional and show little similarity in the three regions. For the more requent light and moderate damaging ones, the study suggests that dynamics may be the result of pulsating phenomena.
A reappraisal of rainfall trends in the sahel
Authors: Dennett M. D. , Elston J. , Rodgers J. A.
Published: February 2007

Two rainfall series for the Sahel region of West Africa have been updated to 1983. Annual and monthly series are presented and analysed. Relatively dry conditions have persisted in this region since 1968 due mainly to a decline in rainfall during August, the wettest month. Drought has probably been less severe in this region during the late rather than the early 1970s because of better rainfall early in the season. It is suggested that agricultural planning should be based on rainfall records for the last twenty years.
The separate contributions of line squalls, thunderstorms and the monsoon to the total rainfall in nigeria
Authors: Bayo Omotosho J.
Published: February 2007

Using thunderstorm and rainfall information from five Nigerian stations for a five year period, the separate contributions of line squalls, thunderstorms and ordinary monsoons to the total rainfall and their variations with latitude are investigated. Total and thunderstorm rainfall decreases with increasing latitude but monsoon precipitation decreases exponentially while line squall rainfall is at a maximum around 9°N. Rainfall from thunderstorms shows a single annual peak in July/August at stations north of about 8°N whereas line squall precipitation exhibits a double maximum for all stations south of 12°N. It is also shown that, in the mean, line squalls are the most important rain producing systems, giving 47‐6 per cent of the mean total annual precipitation compared with 39 per cent and 13‐4 per cent from thunderstorms and ordinary monsoon rain, respectively.
A multivariate statistical model for forecasting anomalies of half‐monthly mean surface pressure
Authors: Maryon R. H. , Storey A. M.
Published: February 2007

A multivariate statistical model for forecasting anomalies of surface pressure over Europe and the North Atlantic Ocean at medium to long range used routinely in the Synoptic Climatology Branch of the Meteorological Office is described. The model discriminates between broad classes of circulation type using a multivariate predictor space (including areal sea surface temperature anomalies). The forecasts may take categorical or probabilistic form, and the likelihood of the occurrence of categories of circulation index, temperature and rainfall over the U.K. can be produced using Bayesian methods. Emphasis is laid on the difficulties of applying classical statistical analysis to atmospheric fields, as this important aspect of long range forecasting by empirical methods tends to be neglected in the literature.
The northwest african depressions affecting the south balkans
Authors: Prezerakos Nicholas G.
Published: February 2007

This paper deals with the north‐west African or the Atlas depressions, named after the region of their formation. The subject is examined from the synoptic climatology point of view, and is based on mean sea level (M.S.L.) pressure and 500 hectopascal (hPa) heights of the five consecutive years from 1970 to 1974. Attention is drawn to the following topics.

1. The positions of the depression centres are determined when they are generated and afterwards. So the numbers of the occurrence of their centres in the subregions into which north‐west Africa is divided and the tracks of these centres are obtained.

2. These depressions are divided into four categories. The first category is divided into four subcategories, whereas each of the remaining categories is divided into two subcategories. These categories are based on the 500 hPa flow patterns.

3. For each subcategory, mean charts of the 500 hPa height for the first occurrence of its depressions have been prepared. For these mean charts, the relative vorticity advection has been calculated. These charts suggest the region of the first occurrence of the depressions is mostly in a region of positive advection of vorticity.

4. The percentage of the number of depressions from each subcategory affecting the weather of Greece can be determined. For each percentage, the mean M.S.L. pressure and 500 hPa height charts showing the time at which these depressions start affecting the weather of Greece are drawn. Thus, the synoptic situations affecting Greece and resulting from the north‐west African depressions are determined.

Finally, the rain, wind and temperatures from each north‐west African depression subcategory occurring in Greece and especially in the Athens major region are discussed.
A preliminary analysis of long‐term visibility trends in central scotland
Authors: Lee D. O.
Published: February 2007

Median visibilities are calculated for four sites in central Scotland for summer and winter seasons over the period 1962‐1982. A steady improvement in visibility at all sites has taken place, but especially in winter at the two urban sites. The relative importance of climatological and air pollution influences is uncertain, but the effects of the 1973 oil crisis on summer visibility, through reduced sulphur emissions, appears to be much less evident than in southern England.
Application of a radiative cooling model to daily minimum temperature prediction
Authors: Gandia S. , Melia J. , Segarra D.
Published: February 2007

A model of exponential decrease of temperature is applied to the study of night cooling in an agricultural area of citrus orchards located near the Valentian Coast (Spain). A set of annual average parameters which determine that cooling is obtained by using temperature measurements at different levels during two years. These parameters appear to be representative of the thermal behaviour of the area of study.

The attainment of such parameters allows a prediction of the minimum temperatures of the area to an accuracy of £1.5 K, knowing the temperature at sunset and some time later.
On the 1983 drought in North‐East Brazil
Authors: Rao V. Brahmananda , Satyamurty P. , De Brito José Ivald O. B.
Published: February 2007

Examination of the rainfall data for north‐east (NE) Brazil showed that the drought of 1983 was extensive. In the interior dry region, rainfall during the rainy season of 1983 was less than 40 per cent of the normal. Analysis of the rainfall revealed that the drought of this year was the worst in the past 20 years. Rainfall anomalies over NE Brazil are related to the Southern Oscillation and sea surface temperature (SST) anomalies in the tropical Atlantic Ocean. Variations in the Southern Oscillation index preceded the corresponding rainfall anomalies by about 2 months. Correlation coefficient between the NE Brazil seasonal rainfall and mean monthly SST anomaly in the tropical Atlantic showed a gradual increase from January to March. However, examination of sea surface temperature anomalies in the Atlantic for the first 3 months of 1983 indicated only a weak relationship with rainfall anomalies. This suggests that for the 1983 event east‐west Walker type circulation was more important than the north‐south meridional circulations forced by SST anomalies in the Atlantic.
Variability of climatic boundaries in Israel—Use of modified Budyko‐Lettau aridity index
Authors: Joseph Joachim H. , Ganor Eliezer
Published: February 2007

A modified Budyko‐Lettau dryness, ratio, D*, has been used to depict the fluctuation of climatic boundaries in Israel during the period 1963–1973. The analysis is partly based on and partly compared with the available climatic data.

The use of D* for the analysis of regional year‐to‐year climatic fluctuations in nature or in numerical climate simulations seems to be warranted.
Some aspects of rainfall associated with cyclonic storms of the Bay of Bengal
Authors: Mooley D. A. , Mohile C. M.
Published: February 2007

Mean and maximum rainfall associated with cyclonic storms of the Bay of Bengal striking the two sections of the east coast of India are studied by examining the rainfall distributions along the coast on both sides of a point (P) at which the storms struck the coast at a right angle during the period 1877–1980. The distributions are presented for mean and maximum rainfall recorded during the 24 hours of the day of crossing and the previous two days. Extensive rainfall, of wavy pattern to the north of P and intensive rainfall to the south of P are observed. Possible reasons for these are given.

Rainfall recorded within 1° on either side of P associated with each storm has been examined from the viewpoint of suitability of a statistical model. The distribution is highly skewed. The gamma distribution, which covers a wide range of skewness, has been tried. It is seen that a gamma probability model shows a good fit to the mean rainfall over this area.

Variability of rainfall within a distance of 1° on either side of P is also studied and it is found that variability is more in the southern sector than in the northern sector.
On a relationship for estimating precipitable water vapour aloft from surface humidity over West Africa
Authors: Adedokun J. A.
Published: February 2007

A relationship of the form W = αqb(α, b constants) has been established between precipitable water W(cm) aloft and the surface specific humidity, q(g/kg) over West Africa using an analysis of variance (ANOVA) technique on upper air climatological data spanning over a decade.

Owing to the difference in the climatological patterns of the precipitable water between the southern and northern zones of the region, no single relationship was found suitable for both zones. Consequently, separate values of α, b have been obtained for each of the Northern and Southern zones; namely for the Northern zone (α, b) = (0.271, 1.039) and for the Southern zone, (α, b) = (6.45 × 10−4, 3.154).

Initial tests carried out on the model using daily soundings made over the region during the West African Monsoon Experiment (WAMEX) gave encouraging results as established by use of Kolmogorov‐Smirnov tests. Earlier models, generally of the form: In W = A + Btd (A, B constants and td, dew‐point temperature (°F)) tried on the same basis were found to be rather inadequate over the region.
Minimum temperature surveys based on near‐surface air temperature measurements and airborne thermal scanner data
Authors: Kalma J. D. , Laughlin G. P. , Green A. A. , O'Brien M. T.
Published: February 2007

Minimum air temperature measurements and airborne thermal scanner measurements of apparent surface temperature were obtained in a regional frost risk study in gently undulating grazing country in the Southern Tablelands of New South Wales, Australia.

The minimum air temperature data obtained at 7 sites on 100 nights have been used to derive a predictive relationship between temperature lapse rate and night‐time wind speed and net radiation loss. An extended network was used on 30 nights using an additional 24 sites. Excellent agreement was observed between the lapse rates collected from both the 7‐station and 31‐station networks on 24 nights.

Maps of minimum air temperature across the region have been obtained for selected individual nights using Laplacian smoothing spline functions based on elevation and map co‐ordinates.

Thermal scanner data were obtained with an aircraft on two nights and the paper presents detailed comparisons between apparent surface temperature data and minimum air temperatures obtained from the regional maps.

These comparisons have made it possible to successfully distinguish between broad topographic controls and the effect of local surface characteristics, especially in the case of high‐resolution thermal scanner data. Such local controls include the effects of trees, surface water and various man‐made features, as well as very local topographic features such as narrow depressions, which are only noticeable from site surveys and detailed aerial photography. It is concluded that thermal imagery is an important aid in understanding spatial distribution patterns of night‐time air temperatures and hence in regional frost risk assessment.
An index method for analysing precipitation surplus or deficit: Preliminary developments
Authors: Sefe F. T. K.
Published: February 2007

An index method for analysing precipitation surplus or deficit is presented. By indexing the surplus or deficit to the long‐term mean annual precipitation, temporal and spatial comparisons are facilitated. Preliminary results indicate that the computed indices are normally distributed and are amenable to the types of frequency and probability analyses normally used in water resources problems. It seems that the computed indices could be used for characterizing the intensity and severity of a precipitation deficit or drought spell.
Chinooks in Southern Alberta: Some distinguishing nocturnal features
Authors: Nkemdirim Lawrence C.
Published: February 2007

Various attempts to define chinooks from commonly observed surface weather phenomena have met with limited success. It is now apparent that many of the features normally considered unique to chinooks in southern Alberta are shared with other weather types. A new study found that there were statistically significant differences between both the means and variances of weather variables measured in chinooks and non‐chinooks in only one of eight variables considered. The means differed significantly in three parameters whereas the variances differed in four. But the significance attained by the difference in variance was always higher than attained in the mean, indicating that discrimination between the two weather types was more strongly expressed in the range of conditions experienced than in the mean condition. Collectively the variables were able to separate chinooks from non‐chinooks in all but one of the events studied.
Synoptic‐dynamic character of ‘bursts’ and ‘breaks’ in the South‐West U.S. summer precipitation singularity
Authors: Carleton Andrew M.
Published: February 2007

Marked intraseasonal variations in the intensity of the south‐west U.S. summer precipitation singularity (the ‘Monsoon’) are identified for the years 1980–1982 from a previously developed satellite cloud climatology. These ‘bursts’ and ‘breaks’ are examined synoptically by compositing sea level pressure and 500 mb height data. Both types of events are controlled by the upper‐level flow. This typically involves, for bursts, the intrusion into subtropical latitudes of a trough in the westerlies with attendant cold air advection. In conjunction with intense surface heating, this produces widespread atmospheric destabilization over the South‐west. Monsoon breaks are characterized by enhanced ridging of the Bermuda and North Pacific subtropical anticyclones with associated subsidence over southern Arizona/California. Between‐year differences in these composite patterns are identified, and it is suggested that wetter summers may be characterized by larger within‐season variations in 500 mb heights and isobaric curvature compared with drier summers. Several 500 mb synoptic types associated with burst events are determined subjectively, and composite patterns are derived. These indicate that bursts occasionally occur with anticyclonic conditions aloft, but the latitude of the ridge seems critical in determining the extent of moist air penetration from the south.

Twice‐daily aerological soundings at five stations in the South‐west and northern Mexico are also used to determine the thermodynamic characteristics of bursts and breaks and the dominant source of monsoon moisture. Monsoon bursts in Arizona are evidently a combination of moisture from the Gulf of Mexico, transported on a light south‐easterly flow, and more rapid lower‐level ‘surges’ originating in the Gulf of California. Moisture from the latter source is transported rapidly into the Great Basin on a low‐level wind‐speed maximum of marked directional constancy. This study has implications for longer‐term summer rainfall‐synoptic circulation variations in the American South‐west.
A Technique for estimating regional surface albedos using geostationary satellite data
Authors: Nunez M. , Skirving W. J. , Viney N. R.
Published: February 2007

Data from the Japanese geostationary meteorological satellite are used to map surface albedo in Tasmania, Australia. Satellite data are corrected for atmospheric depletion and the narrow spectral window of the satellite sensor. The effect of non‐Lambertian reflection is discussed.

A composite albedo map is presented based on eight mostly cloudless images taken at 10.00 and 13.00 local time in a period spanning the end of January to the beginning of February, 1985. The map features a distinct east west gradient in the albedo, with lowest values measured in the rain‐forest environment of the western highlands. Highest values are observed among areas of cleared farmland in the eastern midlands.
Subjectivity in A computer‐assisted synoptic climatology I: Classification results
Authors: Yarnal Brent , White Dale A.
Published: February 2007

Numerous computer‐assisted synoptic climatological classifications were performed to determine the validity of a commonly used ‘objective’ typing scheme. In this study, the correlation‐based Kirchhofer technique was used to classify a large population of daily mean sea level pressure grids. Unlike previous methodological studies, metric parameters were held constant while the form of the data used in the classifications was varied. It is demonstrated that sample size, number of grid points and the particular random sample used will affect the classification results, thereby confirming previous work that has suggested that such typing schemes are extremely subjective. It is recommended that users of correlation‐based techniques obtain a number of relatively large random samples of size n ≥ 1000 and perform several classification runs in order to reach an ‘optimum’ solution.
A note on the effect of urbanization on temperature in Ibadan
Authors: Adebayo Yinka R.
Published: February 2007

The effects of urbanization on the temperature characteristics of a tropical city are examined. Twenty‐year records of maximum, minimum and mean temperatures were extracted from four established meteorological stations in the Ibadan area. Three stations are within the urban region and the remaining one, which serves as the control station, is situated in a rural environment, outside the city. Analysis shows that the urban heat island effect of the city is clearly reflected in the magnitudes of night‐time minimum and mean temperatures, whereas the day‐time maximum temperature is slightly lower, in the city. There is no clear evidence of any change in the urban temperature excess over time. The heat island effects of the city are more noticeable towards the end of the dry season and in the early part of the rainy season. The mean heat island, as reflected by the night‐time minimum temperature, is about 1.0 K during the dry season, and 0.5 K during the rainy season.
The CO2 temperature response. A comparison of the results from general circulation models with statistical assessments
Authors: Schönwiese Christian‐D , Malcher Jürgen
Published: February 2007

General circulation models (GCMs), which simulate the climate response to a doubling of the atmospheric carbon dioxide (CO2) concentration show a considerable variety of results even in respect to the globally averaged air temperature response near the ground. There is a need to verify the GCM results against an observational climatic data basis where noi only the global average but also the regional patterns and seasonal variations in the response are important. The statistical assessments described here are based on an annual time series 1851–1984 of the mean northern hemisphere surface air temperature and on corresponding monthly gridded data 1881–1980. The noise is reduced using a Gaussian 10 year low‐pass filter. Natural forcing is taken into account in terms of volcanic and solar forcing parameters. The sensitivity of the CO2‐induced temperature signal obtained from the statistical regression model is tested using different CO2 time series and both a linear and a logarithmic CO2‐temperature relationship. The statistical CO2 doubling simulations give results that are similar to most of the GCM experiments with respect to the zonal mean and seasonal response but not always with respect to the regional changes. Finally, the regional CO2 induced signals are statistically compared with those due to volcanic forcing.
An analysis of the rainfall regimes on the coastal region of Guyana
Authors: Shaw Anthony B.
Published: February 2007

Rainfall on the Guyana coastal region is produced by mesoscale synoptic systems occurring throughout the year and by large‐scale systems associated with the seasonal movement of the ITCZ. Consequently, the rainfall is highly variable in time and space. This variability has often adversely affected crop production.

Daily rainfall data are examined for a selected sample of stations in order to establish the onset dates of effective and persistent rainfall within the two major rainfall seasons. Onset dates show significant inter‐station and yearly variations for the winter (short wet) season while they vary only moderately for the summer (long wet) season.

Correlation analysis has also been used to examine the spatial coherence of the rainfall. Seasonal differences have been found. Winter rains tend to be more localized and appears to be produced by a larger number of small‐scale systems. Summer rains appear to be more spatially coherent owing to the influence of energetic large‐scale systems associated with the ITCZ.
Climate patterns derived from chinese proxy precipitation records: An evaluation of the station networks and statistical techniques
Authors: Ronberg Baruch , Wang Wei‐Chyung
Published: February 2007

The 510‐year, 120‐stalion proxy precipitation records published by the State Meteorological Administration of the People's Republic of China were used to study the large‐scale climate patterns, including the climate regions and interregional relationships. In this paper, we present a study of the sensitivity of the climate patterns of recent years (1950–1979) to choice of stations and statistical techniques. First, the original highly inhomogeneous 120‐station network is reduced to a quasi‐uniform network comprising 93 stations. Next, based on the reduced network, two new networks arc derived‐a47‐station network with the same spatial domain and a 29‐station network with half the domain. The climate patterns for these station networks are compared by use of two different statistical procedures, principal component analysis/cluster analysis and factor analysis with orthogonal and oblique rotations. It is found that the climate patterns remain similar when the density and domain of the 120‐station network are systematically reduced. It is also found that similar climate patterns are obtained using either of the chosen statistical techniques, although factor analysis appears to be more sensitive to changes in the network than principal component/cluster analysis. Examination of measurement data also reveals large‐scale climate patterns similar to those derived from the proxy data. Finally, the climate patterns are shown to be consistent with geophysical factors.
Subjectivity in a computer‐assisted synoptic climatology II: Relationships to surface climate
Authors: Yarnal Brent , White Dale A. , Leathers Daniel J.
Published: February 2007

Earlier work has demonstrated that the results of a correlation‐based (Kirchhofer) synoptic classification are dependent on the way that the internal parameters and data are used. In this study, varying classifications are compared to the climate at one location. The results show that associations between temperature and the synoptic patterns are usually physically interpretable and somewhat stable, whereas precipitation‐synoptic type relationships are more difficult to explain and highly variable. We conclude that varying classifications do not produce equivalent synoptic climatologies. Furthermore, we know of no apparent objective or subjective means for determining a ‘best’ classification. Based on these findings, we discourage the use of correlation‐based techniques in all but the most controlled situations.
Alternative strategies for the UK department of health and social security (DHSS): Some comments
Authors: Moores W. H.
Published: February 2007

Giles and Kings (1987) suggest the use of windchill as an alternative indication of coldness for use in the UK Department of Health and Social Security's exceptionally cold weather payments scheme. It is argued here that the use of windchill confers no obvious benefit and would result in added problems.
Comments on ‘power spectra and coherence of drought in the interior plains by E. O. Oladipo’
Authors: Currie Robert Guinn
Published: February 2007

Oladipo failed to detect any long‐period signals in precipitation records from North America, in particular those from the states of Arkansas, Illinois and Iowa. In this paper evidence is presented for signals near 19 years and 10 to 11 years in 64 records from these three states. A series of errors led to Oladipo's failure to detect the terms, and these are discussed.
An approach to the variability of urban surface energy budgets under stratified synoptic weather types
Authors: Todhunter Paul E.
Published: February 2007

A simulation‐based method for examining the response of urban canyon energy budgets to stratified synoptic weather types is outlined and briefly illustrated. The approach contains three steps: (1) an objective grouping procedure consisting of a principal components analysis of sixteen climatic variables followed by a cluster analysis of the resulting component scores is applied to the Boston, Massachusetts Typical Meteorological Year data set to group each day into a limited number of synoptic weather types; (2) a characteristic day is identified for each weather type based upon a minimized sum‐of‐squares criterion; (3) the URBAN3 numerical model is used to simulate the surface energy budget of a standard urban canyon for each of the synoptic weather types.

Results illustrate the response of urban canyon surface energetic patterns to stratified synoptic weather types. The objective grouping procedure utilized should be applicable to a wide variety of computer modelling applications involving complete daily climatic data sets.
Recent decadal climate variations in the tropical Pacific
Authors: Cooper Neill S. , Whysall Kim D. B. , Bigg Grant R.
Published: February 2007

The existence of two major variations in the climate of the tropical Pacific during the period 1920–1983 is demonstrated. During 1937–1946 an anomaly of much longer duration than, but of somewhat similar character to, an El Niño event occurred. It contained within it several swings of the Southern Oscillation Index previously thought to be separate events, but which we hypothesize to be part of a longer coherent disruption to the tropical Pacific ocean‐atmosphere system. This anomaly is described using ship observations of winds and sea‐surface temperature, island sea‐level pressure records and length‐of‐day measurements. In all records examined the anomaly was persistent, and as strong as the recent 1982/1983 El Niño, though of far different character. Evidence for a long‐term change in the atmospheric circulation over the tropical Pacific in the 30 years since 1950 is also presented. A combination of the trade winds gradually strengthening by 1 ms−1 over this time and changes in subtropical pressure of up to 1 mb leads to a hypothesized change in the circulation.
Macro‐regional definition and characteristics of Indian summer monsoon rainfall, 1871–1985
Authors: Gregory S.
Published: February 2007

A case is made for regional‐scale Indian summer monsoon rainfall data and analysis, intermediate between the widely used all‐India and meteorological subdivision data sets. Macro‐regional units are constructed from the data provided by Parthasarathy et al., 10 being defined using principal components analysis and a classification algorithm. The temporal changes of summer monsoon rainfall over the period 1871–1985 are analysed and described for each of these regions, and the marked diversity of fluctuations between the regions is emphasized by a variety of methods. The degree of relationship is considered for each region between drier and wetter conditions and (i) El Niño and non‐El Niño years, and (ii) SST anomalies in the eastern tropical Pacific. Clear regional differences are apparent, but even statistically highly significant relationships are not large in any absolute sense. The need for explanatory analyses at the regional scale, in addition to those at the more common all‐India scale, is stressed.
Statistical distribution of daily rainfall and its association with the coefficient of variation of rainfall series
Authors: Ananthakrishnan R. , Soman M. K.
Published: February 2007

The paper deals with the statistical analysis of the daily rainfall series (monthly, seasonal, and annual) of 15 Indian stations representing a wide variety of rainfall regimes, utilizing the data for the period 1901–1980. The study focuses attention on the normalized rainfall curve (NRC) depicting the association between cumulated percentage rain amount (x) and cumulated percentage number of rain days (y) of the rainfall series. It is shown that the NRC is uniquely determined by the coefficient of variation (CV) of the rainfall series. There is no universal NRC that can represent all rainfall regimes.

The equation x = y exp[ — b(100 — y)c], where b and c are two empirical constants, gives a good analytical representation of the NRCs over a wide range of CV values of the rainfall series. This analytical equation is able to account for the occurrence of high rainfall intensities towards the upper extremity of the NRC for rainfall series with high values of CV. The rain intensity corresponding to any point on the NRC is inversely proportional to the slope of the tangent at that point. The point where the slope is 45° corresponds to the mean rain amount per rain day (r) of the rainfall series. It is shown that days with rain amount greater than r (considered as days of significant rainfall) constitute about 30 per cent of the rain days and contribute 75–80 per cent of the total rain amount, with some local and seasonal variations.