bluuebunny/crossref_metadata_2025 huggingface dataset:
The low latitude influence on winter rainfall in Victoria, south‐eastern Australia—I. Climatological aspects
Authors: Wright W. J.
Published: February 2007

A synoptic mechanism is proposed for a long‐known, but synoptically little‐studied, tropical influence on northern Victorian rainfall during the winter half‐year, based on results from a 12 winter (June‐September) climatology covering the period 1971–82. It is shown that heavy precipitation events in northern Victoria commonly result from ‘interactions’ between cloud masses originating at low latitudes within the Australian region, and high amplitude frontal troughs moving within the midlatitude westerly flow. Most of the precipitation falls ahead of surface cold fronts, within moist northerly airstreams. The low latitude cloud masses involved may originate in several ways, but most commonly take the form of so‐called ‘northwest cloudbands’ originating over the tropical Indian Ocean northwest of Australia.

‘Interacting’ frontal systems contribute some 50 per cent of northern Victoria's winter precipitation, but the presence of a relatively modest topographical barrier across the centre of the State substantially reduces their contribution to total rainfall in southern and southeastern Victoria. A distinction is made between these ‘interacting’ (or I) fronts, and ‘non‐interacting’ (NI) fronts: although I fronts occur less frequently than NI fronts, they produce considerably heavier rainfall. Analysis of the moisture content of prefrontal airmasses reveals that the airmasses ahead of I fronts are generally much moister than those ahead of NI fronts, and that the heavier I frontal rainfall is largely attributable to this moisture. An investigation is also made of moisture‐rainfall relationships for cold lows, also a significant source of precipitation throughout Victoria.
Seasonal forecasting of the Kenya coast short rains, 1901–84
Authors: Farmer Graham
Published: February 2007

A rainfall anomaly time series for the Short Rains (September to December) on the Kenyan Coast (KCS) is derived for the period 1901–84. On the year‐to‐year time scale a high degree of association can be seen between high/low extremes of a Southern Oscillation Index and negative/positive anomalies in the KCS series.

The SOI‐rainfall relationship is investigated seasonally with KCS lagging the SOI series by one, two and three seasons. A decay of the correlation with increasing lag can be seen. When the time series is divided into 1901–42 and 1943–84 the relationships are stronger in the more recent period. Some forecasting skill does seem possible using the June to August (JJA) SOI to predict the September‐December rains. While the 1901–42 period shows a skill not much improved from using a simple climatological forecast, the 1943–84 period shows a much stronger relationship. Possible reasons are discussed for the disparity between the two time periods, also evident in results from others parts of Africa and Asia. There may well have been a change in some underlying climate mechanism between the early decades of this century and the more recent decades.
Seasonal frequency variations in the 40–50 day oscillation
Authors: Gray B. M.
Published: February 2007

The effect of local sea surface temperature changes on frequency shifts in the 40–50 day oscillation is examined using seasonal means. Data were stratified into ENSO (El Niño‐Southern Oscillation) and non‐ENSO years and a significant difference found. In non‐ENSO years, a seasonal shift was noted at some sites. Seasonal frequency means were described qualitatively in terms of sea surface temperatures and changes in zonal circulation cells.
On drought in south‐eastern United States
Authors: Henry James A. , Dicks Steven E.
Published: February 2007

The temporal characteristics of drought in Florida are compared with drought behaviour in the remainder of the southeastern United States, and are discussed in relation to previous studies by other researchers. Florida's wet/dry episodes are frequently out of phase with other south‐eastern States. Possible causes for this phenomenon are presented.
Homogenized long‐period Southern Oscillation indices
Authors: Wright Peter B.
Published: February 2007

Many research workers require indices of the Southern Oscillation that are continuous for a long period, homogeneous and easily updated. This paper aims to provide such indices. The method used is to compare indices based on sea‐surface temperature (SST), rainfall and pressure, and thereby to make some corrections to improve homogeneity. To fill data gaps, substitutions are proposed based on regressions between indices over 1950–1979. Tabulations are presented of the recommended long‐period indices: SST monthly 1872–1985; rainfall monthly 1893–1983; and pressure seasonal 1851–1984. The most extreme years according to the two monthly indices are listed.
Advances in the study of sub‐saharan drought
Authors: Druyan Leonard M.
Published: February 2007

The scientific community has responded to the protracted sub‐Saharan drought with a variety of research projects and publications. Related research has dealt with the spatial or temporal analysis of rainfall anomalies, the local or distant atmospheric circulation characteristics that precede or accompany the anomalies, or the influence via teleconnections of remote sea‐surface temperature (SST) anomalies on Sahel precipitation. General circulation models (GCM) have been profitably utilized to test several hypotheses related to sub‐Saharan drought, including the impact of changed albedo, surface roughness, surface evapotranspiration, and SST. This article reviews a selection of the relevant literature and offers an integrated discussion of research results. Conclusions indicate that certain ocean‐atmosphere climate systems combine to deprive the sub‐Sahara of the moisture required for copious monsoon rains during some drought years, while during others, atmospheric dynamics over North Africa limit the number or intensity of the wave disturbances that initiate the moist convection associated with much of that region's summertime rainfall.
The control by atmospheric pressure patterns of sulphate concentrations in precipitation at Eskdalemuir, Scotland
Authors: Farmer G. , Davies T. D. , Barthelmie R. J. , Kelly P. M. , Brimblecombe P.
Published: February 2007

It is shown that, on a monthly basis, certain sea‐level atmospheric pressure patterns can be identified which are conducive to, or mitigate against, high excess sulphate concentrations in precipitation at Eskdalemuir, Scotland. This is not simply a consequence of the amount of precipitation influencing the concentration. The differences in the pressure patterns for months grouped into ‘high’ and ‘low’ excess sulphate concentration reflect the relative importance‐of transport from pollutant source regions and from regions with relatively small source strengths. It is the intensity of the pressure gradients over Europe and the Atlantic, combined with the position of the meridional axis of the Iceland Low/Azores High couplet, which appears to influence the monthly excess sulphate concentration in precipitation. The existence of these relationships on a monthly time‐scale points towards a climatic control on acidic deposition, and introduces the possible role of climatic change.
A study of climatic variability in Nigeria based on the onset, retreat, and length of the rainy season
Authors: Olaniran O. J. , Sumner G. N.
Published: February 2007

The long‐term variability of rainfall conditions in Nigeria in terms of the onset, retreat, and length of the rainy season has been analysed, using pentad data for the period 1919–1985. Data were grouped into four areas, arranged in a south‐north transect; the Coastal, Guinea‐Savanna, Midland and Sahelian Zones. The series for retreat of rainfall showed evidence for quasi‐triennial and quasi‐6‐year oscillations, while that for rainy season length displayed quasi‐biennial and quasi‐triennial oscillations. No consistent spectral peaks emerged for changes in the date of onset of the rainy season. There is spatial coherence in variation in the date of the retreat of rainfall over the whole country, whilst for the date of onset of the season spatial coherence is limited to southern Nigeria (Coastal and Guinea‐Savanna Zones). Northern Nigeria (Midland and Sahelian Zones) and southern Nigeria (Coastal and Guinea‐Savanna) emerge as distinct areas in terms of spatial coherence in the variation of the length of the rainy season. There is also evidence for a secular change in the date of the retreat of rainfall for the whole country during the period 1939–1985, and in the date of onset of rainfall for southern Nigeria for 1968–1985.
Classification of the climate of England and Wales based on agroclimatic data
Authors: White E. J. , Perry A. H.
Published: February 2007

Classifications of the climate of England and Wales, based on agroclimatic data from L. P. Smith, are described. A principal component analysis was carried out on these data in order to simplify them by removing inessentials. This showed that most variation in the variables was associated with maximum soil moisture deficit in summer and effective transpiration, both important for plant response. Six methods of cluster analysis were then used, two of which, further neighbour and minimum variance, were selected for comparison. The groups into which areas were classified are discussed in terms of the two climatological variables. The resulting classification was compared with others in the literature.
Principal components of the surface wind field in the United States: A comparison of analyses based upon wind velocity, direction, and speed
Authors: Klink Katherine , Willmott Cort J.
Published: February 2007

Three statistical summaries of the 1975 surface wind field in the United States are computed using principal components analysis (PCA). Separate analyses of wind velocity and direction are made with vector‐based PCA, and the scalar (zonal and meridional) components of wind are described using a scalar‐based PCA. Comparisons indicate that results of the three PCAs are not equivalent. Vector PCA yields the most physically comprehensive components because the velocity observations are not decomposed into direction and speed, or into zonal and meridional coordinatesa priori.Directional and scalar‐based PCAs appear similar but since they only summarize one coordinate of velocity at a time, they represent incomplete descriptions of the wind field. Vector‐based PCA then is the most appropriate of the three for investigating wind fields or other vector‐valued data sets.
Topographical and coastal influence on spatial precipitation patterns in Tunisia
Authors: Berndtsson Ronny
Published: February 2007

The spatial properties of the correlation structure based on daily rainfall data from 67 stations throughout Tunisia over a 5‐year period are examined. The correlation structure is generally markedly anisotropic as influenced by topography and the coast. These two factors seem to influence the correlation pattern differently during different months. The mean areas within the 0.7 correlation isoline for all subgroups vary from about 1000 km2 in the early autumn to about 7000 km2 in the winter months.
Application of a climate departure index to the study of freeze dates and growing season length in the south‐eastern United States
Authors: Suckling Philip W.
Published: February 2007

A climate departure index (CDI) is utilized to study the variability of last spring‐freeze dates, first autumn‐freeze dates, and growing season length in the south‐eastern United States for the period 1911–1986. The CDI is useful for determining how ‘normal’ or ‘unusual’ a particular year is compared to the long‐term situation for the region under consideration. This study shows that when distinct long‐term climatic trends exist for the climatic element under study, the CDI should be calculated using residuals from a trend line rather than simply comparing individual yearly values to the long‐term average.

With respect to last spring‐freeze and first autumn‐freeze dates and growing season length in south‐eastern United States, the CDI analysis illustrates that a period of rather ‘normal’ conditions occurred during the late 1950s to early 1970s. Slightly higher CDI values for the 1980s, which implies a greater occurrence of extreme events (i.e. greater climatic variability), is not unprecedented given the high CDI values earlier in the century. The decade of the 1940s especially experienced a greater frequency of unusual last spring‐freeze dates and first‐autumn‐freeze dates (either extra early or late) as well as larger variations in growing season length.
Spatial and temporal variations in Australo‐Indonesian region cloudiness
Authors: Kuhnel Ivan
Published: February 2007

Spatial and temporal variations in cloudiness of the Australo‐Indonesian region are examined with the help of a newly created cloudiness data set, based on GMS‐IR imagery. As represented by the first Varimax rotated principal component pattern of the Australo‐Indonesian region cloudiness, the band of tropical cloudiness is dominated by a clearly defined eastward cluster propagation, as well as a more complicated 40–50‐day oscillation pattern. Details of these phenomena are discussed.
Surface humidity and precipitable water vapour linkage over west and central Africa: Further clarification and evaluation of existing models
Authors: Adedokun J. A.
Published: February 2007

In the light of currently available upper air data for West Africa, an intensive examination is carried out on the linkage between surface humidity and precipitable water vapour, W, over the region, with a view to validating existing empirical models as well as identifying seasonal variability in their applicability.

For this objective, calculations of precipitable water vapour using available monthly mean upper air data from 13 stations in West and Central Africa (for the period 1971–1984) have been carried out and a comparison made with results from empirical models using the Kolmogorov‐Smirnov test.

While overall fair agreement was obtained between actual and estimated values of W, using the power law relationship of Adedokun, it was found that the model performed better during the rainy season than during the Harmattan. Ojo's InW‐td(td, dew‐point temperature) linear model, however, performs better during the Harmattan than the rainy season.

The location of the Inter Tropical Discontinuity (ITD) relative to the various stations and ocean‐atmosphere interaction effects pose as controls to the regime of application of these surface humidity based models. An update of the regression base period used may be necessary for better performance.
Tropical‐extratropical cloudband climatology based on satellite data
Authors: Kuhnel Ivan
Published: February 2007

A global tropical‐extratropical cloudband (TECB) climatology, using a clear definition of TECBs, and based on NOAA IR satellite imagery for the period 1979–1983, is presented. It is shown that on a global scale we can distinguish between 14 different TECBs, seven of them in each hemisphere. The cross‐correlations of the TECB frequency anomalies with tropical pressure and sea‐surface temperature anomalies indicate that the activity of these phenomena can respond strongly to tropical forcing from different parts of the world. Whereas only 10 TECBs show a significant response in their activity to the Southern Oscillation, the frequency anomalies of all 14 TECBs correlate significantly with other pressure anomaly indices.
A satellite‐derived climatology of polar‐low evolution in the North Pacific
Authors: Yarnal Brent , Henderson Keith G.
Published: February 2007

A climatology of polar‐low evolution for seven low‐sun seasons (November to March) in the North Pacific is presented. The data were collected by the subjective interpretation of Defense Meteorological Satellite Program (DMSP) infra‐red imagery, using a cloud vortex classification scheme designed especially for use with medium to high resolution imagery. For the study period, about two‐thirds of all polar lows that formed over the North Pacific evolved to a higher stage. Approximately one‐half of those (one‐third of the total) passed through all stages of development from cyclogenesis to decay. The more common form of cyclogenetic polar low in the North Pacific, the comma cloud, continued to develop two‐thirds of the time, while the less common spiraliform only evolved to a higher stage of development in two‐fifths of the cases. Those polar lows that formed in certain key areas were likely to evolve to a higher stage, while other specific locations discouraged continued development. No readily discernible difference between gross size and cloud characteristics of evolving and non‐evolving polar lows was present in the satellite data, suggesting that additional data are needed to forecast correctly which will develop into mature cyclones.
Regionalization of thunderstorm rainfall in the contiguous United States
Authors: Easterling David R.
Published: February 2007

The amount of precipitation recorded during individual thunderstorms was determined at 220 stations in the contiguous United States of America for a 30‐year period. The probability distribution of thunderstorm rainfall amounts at each station during each season was summarized by use of the incomplete gamma distribution. The incomplete gamma distribution is completely described by two parameters, which were used in a clustering routine to determine whether regionalizing tendencies exist in the probability distributions. Large‐scale regions were found when the results of the clustering were mapped. In general, these regions corresponded well with the areas of dominance of many of the proposed mechanisms for thunderstorm development.
Hawaiian drought and the Southern Oscillation
Authors: Chu Pao‐Shin
Published: February 2007

Long‐term rainfall records at key locations on the Hawaiian Islands and the Southern Oscillation Index (SOI) are examined to reveal the impact of large‐scale atmospheric circulation on Hawaiian rainfall. By compositing six major drought winters, it is found that they were preceded by a persistently low phase of the Southern Oscillation starting from March of the preceding year. Correlation analysis indicates that the spring SOI is not significantly correlated to rainfall in the subsequent seasons. In contrast, changes of the SOI in summer lead corresponding changes of rainfall by two to three seasons. Similarly, changes of the SOI in autumn lead changes of rainfall by one to two seasons. These results are also confirmed by scatter diagrams. Although a large negative SOI anomaly in summer or autumn can be regarded as a precursor to a drought for the following winter or spring, the inverse relation, namely, a positive SOI anomaly leading abundant rainfall does not necessarily follow. As an empirical rule, a value for the summer SOI of −2 or below, or a value for the autumn SOI of −1 or below, or both, indicate the occurrence of a dry winter.

During drought episodes, Hawaii was located under an area of strong subsidence, and synoptic systems that normally produce winter and spring rainfall in the Hawaiian Islands were retarded. An anomalously cold sea‐surface temperature in the north‐central Pacific may also further enhance and prolong the dryness by reducing the rate of evaporation from the sea surface and by stabilizing the overlying air.

Individual forecasts carried out for recent years reveal that severe drought during an El Niño/Southern Oscillation (ENSO) winter could be predicted two seasons in advance using simple regression models. For the non‐ENSO drought winter, forecasting ability degrades somewhat. Overall, by means of a cross‐validation technique, antecedent conditions of the large‐scale pressure see‐saw are useful predictors for Hawaiian winter rainfall anomalies, particularly when an ENSO‐like phenomenon has started to develop.
Preliminary measurements of net radiation and evaporation over bare soil and fallow bushland in the Sahel
Authors: Wallace J. S. , Gash J. H. C. , Icrisat M. V. K. Sivakumar
Published: February 2007

Net radiation and evaporation are compared over two contrasting land surfaces, fallow bushland and bare soil, in Niger, West Africa. Data are presented for 6 days, before and after a large rainstorm (39 mm), which illustrate how evaporation from the bush vegetation changed little in comparison with the larger change in evaporation observed over the bare soil. Net radiation over the bush vegetation was 20 per cent greater than that over the dry bare soil, but only 12 per cent greater than that over wet bare soil. These differences are consistent with the expected difference in albedo and surface temperature of the two surfaces.
Satellite climatology of ‘polar lows’ and broadscale climatic associations for the Southern Hemisphere
Authors: Carleton Andrew M. , Carpenter Duane A.
Published: February 2007

A climatology of polar air cloud vortices (so‐called ‘polar lows’) is derived for the Southern Hemisphere using sets of medium resolution (5–4 km) DMSP (Defense Meteorological Satellite Program) imagery. The climatology is for the winter season (June through to September) and covers the 7–year period 1977–1983. Both comma cloud and spiraliform polar air signature types are considered, as identified in recent satellite studies for the Northern Hemisphere. The comma clouds dominate over a wide range of ocean latitudes, whereas the spiraliform systems occur less frequently (about 1:10 for the hemisphere), and show maximum frequencies in sea ice latitudes around mid‐winter (about 1:3).

Within‐season variations in the locations of maximum occurrence of polar air systems are consistent with the large‐scale changes in the longwaves associated with the semi‐annual oscillation of surface pressures. Interannual variations in polar low occurrence for the seven winters appear connected, at least in part, with changes in the amplitude of sea‐level pressure (SLP) wavenumber one. When the seasonal cycle is amplified, as in the year of a ‘warm’ ENSO (El Nino/Southern Oscillation) event (e.g. 1982), large numbers of polar lows are observed south‐east of Australia and around New Zealand. This contrasts with the situation for year (−1) of a warm event (e.g. 1981), when the annual cycle of the trough is suppressed. At that time, reduced frequencies of cold air outbreaks in the New Zealand area are accompanied by fewer polar lows.

On a seasonally averaged basis, and in most winters, there is a positive relationship between the regional extent of the Antarctic sea ice, the longitudes of preferred occurrence of cold air outbreaks and the incidence of polar lows. This effect may be enhanced just downstream of areas of strongest oceanic heat loss to the atmosphere.
A quasi‐biennial oscillation in the intensity of the intra‐seasonal oscillation
Authors: Kuma Ken‐Ichi
Published: February 2007

The interannual and annual variations in the intra‐seasonal oscillation (ISO) are examined using upper air radiosonde data at Singapore. Spectral analysis of the zonal wind using the maximum entropy method (MEM) was made for each season, starting from the autumn of 1960 through to 1985. It is shown that the strongest signal of the ISO occurs during the Northern Hemisphere winter, while the weakest occurs in the Northern Hemisphere summer.

The main finding of this study is a quasi‐biennial oscillation (QBO) in the intensity of the ISO. The cross‐spectral analyses indicate that the intensity of the ISO at 150 mbar is well correlated for a time‐scale of 2–3 years with the stratospheric QBO as well as with the strength of the zonal wind and the static stability of the upper troposphere.

These results suggest that the stratospheric QBO may act as a trigger for the tropospheric QBO. The physical interpretation of this interaction requires further work, especially in the field of numerical modelling.
Four‐dimensional empirical orthogonal analysis of climate variables
Authors: Weare Bryan C.
Published: February 2007

An empirical orthogonal analysis method for analysing four‐dimensional geophysical data is derived. The potential utility of this method is illustrated in a sample analysis of the latent heating rates generated by the UCLA atmospheric general circulation climate model. In this example the four dominant eigenfunctions, which explain more than 64% of the total variance, are illustrated. The results show vertical structures, spatial patterns, and time variations that are consistent with a previous diagnosis of the UCLA model heating rates and observed climatology. Possible limitations of this methodology are discussed.
Caribbean tropical storm activity over the past four centuries
Authors: Reading Alison J.
Published: February 2007

This paper examines the frequency and distribution of tropical cyclones and hurricanes throughout the Caribbean using data derived from written accounts, chronologies, and published charts. Problems of incomplete and inaccurate data are overcome by conducting two levels of analysis; a 5° grid square analysis for modern charted data (after 1871) and a subregional analysis for data stretching back to the late fifteenth century. Significant variations in favoured tracks and levels of cyclone activity are identified for the charted and pre‐charted period. High levels of cyclone activity are suggested for the whole or part of the Caribbean during the 1770s to 1780s, 1810s and 1930s to 1950s while troughs in activity are noted around the 1650s, 1740s, 1860s and during the early twentieth century. A noticeable drift eastward in favoured tracks is reported from the mid‐twentieth century onwards, while data available so far this decade suggests a strong midlatitude (15–25 °N) preference by cyclones and hurricanes.
Lengths of very warm and very cold spells at Edgbaston
Authors: Jolliffe I. T.
Published: February 2007

In a recent paper, Hamilton examined the distribution of very warm spells and very cold spells at Edgbaston, Birmingham, during the period 1920–1979. The present paper takes the analysis of these data further by modelling them with a simple statistical distribution, namely the geometric distribution. It is shown that this distribution provides a good fit to the lengths of both warm and cold spells, although there is clear seasonal variation in the mean of the distribution.
THERMAL PATTERNS OF PACIFIC SOUTH AMERICA ASSOCIATED WITH EL NIÑTO/SOUTHERN OSCILLATION
Authors: Walsh Kevin J. , Cerveny Randall S.
Published: February 2007

This study quantifies the magnitude of temperature anomalies associated with extremes of the Southern Oscillation (SO) for 12 long‐record stations and five shorter‐record stations along the west coast of South America. Analysis of t‐tests indicates that nine stations north of 35°S have a strong inverse relationship between their mean annual temperature and the sign of the Tahiti–Darwin Southern Oscillation Index (SOI). Significant inverse relationships are determined between the phase of the Southern Oscillation and (i) summer temperatures (five stations), (ii) autumn temperatures (eight stations), (iii) winter temperatures (eight stations), and (iv) spring temperatures (four stations) for the region north of 35°S. In particular, the northern mid‐latitude stations (18°S–33°S) along the‐west coast of South America show a pronounced seasonal pattern in temperature differences between extremes in the SO. The summer temperature increases associated with negative SOI values may be due to warm air advection from the equatorial regions. The increase in winter temperatures may be caused by warm air advection from the mid‐latitudes associated with greater zonal flow caused by weakening of the South Pacific subtropical high. Stations south of 35°S display little temperature contrast between extremes of the SO.
The Greek heatwaves of 1987 and 1988
Authors: Giles Brian D , Balafoutis Christos J
Published: February 2007

Heatwaves, which occurred in both July 1987 and July 1988 in Greece, are considered from the point of view of human discomfort. Hourly values of dry bulb temperature and relative humidity at Thessaloniki, Larissa, and Athens were used to define various limits of discomfort defined by Terjung, Herrington, Thom, and Tromp. On both occasions the heatwave was most severe in Thessaloniki, although both Greek and British press reports concentrated on morbidity and mortality in Athens. Finally, the synoptic situation at the time of each episode is briefly described.
Changes in the surface temperature of the dead sea and its heat storage
Authors: Stanhill G.
Published: February 2007

Twenty‐seven thermal survey cruises made over 4 years, and 1 year of remotely sensed surface temperatures were used to examine areal, diurnal, seasonal and interannual changes in the temperature of the Dead Sea and in its heat storage.

The satellite data, corrected for a cold bias attributed to the anomalous depth and turbidity of the Dead Sea's atmosphere, indicate a very small areal variation in sea‐surface temperature (SST), typically less than 0·3°C over two‐thirds of the sea surface. The maximum value measured, 4·5°C, was at night in mid‐winter. Below‐surface temperatures showed much larger areal variations caused by the shallower thermocline in the north of the sea. This variability was the reason for the large number of measurements required to assess accurately seasonal changes in heat storage.

Diurnal variations in SST were at their maximum, 3°C, in May, and at their minimum, 0·3°C, in December. During the summer, diurnal differences were clearly evident at a depth of 5 m, with some evidence that a layer twice as deep could be affected.

Seasonal variation in SST was not symmetrical. From mid‐March to early July, surface temperature increased uniformly at 0·10°C day−1, between mid‐September and mid‐November the cooling rate, 0·13°C day−1, was also constant. In January and February, and July and August, SST was almost constant, with day‐to‐day changes less than 0·01°C. The seasonal amplitude in SST was 11·5°C at the surface, 9·6°C at 25 m depth, halved at 35 m, and was reduced to one‐tenth, 1·4°C, at 50 and 75 m.

No significant interannual changes in surface temperature were found since the mid‐winter rise of 3·4°C that occurred 30 years ago. During the last decade the maximum seasonal depth of the thermocline has progressively deepened to 30 m. and below this depth an increase in the temperature of the deeper waters is evident. Possible sources of this heating are discussed.

Seasonal changes in the heat storage were in phase with those in the surface temperature, with maximum values of 9·1 MJ m−2 day−1 in June and –8·7 MJ m−2 day −1 in December. The heat budget (intra‐annual range) of the Dead Sea. 1.16 GJ m2, is one of the highest reported in the literature, although less than that expected from its depth and radiation balance. The sea's heat content increased by an average of 224 MJ m−2 year−1 during the 4 years of this study; the large year‐to‐year variation in this heating was negatively correlated with the fall in sea level.
A theoretically derived distribution for annual rainfall totals
Authors: Revfeim K. J. A.
Published: February 2007

Rainfall occurs as synoptic events, and in many climates annual totals are made up of a moderate to large number of events of varying amounts. Assumption of an underlying Poisson process of event occurrence leads to a simple statistical density, in terms of physically meaningful parameters, for the fourth root of annual totals. Analysis of data for four locations gives estimates of event‐recurrence rates in agreement with the number of rain‐days in the local climates.
Basis for prediction of the sharp reversal of climate from autumn to winter 1988–1989
Authors: Namias Jerome
Published: February 2007

A major reversal in the pattern of temperature anomalies occurred over the contiguous United States of America between autumn of 1988 and winter 1988–1989, a climatic break which reflected a change in phase of the prevailing midtropospheric wind pattern over much of the Western Hemisphere. This transformation is described and attributed to forcing by remote and persistent circulations acting in concert with seasonal forcing. Practically all conventional forecast tools, especially those involving local persistence and climatic contingencies, failed to predict the break. However, the instability of autumn's and November's flow pattern was indicated by: (i) conserving the standardized November height anomalies into winter; (ii) testing the stability of this new hypothetical pattern with the help of statistically derived teleconnections; (iii) applying a modified mean barotropic model to the hypothetical chart; and (iv) extrapolating the winter pattern from trends of circulation within the autumn months. Making use of all this material, a forecast was made for winter at the end of November that turned out highly successful despite the failure of persistence between seasons.
Atmospheric synoptic conditions associated with the initiation of north‐west African depressions
Authors: Prezerakos N. G. , Michaelides S. C. , Vlassi A. S.
Published: February 2007

This study presents a discussion of the main characteristics, and at the same time gives a detailed classification, of the north‐west African depressions within the framework of the close relationship between the 500‐hPa flow and the origin, development, and movement of surface depressions.

The classification relies mainly on the similarities and differences present in the 500‐hPa flow patterns when each north‐west African depression first appears on the surface synoptic chart. For a detailed discussion and, especially for a record of the synoptic conditions that are favourable for the formation of north‐west African depressions, mean 500‐hPa hight and anomaly charts and mean temperature charts, for the years 1970–1974, have been drawn for each subcategory into which the 79 cases fall.

For each of these subcategories, mean charts have also been drawn for 850‐hPa hight and temperature, mean sea‐level (MSL) pressure, and MSL pressure anomalies. The classification resulted in the north‐west African depression being divided in five main categories A, B, C, D, and ST. Category A is divided into four subcategories, the depressions of which appear only during spring. Categories B and C are divided into two subcategories, B1, B2 and C1, C2, and these too occur only in spring, except for subcategory C2, which also appears in autumn. Category D is also divided into two subcategories, which appear only during winter. Category ST (stationary depressions) includes only four cases out of 79 north‐west African depressions. These are shallow, warm‐cored atmospheric circulation systems having no correspondence with the 500‐hPa flow and which appear in late spring and early autumn.

The study showed that the north‐west African depressions do not exhibit significant differences from other extratropical depressions. Their origin, development, and movement largely follow (except for category ST) Sutcliffe's and Petterssen's traditional theories of development.
Development of an automated spatial synoptic climatological classification
Authors: Davis Robert E. , Kalkstein Laurence S.
Published: February 2007

A spatial synoptic climatological index is developed that both characterizes the dynamic and thermodynamic surface weather regime and is capable of assessing and analysing the impact of synoptic‐scale variations on numerous environmental parameters. Based upon surface weather data for the contiguous USA for 1984, daily maps are produced that show those areas under the influence of similar weather conditions. The index is developed by applying principal components analysis to a daily matrix of 141 stations by 24 weather elements (chosen to represent the thermal‐moisture and surface flow characteristics). The resulting component scores are grouped using a two‐stage clustering technique. This yields a map showing lobes of air having relatively homogeneous weather characteristics. These lobes (clusters) are spatially coherent and correspond closely to surface weather map features.

To allow for daily tracking of the clusters and identification days or weeks after disappearance, the means of each of the daily clusters are grouped across days. The resulting 90‐cluster categorization describes all of the major synoptic situations that occurred in 1984. Some of the common categories include maritime and continental polar air masses, frontal passages, and continental high dominance. These groups demonstrate seasonality, regionality, and high within‐category similarity. The resulting maps are useful since they are surface weather maps yet add clarity for environmental interpretation.
USA corn yields, the El Niñmo and agricultural drought: 1867–1988
Authors: Handler Aul
Published: February 2007

The magnitude of spatial and lagged correlation between the sea‐surface temperature anomalies of the eastern tropical Pacific Ocean (El NiñMo) and corn yield in the USA is presented. The record is not homogeneous in that the correlation level varies quite strongly over time. The period between 1910 and 1950 shows completely uncorrelated behaviour. In the most recent 40 years the correlation is found to be strongest in the region just south of the Great Lakes in the states of Illinois, Iowa, and Indiana. Correlation maps are presented that show the degree of association for the corn yield in those 41 states for which records are available. For the entire record the highest correlations occur with the sea‐surface temperature anomalies appearing after the corn is harvested in September to February of the following year. Since corn yields are a proxy for summer agricultural drought in the central part of the USA, the droughts during the period 1910 to 1950 must have had some other cause.
Onset of thunderstorms and precipitation over Northern Nigeria
Authors: Omotosho J. Bayo
Published: February 2007

An empirical prediction scheme for the start of thunderstorms, and the onset and expected amount of rainfall for any year at Kano, Nigeria, is presented, using 8 years' upper air data. The years investigated include two drought years (1973 and 1974) and 3 years of above average rainfall (1978, 1980, and 1988).

Agriculturally sufficient and reliable rainfall begins 5–6 weeks after the vertical wind shear below the African Easterly Jet, ΔUL(surface, 700 hPa), and the mid‐tropospheric shear ΔUM (700–400 hPa), simultaneously satisfy the condition −20≤UL≤−5 ms−1 and 0≤UM ≤10 ms−1, as previously put forward by Omotosho. The total precipitation for any year is found to be well correlated with the total moisture anomaly (specific humidity) from the week of the above‐critical wind shear to the week of rainfall onset. This makes it possible to estimate the expected rainfall total at the very onset of the rains.
Interhemispheric contrasts of mean global temperature anomalies
Authors: Gordon A. H.
Published: February 2007

Northern and Southern Hemisphere series of surface temperature anomalies are compared. The series studied are the University of East Anglia Climatic Research Unit (CRU) monthly series (1854–1986) and the UK Meteorological Office (MO) quarterly series (1856–1989). A major difference is the marked seasonal variation of the warming trend in the Northern Hemisphere, with maximum in winter and minimum in summer. Analysis of the annual cycle of the CRU set suggests a shift in phase of the warm peak in the annual cycle of temperature anomalies from July to January for the period. This shift is a characteristic of the annual cycle itself and does not have to be associated with a greater warming trend in winter than in summer, although it may be.

The series were converted into interannual differences from one month or quarter to the corresponding month or quarter in the following year. Globally, the sequential values of the positive and negative modes of the interannual differences suggest a slow relaxation towards zero with the absolute values of the interannual coolings decreasing faster than those of the interannual warmings. Spectral analyses of the first‐order interannual differences of the monthly CRU and of the quarterly MO series suggest that the temperature field reacts to a Quasi‐Biennial Oscillation pulse in the Northern Hemisphere and to a stronger ENSO pulse in the Southern Hemisphere.
Climate anomalies in Europe associated with ENSO extremes
Authors: Fraedrich Klaus , Müller Klaus
Published: February 2007

Surface pressure, temperature and precipitation anomalies in Europe are composed for the El Niño‐Southern Oscillation (ENSO) warm and cold extremes. During warm event winters, negative pressure departures at western and central European stations are associated with positive temperature and precipitation anomalies; the reverse signals are observed in northern Europe. During cold episodes the field of negative pressure deviations is shifted northward with positive temperature and precipitation anomalies, whereas higher pressure is observed over central Europe. This shift of the anomalies corresponds to a shift in the dominating cyclone track (deduced from weather maps), which may be interpreted as the response of the (sensitive tail end of the) cross‐Atlantic storm track on the high‐pressure anomalies occurring at times in the northern or central part of the North Atlantic/European sector during warm or cold ENSO winters, respectively.
The influence of pre‐existing soil moisture content on Australian winter climate
Authors: Simmonds Ian , Lynch Amanda H.
Published: February 2007

We have performed some experiments with the University of Melbourne General Circulation Model to determine the transient response of the climate system to the imposition of soil moisture anomalies over the Australian continent. Two sets of cases have been performed in which the soil over the entire continent was saturated and was completely dried on the first day of winter and then allowed to evolve normally for 4 months.

The evaporation over most of the Australian continent in the ‘saturated’ case initially was significantly greater than that in the mean and this situation persisted for the 4 month's duration of the experiments, into the spring. A similar statement is true for the reduction of evaporation in the ‘dry’ experiments, although the magnitude was not as great. As dictated by surface energy considerations, the sensible heat fluxes over most of Australia assumed signs opposite to those of the evaporation and magnitudes somewhat smaller, but the residual differences were still significant in September. Other atmospheric parameters, such as precipitation, surface temperature and mean sea‐level pressure tend to show much less persistence when averaged over Australia as a whole. However, many regions do show longer influence of the perturbed initial conditions.

Of considerable interest to the value of Australian winter and spring crops is the finding that the soil moisture content still showed significant anomalies persisting into the fourth month, with an areal mean of 2.7 cm more than the control in the ‘wet’ case and 1.5 cm less in the ‘dry’. This persistence of, albeit exaggerated, initial anomalies of winter soil moisture suggests that early winter soil moisture conditions may hold some potential for forecasting Australian winter crop productivity. We have found the ‘halving time’ of these large‐scale soil moisture anomalies to be about 2 months and somewhat longer at higher latitudes. These findings are consistent with many other studies and are encouraging in that most of Australia's wheat is grown in that part of the continent.
Climatological criteria for estimation of runoff by linear regression
Authors: Schwarzmaier Gertrud , Mayer Helmut , Beyer Ulrich
Published: February 2007

Monthly runoff data of the southeast of North America were analysed by a linear regression model. The model is to be validated for the prognosis of runoff and the description of runoff and its influencing meteorological and geoecological variables. The area studied was a region in the southeast of North America chosen on the basis of the climatological criteria of the Köppen‐Geiger climate classification. A further differentiation was also made between the four seasons and the two predominant types of land cover. Every single examination of the individual influencing variables revealed reasonable results according to the physical context between runoff and its influencing variables. The comparison between measured runoff values and estimated runoff values also showed an excellent coincidence in 35 out of 39 cases examined.
Energy balance differences and hydrologic impacts across the northern treeline
Authors: Lafleur Peter M. , Rouse Wayne R. , Carlson Derek W.
Published: February 2007

Energy balance measurements were made over wet tundra and a nearby open conifer forest near Churchill, Manitoba during the summer periods of 1989 and 1990. Little difference was found between net radiation, Q*, and ground heat fluxes, QG, for the two sites: Q* at the forest exceeded Q* at the tundra by only 2–5 per cent; QG averaged 9 and 12 per cent of Q* for the forest and tundra, respectively.

The sensible, QH, and latent, QE, heat fluxes showed the greatest differences between the sites. When surface moisture was not limiting, QE was largest for the tundra and QH was largest at the forest. During a drying cycle in 1989 the energy balances for the two sites were similar. An analysis of wind direction on energy partitioning suggests that the tundra was more responsive to meteorological changes than the forest. The implications of this study for surface water balances in the subarctic are discussed.
Classification of summer monsoon rainfall patterns over India
Authors: Kulkarni Ashwini , Kripalani R. H. , Singh S. V.
Published: February 2007

Seasonal (June through September) percentage departure from normal rainfall patterns over India have been classified by objective methods utilizing data for a 120‐year period (1871–1990). The methods used are the map‐to‐map correlation method and the k‐means clustering method. Empirical orthogonal functions (EOFs) are also presented.

It is seen that 75 per cent of the charts can be classified into six distinct types by the map‐to‐map method. Six distinct types also are obtained by the k‐means method. The first four dominant EOFs explain 52 per cent of the variance.

Intercorrelations and contingency tables among the types obtained by these methods and visual examination suggests that the dominant patterns are similar, irrespective of the method used. It is also seen that the monsoon rainfall for the country as a whole and the spatial patterns may have no relationship. Even during normal monsoon years, the spatial patterns may be different.

The advantages and disadvantages of the methods used are discussed.
Deterministic signals in USA precipitation records: Part II
Authors: Currie Robert G. , O'Brien Douglas P.
Published: February 2007

Power spectra of 1203 American rainfall records show evidence for two peaks with mean periods of 18.5 ± 1.8 and 10.6 ± 0.6 years, and statistical tests show that both are significant at confidence levels of 99.9 per cent. These are identified as induced by the luni‐solar 18.6‐year constituent tide and a 10–11‐year solar cycle variation in the sun's luminosity of the order of 0.1 per cent. Amplitude and phase of the 18.6 year wavetrains are highly non‐stationary, and abrupt 180° phase changes in wave polarity are often observed. Wave maxima/minima are generally in phase or out of phase with epochs (epochs are dates of maximum in tidal forcing which occurred at 1898.9, 1917.5, etc.). Polarity maps show that for epochs 1898.9, 1917.5, 1936.1 and 1954.7 the major part of the nation's landmass experienced droughty conditions, which reached a maximum in both amplitude and areal extent at 1936.1, the Dust Bowl era. At mid‐epoch 1964.0 and epoch 1973.3 so many waves changed phase by 180° that the major part of the landmass was wet at the epoch. Analogous phenomena have been found in tree‐ring data from several continents, and implications for economic science are briefly discussed.