bluuebunny/crossref_metadata_2025 huggingface dataset:
Persistence of anomalous moisture conditions in the interior plains of North America
Authors: Oladipo E. O. , Hare F. K.
Published: February 2007

Mean growing season (April‐September) climatic conditions in the Interior Plains of North America, as measured by the Bhalme and Mooley drought index, were subjected to the length of runs (Gold), chi‐squared and autocorrelation tests of dependence. Only a maximum of about 3 per cent of the total variation in the seasonal drought in any year is explained by the previous year. Based on the results from the three tests, it can be concluded that the mean seasonal moisture conditions during the growing season in the region can be considered to be an independent time process. In other words, the series of the seasonal drought index, statistically speaking, cannot be distinguished in its sequential pattern of occurrence from a random series.
Spatial patterns of drought in the interior plains of North America
Authors: Oladipo E. Olukayode
Published: February 2007

A long‐period data set (1975–1978) of monthly growing season (April‐September) rainfall totals for over 400 stations in the Interior Plains of North America is used to derive a Bhalme‐and‐Mooley‐type drought index. A map‐pattern correlation technique is used to stratify the time period into distinct drought severity patterns, and maps of the mean drought patterns for each year are generated by SYMAP and examined for consistency.

Based on the analyses, there are four patterns of moisture anomaly with distinct differences between the eastern, western, southern and extreme northern parts of the study region. In general, large‐scale droughts do not frequently cover the region as a whole. Indeed it seems to be the exception rather than the rule, with distinct spatial differences dominating the wet and dry years. The length and severity of drought varies from subarea to subarea, and although discrete areas do catch the brunt of drought on a year‐by‐year basis, drought occurrence in the region is largely spatially incoherent. It can therefore be concluded that drougth in the Interior Plains of North America is predominantly a non‐continental phenomenon.
Circulation and daily rainfall in the North Queensland wet seasons 1979–1982
Authors: Sumner Graham , Bonell Mike
Published: February 2007

Daily rainfall data for 72 sites in tropical north Queensland have been analysed to yield indices of rainfall activity associated with ten identified surface circulation types which occur in the summer wet season (November to March). The influence on rainfall distribution of local topography and exposure to moist air flows emerges as an important determinant, so that the locations of larger scale rain‐producing systems relative to the area, and the direction of air flow, emerge as prime controls on rainfall presence and amount.
A homogeneity test applied to precipitation data
Authors: Alexandersson Hans
Published: February 2007

In climate research it is important to have access to reliable data which are free from artificial trends or changes. One way of checking the reliability of a climate series is to compare it with surrounding stations. This is the idea behind all tests of the relative homogeneity. Here we will present a simple homogeneity test and apply it to a precipitation data set from south‐western Sweden. More precisely we will apply it to ratios between station values and some reference values. The reference value is a form of a mean value from surrounding stations. It is found valuable to include short and incomplete series in the reference value. The test can be used as an instrument for quality control as far as the mean level of, for instance, precipitation is concerned. In practice it should be used along with the available station history. Several non‐homogeneities are present in these series and probably reflect a serious source of uncertainty in studies of climatic trends and climatic change all over the world. The significant breaks varied from 5 to 25 per cent for this data set. An example illustrates the importance of using relevant climatic normals that refer to the present measurement conditions in constructing maps of anomalies.
Spatial and temporal analysis of the palmer drought severity index over the south‐eastern United States
Authors: Eder Brian. K. , Davis Jerry M. , Monahan John F.
Published: February 2007

The spatial and temporal variability of the Palmer drought severity index (PDSI) over the south‐eastern United States during the period 1931–1982 was examined through the use of principal component analysis. Spatial mapping of the component loadings identified six statistically significant modes of variability or PDSI anomaly patterns, which together account for 77.3 percent of the total variance. The first component, which represents the dominant pattern, accounted for 43.4 per cent of the total variance and identified an in‐phase oscillation across the entire study area, indicating a general tendency for all sections to experience either a drought or a wet spell concurrently. The remaining five components, which account for 33.9 per cent of the total variance, each identified an out‐of‐phase oscillation. Application of Kaiser's Varimax orthogonal rotation on the six retained principal components led to the identification of six contiguous subregions of nearly equal size, each of which displays unique drought characteristics.

Examination of the time series derived from the principal component scores within each subregion revealed a general trend in which the occurrence of drought was much more prevalent during the first three decades of the study period, culminating during the mid 1950s when most of the subregions experienced their worst drought episode.

After removal of the inherent ‘red noise’ persistence found in the monthly PDSI data, spectral and cross‐spectral density analysis performed on the time series indicated that no cyclical patterns or periodicities were present.
A regionalization of Austria's precipitation climate using principal component analysis
Authors: Ehrendorfer Martin
Published: February 2007

S‐mode principal component analysis (PCA) is performed on correlation matrices of precipitation data of Austria for summer and winter half‐year totals for the period 1951–1980. Application of the dominant‐variance selection Rule N (Overland and Preisendorfer, 1982) proves two or three eigenvalues to be significant, where three principal components (PCs) on average account for 68.3 and 79.4 per cent of total variance in the summer and winter half‐years, respectively. The Varimax‐rotated PC loadings allow for a subdivision of Austria into three homogeneous (with respect to the underlying processes) regions.

Intercomparison of the PC primary patterns, variances and time series of the principal components of three different networks confirms the spatial stability of these regions and turns attention towards seasonal differences. The three PCs are identified by assignment of large‐scale weather types to them which are known to be precipitation producing in the region wherein the respective PC is dominant.

The results of this study and their wide variety of applicability reveal PCA and Rule N as useful tools in identifying homogeneous groups of variables which can be ascribed a physical meaning. The paper contains a short account of the analysis of empirical orthogonal functions, the theory of PCA and its connection to factor analysis.
On the estimation of annual and monthly mean values of sunshine duration over Greece
Authors: Flocas A. A.
Published: February 2007

Annual and monthly values of sunshine duration at thirty‐seven stations in Greece are examined with the three factors of latitude, longitude and altitude by means of stepwise multiple regression analysis. The validity of the assumption that there is a linear relationship between the mean values of sunshine duration and these three factors is examined. A seasonal variation is evident in all the computed gradients of the sunshine duration, with altitude effects being at a maximum in summer, whereas the effects of latitude were most pronounced during the cold season. The thirteen empirical formulae produced do not account completely for all the variability in the data, but the resultant correlation coefficients range from 0.830 to 0.906. The residuals (i.e. differences) between actual and calculated values of sunshine duration are shown on representative maps which may be used (with the regression equations) to estimate sunshine at any locality in Greece.
The energy balance in the coastal environment of James Bay and Hudson Bay during the growing season
Authors: Rouse Wayne R. , Hardill Steven G. , Lafleur Peter
Published: February 2007

Energy balance measurements were made simultaneously at a terrestrial site in southern James Bay (SJB) and one in central Hudson Bay (CHB) during the growing season of 1985. Both sites were located 1 km inland from east‐west trending coastlines and both were fully vegetated with sedge grasses growing in standing water. The SJB site is in a non‐permafrost environment, whereas the CHB site is underlain by continuous permafrost.

The measurements indicate that the magnitudes of all components of the energy balance, except net radiation, are strongly dependent on wind direction. Onshore winds are dominant. With onshore winds, the ground heat flux, evaporative heat flux and air temperature are smaller than for offshore winds and the sensible heat flux is larger. These relationships are apparent when the wind is directionally persistent for a full day and when there is a major wind shift between onshore and offshore during the day.

With colder air temperatures the Bowen ratio becomes much larger than would be expected under conditions of potential evapotranspiration. This appears to be caused by a rapid increase in the canopy resistance of sedge grasses which occurs when air temperatures drop below 16°C.

Components of the energy balance are linearly correlated with air temperature. This could be useful in predicting the impact of human activities which result in long term temperature change in the Hudson Bay lowlands, which is a large area with a very sparse climate database.
Estimates of global radiation at the ground from the reduced data sets of the international satellite cloud climatology project
Authors: Raschke E. , Gratzki A. , Rieland M.
Published: February 2007

The global radiation at the ground is determined from monthly samples of imaging data from the geostationary satellites METEOSAT 2 and GMS 2 with a method which has earlier been developed by Möser and Raschke (1983). These radiance data are reduced to obtain resolutions of 30 to 40 km in space and 3 h in time according to the B3 format of the ISCCP procedures.

If compared with simultaneous pyranometer measurements these results agree within an uncertainty of better than 8–10 per cent for monthly averages of daily sums and of better than 25 per cent for individual daily sums. Possible error sources are not only contained in the retrieval procedure but are also due to errors in navigation of satellite images. Further, local orographic effects can contribute to differences between calculated and measured downward irradiances.
The radiation climate of the dead sea
Authors: Stanhill G.
Published: February 2007

Three years of continuous measurements on the NW coast of the Dead Sea, together with a series of shipborne observations made above its water surface, were used to characterize and analyze the radiation climate of the sea.

Incident global radiation on the coast, averaged 6.64 GJm−2 per year, less than values measured both at sea and at nearby pyranometer stations despite the greater cloud cover of the latter. The relatively low insolation was attributed to the considerable back scatter from the sky shown by the high values of diffuse sky radiation recorded even during cloudless conditions. Short‐wave radiation reflected from the sea was calculated, on the basis of a quadratic relationship between reflectivity and solar altitude, to total O50GJ m−2 annually. Above a critical solar altitude of 45° reflectivity averaged 6 per cent. Monthly values of reflectivity from the Dead Sea agreed with those calculated for a standard sea surface.

Atmospheric long wave radiation measured on the coast totalled ll.44 GJ m−2 annually. Its seasonal and diurnal variations closely followed those in air temperature. Small variations in the apparent sky emissivity, which averaged 0.80, could be accounted for by reference to accompanying changes in the water content and transmissivity of the atmosphere.

Midsummer and midwinter in situ determinations of the emissivity of the Dead Sea yielded near‐black body values which, with the high surface temperatures of the sea, resulted in a terrestrial radiation flux totalling 14.69 GJ m−2 annually.

Direct pyrradiometer measurements over the Dead Sea were used to establish the accuracy of long term estimates of the radiation balance of the sea and to develop a method of calculating it from routine, shore‐based measurements of global radiation.

The radiation balance of the Dead Sea, normalized to the incident radiation, was 0.45,22 per cent less than the average for eight other non‐saline water bodies in comparable mid‐latitude climates. The relatively low radiation balance of the Dead Sea was attributed to the enhanced long‐wave radiation loss caused by the elevated surface temperature of its salt‐saturated waters.

Thus the salinity of the Dead Sea reduces its evaporation loss by two mechanisms; the direct effect of the reduced vapour pressure of the water surface and the indirect effect of the reduced radiation balance.
A study of climatic stress and physiological regions in Greece
Authors: Giles B. D. , Balafouti C. , Arseni‐Papadimitriou A.
Published: February 2007

Daytime and nighttime mean temperature and humidity values are used to calculate a monthly Comfort Index for 41 stations in Greece. These indices are related to heat and cold stress using a psychrometric chart and combined to provide values of Annual Stress, Proportional Cumulative Stress, and Annual Physio climatic Regime following the methods proposed by Terjung (1966,1967). In addition alternative methods of showing the temporal and spatial distribution of the parameters are considered and illustrated.
Tropical Quasi‐Biennial Oscillation of the 10‐mb wind and Indian monsoon rainfall‐implications for forecasting
Authors: Bhalme H. N. , Rahalkar S. S. , Sikder A. B.
Published: February 2007

The interannual variability of the Indian monsoon (June–September) rainfall has been examined in relation to the monthly zonal wind anomaly for 10‐mb (30km) and 30‐mb (24km) at Balboa for the 28‐year period 1958–85. The fluctuations in the zonal wind anomalies in January at 10‐mb appear to be highly related to the monsoon rainfall, with rainfall tending to be less (more) than normal during easterly (westerly) anomaly, suggesting some predictive value for the Indian monsoon rainfall. The zonal wind anomalies at 10‐mb lead those at 30‐mb by 6 months. This lead time is consistent with the well‐known downward phase propagation with a speed of 1 km/month in the QBO of tropical stratospheric wind. Large‐scale flood never occurred during easterly wind anomalies, and drought almost never during westerly anomalies in January at 10‐mb. This suggests that useful probability forecasts of droughts or floods could be prepared.
Arctic cloudiness in spring from satellite imagery
Authors: Barry R. G. , Crane R. G. , Schweiger A. , Newell J.
Published: February 2007

Maps of cloud cover over the Arctic have been prepared from manual interpretation of Defense Meteorological Satellite Program images at 3‐day intervals for April, May and June, 1979,1980. Additional maps were prepared for selected dates to give a 10‐day sample for each of eight synoptic MSL pressure pattern types over the same area. Synoptic and monthly cloud distributions are compared with previous estimates. A large bias in our low cloud estimates for April may be caused by springtime Arctic have layers. The identification of substantial geographical and interannual variability of cloud amounts suggests that synoptic controls are important at this season.
Variations of trough positions and precipitation patterns in the mediterranean area
Authors: Jacobeit J.
Published: February 2007

Recent variations of circulation and climate can be studied by investigating even rather short periods of time as far as they display different modes or anomalies which may also act on larger timescales as more persistent ones. Thus a period of 10 years (September 1966 to August 1976) which could be covered by daily sets of 500hPa airflow data in the Atlantic‐European region and of precipitation data at 101 Mediterranean stations was chosen to examine the variable distribution patterns of upper troughs in the Mediterranean area and their corresponding patterns of precipitation anomalies. After the outline of trough axis distribution to eight successive longitudinal bands and of the different percentages of trough precipitation at various trough axis positions for the whole period of 10 years a subdivision into individual years was made to show some of the operative deviations both of the upper trough distribution and of the corresponding precipitation pattern in relation to the overall mean situation. Together with some circulation indices (zonal index, geopotential anomaly, measure of (he relative vorticity, specifications about the Westerlies' main branch) which have been calculated for the crucial upstream region of the North Atlantic, some basic tendencies concerning different circulation patterns and their consequences for the Mediterranean region could be outlined. Considering within‐type changes and the variations of further cyclonic elements this might serve for estimating climatological effects on larger time‐scales of more persistent anomalies of circulation.
Power spectra and coherence of drought in the interior plains
Authors: Oladipo E. Olukayode
Published: February 2007

Mean growing season (April‐September) precipitation series at 407 stations in the Interior Plains of North America, dating back to 1985 in some stations, are used to derive a Bhalme and Mooley‐type drought index for the region. Linear trend, representing first order non‐stationarity, is first removed from the drought series. Then the periodogram via the Fast Fourier Transform (FFT), Maximum Entropy (ME) and Non‐Integer (NI) spectral techniques are applied to search for significant periodicities in the temporal characteristics of the drought series. Cross‐spectral technique is also used to characterize the extent of spectral coherence in the drought series.

It is found that no significant power in drought is present at periods greater than about 6 years. Spectra of drought in the Interior Plains are dominated by three peaks in the quasi‐biennial, quasi‐triennial and quasi‐5‐year oscillations. The periodic 186‐year lunar nodal cycle obtained by others for the Drought Area Index (DAI) for the region is completely absent in the spectra of the analysed drought index series. Also the well‐known 11‐year sunspot cycle is only evident in the drought index series for a few of the stations. In general there is an ill‐defined drought recurrence interval.

Moreover the areal extent of peaks contained within these oscillations do not indicate any significant spatial coherence. These periodicities can be evident at one station while being absent at another a few hundred kilometres away. On the basis of the spectral results, it is concluded that obtained significant periodicities are only short‐lived time variabilities in drought as recorded by individual stations and do not represent any persistent drought characteristics over a broad geographical region. A cross‐spectral analysis of the drought series with sunspot numbers shows no evidence to indicate a significant relation between drought and the single sunspot cycle. In general, the growing season drought series in the Interior Plains displays only what appears to be a random variation, with the possible superimposition of the quasi‐biennial oscillation.
Rotation of principal components: Some comments
Authors: Jolliffe Ian T.
Published: February 2007

A recent paper by Richman (1986) provides a very useful review of the ideas of rotation in principal component analysis, in the context of climatology. However, the paper also raises a number of points which are open to discussion. The present note comments on a number of these points, and aims to give a balanced view of the usefulness of principal component analysis, both with and without rotation, in climatology.
The variations of dry spells in marseilles from 1865 to 1984
Authors: Douguedroit Annick
Published: February 2007

The study of dry spells gives a better characterization of the structure of a dry season than the monthly totals or means of rainfall. The dry season is characterized by the mean lengths of all dry spells and of the long dry spells (≥ 30 days), and by their persistence during 19 overlapping 30‐years series. A model based on shifted negative binomial distributions which fits well most of the monthly distributions of the frequency of the observed dry spells allows us to compute the probability of occurrence of a dry spell ≥ n days.
The time scale of the soil hydrology using a simple water budget model
Authors: Serafini V. V. , Sud Y. C.
Published: February 2007

A simple water budget model is used to get a characteristic time scale of the soil hydrology, which is defined as the time scale for the onset of agricultural droughts. Assuming that there is no rain, our estimation requires as input the knowledge of the initial soil moisture content and an evaluation of the potential evaporation. Two applications at a global scale are shown. In a first case an initially saturated soil is considered to get an estimation of the time needed by a climate model to adjust realistically to initial errors in the soil moisture distribution. In a second case climatological values are used as initial conditions to get a measure of the sensitivity of the hydrological cycle to the atmospheric forcing.
The impact of rapid urbanization on pan evaporation in phoenix. Arizona
Authors: Balling Robert C. , Brazel Sandra W.
Published: February 2007

Rapid urbanization in Phoenix, Arizona over the past few decades has been associated with large increases in local temperature and wind speed values, and decreases in local dew point and relative humidity levels. In this study, the impact of these urban‐induced climatic changes on long‐term pan evaporation rates is identified. The results indicate an increase from 1917 to 1985 in the local pan evaporation in all months of the year. Following a long period of generally increasing pan evaporation levels, a sharp jump in the pan measurements occurred in the late 1960s. This pronounced discontinuity in the long‐term record appears to be associated with the construction of a nearby regional shopping centre in 1968. Given widespread similar land‐use changes throughout this rapidly growing desert city, and given the well‐documented changes in local climatic conditions, potential evapotranspiration increases are probably occurring throughout much of the metropolitan area.
Diurnal variation of outgoing longwave radiation
Authors: Gruber Arnold , Chen T. S.
Published: February 2007

The global and monthly distribution of the diurnal variation of outgoing longwave radiation (OLR) has been calculated by compositing estimates of the planetary OLR obtained from polar orbiting satellites at different equator crossing times. These data include NOAA and NASA polar orbiting satellites for the year 1974 through 1983, giving a total of ten different local observations per day throughout the whole data period. A Fourier analysis was then applied to calculate the phase and amplitude of the diurnal cycle on a 2.5° latitude/longitude grid for each month of the year. Assumption was implicitly made that the first harmonic alone explains most of the diurnal variation.

The results are represented on maps extending from 55° south to 55° north for four different seasons from which a large seasonal variability of the diurnal harmonic primarily experienced by the mid‐latitude continents was clearly depicted. Over land areas the amplitude of the diurnal variation was large. In desert and semi‐arid areas it seem to be clearly related to surface solar heating i.e. phases of maximum OLR generally occurring near noon during summer and afternoon during winter months. Over the oceans, the amplitude is generally small even in the convectively active regions, such as the ITCZ, and the diurnal cycle appears to be modulated primarily by clouds.

Finally, a ‘harmonic dial’ was constructed to examine the most dramatic features of the diurnal variation representative of such areas as the ITCZ, deserts, tropical convective clouds regions and highly variable mid‐latitude areas. Results of this study are consistent with other studies of the diurnal variability of clouds and radiation budget parameters.
Relationships between seasonal rainfall in East Africa and the Southern Oscillation
Authors: Ogallo L. J.
Published: February 2007

Teleconnections between the Southern Oscillation and seasonal rainfall over East Africa during the period 1923–1984 were investigated using correlation methods. The results from the study indicated significant negative zero lag correlations between Southern Oscillation and seasonal rainfall over parts of East Africa during the months of October—December. Maximum correlations were concentrated along the coast and over some western parts. Peak values in the range — 0.6 were, however, centred along central and northern coastal regions.

During the months of July—September significant positive zero lag correlations in the range of 0.5 were observed over some western parts. Low zero lag correlations were, however, obtained over most of the regions with the January—May and annual rainfall records. The computed lagged correlation values displayed characteristics similar to those observed from the zero lag correlations. Highest month to month persistences were again centred within October/November when significant lag correlations persisted for time lags greater than 2 months at some locations.

It was, however, noted that although there were some relationships between the Southern Oscillation and seasonal rainfall over parts of East Africa, some of the extreme wet and dry episodes were not related to the Southern Oscillation.
A detailed examination of the extratropical response to Tropical El Niño/Southern Oscillation events
Authors: Hamilton Kevin
Published: February 2007

It is now clear that conditions in the tropical Pacific Ocean and the overlying atmosphere can have significant associations with the seasonal—mean circulation of the mid‐latitude atmosphere, particularly in winter. Notable is a tendency for an intensification of the climatological standing wave pattern over the North Pacific and North America during the warm tropical conditions associated with El Niño/Southern Oscillation (ENSO) events. However, the actual mid‐latitutde circulation anomalies do show a great deal of variability among individual ENSO years. This paper addresses the question of whether the variability of the mid‐latitude response to ENSO events can be attributed to differences in the details of the tropical anomalies from event to event. The investigation embraced the period 1899–1982 and employed data on tropical sea surface temperatures (SSTs), tropical rainfall, and mid‐latitude atmospheric surface pressures and air temperatures.

The results suggest that a major factor in determining the strength of the Northern Hemisphere extratropical response is the SST anomaly in the far western Pacific/Indonesian region. In particular, it appears that the strong extratropical teleconnections with ENSO events occur more frequently when the SST in the far western Pacific is anomalously warm (or at least not overly cold). This finding appears to be consistent with the results of at least some recent numerical experiments conducted with comprehensive general circulation models.
A synoptic climatological analysis of rainfall variability in south‐eastern Australia
Authors: Whetton P. H.
Published: February 2007

Monthly rainfall data for the state of Victoria in south‐eastern Australia were analyzed using principal component analysis and Varimax orthogonal rotation, with the intention of revealing typical patterns of rainfall variability. Two data sets were used: a spatially detailed set for 1970–1980, and a less spatially detailed set for 1905–1980. The first five rotated principal component patterns (RPCPs) produced from the two data sets showed the same structure. These five RPCPs each dominated rainfall over a particular sub‐region of the study region, and the climatic regionalization that this suggested appeared to be one strongly determined by topography.

The anomalies of Australian region mean monthly mean sea‐level (MSL) pressure associated with these five RPCPs of rainfall were determined using correlational techniques. Of the five main RPCPs of rainfall, the pattern based in the south‐west of the state showed the strongest relationship with monthly pressure anomalies, and was associated with the occurrence of onshore westerly winds. The results for the rainfall pattern based in northern Victoria were perhaps the most interesting. Rainfall in this region was related to the occurrence of anomalous northerly winds through southeastern Australia, although through the cooler months of the year these winds accompanied a low pressure anomaly centred over central Australia, whereas in the warmer months they were associated with a high pressure anomaly centred to the south‐east of the continent. This northern rainfall pattern also showed some month to month persistence, and a distinct correlation with the Southern Oscillation.
Use of cross correlations in the search for teleconnections
Authors: Katz Richard W.
Published: February 2007

The search for teleconnections usually involves the calculation of sample cross correlation functions for pairs of atmospheric/oceanic time series. Properties of the theoretical cross correlation function are derived by means of analytical techniques, and properties of the sample cross correlation function are obtained by means of simulations. In particular, the effect of autocorrelation of the individual time series is to ‘smear out’ any contemporaneous cross correlation that might be present, producing nonzero cross correlations at nonzero lags. To combat this problem, the advantages of ‘prewhitening’ before computing cross correlations are demonstrated. Moreover, the operation of smoothing individual time series has the effect of inflating the values of the cross correlation coefficients at nonzero lags. Finally, the behaviour of running cross correlation coefficients is somewhat counterintuitive, making this technique potentially very misleading for detecting changes in relationships over time. For illustrative purposes, these calculations are also performed for Darwin and Tahiti time series of monthly sea level pressure.
Periodic 18.6‐year and cyclic 10 to 11 year signals in northeastern United States precipitation data
Authors: Currie Robert G. , O'Brien Douglas P.
Published: February 2007

Evidence for a narrow band‐limited signal with period near 18.6‐years is found in 126 out of 136 yearly total precipitation records, and in 1531 out of 1668 monthly records in the northeastern United States. From 1840 to near the end of the 19th century, rainfall minima in the wavetrain are highly correlated with tidal maxima of the 18.6‐year luni‐solar tide, the twelfth largest tidal constituent in Newton's theory; the wavetrain then switched phase by 180° and for most of the 20th century rainfall maxima are correlated with tidal maxima at 1917.5, 1936.1, 1954.7, and 1973.3. This bistable phenomenon of atmospheric science was discovered by Currie (1983) in a study of tree‐rings from the Patagonian Andes, and O'Brien and Currie (1988) have suggested a dynamical explanation in terms of mathematical physics. In terms of yearly rainfall, the mean percentage amplitude modulation of the wave was near ±6% until 1940 after which it began to increase rapidly, reaching ±10% in the 1960s and 1970s. These results provide a rational explanation for the severe water shortage crisis that occurred at tidal minimum 1964.0 (Namias, 1966; 1967), and reoccurred 19 years later. In addition, a smaller band‐limited term with period 10 to 11‐years is found in a little more than half of the records.
The onset of the southwest monsoon over Kerala: 1901–1980
Authors: Ananthakrishnan R. , Soman M. K.
Published: February 2007

Utilising daily mean rainfall from dense rain gauge networks, the dates of onset of the southwest monsoon over south and north Kerala have been derived on the basis of objective criteria for the years 1901 to 1980. These dates have been compared with the onset dates as per records of the India Meteorological Department. Statistics of the onset dates are presented. The mean onset date for south Kerala is found to be 30 May and for north Kerala 1 June with a standard deviation of about 9 days in both cases. The sharp increase in rainfall that heralds the onset of the monsoon is highlighted by superposed epoch analysis. The prevailing notion that rainfall from pre‐monsoon thunderstorms progressively increases and merges with the monsoon rainfall is shown to be not valid.
Comparison of satellite and surface cloud cover observations and cloud cover regions over Europe
Authors: Róth Renata
Published: February 2007

A five year data set of satellite cloud cover observations and a thirty year data set of surface cloud cover observations were compared over Europe. There is good agreement between the general characteristics of these two cloud climatologies. Differences between monthly means (January, April, July and October) of the two data sets were formed in 5° × 5° grid cells. These differences, regarding all grid points and months are less than half of one tenth of sky cover in 46 per cent of all cases.

The defining parameters (a and b) of the Beta distribution were calculated also for the months of January, April, July and October representing the four seasons. On the basis of a and b values, different cloud cover regions were determined over Europe and these were characterized by averaged curves of the Beta probability density functions. These regions correspond well to distinct areas of geographical environments, as well as to the regimes of the general circulation. Thus, the character of cloud conditions within these regions can be expressed in a numerical way by means of a and b parameters.
Principal component analysis of precipitation in the Adriatic‐Pannonian area of Yugoslavia
Authors: Pandžić Krešo
Published: February 2007

Using the principal component method, some characteristics of the precipitation pattern are established for an area from the Adriatic Sea to the Pannonian lowland (territory of Croatia). The data of monthly precipitation amounts for the 20‐year period (1961–1980) from 108 meteorological stations are used. The first four principal components (PCs), which describe 79‐4 per cent of the total precipitation field variance, are considered. It is shown, graphically and numerically, that the first PC is related to the frequency of cyclones on van Beber's paths IVb, Vb and Vc, the second one is related to their frequency on the paths Vd, Vd1 and Ve, the third to the anticyclonic and non‐gradient weather type and the fourth one is related to the frequency of cold fronts crossing Yugoslavian territory. Using the loadings of the PCs, four homogeneous precipitation sectors are determined and compared to those obtained by Koppen's scheme. Finally, some details of the annual pattern of precipitation for these sectors are discussed.
Potential wind erosion in Australia: A continental perspective
Authors: Kalma J. D. , Speight J. G. , Wasson R. J.
Published: February 2007

Seasonal and annual patterns of potential wind erosion in Australia are mapped. Potential erosion is estimated by applying Fryberger's sand drift potential concept to 3 p.m. wind data from 732 stations. Contour maps for January, April, July and October show monthly total drift potential, resultant drift potential, and drift directionality. Stream line maps show resultant drift direction. Annual resultant drift potential and drift direction are also mapped.

Monthly total drift potential is maximal in October and minimal in April. Highest values occur on the coast, in the Nullarbor Plain, and in Tasmania; lowest values are scattered across the northern inland. Monthly resultant drift potential is similarly distributed. Monthly drift directionality is higher in the north.

Monthly drift direction stream lines mainly express the general circulation of the atmosphere. Some local disturbances occur over ranges; others have cyclonic form. Annual resultant drift potential stream lines are broadly confluent and have anticyclonic curvature.

These maps of potential wind erosion, linked to measures of erodibility, provide a basis for studying wind erosion hazard in Australia.
Daily rainfall over Northern Australia: Deviations from the world pattern
Authors: Jackson I. J.
Published: February 2007

In an earlier paper examining relationships between monthly rainfall, raindays and mean daily rainfall intensity in the tropics, two Australian stations showed a consistent pattern of deviations from the worldwide regression equations. Using data from some 50 stations, this present paper demonstrates that this pattern applies generally over northern Australia. Rainfall is much more concentrated, with fewer raindays and higher mean daily intensities, than would be predicted from monthly totals and the worldwide tropical regressions. This marked concentration will have varied implications for hydrology, soil erosion and agriculture. The importance of tropical cyclones and other closed low pressure systems over northern Australia provides a reasonable explanation of the deviations, with support from some other tropical regions. However, a simple distinction between tropical cyclonic and non‐cyclonic areas is inadequate to explain patterns on a worldwide basis.
Relationship of the Indian monsoon rainfall to the northern hemispheric 700 MB height tendency
Authors: Mooley D. A. , Paolino D. A.
Published: February 2007

In this study, the fields of northern hemispheric 700 mb height tendency from January to April and from March to April are examined for the period 1950–1984 in relation to Indian monsoon (June to September) rainfall. The height tendency from January to April at three locations (near Pacific high and near Siberian high at sea level, and over southwest U.S.A) and from March to April at one location (about 50° of longitude west of sea level Aleutian low) are found to be significantly related to the Indian monsoon rainfall. These four variables are generally not inter‐related amongst themselves, and are not significantly related to the April 500 mb ridge, the tendency of the Southern Oscillation Index (SOI), and the eastern equatorial Pacific sea surface temperature tendency from DJF to MAM season.

The best amongst the height tendency variables is the height tendency from January to April near sea level Pacific high. This variable is not as good as the tendency of SOI; however, when used in conjunction with April 500 mb ridge and the tendency of SOI, it makes a highly significant contribution to the explained variance and improves the forecasts for independent years as judged by different measures of assessment. This height tendency thus makes a useful additional predictor for the Indian monsoon rainfall.

The mechanism of the influence of the development of the Pacific high on the Indian monsoon rainfall is not clear. It is, however, possible that the linkage between the development of the Pacific high and the Indian monsoon rainfall is through linkage of the Pacific high with the development of the summer season trough of low pressure over the Indian sub‐continent. This, however, needs to be investigated.
On the reality of climatic changes in wind over the Pacific
Authors: Wright P. B.
Published: February 2007

It is important to be aware of systematic errors when using data from ship observations to infer climatic changes. The development of our understanding of systematic errors in sea and air temperatures and cloudiness is reviewed. Many reasons for suspecting similar errors in wind data are noted. Wind data for the tropical Pacific for 1920–1979 are then analysed. Trends to stronger trade winds in both the north and south Pacific, and also large anomalies in the winds in these areas during the Second World War, are found in the data. Quantitative comparisons are made with the associated pressure gradients, and qualitative comparisons with rainfall at Pacific island stations. These series provide no support for the suggestion that the wind changes were real.
Arctic cloudiness in spring from satellite imagery: Some comments
Authors: Curry Judith A.
Published: February 2007

The April cloud amounts recently presented by Barry et al. (1987) were significantly larger than expected. It was suggested that this discrepancy was caused by the obscuration of surface features by Arctic haze, which is believed by Barry et al. to consist of pollution aerosol transported from middle latitudes. The present note suggests that a significant portion of the surface obscuration that occurs in April is due to small ice crystals that form in the lower troposphere of high latitudes before the summer warming begins. These ice crystals appear to be a major feature of the Arctic heat regime, and should be included in cloud statistics.
Weather types at Brisbane, Queensland: An example of the use of principal components and cluster analysis
Authors: Stone Roger C.
Published: February 2007

Principal components analysis was conducted on 15 years data of surface weather observations at Brisbane, Queensland. Component scores from each year's analysis were grouped using an hierarchical clustering method. Each of the 10,920 observations used in the study was able to be placed into a distinctive class so that the weather in Brisbane from 1967 to 1981 may now be described in terms of nine broad weather complexes, or weather yatypes’, and 63 hybrid types at a finer level of refinement. The nine broad weather types uniquely describe variation in Brisbane's climate during the period studied and hint at an ability to identify important variations in controlling mechanisms—in this case the subtropical ridge.
The influence of general circulation patterns on humid and dry years in the cuyo andean region of argentina
Authors: Minetti Juan L. , Sierra Eduardo M.
Published: February 2007

Due to the population growth in the agricultural areas under irrigation in Cuyo (West Central Argentina), the consequences of fluctuations in cordillerean river regimes, whose snowfalls provide water for irrigation, have begun to be felt acutely in recent years.

Hemispheric and regional circulation patterns associated with two extreme hydrological (drought and excess) situations in Cuyo were investigated, searching for links between both scales.

Important anomalies of hemispheric and regional occurrences have been observed when droughts and floods occur at the regional scale (upper level of the mountain range central Andes and Chilean Mediterranean zone).

Precipitation fluctuations show a direct or inverse association with other South American Regions (Uruguay and Islas Orcadas del Sur) and also an important teleconnection between phenomena of extratropical latitudes.

The anomalous monthly average pressure fields (regional scale) are generated by an increase (20 to 30 per cent over the normal frequency) of a few persistent synoptic models, and by a westerly wave with ridge or trough over Islas Orcadas del Sur (South Orkneys Is.) or towards the west of Juan Fernández.
Global‐scale sea‐surface temperature anomalies and rainfall characteristics in northern Nigeria
Authors: Adedoyin J. A.
Published: February 2007

Composite rainfall data over the 35‐year period 1951–1985 from seven Nigerian synoptic stations, all around latitude 12°N, have been used to examine the correlation, or otherwise, between global‐scale sea‐surface temperature (SST) anomalies and rainfall characteristics on the fringe of the Sahel. Results show that SST anomalies of the Indian, North Atlantic and South Atlantic Oceans are correlated with total rainfall and number of rain days while the anomalies of the tropical East Pacific may have influence on rainfall intensity at the beginning of the rainy season. It is indicated that Pacific El Niño events may affect the frequency of occurrence of the main rain‐producing mechanism in the Sahel; namely, squall lines. Extraordinary warmings in the South Atlantic are also shown to cause considerable shortfalls in expected mean monthly distribution of rainfall, especially in August, the main rainy month in the Sahel.
The spatial and temporal patterns of the East African seasonal rainfall derived from principal component analysis
Authors: Ogallo L. J.
Published: February 2007

In this study, rotated principal component analysis (RPCA) was used to study the spatial and temporal characteristics of seasonal rainfall over East Africa during the period 1922–1983. The RPCA solutions were derived from both spatial and temporal correlation matrices. The spatial correlation matrices described intercorrelation between pairs of stations, while the temporal matrices gave correlations between pairs of map patterns.

Results obtained with the spatial correlation matrices indicated seasonal shifts in the patterns of the dominant RPCA modes which closely resembled the seasonal migration patterns of the rainfall belts induced by the Inter Tropical Convergence Zone (ITCZ). The influence of the large water bodies, especially Lake Victoria and the Indian Ocean, were however, outstanding throughout the year. Twenty‐six homogeneous regional groups were delineated from the spatial characteristics of the dominant eigenvectors.

Solutions based on the temporal correlation matrices clustered together some of the wet and dry episodes. Some of the map patterns clustered together could be associated significantly with the El‐Niño/Southern Oscillation events.
The dust storms of Mexico City
Authors: Jauregui Ernesto
Published: February 2007

Dust storms represent an important environmental problem affecting the comfort and health of one of the largest urban agglomerations in the tropical world. Data for dust events of varied intensities have been used in order to describe the seasonal and annual variation of dust storms in Mexico City.

The maximum frequency of dust events occurs in March at the end of a three‐month period characterized by monthly rainfall amounts of about 13 mm.

The frequency of intense (visibility less than 1 km) dust storms has markedly declined (to 0.6 year−1 for the period 1981–1987), apparently as a result of repasturing of Lake Texcoco's dry bed. However, dust activity of low magnitude as observed from Tacubaya has considerably increased in the Mexico Basin, apparently as a result of both accelerated deforestation and urbanization as well as a decrease in precipitation in recent years at the dust source. In spite of the low frequency of intense/moderate dust events, dustfall deposition rates observed near the dust sources are comparable to those measured elsewhere in arid environments.
Summer snowfalls over the mount Olympus area
Authors: Sahsamanoglou H. S.
Published: February 2007

The present paper is a study of summer snowfalls over the Mount Olympus range (altitude > 2500 m) in northern Greece. This occurs about three times every summer and is, of course, linked to the atmospheric circulation over Europe. At least two days before snowfall, a deep trough, reaching almost to the northern end of the western Mediterranean, causes a strong southward invasion of cold air. This cold air‐mass movement results in cyclogenesis near northern Italy. A depression is formed which moves to the east, causing bad weather over northern Greece and a snowfall over the higher part of Mount Olympus. The freezing of air masses over the mountain area is so strong that the dry‐bulb freezing level found at 640 hPa two days before snowfall, reaches 710 hPa immediately after snowfall.