bluuebunny/crossref_metadata_2025 huggingface dataset:
The role of radiation geometry in the climate response of Mount Kenya's glaciers, part I: Horizontal reference surfaces
Authors: Kruss Phillip D. , Hastenrath Stefan
Published: February 2007

Model calculations of incident shortwave radiation were performed for the Mount Kenya massif with the objectives of: (i) exploring the major factors controlling the ice distribution in the peak region: and (ii) determining the primary forcings that led to the differential retreat of the various glaciers.

The ice distribution on Mount Kenya, characterized by largest glaciers lo the south and east, is primarily controlled by the precipitation pattern. By contrast, the radiation pattern is unconducive to maintaining this ice distribution, as insolation tends to be higher on these largest glaciers. Spatial variability in the incident radiation is mostly due to shading effects, with cloudiness however being more important in reducing absolute values. Steep slopes, essentially above 5,100 m, and higher temperatures below 4,600 m are further limiting factors.

A drastic glacier recession is borne out by mappings of the ice extent in 1899 and 1963. Over this time span, the number of glaciers diminished from 18 to 11, and another disappeared since 1978. Of the eight defunct ice entities, six were small. By far the largest glacier to disappear since the turn of the century was the Kolbe, in a precipitation‐abundant but radiationally very exposed location on the eastern flank of the mountain. The largest and now easternmost ice body, the Lewis, which occupies the radiationally most exposed location of all the glaciers, has experienced the greatest ice wastage.

The model calculations indicate that the drastic ice recession since the late 1800s is largely due to an increase in absorbed shortwave radiation accompanying, and in part brought about by, changes in cloudiness, precipitation, and temperature. In addition to the consequences for the overall ice amount, the spatial distribution of radiation totals, as influenced by topographical shading, appears to account for the remarkably diverse shrinkage of the glaciers on Mount Kenya.
Cave climate: Assessment of heat and moisture exchange
Authors: de Freitas C. R. , Littlejohn R. N.
Published: February 2007

Earlier work on the role of airflow and ventilation in cave climate is extended to include the processes of heat and mass transfer. The study site is Glowworm Cave in New Zealand which is of special interest because of the existence of climate sensitive cave fauna on which the value of a cave as a tourist resource depends. However, the purpose is to provide greater insight into processes governing cave climate generally. Detailed measurements of temperature, humidity and evaporation were made over a 12‐month period and a thermodynamic advection model calibrated to help explain climatic patterns observed and processes operating. The results show that the spatial and temporal distribution of cave air temperature and humidity, as well as direction of airflow, can be determined from external air temperature and humidity. The dominant processes are the vapour and sensible and latent heat fluxes to and from both the air moving through the cave and the cave surfaces. Tn winter there is strong drying and cooling of the cave environment as external air entering the cave is warmed. In summer, humidity levels in the cave rise substantially and result in condensation (wetting) through the cave despite general warming of the cave air.
Soil heat flux in permafrost: Characteristics and accuracy of measurement
Authors: Halliwell David H. , Rouse Wayne R.
Published: February 2007

Soil heat flux plates are a standard method of measuring soil heat flux in energy balance and related studies. Recent work has suggested that heat flux plates significantly underestimate the true flux value in permafrost terrain. Using data from two sites near Churchill, Manitoba, collected over two summer thaw periods, the calorimetric method of soil heat flux determination is used to assess the reliability of heat flux plate data. It is found that the heat flux plates underestimate the surface heat flux in organic permafrost terrain by about 50 per cent. The most likely cause of the error appears to be a combination of poor thermal contact between the plate and the peat soil, and possible vapour transport through the porous material. Recommendations are made to reduce errors in field determinations of soil heat flux.

The calorimetric calculations indicate that the largest portion of the soil heat flux is stored as latent heat in the thawing of ground ice. The flux at 1–5 m depth constitutes a significant portion of the surface flux. The smallest component of the surface flux is the portion stored as sensible heat in the layer between the surface and the 1–5 m depth. Overall, the soil heat flux represents a high fraction (from 16 per cent to 18 per cent) of the net all‐wave radiation available at the surface.
Odelling radiation on south‐facing slopes
Authors: Wahab M. M. Abdel
Published: February 2007

The purpose of this study is to evaluate two models, the isotropic and the anisotropic, for estimating solar radiation on inclined surfaces. The models validation and analysis were applied to south‐facing slopes with inclinations of 30, 60, and 90°. A better performance was shown for the anisotropic one and this performance decreases with the increase of slope surface.
Objective analysis of monthly climatological fields of temperature, sunshine, rainfall percentage and rainfall amount
Authors: Hamilton J. E. M. , Lennon P. , O'Donnell B.
Published: February 2007

An objective method of drawing climatological maps of sunshine, temperature, rainfall percentage and rainfall amount, which is used operationally at the Irish Meteorological Service in Dublin, is described. The interpolation is based on McLain's method of distance weighted least squares quadratic approximation. The observations are interpolated directly to a regular (rectangular) mesh, without the use of a first‐guess, and the resultant field is contoured and shaded using a standard contouring package.

This basic interpolation gave some spurious results near the coast and in data void areas when it was applied in its original form. These problems were overcome by the introduction of dummy values in such regions and a method was developed for calculating such values automatically based on nearby observations and various climatological normals.

The method has been in operational use since February 1985 and the results are of quality comparable to the manual method which this computer method has replaced.
Tropical circulations and the associated rainfall anomalies during two contrasting years
Authors: Kayano Mary Toshie , Rao Vadlamudi Brahmananda , Moura Antonio Divino
Published: February 2007

The severe drought conditions observed during 1983 over a large extent of tropical lands were associated with the 1982–1983 El Niño event. In contrast, above normal rainfall was observed over these areas during 1984. The tropical circulations have been examined for these two contrasting years. The intensity and location of the rising and sinking motions were consistent with the rainfall anomalies and also with the outgoing longwave radiation anomalies. It was found that the north‐south migration of the tropical trough played an important role in modulating the tropical rainfall during these two years. In the context of the currently acceptable theoretical notions of the tropical circulation, some of the observed characteristics could be explained in terms of an atmospheric response to tropical heat sources. The results suggest that seasonal changes were involved in the 1982–1983 El Niño collapse.
The influence of upwelling extent upon fog incidence at Lüderitz, southern Africa
Authors: Olivier J. , Stockton P. L.
Published: February 2007

This paper examines the influence of the horizontal extent of the cold‐water upwelling on the incidence of fog at Lüderitz, Namibia, during 1983–1984. The spatial extent of the upwelling was measured on days with synoptic conditions conducive to fog formation, i.e. when a coastal low was centred to the south of the study area. A significant relationship was identified, indicating increased fog occurrence with an upwelling extent of less than 200 km and vice versa. The moisture necessary for fog formation was postulated as originating from the warm water to the seaward side of the upwelling zone. With a narrow upwelling, the circulation around the coastal low extends beyond the cold‐water mass, whereas when the extent of the upwelling exceeds that of the coastal low circulation, evaporation is limited, resulting in a relatively dry onshore air flow.
Local and remote response to zonally uniform sea‐surface temperature in a July general circulation model
Authors: Simmonds Ian , Dix Martin , Rayner Peter , Trigg Glenn
Published: February 2007

To investigate the effect of longitudinal sea‐surface temperature gradients this paper reports on three experiments in which they were removed over the entire globe, and separately in the two hemispheres. The first of these is compared to an analogous experiment for January and the response is found to be generally greater.

An almost‐hemispheric region of sea‐level pressure increase is simulated centred on Papua New Guinea with decreases centred on the Atlantic. In the anomalous upper level streamfunction there is an anticyclonic pair straddling the Equator in the Western Hemisphere with a corresponding cyclonic pair in the Eastern Hemisphere. The velocity potential is dominated by a wave 1 response. Precipitation anomalies tend to be confined to and follow the sea‐surface temperature anomalies and their magnitudes are much larger than evaporation changes. This highlights the role of moisture advection in maintaining these anomalies. The Hadley cell intensifies while the Walker circulation is weakened. The root‐mean‐square deviation of geopotential height waves generally decreases, particularly in the Southern Hemisphere, mainly due to reductions in the strength of wave 1.

The experiments with hemispheric anomalies allow us to investigate the relative importance of local and remote forcing. It is found that most of the global response can be explained by the Northern Hemisphere forcing alone. This is true even in the Southern Hemisphere. The implications of this for cross‐equatorial propagation of information are discussed. The results highlight the importance of the meridional component of the wind in this connection.
Multiple reflections across a linear discontinuity in surface albedo
Authors: Barker Howard W. , Davies John A.
Published: February 2007

Solar radiation received and absorbed at the surface beneath an overcast sky is calculated as a function of distance d from a linear discontinuity in surface albedo, cloud base altitude h, cloud optical thickness τ, surface albedo α, and precipitable water. Horizontal variation of multiple reflections between surface and cloud is accounted for. Cases of snow or ice surfaces adjacent to open water or snow‐free land surfaces are considered because of large albedo differences. Irradiance on all surfaces and absorptance on the darker surfaces are shown to depend on d, h, τ, α and water vapour beneath the cloud base. Absorption by snow and ice surfaces is less sensitive to changes in d, h and τ because of weak absorptance in the spectral region where multiple reflections are most prevalent; λ<0.7 μm. Ground‐based, radiometrically measured (point) surface albedo depends weakly on d and h but more strongly on τ. Estimates of cloud base albedo from surface measurements may be in error if surface irradiances are measured too close to large albedo discontinuities.
The walker circulation and atmospheric water vapour characteristics over the Pacific for two contrasting years
Authors: Kayano Mary Toshie , Rao Vadlamudi Brahmananda , Moura Antonio Divino
Published: February 2007

The Walker circulation for two contrasting years 1983 (ENSO year) and 1984 (non ENSO year) is determined. Principal changes in the upper level divergence are noted in the western and central Pacific regions. Thus, this part seems to form the principal branch of the Walker circulation, where a reversal takes place during the two contrasting years. Water vapour characteristics of the atmosphere over the western and central Pacific regions are determined using radiosonde data. During the ENSO event of 1983 an unusual accumulation of water vapour over the central Pacific and a depletion of it over the Indonesian region is noted. Further, the correlation coefficient between the SO index and water vapour variation showed significant values. Another aspect of the tropical atmosphere discussed here is the thermodynamic structure and its implications for the development of convection. Our study revealed a spectacular reversal of atmospheric properties such as the upper level divergence, water vapour, and thermodynamic structure during the two contrasting years.
Onset dates of the south‐west monsoon over Kerala for the period 1870–1900
Authors: Ananthakrishnan R. , Soman M. K.
Published: February 2007

This communication presents the dates of onset of the south‐west monsoon over south Kerala for the period 1890–1900 and over north Kerala for the period 1870–1900.
Bivariate normal classification of North American air masses using the normix program
Authors: Epperson David L. , Davis Jerry M. , Watson Gerald F. , Monahan John F.
Published: February 2007

This preliminary study employs Wolfe's cluster analysis program (NORMIX) in the bivariate normal classification of North American air masses. Once‐daily observations of potential temperature and mixing ratio were classified by the NORMIX program into ‘types’ which represent different air masses. The cluster analysis was performed at the surface, at 850 mbar, at 700 mbar, and at 500 mbar for each of seven stations located along the 80th meridian. Individual data sets were composed of 10 years of observations taken during January or July at each level.

Analyses derived from the NORMIX results showed more types at the middle latitudes than at source region latitudes. A different number of NORMIX types was found at each level above each station, except at Miami in July. Frequency tables for the Greensboro station showed that some NORMIX types at upper levels occurred in conjunction with two or more surface NORMIX types, thereby indicating the presence of overrunning. Synoptic analyses for the Greensboro station showed that each NORMIX type was associated with a specific synoptic air mass type.

The NORMIX program generated discriminant functions which were used to objectively classify independent potential temperature and mixing ratio data for the Greensboro station. The results of the independent data classification compared favourably with synoptic air mass types and with the original NORMIX results.
Deterministic signals in precipitation records from the American corn belt
Authors: Currie Robert G. , O'Brien Douglas P.
Published: February 2007

Maximum entropy spectrum analysis of 120 yearly total precipitation records in the Corn Belt (States of Illinois, Indiana, Iowa, and Missouri) yield evidence for the 18·6‐year luni‐solar term in 109 instances, while the 10‐ to 11‐year solar cycle signal was found in 100 records. For Illinois, minima in the 19‐year wavetrains were highly correlated with epochs 1898·9, 1917·5, and 1936·1. For eighteen stations wave minima were still correlated with the next epoch, epoch 1954·7; however, a bistable phase switch of 180° then occurred and wave maxima came into phase with epoch 1973·3. In two instances in northern Illinois the switch occurred a cycle earlier at epoch 1954·7, and in five instances a half cycle earlier at mid‐epoch 1964·0. O'Brien and Currie (1989) have provided a construct in mathematical physics that explains how bistability can occur at air‐pressure recording stations, and Currie (1987a) has provided many examples of bistability in air pressure and air temperature data from around the world.
Southern Oscillation influences on tropical cyclone activity in the Australian/south‐west Pacific region
Authors: Hastings Peter A.
Published: February 2007

Tropical cyclone activity within the Australian (105°–165°E) and south‐west Pacific (145°E–150°W approximately) regions is examined during seasons affected by contrasting extremes of the Southern Oscillation (SO). In the Australian region, the most pronounced and consistent contrast of tropical cyclone frequency variability was within the eastern Australian region (145°–165°E) where anti‐ENSO (ENSO) conditions were associated with a higher (lower) incidence of tropical cyclogenesis. This relationship appears to be a manifestation of tropical cyclone behaviour in the wider south‐west Pacific region, wherein tropical cyclone origin points exhibit distinct areal patterning associated with times of extreme SO states. Intra‐seasonal temporal distributions of the Australian region tropical cyclogenesis and the south‐west Pacific tropical cyclone incidence are also examined.
A climatological approach for estimations of hourly averages of global irradiation
Authors: Castro‐Diez Y. , Jimenez J. I.
Published: February 2007

Monthly mean values of daily and hourly global solar irradiation at eight stations in Spain are analysed on the basis of the similarity between the shape of extraterrestrial irradiance during the day and the Gaussian curve. This shape is found to be the same on the Earth's surface after attenuation through the atmosphere whenever the averaged‐out period is long enough. Bearing this in mind, it is possible to obtain values for the ratio between the hourly irradiance and the daily global irradiation, from one parameter σ, with the normal distribution curve. This curve is found to fit closely with experimental results. The mean of the normal distribution is taken at solar noon and the parameter σ is determined for each month by matching the experimental and the theoretical values at this time. The σ‐values thus obtained are found to bear an excellent linear correlation with N (monthly mean of maximum sunshine duration). The close correlation of the regression constants with latitude, altitude, and relative bright sunshine duration provides a simple technique for estimating hourly irradiance from the daily values within a certain range of latitudes. This technique makes the estimation of global irradiation for any smaller time interval possible. The errors involved in the estimations obtained are less than 10 per cent in most cases.
Occurrence and characteristics of lower tropospheric ice crystals in the arctic
Authors: Curry J. A. , Meyer F. G. , Radke L. F. , Brock C. A. , Ebert E. E.
Published: February 2007

This paper discusses the occurrence and characteristics of small ice crystals that are encountered in the lower troposphere of the Arctic during the cold half of the year, when large reductions in visibility are present. Because of the difficulties in observing these ice crystals, both from surface and satellite observations, and owing to the ambiguities of cloud classification in the polar regions, these ice crystals are not included in current cloud climatologies. A summary is presented of what is known about the Arctic ice crystal climatology, formation mechanisms, and physical properties. Data obtained from the University of Washington Convair C‐131A research aircraft during April 1983 and 1986 are presented, including the frequency of occurrence of ice crystals as a function of height, temperature, and relative humidity. Radiative transfer calculations were made using the observed ice crystal size distributions. The radiative transfer through the ice crystal layers is inferred to have a substantial impact on visibility in the Arctic, the vertical temperature structure of the Arctic troposphere, and on the surface energy balance.
Deterministic signals in USA precipitation records: Part I
Authors: Currie Robert G. , O'Brien Douglas P.
Published: February 2007

Evidence for the 18–6‐year luni‐solar MN signal is found in 220 out of 288 rain‐gauge records (76 per cent detection ratio) in the states of California, Colorado, Kansas, Missouri, North Carolina, Ohio. Oregon, Washington, and West Virginia, with a mean period of 18·4 ± 1·5 years. This detection ratio is less than that for the nation, which is 1015 out of 1219 records, or 83 per cent. The solar cycle Sc signal was found in 70 per cent of these records, with a period of 10·6 ± 0·5 years. For Colorado, and states directly to the east as far as Illinois, minima in most 19‐year Mn wavetrains were generally in phase with epochs 1898·9 through to 1954·7 (epochs are dates of maximum in tidal forcing). However, by 1973‐3 virtually all records east of Colorado had experienced a 180° phase switch and wave maxima were in phase with this epoch. In Oregon and Washington most MN waves recorded maxima in wetness at epoch 1898·9 through to 1973·3, and thus have historically been out of phase with the continental interior. California records displayed evidence for two 180° phase switches in the past 100 years. The apparent reason for this is that California is near the edge of a fairly stable continental interior cell that has historically been dry at epochs; and when the dry cell waxes or wanes in areal extent, frequent 180° phase switches are produced in areas adjacent to it. The phenomena described have been found in other regions of the USA, and in records of air temperature and air pressure world‐wide.
Signatures of A universal spectrum for atmospheric interannual variability in rainfall time series over the Indian region
Authors: Selvam A. Mary , Pethkar J. S. , Kulkarni M. K.
Published: February 2007

A recently developed non‐deterministic cell dynamic system model for atmospheric flows is summarized in this paper. The model predicts quantum‐like mechanics for atmospheric flows with inherent long‐range spatiotemporal correlations, now identified as signatures of self‐organized criticality or deterministic chaos. The model enables quantification of the power spectrum of temporal fluctuations of atmospheric flows in terms of the universal and unique characteristics of the statistical normal distribution. The model predictions are in agreement with continuous periodogram analysis of three sets each of 30 years (1871–1900, 1901–1930, 1956–1985) and one set of 25 years (1931–1955) summer monsoon rainfall time series for 29 meteorological subdivisions in the Indian region. The important results of the present study are as follows. (i) The power spectrum of the temporal fluctuations of rainfall follows the universal inverse power law form of the statistical normal distribution, with the square of the eddy amplitude representing the eddy probability density corresponding to the normalized standard deviation t equal to (logλlogλ50)‐1; where λ is the period length in years and λ50 the period up to which the cumulative percentage contribution to total variance is equal to 50 and t=0. (ii) Periodicities in rainfall up to 3–4 years contribute to as much as 50 per cent of the total variance.

A universal spectrum for interannual variability in summer monsoon rainfall indicates predictability of the overall pattern of rainfall fluctuations. A relatively recent and short period rainfall time series, such as the 30‐year period 1956–1985 in this study, enables identification of the universal structure of atmospheric variability. Further, short period fluctuations that are major contributors to interannual variability can be identified accurately in the 30‐year data sets and provide means for estimating the near future (up to 4 years) rainfall variation.
A procedure for removing the synoptic climate signal from environmental data
Authors: Comrie Andrew C.
Published: February 2007

Using weather‐type frequencies from a synoptic climatology, a technique is presented that discriminates between within‐type and between‐type variations in a time series of climate‐related environmental data. The removal of the synoptic climate signal, or declimatizing, is based on normalizing the data by the mean annual weather‐type frequencies for the study period. Declimatizing is illustrated symbolically and with a worked hypothetical example. An application of the procedure to visibility data from Pittsburgh, Pennsylvania demonstrates its utility in decomposing complex climate‐related environmental data into its component synoptic and non‐synoptic influences. The methodology can also distinguish the relative importance of between‐type and within‐type changes in a synoptic climatology.
Cellular convection over the north‐eastern Atlantic
Authors: Bakan S. , Schwarz E.
Published: February 2007

Convective clouds over the ocean frequently exhibit organized meso‐scale patterns. A statistical evaluation of 4 years of NOAA satellite images over the north‐eastern Atlantic yields climatological data of the appearance of these patterns and shows that open cellular convection is most abundant. For this convection type, surface and radiosonde data from Weathership M have been analysed. Open convection cells appear at a wide range of positive sea‐air temperature differences up to 12°C and at wind speeds up to 25 m s−1. All diameters have been found to be less than 80 km (average 41 km). Larger diameters are, on average, associated with slightly larger convection heights and, thus, with larger aspect ratios.

The scene‐averaged brightness temperature of AVHRR channel 4 exhibits a definite correlation with the sea‐air temperature difference and, less well expressed, with the sensible and latent heat flux. This, in turn, provides a possibility of estimating those quantities by using easily accessible AVHRR satellite data.
Monthly mean pressure model for Chile
Authors: Saavedra N. , Foppiano A. J.
Published: February 2007

A simple empirical model to describe the latitudinal distributions of monthly mean surface pressure along the Chilean coast is proposed. Model hypotheses, such as regions into which latitude distributions are to be divided and latitude dependencies of pressure within these regions to be assumed, are discussed with reference to a climatic scenario that has been found of value in developing simple empirical climatic models for coastal stations in Chile. Equations are derived giving pressure at any latitude as a function of the latitude of the location of maximum monthly mean pressure in Chile (LMP) and of pressure at that location. It is concluded that the proposed model describes adequately the observed latitudinal distributions. Moreover, it is found that the coupling between the Pacific Anticyclone and the continent is particularly simple for locations north of the LMP's latitude, leading to a unified quantitative description of climate for those latitudes. Furthermore, the model allows qualitative inferences to be made regarding the interaction mechanisms between the main meteorological centres of action on a regional scale, which may prove of value to identify trends of regional climatic change.
Wind persistence in Croatia
Authors: Poje Dražken
Published: February 2007

On the basis of mean hourly wind direction and wind speed data from 11 anemograph stations in the eastern part of the Adriatic sea and seven inland stations in Croatia, and records of different length, the basic characteristics of wind persistence are discussed. In continuation of our earlier work, which dealt with wind persistence regardless of wind direction, this paper presents the results of investigation on wind persistence for wind groups of three combined directions. On the Adriatic three dominant winds are analysed: Bora, ‘Jugo’, and Etesian winds. The mean run length, run duration for 90 per cent and 95 per cent of all cases, as well as the longest recorded duration for run levels of v ⩽ 3m s−1, v 3 m s−1, v > 5 m s−1, v > 8 m s−1, v > 12 m s−1 and v > 18 m s−1, are elaborated. With regard to the potential utilization of wind, the most promising areas regarding wind persistence are the Velebit Channel in the northern Adriatic and the exposed islands in the southern Adriatic.

The second part deals with different methods and analytical functions describing wind persistence depending on different parameters that could be assessed on the basis of observed wind runs or by using only the mean annual wind speed. The best results were achieved using the power exponential function, especially for long wind runs.

The third part includes the testing of the methods used on the data for the station Sinj, with satisfactory results.
Temporal variation of relations between New South Wales rainfall and the Southern Oscillation
Authors: Opoku‐Ankomah Yaw , Cordery Ian
Published: February 2007

Principal component analysis with varimax rotation was used to identify major spatial patterns of New South Wales (eastern Australia) district rainfalls in each season. Four spatial patterns of the principal components of rainfall, each dominant in a subregion of the State, were evident. Plots of correlation coefficients between the amplitudes of the spatial patterns and the Southern Oscillation Index (SOI) revealed temporal instability of the relationships. Results show that the relationships have changed dramatically with time and that they have changed differently from region to region. Over the 55 years (1933–1987) for which data were available, in some regions the correlation coefficients changed from being highly significant, to showing no relationship, in others the reverse was the case, and in some very little change occurred. This meant that over time the spatial pattern of relationships for a given season also changed quite dramatically.

These findings have profound implications for studies based on assumptions of stationarity of geophysical phenomena and relationships and suggest there are other, as yet unrecognized, phenomena influencing rainfall in the long‐term.
Long‐term variations in regional rainfall in the south‐west of Western Australia and the difference between average and high intensity rainfalls
Authors: Yu B. , Neil D. T.
Published: February 2007

The south‐west of Western Australia is characterized by a ‘Mediterranean’ climate with dominantly winter rainfall. It is the only Australian region where the annual rainfall has significantly decreased during the period 1911–1990. Based on daily rainfall records from 70 stations in the area, high intensity rainfall (which is closely related to flooding, soil erosion, and gully formation) does not show a concurrent decrease. Reasons for this unconformable trend include a greater temporal variability of high intensity rainfall and an increase in the frequency of occurrence of rainfall events at high intensities during the summer. This tends to balance out a decrease during the winter months. While it is unwise to assume that there will be similar trends for average rainfall and high intensity rainfall for a given region, evidence from the instrumental records supports, to some extent, the notion that in a CO2‐warmed world, high intensity rainfall could occur more frequently irrespective of local change to average rainfall.
Comments on: ‘The effect of domain shape on principal components analyses’
Authors: Richman Michael B.
Published: February 2007

In a recent article claiming to deal with the effect of domain shape on principal component analysis, Legates attempts to use previously published research and analyses of two exploratory data sets to try to dismiss Buell's work on the topography of empirical orthogonal functions. Legates' logic and data sets suffer from a number of flaws, including omission of key results from Buell, neglect of dozens of published papers discussing domain dependence, misinterpreting and misrepresenting numerous references to Richman, and using data sets with inhomogeneities between land and water as well as very low temporal degrees of freedom. This Comment addresses some of these shortcomings by exploring what other researchers have concluded about Buell patterns and how they have minimized the problem. It also serves to provide a proper interpretation of PC loading fields consistent with Richman, and to point out several potential problems in the two data sets used by Legates, which might lead to inferior results.
A re‐evaluation of rainfall variability in the sahel. Part I. Characteristics of rainfall fluctuations
Authors: Nicholson Sharon E. , Palao Ian M.
Published: February 2007

This article deals with the characteristics of rainfall variability in West Africa. Time series of June—July, August—September and annual rainfall anomalies are derived for 19 regions, most of which are in the Sahel—Soudan zones of West Africa. The temporal characteristics of the series, such as trend, persistence, and low frequency variance are evaluated using regression, lag‐1 autocorrelation, and spectral analysis. High‐frequency‐filtered series are also derived. The spatial teleconnections among the regions are examined using linear correlations and principal component analysis. The study shows that there are primarily three spatial modes of rainfall variability in the region and these differ with respect to the part of the rainy season in which they are most important and to what extent they describe high and low‐frequency components of the variability. The study also defines three broad homogeneous sectors and demonstrates that the characteristics of rainfall variability in these sectors differ markedly. A strong contrast between the bulk of the Sahel—Soudan and its West Coast sector is apparent.
Seasonal and annual rainfall variations over Nigeria
Authors: Anyadike R. N. C.
Published: February 2007

Variations of monthly and annual rainfall over the southern, middle belt and northern regions of Nigeria as well as the country as a whole are examined for a 72–year period (1916–1987). In this way the zonal distribution of the country's rainfall is taken into account. The extent and nature of non‐random changes, such as fluctuations, trend, and persistence, are investigated. The fluctuations were filtered by a Gaussian low‐pass filter and the resulting curves are discussed. Trend analysis showed a tendency towards decreasing annual rainfall totals in all the regions, with rates of decrease being greatest after 1961 in the southern region. All regions experienced the reverse of the trend during the 1931–1960 period. Overall, no significant persistence was evident in all the series. Power spectrum analysis revealed the existence of significant oscillations in the rainfall totals. These have time periods of 2·00–2·82 years in the middle belt and northern regions. 3·00–4·80 years in the middle belt, and 8·009·60 years in all the regions. The implications of these fluctuations, and continued application of the 1931–1960 normal for planning purposes, are pointed out, as well as suggestions for further lines of inquiry.
The climatology and characteristics of drought in the eastern Cape of South Africa
Authors: Jury Mark R. , Levey Kevin
Published: February 2007

Along the south‐eastern seaboard of Africa, a drought‐prone area is found between the humid subtropics and a deser. Convective mid‐summer precipitation in the north‐east is contrasted with stratiform winter rains in the west. Mean annual precipitation is <500 mm while potential evaporation is >2000 mm. According to time series analysis of rainfall records, dry spells recur at intervals of 3·5 and 18·2 years, most notably in the period 1940–1970. By contrast, excessive rainfall characterized the mid‐1970s. Extreme dry and wet years are analysed for circulation, convection and sea‐temperature differences. Below‐normal sea temperatures to the south‐west and east of the study area are associated with drought in the eastern Cape. Circulation differences indicate that low‐level westerly winds sweep across the region, in association with a stationary subtropical westerly wave of wavelength 3000 im and amplitude 1500 km. A positive outgoing longwave radiation anomaly indicative of reduced cloudiness and water vapour is noted in a north‐west—southeast band extending from Namibia across the eastern Cape watershed. Anticyclonic vorticity anomalies of the order of 10−5s−1 across the subtropics of southern Africa are common in dry years. Lower divergence to upper convergence anomalies of the order of 2 × 10−6s−1 are the driving forces of subsidence over the eastern Cape. The analysis of climatic patterns associated with dry spells will assist in forcasting seasonal rainfall, planning agricultural production, and optimizing water resources.
An assessment of air quality variations in the south‐western USA using an upper air synoptic climatology
Authors: Davis Robert E. , Gay David A.
Published: February 2007

Daily particulate concentrations in the Desert South‐west from 1984 to 1988 are analysed using a synoptic climatology based upon tropospheric thermal, moisture, and flow conditions. Using a combination of principal components analysis and cluster analysis, 13 distinct synoptic types (clusters) are identified that correspond to seasonal variations in the atmosphere's general circulation. These include summer clusters, which reflect monsoonal and non‐monsoonal conditions, winter clusters defined by the positions of the polar and subtropical jets and shortwave ridges and troughs, and clusters that predominate in the transition seasons.

Particulate concentrations vary significantly by synoptic type. Three clusters have poor air quality. ‘Summer monsoon’ days have high humidity and cloud cover, conditions that encourage aerosol growth. ‘Continental high’ days have a slow‐moving anticyclone centred over the Great Basin that traps particulates within the boundary layer. ‘Rockies ridge’ days are associated with strong south‐westerly flow and the advection of regional haze from southern California into the Desert South‐west. In all of these clusters, high humidity or cloud cover enhance particulate growth. Good air quality in the summer occurs on monsoonal ‘break’ days when relative humidity and cloud cover decrease. In the winter, good air quality occurs when Arctic or continental polar air masses are present, or when either the polar or subtropical jets are strong and positioned over the South‐west. In some of these latter situations, widespread precipitation removes particulates through wet deposition.

These results suggest that the Navajo Generating Station (NGS), a large coal‐fired power plant on the Arizona‐Utah border, does not contribute significantly to air quality degradation in the Grand Canyon National Park, Arizona. Most of the days with high particulate levels are associated with transport from southern California or unstable summer days with high humidity and contributions from many point and regional sources. There may be some contribution from the NGS on ‘continental high’ days, but when this cluster occurs on consecutive days, air quality improves rather than declines. This research provides a useful framework for future mesoscale modelling studies of air quality in south‐western USA.
Adjustment of temperature and rainfall records for site changes
Authors: Rhoades D. A. , Salinger M. J.
Published: February 2007

Methods are presented for estimating the effect of known site changes on temperature and rainfall measurements. Parallel cumulative sums of seasonally adjusted series from neighbouring stations are a useful exploratory tool for recognizing site‐change effects at a station that has a number of near neighbours. For temperature data, a site‐change effect can be estimated by a difference between the target station and weighted mean of neighbouring stations, comparing equal periods before and after the site change. For rainfall the method is similar, except for a logarithmic transformation. Examples are given. In the case of isolated stations, the estimation is necessarily more subjective, but a variety of graphical and analytical techniques are useful aids for deciding how to adjust for a site change.
Early detection of the start of the wet season in tropical climates
Authors: Jolliffe Ian T. , Sarria‐dodd Doris E.
Published: February 2007

In many tropical and sub‐tropical climates the year is divided into well‐defined wet and dry seasons. To maximize agricultural production it is important that crops are planted as early as possible in a wet season, but deciding exactly when the wet season has started may be a problem. A decision can be made on the basis of previous years' data, or we may try to incorporate information from the current season. The latter approach is discussed in the present paper, and shown to be potentially of greater value than relying solely on historical data.
Albedo of tropical grass: A case study of pre‐ and post‐burning
Authors: Fisch G. , Wright I. R. , Bastable H. G.
Published: February 2007

Measurements of reflected shortwave radiation were made at an Amazonian ranchland site for a period in which the grass was completely burnt and then subsequently regrew. For the 35 days prior to the fire the mean albedo was 0.19. After the fire the albedo was reduced by a factor two and thereafter took about 80 days to recover to its previous value. The influence on the energy balance is described and it is suggested that such seasonal albedo changes during the dry season may need to be described in climate models for the prediction of the seasonal impact of deforestation.
Luni‐solar 18.6‐ and 10—11‐year solar cycle signals in H. H. lamb's dust veil index
Authors: Currie Robert G.
Published: February 2007

Maximum entropy and Yule‐Walker methods of spectrum analysis applied to Lamb's dust veil indices (dvi) for the Northern Hemisphere (1500–1968) show two strong peaks, with periods of 18.6±0.5 and 10.8±0.3 years. They are identified as the 18.6‐year luni‐solar Mn and 10–11‐year solar cycle Sc signals, which have recently been reported in a wide variety of climate and economic time series. The signals were transformed into the time domain by band‐pass filters, their wavetrains summed, and the sum superimposed on trend‐like components of the dvi; it is found that they account for 48 per cent of variance in the index.
Indian ocean sea‐surface temperature patterns and australian winter rainfall
Authors: Smith Ian
Published: February 2007

Indian Ocean sea‐surface temperatures (SSTs) for the period 1950–1988 are analysed using principal component analysis, and their relationships with Australian winter rainfall totals for the period 1950–1979 are studied using regression analysis. As has been demonstrated by others, significant simultaneous correlations exist between the dominant patterns in the Indian Ocean and the wintertime rainfall over a large part of Australia. There is also evidence of significant correlations between autumn SST patterns and winter rainfall.

These relationships are tested using multiple linear‐regression‐based predictions of winter rainfall categories for the period 1980–1988. Skill is quantified in terms of categorical predictions. Predictions based on the autumn SSTs exhibit more skill than those based on the autumn SOI, but much less than predictions based on the concurrent winter indices.
Linking air mass analysis to daily and monthly mid‐tropospheric flow patterns
Authors: Schwartz Mark D. , Skeeter Brent R.
Published: February 2007

Air mass analysis, though widely used in early atmospheric studies, has seldom been employed in recent decades. In part, this may be due to the lack of agreement on a quantitative air mass classification technique. Synoptic analyses (of which air mass analysis is one example) have much potential for examining the relationships among a variety of surface processes and climate. Schwartz (1991) proposed an integrated air mass classification system that was able to overcome some of the limitations of previous methods. This study further validates that approach by quantitatively linking these air masses to 500‐hPa height and surface pressure patterns. Cluster analysis was used with daily and average monthly air mass distributions in the north‐central USA to identify similar groups. For the daily analyses, average 500‐hPa height, surface pressure, and air mass percentage coverage patterns were determined for the groups in each season. In the monthly analyses, transects of 500‐hPa height difference were examined with the multiple analysis of variance (MANOVA) technique in order to detect significant changes relative to the clusters. Our results show that: (i) integrated‐method air mass percentage coverage distributions can be related quantitatively to a small number of meaningful 500‐hPa height and surface pressure patterns in all seasons; (ii) key transects can be used to describe changes in average monthly air mass dominance and 500‐hPa flow patterns from one year to another; and (iii) for the period 1958–1981, cool air masses decreased in frequency over the study area during spring and summer.
Experimental predictions of climatic variability for lead times of twelve months
Authors: Hunt B. G. , Zebiak S. E. , Cane M. A.
Published: February 2007

Interannual variability of present‐day climate has been clearly linked to the occurrence of large‐scale sea‐surface temperature anomalies, particularly in the Pacific Ocean. Prediction of such anomalies many seasons in advance by using relatively simple, coupled oceanic‐atmospheric models provides a basis for predicting the atmospheric climate over the same period. This is achieved by inserting the sea‐surface temperature anomalies predicted by the coupled model at appropriate time intervals into a global climatic model and integrating forward in time. Prediction experiments for 1991 and 1992 have been conducted on this basis using sea‐surface temperature anomalies predicted for the Pacific Ocean. Global and regional rainfall outcomes are presented here, although the predictions are not expected to be valid for the whole globe. Detailed results are given for Australia and southern Africa, which experienced severe drought conditions in 1991 and 1992. Useful skill, with statistical significance for predictions when substantial rainfall anomalies occurred, was obtained for these regions, indicating the potential utility of the method. Considerable scope exists for improvements in the technique presented here, particularly in the global climatic model used, so that increasing accuracy should result as the technique is developed. Operational implementation of this method is essentially straightforward.
Box‐jenkins univariate modelling for climatological time series analysis: An application to the monthly activity of temperature inversions
Authors: Davies T. D. , Milionis A. E.
Published: February 2007

Box‐Jenkins modelling has some advantages over other techniques for the analysis of time series of climatological variables. Not only does it provide more information than other methods of anlysis, in a more elegant way, but it is also perfectly acceptable from the mathematical point of view. Other methods may not be immediately applicable because of the problem of autocorrelation in time series. The method of Box‐Jenkins univariate modelling is briefly discussed. As an example of its application to climatological time series analysis, and as an illustration of its usefulness, we examined the monthly activity of temperature inversions over Hemsby (eastern England) over a 14‐year period. The results showed that the monthly activity series, for both surface and elevated inversions, are stationary. However. the series for surface midnight inversions has a seasonal non‐stationarity of lag 12. There is a 1Zmonth seasonality for surface inversions and a weaker 6‐month seasonality for elevated inversions. The monthly activity of surface inversions exhibits less variation than the monthly activity of elevated inversions. This simply reflects the fact that the physical processes responsible for the formation of surface midnight inversions have a more regular evolution overtime than those responsible for the formation of elevated inversions. These results are in accordance with those obtained by using standard statistical techniques.