bluuebunny/crossref_metadata_2025 huggingface dataset:
Variations in heating and cooling degree‐days in the south‐eastern USA, 1960–1989
Authors: Soulé Peter T. , Suckling Philip W.
Published: February 2007

Temporal trends and spatial variability of heating and cooling degree‐days are examined for a portion of the south‐eastern USA for the period 1960–1989. Temporal variability is examined through simple time‐series analyses, regression analyses, and a climate departure index (CDI). Maps of 30‐, 15‐, 10‐, and 5‐year climatic normals for degree‐days are presented.

The CDI indicates that heating degree‐day (HDD) variability was high during the 1970s with a sudden drop to low variability during the 1980s. Simple regressions show weak downward trends for actual HDD values across the region during the study period. However, the HDD decline was more pronounced through the 1980s, coinciding with the period of low year‐to‐year variability. Isoline maps show that most sites recorded distinctly fewer HDD in the most recent 5‐year period compared with longer term averages.

Although the long‐term trend for cooling degree‐days (CDD) is slightly positive, there is considerable interyearly and interdecadal variability. Unlike HDD, there were no sustained periods with consistently high or low variability for CDD. Mapped patterns of climatic normals show that CDD values peaked across the study area during the most recent 5‐year period.

Mapped patterns for both HDD and CDD can be influenced by data for large urban sites. Repeating the analyses without the seven largest urban centres resulted in less anomalous spatial patterns but almost no shift in study area mean‐degree‐day or CDI values and their temporal patterns. Atlanta emerged as the most distinct anomaly for the mapped patterns.

From an applied viewpoint, the most significant finding occurred for the heating season with the combination of a sustained downward trend in HDD and comparatively low variability around the long mean (low CDI values) during the last 13 years of the study period. This period represents a span where the climate‐driven demand for space heating was decreasing and the heating‐season generating capacities for power generation utilities were not challenged.
A new method for detecting undocumented discontinuities in climatological time series
Authors: Easterling David R. , Peterson Thomas C.
Published: February 2007

The development of homogeneous climatological time series is a crucial step in examining climate fluctuations and change. We review and test methods that have been proposed previously for detecting inhomogeneities, and introduce a new method we have developed. This method is based on a combination of regression analysis and non‐parametric statistics. After evaluation against other techniques, using both simulated and observed data, our technique appears to have the best overall performance.
Temporal variability of the 40–50‐day oscillation in tropical convection
Authors: Anyamba Ebby Kamila , Weare Bryan C.
Published: February 2007

The temporal variability of the structure and two‐dimensional phase propagation of the 40–50‐day oscillation in tropical convection are diagnosed using complex empirical orthogonal function (CEOF) analysis of the 1974–1988 outgoing longwave radiation (OLR) data.

Results from autoregressive spectrum analysis of the OLR time series indicate that apart from the well‐known 40–50‐day peak, there are other significant spectral peaks near 20–30 and 17 days. In much of the tropics, excluding the equatorial Indian and western Pacific Oceans, these higher frequency peaks appear to be distinct from the 40–50 day spectral peak.

The dominant spatial mode of the 40–50‐day oscillation consists of the well‐known equatorial dipole and associated eastward propagation. Interactions between this mode and the extratropical 40–50‐day oscillation are manifested through the propagation of convection anomalies to and from the tropics via the North Pacific, north‐east Atlantic and north‐east African subtropics. The sense of this propagation varies from season to season and year to year.

Analysis of the oscillation during individual summers and winters and each of the 1976–1977, 1982–1983 and 1986–1987 El Niño‐Southern Oscillation (ENSO) events revealed marked variability in the oscillation's characteristics. The characteristic dipole and associated eastward propagation were suppressed during the winter of 1980–1981 and the entire 1982–1983 ENSO episode. In 1975–1976 and 1983–1984, convection anomalies were confined to the Indian Ocean and Australia sector and the spatial pattern differed from the characteristic equatorial dipole. The equatorial dipole was most pronounced in February‐May 1981, December 1984 to May 1985 and during the 1976–1977 ENSO. During certain occasions, such as the 1981–1982 and 1983–1984 winters, there was westward as well as eastward propagation from an apparent heating source in the east Indian Ocean.
Associations between Antarctic katabatic flow and the upper level winter vortex
Authors: Simmonds Ian , Law Rachel
Published: February 2007

We address the extent to which modifications to the surface wind field over Antarctica impact on the upper level winter vortex. This is approached by performing two sensitivity studies with a general circulation model. In the first experiment we have eliminated the katabatic outflow from the continent by removing the slope (i.e. we removed the topography of Antarctica). In the second experiment we weaken the surface flow by increasing the surface momentum drag coefficient over Antarctica.

The results show a weakened upper level circulation in the no‐topography experiment but a strengthened vortex in the increased drag experiment. The different response is related to the effect of the boundary forcings on the thermal structure of the atmosphere. In the no‐topography simulation, significant warming occurs throughout the Antarctic troposphere and this is apparently associated with changes in cyclone behaviour. This appears to be the dominant effect on the upper level vortex. In the drag case the impact on temperature is much smaller but is still an important influence on the upper level circulation.

We find that there is no simple, unambiguous relationship between the strength of the katabatic flow and the depth of the upper level vortex; it is clear that thermodynamic processes are important in determining the latter.
Comparison of observed and modelled radiation budget over the Tibetan Plateau using satellite data
Authors: Sun Zhian
Published: February 2007

The radiation budget over the Tibetan Plateau is investigated using radiation models together with the data from the International Satellite Cloud Climatology Project (ISCCP) and the Earth Radiation Budget Experiment (ERBE). A method of using the ISCCP spectral surface albedo in determining the radiation budget is proposed and tested against observations. Three cloud levels (low, middle, and high) with different phase states are considered in the radiative simulations. The effect of dust aerosols on the radiation budget is also taken into account in the study. The simulations are performed using climatology monthly mean radiosonde profiles observed at 35 stations on the Tibetan Plateau and compared with the ERBE observations.

The results indicate that the radiation budget in clear sky conditions can be well modelled using the monthly mean radiosonde data. The monthly mean total scene radiation budget is also simulated satisfactorily using the radiation models in conjunction with the ISCCP data, although significant discrepancies can be found in certain regions owing to uncertainties in the calculations. The cloud properties over this high plateau are found to be different from elsewhere. The most significant differences in the cloud properties are their altitude, which is much higher, and water content, which is less than at lower altitudes. As a result, cloud over the Tibetan Plateau has positive forcing in the winter and less negative radiative forcing in the summer compared with low altitudes.
Interdecadal variations of surface wind direction in Lund, southern Sweden, 1741–1990
Authors: Jönsson Peter , Fortuniak Krzysztof
Published: February 2007

By uni‐ and bimodal mean vector analysis it is concluded that the decadal pattern of surface‐wind‐direction frequencies in Lund, southern Sweden, has changed substantially between 1741 and 1990. Trend analysis shows that statistically significant decreasing trends for north and north‐east winds are present during all seasons, whereas a decline in easterly wind is most prominent in July‐September. These trends are paralleled by increases of south‐east (January‐May and August‐November) and south‐west winds (April‐September and November‐January). These trends promote milder autumns, winters, and springs and a somewhat cooler summer.

The investigation period is divided into three phases on the basis of similar flow patterns, which in general terms agree with Scandinavian temperature records: (i) 1741–1840‐a continental low‐zonality period featuring extreme bimodal flow of wind with relatively high frequencies of east winds, which indicate a continental climate. Warm summers and cold winters are produced by this flow pattern. The severity of winters was enhanced by a high frequency of north and north‐east winds. (ii) 1841–1910‐a transition period with decreased continentality and low yearly temperatures. This circulation type caused a temperature drop except during winter. (iii) 1911–1990‐a maritime high‐zonality period featuring further strengthening of the westerly flow. A warm maritime phase with least expressed warming in summer. Severe winters are further counteracted by low frequencies of north and north‐east winds.
Maximum entropy spectral analysis of the Duero Basin
Authors: Leite Solange Mendonça , Peixoto José Pinto
Published: February 2007

Maximum entropy spectral analysis for the estimation of power spectra is used to study monthly and annual spectra of air temperature and precipitation at 63 weather stations in Duero Hydrographic Basin. Annual data are first submitted to the maximum entropy method (MEM) and the resulting power found are analysed. These spectra were then stratified according to the spectral peaks and on this basis several climatic regions were defined for the Duero Basin. The MEM spectral estimates of monthly values clearly show the annual and semi‐annual cycle.
Towards a consistent global climatological rawinsonde data‐base
Authors: Parker D. E. , Cox D. I.
Published: February 2007

An archive of monthly temperatures, dew points, geopotentials, and winds at standard tropospheric and stratospheric levels from about 800 rawinsonde stations has been developed from routinely transmitted monthly data, and supplemented with published or national archive data. Many stations' data commence in the 1950s and the archive is continually updated. The raw data, however, contain both random and systematic errors. Quality control of random errors includes hydrostatic, wind‐shear, and climatological checks, and comparisons with neighbouring stations and operational model analyses. Systematic errors in the wind speeds have resulted from the inadequately documented use of knots by some nations and metres per second by others in monthly messages. These errors are being amended by using geopotential height gradients, by comparing wind speeds reported from opposite sides of national borders, by averaging independently coded and transmitted daily data, and by the acquisition of original data from national archives. Other systematic errors result from changes of rawinsonde instrumentation, evolving operationally applied radiation and lag corrections, and changes of ascent times. Accordingly, the archive includes station histories where available, but these are far from complete. If the data are to be used in trustworthy analyses of interannual and longer term climatic variations, adjustments will need to be applied, using fully documented station histories and a knowledge of the effects of instrumental and other changes. Techniques for estimation of systematic adjustments include comparisons between neighbouring stations, comparisons with operational model analyses, the use of extended international radiosonde comparisons, and models of the thermodynamics of radiosonde instruments.
Relationships between 700 hPa height anomalies and 1 April snowpack accumulations in the western USA
Authors: McCabe Gregory J. , Legates David R.
Published: February 2007

Relationships between atmospheric circulation and the temporal and spatial distributions of snowpack accumulations in the western USA are examined. Winter mean 700 hPa height anomalies, representing the average atmospheric circulation during the snow season, are compared with snowpack measurements made on or about 1 April at 311 snowcourse 7stations in the western USA during the winters of 1947–1948 through 1986–1987. Correlation and anomaly pattern analysis are used to identify relations between atmospheric circulation and the temporal and spatial distributions of snowpack accumulations, and to quantify the degree to which the temporal and spatial variability in snowpack accumulations can be attributed to variations in atmospheric circulation.

Results indicate that winter mean 700 hPa height anomalies account for a statistically significant portion of both the temporal and spatial variability in the snowpack accumulations. In general, above‐average snowpack accumulations are associated with negative 700 hPa height anomalies over the eastern North Pacific Ocean and the western USA. These anomalies are indicative of anomalous cyclonic circulation, which produces an anomalous westerly flow of moist air from the eastern North Pacific Ocean into the western USA and increases winter precipitation and snowpack accumulations. Below‐average snowpack accumulations at most of the snowcourse stations are associated with positive 700 hPa height anomalies over the western USA. These positive anomalies indicate anomalous anticyclonic circulation which prevents the intrusion of moist air from the eastern North Pacific Ocean into the western USA, increases subsidence, and decreases winter precipitation. Five winter mean 700 hPa height anomaly patterns also were identified that explain the spatial variability in snowpack accumulations.
Precipitation over Scotland, 1757–1992: Some aspects of temporal variability
Authors: Smith Keith
Published: February 2007

A 236‐year time series (1757–1992) of monthly areal average precipitation for Scotland is produced using the ‘official’ record compiled by the Meteorological Office (UKMO) from 1869 onwards, corrected for known inhomogeneities, and extended back to 1757 using previously unpublished data from the UKMO. The complete series is evaluated and examined for fluctuations and extreme values with particular reference to observed precipitation increases over the last two decades. Recent increases in annual precipitation, and associated seasonal variations, are judged to be unusual despite the recognition of a longer term trend to higher annual and winter values. Correlations of precipitation since 1869 with Lamb weather types show differences within the record and from other work, which suggest that this index does not fully capture the synoptic conditions relevant to precipitation over Scotland as a whole. The series since 1869 was also used to test the predictive value of climatic normals for 3, 5, 10, 15, 20, and 25 years alongside the standard 30‐year averages of precipitation. It is suggested that the best estimate of seasonal and annual precipitation totals for the following year can be achieved by the application of 3‐ and 5‐year normals, rather than by using precipitation averages of longer duration.
Universal spectrum for interannual variability in COADS global air and sea‐surface temperatures
Authors: Selvam A. Mary , Joshi R. R.
Published: February 2007

Continuous periodogram spectral analyses of 28 years (1961–1988) of seasonal (September‐November) mean COADS global surface (air and sea) temperature time‐series show that the power spectra follow the universal inverse power law form of the statistical normal distribution. An inverse power law form for power spectra of temporal fluctuations implies long‐range temporal correlation and is a signature of self‐organized criticality. Universal quantification for self‐organized criticality presented in this paper is consistent with a recently developed cell dynamical system model for atmospheric flows, which predicts such non‐local connections as intrinsic to quantum‐like mechanics governing flow dynamics. The universal spectrum for interannual variabiality rules out linear secular trends in global surface (air and sea) temperatures.
Relations between winter precipitation and atmospheric circulation simulated by the geophysical fluid dynamics laboratory general circulation model
Authors: McCabe Gregory J. , Dettinger Michael D.
Published: February 2007

General circulation model (GCM) simulations of atmospheric circulation are more reliable than GCM simulations of temperature and precipitation. Thus, some researchers are developing empirical relations between observed atmospheric circulation and observed temperature and precipitation to translate GCM estimates of future atmospheric circulation into estimates of future regional temperature and precipitation. Developing climate‐change scenarios in this manner assumes, at least, that relationships between atmospheric circulation and surface climate variables, such as temperature and precipitation, are properly simulated by GCMs.

In this study, temporal correlations between 700 hPa height anomalies (700 hPa anomalies) over North America simulated by the Geophysical Fluid Dynamics Laboratory (GFDL) GCM and GFDL‐GCM‐simulated (GFDL‐simulated) winter precipitation at eight locations in the conterminous United States are compared with corresponding correlations in observations. The objectives are to (i) characterize the relations between atmospheric circulation and winter precipitation simulated by the GFDL GCM for selected locations in the conterminous USA, (ii) determine whether these relations are similar to those found in observations of the actual climate system, and (iii) determine if GFDL‐simulated precipitation is forced by the same circulation patterns as in the real atmosphere.

Results indicate that the GFDL GCM simulates relations between 700 hPa anomalies and local winter precipitation that are similar to relations found in observed data for most of the locations analysed in this study. Results also indicate that at regional scales GFDL GCM simulations of the relations between 700 hPa anomalies and winter precipitation are most similar to observed relations for locations near oceanic sources of atmospheric moisture. These results suggest that the GFDL GCM may not adequately simulate variations in advection of atmospheric moisture into the interior parts of the USA and/or that this moisture is not adequately converted into precipitation in the interior parts of the country. This problem may be due, in part, to (i) the inadequate representation of topography in the GFDL GCM, (ii) stronger‐than‐observed mean winter zonal winds simulated by the GFDL GCM and the consequent more west‐to‐east paths of air flow and storm systems across North America, (iii) the relative weakness of important synoptic patterns in GFDL simulations, such as the Pacific North American circulation pattern, and (iv) the occurrence of ‘spectral rain’.

In addition, for some locations, the GFDL‐simulated relationships between precipitation and 700 hPa anomalies can be quite different from observed relations. The differing relationships suggest that GFDL‐simulated changes in regional precipitation in response to changes in atmospheric circulation could differ from changes that would occur in the actual climate system.
Seasonal phase lag between rainfall and vegetation activity in tropical Africa as revealed by NOAA satellite data
Authors: Shinoda Masato
Published: February 2007

A seasonal phase lag in the response of vegetation to rainfall and its dependence on the type of vegetation in tropical Africa have been investigated, using weekly‐basis data of the NOAA/AVHRR‐derived NDVI (normalized difference vegetation index) and OLR (outgoing longwave radiation) for April 1985 to September 1987.

The lag‐correlation analysis of the NDVI and OLR data demonstrates that the seasonal phase lag, by which the NDVI responds most markedly to the OLR, tends to increase from the Equator to the pole in the Northern and Southern Hemispheres. The lag ranges from 1–3 weeks in the equatorial rain forest to about 2–6 weeks in the wet savanna and about 6–9 weeks in the dry savanna.

The strongest negative lag‐correlation coefficients at the above lags are characterized by a spatial pattern which has a maximum absolute value near the latitudes 7.5°–10° in the savanna areas of both hemispheres. The equatorial rain forest, especially its north‐eastern part, shows the weakest correlation. The results suggest that the response of vegetation to rainfall is more pronounced and has a longer lag in the savanna than in the equatorial rain forest. A regional analysis of the NDVI‐rainfall relationship for Cameroon confirms the above NDVI‐OLR lag‐correlation on the continental scale.
Variability of the summer monsoon rainfall over Thailand—comparison with features over India
Authors: Kripalani R. H. , Singh S. V. , Panchawagh Nalini , Brikshavana M.
Published: February 2007

In this study, 20 years (1961–1980) of rainfall data for 34 stations over Thailand are used to investigate and understand the intraseasonal and interannual variability of the summer monsoon. Dominant structures of 5‐day and seasonal rainfall are determined through empirical orthogonal functions (EOFs). Monthly and seasonal spatial patterns and a map showing the coefficient of variation are also presented.

On an intraseasonal time‐scale regions with high 30‐60‐day variances (Madden Julian oscillations—MJOs) and 10‐20‐day variances (Quasi‐biweekly oscillations—QBWOs) are identified using a band‐pass Butterworth filter for 5‐day rainfall. It is seen that the MJOs are dominant over the Indian region and the QBWOs are dominant over the Thailand region. Extended EOFs (EEOFs) have shown that the most important evolutionary feature over India is the northward propagation associated with the MJOs, whereas over the Thailand region it is westward, associated with the QBWOs. Northward propagation of rainfall anomalies is not observed over the Thailand region.

On the interannual scale the area over north‐west Thailand is related well with rainfall variation over west‐central India. The Darwin pressure tendency (DPT) and the subtropical ridge over India shows significant relation with rainfall over northwest Thailand. However, the Northern Hemisphere surface temperature (NHST), Quasi‐biennial Oscillation (QBO), and West Pacific ridge (WPR) show no significant relation.
The impact of surface circulation on significant daily rainfall patterns over Mallorca
Authors: Sumner Graham , Guijarro José A. , Ramis Clemente
Published: February 2007

This study is a preliminary attempt to associate the distribution of significant rainfalls over the island of Mallorca with recognized dominant surface circulation types. Based on the extraction of five prominent PCs from a principal components analysis using a T‐mode (time) correlation matrix, six dominant daily rainfall spatial patterns have been isolated using cluster analysis for significant rainfall days (area mean ⩾ 5–0 mm) for the island of Mallorca in the western Mediterranean. These six ‘pattern groups’, and a number of important subgroups, are linked closely to the prevailing near‐surface circulation. Seven dominant circulation types have been identified, which are closely, although not perfectly, associated with rainfall distribution, so that a conceptual spatial rainfall model for the island seems possible. Such a model would be most useful if used in conjunction with NWP forecasts of probable rainfall amount issued for the area, and would provide valuable local information on likely heavy rainfall occurrence.
On the severe drought of 1993 in north‐east Brazil
Authors: Rao V. Brahmananda , Hada Kioshi , Herdies Dirceu L.
Published: February 2007

During the period 1990 through to 1993 a dry spell occurred over north‐east Brazil. The drought of 1993 was very severe. Rainfall series for north‐east Brazil are updated to 1993 and the drought conditions during 1993 are discussed. The 1993 drought seems to be connected at least partially to the unusual ENSO conditions during that year.
Prediction of the dry and wet spell of the Australian monsoon
Authors: Krishnamurti T. N. , Han Sang‐Ok , Misra Vasubandhu
Published: February 2007

This study is a sequel to two recent studies on the monsoonal dry and wet spells. The previous studies addressed the dry and wet spells of the monsoon over India and China on the intraseasonal time‐scales. The present study is intended to provide an outlook for the occurrence of dry and wet spells in reference to the Australian monsoon, within roughly a 1 ‐month period from the time of start of the forecast with a global model. In the global model, the definition of a time mean state and an intraseasonal component are retained. The high‐frequency component is viewed as one where inclusion in the initial state can contribute to a degradation of month long forecasts and hence is excluded initially. Sea‐surface temperature anomalies on intraseasonal time‐scales are included in this analysis. The prediction of the wet spells of the monsoon is assessed from the superposition of the predicted intraseasonal cyclonic circulation anomaly on top of the climatological cyclonic anomaly. The dry spell is assessed from an inverse superposition. We consider here a specific period, i.e. March 1992. The early part of this month was characterized by a wet spell over Northern Australia. A dry spell prevailed during the middle of this month and was followed by a wet spell during the latter part of the month. The prediction experiments with a prescribed and a modelled sea‐surface temperature anomaly successfully demonstrated the passage of the intraseasonal anomaly, with the superposition of the geometries of the intraseasonal and the climatic components favouring the wet and the dry spell during different periods of the month.
June‐september rainfall in north‐eastern Africa and atmospheric signals over the tropics: A zonal perspective
Authors: Camberlin Pierre
Published: February 2007

The connection between rainfall in northeast Africa (Djibouti, Eritrea, Ethiopia, Kenya, Somalia, Sudan, and Uganda) and various atmospheric indicators from the tropics have been investigated for the northern summer season. Variables used include zonal wind at 700 hPa and 200 hPa, sea‐level pressure, and rainfall over other tropical areas, for the period 1951–1988.

Strong significant correlations are shown with the Southern Oscillation and the components of the Walker cell in the Pacific Ocean. Droughts in the Ethiopia‐Uganda area are associated with El Niño events and, moreover, with above normal pressure and droughts over India. Other significant relationships exist with the African monsoon. Westerly (easterly) anomalies in the lower (upper) levels are associated with abundant summer rainfall years in north‐east Africa.

These results are all consistent with the previously defined Walker‐type circulations over the tropics, particularly as far as the Indo‐Pacific and African cells are concerned. Although the Southern Oscillation has a dominant impact in this respect, the specific coherence of the African cell is further evidenced. Preliminary findings suggest that the summer rainfall areas of East Africa could qualify as a location for the rising branch of this cell.
A study of sea and land breezes in an archipelago on the west coast of Sweden
Authors: Gustavsson T. , Lindqvist S. , Borne K. , Bogren J.
Published: February 2007

This paper reports analyses of recordings made on three tower masts in order to study the dynamics of sea and land breezes as well as the development of these systems in an archipelago along the west coast of Sweden. Intensive studies have focused on the duration and strength of sea and land breezes and the development of small‐scale systems controlled by the irregular coastline in the study area. The internal dynamics of the land breeze and the occurrence of temperature variations in the coastal area are discussed as well as the interrelationship between these factors.

The studies show that the sea and land breezes are well developed when the synoptic‐scale pressure gradient is relatively weak. However, a division into smaller systems has been observed, i.e. small islands outside the coastline develop their own wind systems. In the archipelago, a primary sea breeze with no interaction with the main coastline develops during the first hours after sunrise. The primary sea breeze continues to act until a stronger sea breeze, developed in interaction with the main coastline, begins to blow. This phenomenon was not observed for the land breeze. Here, no general land breeze develops, instead a breeze was recorded which always blew towards the coastline.
Long‐term variability of sea—air heat transfer in the North Atlantic ocean
Authors: Gulev Sergey K.
Published: February 2007

There is evidence that climatological variations of the ocean‐atmosphere fluxes in the North Atlantic are significant with respect to long‐term climate changes. To study year‐to‐year changes of ocean‐atmosphere interaction processes in the North Atlantic Ocean, two meteorological data sets were used: the Comprehensive Ocean‐Atmosphere Data Set (COADS) and the Soviet National Meteorological Centre (SNMC) data set for the period from 1957 to 1990. Data sets were compared with each other in order to find out set‐to‐set variations of ocean‐atmosphere interaction parameters. The next step was to calculate sea‐air interaction characteristics on the basis of one data set, but with the use of different schemes for the parameterization fluxes. Both set‐to‐set and scheme‐to‐scheme variations are significant, but at the same time annual and interannual changes in radiation and heat fluxes indicate that variability patterns are close to each other. Differences obtained in the parameters of variability were taken to determine the confidence level for future consideration of climatological variability. Long‐term changes in net air‐sea heat fluxes were explored for the period from 1950 to 1990. Results demonstrate the different character of variations in the tropics, mid‐latitudes and high latitudes. Meridional heat transport for different climatological periods has been calculated in order to discuss the variations obtained in terms of ocean circulation. Two significantly different regimes of meridional heat transport were obtained. The first regime is characterized by high values in the tropics and a sharp decrease in mid‐latitudes. The second regime is connected with relatively high values of heat transport in mid‐latitudes.
A study of air and road‐surface temperature variations during clear windy nights
Authors: Gustavsson Torbjörn
Published: February 2007

In this paper, temperature recordings from mobile measurement and field stations in the Swedish Road Weather Information System were analysed to determine the variation in temperatures during clear nights with varying mean night‐time wind speeds. It was found that the differences in air temperatures could amount to as much as 10°C owing to local variations in wind shelter. The largest variations occur during nights with a mean wind speed of 1 to 1·5 m s−1, as this wind is strong enough to prevent stabilization of the surface‐cooled air at wind‐exposed locations, whereas such a stabilization can occur at wind‐sheltered locations.

There is normally a close relation between areas with low air and road‐surface temperatures. However, the effect of the air temperature variations on the road surface temperature is found to be reduced as a result of the obstruction of the longwave cooling caused by the wind shelters. The cooling rate especially has been found to differ between stations with varying sky view factors. The paper further includes a discussion of the factors that must be taken into account for the calculation and forecasting of air and road‐surface temperatures in areas where wind shelters have a pronounced effect on temperature variations.
Global distribution of surface shortwave fluxes derived from satellite data for the world climate research programme
Authors: Dipasquale R. C. , Whitlock C. H.
Published: February 2007

The World Climate Research Programme has established the Surface Radiation Budget Climatology Project with the ultimate goal of providing, for the scientific community, a long‐term (10 years) data set of the global surface radiation budget. This report describes the first global product produced and archived as part of that effort. It reviews product content and accuracy, and highlights sample data from several regions around the globe. Interested users can obtain global data sets, at no cost, from the Langley Distributed Active Archive Center.
Classification of tropical rainfall stations: A comparison of clustering techniques
Authors: Jackson I. J. , Weinand H.
Published: February 2007

Following an earlier paper, which classified tropical rainfall stations using 34 variables and a single clustering approach, this paper compares the results with those utilizing three other methods. A variety of measures were used to assess ‘performance’ of the methods. Three of the methods (Ward, Average Linkage, and Lance‐Williams) produced very similar results, and even the other one (Centroid) showed a reasonably similar pattern. The similarity in results from the different methods suggests that the station groups obtained are meaningful. However, minor differences are worthy of consideration when climatological interpretation is undertaken at a later stage of the project.
Interannual variability of deep convection over the tropical South American sector as deduced from ISCCP C2 data
Authors: Marengo José A.
Published: February 2007

The interannual variability of deep convection over the South American sector and regional hydrometeorological anomalies are studied using International Satellite Cloud Climatology Project (ISCCP) data for 1984–1988. Satellite‐derived convection anomalies are compared with regional rainfall and river runoff anomalies.

At the height of the austral summer, the deep convective clouds (DCC) and ISCCP depict the centres of intense convection over central Amazonia and the mouth of the River Amazon, as well as the enhanced convection over north‐east Brazil, which is related to the Atlantic Intertropical Convergence Zone (ITCZ). Positive/negative regional hydrometeorological anomalies are consistent with positive/negative anomalies in the deep convection over northern Amazonia, the mouth of the River Amazon and north north‐east Brazil, whereas this is not always true over southern Amazonia and southern Brazil. Over north‐east Brazil and the mouth of the River Amazon, abundant rainfall and large DCC are both in agreement with variations in the latitudinal position and intensity of the Atlantic ITCZ, which extends between 4°N and 5°S along the Atlantic coast, where the precipitation maximum is found. The related rainfall anomalies over Amazonia and north‐east Brazil during years with anomalously warm or cool surface waters in the central equatorial Pacific (e.g. the El Niño event in 1987), are consistent with the convection anomalies as depicted by the ISCCP deep convective clouds. For the Amazon Basin and north‐east Brazil, DCC based on 2.5°×2.5° horizontal resolution explained about 50 per cent of the variance of rainfall at individual surface stations.

A new finding is the enhanced convective activity located at the east side of the central Andes and over central Amazonia around 5°S, with a region of reduced convection in between. These two subcentres are oriented west‐east and are part of the summertime semi‐permanent centre of convection over the Amazon Basin, and have not been identified previously from the analysis of outgoing longwave radiation (OLR) or highly reflective clouds. These subcentres of large DCC exhibit interannual variations in intensity and location, where the centre located near the east flank of the Andes shows a wider range of latitudinal variations than that located over central Amazonia. South of this area convection and rainfall decreases rapidly.
Simulation of rain events from rain‐gauge measurements
Authors: Cosgrove Claire M. , Garstang Michael
Published: February 2007

Point rainfall as measured by a rain‐gauge is examined in terms of a space and time dependent rain event. The rain event is determined such that the total number of rain events in any one year account for at least 80 per cent of the annual area rainfall. The remaining fraction of annual rainfall is considered to be rainfall due to isolated unorganized rain systems. A 1‐year record from 19 digital rain‐gauge recorders over a 600 km2 area in the vicinity of the Kennedy Space Flight Center is used. Each tipping bucket rain‐gauge has a resolution of 1 minute 0.25 mm.

Rain rates, duration, areas and frequency of occurrence are presented for nearly 200 rain events identified in a single year. Strong seasonal signals are seen particularly in extreme rain events, which produce more than 90 mm of rain per event, account for 60 per cent of the total network rainfall but occur less than 22 per cent of the time. A simulation of the detection of the extreme rainfall events by a remote sensing system such as TRMM suggests that the satellite will see only 10 per cent of the rainfall due to extreme rain events. The results illustrate the difficulties of sampling convective rainfall, especially over a continental tropical area such as Florida, by an orbiting platform.
The energy balance of snow and partially snow covered areas in western Greenland
Authors: Harding R. J. , Johnson R. C. , Soegaard H.
Published: February 2007

Surface meteorology and flux data are presented from five sites in a transect crossing a 100‐km‐wide coastal region of west Greenland. The sites cover a variety of Arctic types: snow covered, bog and arid. The measurements show a comparatively small variation of the driving variables: solar radiation, wind and humidity, but a large variation in the net radiation and surface fluxes. The net radiation is much reduced in the snow covered areas because of the high albedo, ameliorated to some extent by a reduced longwave emission. The turbulent fluxes are also small over the snow covered areas, an effect of the smooth surface and low surface temperature. The sensible heat flux at these sites is downward. The evaporation fluxes in the snow‐free areas are strongly affected by the availability of soil‐water, thus in the arid, eastern site the evaporation is small. Simple flux‐gradient equations appear to be able to describe the surface fluxes adequately, especially considering the comparatively large error in these types of data. The relevance of these data to the parameterization of Arctic surfaces in global models is discussed.
Hierarchical clustering of atmospheric soundings
Authors: Živkovíć Marina
Published: February 2007

This is a procedural paper that compares six commonly used hierarchical clustering techniques applied to atmospheric soundings. The following techniques are compared: single‐, complete‐, and two average‐linkage techniques, the Ward's technique, and one centroid type technique. Vertical profiling of the atmosphere is based on common soundings sampled on synoptic scales over the Northern Hemisphere. At each analysis point, the atmospheric profile is represented by an ‘atmospheric state vector’ consisting of surface pressure, total column (precipitable) water, and temperature, wind and relative humidity values at 12 discrete vertical levels.

An evaluation of the techniques is performed by comparing the mean state vectors of final clusters. Four techniques produce comparable results, with the largest differences between the techniques appearing for the surface pressure component of the cluster state vector. Also, large differences are found in the temperature and wind vector components at the 850 hPa pressure level, and the smallest differences are found for the relative humidity components. The results support findings of studies on airmass typing on local or regional scales: the average‐linkage method based on group average provides the most distinct and homogeneous clusters.
Harmonic analysis of the seasonal cycle in temperature over the Biokovo area (Croatia)
Authors: Cvitan Lidija
Published: February 2007

Harmonic analysis has been used to investigate the seasonal cycle in thermal regime at five locations over the Mount Biokovo region (Croatia): Makarska, Opuzen, Šestanovac, Imotski, and Vrgorac. The monthly averages of temperature as well as monthly means of minimum and maximum temperatures from 1961 to 1980 have been subjected to analysis. Decomposition of the harmonic analysis of temperature into three temperature types enabled, besides the conventional physical explanations of the annual harmonic oscillations, explanation in terms of shorter period harmonic oscillations. These results should be particularly important for botanical investigations.
Delineation of Uganda into climatological rainfall zones using the method of principal component analysis
Authors: Basalirwa C. P. K.
Published: February 2007

This paper attempts to delineate Uganda into climatological rainfall zones using the method of principal component analysis (PCA). Monthly rainfall records from 102 Uganda rain‐gauge stations for the years 1940–1975 inclusive are used in the study. The rotated dominant PCA modes were used to delineate the temporal rainfall characteristics into homogeneous spatial regions. Statistical and other methods were then used to determine the physical reality of the spatial patterns of the delineated zones of the rainfall network in describing the climatological rainfall patterns of Uganda.

The PCA varimax rotated solutions showed that for the climatological data a maximum of four PCA modes, accounting for about 65 per cent of annual rainfall variance, were significant. However, a maximum of 16 PCA modes, accounting for over 81 per cent of the rainfall variance were obtained with the seasonal/monthly records. The PCA regional patterns delineated Uganda into 14 homogeneous climatological zones, which were also indicated by the spatial patterns of the physical features of Uganda and other tests. The derived rainfall zones would be useful in the planning and management of rainfall dependent activities in the country.
Surface temperature trends and variations in New Zealand and the surrounding ocean, 1871–1993
Authors: Folland Chris K. , Salinger M. Jim
Published: February 2007

We compare homogenized series of maximum, minimum, and mean air temperature averaged over New Zealand, measured between 1871 and 1993, with rigorously quality controlled marine temperature data measured over the surrounding ocean surface. The marine data are those of sea‐surface temperature (SST) and air temperature measured at night (NMAT) on board ship, both corrected for time‐varying instrumental biases. There is mostly very good agreement between the variations in the three data sets on time‐scales down to a season. Some disagreements are related to short periods of sparsely observed marine data, particularly during the World Wars. Differences also exist between trends in the maximum and minimum New Zealand temperatures (NZT), particularly in winter. In addition, interannual variations in winter NZT tend not to track those of nearby marine temperatures quite as well as happens in other seasons.

Although it is not the main purpose of the paper to discuss the causes of NZT change, New Zealand temperature is known to be influenced by the El Niño‐Southern Oscillation (ENSO) phenomena. Tropical East Pacific SST variations are strongly related to ENSO and so are well correlated with NZT on time‐scales of a few years to near a decade. We discuss these relationships, and also associations with Southern Hemisphere SST.

We conclude that annual NZT and NMAT over the nearby ocean surface have both warmed by about 0.7°C since the beginning of the century, with a slightly smaller increase in SST. This confirms previous work on the magnitude of the warming of New Zealand climate this century. Warming in NMAT and NZT in each season varies in a similar way, with consistently slightly smaller increases in SST. We also conclude that the UK Meteorological Office seasonal historical marine temperature data set appears to be generally of very good quality in the New Zealand region.
A series of global radiation at Wageningen for 1928–1992
Authors: De Bruin H. A. R. , van den Hurk B. J. J. M. , Welgraven D.
Published: February 2007

A series of daily total incoming radiation measured at Wageningen, The Netherlands, for the period 1928–1992 is described. These data are presented as relative global radiation (Kr), which is defined as the global radiation divided by the corresponding extraterrestrial value. Both the year‐to‐year variation and the mean annual cycles of Kr averaged over a year, season, month, decade (10 days), and a day are considered. Also, frequency distributions are evaluated. It is found that the maximum of Kr does not occur in June, when the solar elevation is highest, but in May. This is due partly to the west European monsoon, causing a decline of Kr in the last decade of June and second decade of July. Also, it is found that ‘sunny’ weather (Kr relatively large) appears to be significantly persistent in May especially. The persistence of ‘cloudy weather’ (Kr relatively small) is less pronounced.
Studies on the monthly variation of the static stability parameter using harmonic analysis
Authors: Kumar P. Pradeep , Salvekar P. S.
Published: February 2007

Using the monthly mean values of temperature for different pressure levels from 1000 to 1 hPa at every 5° latitude the static stability parameter has been determined. The technique of harmonic analysis has then been used to study the seasonal variation of global temperature and the static stability parameter.
Variability of summer rainfall over Madagascar: Climatic determinants at interannual scales
Authors: Jury Mark R. , Parker B. A. , Raholijao Niri , Nassor Abdallah
Published: February 2007

Variability of convective rainfall in the austral summer season over central Madagascar is studied using an area‐rainfall index, local radiosonde data, and gridded information on outgoing longwave radiation (OLR), sea‐surface temperature, and tropospheric winds. Seasonal rainfall patterns are influenced by topography, monsoon and trade wind circulations, and tropical cyclone events. The Inter Tropical Convergence Zone overlies the north‐west coast, where summer rainfall averages 47 cm month−1. Climatic conditions that affect convective rainfall at interannual time‐scales are studied through spatial lag correlation analysis. Sea‐surface temperature is weakly correlated with rainfall departures, with positive values in the central Indian Ocean reaching +0.41 at lags −4 and 0 months. Strongest positive correlations (+0.45) gradually shift to the central South Atlantic Ocean at lag 0 and +2 months. Wind correlations imply that increased upper level tropical easterly flow overlying enhanced low‐level north‐west monsoon flow favours above normal rainfall. Regional teleconnection patterns identified by rainfall‐OLR correlations are remarkably similar to those for Quasi‐biennial oscillation (QBO)‐OLR correlations, suggesting that up to one‐third of the interannual convective variance can be explained by the phase of the QBO.
Onshore flow in an urban area: Microclimatic effects
Authors: Tuller Stanton E.
Published: February 2007

Afternoon field observations contrasting waterfront and inland environmental conditions during summer, onshore flows from a cool water surface were conducted in residential areas of Victoria, British Columbia, Canada. The waterfront, under the direct influence of the onshore flow, had lower air temperature, vapour pressure, sky and ground radiant temperatures and a higher wind speed than did inland sites. Areas under the influence of the onshore flow would have a cooler environment for people and plants, lower interior building temperatures, and less evaporation demand.