bluuebunny/crossref_metadata_2025 huggingface dataset:
Cold windchill spells in the south Balkans: A study of the synoptic situations
Authors: Giles B. D. , Balafoutis C. J.
Published: February 2007

Using hourly data of temperature and wind speed for Thessaloniki over the period October 1959 to April 1978, values of windchill in excess of 1000 Kcal m−2 h−1 were abstracted. Windchill days and windchill spells are defined and 67 of the latter noted, all occurring in winter between November and March. Within these spells, windchill episodes were identified from an hour by hour analysis of the data and 22 discontinuous episodes were excluded from further consideration. The surface and 500‐hPa charts for the remaining 45 episodes were used to note the main synoptic features over Europe and the Mediterranean. None of the standard synoptic classifications were found to be suitable for this purpose but a basic patterns did emerge. We identified six surface and seven 500‐hPa patterns and these are discussed in association with the windchill episodes.
Connections between air temperature and precipitation and the geopotential height of the 500 hPa level in A meridional cross‐section in Europe
Authors: Kożuchowski K. , Wibig J. , Maheras P.
Published: February 2007

The correlation coefficients between air temperature, precipitation, and geopotential heights of the 500 hPa level for six stations in Europe, located along the 20°E meridian from Scandinavia to Greece, for the period of 1951–1985 are calculated. The fields of correlation coefficients for each station and season are described. It is observed that the correlation coefficients of temperatures are, as a rule, significantly greater than for precipitation. How meridional and zonal circulation determine temperatures and precipitation has been examined.
Long‐range prediction of the onset and end of the rainy season in the West African Sahel
Authors: Omotosho J. 'Bayo
Published: February 2007

Using upper‐wind data for three stations across the West African Sahel, simple empirical schemes for predicting the onset and cessation of the rainy season for more than 2 months ahead are presented. Agriculturally reliable rainfall commences about 70 days after the first sudden changes in wind direction from westerly to easterly at the 400 hPa level and above. These sudden changes signal the withdrawal of the subtropical (westerly) jet, thus leading to the establishment of the African easterly jet at the 700 hPa level. Cessation of rainfall occurs about 80 days after the destruction, at the peak of the rainy season, of the mid‐tropospheric (700–400 hPa) vertical wind shear. A method for estimating the length of the rainy or growing season also is proposed.
Heat balance characteristics during fine periods on the lower parts of the Franz Josef Glacier, South Westland, New Zealand
Authors: Ishikawa N. , Owens I. F. , Sturman A. P.
Published: February 2007

Heat balance observations were carried out during fine conditions at a site on the lower Franz Josef Glacier in June 1988 and February 1990 and compared with results obtained in August, October, and December 1981. Surface ice melt occurred during all seasons, with the mean melt rate in summer about eight times larger than in winter. The seasonal variation of the various contributions to ice melt was also identified. Sensible heat flux was the dominant heat source, contributing 80 per cent and 55 per cent of the total energy gain in winter and summer, respectively. Latent heat transfer contributed similar amounts in winter (20 per cent) and summer (25 per cent). Net radiation was a heat sink in winter (—13 per cent) and was similar to latent heat transfer in summer at 21 per cent. A newly developed simple method for estimating ice melt using only air temperature is presented and helps to explain the seasonal variations of ice melt.
Consequences of winter tropical pressure anomalies in the Australian region
Authors: Simmonds Ian , Rocha Alfredo , Walland David
Published: February 2007

We have performed three general circulation model (GCM) experiments with a view to isolating the direct thermal effects of imposed sea‐surface temperature (SST) anomaly patterns to the north of Australia from the dynamic effects associated with the circulation changes they induce. We have done this by a novel technique of adding bias terms to the pressure‐tendency equation but leaving all other aspects of the model unchanged. The nature of the three pressure ‘nudging’ terms were designed so that in long model runs the simulated sea‐level reductions would be similar to those induced in the SST anomaly experiments performed previously. Hence, we have forced low‐level circulation anomalies without imposing any direct surface thermal forcing. The results are compared with standard runs performed with SST forcing.

The changes in evaporation in the Australian region were rather different in the comparable pressure‐forcing and SST‐forced experiments. However, most of the parameters considered here responded to the surface‐pressure forcing in a very similar way to that due to ocean‐temperature forcing considered in our earlier study. This was true, in particular, for winter precipitation over Australia. The results suggest that, at least in the Australian tropics, the apparently large impacts of SST anomalies are associated fundamentally with the anomalous circulations they set up rather than the direct impact of the heated ocean waters themselves. We find, as have others, that precipitation anomalies are associated closely with changes of the low‐level convergence of moisture. Indeed, an intriguing finding from our present study is that anomalies of evaporation and precipitation assume opposite signs over most of the domain.

Analyses with the comprehensive ocean‐atmosphere data set (COADS) imply that there is some persistence of winter tropical sea‐level pressure in the Australian region, independent of the local endurance of SST. Such persistence may provide some independent skill for Australian winter climate outlooks.
Temporal and spatial characteristics of coastal rainfall anomalies in Papua New Guinea and their relationship to the Southern Oscillation
Authors: McGregor Glenn R.
Published: February 2007

Thirty‐year rainfall records for seven coastal locations in Papua New Guinea were analysed to assess the spatial and temporal characteristics of rainfall anomalies and the general response of coastal rainfall to the Southern Oscillation (SO). Spatial and temporal variability of rainfall anomalies are a distinct feature of the coastal locations analysed. Despite the spatial variability of rainfall anomaly behaviour, an all Papua New Guinea rainfall anomaly index shows significant concurrent and lag inverse associations with the Southern Oscillation Index of Wright. Anomalously high (low) pressure in the Papua New Guinea region leads to low (high) rainfall in the concurrent and ensuing season. Rainfall anomaly periodicities of 7–8 years lie within the time‐scale of 2–10 years for ENSO events, but individual locations demonstrate a variable response to ENSO events. Study results fill an important geographical gap in the understanding of the spatial and temporal characteristics of rainfall variability in the western tropical Pacific.
Summertime along‐valley wind variations in the wright valley Antarctica
Authors: McKendry Ian G. , Lewthwaite Errol W. D.
Published: February 2007

Observations from several sites are utilized to investigate spatial and temporal variations in the local wind regime. The average condition consists of a tongue of easterly up‐valley winds extending the length of the valley. About 23 per cent of the time this tongue is pushed down‐valley beyond the western edge of Lake Vanda by westerly downslope winds. These winds seldom penetrate to the mouth of the valley and instead, a ‘front’ is formed between the up‐valley and down‐valley flows. Migration of the front appears to be related to synoptic controls rather than local thermal forcing. Support is provided for the view that the westerlies are episodic downslope winds associated with the deflection of strong upper level flow into the valley system. Superimposed on this broad pattern are diurnal variations in the strength of valley winds associated with changing stability.
Spatial variations and trends in the Indian monsoon rainfall
Authors: Subbaramayya I. , Naidu C. V.
Published: February 2007

The spatial and temporal variations of the monsoon rainfall over India have been studied using the subdivisional rainfall data for the years 1871–1988. North‐west India and north peninsular India are found to constitute two homogeneous regions. North‐east India does not constitute a single homogeneous region since the rainfall variations in Bihar and Bengal are somewhat different from those in Assam and the Sub‐Himalayan region.

Trends in the monsoon rainfall in different subdivisions and in the whole of India also have been examined. In the monsoon rainfall, decreasing trends during late nineteenth century and again in the 1960s are observed. The latter trend was reversed in the early 1970s. These trends are seen prominently in central and western Indian subdivisions, however, there are major differences in the epochs of changes in the trends in different subdivisions. The decreasing trend observed in the 1960s is still continuing in the central north Indian divisions, while in the adjoining divisions, the reversal took place in the early 1970s.
An observed poleward shift of the southern hemisphere subtropical wind maximum—a greenhouse symptom?
Authors: Gibson Timothy T.
Published: February 2007

A 16–year (1976–1991) record of mean winter values of the zonally averaged latitude of the subtropical wind maximum (STWM) in the Southern Hemisphere is examined, and reveals a significant trend towards higher latitudes. This poleward shift of the STWM, which has a magnitude of 0.18° of latitude per year, is in agreement with the expected consequences of an enhanced greenhouse effect (EGE), and may indeed be regarded as a rather sensitive indicator of the reality of climatic impacts of the EGE, as it is a result of changes in temperaturegradients, rather than general increases in temperature.
Daily meso‐scale rainfall in the tropical wet/dry climate of the Townsville area, north‐east Queensland during the 1988–1989 wet season: Synoptic‐scale airflow considerations
Authors: Lyons W. F. , Bonell M.
Published: February 2007

Daily rainfall during the 1988–1989 summer wet season, occurring at a dense meso‐scale network of 133 rain‐gauge sites in the Townsville region (3450 km2) of tropical north‐east Queensland, is analysed to yield indices of rainfall activity for 13 distinct synoptic circulations. Composite correlation field maps for the three most common synoptic circulations are also presented. The influence of topography and exposure to moisture sources emerges as the major control of rainfall distribution and amount, such that meso‐scale rainfall activity relates to synoptic‐scale wind vectors, which provide the steering of rainfall‐producing systems. In addition, the interaction between local winds, topography, and synoptic circulation is demonstrated, through the use of case studies, to be important for generating localized uplift and precipitation. This rainfall is then steered by the prevailing upper synoptic flow. Previous studies of rainfall in the tropics have not emphasized the importance of the interaction between local controls and the synoptic circulation for providing distinct meso‐scale rainfall patterns, and have rarely used a dense network of rain‐gauges.
Specification and prediction of monthly and seasonal precipitation amounts in California and Arizona river drainage basins
Authors: Klein William H. , Bloom Hal J.
Published: February 2007

A forward selection procedure of stepwise regression is applied to 30 years of data to develop a set of multiple regression equations for percentiles of monthly and seasonal precipitation amounts (P) in high altitude river basins of California and Arizona during periods of 1–4 months in duration. Two main methods are used. The first is specification of P from simultaneous values of the field of 700 hPa mean height anomalies (H). The second is pure prediction, which uses only previous (observed) data as potential predictors. On average, 61 per cent of the monthly P variance is explained by specification equations containing about three concurrent values of H; seasonal specification equations explain about 2 per cent more of the variance by means of slightly fewer heights. In contrast, only 16 per cent of the prediction equations are significant at the 95 per cent level determined by a Monte Carlo test. All these equations select the local value of P observed during the month prior to the target period as the most important predictor.
Supplementing solar radiation network data by co‐Kriging with satellite images
Authors: D'Agostino V. , Zelenka A.
Published: February 2007

Observations made in 1982 from the Swiss meteorological network are used to assess the precision of geostatistically predicted daily global horizontal insolation. Results of such predictions are compared with insolation estimates obtained from the imagery of the meteorological satellite METEOSAT.

Application of Kriging to the network data yields cross‐validation results that are very close to the validation results of the satellite estimates, namely unbiased prediction with about 3 MJ m−2 root mean square error (RMSE) on a daily total measured mean (MM) of 18.9 MJ m−2. Co‐Kriging applied to both data sets helps to reduce the RMSE to about 2.5 MJ m−2. As the application occurs under simplifying assumptions to allow use of a PC, and that there is, therefore, much room for improvements, we conclude that co‐Kriging appears promising for detailed global insolation mapping.
Variations of sea‐surface temperatures off north‐eastern Australia and associations with rainfall in Queensland: 1956–1987
Authors: Lough J. M.
Published: February 2007

Spatial, seasonal, and interannual variations of sea‐surface temperatures (SSTs) in the area 0.30°S, 130–180°E are examined for the period of 1956–1987. Sea‐surface temperatures in this region are high throughout the year with an annual range of only 0.5°C close to the Equator, increasing to 5.0°C, south of 24°S. Interannual variability of SSTs is highest and year‐to year persistence of anomalies is lowest in October‐November. Interannual variability is lowest and year‐to‐year persistence is highest in April‐May. Sea‐surface temperature anomalies developed in June‐July are more likely to persist through subsequent seasons than SST anomalies developed in December‐January. Interannual variations of SSTs are related more closely to Queensland rainfall variations in the winter season than in the summer season. In the summer season, SST‐rainfall linkages are dominated by co‐variations of these two variables with the Southern Oscillation. In the winter season, significant associations between SSTs and rainfall are present in the absence of large variations of the Southern Oscillation.
Numerical simulation of cut‐off lows on the Australian east coast: Sensitivity to sea‐surface temperature
Authors: McInnes Kathleen L. , Leslie Lance M. , McBride John L.
Published: February 2007

The occurrence and synoptic‐scale structure of cut‐off lows near the Australian east coast are documented. These systems are associated with severe weather in the south‐east Australian states of New South Wales and Victoria. Two types of cutoff low formation are identified, described here as coastal lows and blocking lows.

Twenty‐four hour numerical simulations are performed for four systems in order to investigate the model‐reproduced structure of the large‐scale rainfall and gale‐force wind. The numerical experiments demonstrated that the regional‐scale model is capable of simulating the heavy rainfall and gale‐force winds associated with these systems. All systems are characterized by a major rain band curling around the south and east of the surface low. To the south of the system the rain band is paralleled by a curved band of gale‐strength winds. The sensitivity of these parameters and of mean sea‐level pressure to underlying sea‐surface temperature (SST) fields also is investigated through numerical experimentation.

When the SSTs were increased by between 2° and 3°, the simulated cut‐off lows had deeper central pressures, usually of 1–2 hPa. In one case the extra deepening was dramatic, being 7 hPa at 24 h. The impact on rainfall was considerable, especially on the peak values, which were increased by between 45 per cent and 80 per cent, and on the areal mean values in ‘catchment size’ areas surrounding the peak value. In contrast the peak surface winds were increased only by about 10 per cent, but the areal extent of gale‐force winds increased greatly, by between 50 per cent and 70 per cent.

The large sensitivity of these weather elements to SST is discussed in terms of possible implications for both short‐term operational forecasting and for regional effects of enhanced greenhouse climate change.
Australian runoff scenarios from A runoff‐climate model
Authors: Morassutti M. P.
Published: February 2007

Data of changes in precipitation and evaporation as computed from the GISS GCM for three scenarios of transient levels in trace gas concentration were used as input into the runoff‐climate model of Wigley and Jones to estimate changes in annual runoff regimes for three regions in Australia: Murray‐Darling (south‐east), Lake Eyre (central), and Timor Sea (northern) Drainage Divisions. All regions were calculated to have significant increases in mean annual runoff regardless of the GISS scenarios, due chiefly to the combination of intense aridity (e.g. low runoff ratios) and substantial changes in precipitation and evaporation as predicted by the GISS GCM. Also, attributes of the runoff‐climate model are related to their applicability and accuracy in runoff prediction.
Temporal characteristics of USA snowfall 1945–1946 through to 1984–1985
Authors: Leathers Daniel J. , Mote Thomas L. , Kuivinen Karl C. , McFeeters Stuart , Kluck Douglas R.
Published: February 2007

The temporal variability of USA snowfall is investigated for the period 1945–1946 through to 1984–1985 using linear trend and principal components analyses. The results of the linear trend analysis indicate that two regions of the USA evidence significant changes in monthly snowfall over the period. These areas include the Great Lakes/upper mid‐west and high plains regions of the USA. In the Great Lakes/upper mid‐west sector, positive linear trends are found in monthly snowfall totals for the mid‐winter months (December, January, February). For the high plains region, positive linear trends are found for the month of December. Principal components analysis (PCA) is used with seasonal snowfall data in order to better understand the spatial and temporal nature of seasonal snowfall variations across the USA. The PCA isolates six spatially coherent regions in which seasonal snowfall varied similarly over the 40‐year period. Only one of these regions, centred on the Great Lakes and upper mid‐west, displays any long‐term change in seasonal snowfall, a positive trend during the period 1945–1946 through to 1984–1985. These results are discussed in the context of man‐induced and natural environmental changes.
Water vapour transport over Southern Africa during wet and dry early and late summer months
Authors: D'Abreton P. C. , Lindesay J. A.
Published: February 2007

Southern Africa is semi‐arid to arid, and the moisture that contributes to rainfall over the summer rainfall region is largely imported from other areas. Interseasonal and interannual variations in rainfall must result from changes in the circulation and in vapour fluxes over the subcontinent. It is shown that important changes in vapour fluxes occur between October (early summer) and January (late summer), with zonal fluxes being more important in October and meridional fluxes in January. Wet and dry months of October and January are characterized by enhanced zonal (meridional) flow in wet Octobers (Januaries), and reduced importance of these flows in the dry months. Adjustments in the areas of vapour flux convergence and divergence are as important as changes in the fluxes. The convergence and divergence changes between wet and dry months are confirmed by decreases in outgoing longwave radiation over central southern Africa in wet months and increases in dry months. Tropical zonal circulations, and tropical—subtropical meridional circulation cells, conform to the patterns of enhanced (reduced) convection over the central subcontinent in wet (dry) months.
Satellite OLR and microwave data as a proxy for summer rainfall over sub‐equatorial Africa and adjacent oceans
Authors: Jury Mark R. , Pathack Beenay , Waliser Duane
Published: February 2007

The potential for using satellite outgoing longwave radiation (OLR) and passive microwave data as a proxy for rainfall over sub‐equatorial Africa and adjacent oceans is explored. Correlations between anomalies of field OLR and a summer rainfall index are −0.67 to −0.93 over central southern Africa, where the amplitude of interannual fluctuation in the decade 1975–1984 is largest. OLR‐rainfall correlations decline to −0.42 over Madagascar owing to a less homogeneous distribution of rainfall. Over South Africa during the winter dry season the correlation becomes positive except over the eastern seaboard where sea‐surface temperatures remain high.

Satellite microwave estimates of cloud liquid water (LW) over the oceans surrounding southern Africa are presented for selected months during 1988 and 1989. Agreement is found between coastal rainfall and adjacent oceanic LW patterns. Contrasting distributions of interior and coastal rains in January and October 1989, respectively, are associated with the positioning of standing troughs evident in concentrated areas of high LW values in the mid‐latitudes. The advance and structure of the Inter Tropical Convergence Zone (ITCZ) over the tropical South‐west Indian Ocean is illustrated in monthly composites.
West African rainfall deficits and sea surface temperatures
Authors: Fontaine Bernard , Bigot Sylvain
Published: February 2007

Comparisons between years of below average rainfall over West Africa, sea‐surface temperatures (SST) over the Atlantic Ocean and the world ocean, and latitudinal positions of the Inter Tropical Convergence Zone (ITCZ) over the Atlantic Ocean show that the relationships depend mainly on the rainfall anomaly patterns. The well‐known SST dipole (cold northern ocean and warm equatorial and southern ocean) is only apparent during those August months with below average Sudano‐Sahelian rainfall and above average Guinean rainfall (rainfall type ‘−/+’) and an abnormal southward position of the ITCZ. In contrast, those August months that experience rainfall deficits over the whole of West Africa (rainfall type ‘−/−’) are associated with warm SST anomalies over the eastern Pacific Ocean, cold persistant SST anomalies over the equatorial Atlantic Ocean and a more northward position of the ITCZ. Those patterns first appear in northern spring before the Sahelian rainy season.

The composite SST differences for the ‘−/+’ and ‘−/+’ rainfall types computed with August or July‐September amounts have a good resemblance with each other. Comparison of results related to the reverse July‐September rainfall patterns (the ‘+/−’ and ‘+/+’ patterns) during the 1950s shows that the SST anomalies were globally colder when, on average, the Sahelian rainy seasons experienced significant excesses while the Guinean little dry seasons were more marked.
Comparison of coastal wind and pressure trends over the tropical atlantic: 1946–1987
Authors: Bigg Grant R.
Published: February 2007

Strengthening of the Atlantic Trade Winds since 1946 has been documented by several workers. This is broadly consistent with changes in the atmospheric pressure patterns over the tropical Atlantic. Here ship‐recorded pressures are compared with sea‐level pressures recorded from 49 coastal sites in order to validate the trends in the pressure patterns. Good correlation is found between the two independent sets of pressure measurements; a comparison of trends reveals statistically significant agreement along the African coast but disagreement in the western Atlantic and Caribbean. Island stations generally show poorer correlation with adjacent marine pressures than do continental stations. A degree of support for the observed marine trends is therefore provided by this analysis but it appears that, particularly for islands, marine and adjacent land areas are not always strongly coupled meteorologically.
A connection between mean wave height and atmospheric pressure gradient in the North Atlantic
Authors: Bacon S. , Carter D. J. T.
Published: February 2007

Comparison of long‐term trends in mean wave height in the North Atlantic with values of annual mean atmospheric pressure gradient in the North Atlantic measured between the Iceland Low and the Azores High suggests, for the period of overlap between the data set of Bacon and Carter and of Sahsamanoglou (early 1950s to 1980), a correlation between these two measures. This paper, using monthly mean values of significant wave height (HS) derived from measurements at two sites, one oceanic (Ocean Weather Station Lima) and one coastal (Seven Stones Light Vessel), covering the period 1962–1988, investigates correlation between (firstly) annual mean values and (secondly) monthly mean values of HS and of pressure gradient. The annual mean values of pressure gradient are shown to be linked to the long‐term changes in wave climate described by Bacon and Carter. The large annual cycles in the monthly mean values of both variates are found to be in phase; furthermore, correlation between the two variates independent of the annual cycle is found. Finally, the correlation between the annual means is used to generate a hindcast mean wave climate for Seven Stones Light Vessel (and also, tentatively, for the whole north‐east Atlantic) from 1873 to the present, which suggests that present conditions are as high as have been observed since 1873.
Temporal variations of the vertical profile of temperatures of Argentina
Authors: Duarte Maria Luz
Published: February 2007

Characteristics of the spatial and temporal variability of tropospheric and low stratospheric temperatures of Argentina during the period 1965–1982 are investigated.

Empirical orthogonal functions (EOFs) were used to obtain the main characteristics of the vertical profile of temperature in three climatic regions, and time series of the temporal coefficients are analysed as indicators of temporal variations. The results indicate that there was an almost homogeneous upward trend in summer of the tropospheric temperatures (downward for stratospheric temperatures) in tropical and mid‐latitude regions.
The influence of variable weather patterns on river water quantity and quality regimes
Authors: Wilby R. L.
Published: February 2007

There is growing awareness as to the potential sensitivity of hydrological systems to climate change. In particular long‐term changes in precipitation variability will have consequences for runoff regimes and thence solute transport. By utilizing the Lamb's Weather Type register in conjunction with observed 24 h rainfall totals it was possible to determine daily precipitation event probabilities and magnitudes for eight dominant synoptic classes. The stochastic rainfall series thus generated were then used to drive a robust hydrochemical model of an experimental catchment in the East Midlands, UK. The model results indicate that the frequencies of flood and drought are dependent upon the synoptic scenario, and especially the historical prevalence of both the anticyclonic and cyclonic patterns. Given that there have been marked fluctuations in the annual frequencies of these classes since the mid‐nineteenth century, long‐term variations in the severity and incidence of extreme flows may be anticipated. Clearly this will have major implications for the episodic export and dilution of solutes, sediments and microorganisms originating from both pristine and polluted hydrosystems.
Global land‐surface albedo modelling
Authors: Rowe Clinton M.
Published: February 2007

The climatic impact of changes in terrestrial albedo has been studied using numerous climate models, ranging from simple, one‐dimensional energy balance climate models to the most complex, three‐dimensional general circulation models of the atmosphere. In the majority of these studies, the land‐surface albedos have been prescribed both spatially and temporally from albedo observations. The effects of variations in albedo, due to such factors as the angular distribution of incident radiation and plant phenology (especially leaf emergence, senescence, and drop), cannot be deduced from these observation‐based albedos.

To overcome the limitations of using observed land‐surface albedos in climate models, a model of radiation transfer in plant canopies was used to predict vegetation albedo. This model incorporates the optical properties of the vegetation and soil surface as well as the micro and macrostructure of the canopy. Because of the model's reliance on these physical properties of the land‐surface cover, it is able to account explicitly for albedo variations caused by factors both internal and external to the vegetation canopy.

Using the physiognomic classification of natural vegetation developed by Küchler, representative canopy architectures for each of 31 vegetation types were developed for each month of the year. Monthly albedos were then simulated for each vegetation type under a range of irradiance distributions. When these results are compared with existing observations of plant canopy albedo, the degree of correspondence is, in many cases, quite good. Moreover, the dependence of albedo on irradiance distribution predicted by the model agrees well with established theory.

Global maps of land‐surface albedo are produced for both clear‐sky and overcast conditions in January, April, July, and October using a simple solar radiation model to determine the incident radiation field. These maps are compared with previously compiled maps of land‐surface albedo. Large differences between the model‐ and observation‐based global albedo maps occur for each of the four months. However, the model reproduces many of the large‐scale features and seasonal trends evident in albedo observations.
Cyclone tracks and wintertime climate in the mid‐atlantic region of the USA
Authors: Knappenberger Paul C. , Michaels Patrick J.
Published: February 2007

The relationship between cyclone tracks and the climate has been studied for over two centuries. Most studies, however, describe only qualitatively the link between these phenomena. Thus, the understanding of the true nature of this relationship is not complete. The goal of this work is to help fill this lack of understanding by describing quantitatively the relationship between cyclone tracks and wintertime climate in the mid‐Atlantic region of the USA.

Canonical correlation analysis (CCA), which is used to help achieve this goal, is a statistical technique that finds the optimum correlation between two fields of data. Canonical correlation analyses are performed to relate a gridded cyclone frequency data set to precipitation, snowfall, and temperature data sets for the winter seasons from 1930 to 1989.

The results of these analyses reveal a strong correlation between an abundance of cyclones in the Ohio Valley, and below normal precipitation and snowfall amounts, and above normal temperatures across most of the mid‐Atlantic region. Conversely, an abundance of storms along the southeastern Atlantic coast is associated with above normal precipitation and snowfall amounts, and lower than normal temperatures over the region. Since these relations are described by the first canonical variable pair in each analysis, they represent the strongest relationship between the data fields. Therefore, these results indicate that the oscillation between the frequency of Ohio Valley cyclones and the frequency of Atlantic coastal cyclones plays an important role in the year‐to‐year patterns of wintertime climate in the US mid‐Atlantic region.
Coherent rainfall zones of the Indian region
Authors: Gadgil Sulochana , Yadumani  , Joshi N. V.
Published: February 2007

We have delineated rainfall zones for the Indian region that are coherent with respect to the variations of the summer monsoon rainfall. Within each zone, the time series of the summer monsoon rainfall at every pair of stations are significantly positively correlated, and the mean interseries correlation for each zone is high. The interseries correlation data set is analysed in order to delineate the rainfall zones, using an objective method specifically developed for the purpose. Each of the zonal averages are shown to be representative of the zone as a whole. We suggest that this regionalization is appropriate for study of the variation of the summer monsoon rainfall over the Indian region on interannual and larger scales.
Global cloud cover and cloud water path from ISCCP C2 data
Authors: Drake Frances
Published: February 2007

The International Satellite Cloud Climatology Project (ISCCP) C2 data from 1984 to 1987 are used to form average extreme season zonal means and global climatologies of cloud parameters. The total cloud amount, in general, agrees well with previous cloud climatologies. The level of agreement between the zonal total cloud climatology of Warren et al. and the ISCCP C2 data is extremely good. The main features of the general circulation of the atmosphere are observed in the global climatology, notably the equatorial maximum associated with the Inter Tropical Convergence Zone, the subtropical minima, and mid‐latitude maxima. The polar regions are areas of large disagreement with previous cloud climatologies. For both poles the ISCCP C2 data show that maximum cloudiness occurs in the winter, whereas most previous cloud climatologies indicate that maximum cloudiness occurs in summer. The ISCCP data indicate that Antarctica is an area of relatively small cloud amounts, which concurs with most previous climatologies. However, the amount and season of minimum cloudiness is in disagreement. Results from the amount of cloud types also show features that can be related to the general circulation of the atmosphere. Low clouds are found to be the most common cloud type over the ocean. Large amounts of low cloud are found on the west coasts of subtropical continents, consistent with the presence of marine stratocumulus. The subtropical high pressure zones are areas with small amounts of middle and high cloud types. The Indian south‐west monsoon is easily visible by an increase in the amount of high cloud in the region during Northern Hemisphere summer. The total water‐path results highlight the difficulties of cloud retrieval over permanent snow or ice cover. At present the water path results are unreliable.
The development of a satellite‐based insolation model for the tropical western Pacific Ocean
Authors: Nunez M.
Published: February 2007

Concurrent pyranometer and GMS (Japanese Geostationary Meteorological Satellite) data were collected for the western tropical Pacific during a 21‐month period in 1987 and 1988. Data from 10 pyranometer stations in 1987 were used to build a satellite insolation model. Such processes as surface albedo, narrow band to broad band conversion, and depletion by water vapour and aerosols were taken into account. The model was then tested with an independent pyranometer data set comprising 9 months in 1988.

Results show that aerosol depletion is site‐specific, with typical long‐term values ranging from 19·8 per cent of the extraterrestrial value for Kuala Lampur, to 4·8 per cent for Willis Island. Monthly insolation may be mapped over the oceanic regions of the study area assuming that the Willis Island aerosol depletion values apply. The model gave root‐mean‐square (RMS) errors of 14·08 W m−2 when tested against all monthly average pyranometer data for 1988. Corresponding RMS errors are 11·67 W m−2 when only Willis Island data are used. Sources of errors are discussed, as are suggestions for future research.
Arrival and withdrawal dates of the summer monsoon in Bangladesh
Authors: Ahmed Rafique , Karmakar Samarendra
Published: February 2007

Daily data of (a) rainfall amount, (b) prevailing wind direction, (c) wind speed, (d) mean temperature, and (e) mean relative humidity of 19 stations in Bangladesh for the months May through to October, for the period 1958 through to 1987, have been analysed in order to determine various spatio‐temporal patterns of the arrival and withdrawal dates of the summer monsoon in the country. Statistical characteristics of these dates have been presented.

The summer monsoon arrives first in the extreme south‐eastern part of the country, and initially moves towards the north. After being diverted by the Meghalaya Plateau, the flow turns towards the west. The mean arrival date of the summer monsoon in the extreme south‐eastern coastal part and in the extreme north‐western part are 2 June and 15 June, respectively. Withdrawal of the summer monsoon proceeds in the opposite direction to the arrival. Mean withdrawal dates of the summer monsoon from the extreme north‐western part and extreme south‐eastern part of the country are 30 September and 17 October, respectively. Standard deviations of both arrival and withdrawal dates in different parts of the country vary from 7 to 10 days.

Probabilistic early dates of arrival of the summer monsoon in Cox's Bazar area in 1 year out of 4 years, 10 years, and 25 years are 28 May, 23 May, and 19 May, respectively. Probabilistic late dates of arrival in 1 year out of 4 years, 10 years, and 25 years are 8 June, 13 June, and 16 June, respectively.

Probabilistic early dates of complete withdrawal of the summer monsoon from Bangladesh in 1 year out of 4 years, 10 years, and 25 years are 10 October, 5 October, and 1 October, respectively. Probabilistic late dates of complete withdrawal in 1 year out of 4 years, 10 years, and 25 years are 23 October, 28 October, and November 1, respectively.
A statistical approach towards a regionalization of daily rainfall in Sri Lanka
Authors: Domroes Manfred , Ranatunge Edmound
Published: February 2007

Regionalization of daily rainfall in Sri Lanka was examined using orthogonal factor analysis (OFA) based on daily rainfall data of 42 stations for a 15‐year period (1971–1985). The number of potential rainy days was computed from the original data matrix and subjected to S‐mode OFA. The first 10 orthogonal factors were shown as highly significant, explaining 65.1 per cent of the total variance of the whole data matrix, where the level of eigenvalues represented was > 1.0. Noticeably, the 10 orthogonal factors clearly revealed the different homogeneous daily rainfall regions in Sri Lanka (labelled as A to J), according to the orthogonal factor high loadings matrix. Delimitation of the daily rainfall regions was carried out in accordance with the ‘variance boundaries’ resulting from the rotated factor loadings matrix. The number of potential rainy days has been identified for each region, showing an increasing trend with elevation. The probability of rainy days, wet spells and their mean length have been computed separately on a monthly and yearly basis in order to analyse the nature of the daily rainfall reliability in each region. The main factors for the daily rainfall fluctuation patterns in Sri Lanka are the typical monsoon rainfall, the dominant influence of the Inter Tropical Convergence Zone and topography.
Urban climate effects of artificial heat sources and ground shadowing by buildings
Authors: Swaid Hanna
Published: February 2007

Simulations are presented for the effects of artificial heat sources and ground shading by buildings on air temperature variations in the urban canopy layer. An idealized urban cluster composed of repeated street canyons oriented east‐west with an aspect ratio of 0.5 is used to evaluate these effects. The simulations by the cluster thermal time constant model show that a daily mean artificial heat flux of 11 Wm−2 causes an almost invariant temperature rise of 0.7 K around‐the‐clock. Conversely, increasing the shade area in the streets by means of vertical screens fitted at the building roof‐level can produce a pronounced temperature lowering at midday.
ENSO phenomenon and 30–50 day variability in the Australian summer monsoon rainfall
Authors: Suppiah Ramasamy
Published: February 2007

The characteristics of 30–50 day variability in the Australian summer monsoon rainfall has been investigated by using station rainfall data. In particular, the influence of the El Niño/Southern Oscillation (ENSO) phenomenon on the Australian summer monsoon rainfall is analysed. Results of the power spectrum analysis indicate statistically significant peaks in the 30–50 day band during anti‐ENSO events in the north‐central, and north and east coast regions. The spectral analysis also reveals a statistically significant peak in this band during ENSO events in the inland desert and north and east coast regions. Filtered rainfall values show an eastward propagation pattern during anti‐ENSO events, whereas ENSO events demonstrate a pattern characteristic of a standing oscillation and sometimes a westward propagation pattern. The present study also suggests some tendency for the 30–50 day oscillation to be phase‐locked to the seasonal cycle of this region. The phase‐locking phenomenon is also observed in the daily mean sea‐level pressure at Darwin, which is very clear during the anti‐ENSO events.
Teleconnections between North Pacific SST anomalies and growing season extended dry spells on the canadian prairies
Authors: Bonsal B. R. , Chakravarti A. K. , Lawford R. G.
Published: February 2007

This investigation documents the relationships between anomalous North Pacific sea‐surface temperatures (SSTs) and the occurrence of growing season extended dry spells on the Canadian Prairies. Results show a significant correlation between extended dry spells and a positive SST anomaly gradient in the east‐central North Pacific. The gradient exists between an area of anomalously cold water in the east‐central North Pacific in the area 30°N–40°N latitude and 165°W‐135°W longitude, and an area of anomalously warm water along the central west coast of North America in the area 45°N–55°N latitude and 130°W‐125°W longitude. A probability model shows that the longer this positive gradient persists, the greater the probability of a major extended dry spell on the Canadian Prairies.
Climatological study of the total ozone field around the subtropical jet stream
Authors: Begum D. A.
Published: February 2007

A study of the average distribution of total ozone was accomplished for the period from October 1982 to September 1983 in the area 20–50°N, 90–160°E, i.e. the entrance region of the East Asian subtropical jet stream. Total ozone data were obtained from the Total Ozone Mapping Spectrometer on the Nimbus‐7 satellite.

Normally, the subtropical jet stream (STJ) marks a steep gradient in total ozone. From the monthly mean study of total ozone and wind fields at the 200 hPa surface, it was found that in winter the total ozone contours are almost parallel to the wind directions; the horizontal gradient in total ozone increases as the wind speed strengthens. In winter and spring, a sharp gradient in total ozone is found on the cyclonic side of the STJ because of the strong Hadley circulation. As the Hadley cell ceases in summer, the jet weakens and horizontal gradients in total ozone become much smaller, disappearing almost entirely by early autumn.
Noaa tovs‐derived moisture fields over the arabian sea and the bay of bengal and their association with the south‐west monsoon
Authors: Gautam N. , Kishtawal C. M. , Pandey P. C.
Published: February 2007

Moisture fields derived from the Tiros‐N Operational Vertical Sounder (TOVS) data onboard previous National Oceanic and Atmospheric Administration (NOAA) series of satellites have been used to study monthly moisture fields over the Arabian Sea and the Bay of Bengal for the years 1979–1981. It is observed that monthly averaged moisture fields over the Bay of Bengal are always more than those over the Arabian Sea at a given latitudinal belt. Further, the monthly mean moisture flux divergence has been calculated using monthly mean winds from ship observations over the same areas of the Arabian Sea and the Bay of Bengal. It is found that net moisture flux divergence over the Arabian Sea is consistently higher than that over the Bay of Bengal for the years, 1979, 1980, and 1981, which are deficient, and excess monsoon rainfall years in terms of departure from long‐term climatological rainfall values. Moisture variability over the Arabian Sea and the Bay of Bengal on a monthly scale has also been studied for the months of June, July, and August for the years 1979–1981.

A plot of the zonally averaged (at every 2° latitude) differential moisture signal (DMS) by latitude indicates the approximate position of the low‐level westerly jet. The overall differential signal between zonally averaged moisture fields over the Arabian Sea and the Bay of Bengal has also been found to be an indicator of total Indian rainfall excluding orographically influenced regions, although more data is needed to firmly establish the relationship quantitatively.
Comparison of global ultraviolet (290–385 nm) and global irradiation measured during the warm season in valencia, spain
Authors: Martinez‐Lozano J. A. , Casanovas A. J. , Utrillas M. P.
Published: February 2007

This paper studies data of ultraviolet (290–385 nm band) horizontal solar irradiation and global horizontal solar irradiation measured at Valencia (Spain) during the period March 1991 to September 1991. Analysis of error estimations and correlation coefficients show that the 10 minute, hourly, and daily values of ultraviolet (UV) and global irradiation are highly correlated. Improved figures and less dependence on location are achieved by defining a clearness index for the UV 290–385 nm band and relating it to the conventional whole‐band clearness index. The novel clearness index obtained from Valencia data is approximately half of the conventional clearness index. Considering solar elevation as an additional parameter, the correlation coefficients increase to values in the 0.94 to 0.96 interval for solar elevations greater than 55°, both for hourly and 10‐minute values.
Regional and temporal variations in heavy precipitation in south carolina
Authors: Changnon David
Published: February 2007

Daily precipitation amounts greater than 50 mm from long‐term weather stations in South Carolina were analysed in order to determine their seasonal and annual frequencies and spatial variability. Year to year, the annual amount of precipitation produced by heavy rainfalls was not well correlated between stations ( –0.10≤r≤ + 0.65). The seasonal analysis detected three heavy precipitation regimes: (i) the mountainous region in western South Carolina with a winter maximum; (ii) the coastal plain with a distinct summer maximum; and (iii) the region in between with a summer‐autumn maximum. Such results indicate that site‐specific data should be used to examine large daily precipitation amounts rather than regionally averaged data because the primary four climatic and synoptic controls that create heavy precipitation vary considerably across South Carolina. Temporal analyses of the site‐specific, annual, large daily precipitation amounts and regional average annual precipitation showed generally weak to moderate correlations (+0.25 ≤r ≤0.57), indicating that interannual changes in annual precipitation are not well related to changes in annual contributions due to large daily precipitation amounts. Differences between regional wet and dry decadal periods were associated with significant changes in the annual large daily precipitation amounts at some but not all stations, indicating that similar long‐term changes cannot be assumed across a region as small as South Carolina. This information is useful to water managers and has potential utility for estimating conditions in a changing climate.