Showing papers in "International Journal of Climatology in 1981"
TL;DR: In this paper, a simple hardware scale model is used to simulate nocturnal cooling rates for rural and urban environments under calm and cloudless conditions, and the results of the experiments show that canyon geometry in the central portion of a city (as measured by the sky view factor) is a relevant variable in producing nocturnurnal urban heat islands due to its role in regulating long-wave radiative heat loss.
Abstract: A simple hardware scale model is used to simulate nocturnal cooling rates for rural and urban environments under calm and cloudless conditions. Comparison with field observations gathered under similar conditions shows the model capable of reproducing many of the features of the temporal development of urban heat islands and the long-wave radiative exchange in urban canyons. The model is used to investigate the roles played by rural/urban differences in geometry and thermal admittance. The results of the experiments show that canyon geometry in the central portion of a city (as measured by the sky view factor) is a relevant variable in producing nocturnal urban heat islands due to its role in regulating long-wave radiative heat loss. It is also demonstrated that this measure is central to the relationship between city size and heat island intensity. The importance of canyon geometry as a feature of urban design is discussed. Thermal admittance differences can also produce realistic heat island features but their magnitude requires quantification in the field.
1,055 citations
TL;DR: A climatological study of the North Pacific Oscillation (NPO) during Januaries and winters (D-J-F) between 1906 and 1978 is presented in this article.
Abstract: A climatological study of the North Pacific Oscillation (NPO) during Januaries and winters (D-J-F) between 1906 and 1978 is presented. The NPO is defined in terms of opposition in sign of mean temperature anomaly between western Alaska-eastern Siberia (as represented by the stations at Dutch Harbor and St. Paul, Alaska) and western Canada (as represented by Edmonton). The two oscillation modes, Aleutians below normal temperature (Edmonton above normal) and Aleutians above normal temperature (Edmonton below normal), are associated with variations in the strength of the zonal westerlies over the Pacific and North America which in turn result from longitudinal variations in the mean position of the Aleutian low. A westward location of the mean low. over the Sea of Okhotsk, is associated with the development of intense mean high pressure cells over western North America while zonal flow is associated with a more eastward location of the mean low over the Gulf of Alaska. Significant spatial correlations exist between the strength of the zonal component of the geostrophic wind over the Pacific Ocean and the zonal component of the polar and subtropical easterlies over the Pacific sector.
The NPO modes are associated with large regional variations in air temperature and precipitation over North America, sea surface temperatures in the North Pacific, and Bering Sea ice. The NPO is found to resemble the second eigenvector of January and winter sea level pressure anomalies. In contrast to its more frequently occurring counterpart, the North Atlantic Oscillation, the NPO is not clearly associated with hemispheric mean temperature trends and its modes occur randomly with time. The two oscillations represent separate patterns of teleconnections of sea level pressure and zonal geostrophic winds over the Northern Hemisphere.
356 citations
TL;DR: In this paper, the authors defined the start of the rains as the first occurrence of a specified amount of rain within two successive days and derived the probability distribution of the date of the start date from the rainfall models of Stern (1980a).
Abstract: The start of the rains is defined as the first occurrence of a specified amount of rain within two successive days. The probability distribution of the date of the start of the rains is derived from the rainfall models of Stern (1980a). The probabilities of occurrence of dry spells are used to define an earliest practical starting date. Results are presented for eleven stations on a N-S transect in West Africa. The variation in starting date with latitude is described. Advantages of the model approach over conventional analyses are discussed.
128 citations
121 citations
TL;DR: In this paper, the authors explain variations in rainfall over southern Africa in terms of variations in pressure and circulation patterns, and suggest that the 10-11 year rainfall oscillation of the southern Cape may be forced by longitudinal changes in the position of the first ridge of standing wave 3 which may oscillate with a similar quasi-periodicity.
Abstract: Variations in rainfall over southern Africa are explained in terms of variations in pressure and circulation patterns. The extended wet spells of the quasi 18-year oscillation in rainfall that have affected the subcontinent are shown to have occurred in association with increased pressures in the region where the subtropical ridge of the first zonal standing wave in the 500-mb surface has its expression in the southern hemisphere, in association with the eastwards displacement or weakening of the Indian Ocean high and a probable lowering of pressure over the subcontinental interior. It is further suggested that the 10-11 year rainfall oscillation of the southern Cape may be forced by longitudinal changes in the position of the first ridge of standing wave 3 which may oscillate with a similar quasi-periodicity.
105 citations
TL;DR: In this paper, spatial correlation analysis has been applied to Namib rainfall, in an attempt to identify possible patterns of the spatial organization of localized storms in this area, and the utility of the above technique for areas with only sparse raingauge networks is explained.
Abstract: Spatial correlation analysis has been applied to Namib rainfall, in an attempt to identify possible patterns of the spatial organization of localized storms in this area. The utility of the above technique for areas with only sparse raingauge networks is explained. Results indicate that convective storms are not randomly scattered in space but, tend to form at preferred distances from each other, around 40-50 and 80-100 km, with no preferred locations of, or directions between, storms. Benard cells are mentioned as possibly imposing the inferred organization of convective storms in space.
82 citations
TL;DR: In this paper, empirical relations for net radiation over green grass are found from routine hourly observations reported during 5 years at one site in Denmark, and the derived procedure is used on another site in Danish with another representative surface albedo.
Abstract: From routine hourly observations reported during 5 years at one site in Denmark, empirical relations for net radiation over green grass are found. These relations give an estimate of the net radiation for the measuring site from the geographical position, local time, representative surface albedo, measured global radiation and/or total cloud cover in oktas. Cloud types are taken into account, if the reported clouds are mainly cirrus forms. This is a result of a classification of the net radiation according to cloud cover and type, i.e. a total of 90 classes. Different relations are found for different cloud covers.
The derived procedure is used on another site in Denmark with another representative surface albedo. From 10 years of data, consistency is found for net radiation measurements at the two sites, allowing extrapolation of the derived net radiation procedure to other sites in Denmark. Data from the Wangara experiment (Clarke, 1971), covering 40 days, showed a similar relation for clear sky conditions, but revealed another general dependency of net radtation upon cloud cover than that found in Denmark. Therefore, relations of the kind found in this study are related to the weather and climate of the measuring site. Comparisons between net radiation estimated from the models and measurements from different sites is r2 ⋍ 0.9.
77 citations
TL;DR: In this article, the total volume of rain-water over India has been computed for each of the years during the period 1871-1978 on the basis of the rainfall data for a fixed network of 306 raingauges.
Abstract: The total volume of rain-water over India has been computed for each of the years during the period 1871-1978 on the basis of the rainfall data for a fixed network of 306 raingauges. The mean, the standard deviation and the coefficient of variation of the series of annual rain-water volume are 3143 km3, 300 km3 and 9.5 per cent, respectively. The series is homogeneous and random. The serial correlation is 0.013 which is too low to suggest any relationship between successive terms. Gaussian distribution gives a good fit to the series.
The series giving the percentage area of the country with a deficiency of 20 per cent or more, as well as the percentage area with an excess of 20 per cent or more have been obtained. These bring out the variability in the deficiency and excess of rain-water over the country during the period. The years of well-marked rain-water deficiency/excess over India have been identified by utilizing the criterion of 40 per cent or more area under rain-water deficiency/excess. The occurrence of such years has been found to be random and the number of such years in five-year periods appears to be distributed in accordance with the Binomial and the Poisson Probability models.
The impact of marked deficiency/excess on the All India Index of food grain prices and All India Index of food grain production has been examined. It is found that the impact of well-marked deficiency can generally be seen clearly but that of well-marked excess is seen clearly in some cases only. This is understandable. Overall excess in a year may or may not result in floods which have the potentiality to damage crops. The impact of the well-marked deficiency of 1918 has been maximum.
Remedial measures which would make the economy of the country less dependent on the variability of the annual rain-water have been discussed.
70 citations
TL;DR: In this article, an objectively derived catalogue of daily pressure patterns for 1899-1974 has been prepared for the western United States and the temperature and precipitation characteristics of the major types are described and a more detailed analysis for Colorado in extreme cold and warm months shows that the sign of the anomalies for each type is generally consistent with expectation based on the probable airflow patterns.
Abstract: An objectively derived catalogue of daily pressure patterns for 1899-1974 has been prepared for the western United States. The temperature and precipitation characteristics of the major types are described and a more detailed analysis for Colorado in extreme cold and warm months shows that the sign of the anomalies for each type is generally consistent with expectation based on the probable airflow patterns. A regression analysis of type frequencies versus temperature and precipitation anomalies for 1899-1970 at stations east and west of the Continental Divide in the Rocky Mountain states shows that useful explanation of variance is obtained only for temperatures in the transition seasons and for precipitation west of the Divide in winter and east of the Divide in spring. Within-type variability of the climatic characteristics is one source of the discrepancy. The results underline the problems encountered in trying to link climatic anomalies with atmospheric circulation characteristics.
64 citations
TL;DR: A satellite-derived climatology of cloud vortices for the Southern Hemisphere winter (June to September) indicates that significant within-season changes occur in the areal frequencies of extratropical depressions, while on a zonally-averaged basis, the semi-annual oscillation of the circumpolar vortex appears to dominate the latitudinal changes in cyclonic activity as mentioned in this paper.
Abstract: A satellite-derived climatology of cloud vortices for the Southern Hemisphere winter (June to September) indicates that significant within-season changes occur in the areal frequencies of extratropical depressions. This variability is found to be most strongly associated with the climatic frontal zones, while on a zonally-averaged basis, the semi-annual oscillation of the circumpolar vortex appears to dominate the latitudinal changes in cyclonic activity between June and September. Surface-atmosphere interactions evidently play a key role in the wintertime circulation at middle and high latitudes. Cyclogenesis over the Southern Oceans is observed to be linked closely to the baroclinity associated with the Oceanic Polar Front, while on a regional scale, the presence of a time-averaged zone of in situ cyclogenesis over sub-antarctic latitudes of the South Pacific is found to be augmented by the influence of the unique winter season sea ice regime in that sector.
58 citations
TL;DR: In this paper, the main patterns of European rainfall anomalies were obtained from a principal component analysis of 182 homogeneous rainfall series from 1861 to 1970, and the most important component corresponded to an anomaly of the same sign and magnitude covering most of the area examined.
Abstract: The main patterns of European rainfall anomalies were obtained from a principal component analysis of 182 homogeneous rainfall series from 1861 to 1970. The most important component corresponded to an anomaly of the same sign and magnitude covering most of the area examined. The principal components were essentially the same for all seasons and limited networks of stations back to 1786 showed that they were stable with lime. Spectral analysis of the patterns revealed cycles in European rainfall at periods of 2.4 years in summer and 2.1 and 5 years in the winter half year. The first of these is the most likely to represent a permanent feature of the atmosphere.
TL;DR: In this article, the significance of sea breezes in producing distinctive diurnal boundary layer oscillations over Christchurch is discussed, and it is argued that a sea breeze return current may be discerned.
Abstract: Observations are presented suggesting the significance of sea breezes in producing distinctive diurnal boundary layer oscillations over Christchurch. Sea breeze effects are shown to be an all-year phenomenon reaching their maxima in summer. The interaction of onshore wind components with south-westerly gradient winds (even under cloudy conditions) appears to produce a distinctive all-seasons diurnal rhythm in the gradient wind. The development of shallow north-easterlies blowing into an orographically-induced lee trough, preceding the onset of ground north-westerlies, is shown to produce a complicated system of onshore airflow when combined with the sea breeze. Under such conditions it is argued that a sea breeze return current may be discerned.
Canterbury sea breezes are an important feature of the local climate and correspond in many respects to classical sea breeze models. Notwithstanding, it is their site-specific characteristics that render them of particular interest.
TL;DR: In this article, the long-term changes of temperature and of characteristic circulation patterns over the British Isles have been studied using catalogues of daily Central England temperature and daily Lamb circulation types for 1861 to date.
Abstract: Long-term changes of temperature and of characteristic circulation patterns over the British Isles have been studied using catalogues of daily Central England temperature and daily Lamb circulation types for 1861 to date. Most inter-decadal temperature variability appears to have been linked with fluctuations in circulation. For given Lamb circulation types much of the observed long-term variability of temperature appears to derive from lack of precision in the circulation classifications.
TL;DR: In this paper, it was shown that the 11-year fluctuations in tree-ring series correspond to almost each cycle of the sunspot number except for periods of low solar activity.
Abstract: It has been pointed out previously that tree-ring series from Formosa show an 11-year periodicity related to the sunspot cycle. However, significance tests of this finding have not been made and therefore the statistical reliability has not been known. Spectra of tree-ring series from other sites reported before show no evidence that the 11-year sunspot cycle appears in tree-ring series. Spectral analyses have been made of published tree-ring data from Formosa and previous studies have been re-examined. Tree-ring series from two different sites in Formosa show an 11-year spectral peak at the level of confidence higher than 90%. Cross spectral analysis between the tree-ring series and the Zurich annual sunspot number shows that the 11-year fluctuations in the tree-ring series are related to the sunspot cycle with a time lag of 1/4 phase at the 99% confidence level. Using a band-pass filter technique, it is found that the 11-year fluctuations in tree-ring series correspond to almost each cycle of the sunspot number except for periods of low solar activity. Significant 11 -year fluctuations in the tree-ring series appear during most of the periods of an ‘active’ sun as estimated by carbon 14 abundance in tree-rings.
TL;DR: In this article, the authors attempted to identify methodological problems inherent in the study of climatic fluctuations, suggest a methodology to overcome some of the difficulties, and develop discrete regions of temperature variation.
Abstract: The identification of global trends in secular temperature has resulted in various theories explaining temporal climatic fluctuations. Few investigators have attempted to regionalize these trends as derived from climatic statistics. This study attempts to: (1) review methodological problems inherent in the study of climatic fluctuations; (2) suggest a methodology to overcome some of the difficulties; and (3) develop discrete regions of temperature variation. The results presented in this study significantly complement the information derived by depicting large areal units by climatic summary statistics. Nine discrete regions of temperature trend are developed for the United States, and the contiguity of the resulting regions suggests that climatic fluctuations display distinct spatial patterns.
TL;DR: In this article, the authors demonstrate the degree of control exercised by synoptic-scale meteorological conditions upon the development and characteristics of a katabatic layer above a melting glacier.
Abstract: The objective was to demonstrate the degree of control exercised by synoptic-scale meteorological conditions upon the development and characteristics of a katabatic layer above a melting glacier. Field measurements were undertaken at a point on the snout of a temperate-alpine type valley glacier in Alberta during part of the 1979 ablation season. At this site vertical wind velocity profiles were recorded within a 7 m layer above the glacier surface, together with vertical air temperature difference over 1-4 m and wind direction at 2 m. An hourly sampling period was chosen to facilitate investigation of the variation of near-ice wind and temperature conditions under varying large-scale synoptic weather patterns.
Five synoptic types were identified for the study period using a subjective classification. The greatest number of significant differences between pairs of types occurred for 700 mbar temperature and relative humidity, 500 mbar temperature, and local cloud-cover and barometric pressure at the glacier site. Representative estimates of the glacier katabatic force and synoptic pressure-gradient force indicated the former exceeded the latter by about 12:1 under strongly developed warm anticyclones and by about 3:1 during cool cyclonic situations.
Consequently under anticyclonic conditions a well developed katabatic layer was often observed with a wind velocity maximum below 5 m, whereas weaker katabatic layer development characterized cyclonic conditions. During anticyclonic influence increased deviation of ambient (700 mbar) winds from the down-glacier direction produced significantly stronger katabatic layer inversion strength but had little impact on katabatic wind velocity or direction. Under cyclonic control across-slope ambient winds were associated with weaker katabatic wind velocity and inversion strength, together with deflection of surface wind direction. An inverse relationship between katabatic layer wind velocity and inversion strength was significant for two synoptic types.
TL;DR: In this paper, the authors analyzed the pentad rainfall data of six stations in the Andaman-Nicobar group of islands for the period 1953-1978 to study the northward advance of the ITCZ and the onset of the summer monsoon rainfall over the southeast Bay of Bengal.
Abstract: The pentad rainfall data of six stations in the Andaman-Nicobar group of islands for the period 1953-1978 have been analysed to study the northward advance of the ITCZ and the onset of the summer monsoon rainfall over the southeast Bay of Bengal. It is found that at the island stations south of 10°N the summer monsoon rains set in on the average towards the end of April which is a month in advance of the onset of the monsoon over the south Kerala coast of peninsular India. At the island stations to the north of 10°N the onset occurs about the first week of May. These dates are ahead of those shown in the existing diagrams giving the average onset dates of the summer monsoon over the southeast Bay of Bengal. Examination of the frequency and latitude of formation of cyclonic disturbances in the Bay of Bengal and the progressive seasonal variations of the tropospheric winds over the aerological station of Port Blair during April-May lend support to the earlier onset dates.
TL;DR: In this article, the eigenvector spatial patterns for European temperatures have been investigated for seven periods between 1761 and 1969, and the main patterns of anomaly are seen to be stable in time, appearing in the same position in the ranking order in each period.
Abstract: Eigenvector spatial patterns for European temperatures have been investigated for seven periods between 1761 and 1969. When the number of observations greatly exceeds the number of stations used in the analysis, the main patterns of anomaly are seen to be stable in time, appearing in the same position in the eigenvalue ranking order in each period. Patterns which are time-invariant are concluded to have physical significance.
TL;DR: In this paper, a 29-month period from an intense network of extended scale autographic raingauges at Dar es Salaam, various different storm types are identified, which are thought to be representative of the East African coast as a whole.
Abstract: Using data for a 29-month period from an intense network of extended scale autographic raingauges at Dar es Salaam, various different storm types are identified, which are thought to be representative of the East African coast as a whole. The primary means of identification of storm types were storm morphology, mode of development and movement. Three major storm groups are proposed: (i) linear storms which develop parallel to the coast along sea or land-breeze fronts, (ii) smaller elliptical outbreaks developing in situ, and (iii) small, moving elliptical ‘air mass’ storms apparently associated with the prevailing trade wind circulation. A fourth but far less numerous group is composed of large, often heavy, amorphous storms whose origins probably lie with larger-scale tropospheric perturbations, rather than with local causes.
TL;DR: In this paper, the first five dominant functions explain about 80 percent of the total original variance, thereby affording a method by which 93 per cent of the data reduction is possible in each of the months considered.
Abstract: Mean monthly 700 mb geopotential anomaly fields over the Asiatic region for the four summer monsoon months June to September based on 15 years data (1964 to 1978) have been analysed through an empirical orthogonal functions technique. The analysis shows that the first five dominant functions explain about 80 per cent of the total original variance, thereby affording a method by which 93 per cent of the data reduction is possible in each of the months considered. Correlations have been derived for the first three dominant functions of a month with the corresponding functions of the other months. Similarly, the time amplitudes of the first three functions of a month have been correlated with the corresponding time amplitudes of the other three months. The correlation analyses show that the first function and its associated amplitude for June are significantly correlated with the corresponding functions and amplitudes of the other three months. The time amplitudes of the first and the second functions have been used to determine analogous mean monthly anomaly patterns among different years of the data under study.
TL;DR: The relation between the duration of sunshine hours and radiation derived from ten years of daily records at Eskdalemuir and Cawood differs significantly from formulae in general use with the Penman formula.
Abstract: The relation between the duration of sunshine hours and radiation derived from ten years of daily records at Eskdalemuir and Cawood differs significantly from formulae in general use with the Penman formula. When used in the Penman formula with meteorological data from North East England evaporation estimates were more satisfactory than those based on commonly used formulae. While winter months showed different relations between sunshine and radiation their use in estimating evaporation made no significant difference on cumulative evaporation over a year. The regression R/RA = 0.1894-0.624(n/N) derived from Eskdalemuir is satisfactory for use in North East England.
TL;DR: In this paper, the authors developed a method for finding statistics to describe the latest state of a climatic time series without assuming that the character of the series will remain unchanged with time.
Abstract: Formulae are developed for finding statistics to describe the latest state of a climatic time series without assuming that the character of the series will remain unchanged with time. The choice of formulae is discussed, and reasons given for the parameter settings which make the operations specific. Applications of the technique are illustrated by the extracts from analyses of British records covering most of the years 1821 to 1980, six being of rainfall and two of temperature.
TL;DR: In this article, the authors describe how regional weather centres in Britain supply meteorological information to the community and how the demand for such information is likely to reflect a mix of socio-economic and atmospheric factors.
Abstract: This paper describes how regional Weather Centres in Britain supply meteorological information to the community. With reference to the public enquiries directed to the Glasgow Weather Centre, it is shown how the demand for such information is likely to reflect a mix of socio-economic and atmospheric factors. Spontaneous daily enquiries recorded over a 2-year period in Glasgow are analysed through a regression model to demonstrate wide differences in weather sensitivity between demand categories. The most numerous enquiry types are shown to be those most dependent on weather conditions. Finally, it is suggested that any future work should incorporate a measure of behavioural influences in order to provide the best delineation of enquiry demand characteristics.
TL;DR: This paper examined the role of each of many physical components while allowing for interaction between the planetary circulation, sometimes even the oceanic circulation, and the monsoonal one over South Asia.
Abstract: The agricultural economy of India depends on the regularity of the summer monsoon rains although this climatic phenomenon exhibits a natural variability which often brings disaster. There exists much literature which discusses the physical mechanisms of the monsoon in its general aspects and some attention has been given to explanations of the variability of its main characteristics. Global circulation models afford an opportunity to examine the role of each of many physical components while allowing for interaction between the planetary circulation, sometimes even the oceanic circulation, and the monsoonal one over South Asia. Experiments to date have investigated the influence of Arabian Sea and Indian Ocean surface temperature anomalies, the influence of the Himalayan Mountains, of surface albedo and of the relative importance of sensible versus latent heating in maintaining the summertime regime. Armed with a greater understanding of the causes of monsoon variability, researchers will perhaps be able to begin developing techniques for seasonal forecasting.
TL;DR: In this paper, a new equation from a knowledge of evaporation on land was derived, which can be used in a wide range of climatological calculations and hydrologic calculations.
Abstract: This paper derives a new equation from a knowledge of evaporation on land. Along with the heat balance equation and the water balance equation, it can be used in a wide range of climatological calculations and hydrologjcal calculations.
TL;DR: The track, the variations in intensity and the landfall were predicted efficiently and errors in track positions were smaller than the longer period averages for different forecast periods for other tropical cyclones as mentioned in this paper.
Abstract: Hurricane Allen threatened to be a storm of devastating potential in the Caribbean and on the Gulf coast of Texas or Louisiana. Although it deepened on three occasions to the intensity of a category 5 storm on the Saffir-Simpson Scale, its track was such that the islands escaped the worst possible effects. By the time it had reached close to the Texas coast the storm had started to fill. Storm surge damage was the major cause of damage, though locally in the Caribbean islands and to some extent in Texas, this was compounded by wind and/or rain effects. The forecasts gave a clear indication of the magnitude of the impending threat and, except in Haiti, the loss of life was fortunately very small. The track, the variations in intensity and the landfall were predicted efficiently and errors in track positions were smaller than the longer period averages for different forecast periods for other tropical cyclones.