Showing papers in "International Journal of Climatology in 1988"

Relationships between seasonal rainfall in East Africa and the Southern Oscillation

Abstract: Teleconnections between the Southern Oscillation and seasonal rainfall over East Africa during the period 1923–1984 were investigated using correlation methods. The results from the study indicated significant negative zero lag correlations between Southern Oscillation and seasonal rainfall over parts of East Africa during the months of October—December. Maximum correlations were concentrated along the coast and over some western parts. Peak values in the range — 0.6 were, however, centred along central and northern coastal regions. During the months of July—September significant positive zero lag correlations in the range of 0.5 were observed over some western parts. Low zero lag correlations were, however, obtained over most of the regions with the January—May and annual rainfall records. The computed lagged correlation values displayed characteristics similar to those observed from the zero lag correlations. Highest month to month persistences were again centred within October/November when significant lag correlations persisted for time lags greater than 2 months at some locations. It was, however, noted that although there were some relationships between the Southern Oscillation and seasonal rainfall over parts of East Africa, some of the extreme wet and dry episodes were not related to the Southern Oscillation.

South African rainfall, the Southern Oscillation and a Southern Hemisphere semi-annual cycle

Abstract: Significant differences in rainfall over central South Africa are known to occur between opposite extremes in the phase of the Southern Oscillation, but details of both temporal and spatial aspects of the modulation of South African rainfall with the phase changes of the Oscillation remain to be described. Zero-lag correlations between the Tahiti—Darwin Southern Oscillation Index and monthly and 3-month seasonal rainfall over South Africa suggest that the rainfall—Southern Oscillation Index association is best defined in the late summer season January—March and in a north-west to south-east aligned zone across the central summer rainfall region of South Africa. Rainfall in this zone is directly related to the Southern Oscillation Index, increasing during high phase summers. An apparent semi-annual cycle in the rainfall—Southern Oscillation Index correlations over central South Africa is in phase with the November and February turning points of a semi-annual cycle in atmospheric circulation parameters over southern Africa. A plausible circulation mechanism is suggested to account for some of the spatial and temporal characteristics of the association between the Southern Oscillation and South African rainfall.

The onset of the southwest monsoon over Kerala: 1901–1980

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

El Nino and its effect on precipitation in Arizona and Western New Mexico

Abstract: This paper focuses primarily on the effect of El Nino on seasonal and annual precipitation at 26 locations in Arizona and western New Mexico for an 86-year period from 1900 to 1985. Following Rasmusson (1984), each year is classified as either a non-El Nino year (51) or an El Nino year (35), with the El Ninos designated as being very weak (4), weak (8), moderate (12), or strong (11). Using the Mann-Whitney U-test for the 19 stations in Arizona, we find that, in the spring (March-May) and in the autumn (September-November), there is a positive relationship between precipitation in Arizona and both moderate and strong El Ninos. These results are verified by correlating seasonal and annual precipitation for the complete 26-station network with the pressure difference between Tahiti and Darwin. Plausible physical explanations for these results are given.

Changes in precipitation conditions in the western mediterranean over the last century

Abstract: A study of precipitation variations over the western Mediterranean is given, for a period of 95 years (1891 to 1985), based on the use of Principal Component Analysis. The curves for the scores are traced and then analyzed for annual as well as seasonal precipitation. Two principal moist periods are found (1901 to 1921 and 1930 to 1941) and two principal dry periods (1922 to 1929 and 1942 to 1954). A comparison of variations in precipitation and zonal indices (ZIa) indicates that with a meridional circulation dominating over the western Mediterranean, we have an increase in precipitation; with a zonal circulation dominating we have a decrease in precipitation.

Periodic 18.6-year and cyclic 10 to 11 year signals in northeastern United States precipitation data

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

Tropical circulations and the associated rainfall anomalies during two contrasting years

Abstract: The severe drought conditions observed during 1983 over a large extent of tropical lands were associated with the 1982–1983 El Nino event. In contrast, above normal rainfall was observed over these areas during 1984. The tropical circulations have been examined for these two contrasting years. The intensity and location of the rising and sinking motions were consistent with the rainfall anomalies and also with the outgoing longwave radiation anomalies. It was found that the north-south migration of the tropical trough played an important role in modulating the tropical rainfall during these two years. In the context of the currently acceptable theoretical notions of the tropical circulation, some of the observed characteristics could be explained in terms of an atmospheric response to tropical heat sources. The results suggest that seasonal changes were involved in the 1982–1983 El Nino collapse.

Use of cross correlations in the search for teleconnections

Abstract: The search for teleconnections usually involves the calculation of sample cross correlation functions for pairs of atmospheric/oceanic time series. Properties of the theoretical cross correlation function are derived by means of analytical techniques, and properties of the sample cross correlation function are obtained by means of simulations. In particular, the effect of autocorrelation of the individual time series is to ‘smear out’ any contemporaneous cross correlation that might be present, producing nonzero cross correlations at nonzero lags. To combat this problem, the advantages of ‘prewhitening’ before computing cross correlations are demonstrated. Moreover, the operation of smoothing individual time series has the effect of inflating the values of the cross correlation coefficients at nonzero lags. Finally, the behaviour of running cross correlation coefficients is somewhat counterintuitive, making this technique potentially very misleading for detecting changes in relationships over time. For illustrative purposes, these calculations are also performed for Darwin and Tahiti time series of monthly sea level pressure.

Seasonal forecasting of the Kenya coast short rains, 1901–84

Abstract: A rainfall anomaly time series for the Short Rains (September to December) on the Kenyan Coast (KCS) is derived for the period 1901–84. On the year-to-year time scale a high degree of association can be seen between high/low extremes of a Southern Oscillation Index and negative/positive anomalies in the KCS series. The SOI-rainfall relationship is investigated seasonally with KCS lagging the SOI series by one, two and three seasons. A decay of the correlation with increasing lag can be seen. When the time series is divided into 1901–42 and 1943–84 the relationships are stronger in the more recent period. Some forecasting skill does seem possible using the June to August (JJA) SOI to predict the September-December rains. While the 1901–42 period shows a skill not much improved from using a simple climatological forecast, the 1943–84 period shows a much stronger relationship. Possible reasons are discussed for the disparity between the two time periods, also evident in results from others parts of Africa and Asia. There may well have been a change in some underlying climate mechanism between the early decades of this century and the more recent decades.

The synoptic climatology of ablation on a New Zealand glacier

Abstract: Local scale ablation and energy budget measurements are reported for the Ivory glacier in the Southern Alps of New Zealand over 53 days during two consecutive summer periods. Ablation averaged 38 mm day−1, but varied from less than 10 mm day−1 to over 70 mm day−1. Radiation supplied 52% of the energy for glacier melt, with the convective fluxes contributing most of the remainder. The results are related to large scale synoptic weather patterns over the southwest Pacific region. Different synoptic situations generate distinctive energy budgets, with radiation important during southerly circulation patterns and the convective fluxes relatively more important with northerly circulation patterns. These findings are discussed in the context of the retreat of New Zealand glaciers this century and possible circulation changes.

A detailed examination of the extratropical response to Tropical El Niño/Southern Oscillation events

Abstract: It is now clear that conditions in the tropical Pacific Ocean and the overlying atmosphere can have significant associations with the seasonal—mean circulation of the mid-latitude atmosphere, particularly in winter. Notable is a tendency for an intensification of the climatological standing wave pattern over the North Pacific and North America during the warm tropical conditions associated with El Nino/Southern Oscillation (ENSO) events. However, the actual mid-latitutde circulation anomalies do show a great deal of variability among individual ENSO years. This paper addresses the question of whether the variability of the mid-latitude response to ENSO events can be attributed to differences in the details of the tropical anomalies from event to event. The investigation embraced the period 1899–1982 and employed data on tropical sea surface temperatures (SSTs), tropical rainfall, and mid-latitude atmospheric surface pressures and air temperatures. The results suggest that a major factor in determining the strength of the Northern Hemisphere extratropical response is the SST anomaly in the far western Pacific/Indonesian region. In particular, it appears that the strong extratropical teleconnections with ENSO events occur more frequently when the SST in the far western Pacific is anomalously warm (or at least not overly cold). This finding appears to be consistent with the results of at least some recent numerical experiments conducted with comprehensive general circulation models.

Potential wind erosion in Australia: A continental perspective

Abstract: Seasonal and annual patterns of potential wind erosion in Australia are mapped. Potential erosion is estimated by applying Fryberger's sand drift potential concept to 3 p.m. wind data from 732 stations. Contour maps for January, April, July and October show monthly total drift potential, resultant drift potential, and drift directionality. Stream line maps show resultant drift direction. Annual resultant drift potential and drift direction are also mapped. Monthly total drift potential is maximal in October and minimal in April. Highest values occur on the coast, in the Nullarbor Plain, and in Tasmania; lowest values are scattered across the northern inland. Monthly resultant drift potential is similarly distributed. Monthly drift directionality is higher in the north. Monthly drift direction stream lines mainly express the general circulation of the atmosphere. Some local disturbances occur over ranges; others have cyclonic form. Annual resultant drift potential stream lines are broadly confluent and have anticyclonic curvature. These maps of potential wind erosion, linked to measures of erodibility, provide a basis for studying wind erosion hazard in Australia.

Climatic changes in and around the Rajasthan desert during the 20th century

Abstract: Rainfall and temperature data during the period 1901–1982 are studied for the northwest Indian region consisting of the meteorological subdivisions of Punjab, Haryana, west Rajasthan, east Rajasthan and west Madhya Pradesh. The results indicate a decreasing trend in the mean annual surface air temperature, which is mainly contributed by the south-west monsoon season (June through September), The mean annual and south-west monsoon season rainfall series over most parts of the region indicate a conspicuous increasing trend. The increasing trend is significantly marked for the subdivisions constituting the peripheral areas of the Rajasthan desert. These trends in rainfall and temperature are examined in relation to the changing land use pattern of the region due to extensive irrigation. Earlier findings of Winstanley (1973) reporting a decreasing trend in rainfall are found to be unacceptable due to the unrealistic assumptions of his study.

Variability of mean monthly temperatures and semi‐annual precipitation totals in Europe in relation to hemispheric circulation patterns

Abstract: The influence of general hemispheric circulation on European temperature and precipitation was investigated. Data from the period 1901–1976 were utilized: the monthly frequencies of occurrence of W, E, C circulation pattern types according to the Wangenheim-Girs classification, monthly values of pressure differences between 35° an 65°N (zonal index), mean temperatures of January and July at 30 stations in both the warm season (May-October) and the cold season (November-April) and semi-annual precipitation totals for 21 stations in Europe. The correlation coefficients between the circulation characteristics and climate elements indicated above in Europe were calculated. Maps of these correlation coefficients have been produced, with the areas of their statistical significance. The results show that variability of temperature, and also partly of precipitation in Europe are significantly correlated with changes of circulation pattern types. January temperature also depends on the zonal index. If it is assumed that in future, until the end of this century, an increase of W type frequency and a decrease of C circulation pattern types will take place—it may be expected that temperature and precipitation will undergo appropriate changes in certain parts of Europe. Northern and some central areas of Europe are likely to change from continental to oceanic climate as regards temperature; precipitation is likely to increase in northern Europe.

Reginalization of daily rainfall in Kenya by means of common factor analysis

Abstract: Daily rainfall data from 73 stations distributed throughout Kenya were subjected to maximum likelihood factor analysis. Data for the period January 1971 to December 1985 were used. A brief analysis of data quality and representativity and the problem of missing data are included. The data were transformed by natural logarithms. Scree and LEV plots together with the Kendall/North criterion for eigenvalue separation indicated break points at 5, 11 and 15 factors. The 11-factor model was judged as being the most parsimonious, for both statistical and climatological reasons. It explained 38 per cent of the total variance. The general features of the regionalization are found to be reasonably consistent with other studies. The major regions (the coast, the Highlands, the Lake Victoria area, and the dry northern/eastern areas) appear in this regionalization but are divided into several subregions. It can be concluded that this subdivision is partly linked to physiographical regions and orographic influence. In addition, possible links to regional circulation patterns are discussed.

Daily rainfall over Northern Australia: Deviations from the world pattern

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

Low latitude volcanic eruptions and the El Niño-Southern Oscillation

Abstract: An apparent association between low latitude volcanic eruptions and the El Nino-Southern Oscillation (ENSO), has been examined using a superposed epoch composite analysis of Darwin monthly mean pressure, an index of ENSO. Ten eruptions have been included in the analysis. In the composite, the date of eruption tends to be preceded by lower than average pressure at Darwin, and followed by above average pressure. A strong linear upward trend in the composite pressure anomaly starts well before the date of eruptions and continues for several months after the eruption. The analysis suggests that ENSO events are not caused by low latitude volcanic eruptions, since significant anomalies in Darwin pressure, and an upward trend in the anomalies, are observed well before the date of eruption. Low latitude eruptions tend to be preceded by the start of the sequence of events which leads to ENSO.

A synoptic climatological analysis of rainfall variability in south‐eastern Australia

Abstract: Monthly rainfall data for the state of Victoria in south-eastern Australia were analyzed using principal component analysis and Varimax orthogonal rotation, with the intention of revealing typical patterns of rainfall variability. Two data sets were used: a spatially detailed set for 1970–1980, and a less spatially detailed set for 1905–1980. The first five rotated principal component patterns (RPCPs) produced from the two data sets showed the same structure. These five RPCPs each dominated rainfall over a particular sub-region of the study region, and the climatic regionalization that this suggested appeared to be one strongly determined by topography. The anomalies of Australian region mean monthly mean sea-level (MSL) pressure associated with these five RPCPs of rainfall were determined using correlational techniques. Of the five main RPCPs of rainfall, the pattern based in the south-west of the state showed the strongest relationship with monthly pressure anomalies, and was associated with the occurrence of onshore westerly winds. The results for the rainfall pattern based in northern Victoria were perhaps the most interesting. Rainfall in this region was related to the occurrence of anomalous northerly winds through southeastern Australia, although through the cooler months of the year these winds accompanied a low pressure anomaly centred over central Australia, whereas in the warmer months they were associated with a high pressure anomaly centred to the south-east of the continent. This northern rainfall pattern also showed some month to month persistence, and a distinct correlation with the Southern Oscillation.

Subjectivity in a computer‐assisted synoptic climatology II: Relationships to surface climate

Abstract: Earlier work has demonstrated that the results of a correlation-based (Kirchhofer) synoptic classification are dependent on the way that the internal parameters and data are used. In this study, varying classifications are compared to the climate at one location. The results show that associations between temperature and the synoptic patterns are usually physically interpretable and somewhat stable, whereas precipitation-synoptic type relationships are more difficult to explain and highly variable. We conclude that varying classifications do not produce equivalent synoptic climatologies. Furthermore, we know of no apparent objective or subjective means for determining a ‘best’ classification. Based on these findings, we discourage the use of correlation-based techniques in all but the most controlled situations.

Development processes for five depression systems within the Polar Basin

Abstract: Five synoptic sequences in the Polar Basin are studied on a day by day basis. A diagnostic model is used to illustrate the relative roles of the dynamic properties of the advected air flow in comparison to mechanisms related to the characteristics of the underlying surface. It is found that the properties of the advected air flow are the major contribution to the vertical circulation associated with synoptic evolution and are a necessary condition. Latent heat release may also be a significant mechanism which supports the proposal by others that a CISK type process may contribute to further development in the Arctic. The surface sensible heat flux is not a necessary process and it may at times oppose the vertical circulation when warm air is advected into the region of development within the circulation of the depression. The surface frictional effect is a minor contribution within the central Polar Basin but is a significant process in systems migrating along the Asiatic coastline. A feedback linkage between synoptic evolution and intensification of the baroclinicity is proposed in the Greenland region for a cold low type of vortex. A cold pool, apparently created by intense radiative cooling over Greenland, was identified in early July. There was significant advective convergence associated with the thermal gradients which contributed to synoptic development as the depression migrated around this pool. It appears that the intensification of the potential temperature gradient with the advection maintained the baroclinicity, despite warm air advection into the centre of the pool. This is an interesting feature which requires further study and confirmation.

Diurnal variation of outgoing longwave radiation

Abstract: The global and monthly distribution of the diurnal variation of outgoing longwave radiation (OLR) has been calculated by compositing estimates of the planetary OLR obtained from polar orbiting satellites at different equator crossing times. These data include NOAA and NASA polar orbiting satellites for the year 1974 through 1983, giving a total of ten different local observations per day throughout the whole data period. A Fourier analysis was then applied to calculate the phase and amplitude of the diurnal cycle on a 2.5° latitude/longitude grid for each month of the year. Assumption was implicitly made that the first harmonic alone explains most of the diurnal variation. The results are represented on maps extending from 55° south to 55° north for four different seasons from which a large seasonal variability of the diurnal harmonic primarily experienced by the mid-latitude continents was clearly depicted. Over land areas the amplitude of the diurnal variation was large. In desert and semi-arid areas it seem to be clearly related to surface solar heating i.e. phases of maximum OLR generally occurring near noon during summer and afternoon during winter months. Over the oceans, the amplitude is generally small even in the convectively active regions, such as the ITCZ, and the diurnal cycle appears to be modulated primarily by clouds. Finally, a ‘harmonic dial’ was constructed to examine the most dramatic features of the diurnal variation representative of such areas as the ITCZ, deserts, tropical convective clouds regions and highly variable mid-latitude areas. Results of this study are consistent with other studies of the diurnal variability of clouds and radiation budget parameters.

Principal component analysis of precipitation in the Adriatic-Pannonian area of Yugoslavia

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

The low latitude influence on winter rainfall in Victoria, south‐eastern Australia—I. Climatological aspects

Abstract: A synoptic mechanism is proposed for a long-known, but synoptically little-studied, tropical influence on northern Victorian rainfall during the winter half-year, based on results from a 12 winter (June-September) climatology covering the period 1971–82. It is shown that heavy precipitation events in northern Victoria commonly result from ‘interactions’ between cloud masses originating at low latitudes within the Australian region, and high amplitude frontal troughs moving within the midlatitude westerly flow. Most of the precipitation falls ahead of surface cold fronts, within moist northerly airstreams. The low latitude cloud masses involved may originate in several ways, but most commonly take the form of so-called ‘northwest cloudbands’ originating over the tropical Indian Ocean northwest of Australia. ‘Interacting’ frontal systems contribute some 50 per cent of northern Victoria's winter precipitation, but the presence of a relatively modest topographical barrier across the centre of the State substantially reduces their contribution to total rainfall in southern and southeastern Victoria. A distinction is made between these ‘interacting’ (or I) fronts, and ‘non-interacting’ (NI) fronts: although I fronts occur less frequently than NI fronts, they produce considerably heavier rainfall. Analysis of the moisture content of prefrontal airmasses reveals that the airmasses ahead of I fronts are generally much moister than those ahead of NI fronts, and that the heavier I frontal rainfall is largely attributable to this moisture. An investigation is also made of moisture-rainfall relationships for cold lows, also a significant source of precipitation throughout Victoria.

Seasonal frequency variations in the 40–50 day oscillation

Abstract: The effect of local sea surface temperature changes on frequency shifts in the 40–50 day oscillation is examined using seasonal means. Data were stratified into ENSO (El Nino-Southern Oscillation) and non-ENSO years and a significant difference found. In non-ENSO years, a seasonal shift was noted at some sites. Seasonal frequency means were described qualitatively in terms of sea surface temperatures and changes in zonal circulation cells.

Changing rainfall patterns in Western Sudan

Abstract: Rainfall series to 1986 have been examined for North Darfur and North Kordofan. Annual and monthly series are presented and analysed. Relatively dry conditions have persisted in this region since 1966 due mainly to a decline in rainfall during July, August and September, the critical months for the annual agricultural cycle. Changes in daily rainfall magnitude and frequency are examined for these four rainy season months. It is recommended that agricultural planning and government policies be based on recent meteorological patterns.

Statistical analysis of freezing temperatures in Central and Southern Florida

Abstract: The probability distributions of the number of freezing periods per year, their timing and severity are examined at 25 stations in southern and central Florida. The proposed distributions, derived from stochastic crossing theory, provide adequate fits with the exception of three variables at different stations. The estimated parameter values reflect the changing geography of the freeze hazard. The freeze variable that exhibits the greatest variability over the area appears to be the number of periods, while the average severity of freezes and their timings are fairly homogeneous. The theoretical basis of the method permits estimation of the distribution of the dates of first and last freezes and the distribution of the coldest temperature likely to be encountered during any period of interest. The risks of periods of extremely cold temperatures, rarely observed in the historic records, may also be obtained from those at the more commonly encountered level. The technique provides a thorough yet easily interpreted summary of cold-spell risks at any location.

The low latitude influence on winter rainfall in Victoria, South-Eastern Australia. II: Relationships with the southern oscillation and Australian region circulation

Abstract: In this companion to Part I (Wright, 1988a) of the study on low latitude influences on Victorian rainfall, northern Victorian winter rainfall variability is shown to be dominated by ‘interacting’ (I) fronts, and both parameters are then related to atmospheric circulation anomalies in the Australian region and the Southern Oscillation. The major circulation features accompanying extreme wet and dry winter months in northern Victoria are identified from composited sea level pressure, 500 h Pa height, and 200 h Pa wind fields. Wet winters are characterized by a vigorous subtropical westerly circulation at middle and upper tropospheric levels, a relatively weak subtropical high pressure belt over Australia, and above normal amplitude of the climatological mean long-wave trough in western Australian longitudes. The intensity and frequency of I frontal systems influencing southeastern Australia is shown to be strongly related to these features, and to cloudiness over the tropical Indian Ocean northwest of Australia, a major source-region for cloudbands involved in the interactions. In turn, above normal trough amplitude and cloudiness, a weak subtropical high pressure belt, and frequent and relatively well-developed interactions, are all shown to be characteristic of winters in which the Tahiti-Darwin Southern Oscillation Index (SOI) is positive. Anomalies tend to be in the opposite sense during negative SOI winters, which feature infrequent, generally poorly developed, interactions, and much lighter rainfall. The dual association of these circulation and cloudiness features with both the SOI and northern Victorian rainfall strongly suggests that I fronts provide the well-known link between the SOI and northern Victorian rainfall. The current results are discussed in relation to results from other recent studies on synoptic associations with anomalous heat-sources.

On the reality of climatic changes in wind over the Pacific

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

The role of radiation geometry in the climate response of mount kenya's glaciers, part 2: Sloping versus horizontal surfaces

Abstract: This part of the study expands the modelling of incident solar radiation on Mount Kenya and its glaciers to include the behaviour for sloping as compared to horizontal surfaces. It is concluded that for the purposes of the ongoing climate study the broad-scale generalizations reached in part 1 of the study for horizontal reference surfaces remain inviolate for sloping reference surfaces. However, significant additional information is brought out by reference to sloping surfaces. Further, differences in absolute radiation magnitudes are significant for realistic situations of cloudiness and shading when modelling short-term (e.g. monthly) radiation means. In the annual case, these differences are small for glaciers having mean gradients up to 45°; for the one extremely steep glacier with mean slope approaching 60°, these differences are significant. It is anticipated that for higher latitudes the discrepancies between sloping and horizontal reference surfaces in the annual case may well be more substantial. For Mount Kenya, located as it is almost directly under the Equator, it must be concluded that the conventional horizontal reference surface is indeed appropriate for climatic heat and mass budget analyses.