This review paper presents an assessment of the current state of knowledge and capability in seasonal climate prediction at the end of the 20th century. The discussion covers the full range of issues involved in climate forecasting, including (1) the theory and empirical evidence for predictability; (2) predictions of surface boundary conditions, such as sea surface temperatures (SSTs) that drive the predictable part of the climate; (3) predictions of the climate; and (4) a brief consideration of the application of climate forecasts. Within this context, the research of the coming decades that seeks to address shortcomings in each area is described. Copyright © 2001 Royal Meteorological Society

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Current Approaches to Seasonal to Interannual Climate Predictions

Quasi-periodicities in annual rainfall totals over southern Africa have been identified; in particular, an approximately 18-year cycle may be related to interdecadal variability in sea-surface temp...

Climatic variability and change over southern Africa: a reflection on underlying processes:

The temporal characteristics of rainfall variability in Africa are examined using departure series for 84 regions of the continent and five larger-scale zones. The forms of non-randomness which are investigated include linear trends, persistence and quasi-periodic fluctuations. No long-term trends in African rainfall are evident. In some sectors, most noteably along the Benguela coast and equatorial Africa, rainfall anomalies tend to persist over several months and interseasonal correlations are also high. Spectral analysis revealed significant quasi-periodicities clustered in four bands at 2.2–2.4, 2.6–2.8, 3.3–3.8 and 5.0–6.3 years. These are common throughout equatorial and southern Africa, but only weakly evident in northern Africa. A cross-spectral analysis with the Southern Oscillation suggests a strong influence on rainfall variability in southern Africa and parts of the equatorial region and minimal influence in northern Africa. Coherence with the Southern Oscillation is particularly strong in the QBO range of 2.2–2.4 years. In general, the co-spectra suggest an inverse relationship between the SOI and rainfall in equatorial regions (i.e., higher rainfall during low-index years) and a positive relationship with rainfall in most other regions where an influence can be demonstrated.

The quasi-periodic behavior of rainfall variability in Africa and its relationship to the southern oscillation

Many and varied claims have been made over many years for a relationship between weather or climate and solar variations, notably sunspot cycles. Those relating primarily to the single and double sunspot cycles (of about 11- and 22-year quasi-periodicities) are critically reviewed in the light of what is known about solar variations, the observed variability of weather and climate, and possible physical connections between the two. Various pitfalls in the application or lack of application of statistics to the problem are discussed and illustrated from the literature. Following a survey of the literature it is concluded that despite the great number of recent papers on the subject, little convincing evidence has yet been produced for real correlations between sunspot cycles and the weather/climate on the 11- and 22-year time scales, although evidence for correlations with solar events on time scales of days appears to exist. The state of the literature in this particularly controversial area must raise doubts as to the prevailing standards of objectivity and critical analysis in other areas of science as well. Clearly, in the case of sun-weather relationships, further research requires much higher standards of objectivity, with the rigorous and critical application of statistics, and step by step investigation of hypothetical mechanisms. This criticism is not addressed to the recent studies of apparently significant correlations between certain meteorological indices and the passage of interplanetary magnetic sector boundaries; however, the relevance of such correlations to time scales of climatic interest has yet to be demonstrated.

A critical look at long-term Sun-weather relationships

Surfers at Durban, South Africa, reveal a tendency to cluster in a number of different spaces off the bathing beaches. While this activity appears to function in a social environment that is at the same time companionable, competitive or exclusive, the manner in which the usually robust interaction with the material environment contributes to the construction of surfing space is not visibly evident to the outsider. A survey reveals that surfers construct surfing space out of images of a normative wave environment and practices and processes that are both sensory and social. Images of the perfect wave that describe the normative wave environment sought by surfers are acquired from surfing magazines and other media sources. Knowledge of wave shapes, winds and currents is provided by sensory-derived experience gained in the waves. Individual and group attitudes and behaviour in surfing spaces are socially constructed around issues of identity and exclusion. The path of surfing space construction is shown to ...

Constructions of surfing space at Durban, South Africa

By fitting a trigonometrical regression model to a regionally averaged time series for the period 1910–72, and by extrapolation to the year 2000, an estimate of future extended wet and dry spells has been made for the summer rainfall region of South Africa. It is suggested that the periods 1972–81 and 1991–2000 will experience above normal rainfall and the period 1981–90 will be drier than normal. Results to date show that mean regional rainfall for the hydrological years 1972–73 to 1975–76 has conformed to the suggested pattern.

Estimating Above and Below Normal Rainfall Periods over South Africa, 1972–2000

Observations are presented to show the occurrence of boundary layer oscillations in the form of widespread and large-scale topographically-induced mountain-plain and plain-mountain winds over the deeply dissected eastern plateau slopes of Natal. By night, extensive northwesterly advection of cool air occurs between the Drakensberg escarpment zone and the coast; by day, the flow is reversed and southeasterly inland advection is characteristic of clear, fine conditions. The distinctive temporal and spatial characteristics of regional winds correspond in a near-ideal manner to those expected in a thermodynamically direct circulation caused by the diurnal cycle of insolation.

P. D. Tyson

Papers

Estimating Above and Below Normal Rainfall Periods over South Africa, 1972–2000

Observations of Regional Topographically-Induced Wind Systems in Natal