The Space-time characteristics of minimum and maximum temperature values over the tropical Eastern Africa region

This study examined the space-time characteristics of minimum and maximum temperature values over the Tropical Eastern Africa region in order to delineate any significant changes in the traditional space-time temperature characteristics over the region. The temporal characteristics investigated in the study included the inter-annual patterns of the trend, seasonal and cyclical variations at the individual stations. Both graphical and statistical methods were used in the trend analysis. In the graphical approach, visual examination of the inter-annual trend was used whilst analysis of variance (ANOVA) and non-parametric methods were used in the statistical approach The recurrences of low/high inter-annual temperature values were examined using the maximum entropy method (MEM) of spectral analysis The last part of the study attempted to provide some insight into the potential causes of the observed inter-annual variability in the temperature characteristics. ElNifio/Southern oscillation (ENSO), the Quasi-Biennial Oscillation (QBO), cloudiness, and OLR data were used in the study to quantify the regional/global scale systems that may be associated with the observed temperature characteristics Relationships between these systems and the observed temperature characteristics were investigated using Simple correlation analysis x" -tests were used in case of grouped minimum and maximum temperature observations r The data used in the study was from 53 stations with record lengths of 24 and 53 years. All the data were quality-controlled before they were used in any analysis Results of the quality-control analysis declared most of the temperature records within Tropical Eastern Africa to be homogeneous as most of the mass curves were linear. Instrumental records world-wide have been affected by changes in instrument types, IX changes in observational schedules and methods, and changes in the station environment. The inter-annual minimum and maximum temperature patterns showed distinct decadal variability signals in the observed minimum and maximum temperature records. The 1980’s decade was generally the warmest in record at most of the locations The late 1970’s and the early 1990’s were also relatively warm periods in most areas. These patterns were however reversed at maritime and lake areas The warming/cooling observed at some locations in recent years introduced significant linear trends when the records were subjected to trend analysis. The observed minimum and maximum temperature trend patterns however showed a lot of geographical and seasonal variations. Some locations did not indicate any significant trend signals. ' jt' Recurrences of extremely high/low values were the commonest feature of the inter-annual variability patterns of the minimum and temperature records Results of the spectral analysis showed recurrences of extremely high/low temperature values centred around four major spectral peaks namely, 2-2.9 years, 3-4 years, 4 5-6 5 years, and 1012.5 years Few spectral peaks also appeared with longer periods of recurrence The long-period cycles were however not statistically significant at most of the locations. The 2-2.9 years spectral peak was associated with the QBO whilst the 3-4 and 4.5-6 5 years peaks were associated with the inter-annual variability in ENSO characteristics. The 10-12.5 years cycle was associated with the solar variability cycle These quasi-periodic oscillations have also been observed in many other Climatic parameters over the region. They however explained a very small proportion of the total inter-annual temperature variation Results of the Simple correlation analysis indicated that both morning and afternoon cloudiness were negatively correlated with the observed minimum and maximum temperature values and the subsequent temperature range. Maximum temperature values were also found to be significantly correlated with QBO phases. Statistically significant correlations were also found between the minimum and maximum temperature values and the Southern Oscillation Index (SOI), especially for time-lagged