Abstract:The Saudi Arabia (SA) climate varies greatly, depending on the geography and the season. According to Köppen and Geiger, the climates of SA is "desert climate". The analysis of the seasonal rainfall detects that spring and winter seasons have the highestrainfall incidence, respectively. Through the summer,small quantities of precipitation are observed, while autumn received more precipitation more than summer season considering the total annual rainfall. In all seasons, the SW area receives rainfall, with a maximum in spring, whereas in the summer season, the NE and NW areas receive very little quantities of precipitation. The Rub Al-Khali (the SE region) is almost totally dry. The maximum amount of annual rainfall does not always happen at the highest elevation. Therefore, the elevation is not the only factor in rainfall distribution.A great inter-annual change in the rainfall over the SA for the period ) is observed. In addition, in the same period, a linear decreasing trend is found in the observed rainfall, whilst in the recent past (1994-2009) a statistically significant negative trend is observed. In the Southern part of the Arabian Peninsula (AP) and along the coast of the Red Sea, it is interesting to note that rainfall increased, whilst it decreased over most areas of SA during the 2000-2009 decade, compared to 1980-1989.Statistical and numerical models are used to predict rainfall over Saudi Arabia (SA). The statistical models based on stochastic models of ARIMA and numerical models based on Providing Regional Climates for Impact Studies of Hadley Centre (PRECIS). Climate and its qualitative character and quantified range of possible future changes are investigated. The annual total rainfall decreases in most regions of the SA and only increases in the south. The summertime precipitation will be the highest between other seasons over the southern, the southwestern provinces and Asir mountains, while the wintertime rainfall will remain the lowest.The climate in the SA is instructed by the El Niño Southern Oscillation (ENSO) and other circulations such as centers of high and low pressure,
Mean wintertime temperatures (December, January, February) recorded during the period 1905-2000 at 18 weather stations distributed across Egypt were analysed to reveal spatial and temporal patterns of long-term trends. The relationship between winter atmospheric circulation indices and winter temperature in Egypt is examined using correlation analysis. The atmospheric circulation is represented by four indices: the well-known El Niño-southern oscillation (ENSO), North Atlantic oscillation (NAO) index, East Atlantic-West Russia (EAWR) index, and East Atlantic (EA) index.Surface temperature is a stable climatic element whose coefficient of variation (COV) is lower during winter. A statistically significant relation between COV and latitude indicates that stations in the south, Upper Egypt, are more variable than stations in the north, Lower Egypt. Increasing and decreasing winter surface temperature trends were found. In general, wintertime temperature has increased (warming) at most stations. Decreasing trends (cooling) are observed mainly over Upper Egypt. The upward trends in mean winter temperature during the 1910s-30s, mid 1970s, and early 1980s-2000 and the downward trends during the 1940s and 1960s are prominent features of the temporal distributions. The warming period that occurred early in the century may be explained by changes in circulation. Striking upward trends are most remarkable during the last 20 years. This could be attributed not only to human activities, but also to atmospheric circulation changes. No detectable connection between Egypt temperature and either ENSO or EA index was found during winter. A statistically significant negative relationship between winter temperature and winter NAO index can be observed. The NAO index is more dominant in determining winter temperature than ENSO circulation. A significantly stronger negative relationship between temperature over Egypt and the winter EAWR index values is detected.
Based on generated time series of the central pressure of the subtropical high, the behaviour of this atmospheric centre of action has been examined since 1950 with regard to the inter-annual variations, persistence, linear trends, abrupt change, spectral analysis and interactions. The year-to-year variations in the central pressure of the subtropical high are considerable. The pronounced strengthening of the subtropical high during approximately the last 20 years is its most remarkable feature. Variations in the subtropical high's intensity seem to follow a cyclic pattern. Statistically significant abrupt onset events are found, with the majority occurring in winter. Increasing and decreasing episodes have occurred in the late 1960s and early 1980s. According to spectral analysis, it can be assumed that the centre of action of the subtropical high is characterized by non-periodic behaviour. The peaks occur only at the lowest frequency. The quasibiennial oscillation may affect the subtropical high in the winter season, whereas the North Atlantic Ocean may affect the subtropical high in summer. There is no detectable connection between El Niño-southern oscillation and the subtropical high in either season. The subtropical high has been affected by sea-surface temperatures of the north and south tropical Atlantic, with negative and positive signs respectively in the winter season. Interactions between the subtropical high and sea-surface temperatures over the tropical Atlantic Ocean are absent in the summer season.
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