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A survey of publicly available data from the Intergovernmental Panel on Climate Change (IPCC) suggests that the Middle East will become significantly drier as greenhouse gas levels rise – with potentially devastating consequences. Simulating the climate of the eastern Mediterranean and the Middle East is, however, a tough challenge for climate models and those results should be interpreted with caution. The cyclones which migrate from west to east across the Mediterranean in winter and early spring, and which deliver much of the annual precipitation to the Middle East, are not well resolved by global climate models of the type included in the IPCC archive. Furthermore, the local climate is modified by coastlines and mountains throughout the region. For these reasons we provide a supplement to the IPCC results with simulations from a regional climate model. As in the global models, the regional model projects that, under an A2 (business-as-usual) scenario, precipitation will decrease significantly in the Middle East. Further investigation of the daily statistics of the weather, along with tracking of weather systems in the present day and future climate scenarios, suggest that the dominant mechanism for these changes is a reduction in the strength of the Mediterranean storm track. The Mediterranean storm track is fairly well simulated by the regional climate model, increasing confidence in this projection. […]
In this chapter, we develop an improved understanding of the Mediterranean's past climate through a series of ‘time-slice’ climate integrations relating to the past 12,000 years, performed using a version of the Met Office Hadley Centre's global climate model (HadSM3). The output is dynamically downscaled using a regional version of the same model to offer unprecedented spatial detail over the Mediterranean. Changes in seasonal surface air temperatures and precipitation are discussed at both global and regional scales along with their underlying physical drivers.
In the experiments the Mediterranean experiences more precipitation in the early Holocene than the late Holocene, although the difference is not uniform across the eastern Mediterranean. The results suggest that there may have been a relatively strong reduction in precipitation over the eastern Mediterranean coast during the period around 6–10 thousand years before present (kaBP). The early Holocene also shows a stronger seasonal cycle of temperature throughout the Northern Hemisphere but, over the northeast Mediterranean, this is mitigated by the influence of milder maritime air carried inland from the coast.
Understanding the changes in the Mediterranean climate during the Holocene period is a challenging problem, but one that is critical to interpreting long-term change in human settlement. The region at present displays marked seasonality with dry, hot summers and cool, wet winters.
The arid climate of the Middle East means that variations in rainfall on all timescales from days to years have an enormous impact on the people who live in the region. Understanding this variability is crucial if we are to interpret model simulations of the region's climate and make meaningful predictions of how the climate may change in the future and how it has changed in the past (Chapters 3 and 4). This study uses rain gauge measurements in conjunction with other meteorological data to address the following questions. How does rainfall vary from day to day and from year to year? How does rainfall vary spatially within Jordan and Israel? How does the atmospheric circulation over the Mediterranean region affect the daily probability of rain? What effect do large-scale modes of variability such as the North Atlantic Oscillation have on rainfall variability in the region?
Variability in precipitation has posed a considerable challenge to the population of the Middle East throughout the Holocene, and continues to be a key issue today. Understanding this variability is crucial for the design and interpretation of climate model experiments that characterise how precipitation has changed in the past and predict how it will change in the future.
Some people with phenylketonuria who were born before screening began were never treated and are still alive. Here we report that far fewer people with untreated phenylketonuria were detected than are thought to exist (about 2000). The majority of those traced had high support needs, challenging behaviour and other symptoms of phenylketonuria. No significant differences were found between those who had or had not tried the phenylalanine-restricted diet. A randomised controlled trial is required to examine the effect of trying the low-phenylalanine diet for people with untreated phenylketonuria.
A physical discussion of vorticity and its change by stretching and tilting is presented. The discussion naturally leads on to the conservation of quasi-geostrophic potential vorticity, q, and the flow associated with anomalies in q. The extension to full potential vorticity (PV) and the associated conservation and inversion properties is made. The use for illustrating and understanding synoptic developments of maps of PV on isentropic surfaces and potential temperature (θ) on PV surfaces is shown by considering two recent examples in the North Atlantic-Europe regions. The first is a summer situation and the second is the major blocking in January 1996. Concluding comments about the role of diabetic processes and other possible uses of these diagnostics are made.
An analytical study is made of simple models of steady fronts in the atmosphere in which the temperature field is subjected to deformation as the fluid moves downstream in a large-scale horizontal flow. One fundamental approximation is made and then a Lagrangian method, in which fluid particles are identified by conservation of entropy and potential vorticity, and by Bernoulli's theorem, enables the steady problem to be solved. Solutions for models of surface fronts and upper tropospheric fronts are compared with those obtained from a model in which there is no variation along the front and the frontogenesis proceeds in time. If the thermal wind is comparable with the basic wind, and the potential vorticity is not negligible in some sense, the frontogenesis is increased where the thermal wind opposes the basic flow but, decreased where it reinforces the flow.
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