Celine Herweijer

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The causes of persistent droughts and wet periods, or pluvials, over western North America are examined in model simulations of the period from 1856 to 2000. The simulations used either (i) global sea surface temperature data as a lower boundary condition or (ii) observed data in just the tropical Pacific and computed the surface ocean temperature elsewhere(More)
Unlike the major droughts of the twentieth century that are readily identified in the instrumental record, similar events in the nineteenth century have to be identified using a combination of proxy data, historical accounts and a sparse collection of early instrumental records. In the USA, three distinct periods of widespread and persistent drought stand(More)
According to tree ring and other records, a series of severe droughts that lasted for decades afflicted western North America during the Medieval period resulting in a more arid climate than in subsequent centuries. A review of proxy evidence from around the world indicates that North American megadroughts were part of a global pattern of Medieval(More)
IPCC Assessment Report 4 model projections suggest that the subtropical dry zones of the world will both dry and expand poleward in the future due to greenhouse warming. The US Southwest is particularly vulnerable in this regard and model projections indicate a progressive drying there out to the end of the 21st century. At the same time, the USA has been(More)
[1] The role of tropical Pacific SSTs in driving global medieval hydroclimate is assessed. Using fossil coral records from Palmyra Atoll, tropical Pacific sea surface temperature (SST) boundary conditions are derived for the period 1320–1462 A.D. These boundary conditions consist of La Niña‐like mean state conditions in the tropical Pacific with(More)
The major North American droughts as per instrumental records are shown to be part of a larger, global pattern of low-frequency drought variability. Drought in western North America during the 1850s–1860s, 1870s, 1890s, 1930s and 1950s, is shown to coincide with the occurrence of prolonged dry spells in parts of Europe, southern South America and western(More)
At all longitudes oceanic evaporation rates are lower on the equator than at latitudes to the north and south. Over the oceanic cold tongues this is related to the presence of cold water and divergence of heat by the ocean circulation. Herein is investigated why there is also a minimum over the Indo-Pacific warm pool. Model results confirm the recent(More)
The small number of cases of Aujeszky's disease in goats referred to in the literature is stressed, and an outbreak in goats causing many deaths is reported. The flock of goats concerned was occasionally housed in a barn during the night in which there also were fattening pigs. The first deaths occurred without previous symptoms, the animals being found(More)
When deaths and symptoms of chronic emaciation not due to any apparent cause occurred in weaned lambs, the morphological changes observed suggested that the liver probably was the main organ, the function of which was impaired. This was believed to be so because of the homogenity of the changes in this organ and the disseminated character of the lesions of(More)