The angular momentum constraint on climate sensitivity and downward influence in the middle atmosphere

It is shown that under reasonable assumptions, conservation of angular momentum provides a strong constraint on gravity wave drag feedbacks to radiative perturbations in the middle atmosphere. In the time mean, radiatively induced temperature perturbations above a given altitude z cannot induce changes in zonal mean wind and temperature below z through feedbacks in gravity wave drag alone (assuming an unchanged gravity wave source spectrum). Thus, despite the many uncertainties in the parameterization of gravity wave drag, the role of gravity wave drag in middle-atmosphere climate perturbations may be much more limited than its role in climate itself. This constraint limits the possibilities for downward influence from the mesosphere. In order for a gravity wave drag parameterization to respect the momentum constraint and avoid spurious downward influence, any nonzero parameterized momentum flux at a model lid must be deposited within the model domain, and there must be no zonal mean sponge layer. Examples are provided of how violation of these conditions leads to spurious downward influence. For planetary waves, the momentum constraint does not prohibit downward influence, but it limits the mechanisms by which it can occur: in the time mean, downward influence from a radiative perturbation can only arise through changes in reflection and meridional propagation properties of planetary waves.

Late Quaternary hydrological dynamics in the Middle Kalahari: forcing and feedbacks

The Kalahari region has become a major source of Quaternary palaeoenvironmental data derived primarily from the analysis of geomorphological proxies of environmental change. One suite of data, from palaeolacustrine landforms, has recently provided a new record of major hydrological changes in the last 150 ka [Burrough, S. L., Thomas, D. S. G., Bailey, R. M., 2009. Mega-Lake in the Kalahari: A Late Pleistocene record of the Palaeolake Makgadikgadi system. Quaternary Science Reviews, in press.]. Here we present an improved analysis of the drivers and feedbacks of lake level change, utilising information from three main sources: data from the lake system itself, from analyses of other late Quaternary records within the region and from climate modelling. Simulations using the Hadley Centre coupled climate model, HadCM3, suggest that once triggered, the lake body was large enough to potentially affect both local and regional climates. Surface waters and their interactions with the climate are therefore an important component of environmental dynamics during the late Quaternary. Through its capacity to couple Middle Kalahari environments to distant forcing mechanisms and to itself force environmental change, we demonstrate that the existence or absence of megalake Makgadikgadi adds a new level of complexity to the interpretations of environmental proxy records in southern Africa's summer rainfall zone.

A review of drought in the Middle East and Southwest Asia

The Middle East and Southwest Asia comprise a region that is water-stressed, societally vulnerable, and prone to severe droughts. Large-scale climate variability, particularly La Niña, appears to play an important role in region-wide drought, including the two most severe of the last fifty years—1999-2001 and 2007-2008—with implications for drought forecasting. Important dynamical factors include orography, thermodynamic influence on vertical motion, storm track changes, and moisture transport. Vegetation in the region is strongly impacted by drought and may provide an important feedback mechanism. In future projections, drying of the eastern Mediterranean is a robust feature, as are temperature increases throughout the region, which will affect evaporation and the timing and intensity of snowmelt. Vegetation feedbacks may become more important in a warming climate. There are a wide range of outstanding issues for understanding, monitoring, and predicting drought in the region, including: dynamics of the regional storm track, the relative importance of the range of dynamical mechanisms related to drought, regional coherence of drought, the relationship between synoptic-scale mechanisms and drought, predictability of vegetation and crop yields, stability of remote influences, data uncertainty, and the role of temperature. Development of a regional framework for cooperative work and dissemination of information and existing forecasts would speed understanding and make better use of available information.

Rerum Britannicarum medii ævi scriptores, or, Chronicles and memorials of Great Britain and Ireland during the Middle Ages.

Mode of access: Internet.

The classical heritage of the middle ages,

"New and revised edition [first] published October, 1911."

The classical heritage of the Middle Ages.

Mode of access: Internet.

Sketches, graphic and descriptive, &c. for a history of the decorative painting applied to English architecture during the middle ages.

Binder's title: History of decorative painting.

The history of the middle ages.

Mode of access: Internet.

A history of the Inquisition of the middle ages.

Mode of access: Internet.

History of Europe during the middle ages,

Plates accompanied by guard sheets with descriptive letterpress.

The study-book of mediæval architecture and art; being a series of working drawings of the principal monuments of the middle ages. Whereof the plans, sections, and details are drawn to uniform scales.

Mode of access: Internet.

The history of England during the middle ages.

v.1. Comprising the reigns from the Norman conquest to the accession of Edward the Third.--v.2. From the accession of Edward the Third to the reign of Edward the Fourth.--v.3. Comprising the reigns of Edward the Fourth, Edward the Fifth, Richard the Third, and Henry the Seventh, and the first part of the literary history of England.--v.4. Containing the conclusion of the literary history of England.

The history of the popes from the close of the Middle Ages. Drawn from the secret archives of the Vatican and other original sources.

Vols.1-6 edited by F. I. Antrobus; Vols. 7-24 edited by R. F. Kerr; Vols.25-34 edited by Ernest Graf; Vols. 35- edited by E. F. Peeler.