Effect of remote forcings on the winter precipitation of central southwest Asia part 1: observations

Summary We investigate the effects of the North Atlantic Oscillation (NAO) and the El Nino Southern Oscillation (ENSO) on winter precipitation in Central Southwest Asia (CSWA) using an analysis of available observed climate data. The analysis is based on correlations, composites and Singular Value Decomposition (SVD) performed using the gridded dataset of the Climatic Research Unit (CRU) and station data for the region. We find that both the NAO and ENSO affect climate over the region. In particular a positive precipitation anomaly is typically found in correspondence of the positive NAO phase and warm ENSO phase over a sub-region encompassing northern Pakistan, Afghanistan, Tajikistan and southern Uzbekistan. This conclusion is supported by a consistency across the different analysis methods and observation datasets employed in our study. A physical mechanism for such effect is proposed, by which western disturbances are intensified over the region as they encounter a low pressure trough, which is a dominant feature during positive NAO and warm ENSO conditions. Our results give encouraging indications towards the development of statistically-based prediction tools for winter precipitation over the CSWA region.     

Depositional history of organic contaminants in Narragansett Bay, Rhode Island, USA

Sediment cores were taken at three locations in Narragansett Bay, Rhode Island, USA in 1997 and analyzed for a variety of organic contaminants including polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), chlordanes, linear alkyl benzenes (LABs), benzotriazoles (BZTs) and dichlorodiphenyltrichloroethanes (DDTs) and metabolites. The distributions of these chemicals at Apponaug Cove and in the Seekonk River indicate that there was a disturbance in the depositional environment relative to cores collected at these locations in 1986 demonstrating the potential for buried contaminants to be remobilized in the environment even after a period of burial. Sharp breaks in the concentration of several organic markers with known dates of introduction were successfully used to determine the sedimentation rate at Quonset Point. Both the Quonset Point and Seekonk River cores had subsurface maximums for DDTs, PCBs, PAHs and BZTs, which are consistent with expected inputs to the environment. The Apponaug Cove core showed an increase of most contaminants at the surface indicating a recent event in which more contaminated sediments were deposited at that location.     

The magnetic fabric of some Irish Granites

Magnetic anisotropy measurements have been made on fifty-four oriented samples from the Carna and Screeb areas of the Galway Granite, and from the Ardara pluton and the Main Granite (including the Trawenagh Bay Granite) in Donegal. The origin of magnetic anisotropy in plutonic magnetic rocks is discussed, and it is concluded that it is probably due to grain alignment of inequant magnetite, which may occur either as free grains or as secondary inclusions in ferromagnesian minerals. The grain alignment may occur either whilst the magma is essentially fluid, giving a magnetic lineation transverse to the flow, or at a much later stage of consolidation during plastic deformation, in which case the magnetic lineation parallels the direction of greatest elongation. The results of the measurements are consistent with macroscopic foliations and lineations where these have been observed, but also indicate the existence of fabrics too weak to observe by conventional methods. This is because the magnetic method assesses the alignment of a very large number of grains, and is therefore much more sensitive than conventional fabric analysis. The weak fabrics can be qualitatively explained in terms consistent with other evidence relating to the emplacement of the granites, and experimental work now in progress may make possible a more quantitative interpretation.