Evidence for Absorption in NGC 1068

We present evidence that interstellar absorption is responsible for producing much of the complex morphology seen in the inner few arcseconds of NGC 1068. This revised version was published online in July 2006 with corrections to the Cover Date.     

Notes and correspondence

Abstract

This paper is an expansion of the lectures presented by the authors at the Canadian Middle Atmosphere Model (CMAM) summer school, 25–29 August 1997. It attempts to fulfill several goals as did the curriculum for the summer school. Firstly, it has a large tutorial component allowing newcomers a rapid introduction to the field, secondly it surveys the field of stratospheric chemistry, and thirdly it attempts to bring the reader to the forefront of some of the problem areas in stratospheric chemistry. As such, it includes much background information such as the magnitude of rate coefficients, photolysis rates and their calculation and time constants. The intended audience is individuals about to commence study or research in the field of atmospheric chemistry or established atmospheric scientists in other areas wishing to expand their knowledge of this topic.

The basic chemistry of the ozone layer is described with an emphasis on the catalytic cycles and the equilibria between “reservoir” and “active” species. To this end, a compendium of the important aspects of heterogeneous chemistry is also provided. The application of box (0‐dimensional) and more elaborate (1‐, 2‐ and 3‐dimensional) models to compare and validate with measurements is discussed. Also, factors affecting the present and future trends in ozone concentration, both at mid‐latitudes and in the polar region, are presented.     

Severe summer ice in Hudson Strait and Hudson Bay following major volcanic eruptions, 1751 to 1889 A.D.

Indices of summer sea ice severity in the eighteenth and nineteenth centuries have been reconstructed from sailing ships' log-books. The ice record for Hudson Strait extends from 1751 to 1889. Ice records are available for two parts of Hudson Bay and these extend from 1751 to 1870. The three records were derived from the same sources but the method of derivation applied in the bay was different to that applied in the strait. The years having the five largest ice indices in each of these records were identified. Also identified were the years in which major volcanic eruptions occurred between 1751 and 1889. The number of concurrences between the years with severe ice in Hudson Strait and the years with major eruptions was significant at the 99.5% level. In the western part of Hudson Bay this significance level was 95%. The years with severe ice in eastern Hudson Bay did not concur with major eruptions.     

Resolving the discard problem—A case study of the English Nephrops fishery

The phenomenon of discarding was studied using a multidisciplinary approach to allow the integration of biological, social and economic data. The research aimed to evaluate the strength of the case to reduce discarding in a single case study fishery, the English Nephrops fishery; to identify specific objectives for discard reduction; to identify factors that inhibit discard reduction and to determine the best means of achieving those objectives. Changes in trawl structure offered the best solution while having the least impact on fishing opportunities. However, the inadequate level of incentive was identified as the main impediment to discard reduction rather than the lack of technical ability. To implement effective measures to reduce discarding in this fishery, an increased level of incentive is required. Three measures are identified as a means to achieve this.     

Summer sea ice severity in Hudson Strait, 1751–1870

Annual indices of sea ice severity in Hudson Strait, for the period 1751 to 1870, are derived from written historical evidence contained in ships' log-books. These logs were all kept on Hudson's Bay Company ships sailing from London to the Company's trading posts. The log-books are homogeneous in nature and this property facilitates their numerical interpretation. The annual indices are subjected to face validity testing which indicates that they may plausibly be accepted as measures of sea ice severity. The results are examined in relation to the presentday behaviour of sea ice in Hudson Strait and they provide evidence that the summer severity of ice conditions is mainly determined by atmospheric circulation conditions.