Using Dummy Variables to Estimate Economic Base Multipliers

Economic base analysis is a cost-effective and accurate means of predicting employment impacts in relatively small and uncomplicated regional (community) economies. Extending previous research using the Arizona Community Data Set, this paper estimates economic base multipliers in different types of communities by introducing dummy variables into regression equations. Total employment, transfer payments, and population potential are used as explanatory variables. Manufacturing centers are shown to have larger multipliers than diversified places, mining settlements, service and trade communities, and utility towns.     

Role of methane clathrates in past and future climates

Methane clathrates are stable at depths greater than about 200 m in permafrost regions and in ocean sediments at water depths greater than about 250 m, provided bottom waters are sufficiently cold. The thickness of the clathrate stability zone depends on surface temperature and geothermal gradient. Average stability zone thickness is about 400 m in cold regions where average surface temperatures are below freezing, 500 m in ocean sediments, and up to 1,500 m in regions of very cold surface temperature (<-15 °C) or in the deep ocean. The concentration of methane relative to water within the zone of stability determines whether or not clathrate will actually occur. The geologic setting of clathrate occurrences, the isotopic composition of the methane, and the methane to ethane plus propane ratio in both the clathrates and the associated pore fluids indicate that methane in clathrates is produced chiefly by anaerobic bacteria. Methane occurrences and the organic carbon content of sediments are the bases used to estimate the amount of carbon currently stored as clathrates. The estimate of about 11,000 Gt of carbon for ocean sediments, and about 400 Gt for sediments under permafrost regions is in rough accord with an independent estimate by Kvenvolden of 10,000 Gt.The shallowness of the clathrate zone of stability makes clathrates vulnerable to surface disturbances. Warming by ocean flooding of exposed continental shelf, and changes in pressure at depth, caused, for example, by sea-level drop, destabilize clathrates under the ocean, while ice-cap growth stabilizes clathrates under the ice cap. The time scale for thermal destabilization is set by the thermal properties of sediments and is on the order of thousands of years. The time required to fix methane in clathrates as a result of surface cooling is much longer, requiring several tens of thousands of years. The sensitivity of clathrates to surface change, the time scales involved, and the large quantities of carbon stored as clathrate indicate that clathrates may have played a significant role in modifying the composition of the atmosphere during the ice ages. The release of methane and its subsequent oxidation to carbon dioxide may be responsible for the observed swings in atmospheric methane and carbon dioxide concentrations during glacial times. Because methane and carbon dioxide are strong infrared absorbers, the release and trapping of methane by clathrates contribute strong feedback mechanisms to the radiative forcing of climate that results from earth's orbital variations.Gordon J. MacDonald is Vice President and Chief Scientist of The MITRE Corporation, 7525 Colshire Drive, McLean, VA 22102.     

Icy craters on the Galilean satellites?

A model which possibly accounts for the unusual radar scattering behavior observed for Europa, Ganymede, and Callisto postulates a thick surface layer of ice saturated with nearly hemispherical craters. In the development of this model it is noted that a single reflection at normal incidence reverses the rotational sense of circularly polarized incident radiation, in conflict with the radar observations which show an echo predominantly not reversed. Furthermore, an ensemble of backscattering events, each the result of a large number of successive dielectric reflections, tends to produce a weak and unpolarized echo. However, two coupled reflections can produce the observed backscattering behavior, provided the angles of incidence lie between the Brewster angle and its complement. The effect is maximum when the angles equal 45°, and, for water ice, yields a ratio of 1.9 for components of the echo received in rotational senses the same as, and opposite to, the sense transmitted. Randomly oriented reflecting facets, either of ice on the surface or of rocks in the interior, cannot yield the observed behavior since too few of the total possible backscattering configurations meet the above requirement. Hemispherical surface craters, on the other hand, favor 45° dual reflection. A model consisting of such craters in ice is investigated and found capable of explaining the observed results, not only in respect to polarization, but in respect to albedo and angular scattering law as well.     

The structure of the temperature minimum region in solar flares and its significance for flare heating mechanisms

We analyze Ca ii K-line profiles of one flare and EUV continuum observations of two other flares in order to infer values for the temperature enhancements (over active region values) produced in the upper photosphere around and above the temperature minimum region. The results, obtained through a partial redistribution calculation of the Ca ii K-line profiles and an LTE approach to the continuum observations, show that the flare temperature minimum is depressed some two scale heights below its preflare level, and that substantial temperature enhancements are produced even at this depth. Estimates for the energy release in these photospheric layers are given, and are found to be comparable with that released in chromospheric H and L emission.We then turn our attention to the investigation of possible heating mechanisms which might be responsible for the observed enhancements. Bombardment by both electrons and protons, and irradiation by soft X-rays, are each considered and found to be largely ineffective, due to the large attenuation of flux by photospheric depths, unless new ideas on the precise nature of these mechanisms are invoked, particularly if the same mechanism is also to explain the observed chromospheric emissions. We therefore conclude that it is most likely that some other mechanism must be advocated in order to explain the observed heating. Possibilities for this are (a) heating by EUV radiation, (b) proton beams with low dispersion energy spectra centered around 10–20 MeV, and (c) localized heating at temperature minimum levels.On leave from: Department of Astronomy, The University, Glasgow G12 8QQ, Scotland, United Kingdom.     

Canonical Correlation Analysis and climate research

Correlation analysis as used by meteorologists and oceanographers is a tool for the analysisof the spacial or temporal variability of physical fields. In his notes, Dr. Hasselmann pro-posed to combine correlation analysis and linear regression analysis in climate prediction re-search. The main idea is to decompose the physical field into its principal oscillation patterns.     

Incorporating the dynamics of marine systems into the stock assessment and management of sablefish

Progress in ecosystem management requires the characterisation of the dynamics of a species's ecosystem and the influences of climatic oscillations on those dynamics. Within the North Pacific, ecosystem dynamics have been described on decadal-scales (regimes) and have been shown to shift abruptly (regime shifts). The year class success of sablefish (Anoplopoma fimbria) exhibit decadal-scale patterns that relate to decadal-scale patterns in North Pacific climate–ocean conditions. As an example, and a step towards, incorporating the dynamics of marine systems into the stock assessment and management of sablefish, we produce a ‘report card’ that characterises the species's ecosystem on decadal-scales. This report card consists of a matrix of climatological and oceanographic indices for the North Pacific, and regional environmental and biological indices. It indicates that both Pacific-wide and regionally, conditions were generally good for sablefish year class strength during the 1977–1988 regime, but these favourable conditions did not persist into the 1990s. Exploitation scenarios can be developed around the decadal-scale dynamics in sablefish year class success and their life history, in particular longevity. Fisheries managers can begin to develop exploitation strategies that acknowledge these changes in the sablefish ecosystem. The report card presents an aggregation of parameters that, on average, gives an impression of productivity during a specific regime and can be used to augment present stock assessment and management efforts.     

Intra- and inter-species differences in persistent organic contaminants in the blubber of blue whales and humpback whales from the Gulf of St. Lawrence, Canada

Biopsy samples of blubber from adult male and female blue whales, and from female and young-of-the-year humpback whales were collected during the summers of 1992-1999 in the Gulf of St. Lawrence, Canada. In blue whales, concentrations of 25 PCB congeners, DDT and metabolites and several other organochlorine compounds were present at higher concentrations in the blubber of males relative to females; reflecting maternal transfer of these persistent contaminants from females into young. Sex-related differences in concentrations were not observed with less persistent contaminants, such as HCHs. In humpback whale samples, there were no significant differences in the concentrations of PCBs and organochlorine compounds in the blubber of females and calves. These data indicate that calves quickly bioaccumulate contaminants by transplacental and lactational routes to concentrations that are in equilibrium with females. In comparisons between contaminant concentrations and patterns in the blubber of female blue and humpback whales, there were no significant differences in concentrations, but the proportions of some PCB congeners, HCH isomers, and DDT and its metabolites were different in the two baleen whale species. These may reflect differences in the diet of the two species, since fish comprise a large part of the diet of humpback whales and blue whales feed exclusively on euphausiid crustaceans (i.e. krill).     

Pleistocene forest on Tenerife's southern coast: a case study of Montaña Negra

Montaña Negra is a 121 m cinder cone in the Bandas del Sur region of southern Tenerife. Formed in the Middle Pleistocene, it comprises alternating phonolitic pumice deposits and scoria layers; the latter are extremely fossiliferous with good taphonomical fidelity. ⁴⁰Ar/³⁹Ar age determination provides new dates of 302 ± 7.6 ka and 299.9 ± 11.4 ka for the Lower and Upper Aldea Blanca pumice fall deposits, respectively. This chronological constraint allows comparison of the palaeo‐habitat with the global climate at the time of pyroclastic activity. Abundant terrestrial gastropod species and rare disarticulated Coleoptera fragments are to be found. The occurrence of the endemic semi‐slug genus Plutonia (Family Vitrinidae) is significant in indicating a woodland habitat in the region during the Middle Pleistocene. We suggest that this may have been forest, possibly dominated by laurel, which is in stark contrast to the present‐day semi‐desert. Copyright © 2011 John Wiley & Sons, Ltd.