Temperature minimum heating in solar flares by resistive dissipation of Alfvén waves

We examine the possibility that the strong heating produced at temperature-minimum levels during solar flares is due to resistive dissipation of Alfvén waves generated by the primary energy release process in the corona. It is shown how, for suitable parameters, these waves can carry their energy essentially undamped into the temperature-minimum layers and can then produce a degree of heating consistent with observations.Also Department of Applied Physics, Stanford University.     

Impact of Climate, Moisture Regime, and Nutrient Regime on the Productivity of Douglas-Fir in Coastal British Columbia, Canada

Future climate change is expected to have many impacts on forest ecosystems. It is important to have some understanding of these impacts in order to make informed forest management decisions. A major consideration in making forest management decisions is the productivity of a site, as measured by site index. In this study, I relate Douglas-fir site index to accumulated growing degree-days greater than 5^°C (DD5), as well as to soil moisture and nutrient regime. This allows the impact of climate change on forest productivity to be estimated. A two step approach was followed. The first step derived models to estimate various climate variables to latitude, longitude, and elevation using data from climate stations. Then, these climate variables were used along with soil moisture and nutrient data to predict site index for the site index plots. A two step approach was taken because climatic data were not available for the site index plots. The trend was for site index to increase with both increasing soil moisture and nutrients, although the site index decreased on the wetter sites. Site index also increased with DD5 at the rate of 1.2 m for every increase of 100 units in DD5. These models can be used together to evaluate the impact of various climate change scenarios on site index.     

Metal binding capacity of selected maine surface waters

Concentrations of Ca, Cd, Cu, Fe, and Pb and binding capacities for Cd, Cu, and Pb were determined for water samples collected from 12 lakes in southwestern Maine using atomic absorption and ion-selective electrodes, respectively. Surface waters in this area are soft and characterized by low pH. Some lakes were highly colored with refractory organics, whereas others had very low organic carbon concentrations. Both Cu and Pb concentrations were positively correlated with organic carbon content. Copper and Pb binding capacities were significantly correlated with organic carbon content, whereas Cd binding capacity was positively correlated with pH, but not with organic carbon. Surface water binding capacity for Pb was greater than that for Cu or Cd. More than 99% of the Ca from all waters studied was removed onto cationic exchange resins. Less than 1% of the total Cu existed as cationic species in highly humic waters, whereas as much as 65% existed as cationic species in less huic waters. Conversely, more than 99% of the Cd present in humic waters existed as cationic species, whereas as little as 50% existed as cationic species in less humic, more alkaline waters. These correlative studies indicate that binding by organic carbon is important for both Cu and Pb in this area and must be considered in models of trace metal speciation. However, Cd binding in the same waters is not correlated with organic carbon, which does not need to be considered in speciation models for Cd.     

Polymerization of silicate and aluminate tetrahedra in glasses,melts, and aqueous solutions—I. Electronic structure of H6Si2O7, H6AlSiO71−, and H6Al2O72−

As part of a study of the effect of geologically common network modifiers on polymerization in silicate melts, glasses, and silica-rich aqueous solutions, we have studied the energies, electronic structures, and inferred chemical properties of ^IVT-O-^IVT linkages in the tetrahedral dimers H₆,Si₂O₇, H₆AlSiO₇^1?, and H₆Al₂O₇^2? using semi-empirical molecular orbital theory (CNDO/2). Our results indicate that the electron donating character of the bridging oxygen, O(br), linking two tetrahedra increases with increasing T-O(br) bond length but decreases with decreasing T-O(br)-T angles and increasing O-T-O(br) angles. This increase or decrease of the donor character of O(br) coincides with an increase or decrease of the affinity of O(br) for hard acceptors. The calculated electronic structure for the H₆Si₂O₇ molecule is compared with the observed X-ray emission, absorption, and photoelectron spectra of quartz and vitreous silica; the reasonable match between calculated and observed oxygen Kα emission spectra of vitreous silica supports our assertion that non-bonded O(br) electron density energetically at the top of the valence band controls the chemical reactivity of ^IVT-O-^IVT linkages in polymerized tetrahedral environments.     

The spatial context of manpower policy: Implications of current Canadian policy on regional development and planning

Macro government policies are often considered outside the context of their spatial impact. Following recent discussions of the problem, this paper is concerned with a critical review of Canadian Manpower policy in the context of national efficiency, regional equity and their interaction. Thus Manpower policy is analysed with respect to its implications concerning regional development as well as implicit regional policy. It is contended that many of the problems of Manpower policy in the spatial context can be traced back to the implicit theoretical background of Manpower policy; Human Capital theory. A radical critique of Human Capital theory is presented and a brief discussion of the ‘functional’ relationship between regional inequality and national macro-planning is also noted. In general the paper concludes that Manpower and regional policies in Canada tend to be contradictory although more research is needed to analyse the spatial impact of macro-policy which may overwhelm spatial policy and significantly influence the future of the spatial economy.     

Generation of homologous porphyrins under simulated geochemical conditions

Crude oils generally contain at least one symmetrical homologous series of porphyrins, which is usually centered at m/e 476 (DPEP) or m/e 478 (etioporphyrin). Simulated geochemical conditions in the present study resulted in decarboxylations and alkylations which ultimately led to the synthesis of homologous porphyrins from a single porphyrin. In several series of closed tube experiments, mesoporphyrin IX dimethylester (MPDME) was mixed with a variety of constituents including benzene, acetic acid, propionic acid, water and clay; the experiments were performed at temperatures between 135°C and 400°C at time intervals up to 80 days. Dealkylation, alkylation, hydrolysis, decarboxylation and metallation products were observed. An unsymmetrical homologous series of porphyrins was produced from MPDME. The dominant mass was m/e 478 (corresponding to a double deoarboxylation). Dealkylation products in multiples of 14 amu below the m/e 478 peak comprised the other members of the series. Cu-MPDME also produced homologous porphyrins. These, however, exhibited symmetry about the dominant members, similar to the symmetry found for the porphyrins of most petroleums and oil shales.     

Boreal temperature variability inferred from maximum latewood density and tree-ring width data, Wrangell Mountain region, Alaska

Variations in both width and density of annual rings from a network of tree chronologies were used to develop high-resolution proxies to extend the climate record in the Wrangell Mountain region of Alaska. We developed a warm-season (July–September) temperature reconstruction that spans A.D. 1593–1992 based on the first eigenvector from principal component analysis of six maximum latewood density (MXD) chronologies. The climate/tree-growth model accounts for 51% of the temperature variance from 1958 to 1992 and shows cold in the late 1600s–early 1700s followed by a warmer period, cooling in the late 1700s–early 1800s, and warming in the 20th century. The 20th century is the warmest of the past four centuries. Several severely cold warm-seasons coincide with major volcanic eruptions. The first eigenvector from a ring-width (RW) network, based on nine chronologies from the Wrangell Mountain region (A.D. 1550–1970), is correlated positively with both reconstructed and recorded Northern Hemisphere temperatures. RW shows a temporal history similar to that of MXD by increased growth (warmer) and decreased growth (cooler) intervals and trends. After around 1970 the RW series show a decrease in growth, while station data show continued warming, which may be related to increasing moisture stress or other factors. Both the temperature history based on MXD and the growth trends from the RW series are consistent with well-dated glacier fluctuations in the Wrangell Mountains and some of the temperature variations also correspond to variations in solar activity.     

Abrupt changes as indicators of decadal climate variability

 A statistical test has revealed that abrupt regional climate changes are produced in a coupled atmosphere-ocean general circulation model. Abrupt changes are detected over much of the globe although the occurrence frequency is small over the continents. Over the tropical Pacific Ocean and northern Pacific Ocean, surface air temperature (SAT) and sea level pressure (SLP) shift rapidly on decadal time scales. The regional climate changes presented here have been classified into three types. The first type consists of statistically significant shifts in SLP and statistically significant shifts in SAT which are of opposite sign, and which are reinforced through a positive feedback between the atmosphere and the ocean. The second type is for those occurrences where changes are of the same sign. The third type includes those with a significant shift in only one meteorological element. The second and third types are generally generated by changes in air pressure and wind fields induced by changes of the first type. For example, when SLP increases and sea surface temperature (SST) decreases abruptly in the tropical Pacific Ocean, it triggers abrupt regional changes in middle and high latitudes. The abrupt changes in the model climate have characteristics which are very similar to those of observed rapid shifts. Thus, it is concluded that abrupt changes are a predominant part of regional climate change on decadal time scales. Received: 11 February 1999 / Accepted: 18 May 2000