A Moisture Balance Reconstruction for the Drainage Basin of Albemarle Sound, North Carolina

Freshwater discharge into Albemarle Sound and many other large estuaries can have a major impact on the physical and biological properties of the estuary. Earlywood (EW) and latewood (LW) width tree ring chronologies recently developed from ancient trees and sub-fossil logs found at Devil’s Gut of the Roanoke River, North Carolina, were used with new EW and LW width data from Blackwater River, Virginia, to reconstruct the July Palmer Hydrological Drought Index (PHDI) over the drainage basin of Albemarle Sound from 934 to 2005. This reconstruction is based on a principal component regression using millennium-long chronologies of both EW and LW widths, calibrated and verified against instrumental July PHDI from 1895 to 1985. The reconstruction provides a lengthy representation of inter-annual to multi-decadal growing season moisture variability that directly affects water quality in the Albemarle Sound estuarine ecosystem. Single-year drought and wetness extremes were more common in the modern instrumental period (1895–2005), but prolonged droughts reconstructed during the Medieval and Early Colonial eras were more severe and sustained than the reconstructed or observed droughts during the twentieth century. Several abrupt transitions between decadal drought and wetness regimes are reconstructed, especially during the Medieval Era. Composite analysis of lower-magnitude sub-decadal regime shifts in the instrumental record during the twentieth century indicates that major changes in mid-latitude circulation over the Northern Hemisphere may have been involved in these longer decadal transitions between moisture regimes over Albemarle Sound in prehistory.     

The saturation of galactic dynamos

We summarize the current state of the long term discussion about the saturation mechanisms associated with rapid growth of small‐scale magnetic field, that operate in large‐scale galactic dynamos, and related problems with magnetic helicity conservation. Our general conclusion is that, taking into account magnetic helicity fluxes, large‐scale magnetic field can be amplified up to about the equipartition level. In contrast, models without helicity fluxes give an initial temporal magnetic field growth, but then decay. In our opinion, it is more appropriate to refer to the situation as a “potentially catastrophic scenario” rather than as “catastrophic α‐quenching” (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The motion of magnetic fronts in spiral galaxies

Abstract

We study the nonlinear asymptotic thin disc approximation to the mean field dynamo equations, as applicable to spiral galaxies. The circumstances in which sharp magnetic field structures (fronts) can propagate radially are investigated, and an expression for the speed of propagation derived. We find that the speed of an interior front is proportional to η//R _? (where η is the diffusivity and R_t the galactic radius), whereas an exterior front moves with speed of order , where γ is the local growth rate of the dynamo. Numerical simulations are presented, that agree well with our asymptotic results. Further, we perform numerical experiments using the 'no-z' approximation for thin disc dynamos, and show that the propagation of magnetic fronts in this approximation can also be understood in terms of our asymptotic results.     

Nonlinear galactic dynamos

Abstract

We present trial calculations for a simple nonlinear ‘‘thick disk'’ galaxy dynamo. The nonlinearity is a simple α-quenching. Our strictly axisymmetric solution demonstrates the possibility of a nonlinear interaction between modes of opposite parity. We suggest that a three dimensional model might exhibit a similar persistent interaction between axisymmetric and non-axisymmetric modes.     

The periods of stellar models with linked poloidal-toroidal magnetic fields

First-order perturbation theory results for the changes in pulsation frequencies of a Cowling model star containing a magnetic field with both poloidal and toroidal components are presented. A toroidal field large enough to stabilize the poloidal field may reverse the sign of the frequency change caused by a purely poloidal field for some modes, including the fundamental radial mode.     

Water quality guidelines for the Great Barrier Reef World Heritage Area: a basis for development and preliminary values

The Australian and New Zealand Guidelines for Fresh and Marine Water Quality (ANZECC Guidelines) provide default national guideline values for a wide range of indicators of relevance to the protection of the ecological condition of natural waters. However, the ANZECC Guidelines also place a strong emphasis on the need to develop more locally relevant guidelines. Using a structured framework, this paper explores indicators and regional data sets that can be used to develop more locally relevant guidelines for the Great Barrier Reef World Heritage Area (GBRWHA). The paper focuses on the water quality impacts of adjacent catchments on the GBRWHA with the key stressors addressed being nutrients, sediments and agricultural chemicals. Indicators relevant to these stressors are discussed including both physico-chemical pressure indicators and biological condition indicators. Where adequate data sets are available, guideline values are proposed. Generally, data were much more readily available for physico-chemical pressure indicators than for biological condition indicators. Specifically, guideline values are proposed for the major nutrients nitrogen (N) and phosphorus (P) and for chlorophyll-a. More limited guidelines are proposed for sediment related indicators. For most agricultural chemicals, the ANZECC Guidelines are likely to remain the default of choice for some time but it is noted that there is data in the literature that could be used to develop more locally relevant guidelines.     

An initial classification of 10-km squares in Great Britain from a land characteristic data bank

In a pilot classification of 282 10-km squares in Great Britain, data on physiography, climate and geology were extracted. Parallel classifications were run using these variables and also using spatial location. Two classification methods were compared: minimum within-group variance and indicator species analysis. Similarities between the resulting classifications were considered, and the groups were assessed for geographic coherence. Their validity for use as stratifications were tested using analysis of variance and also by matching the classifications with known distributions of a number of bird and plant species.Classifications using spatial variables were geographically more coherent than those without. The different methods resulted in different groupings of the squares which were partly a result of the differences in weightings applied to the four types of variable. However, the analysis of variance showed that either classification method provided a good stratification of the country, in particular with respect to altitude and rainfall. Some bird and plant species distributions correlated well with the classifications, but others did not, dependent on the factors limiting those distributions.     

The relation between magnetic and gas arms in spiral galaxies

The intriguing question of the origin of the arm-like magnetic structures seen between the optical spiral arms of certain spiral galaxies is addressed. Using a two-dimensional approximation to the non-linear disc dynamo equation, it is shown that gas streaming along the arms may produce such a field configuration. Another possibility is a spiral modulation of the turbulent diffusivity, associated with an enhancement of turbulence in the interstellar medium within the arms. The effects of a similar modulation of the alpha-effect are also examined. Finally, the consequences of a non-linear feedback of the large-scale field on the turbulent diffusivity ('η-quenching') are briefly discussed.     

Biomass for energy in developing countries

Biomass, like fossil fuels, can provide cooking and heating energy, electricity, chemicals and liquid fuels. Today about 14% of the worldwide primary energy supply is provided by biomass resources — equivalent to 1000 million tons oil each year. Most of this biomass use occurs in rural areas of developing countries where half the world's population lives. For example Kenya derives about 75%, India 50%, China 33% and Brazil 25% of their total energy from biomass, A number of industrialized countries also derive a considerable amount of energy from biomass, such as Finland 18%, Ireland 16%, Sweden 9% and USA 3%. World ependiture on biomass programmes exceeds S 2 bn/yr; several natioal biomass energy programmes are discussed. Biomass resources and conversion technologies are described, as are the factors necessary for successful regional implementation of biomass energy schemes.