Measurement of the electric fluctuation spectrum of magnetohydrodynamic turbulence

Magnetohydrodynamic (MHD) turbulence in the solar wind is observed to show the spectral behavior of classical Kolmogorov fluid turbulence over an inertial subrange and departures from this at short wavelengths, where energy should be dissipated. Here we present the first measurements of the electric field fluctuation spectrum over the inertial and dissipative wavenumber ranges in a $\beta \gtrsim 1$ plasma. The $k^{-5/3}$ inertial subrange is observed and agrees strikingly with the magnetic fluctuation spectrum; the wave phase speed in this regime is shown to be consistent with the Alfv\'en speed. At smaller wavelengths $k \rho_i \geq 1$ the electric spectrum is softer and is consistent with the expected dispersion relation of short-wavelength kinetic Alfv\'en waves. Kinetic Alfv\'en waves damp on the solar wind ions and electrons and may act to isotropize them. This effect may explain the fluid-like nature of the solar wind.Comment: submitted; 4 pages + 3 figure

Resource management domains: a biophysical unit for assessing and monitoring land quality

With the advent of information technology there is a renewed interest to define and identify homogeneous food production systems. International donor agencies, such as the World Bank and the US Agency for International Development, are especially interested in public/private partnerships to develop and integrate information including the socioeconomic/cultural contexts of farm systems to improve knowledge about food systems, nationally to globally. International agricultural research centres, non-government organizations and national institutions require a spatial-temporal-hierarchical information system describing farm systems and communities from the 'nation to the farm'. Agri-business requires methods to evaluate the performance of crop systems in varied environments in countries and/or around the world. As society is stratified by different information needs, decisions must be made about the units of study and the hierarchy of information integration. The proposed hierarchy, developed on the tenets of hierarchy theory, implies that optimization of biodiversity, ecosystem health and integrity, commodity production, or maintaining soil quality, are each articulated based on the objectives that apply to the planning area. Management goals, therefore, determine the planning area to be defined, the goods and services, and the desired conditions of the ecosystem. Defined biophysical units, such as resource management domains (RMDs), serve as a common denominator for synthesis of information which could be shared by a range of disciplines, such as hydrology, geomorphology, pedology, crop science, economics, sociology, land-use planning, and production technology. In this approach, system dynamics or temporal variations are de-emphasized with the assumption that each RMD has attained an equilibrium or quasi-equilibrium within the planning horizon of the society. This is due to the practical purpose for which land resource assessments are generally made. However, if time periods of 50 or more years are considered, the concept must be refined. The latter approach is required for assessments of forest ecosystems

A MODEL-BASED DECISION SUPPORT SYSTEM FOR REGIONAL AGRICULTURAL PLANNING

Agricultural decision making at the production and policy levels involves processes which can be enhanced by modern computer technologires. Crop and soil models can be used to estimate the impact of different p:roduction strategies at a regional level, and thus provide supplemental lnformation to help decision makers select management practices in accordance with their p.lanning objectives. '.rhls paper describes the structure and implementation of an agricultural decision support system named AEGIS ·• Agricultural and Environmental Get>graphic Information System - designed to evaluate production strategies and to facilitate the creation of a reg:Lonal agricultural plan. AEGIS links s:Lmulation results from two IBSNAT crot? growth models (BEANGRO and CERES-RICE) and a soil erosion model (USLE) to a geographic lnformation·system (pcARC/INFO) and an expert system. A menu-driven interface ls developed to help users with limited expertise in computers interact with AEGIS. Three areas in Puerto Rico were us·ed to develop a prototype of this syste1n. An example ls presented to demonstrate the potential use of thla system as a planning tool for regional policy makers. The role of the models, the organization of the databases, th,~ design of the user interface and lthe expert system are discussed. Thh model-based system demonstrates the effectiveness of modern computer technologies in the processes of agricultural planning, information management, and agrotechnology transfer in Ca1rlbbean countries