Simulations of the mean solar magnetic field during sunspot cycle 21

Regarding new bipolar magnetic regions as sources of flux, we have computed the evolution of the photospheric magnetic field during 1976–1984 and derived the corresponding evolution of the mean line-of-sight field as seen from Earth. We obtained a good, but imperfect, agreement between the observed mean field and the field computed for a nominal choice of flux transport parameters. Also, we determined the response of the computed mean field to variations in the transport parameters and the source properties. The results lead us to regard the mean-field evolution as a random-walk process with dissipation. New eruptions of flux produce the random walk, and together differential rotation, meridional flow (if present), and diffusion provide the dissipation. The net effect of each new source depends on its strength and orientation (relative to the strength and orientation of the mean field) and on the time elapsed before the next eruption (relative to the decay time of the field). Thus the mean field evolves principally due to the contributions of the larger sources, which produce a strong, gradually evolving field near sunspot maximum but a weak, sporadically evolving field near sunspot minimum.E. O. Hulburt Center for Space Research.Laboratory for Computational Physics.     

Seasonal variation of diel vertical migration of zooplankton from ADCP backscatter time series data in the Lazarev Sea,Antarctica

Ten-month time series of mean volume backscattering strength (MVBS) and vertical velocity obtained from three moored acoustic Doppler current profilers (ADCPs) deployed from February until December 2005 at 64°S, 66.5°S and 69°S along the Greenwich Meridian were used to analyse the diel vertical zooplankton migration (DVM) and its seasonality and regional variability in the Lazarev Sea. The estimated MVBS exhibited distinct patterns of DVM at all three mooring sites. Between February and October, the timing of the DVM and the residence time of zooplankton at depth were clearly governed by the day–night rhythm. Mean daily cycles of the ADCP-derived vertical velocity were calculated for successive months and showed maximum ascent and descent velocities of 16 and –15 mm s^?1. However, a change of the MVBS pattern occurred in late spring/early austral summer (October/November), when the zooplankton communities ceased their synchronous vertical migration at all three mooring sites. Elevated MVBS values were then concentrated in the uppermost layers (<50 m) at 66.5°S. This period coincided with the decay of sea ice coverage at 64°S and 66.5°S between early November and mid-December. Elevated chlorophyll concentrations, which were measured at the end of the deployment, extended from 67°S to 65°S and indicated a phytoplankton bloom in the upper 50 m. Thus, we propose that the increased food supply associated with an ice edge bloom caused the zooplankton communities to cease their DVM in favour of feeding.     

Analysis of investments in technology development and resource conservation

A methodology is presented for the economic analysis of investments in research, technology development and water resources conservation. The role of technology development and resource conservation is directly related to the availability of resources. Mathematically speaking, we are dealing with a problem in which part of the control variables are investments on technologies related to the manufacturing of diverse products. The methodology enables the decision maker to distribute efficiently restricted amounts of capital and resources to the different manufacturing systems so as to achieve the most profitable combination of production levels.Using the so called ‘technology function’, the solution procedure consists of a combination of decomposition and dynamic programming. Two specific technology functions are considered as examples and it is shown how analytical consideration can be incorporated in the solution procedure so as to reduce computational requirements.Possible extensions of the problem are also discussed.     

Observable blueshifts near compact objects

We show that observable blueshifted radiation can emanate from material freely falling toward compact objects. Using a fully relativistic treatment and considering possible blocking of photon trajectories by a neutron star or black hole, we demonstrate that blueshifts are observable.Supported in part by the National Science Foundation.     

A variant of the Hori-Lie series method

If the undisturbed Hamiltonian F₀ is a function of the momenta only, then a variant of the Hori-Lie series perturbation method achieves a solution to any order with a single canonical transformation, without the use of the pseudo-time.     

Radar backscatter from plasma irregularities of the lower E region induced by neutral turbulence

Recently, one of the authors (A. V. G.) developed a theory of low-frequency plasma irregularities which are created as a consequence of neutral turbulence in the D and lower E regions. In the following this theory will be applied to coherent backscatter experiments with radars in a frequency range between 5 and 150 MHz. We discuss the dependence of the backscatter cross-section on ionospheric as well as on turbulence parameters. The backscatter increases strongly with decreasing radar frequency. Above 15 MHz the effects discussed here can probably only be detected by very powerful radars with large antenna arrays.