A note on time integration of unsaturated soil-moisture transport

The non-linear soil-moisture diffusivity model can be approximately linearized by using values of diffusivity assumed constant for small intervals of space and time. By a series expansion of the diffusivity function and integrating the resulting series of differential equations with respect to time, an improved numerical model is developed. Results from application of this new approach to a sharp wetting-front soil infiltration problem indicates that a 67% saving in numerical effort is achieved at comparable estimation accuracy levels when using the traditional finite timestep Crank-Nicolson approach.     

The use of pyrolysis and barium distributions to assess the areal extent of drilling fluids in surficial marine sediments

The influence of drilling fluid dispersion on the chemistry of surficial sediments was determined by an integrated study of organic and inorganic parameters. Pyrolysis characteristics and barium, organic carbon, and carbonate content were determined for sediments associated with six drilling sites in coastal Gulf of Mexico waters. The areal extent and magnitude of influence of dispersed fluids were related to water depth, prevailing currents, density of the dispersed material, history of the drill site and platform-induced biological activity. The potential use of pyrolysis techniques for defining the impact area and the various types of inputs derived from off-shore drilling operations was demonstrated.     

Great Lakes Hydrology Under Transposed Climates

Historical climates, based on 43 years of daily data from areas south and southwest of the Great Lakes, were used to examine the hydrological response of the Great Lakes to warmer climates. The Great Lakes Environmental Research Laboratory used their conceptual models for simulating moisture storages in, and runoff from, the 121 watersheds draining into the Great Lakes, over-lake precipitation into each lake, and the heat storages in, and evaporation from, each lake. This transposition of actual climates incorporates natural changes in variability and timing within the existing climate; this is not true for General Circulation Model-generated corrections applied to existing historical data in many other impact studies. The transposed climates lead to higher and more variable over-land evapotranspiration and lower soil moisture and runoff with earlier runoff peaks since the snow pack is reduced up to 100%. Water temperatures increase and peak earlier. Heat resident in the deep lakes increases throughout the year. Buoyancy-driven water column turnover frequency drops and lake evaporation increases and spreads more throughout the annual cycle. The response of runoff to temperature and precipitation changes is coherent among the lakes and varies quasi-linearly over a wide range of temperature changes, some well beyond the range of current GCM predictions for doubled CO₂ conditions.     

Statistical mechanical modeling of the kinetics of order-disorder in omphacitic pyroxenes

A kinetic statistical model based upon a one-dimensional Ising lattice reflecting the nature of the pyroxene octahedral strip, and with nearest-neighbor and mean-field interactions, is applied to the order-disorder transformation in omphacitic pyroxenes. The equilibration temperature of a naturally ordered omphacite and the annealing data of Carpenter (1981a) on omphacites from the same sample, when applied to the model, provide time- temperature-transformation relations for both long-range and short-range ordering. Results indicate that cooling times on the order of tens of millions of years are necessary for the development of significant degrees of long-range order under optimum conditions, whereas short-range order is developed on much shorter time scales. These results are in agreement with observations of naturally ordered and disordered omphacites with the exception of omphacites ordered in a low-temperature subduction-zone regime; the results support the hypothesis that these omphacites crystallize in a highly ordered state.     

Identification of a collapsing protostar

The globular molecular cloud B335 contains a single, deeply embedded, far-infrared source. Our recent observations of H₂CO and CS lines toward this source provide direct kinematic evidence for collapse. Both the intensity and detailed shape of the line profiles match those expected from inside-out collapse inside a radius of 0.036 pc. The collapse began about 1.5 × 10⁵ years ago, similar to the onset of the outflow. The mass accretion rate is about 10 times the outflow rate, and about 0.4M should have now accumulated in the star and disk. Because B335 rotates only very slowly, any disk would still be very small (about 3 AU). The accretion luminosity should be adequate to power the observed luminosity. Consequently, we believe that B335 is indeed a collapsing protostar.Paper presented at the Conference onPlanetary Systems: Formation, Evolution, and Detection held 7–10 December, 1992 at CalTech, Pasadena, California, U.S.A.     

Environments of the Russian Plain during the Middle Valdai Briansk Interstade (33,000–24,000 yr B.P.) Indicated by Fossil Mammals and Plants

Abundant mammal (45 localities) and plant (52 sections) fossil data collected from the Russian Plain deposits of the Middle Valdai Briansk Interstade indicate a period of noticeable warming. These materials were jointly analyzed. The data were organized in the database software PARADOX and then moved to the GIS program ARC/INFO. Mathematical methods as well as traditional research methods were used for the analysis. The reconstructed biogeographical provinces illustrate the specific environmental and climatic conditions of the Briansk Interstade. Analogues of modern natural zones did not exist at this time on the Russian Plain. The Briansk landscapes reflect the moderate-cool climate of this period, when the majority of northern subarctic plant and mammal species extended their ranges considerably to the south to the Central Russian Plain. At the same time, steppe species penetrated farther north and west. This combination shows that the continuous forest zone was destroyed during the Briansk Inter-stade. Five biogeographical provinces have been reconstructed from the north to the south for the Russian Plain during the Briansk warming on the basis of joint analysis of mammalian and botanical data.     

Response to Thrift's “The future of geography”

Reviews and observations about the status of the discipline of geography, no matter how positive, invariably raise programmatic concerns. These concerns have a long history that arise from geography's struggles to find an identity that embraces its many parts and yet are consistent with the logic by which the academy partitions knowledge. Pedagogy and research historically claimed by geography is currently being reinvented and relabeled under such headings as “integrated environmental science” and “spatial science”, and these developments have the potential to change the breadth of the “geographic imagination”. Several observations about dominant explanatory perspectives and substantive domains of geographic enquiry are also provided.     

On the recording of regions with increased plasma density on the Sun

For the purpose of studying the statistics, dynamics, and morphology of parts of the solar surface with enhanced emission measure and considerable inhomogeneities of electron concentration, it is suggested that a new type of solar observation be introduced: taking filtergrams by means of interference filters, calculated for the Balmer continuum limit and the region of the blue continuum. To determine accurately the inhomogeneity of the electron concentration in an object, it is suggested to scan the surface of the object and record the spectrum of the blue continuum by means of a spectrochronograph.