Distributed and integrated response of a geographic information system‐based hydrologic model in the eastern Palouse region,Idaho

Verification of distributed hydrologic models is rare owing to the lack of spatially detailed field measurements and a common mismatch between the scale at which soil hydraulic properties are measured and the scale of a single modelling unit. In this study, two of the most commonly calibrated parameters, i.e. soil depth and the vertical distribution of lateral saturated hydraulic conductivity K_s, were eliminated by a spatially detailed soil characterization and results of a hillslope‐scale field experiment. The soil moisture routing (SMR) model, a geographic information system‐based hydrologic model, was modified to represent the dominant hydrologic processes for the Palouse region of northern Idaho. Modifications included K_s as a double exponential function of depth in a single soil layer, a snow accumulation and melt algorithm, and a simple relationship between storage and perched water depth (PWD) using the drainable porosity. The model was applied to a 2 ha catchment without calibration to measured data. Distributed responses were compared with observed PWD over a 3‐year period on a 10 m × 15 m grid. Integrated responses were compared with observed surface runoff at the catchment outlet. The modified SMR model simulated the PWD fluctuations remarkably well, especially considering the shallow soils in this catchment: a 0·20 m error in PWD is equivalent to only a 1·6% error in predicted soil moisture content. Simulations also captured PWD fluctuations during a year with high spatial variability of snow accumulation and snowmelt rates at upslope, mid‐slope, and toe slope positions with errors as low as 0·09 m, 0·12 m, and 0·12 m respectively. Errors in distributed and integrated model simulations were attributed mostly to misrepresentation of rain events and snowmelt timing problems. In one location in the catchment, simulated PWD was consistently greater than observed PWD, indicating a localized recharge zone, which was not identified by the soil morphological survey. Copyright © 2006 John Wiley & Sons, Ltd.     

Globular Clusters in the Large Magellanic Cloud: An Impact from GAIA Photometry

The goal of this work is to assess the expected scientific output from the photometric studies of globular clusters in the Large Magellanic Cloud with ESA's astrometric space mission GAIA. For this purpose we simulate GAIA photometry of individual stars in synthetic cluster populations, covering a large range of cluster ages and metallicities. We find that accurate effective temperatures (Δ T _eff<10%) can be obtained from GAIA photometry down to V ∼ 18 for stars in populations within the studied metallicity range ([M/H] = -0.4 ... -1.7). GAIA will also provide photometric metallicities (Δ [M/H] ≲ 0.3 dex) for the cluster giants brighter than V ∼ 17.5. The knowledge of the effective temperature sand metallicities will allow to obtain accurate ages of stellar populations younger than about 1 Gyr using the usual procedure of main sequence turn-off point fitting. Ages of older stellar populations (≳ 1 Gyr) may be constrained from the isochrone fits to the giant branches in the observed CMDs. We conclude that GAIA will provide excellent opportunities for studying star formation histories far beyond the Milky Way, providing means for better understanding of stellar and galactic evolution in different astrophysical environments. This revised version was published online in July 2006 with corrections to the Cover Date.     

Hale's attempts to determine the sun's general magnetic field

Hale's attempts to determine the sun's general magnetic field are reviewed. The field reported by Hale was an order of magnitude stronger than that presently measured with photoelectric techniques. The polarity was opposite to that expected from Babcock's theory of the solar cycle. Practically all the reduction work had been made by Van Maanen with a tipping-plate micrometer.To free the reductions from possible personal bias, a few hundred of the plates from the 1914 series were remeasured by the author with the digitized microphotometer at the Sacramento Peak Observatory. The line profiles were recorded on magnetic tape, and the computations of the Zeeman displacements were made using a CD 3600 at Uppsala.The same plates had been measured visually by Van Maanen. His results show a neat variation of field strength with heliographic latitude, with a maximum of about 11 G at latitudes + and –45 °. The solar equator forms a sharp demarcation line between the opposite polarities in the two hemispheres. In contrast, the computer reductions do not reveal any significant field at any latitude. An approximate upper limit for the observed field strength is 5 G. There is no correlation between the new results and the old values by Van Maanen.     

The NASA/NSO Spectromagnetograph

The NASA/NSO Spectromagnetograph is a new focal plane instrument for the National Solar Observatory/Kitt Peak Vacuum Telescope which features real-time digital analysis of long-slit spectra formed on a two-dimensional CCD detector. The instrument is placed at an exit port of a Littrow spectrograph and uses an existing modulator of circular polarization. The new instrument replaces the 512-channel Diode Array Magnetograph first used in 1973. Commercial video processing boards are used to digitize the spectral images at video rates and to separate, accumulate, and buffer the spectra in the two polarization states. An attached processor removes fixed-pattern bias and gain from the spectra in cadence with spatial scanning of the image across the entrance slit. The data control computer performs position and width analysis of the line profiles as they are acquired and records line-of-sight magnetic field, Doppler shift, and other computed parameters. The observer controls the instrument through windowed processes on a data control console using a keyboard and mouse. Early observations made with the spectromagnetograph are presented and plans for future development are discussed.The National Solar Observatory is a Division of the National Optical Astronomy Observatories which is operated by the Association of Universities for Research in Astronomy, Inc., under cooperative agreement with the National Science Foundation.     

Magnetic susceptibility in sediment records of Lake Ådran,eastern Sweden: correlation among cores and interpretation

Magnetic susceptibility was used to test the representativity of the lithostratigraphy of a master sediment sequence from Lake Ådran, eastern Sweden. Five further sediment cores from the same lake were correlated and compared with the master sequence using magnetic susceptibility records. Mineral magnetic correlations are generally based on matching prominent susceptibility features but may be significantly improved by using slot sequence analyses. The result of these analyses show that the sediment in the Lake Ådran master sequence can be considered representative for the basin. The variations in the magnetic susceptibility in relation to pollen and diatom analyses also seem to reflect water level changes and shore displacement in the Baltic between 9900 ¹⁴C years B.P. and the isolation at 5900 ¹⁴C years B.P. The first emergence of scattered non-vegetated islands is characterised by high susceptibility values. Along with a continuous water lowering and the development of the vegetation during the Ancylus fresh water stage, susceptibility values gradually decrease. A rapid phase of the Ancylus regression between 9200 and 9000 ¹⁴C years B.P. is seen as an increase in magnetic susceptibility. During the following Baltic brackish water stage, the Litorina stage, susceptibility values are at their lowest, followed by higher values at the isolation from the Baltic with a maximum around 5000 ¹⁴C years B.P.Shore displacement between 9900 and 5900 ¹⁴C years B.P. is discussed based on the magnetic susceptibility measurements and their relationship to the pollen and diatom analyses.     

Millimeter-wave experiments for cometary space missions

Predicted brightness temperatures for a variety of cometary nucleus models, consisting of homogeneous layers comprised of mixtures of water ice and refractory grains, are presented as functions of wavelength. These illustrative spectra are computed using simple radiative transfer techniques adapted from modeling of terrestrial ice and snow fields. The computed millimeter-wave spectra are sensitive to the values of physically significant nucleus parameters such as crust thickness, the subsurface temperature gradient, and the boundary temperature of the sublimating surface. It appears that millimeter-wave sensing from an interplanetary spacecraft is an effective means for distinguishing between alternate models of the nucleus and for inferring the rough physical state of substrata; modern theories on the nature of the nucleus indicate that sublimation from the substrata provides the gas phase cometary volatiles that are actually observed from ground-based and Earth-orbiting instruments. Antenna beam dilution is a major obstacle for ground-based molecular spectral line radio observations (e.g., water and ammonia) of comets but a modest millimeter-wave radiometer system in the near vicinity of the comet would not be subject to this problem. Such a system can make definitivebservations of several candidate parent molecules in the gas phase and should contribute to the understanding of the physics of the inner coma.     

Test of independence by repeated matching of stratigraphic sections

Two stratigraphic sections of unequal length and uncertain relative position are usually tested for nonrandom similarities by calculating the coefficient of cross-association, using several of their possible mutual alignments. A rigorous statistical test of independence between the two sections is derived, utilizing results of such a procedure. Proper distinction is made between sections consisting of a record of lithological strata (consecutive repetition of the same rock type is allowed),and the situation when adjacent identical strata are merged into an lithological unit (a record of these must contain no contiguous replicates).The presented theory is first developed under assumption of prior knowledge of the exact probabilities of possible rock types, but is extended to accommodate the case of these being unavailable.