Estimated SLR station position and network frame sensitivity to time-varying gravity

This paper evaluates the sensitivity of ITRF2008-based satellite laser ranging (SLR) station positions estimated weekly using LAGEOS-1/2 data from 1993 to 2012 to non-tidal time-varying gravity (TVG). Two primary methods for modeling TVG from degree-2 are employed. The operational approach applies an annual GRACE-derived field, and IERS recommended linear rates for five coefficients. The experimental approach uses low-order/degree $4\times 4$ coefficients estimated weekly from SLR and DORIS processing of up to 11 satellites (tvg4x4). This study shows that the LAGEOS-1/2 orbits and the weekly station solutions are sensitive to more detailed modeling of TVG than prescribed in the current IERS standards. Over 1993–2012 tvg4x4 improves SLR residuals by 18 % and shows 10 % RMS improvement in station stability. Tests suggest that the improved stability of the tvg4x4 POD solution frame may help clarify geophysical signals present in the estimated station position time series. The signals include linear and seasonal station motion, and motion of the TRF origin, particularly in Z. The effect on both POD and the station solutions becomes increasingly evident starting in 2006. Over 2008–2012, the tvg4x4 series improves SLR residuals by 29 %. Use of the GRGS RL02 $50\times 50$ series shows similar improvement in POD. Using tvg4x4, secular changes in the TRF origin Z component double over the last decade and although not conclusive, it is consistent with increased geocenter rate expected due to continental ice melt. The test results indicate that accurate modeling of TVG is necessary for improvement of station position estimation using SLR data.     

Paired‐basin comparison of hydrological response in harvested and undisturbed hardwood forests during snowmelt in central Ontario: I. Streamflow,groundwater and flowpath behaviour

Impacts of forest harvesting on groundwater properties, water flowpaths and streamflow response were examined 4 years after the harvest using a paired‐basin approach during the 2001 snowmelt in a northern hardwood landscape in central Ontario. The ability of two metrics of basin topography (Beven and Kirkby's ln(a/tan β) topographic index (TI) and distance to stream channel) to explain intra‐basin variations in groundwater dynamics was also evaluated. Significant relationships between TI and depth to potentiometric surface for shallow groundwater emerged, although the occurrence of these relationships during the melt differed between harvested and control basins, possibly as a result of interbasin differences in upslope area contributing to piezometers used to monitor groundwater behaviour. Transmissivity feedback (rapid streamflow increases as the water table approaches the soil surface) governed streamflow generation in both basins, and the mean threshold depths at which rapid streamflow increases corresponded to small rises in water level were similar for harvested (0·41 ± 0·05 m) and forested (0·38 ± 0·04 m) basins. However, topographic properties provided inconsistent explanations of spatial variations in the relationship between streamflow and depth to water at a given piezometer for both basins. Streamflow from the harvested basin exceeded that from the forested basin during the 2001 melt, and hydrometric and geochemical tracer results indicated greater runoff from the harvested basin via surface and near‐surface pathways. These differences are not solely attributable to harvesting, since the difference in spring runoff from the harvested basin relative to the forested control was not consistently larger than under pre‐harvest conditions. Nevertheless, greater melt rates following harvesting appear to have increased the proportion of water delivery to the stream channel via surface and near‐surface pathways. Copyright © 2005 John Wiley & Sons, Ltd.     

International cooperation in water resources

Advancements in hydrology proceeded slowly until the late 1800's when new ventures created a surge of interest and accomplishment. Progress waned again until the middle 20th century when an International Hydrological Decade was conceived, eventually receiving wide multinational support from governmental agencies and nongovernmental institutions.Organized by UNESCO, the Decade program was launched January 1, 1965. Participation included 107 nations, six United Nations agencies, and more than a dozen international scientific organizations. The initial program emphasized scientific research, and international cooperation; the second half of the Decade, emphasized technical assistance and technology transfer, largerly through education, training and demonstration.The success of the Decade led to the establishment of the International Hydrological Program, again under the aegis of UNESCO, to continue the work of the Decade indefinitely. The five major program activities, now involving about 90 countries and several international organizations, include: the scientific program, the promotion of education and training, the enhancement of information exchange, support of technical assistance, and the enlargement of regional cooperation.A significant amount of activity related to hydrological data networks and forecasting is carried on in an Operational Hydrology Programme by the WMO, chiefly through its Commission for Hydrology.Other international governmental organizations with a strong interest in water include the UN, the UN Development Programme, the FAO, the WHO, the International Atomic Energy Agency, the UN Environment Programme, the International Standardization Organization, and developmental institutions such as the World Bank.The specialized interests of researchers outside of the governmental structure, are met through association in various scientific and technical organizations which are world wide in scope and membership.Notwithstanding a sometimes bewildering variety of organizations, there certainly exists, for any nation, group, or individual, a demonstrated mechanism for almost any conceivable form of international cooperation in hydrology and water resources.Dr. Heindl, L.A., formerly US Geological Survey, died on October 18, 1978 (see In Memoriam at the end of the paper) before he could finish the final version. His colleagues, James R. Jones, Robert M. Beall and Ennio V. Giusti, Office of International Hydrology, US Geological Survey, Reston, VA. 22092, USA, kindly prepared the paper for publication and wrote In Memoriam. Approved for publication by the Director, US Geological Survey.     

Upper limit on the steady emission of the 2.223 MeV neutron capture γ-ray line from the Sun

Data accumulated by the Solar Maximum Mission Gamma Ray Spectrometer (GRS) have been searched for evidence of the 2.223 MeV neutron capture line from the Sun, outside the times of -ray-emitting solar flares. Background-corrected spectra accumulated over 3-day intervals between 1980 and 1989 show no evidence of the line. Upper limits are reported separately for periods of high and low solar activity.A conservative 3 upper limit of 5.7 × 10^–5 (cm² s)^–1 is placed on the steady flux in the 2.223 MeV line during inactive periods, which is nearly two orders of magnitude lower than previously published results. After correction for limb darkening of the line emission from off-center positions, this upper limit becomes 7.1 × 10^–5 (cm²s)^–1. Our 3 upper limit on the steady flux in the line during periods of high solar activity is 6.9 × 10^–5 (cm² s)^–1, or 8.6 × 10^–5 (cm² s)^–1 after correction for limb darkening. Our results imply that the quiescent solar corona cannot be heated by ions accelerated above 1 MeV in microflares (or a continuous acceleration process), so long as the ion energy spectrum is similar to that measured in large flares. We also use our results to derive the rate of tritium production at the solar surface; our upper limit of 9 nuclei (cm² s)^–1 is about a factor of 9 below the upper limit from searches for ³H in the solar wind. We place upper limits of the order 10³³ on the number of energetic (> 30 MeV) protons which can be stored in active regions prior to being released in solar flares, which imply that the strongest observed flares cannot be produced by such a mechanism.     

Searching for similarity in topographic controls on carbon,nitrogen and phosphorus export from forested headwater catchments

Topography influences hydrological processes that in turn affect biogeochemical export to surface water on forested landscapes. The differences in long‐term average annual dissolved organic carbon (DOC), organic and inorganic nitrogen [NO₃^?‐N, dissolved organic nitrogen (DON)], and phosphorus (total dissolved phosphorus, TDP) export from catchments in the Algoma Highlands of Ontario, Canada, with similar climate, geology, forest and soil were established. Topographic indicators were designed to represent topographically regulated hydrological processes that influence nutrient export, including (1) hydrological storage potential (i.e. effects of topographic flats/depressions on water storage) and (2) hydrological flushing potential (i.e. effects of topographic slopes on potential for variable source area to expand and tap into previously untapped areas). Variations in NO₃^?‐N export among catchments could be explained by indicators representing both hydrological flushing potential (91%, p < 0.001) and hydrological storage potential (65%, p < 0.001), suggesting the importance of hydrological flushing in regulating NO₃^?‐N export as well as surface saturated areas in intercepting NO₃^?‐N‐loaded runoff. In contrast, hydrological storage potential explained the majority of variations among catchments in DON (69%, p < 0.001), DOC (94%, p < 0.001) and TDP (82%, p < 0.001) export. The lower explanatory power of DON (about 15% less) compared with that of DOC and TDP suggests another mechanism influencing N export, such as controls related to alternative fates of nitrogen (e.g. as gas). This study shows that simple topographic indicators can be used to track nutrient sources, sinks and their transport and export to surface water from catchments on forest landscapes. Copyright © 2013 John Wiley & Sons, Ltd.