Interannual variability in net accumulation on the Greenland Ice Sheet: Observations and implications for mass balance measurements

This is the published version, also available here: http://dx.doi.org/10.1029/1998JD200082.Nine 24-year accumulation records from the Summit region in central Greenland are analyzed to separate the effects of spatial noise and interannual fluctuations on the variability in each core. The study shows that both processes are equally important, with standard deviations of 25 mm water equivalent per year and 24 mm water equivalent per year, respectively. A comparison with estimates of surface roughness based on high-resolution laser altimetry of the surface indicates that in the studied region the spatial noise can be reliably estimated from surface roughness. The response of the ice-sheet surface to the interannual fluctuations can be estimated using a simple zero-dimensional ice-sheet response model. For the Summit region of central Greenland, a change in surface elevation of ∼20 mm water equivalent per year measured over a 5-year period, can be attributed with 95% confidence to a trend in climate. This probability decreases rapidly as the observation period is shortened. For intervals greater than ∼5 year, the probability depends only weakly on the measurement interval. This suggests an optimum spacing of ∼5 years between repeat elevation measurements

Multifractal analysis of vertical total electron content (VTEC) at equatorial region and low latitude, during low solar activity

This paper analyses the multifractal aspects of the GPS data (measured during a period of low solar activity) obtained from two Brazilian stations: Belém (01.3° S, 48.3° W) and São José dos Campos (SJC) (23.2° S, 45.9° W). The results show that the respective geographic sites show important scaling differences as well as similarities when their multifractal signatures for vertical total electron content (VTEC) are compared. The <I>f</I>(&alpha;) spectra have a narrow shape for great scales, which indicates the predominance of deterministic phenomena, such as solar rotation (27 days) over intermittent phenomena. Furthermore, the <I>f</I>(&alpha;) spectra for both sites have a strong multifractality degree at small scales. This strong multifractality degree observed at small scales (1 to 12 h) at both sites is because the ionosphere over Brazil is a non-equilibrium system. The differences found were that Belém presented a stronger multifractality at small scales (1 h to 12 h) compared with SJC, particularly in 2006. The reason for this behaviour may be associated with the location of Belém, near the geomagnetic equator, where at this location the actions of X-rays, ultraviolet, and another wavelength from the Sun are more direct, strong, and constant throughout the whole year. Although the SJC site is near ionospheric equatorial anomaly (IEA) peaks, this interpretation could explain the higher values found for the intermittent parameter μ for Belém compared with SJC. Belém also showed the presence of one or two flattening regions for <I>f</I>(&alpha;) spectra at the same scales mentioned before. These differences and similarities also were interpreted in terms of the IEA content, where this phenomenon is an important source of intermittence due the presence of the VTEC peaks at ±20° geomagnetic latitudes

Temporal and spatial variability of snow accumulation in central Greenland

Snow accumulation records from central Greenland are explored to improve the understanding of the accumulation signal in Greenland ice core records. Results from a “forest” of 100 bamboo poles and automated accumulation monitors in the vicinity of Summit as well as shallow cores collected in the Summit and Crete areas are presented. Based on these accumulation data, a regression has been calculated to quantify the signal-to-noise variance ratio of ice core accumulation signals on a variety of temporal (1 week to 2 years) and spatial (20 m to 200 km) scales. Results are consistent with data obtained from year-round automated accumulation measurements deployed at Summit which suggest that it is impossible to obtain regional snow accumulation data with seasonal resolution using four accumulation monitors positioned over a length scale of ∼30 km. Given this understanding of the temporal and spatial dependence of noise in the ice core accumulation signal, the accumulation records from 17 shallow cores are revisited. Each core spans the time period from 1964 to 1983. By combining the accumulation records, the regional snow accumulation record has been obtained for this period. The results show that 9 of the 20 years can be identified as having an accumulation different from the 20 year mean with 99% confidence. The signal-to-noise variance ratio for the average accumulation signal sampled at annual intervals is 5.8±0.5. The averaged accumulation time series may be useful to climate modelers attempting to validate their models with accurate regional hydrologic data sets

Main competencies to manage complex defence projects

This research adds a comprehensive way of assessing competencies, contrasting with the usual reductionist approach that uses off-the-shelf instruments. The study reveals 27 competencies to manage complex projects based upon a comprehensive analysis of 22 interviews with senior practitioners associated with the most strategic projects from the Brazilian Army. These competencies were divided into 10 groups, namely influencing, communication, team working, cognitive, management, contextual skills, professionalism, project management knowledge, and personal skills and attributes. Surprisingly, both emotional skills and social competencies were not prominent. The results contribute to advance our knowledge by revealing that practitioners involved in complex defence projects value more technical and individual competencies. This study analyses competencies across several complex projects in the defence sector, providing insights to practitioners and expanding the academic debate focused on other industries and single cases. Organisations might use the competencies to recruit, select, and develop human resources involved in complex defence initiatives

Surface roughness on the Greenland Ice Sheet from airborne laser altimetry

This is the published version, also available here: http://dx.doi.org/10.1029/1998GL900041.High resolution airborne laser altimetry is used to determine the small-scale surface relief in central Greenland and estimate the contribution from spatial noise to stratigraphic records. The standard deviation of the surface roughness is 1.6 cm water equivalent, corresponding to a standard deviation of annual layer thickness of 2.3 cm we. This estimate agrees with an independent assessment of the spatial variability (2.5 cm we) based on nine shallow ice cores. The agreement suggests that the statistical nature of the surface in central Greenland remains unchanged throughout the year. By conducting airborne altimetry around proposed drilling sites, the expected noise level in the core can be evaluated and sites selected where this level is lowest

Electrical conductance of hydrogen chloride in dimethylsulphoxide at 25°C

The electrical conductance of hydrogen chloride solutions in DMSO at 25°C has been studied. The limiting molar conductance is 38·7 int mho cm2 int mho cm2/mol. Conductivity data were interpreted with the Fuoss' theory for associated 1-1 type electrolytes. The association constant related to pair formation is 115·7 l/mol. The mechanism of electricl conduction of HCl in DMSO at infinite dilution resembles that of other 1-1 type electrolytes in the same solvent, in which charges are transported by simple entities in a viscous continuum.On a étudié la conductivité électrique des solutions de chlorure d'hydrogéne dans le DMSO à 25°C. La conductivité limite molare est de 38,7 mho int cm2/mol. Les données expŕimentalles de la conductivité furent interprétées d'aprés la théorie de Fuoss pour des électrolytes associé du type 1-1. La constante d'association liée à la formation de paires ioniques simple est 115,7 l/mol. Le mechanisme de la conduction électrique du HCl dans le DMSO à dilution infinie ressemble celui des autres électrolytes du type 1-1 dans le même dissulvant, puisque les charges sont transportées par des entités simples dans un milieu visqueux continu.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Effect of temperature on the electrical conductance of hydrogen chloride in dimethylsulphoxide

The electrical conductance of solutions of hydrogen chloride in dimethylsulphoxide at temperature from 25 to 45°C has been studied. Results have been interpreted with the Fouss theory for associated 1-1 type electrolytes. Values of the association constant KA and the J parameter have been computed at each temperature. The temperature dependence of the molar conductance is inferred from the theoretical equation and related to the temperature dependence of viscosity.La conductance électrique des solutions de chlorure d'hydrogène dans le diméthylsulfoxyde à des températures de 25 a 45°C a été étudiée. Les résultats ont et́é inteprétés par la théorie de Fuoss pour de electrolytes associées du type 1-1. Les valeurs de la constante d'association KA et du paramètre J ont été calculées à chaque température. La dépendance de la conductivité molare avec la température est déduite de l'équation théorique et référée a la dépendance de la viscosité avec la température.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada