A detailed assessment of snow accumulation in katabatic wind areas on the Ross Ice Shelf, Antarctica

This is the published version, also available here: http://dx.doi.org/10.1029/97JD02337.An investigation of time dependent snow accumulation and erosion dynamics in a wind-swept environment was undertaken at two automatic weather stations sites on the Ross Ice Shelf between January 1994 and November 1995 using newly developed instrumentation employing a technique which automatically disperses inert, colored (high albedo) glass microspheres onto the snow surface at fixed intervals throughout the year. The microspheres act as a time marker and tracer to allow the accumulation rate and wind erosion processes to be quantified with a high temporal resolution. Snow core and snow pit sampling was conducted twice during the study period to identify microsphere horizons in the annual snow accumulation profile, allowing the snow accumulation/erosion events to be reconstructed. The two sites chosen for this investigation have characteristically different mean wind speeds and therefore allow a comparative examination on the role of wind on ice sheet growth. Mass accumulation rate at the two sites for the 14-day integration periods available ranged from 0.0 to >2.0 kg m−2 d−1. The mean mass accumulation rate during the study period was greater at the site with stronger winds (0.69 kg m−2 d−1) than the site with lower mean wind speeds (0.61 kg m−2 d−1); however, the difference between the two means is not statistically significant. Accumulation rates derived from an ultrasonic snow depth gauge operated at one of the sites are compared to the actual tracer-derived accumulation rates and show the limitations of only having a measure of snow surface height with no instantaneous measurements of the snow density profile. Snow depth gauge derived accumulation rates were found to be greatly overestimated during high-accumulation periods and were greatly underestimated during low-accumulation periods

Geometric Aspects of Confining Strings

Confining strings in 4D are effective, thick strings describing the confinement phase of compact U(1) and, possibly, also non-Abelian gauge fields. We show that these strings are dual to the gauge fields, inasmuch as their perturbative regime corresponds to the strong coupling (large e) regime of the gauge theory. In this regime they describe smooth surfaces with long-range correlations and Hausdorff dimension two. For lower couplings e and monopole fugacities z, a phase transition takes place, beyond which the smooth string picture is lost. On the critical line intrinsic distances on the surface diverge and correlators vanish, indicating that world-sheets become fractal.Comment: 19 pages, 4 figures, harvma

An inventory of glacier changes between 1973 and 2011 for the Geladandong Mountain area, China.

This is the publisher's version, also available electronically from http://www.the-cryosphere-discuss.net/7/507/2013/tcd-7-507-2013.htmlThe snow and ice of the Geladangong Mountain area supply the headwaters of the Yangtze River, and long-term changes to glaciers and ice masses in this region due to a warming climate are of great concern. An inventory of glacier boundaries and changes over decades for the Geladandong Mountain area in China has been conducted using remote sensing imagery from Landsat (MSS, TM, ETM+), CERBES CCD, and GIS techniques. Variations in glacier extent has been measured using a~series of digital images since 1973, including Landsat MSS in 1973, Landsat TM in 1992, Landsat ETM+ in 2004, and CBERS CCD in 2011. All Landsat data are snow-free outside the glacier boundaries, allowing an unsupervised classification method to be used to extract glacier area. For the CBERS CCD data, some areas were covered by clouds and snow, requiring an initial unsupervised classification method to divide glacier, clouds and snow from other land types, followed by a supervised visual interpretation to extract glacier area. The results show a decrease in glacier ice cover in the study area during the past 38 yr. From 1973 to 2011, glacier area decreased from 107 105 hectares to 94 220 hectares, or a change of −12%. The speed at which ice cover is being lost has been decreasing during the past 38 yr. The rate of glacier area loss was 0.47% yr−1 from 1973–1992, 0.19% yr−1 from 1992–2004, and 0.14% yr−1 from 2004–2011. While most of the glaciers are shrinking, some are expanding. For the 1973 to 2004 period, retreating glaciers exposed 14 447 hectares of land, and advancing glaciers spread over 2682 hectares that were not covered by ice in 1973. The net glacier area decrease is 11 765 hectares from 1973–2004. For the 1973 to 2011 period, glaciers expanded over 3791 hectares, and retreated from 16 504 hectares

Direct measurements of episodic snow accumulation on the Antarctic polar plateau

This is the published version, also available here: http://dx.doi.org/10.1029/2000JD900099.During a 1-year field experiment at a remote location on the Antarctic polar plateau (85.67°S, 46.38°W) influenced by moderate magnitude katabatic winds, snow accumulation was characterized at three different spatial and temporal scales using snow stakes, tracer material dispersed periodically on the snow surface, and an acoustic depth gauge. The spatial variability of snow accumulation was found to be large, on both annual and intra-annual timescales, and is attributed to the high frequency of moderate to strong winds at the site. Accumulation throughout the year was observed to be episodic in nature, with a small number of snow accumulation events producing the majority of the annual total accumulation for the site, averaging 0.174 m. In the intervals between observed accumulation events (up to several months), negative changes to snow surface height caused by sublimation and densification of the firn were quantified using an acoustic depth gauge. The rate of decrease in snow surface elevation was largest during the austral summer, as expected, and the overall change in snow surface elevation due to sublimation/densification during the year was estimated to be about −0.10 m. Using the precise timing of accumulation events provided by the acoustic depth gauge, meteorological surface observations, numerical model analyses, and satellite imagery were used to gain insights into whether the event was associated with precipitation or related exclusively to blowing snow and to diagnose the meteorological conditions producing the event. Meteorological conditions during the accumulation events were found to strongly support an association with precipitation events caused by mesoscale or synoptic-scale cyclones along the coastal margin. Dating of the accumulation profile using the dispersed tracer technique identified several other accumulation events that were not measured within the target area of the acoustic depth gauge, suggesting that snow accumulation data from a single acoustic depth gauge cannot be extrapolated over a broad area

An automated tracer dispersal system for snow accumulation and saltation transport investigations

New automated instrumentation to assess detailed spatial and temporal dynamics of snow accumulation and saltation transport of snow in remote, harsh environments is described. The instrumentation and techniques provide important quantitative, time dependent information which current methods are incapable of providing such as precise dating of accumulated snow layers, snow grain saltation transport distance in wind-swept environments, and characteristics of wind generated surface features. This instrument consists of an ultralow power timing system, a pneumatic system, and microsphere generators to periodically disperse a tracer of colored glass microspheres onto the snow surface. Snow sampling must be conducted before melting occurs, and subsequent identification of microspheres has shown this method is capable of providing accurate dating information with detailed spatial-resolution, as well as characterizing wind blown saltation transport of snow. (C) 1998 American Institute of Physics

Rapid ice discharge from southeast Greenland glaciers

This is the published version, also available here: http://dx.doi.org/10.1029/2004GL019474.[1] Interferometric synthetic-aperture radar (InSAR) observations of southeast Greenland glaciers acquired by the Earth Remote Sensing Satellites (ERS-1/2) in 1996 were combined with ice sounding radar data collected in the late 1990s to estimate a total discharge of 46 ± 3 km3 ice per year between 62°N and 66°N, which is significantly lower than a mass input of 29 ± 3 km3 ice per year calculated from a recent compilation of snow accumulation data. Further north, Helheim Glacier discharges 23 ± 1 km3/yr vs 30 ± 3 km3/yr accumulation; Kangerdlugssuaq Glacier discharges 29 ± 2 km3/yr vs 23 ± 2 km3/yr; and Daugaard-Jensen Glacier discharges 10.5 ± 0.6 km3/yr vs 10.5 ± 1 km3/yr. The mass balance of east Greenland glaciers is therefore dominated by the negative mass balance of southeast Greenland glaciers (−17 ± 4 km3/yr), equivalent to a sea level rise of 0.04 ± 0.01 mm/yr. Warmer and drier conditions cannot explain the imbalance which we attribute to long-term changes in ice dynamics

Basal conditions of two Transantarctic Mountains outlet glaciers from observation-constrained diagnostic modelling

This is the published version. Copyright 2014 International Glaciological SocietyWe present a diagnostic glacier flowline model parameterized and constrained by new velocity data from ice-surface GPS installations and speckle tracking of TerraSAR-X satellite images, newly acquired airborne-radar data, and continental gridded datasets of topography and geothermal heat flux, in order to better understand two outlet glaciers of the East Antarctic ice sheet. Our observational data are employed as primary inputs to a modelling procedure that first calculates the basal thermal regime of each glacier, then iterates the basal sliding coefficient and deformation rate parameter until the fit of simulated to observed surface velocities is optimized. We find that the two glaciers have both frozen and thawed areas at their beds, facilitating partial sliding. Glacier flow arises from a balance between sliding and deformation that fluctuates along the length of each glacier, with the amount of sliding typically varying by up to two orders of magnitude but with deformation rates far more constant. Beardmore Glacier is warmer and faster-flowing than Skelton Glacier, but an up-glacier deepening bed at the grounding line, coupled with ice thicknesses close to flotation, lead us to infer a greater vulnerability of Skelton Glacier to grounding-line recession if affected by ocean-forced thinning and concomitant acceleration

Thermal quark production in ultra-relativistic nuclear collisions

We calculate thermal production of u, d, s, c and b quarks in ultra-relativistic heavy ion collisions. The following processes are taken into account: thermal gluon decay (g to ibar i), gluon fusion (g g to ibar i), and quark-antiquark annihilation (jbar j to ibar i), where i and j represent quark species. We use the thermal quark masses, $m_i^2(T)\simeq m_i^2 + (2g^2/9)T^2$, in all the rates. At small mass ($m_i(T)<2T$), the production is largely dominated by the thermal gluon decay channel. We obtain numerical and analytic solutions of one-dimensional hydrodynamic expansion of an initially pure glue plasma. Our results show that even in a quite optimistic scenario, all quarks are far from chemical equilibrium throughout the expansion. Thermal production of light quarks (u, d and s) is nearly independent of species. Heavy quark (c and b) production is quite independent of the transition temperature and could serve as a very good probe of the initial temperature. Thermal quark production measurements could also be used to determine the gluon damping rate, or equivalently the magnetic mass.Comment: 14 pages (latex) plus 6 figures (uuencoded postscript files); CERN-TH.7038/9

Improvement of radar ice-thickness measurements of Greenland outlet glaciers using SAR processing

This is the published version, also available here: http://dx.doi.org/10.3189/172756402781816852.Extensive aircraft-based radar ice-thickness measurements over the interior and outlet-glacier regions of the Greenland ice sheet have been obtained by the University of Kansas since 1993, with the latest airborne surveys conducted in May 2001. The radar has evolved during this period to a highly versatile system capable of characterizing ice thickness over a wide variety of ice-sheet conditions. Before 1997, the digital system was limited, only capable of storing incoherent data or coherent data with a very large number of presumed signals at a low pulse-repetition frequency. In 1998, the radar was upgraded with modern components allowing coherent data to be stored with a small number of presumed returns for 1024 range cells at a high pulse-repetition frequency.The new data on ice thickness of Greenland outlet glaciers are archived and made available to the scientific community in the form of radar echograms and derived ice thickness at http://tornado.rsl.ukans.edu/Greenlanddata.htm. The U.S. National Snow and Ice Data Center (NSIDC) also provides a link to these data, and NSIDC will eventually serve as the permanent archive of these data. Improvements in radar sensitivity in outlet-glacier regions have been achieved by collecting coherent radar data and applying various signal-processing techniques. Deep outlet-glacier channels that were previously unresolved with incoherent data can now be mapped using a coherent signal, signal conditioning and synthetic aperture radar (SAR) processing

Thermoregulation of \u3ci\u3eEscherichia coil pap\u3c/i\u3e Transcription: H-NS is a Temperature-Dependent DNA Methylation Blocking Factor

The expression of Pap pili that facilitate the attach- ment of Escherichia coli to uroepithelial cells is shut off outside the host at temperatures below 268C. Ribo- nuclease protection analysis showed that this thermo- regulatory response was rapid as evidenced by the absence of papBA transcripts, coding for Pap pilin, after only one generation of growth at 238C. The his- tone-like nucleoid structuring protein H-NS and DNA sequences within papB were required for thermoregu- lation, but the PapB and PapI regulatory proteins were not. In vivo analysis of pap DNA methylation patterns indicated that H-NS or a factor regulated by H-NS bound within the pap regulatory region at 238C but not at 378C, as evidenced by H-NS-dependent inhibi- tion of methylation of the pap GATC sites designated GATC-I and GATC-II. These GATC sites lie upstream of the papBAp promoter and have been shown pre- viously to play a role in controlling Pap pili expression by regulating the binding of Lrp, a global regulator that is essential for activating papBAp transcription. Competitive electrophoretic mobility shift analysis showed that H-NS bound specifically to a pap DNA fragment containing the GATC-I and GATC-II sites. Moreover, H-NS blocked methylation of these pap GATC sites in vitro : H-NS blocked pap GATC methyla- tion at 1.4 mM but was unable to do so at higher con- centrations at which non-specific binding occurred. Thus, non-specific binding of H-NS to pap DNA was not sufficient to inhibit methylation of the pap GATC sites. These results suggest that the ability of H-NS to act as a methylation blocking factor is dependent upon the formation of a specific complex of H-NS with pap regulatory DNA. We hypothesize that a func- tion of H-NS such as oligomerization was altered at 238C, which enabled H-NS to repress pap gene expres- sion through the formation of a specific nucleoprotein complex