The 1979-2005 Greenland ice sheet melt extent from passive microwave data using an improved version of the melt retrieval XPGR algorithm

Analysis of passive microwave satellite observations over the Greenland ice sheet reveals a significant increase in surface melt over the period 1979-2005. Since 1979, the total melt area was found to have increased +1.22 x 10ˆ7 kmˆ2. An improved version of the cross-polarized gradient ratio (XPGR) technique is used to identify the melt from the brightness temperatures. The improvements in the melt retrieval XPGR algorithm as well as the surface melt acceleration are discussed with results from a coupled atmosphere-snow regional climate model. From 1979 to 2005, the ablation period increases everywhere over the melt zone except in the regions where the model simulates an increased summer snowfall. Indeed, more snowfall in summer decreases the liquid water content of the snowpack, raises the albedo and therefore reduces the melt. Finally, this melt acceleration over the Greenland ice sheet is highly correlated with both Greenland and global warming suggesting a continuing surface melt increase in the future.Peer reviewe

Decline in Surface Melt Duration on Larsen C Ice Shelf Revealed by ASCAT Scatterometer

Surface melting has been contributing to the surface lowering and loss of firn air content on Larsen C Ice Shelf since at least the mid-1990s. Where the amount of melting and refreezing is significant, the firn can become impermeable and begin to support ponds of surface meltwater such as have been implicated in ice shelf collapse. Although meteorological station data indicated an increase in melt on the Antarctic Peninsula over the second half of the 20th century, the existing Ku-band Quick Scatterometer (QuikSCAT) time series is too short (1999–2009) to detect any significant 21st century trends. Here we investigate a longer 21st century period by extending the time series to 2017 using the C-band Advanced Scatterometer (ASCAT). We validate our recent observations with in situ weather station data and, using a firn percolation model, explore the sensitivity of scatterometry to water at varying depths in the firn. We find that active microwave C-band (5.6-cm wavelength) instruments can detect water at depths of up to 0.75 m below a frozen firn layer. Our longer scatterometry time series reveals that Larsen C Ice Shelf has experienced a decrease in melt season length of 1–2 days per year over the past 18 years consistent with decreasing summer air temperatures. Only in western inlets, where föhn winds drive melt, has the annual melt duration increased during this period

Rise in frequency of surface melting at Siple Dome through the Holocene : evidence for increasing marine influence on the climate of West Antarctica

Author Posting. © American Geophysical Union, 2008. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 113 (2008): D02112, doi:10.1029/2007JD008790.A new melt layer history from Siple Dome, West Antarctica, indicates notable late-Holocene summertime warming. Visual stratigraphic analyses of the 1004-m ice core identified 62 years with melt layers. Melting events began around 11.7 ka, followed by a period of no melting from 8.8–6.6 ka. Melt layer frequency increased from 6.6 ka to the present, with the 1000-year-average melt layer frequency reaching a maximum of 2% at 0.8 ka. We use our millennial-scale archive of melt events as a unique seasonal paleothermometer to elucidate changes in West Antarctic Holocene summer climate. Our calibration suggests the change in melt frequency from 0% to 2% may represent a summer temperature increase of ≥2°C from the middle to late Holocene. This temperature change cannot be explained entirely by local change in ice elevation or summer insolation and is in contrast to East Antarctic climate records, which show peak warmth in the early Holocene followed by stable or decreasing temperature. We interpret the rise in melt frequency as evidence of an increasing marine influence on the Ross Sea sector of West Antarctica. Although the surface elevation of Siple Dome has not changed greatly, the continued lateral retreat of the West Antarctic ice sheet from its Last Glacial Maximum configuration (across the outer continental shelf), and the delayed drawdown in ice thickness from the adjacent coastal Marie Byrd Land region, in conjunction with periods of increased cyclogenesis, perhaps related to variations in ENSO, would allow a moderated maritime climate to more easily reach West Antarctica.This research was supported by NSF grant OPP-9814485 and NASA grant NAG5-7776 to Penn State University and by a NASA Earth System Science Graduate Fellowship and a WHOI Postdoctoral Scholar Fellowship to S. Das. Additional support to R. Alley at PSU is from NSF grants 0440899, 0440447, and 0424589 and the Comer Science and Education Foundation

Contribution à l'étude du climat antarctique : variabilité de la fonte de surface par télédétection micro-onde entre 1979 et 1999 ; et paramétrisation de la couche limite atmosphérique stable

In the first part of this report, partial summer melting of antarctic snow, which significantly affects the microwave emissivity of the surface, is identified and counted over 18 years in the 20-year period 1980-1999. To process the satellite data, an algorithm that adapts to the spatial and interannual variability of the mean brightness temperature of snow was developped. The cumulated product of the surface area affected by melting and the duration of the melting event, called Cumulative Melting Surface (CMS), is one of the three melt indices defined and discussed here. On average over the last 20 years, the Antarctic CMS has decreased by 1.8 ± 1 % year-l, a result which is consistent with a mean January cooling of the continent, recently identified by others from infrared satellite data. In addition, the interannual signature of the Antarctic Oscillation (AO), and possibly of the Southern Oscillation (ENSO), are found in the melt indices. Atmospheric general circulation models (AG CM) are still insufficiently advanced to adequately describe ail polar climate charateristics. In particular, the surface energy balance, and consequently snow melt, is incorrectly simulated by the AGCM LMDz. To improve this, a non local parametrisation of surface turbulent fluxes in highly stable and long-lived boundary layers (typical of the long antarctic polar night) is tested. The parametrisation accounts for vertical propagation of gravit y waves from the free troposphere, creating intermittent turbulence in the stable layer. Despite a high interannual climatic variability, the surface temperature and wind speed are generally better simulated on the continent, but a decoupling between the surface and the first vertical level appears near Vostok.Dans une première partie de ce travail, la fonte estivale partielle de la neige antarctique, qui affecte fortement l'émissivité micro-onde de la surface, est identifiée et comptabilisée au cours de 18 années sur la période 1980-1999. Pour cela, un algorithme de traitement des données satellitales s'adaptant à la variabilité spatiale et inter-annuelle de la température de brillance moyenne de la neige a été développé. Le cumul du produit de la surface affectée par la fonte par la durée de la période de fonte , appelé Cumulative Melting Surface CMS), est un des 3 indices définis et discutés ici. En moyenne sur les 20 années, le CMS Antarctique a diminué de 1.8 ± 1 % an- l, résultat cohérent avec un refroidissement des températures moyennes du mois de janvier sur le continent, récemment identifié par d'autres à partir de mesures dans l'infra-rouge. De plus, les indices de fonte comportent les signatures inter-annuelles de l'Oscillation Antarctique (AO), et peut-être de l'Oscillation Sud El Nino (ENSO). Les modèles actuels de circulation générale de l'atmosphère (MCGA) prennent mal en compte certaines des caractéristiques du climat des zones polaires. Ainsi, la simulation du bilan d'énergie de surface, donc la fonte, par le MCGA LMDz est encore peu fiable. Afin d'améliorer ce point, nous avons testé une paramétrisation non-locale des flux turbulents de surface pour les couches limites très durables et très stables (typiques de la longue nuit polaire antarctique). Cette paramétrisation autorise la propagation verticale des ondes de gravité depuis la troposphère libre, et simule donc l'apparition de turbulence intermittente dans la couche stable. Malgré la forte variabilité climatique inter-annuelle, il semblerait que la température du sol et l'intensité du vent soient généralement mieux décrites à l'intérieur du continent, mais un problème de découplage entre le sol et le premier niveau vertical du modèle apparaît près de Vostok

Un siècle de reconstruction du bilan de masse du glacier de Sarennes dans les Alpes Françaises

International audienceThe 50 year time series of mass balance on Glacier de Sarennes is one of the longest in the French Alps, and so is often used as a reference for glacier variations in the French Alps. Meteorological data can be used to extend the series backwards in time. Martin (1978) proposed such a reconstruction for the 1882-1977 period. With 50 years of observations, we show that the classical method used by Martin is too dependent oil the calibration period. We therefore try to improve the accuracy of this reconstruction using the Vincent and Vallon (1997) method which takes into account the albedo change of the surface during the ablation period (this is called the daily method). This new method appears to be stable in time. Once calibrated, the daily method is applied to reconstruct the 1881-1949 period. The new reconstruction is compared to a volumetric balance between two maps from 1906 and 1981. It appears that both reconstructions (classical and daily) fall to render the trend correctly over a long period of time. The cumulative centred mass balance correlates well (r(2) = 0.62) with the hydrological mass-balance series of Aletschgletscher, Switzerland

Real-time PCR detection of the effect of postweaning on the expression of cytokines and NF-κB in piglets

ig weaning involves radical changes, which affect health, behavior and performance. Weaning stress dramatically impacts the porcine immune system. This study aimed to evaluate the expression of different cytokines and nuclear factor kappa B (NF-kappa B) in growing postweaning pigs. Forty piglets weaned at 28 days of age, with an average starting weight of 10.12 +/- 0.28 kg were considered for the analysis (time 0) and followed up for 28 days (time 1). Growth performance, skin lesions, cytokines and NF-kappa B expression were measured. The results showed an increased expression of two cytokines with pro-inflammatory effect, interleukin (IL)-8 and interferon-gamma (IFN-gamma), a cytokine with anti-inflammatory effect, IL-4, and a cytokine with both pro- and anti-inflammatory effects, IL-6. An effect of time was observed for body lesions. Compared to females, male piglets had higher levels of all cytokines tested (IL-1 beta, IL-6, IL-8, IL-10, TNF-alpha, IL-4) except IFN-gamma. Also NF-kappa B resulted expressed higher in males compared to females. In conclusion, this study demonstrated that weaning in piglets is associated with increased expression of inflammatory cytokines

METHOD FOR MEASURING A FLUID VELOCITY AND RELATED APPARATUS

A method for measuring the mean velocity (VH) of an extracorporeal blood fluid or infusion fluid, by means of retroinjection interferometry, comprises the step of emitting a first laser light beam (41), from the laser cavity (40) of a semiconductor laser source (60), reflection of a second laser beam (45) by the fluid (50) and consequent generation of interference with the first laser beam (41) inside the laser cavity (40), detection of the interference signal by a monitoring photodiode (46), and processing, by means of an electronic processing and control circuit (100), of the interference signal detected. The invention also comprises an apparatus (62) for implementing the method described and an extracorporeal circuit (58) comprising said apparatus. The invention also comprises a method for replacing a laser source in said apparatus

METHOD FOR MEASURING A FLUID VELOCITY AND RELATED APPARATUS

A method for measuring the mean velocity (VH) of an extracorporeal blood fluid or infusion fluid, by means of retroinjection interferometry, comprises the step of emitting a first laser light beam (41), from the laser cavity (40) of a semiconductor laser source (60), reflection of a second laser beam (45) by the fluid (50) and consequent generation of interference with the first laser beam (41) inside the laser cavity (40), detection of the interference signal by a monitoring photodiode (46), and processing, by means of an electronic processing and control circuit (100), of the interference signal detected. The invention also comprises an apparatus (62) for implementing the method described and an extracorporeal circuit (58) comprising said apparatus. The invention also comprises a method for replacing a laser source in said apparatus

Metodo di misurazione della velocita' di un fluido e relativa apparecchiatura.

The present invention relates to a method for measuring the velocity of fluids, in particular infusion fluids, used generally in the sanitary field, or blood flowing in extracorporeal circuits, and the description which follows is provided with reference to this area of application solely in order to simplify illustration thereof. The invention also relates to the apparatus for implementing this method. Measuring the velocity of the fluid is useful for obtaining other important measurements such as the flowrate within a pipe