Browsing by Autor "Patrick Wagnon"

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A Nonlinear Statistical Model for Extracting a Climatic Signal From Glacier Mass Balance Measurements
(Wiley, 2018) Christian Vincent; Álvaro Soruco; M Azam; Rubén Basantes-Serrano; Miriam Jackson; Bjarne Kjøllmoen; Emmanuel Thibert; Patrick Wagnon; Delphine Six; Antoine Rabatel
Abstract Understanding changes in glacier mass balances is essential for investigating climate changes. However, glacier‐wide mass balances determined from geodetic observations do not provide a relevant climatic signal as they depend on the dynamic response of the glaciers. In situ point mass balance measurements provide a direct signal but show a strong spatial variability that is difficult to assess from heterogeneous in situ measurements over several decades. To address this issue, we propose a nonlinear statistical model that takes into account the spatial and temporal changes in point mass balances. To test this model, we selected four glaciers in different climatic regimes (France, Bolivia, India, and Norway) for which detailed point annual mass balance measurements were available over a large elevation range. The model extracted a robust and consistent signal for each glacier. We obtained explained variances of 87.5, 90.2, 91.3, and 75.5% on Argentière, Zongo, Chhota Shigri, and Nigardsbreen glaciers, respectively. The standard deviations of the model residuals are close to measurement uncertainties. The model can also be used to detect measurement errors. Combined with geodetic data, this method can provide a consistent glacier‐wide annual mass balance series from a heterogeneous network. This model, available to the whole community, can be used to assess the impact of climate change in different regions of the world from long‐term mass balance series.
Atmospheric warming at a high‐elevation tropical site revealed by englacial temperatures at Illimani, Bolivia (6340 m above sea level, 16°S, 67°W)
(American Geophysical Union, 2010) Adrien Gilbert; Patrick Wagnon; Christian Vincent; Patrick Ginot; M. Funk
In June 1999, a deep (138.7 m) ice core was extracted from the summit glacier of Illimani, Bolivia (6340 m above sea level, 16°39′S, 67°47′W), and an englacial temperature profile was measured in the borehole. Using on‐site and regional meteorological data as well as ice core stratigraphy, past surface temperatures were reconstructed with a heat flow model. The englacial temperature measurements exhibit a profile that is far from a steady state, reflecting an increasing atmospheric temperature over several years and nonstationary climatic conditions. Englacial temperature interpretation, using air temperature data, borehole temperature inversion, and melting rate quantification based on ice core density, shows two warming phases from 1900 to 1960 (+0.5 ± 0.3 K starting approximately in 1920–1930) and from 1985 to 1999 (+0.6 ± 0.2 K), corresponding to a mean atmospheric temperature rise of 1.1 ± 0.2 K over the 20th century. According to various climate change scenarios, the future evolution of englacial temperatures was simulated to estimate when and under what conditions this high‐elevation site on the Illimani summit glacier could become temperate in the future. Results show that this glacier might remain cold for more than 90 years in the case of a +2 K rise over the 21st century but could become temperate in the first 20 m depth between 2050 and 2060 if warming reaches +5 K.
Degree-day melt models for paleoclimate reconstruction from tropical glaciers: calibration from mass balance and meteorological data of the Zongo glacier (Bolivia, 16&lt;b&gt;°&lt;/b&gt; S)
(2011) Pierre‐Henri Blard; Patrick Wagnon; Jérôme Lavé; Álvaro Soruco; Jean‐Emmanuel Sicart; Bernard Francou
Abstract. This paper describes several simple positive degree-day models (hereafter referred as "PDD models") designed to provide past climatic reconstruction from tropical glacier paleo-equilibrium altitude lines (paleo-ELA). Several ablation laws were tested and calibrated using the monthly ablation and meteorological data recorded from 1997 to 2006 on the Zongo glacier (Cordillera Real, Bolivia, 16° S). The performed inversion analyses indicate that the model provides a better reconstruction of the mass balance if the ablation is modeled with different melting factors for snow and ice. The inclusion of short-wave solar radiations does not induce a substantial improvement. However, this type of model may be very useful to quantify the effects of local topographic (orientation, shading) and to take into account incoming solar radiation changes at geological timescale. The performed sensitivity test indicates that, in spite of the uncertainty in the calibrated snow-ice ablation factors, all models are able to provide paleotemperatures with ~1 °C uncertainty for a given paleoprecipitation. This error includes a 50 m uncertainty in the estimate of the paleoELA. Finally, the models are characterized by different precipitation-temperature sensitivities: if a similar warming is applied, model including different ablation factors for snow and ice requires a lower precipitation increase (by ∼15 %) than others to maintain the ELA.
Glaciers of the Tropical Andes: Indicators of Global Climate Variability
(Springer Nature (Netherlands), 2005) Bernard Francou; Pierre Ribstein; Patrick Wagnon; Edson Ramírez; Bernard Pouyaud
Reduced melt on debris-covered glaciers: investigations from Changri NupGlacier, Nepal
(Copernicus Publications, 2016) Christian Vincent; Patrick Wagnon; J. M. Shea; Walter W. Immerzeel; Philip Kraaijenbrink; Dibas Shrestha; Álvaro Soruco; Yves Arnaud; Fanny Brun; Étienne Berthier
Abstract. Approximately 25 % of the glacierized area in the Everest region is covered by debris, yet the surface mass balance of debris-covered portions of these glaciers has not been measured directly. In this study, ground-based measurements of surface elevation and ice depth are combined with terrestrial photogrammetry, unmanned aerial vehicle (UAV) and satellite elevation models to derive the surface mass balance of the debris-covered tongue of Changri Nup Glacier, located in the Everest region. Over the debris-covered tongue, the mean elevation change between 2011 and 2015 is −0.93 m year−1 or −0.84 m water equivalent per year (w.e. a−1). The mean emergence velocity over this region, estimated from the total ice flux through a cross section immediately above the debris-covered zone, is +0.37 m w.e. a−1. The debris-covered portion of the glacier thus has an area-averaged mass balance of −1.21 ± 0.2 m w.e. a−1 between 5240 and 5525 m above sea level (m a.s.l.). Surface mass balances observed on nearby debris-free glaciers suggest that the ablation is strongly reduced (by ca. 1.8 m w.e. a−1) by the debris cover. The insulating effect of the debris cover has a larger effect on total mass loss than the enhanced ice ablation due to supraglacial ponds and exposed ice cliffs. This finding contradicts earlier geodetic studies and should be considered for modelling the future evolution of debris-covered glaciers.
Tropical climate change recorded by a glacier in the central Andes during the last decades of the twentieth century: Chacaltaya, Bolivia, 16°S
(American Geophysical Union, 2003) Bernard Francou; Mathias Vuille; Patrick Wagnon; Javier Mendoza; Jean‐Emmanuel Sicart
The reasons for the accelerated glacier retreat observed since the early 1980s in the tropical Andes are analyzed based on the well‐documented Chacaltaya glacier (Bolivia). Monthly mass balance measurements available over the entire 1991–2001 decade are interpreted in the light of a recent energy balance study performed on nearby Zongo glacier and further put into a larger‐scale context by analyzing the relationship with ocean‐atmosphere dynamics over the tropical Pacific‐South American domain. The strong interannual variability observed in the mass balance is mainly dependent on variations in ablation rates during the austral summer months, in particular during DJF. Since high humidity levels during the summer allow melting to be distinctly predominant over sublimation, net all‐wave radiation, via albedo and incoming long‐wave radiation, is the main factor that governs ablation. Albedo depends on snowfall and a deficit during the transition period and in the core of the wet season (DJF) maintains low albedo surfaces of bare ice, which in turn leads to enhanced absorption of solar radiation and thus to increased melt rates. On a larger spatial scale, interannual glacier evolution is predominantly controlled by sea surface temperature anomalies (SSTA) in the eastern equatorial Pacific (Niño 1+2 region). The glacier mass balance is influenced by tropical Pacific SSTA primarily through changes in precipitation, which is significantly reduced during El Niño events. The more frequent occurrence of El Niño events and changes in the characteristics of its evolution, combined with an increase of near‐surface temperature in the Andes, are identified as the main factors responsible for the accelerated retreat of Chacaltaya glacier.
Turbulence Characteristics in the Atmospheric Surface Layer for Different Wind Regimes over the Tropical Zongo Glacier (Bolivia, $$16^\circ $$ 16 ∘ S)
(Springer Science+Business Media, 2014) Maxime Litt; Jean‐Emmanuel Sicart; Warren Helgason; Patrick Wagnon