Browsing by Tema "Ablation zone"

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Analysis of seasonal variations in mass balance and meltwater discharge of the tropical Zongo Glacier by application of a distributed energy balance model
(American Geophysical Union, 2011) Jean Emmanuel Sicart; Regine Hock; Pierre Ribstein; Maxime Litt; Edson Ramírez
A distributed energy balance model was applied to Zongo Glacier, Bolivia (16S, 6000-4900 m above sea level, 2.4 km 2 ), to investigate atmospheric forcing that controls seasonal variations in the mass balance and in meltwater discharge of glaciers in the outer tropics. Surface energy fluxes and melt rates were simulated for each 20 20 m 2 grid cell at an hourly resolution, for the hydrological year 1999-2000, using meteorological measurements in the ablation area. Model outputs were compared to measurements of meltwater discharge, snow cover extent, and albedo at two weather stations set up on the glacier. Changes in melt rate in three distinct seasons were related to snowfall and cloud radiative properties. During the dry season (May to August), the low melt rate was mainly caused by low long-wave emission of the cloudless thin atmosphere found at these high altitudes. From September to December, meltwater discharge increased to its annual maximum caused by an increase in solar radiation, which was close to its summer peak, as well as a decrease in glacier albedo. From January on, melt was reduced by snowfalls in the core wet season via the albedo effect but was maintained thanks to high long-wave emission from convective clouds. The frequent changes in snow cover throughout the long ablation season lead to large vertical mass balance gradients. Annual mass balance depends on the timing and length of the wet season, which interrupts the period of highest melt rates caused by solar radiation.
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.
Establishing glacier proximal meteorological and glacier ablation stations in different climatic zones along the South American Andes.
(2024) Owen King; Tom Matthews; Marcos Andrade; Juan‐Luis García; Claudio Bravo; Wouter Buytaert; Juan Marcos Calle; Alejandro Dussaillant; Tamsin Edwards; Iñigo Irarrázaval
Climate change has had a significant impact on the behaviour of the high mountain cryosphere, with widespread glacier retreat and mass loss now occurring in most of the planet&#8217;s glacierised mountain ranges over multi-decadal timescales. If we are to accurately understand the impacts of deglaciation on freshwater availability to communities downstream, robust modelling of future glacier meltwater yield is paramount. Meteorological observations at glacierised elevations are essential to drive simulations of the energy balance at glacier surfaces, and therefore glacier melt, although such records are sparse in most high mountain regions due to the logistical challenges associated with making even short-term measurements. The scarcity of high-altitude meteorological observations has resulted in only limited understanding of factors such as the spatial and temporal variability of temperature lapse rates, precipitation amounts and phase, and the prevalence of conditions suited to sublimation, all of which have an important influence on glacier mass loss rates at high elevation.Here we summarise the installation of meteorological and glacier ablation stations in different climatic zones of the South American Andes - the Tropical Andes of Peru (Nevado Ausangate basecamp, 4800 m, (13&#176;48'45.96"S, 71&#176;12'53.18"W) and Bolivia (Laguna Glaciar, 5300 m, 15&#176;50'10.59"S, 68&#176;33'11.30"W), the Subtropical Andes (Glaciar Universidad, Chile, 2540 m, 34&#176;43'10.07"S, 70&#176;20'44.98"W) and Patagonian Andes (Lago Tranquillo, Chile, 280 m, 46&#176;35'47.00"S, 72&#176;47'38.91"W) &#8211; as part of the NERC-funded Deplete and Retreat Project. Meteorological station records include time series of air temperature and pressure, relative humidity, wind speed and direction, incoming and outgoing short- and longwave radiation, precipitation amount and phase. Coincident glacier ablation is monitored at each site using &#8216;Smart Stakes&#8217;, recording surface elevation change on-glacier. We describe station situation, installation and preliminary measurements, along with aims and objectives of analyses using the meteorological time series.
Modelling melt, runoff, and mass balance of a tropical glacier in the Bolivian Andes using an enhanced temperature-index model
(2016) Pablo Fuchs; Yoshihiro ASAOKA; So Kazama
This paper evaluates the feasibility of applying a coupled melt, runoff, and mass balance model to the tropical Zongo glacier (Cordillera Real, Bolivia) during two hydrological years. Melt rate was estimated using the standard degree-day method (DDM) and an enhanced temperature-index model (ETI). The latter was run with values of parameters obtained for Haut Glacier d’Arolla and a recalibrated parameter set for Zongo glacier. Glacier mass balance was calculated using snowfall inputs and modelled melt and sublimation. Estimated monthly mass balance and discharge were compared with observations from a stake network in the ablation zone and data from a hydrometric station. We concluded that ETI model agrees very well with the reference runoff and mass balance. Net mass balance over the whole glacier was predicted accurately in the ablation zone, but the model overestimated mass balance in the accumulation zone owing to the absence of observations at higher elevations; the equilibrium line altitude and accumulation area ratio were predicted within reasonable limits. The results demonstrate that ETI model is applicable in tropical conditions, provided that the parameters are recalibrated for the climatic settings of this region.
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.