Browsing by Autor "Jean Emmanuel Sicart"

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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.
Can the snowline be used as an indicator of the equilibrium line and mass balance for glaciers in the outer tropics?
(Cambridge University Press, 2012) Antoine Rabatel; Ana Bermejo; Edwin Loarte; Álvaro Soruco; Jesús Gómez; Gonzalo Leonardini; Christian Vincent; Jean Emmanuel Sicart
Abstract Because the glacier snowline is easy to identify on optical satellite images and because in certain conditions it can be used as an indicator of the equilibrium line, it may be a relevant parameter for the study of the relationships between climate and glaciers. Although several studies have shown that the snowline altitude (SLA) at the end of the hydrological year is a good indicator of the equilibrium-line altitude (ELA) for mid-latitude glaciers, such a relationship remains conjectural for tropical glaciers. Indeed, unlike in mid-latitudes, tropical climate conditions result in a distinct seasonality of accumulation/ablation processes. We examine this relationship using direct field ELA and mass-balance measurements made on Glaciar Zongo, Bolivia (~16° S), vand Glaciar Artesonraju, Peru (~9° S), and the SLA retrieved from satellite images acquired in the past two decades. We show that on glaciers in the outer tropics: (1) ablation is reduced during the dry season in austral winter (May-August), the SLA does not change much, and satellite images acquired between May and August could be used to compute the SLA; and (2) the highest SLA detected on a number of satellite images acquired during the dry season provides a good estimate of the annual ELA. However, as snowfall events can occur during the dry season, the SLA detected on satellite images tends to underestimate the ELA. Thus, we recommend validating the SLA computed from satellite images with field data collected on a benchmark glacier before measuring the SLA on other glaciers in the same mountain range for which no field data are available. This study is a major step towards extending the measurement of glacier parameters (ELA and mass balance) at the scale of a whole mountain range in the outer tropics to better document the relationships between climate and glaciers.
Climate controls on the interseasonal and interannual variability of the surface mass balance of a tropical glacier (Zongo Glacier, Bolivia, 16&deg;S): new insights from the application of a distributed energy balance model over 9 years
(2021) Philémon Autin; Jean Emmanuel Sicart; Antoine Rabatel; Álvaro Soruco
Earth and Space Science Open Archive This preprint has been submitted to and is under consideration at Journal of Geophysical Research - Atmospheres. ESSOAr is a venue for early communication or feedback before peer review. Data may be preliminary.Learn more about preprints preprintOpen AccessYou are viewing the latest version by default [v1]Climate controls on the interseasonal and interannual variability of the surface mass balance of a tropical glacier (Zongo Glacier, Bolivia, 16°S): new insights from the application of a distributed energy balance model over 9 yearsAuthorsPhilémonAutiniDJean EmmanuelSicartAntoineRabateliDAlvaroSorucoSee all authors Philémon AutiniDCorresponding Author• Submitting AuthorUniversité Grenoble AlpesiDhttps://orcid.org/0000-0002-5830-1629view email addressThe email was not providedcopy email addressJean Emmanuel SicartIRD /LTHE UMR 5564view email addressThe email was not providedcopy email addressAntoine RabateliDUniv. Grenoble AlpesiDhttps://orcid.org/0000-0002-5304-1055view email addressThe email was not providedcopy email addressAlvaro SorucoUniversidad Mayor de San Andrésview email addressThe email was not providedcopy email address
Contribution of glacier runoff to water resources of La Paz city, Bolivia (16° S)
(Cambridge University Press, 2015) Álvaro Soruco; Christian Vincent; Antoine Rabatel; Bernard Francou; Emmanuel Thibert; Jean Emmanuel Sicart; Thomas Condom
Abstract The supply of glacier water to La Paz city, Bolivia, between 1963 and 2006 was assessed at annual and seasonal timescales based on the mass-balance quantification of 70 glaciers located within the drainage basins of La Paz. Glaciers contributed ∼15% of water resources at an annual scale (14% in the wet season, 27% in the dry season). Uncertainties in our estimation are related to the assumed constant precipitation (∼0.5% for ice-free areas and up to 6.5% for glaciated areas), the constant runoff coefficient (∼1%), the surface areas of the glaciers and catchments (∼5%) and the mean mass-balance uncertainty of the 21 glaciers used to obtain the mass balance of the 70 glaciers (12% of the total discharge). Despite the loss of 50% of the glacierized area during the study period, runoff at La Paz did not change significantly, showing that increase in ice melt rates compensated for reduction in the surface area of the glaciers. In the future, assuming complete disappearance of the glaciers and no change in precipitation, runoff should diminish by ∼12% at an annual scale, 9% during the wet season and 24% during the dry season.
Etude des précipitations et de la fonte sur un glacier tropical: le glacier du Zongo, Bolivie, 16°S
(Taylor & Francis, 2003) Jean Emmanuel Sicart; Pierre Ribstein; Bernard Francou; Robert Gallaire
Résumé Cet article présente les relations entre les précipitations et la fonte sur le glacier du Zongo en Bolivie où l'ablation et l'accumulation sont maximales en saison des pluies (été austral). Les nuages, provenant du bassin amazonien, donnent des précipitations à midi dans les vallées, puis dans l'après-midi en montagne. Lors de l'installation de la saison des pluies de septembre à décembre, les chutes de neige recouvrent temporairement la glace en fusion. Par effet d'albédo, l'énergie solaire absorbée et la fusion varient beaucoup et atteignent leur maximum lorsque le couvert neigeux est réduit. Au cœur de la saison des pluies de janvier à mars, la neige reste à basse altitude sur le glacier, l'albédo est fort et la fonte diminue. La saison sèche de mai à août est une période de faible ablation. La fonte sur les glaciers tropicaux dépend fortement de la répartition saisonnière des précipitations, par l'augmentation d'albédo due aux chutes de neige d'été.
Solid precipitation on a tropical glacier in Bolivia measured with an ultrasonic depth gauge
(Wiley, 2002) Jean Emmanuel Sicart; Pierre Ribstein; Jean Philippe Chazarin; Étienne Berthier
An ultrasonic depth gauge was used to measure snowfall over a 2‐year period near the equilibrium line of the Zongo glacier (2.4 km 2 ), Bolivia (16°S). Study of the influence of wind, air temperature, and air moisture on the measurements gives a quantification of snowfall at a 3‐hour time step, with a sensitivity of 1 cm of snow. The density of fresh snow is estimated by comparison with rain gauge measurements. The year is marked by a dry season from May to August and a wet season from December to April, during which accumulation and melting coincide on the glacier. Snowfall events are associated with a wind of moderate speed from the valley (less than 4 m s −1 ). Masses of moist air originate in the Amazon basin. The orographic effect produces precipitation at midday in the Andean valleys and in the afternoon in the high mountains. Nighttime snowfall events occur during periods of bad weather related to the regional atmospheric circulation and last several days. The density of fresh snow is high, about 250 kg m −3 , because of the high air temperature during snowfall events (over −3°C). The high snow density and the moderate wind speeds prevent snow drifting conditions, which results in low spatial variability of the accumulation on tropical glaciers. Accurate recording of snowfall at a short time step is important for the study of energy fluxes at the glacier surface because snowfall events greatly increase the albedo and solar radiation is generally the main source of melting energy.
Technical note: A low-cost albedometer for snow and ice measurements – theoretical results and application on a tropical mountain in Bolivia
(Copernicus Publications, 2018) Thomas Condom; Marie Dumont; Lise Mourre; Jean Emmanuel Sicart; Antoine Rabatel; Alessandra Viani; Álvaro Soruco
Abstract. This study presents a new instrument called a low-cost albedometer (LCA) composed of two illuminance sensors that are used to measure in situ incident and reflected illuminance values on a daily timescale. The ratio between reflected vs. incident illuminances is called the albedo index and can be compared with actual albedo values. Due to the shape of the sensor, the direct radiation for zenith angles ranging from 55 to 90∘ is not measured. The spectral response of the LCA varies with the solar irradiance wavelengths within the range 0.26 to 1.195 µm, and the LCA detects 85 % of the total spectral solar irradiance for clear sky conditions. We first consider the theoretical results obtained for 10 different ice and snow surfaces with clear sky and cloudy sky incident solar irradiance that show that the LCA spectral response may be responsible for an overestimation of the theoretical albedo values by roughly 9 % at most. Then, the LCA values are compared with two “traditional” albedometers, which are CM3 pyranometers (Kipp &amp; Zonen), in the shortwave domain from 0.305 to 2.800 µm over a 1-year measurement period (2013) for two sites in a tropical mountainous catchment in Bolivia. One site is located on the Zongo Glacier (i.e., snow and ice surfaces) and the second one is found on the crest of the lateral moraine (bare soil and snow surfaces), which present a horizontal surface and a sky view factor of 0.98. The results, at daily time steps (256 days), given by the LCA are in good agreement with the classic albedo measurements taken with pyranometers with R2=0.83 (RMSD = 0.10) and R2=0.92 (RMSD = 0.08) for the Zongo Glacier and the right-hand side lateral moraine, respectively. This demonstrates that our system performs well and thus provides relevant opportunities to document spatiotemporal changes in the surface albedo from direct observations at the scale of an entire catchment at a low cost. Finally, during the period from September 2015 to June 2016, direct observations were collected with 15 LCAs on the Zongo Glacier and successfully compared with LANDSAT images showing the surface conditions of the glacier (i.e., snow or ice). This comparison illustrates the efficiency of this system to monitor the daily time step changes in the snow and ice coverage distributed on the glacier. Despite the limits imposed by the angle view restrictions, the LCA can be used between 45∘ N and 45∘ S during the ablation season (spring and summer) when the melt rate related to the albedo is the most important.
Technical note: A low-cost albedometer for snow and ice measurements –Theoretical results and application on a tropical mountain in Bolivia
(2018) Thomas Condom; Marie Dumont; Lise Mourre; Jean Emmanuel Sicart; Antoine Rabatel; Alessandra Viani; Alavaro Soruco
Abstract. This study presents a new instrument called a low-cost albedometer (LCA) composed of two illuminance sensors that are used to measure in-situ incident and reflected illuminance values on a daily timescale. The ratio between reflected vs. incident illuminances is called the albedo index and can be compared with actual albedo values. Due to the shape of the sensor, the direct radiation for zenith angles ranging from 55° to 90° is not measured. The spectral response of the LCA varies with the solar irradiance wavelengths within the range 0.26 to 1.195 µm, and the LCA detects 85 % of the total spectral solar irradiance for clear sky conditions. We first consider the theoretical results obtained for 10 different ice and snow surfaces with clear sky and cloudy sky incident solar irradiance that show that the LCA spectral response may be responsible for an overestimation of the theoretical albedo values by roughly 9 % at most. Then, the LCA values are compared with two classical albedometers over a one-year measurement period (2013) for two sites in a tropical mountainous catchment in Bolivia. One site is located on the Zongo Glacier (i.e. snow and ice surfaces) and the second one is found on the right-hand side lateral moraine (bare soil and snow surfaces). The results, at daily time steps (256 days), given by the LCA are in good agreement with the classic albedo measurements taken with pyranometers with R2 = 0.83 (RMSD = 0.10) and R2 = 0.92 (RMSD = 0.08) for the Zongo Glacier and the right-hand side lateral moraine, respectively. This demonstrates that our system performs well and thus provides relevant opportunities to document spatio-temporal changes in the surface albedo from direct observations at the scale of an entire catchment at a low cost. Finally, during the period from September 2015 to June 2016, direct observations were collected with 15 LCAs on the Zongo Glacier and successfully compared with LANDSAT images showing the surface state of the glacier (i.e. snow or ice). This comparison illustrates the efficiency of this system to monitor the daily time step changes in the snow/ice coverage distributed on the glacier.