Browsing by Autor "Regine Hock"

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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.
Climate Controls on the Interseasonal and Interannual Variability of the Surface Mass and Energy Balances of a Tropical Glacier (Zongo Glacier, Bolivia, 16°S): New Insights From the Multi‐Year Application of a Distributed Energy Balance Model
(Wiley, 2022) Philémon Autin; Jean‐Emmanuel Sicart; Antoine Rabatel; Álvaro Soruco; Regine Hock
Abstract The application of a distributed energy balance model over nine years at an hourly time step to a 20 × 20 m grid cell over Glacier Zongo (Bolivia, 16°S) enabled assessment of the climate factors that control the interseasonal and interannual variability of its surface mass balance. The model was validated by comparing the measured and simulated discharge at the outlet, albedo at the Automatic Weather Station, surface state and annual mass balance both glacier‐wide and as a function of altitude. Analysis of the mean monthly energy fluxes highlighted the importance of the meteorological conditions over October and November on the variability of the annual surface mass balance. Two sensitivity analyses are presented, one of the distribution of precipitation over time which maintains a physical coherence between the different meteorological variables and one of the impact of prolonged periods of intense cloud radiative forcing on the surface mass balance. The distribution of precipitation events over time and their associated amounts are the main drivers of the interannual variability of the surface mass balance via an albedo feedback effect. Additionally, prolonged periods of negative cloud radiative forcing, specifically over the month of November, notably reduce the melt rate.
Contribution from glaciers and snow cover to runoff from mountains in different climates
(Wiley, 2006) Regine Hock; Gwyn Rees; Mark Williams; Edson Ramírez