HR: 0800h
AN: C31A-0293 INVITED     [Abstracts]
TI: Eddy correlation measurements of sensible and latent heat transfer coefficients over a high altitude glacier snow surface in the Andes Mountains, Bolivia.
AU: * Pomeroy, J
EM: pomeroy@usask.ca
AF: Centre for Hydrology, University of Saskatchewan 117 Science Place, Saskatoon, S7N 5C8 Canada
AU: Wagnon, P
EM: patrick@lgge.obs.ujf-grenoble.fr
AF: IRD-LGGE, BP 96, St Martin d'Heres, 38402 France
AU: Sicart, J E
EM: jms@aber.ac.uk
AF: Centre for Glaciology, University of Wales, Aberystwyth, SY23 3DB United Kingdom
AU: Solohub, M
EM: michael.solohub@usask.ca
AF: Centre for Hydrology, University of Saskatchewan 117 Science Place, Saskatoon, S7N 5C8 Canada
AU: Lejeune, Y
EM: Yves.Lejeune@meteo.fr
AF: Centre d'Etudes de la Neige, Meteo France 1441 Rue de la Piscine, St Martin d'Heres, 38406 France
AU: Essery, R
EM: rie@aber.ac.uk
AF: Centre for Glaciology, University of Wales, Aberystwyth, SY23 3DB United Kingdom
AB: An eddy correlation system was installed at 5100 m elevation on the Zongo Glacier in the Andes Mountains near La Paz, Bolivia in order to evaluate the transfer of sensible and latent heat to ablating snow on the glacier surface. Concomitant measurements of all radiation components, snow surface temperature, vertical gradients of air temperature, humidity and wind speed and of surface melt and sublimation were made. The site was approximately level within several hundred metres, with drainage winds at night and dry conditions prevailed in the austral sub-tropical winter. The results show that in the exceeding dry and thin atmosphere, surface temperatures below freezing are maintained throughout melt with significant cooling of the surface due to sublimation and low longwave radiation input. Turbulent transfer to the snow surface was in the rough flow regime with roughness heights similar to that of seasonal snowcovers. Transfer coefficient of sensible heat and water vapour was enhanced several fold with respect to that for momentum diffusivity, despite frequent stable conditions in the lowest few metres. Over mid-continental seasonal snowcovers, turbulent transfer of latent and sensible heat is usually dampened with respect to momentum transfer; the influence of surrounding melting snowcover on large scale air masses and consequent entrainment is often invoked as the cause. However in the Andes, melting snow on glaciers is surrounded by arid high plateau and mountains which were snowfree at the time of observations. Complex flows over the mountains and drainage winds would permit substantial entrainment of dry, warm air. Cool surface temperatures driven by longwave loss ensured strong temperature gradients. The resulting sublimation rates at the surface exceeded 100 W/m2 latent heat flux at times and were matched by opposing sensible heat fluxes, which are amongst the highest reported for surface snow in the world. These aspects of turbulent transfer help to explain the rapid ablation rates that IRD has observed for tropical glaciers and make important limitations on the water resources that can be derived from the same.
DE: 3322 Land/atmosphere interactions
DE: 1827 Glaciology (1863)
DE: 1863 Snow and ice (1827)
DE: 1894 Instruments and techniques
SC: Cryosphere [C]
MN: 2004 AGU Fall Meeting