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| Titel |
A study of turbulent fluxes and their measurement errors for different wind regimes over the tropical Zongo Glacier (16° S) during the dry season |
| VerfasserIn |
M. Litt, J.-E. Sicart, W. Helgason |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1867-1381
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Measurement Techniques ; 8, no. 8 ; Nr. 8, no. 8 (2015-08-13), S.3229-3250 |
| Datensatznummer |
250116527
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| Publikation (Nr.) |
 copernicus.org/amt-8-3229-2015.pdf |
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| Zusammenfassung |
| Over glaciers in the outer tropics, during the dry winter season, turbulent fluxes are an
important sink of melt energy due to high sublimation rates, but measurements in stable surface
layers in remote and complex terrains remain challenging. Eddy-covariance (EC) and
bulk-aerodynamic (BA) methods were used to estimate surface turbulent heat fluxes of sensible
(H) and latent heat (LE) in the ablation zone of the tropical Zongo Glacier, Bolivia
(16° S, 5080 m a.s.l.), from 22 July to 1 September 2007. We studied the turbulent
fluxes and their associated random and systematic measurement errors under the three most frequent
wind regimes. For nightly, density-driven katabatic flows, and for strong downslope flows related
to large-scale forcing, H generally heats the surface (i.e. is positive), while LE cools it
down (i.e. is negative). On average, both fluxes exhibit similar magnitudes and cancel each other
out. Most energy losses through turbulence occur for daytime upslope flows, when H is weak due
to small temperature gradients and LE is strongly negative due to very dry air. Mean random
errors of the BA method (6 % on net H + LE fluxes) originated mainly from large uncertainties
in roughness lengths. For EC fluxes, mean random errors were due mainly to poor statistical
sampling of large-scale outer-layer eddies (12 %). The BA method is highly sensitive to the
method used to derive surface temperature from longwave radiation measurements and underestimates
fluxes due to vertical flux divergence at low heights and nonstationarity of turbulent flow. The
EC method also probably underestimates the fluxes, albeit to a lesser extent, due to underestimation
of vertical wind speed and to vertical flux divergence. For both methods, when H and LE
compensate each other in downslope fluxes, biases tend to cancel each other out or remain
small. When the net turbulent fluxes (H + LE) are the largest in upslope flows, nonstationarity
effects and underestimations of the vertical wind speed do not compensate, and surface temperature
errors are important, so that large biases on H + LE are expected when using both the EC and the
BA method. |
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