Wintertime high‐altitude surface energy balance of a Bolivian glacier, Illimani, 6340 m above sea level

Wagnon, Patrick; Sicart, J.; Berthier, Étienne; Chazarin, Jean-Philippe

doi:10.1029/2002jd002088

Cited by 86 publications

(98 citation statements)

References 35 publications

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“…, comparable to those on other tropical glaciers [e.g., Wagnon et al, 1999bWagnon et al, , 2003. Since East African precipitation seasonality was disrupted in the investigated period [Waple et al, 2002;Hardy, 2003], the annual cycle with a more negative QL in the typical dry seasons and a less negative QL in the typical rainy seasons [Wagnon et al, 1999a[Wagnon et al, , 2001] is not pronounced.…”

supporting

confidence: 72%

“…Wagnon et al [2003] show this procedure in detail. A note on the stability of the surface boundary layer at the Kibo AWS site is given in section 5.…”

Section: à2mentioning

confidence: 99%

“…The scalar roughness lengths of temperature, z 0h , and of water vapor, z 0v , (both in m) indicate the height above the surface where the logarithmic profile of the respective variable reaches the surface value. Roughness lengths are determined either by profile measurements and the subsequent selection of ''near-neutral'' profiles [e.g., Denby and Snellen, 2002], or alternatively, they are calibrated from sublimation measurements [e.g., Wagnon et al, 2003]. Since such measurements are not yet available from Kibo, a value of 0.1 mm is used for all three roughness lengths, following Lewis et al [1999].…”

mentioning

confidence: 99%

“…[15] Stability correction is usually considered in terms of the bulk Richardson number (Ri b ) [e.g., Schneider, 1999;Wagnon et al, 2003] or the Obukhov length [e.g., Gustafsson et al, 2001]. Here Ri b is calculated as a function of T a , T S , z m , z 0m , v, and the acceleration of gravity (9.81 m s…”

mentioning

confidence: 99%

“…) which is replaced by the heat constant for sublimation, L S (2.848 MJ kg À1 ), if T S is below the melting point [e.g., Wagnon et al, 2003]. The parameter z 0m is the roughness length of momentum (in m) and is a measure of the aerodynamic roughness of the surface.…”

mentioning

confidence: 99%

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Ablation and associated energy balance of a horizontal glacier surface on Kilimanjaro

2004

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[1] The surface energy balance of a glacier describes the physical connection between ice/snow ablation and climatic forcing. To expand knowledge on the response of Kilimanjaro's glaciers to climate variations, this study estimates the energy balance on a horizontal glacier surface at the summit for the periods March to September 2000 and March 2001 to February 2002. An automatic weather station (AWS) operating at 5794 m above sea level provides the data input, and ablation at the AWS site differed considerably between the two periods. The energy balance model employed incorporates radiative fluxes, turbulent heat fluxes, and the energy flux in the subsurface. On a monthly basis, results show that radiative energy dominates energy exchanges at the glacier-atmosphere interface, governed by the variation in net shortwave radiation. The turbulent latent heat flux, which is always negative (i.e., continuous mass loss due to sublimation), is the second important energy flux. In contrast, turbulent exchange of sensible heat remains of minor importance. The marked difference in ablation between the two periods can largely be explained by a difference in surface albedo. Albedo depends on precipitation amount and frequency and directly controls net shortwave radiation receipt. In the context of modern glacier retreat on Kilimanjaro the results support other evidence that Kilimanjaro's glaciers are extremely sensitive to precipitation variability.

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supporting

confidence: 72%

“…Wagnon et al [2003] show this procedure in detail. A note on the stability of the surface boundary layer at the Kibo AWS site is given in section 5.…”

Section: à2mentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Ablation and associated energy balance of a horizontal glacier surface on Kilimanjaro

2004

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Mass and Energy Balances of Glaciers and Ice Sheets

Cogley

2005

Encyclopedia of Hydrological Sciences

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Glaciers exchange energy and mass with the rest of the hydrosphere by snowfall, melting, vapor transfer, and the calving of icebergs. Melting and vapor transfer are significant in both the energy balance and the mass balance, which in consequence are intimately coupled. Glacier energy balances differ from those of other natural surfaces in having small or even negative net radiation. Emission of terrestrial radiation is limited, the surface temperature being no greater than the freezing point, but the surface albedo is always high. The limit on surface temperature, and the year-round tendency for net radiative cooling, means that sensible heat transfer is generally downward, while vapor transfer may be either upward or downward. Once conduction has raised a surface layer to the freezing point, further energy surpluses are used to melt snow or ice. In winter, the energy balance is dominated by radiative cooling. Apart from its close connection with the energy balance, the mass balance is also influenced strongly by glacier dynamics. Glaciers and the flowlines of which they are composed exhibit vertical zonation, with net accumulation at higher and net ablation (mass loss) at lower elevations. This imbalance drives, and is corrected by, the ice flow. The leading methods for the measurement of mass balance are the direct, geodetic, and kinematic methods. Direct measurement involves determining the accumulation and ablation in situ or by equivalent remote sensing, with separate treatment of calving where it occurs. Geodetic measurements require the determination of glacier thickness at two epochs; the change of thickness, approximately equal to the change in surface elevation, gives a volume balance that may be converted to a mass balance if the density of the mass gained or lost can be supplied accurately. In the direct and geodetic approaches, the ice flow is assumed to integrate to zero over any one flowline (correctly, if the entire flowline is measured). Kinematic methods are free of this restriction. They involve measurement of all of the terms in the balance and are therefore more difficult. The need for better understanding of mass balance, at socioeconomic scales from local to global, has stimulated intense study of ways to improve the measurements. Recent and impending methodological advances are coming from radar altimetry, laser altimetry, gravimetry, passive-microwave remote sensing, and interferometry using synthetic aperture radar. A subject requiring increased attention, as the measurements improve in precision and coverage, is improved quantification of the measurement errors. The best current estimates of global average mass balance are equivalent to 0.14-0.44 mm a −1 of sea-level rise, to be compared with the inferred total rate of about 1.9 mm a −1 . This figure is a composite of estimates for "small" glaciers (those other than the ice sheets), whose balance has been growing more negative since the 1960s; the Greenland Ice Sheet, which seems to have a negative balance; and the Antarctic Ice Sheet,...

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A study of the atmospheric surface layer and roughness lengths on the high‐altitude tropical Zongo glacier, Bolivia

et al. 2014

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The atmospheric surface layer of high-altitude tropical glaciers is inadequately understood, particularly concerning turbulent fluxes. Measurements have shown that sublimation reduces melt energy in the dry season, but the errors are large when a katabatic wind maximum occurs at a low height. This study analyzed wind and temperature vertical profiles measured by a 6 m mast in the ablation area of the tropical Zongo glacier (16°S, 5060 m above sea level) in the dry seasons of 2005 and 2007. Surface roughness lengths for momentum and temperature were derived from least squares fits of hourly wind and temperature profile data. Measurement errors were explored, focusing on the poorly defined reference level for sensor heights. A katabatic wind maximum at heights between 2 and 3 m was regularly observed during low wind speed and strong inversion conditions, or about~50%of the time, greatly reducing the surface layer depth. The glacier surface, experiencing melting conditions in the early afternoon and strong cooling at night, remained relatively smooth with z 0~1 mm and z T~0 .1 mm. Sensible heat flux measured at~1 m was not very sensitive to the zero reference level due to two opposite effects: when measurement heights increase, profile-derived roughness lengths increase but temperature and wind gradients decrease. The relation between z T /z 0 and the roughness Reynolds number Re * roughly agrees with the surface renewal model. However, this is mostly due to self-correlation because of the shared variable z 0 in z T /z 0 and Re * , which prevents a sound experimental validation of the model.

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Wintertime high‐altitude surface energy balance of a Bolivian glacier, Illimani, 6340 m above sea level

Cited by 86 publications

References 35 publications

Ablation and associated energy balance of a horizontal glacier surface on Kilimanjaro

Ablation and associated energy balance of a horizontal glacier surface on Kilimanjaro

Mass and Energy Balances of Glaciers and Ice Sheets

A study of the atmospheric surface layer and roughness lengths on the high‐altitude tropical Zongo glacier, Bolivia

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