Variability of air temperature over a debris-covered glacier in the Nepalese Himalaya

Jakob F Steiner,Francesca Pellicciotti

doi:10.3189/2016aog71a066

Jakob F Steiner, Francesca Pellicciotti

Open Access

https://doi.org/10.3189/2016aog71a066

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Abstract

AbstractEstimates of melt from debris-covered glaciers require distributed estimates of meteorological variables and air temperature in particular. Meteorological data are scarce for this environment, and spatial variability of temperature over debris is poorly understood. Based on multiple measurements of air and surface temperature from three ablation seasons (2012–14) we investigate the variability of temperature over Lirung Glacier, Nepal, in order to reveal how air temperature is affected by the debris cover and improve ways to extrapolate it. We investigate how much on-glacier temperature deviates from that predicted from a valley lapse rate (LR), analyse on-glacier LRs and test regression models of air temperature and surface temperature. Air temperature over the debris-covered glacier tongue is much higher than what a valley LR would prescribe, so an extrapolation from off-glacier stations is not applicable. An on-glacier LR is clearly defined at night, with strong correlation, but not during the day, when the warming debris disrupts the elevation control. An alternative to derive daytime air temperature is to use a relationship between air and surface temperature, as previously suggested. We find strong variability during daytime that should be accounted for if these regressions are used for temperature extrapolation.

Highlights

Air temperature is one of the main controls of the energy balance of glaciers, and the main input variable to melt and mass-balance models
We investigate the relationship between the air temperature measurements over Lirung and the environmental lapse rate (ELR) determined for the main valley of the Upper Langtang catchment (Heynen and others, 2016), by calculating the temperature anomaly from this valley ELR
Deviation from the valley lapse rate Air temperature over the lower tongue of Lirung Glacier is consistently higher than predicted by the valley ELR, more so during the day than at night-time and more strongly in pre-monsoon and post-monsoon (Fig. 5)

Summary

Introduction

Air temperature is one of the main controls of the energy balance of glaciers, and the main input variable to melt and mass-balance models. About its variability over melting glaciers, and most modelling studies assume that it varies linearly with elevation, a concept reproduced by so-called lapse rates (LRs) or temperature gradients. This assumption, which is valid in the case of free atmospheric conditions, does not take into account the effect of terrain (Minder and others, 2010), and the presence of glaciers in particular (Greuell and Boehm, 1998; Petersen and Pellicciotti, 2011; Ayala and others, 2015). Because of the lack of a 0°C surface and the movement of air being dominated by surface convection from debris-cover heating under good weather conditions, katabatic flows (i.e. the down-glacier gravitational movement of cooled and denser air parcels) generally do not develop over such glaciers (Shaw and others, 2016)

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