Modelling spatial patterns of near-surface air temperature over a decade of melt seasons on McCall Glacier, Alaska

Patrick Troxler,Álvaro Ayala,Francesca Pellicciotti,Matt Nolan,Ben W Brock,Thomas E Shaw

doi:10.1017/jog.2020.12

Abstract

AbstractWe examine the spatial patterns of near-surface air temperature (Ta) over a melting glacier using a multi-annual dataset from McCall Glacier, Alaska. The dataset consists of a 10-year (2005–2014) meteorological record along the glacier centreline up to an upper glacier cirque, spanning an elevation difference of 900 m. We test the validity of on-glacier linear lapse rates, and a model that calculatesTabased on the influence of katabatic winds and other heat sources along the glacier flow line. During the coldest hours of each summer (10% of time), average lapse rates across the entire glacier range from −4.7 to −6.7°C km−1, with a strong relationship betweenTaand elevation (R2> 0.7). During warm conditions,Tashows more complex, non-linear patterns that are better explained by the flow line-dependent model, reducing errors by up to 0.5°C compared with linear lapse rates, although more uncertainty might be associated with these observations due to occasionally poor sensor ventilation. We conclude thatTaspatial distribution can vary significantly from year to year, and from one glacier section to another. Importantly, extrapolations using linear lapse rates from the ablation zone might lead to large underestimations ofTaon the upper glacier areas.

Highlights

Glacier mass balance is controlled in large measure by the energy balance at the glacier surface during the melt season
The air mass modification induced by a melting glacier, defined as the cooling of a relatively warm air mass flowing over a colder surface, affects the atmospheric layer above the glacier in a manner that compromises the use of off-glacier meteorological variables as the representative of those in the glacier boundary layer, especially for air temperatures
Air temperature in 2013 shows a very high value during warm conditions, but a low value in the P10 percentile group, suggesting that temperature varied over a large range over the course of that summer

Summary

Introduction

Glacier mass balance is controlled in large measure by the energy balance at the glacier surface during the melt season. The air mass modification induced by a melting glacier, defined as the cooling of a relatively warm air mass flowing over a colder surface, affects the atmospheric layer above the glacier in a manner that compromises the use of off-glacier meteorological variables as the representative of those in the glacier boundary layer (van den Broeke, 1997; Oerlemans, 2001), especially for air temperatures. Katabatic winds over valley glaciers are normally shallow, and generate a well-defined low-level jet at only few meters above the surface (Oerlemans and Grisogono, 2002) They act as a ‘heat pump’ for the glacier surface, as they generate turbulence that can disrupt the stable stratification and bring heat to the surface (Klok and others, 2005)

Methods

Results

Discussion

Conclusion