Quantifying the impact of synoptic weather types and patterns on energy fluxes of a marginal snowpack

Andrew J. Schwartz,Alison Theobald,Nik Callow,Hamish A. McGowan

doi:10.5194/tc-14-2755-2020

Abstract

Abstract. Synoptic weather patterns are investigated for their impact on energy fluxes driving melt of a marginal snowpack in the Snowy Mountains, southeast Australia. K-means clustering applied to ECMWF ERA-Interim data identified common synoptic types and patterns that were then associated with in situ snowpack energy flux measurements. The analysis showed that the largest contribution of energy to the snowpack occurred immediately prior to the passage of cold fronts through increased sensible heat flux as a result of warm air advection (WAA) ahead of the front. Shortwave radiation was found to be the dominant control on positive energy fluxes when individual synoptic weather types were examined. As a result, cloud cover related to each synoptic type was shown to be highly influential on the energy fluxes to the snowpack through its reduction of shortwave radiation and reflection/emission of longwave fluxes. As single-site energy balance measurements of the snowpack were used for this study, caution should be exercised before applying the results to the broader Australian Alps region. However, this research is an important step towards understanding changes in surface energy flux as a result of shifts to the global atmospheric circulation as anthropogenic climate change continues to impact marginal winter snowpacks.

Highlights

1.1 Synoptic weather influences on snowpack processesWater generated in mountainous regions is a commodity that over 50 % of the world’s population depends on for daily life (Beniston, 2003)
T5 and T7 are characterized by northnorthwesterly flow from high-pressure centers over the New South Wales (NSW) and Queensland (QLD) coast and directly over the Snowy Mountains region, respectively
Periods of pre-cold-frontal passage contribute the most energy fluxes to snowpack melt due to warm air advection (WAA) ahead of the front, a reduction in cloud cover allowing for higher incoming shortwave radiation, and the gradual development of precipitation that often contributes to rain-on-snow events

Summary

Introduction

1.1 Synoptic weather influences on snowpack processesWater generated in mountainous regions is a commodity that over 50 % of the world’s population depends on for daily life (Beniston, 2003). The most important role in the generation and regulation of these water resources is that of montane snowpacks. These have been referred to as “water towers” (Viviroli et al, 2007) due to their capabilities for storage and slow releases of meltwater. Understanding the physical drivers of snowpack ablation, including synoptic-scale influences, is critical to help assess future water resource availability in mountainous regions as climate change continues. Work on relationships between snowmelt and synoptic weather types is relatively scarce. Similar work has been conducted in North America by Grundstein and Leathers (1998), who were able to identify three main synoptic weather types responsible for significant snowmelt

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