Energy balance and synoptic climatology of a melting snowpack in the Southern Alps, New Zealand

Snow melt is calculated at 1780 m a.s.l., near the Main Divide of the Southern Alps, using a bulk aerodynamic energy balance approach. Results are related to melt measured directly using a lysimeter and to synoptic weather patterns. Measurements are taken half hourly, over a 38 day period from the start of the spring melt season. Melt values at the site average 10 mm day−1 but vary from less than 1 mm day−1 to 63 mm day−1. The energy balance model overestimated measured melt by 8 per cent. The synoptic situation exerts a strong influence on the magnitude of melt. Melt is highest during north‐westerly storms, and three such days contributed one‐third of the total melt recorded during the field season. Melt is also high during anticyclones. Different synoptic situations generate distinctive energy budgets, with radiation dominating during large‐scale anticyclonic patterns, but sensible heat flux also is important during north‐westerly circulation patterns. Distinct pulses of melt, each lasting a period of about 1 week, reflect the cyclical passage of troughs and anticyclones across New Zealand. © 1997 Royal Meteorological Society.