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. Resul ts are related to melt measured directly using a lysimeter and to syno ptic weather patterns. Measurements are taken half hourly, over a 38 d ay 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 magn itude of melt. Melt is highest during north-westerly storms, and three such days contributed one-third of the total melt recorded during the held season. Melt is also high during anticyclones. Different synopti c situations generate distinctive energy budgets, with radiation domin ating during large-scale anticyclonic patterns, but sensible heat flux also is important during north-westerly circulation patterns. Distinc t pulses of melt, each lasting a period of about 1 week, reflect the c yclical passage of troughs and anticyclones across New Zealand. (C) 19 97 Royal Meteorological Society.