Examining wind patterns above the central North Island for ASHFALL tephra dispersion modelling in RiskScape

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Kaye, G.D. 2007 Examining wind patterns above the central North Island for ASHFALL tephra dispersion modelling in RiskScape GNS Science report 2007/36 37 p. +1 CD

Abstract: Realistic modelling of tephra distribution during future eruptions in New Zealand with RiskScape Volcano depends on both geologically sound eruption scenarios and sensible representations of local wind patterns. This report provides a summary of investigations into seasonal and annual patterns of wind speed and direction above the central North Island, with focus on the Rotorua District. Rotorua along with the rest of New Zealand’s North Island faces the threat of volcanic eruption from many volcanoes, including those in the Okataina Volcanic Centre (OVC), where eruptions are capable of quickly ejecting large amounts of volcanic tephra into the atmosphere. As such, it is important to understand wind patterns at both the ground level and at high altitudes above Rotorua and the central North Island to be better able to model potential tephra accumulation and its impact. To better achieve this understanding, three sets of meteorological data were obtained and analyzed for seasonal and annual patterns. The first dataset of “windrun data” consists of twice-daily computer model-forecast atmospheric wind conditions above New Plymouth, Okataina, Whenuapai, Ruapehu, Taupo, and White Island, based on radiosonde data gathered at Whenuapai and Paraparaumu for the period 20th March 2000 to 20th March 2003. The second dataset contains twenty years with of 3-hourly measured surface wind conditions at the Rotorua airport, from 1987 to 2007. The third dataset includes upper-air wind conditions as measured by radiosonde above Hamilton airport from July 2001 to July 2007. A more thorough understanding of how the wind varies from season to season above Rotorua and the central North Island of New Zealand will provide the RiskScape Volcano user with a realistic set of wind conditions on which to construct plausible eruption scenarios that will aid in realistic loss modelling in seasonally sensitive inventory sectors, such as agriculture. (auth)