Analysis of air mass trajectories and implications for predicting pathways of volcanic material from Mt. Ruapehu, New Zealand

.Inter-regional transport of air within the troposphere provides the basis for subsequent assessment of the transport of aerosols and trace gases. In this paper, two independently developed kinematic methods are used to assess the likely transport paths of volcanic material ejected into the atmosphere by Mt. Ruapehu on the North Island of New Zealand. This volcano created problems for air travel over the country during both 1995 and 1996, when extended periods of eruptive activity ocurred. A method developed at the University of the Witwatersrand, South Africa is used together with one developed at the Swiss Federal Institute of Technology at Zurich. ECMWF gridded analysis data of the six-hourly, three-dimensional wind field provide the basis for deriving air transport pathways from forward trajectories of air parcels originating above the volcano. Data for the ten years between 1989 and 1998 are used to provide a climatology of air mass pathways. Swarms of individual trajectories are organised to determine mean transport plumes which illustrate these pathways. Seasonal variability of their locations is examined, along with variations that occur from year to year. Explanations of these variations are provided with regard to changes in atmospheric circulation over this region, while implications for prediction of the impact of future eruptions are discussed