The Southern Oscillation Index and climatic parameters, and their relationship to snow and ski conditions at Mt. Ruapehu, New Zealand
The climatic record of the Chateau, Mt. Ruapehu, an isolated volcanic mountain located at 39ºS in New Zealand's North Island, was investigated for influence from the Southern Oscillation (SO) in an attempt to ascertain whether any relationship between snow and ski conditions and the Southern Oscillation Index (SOI) could be detected. Climatological data for the period 1930-1980 were subjected to linear regression analysis, correlations and principal components analysis. The analyses suggested that temperatures at the Chateau were positively correlated with the SOI for both annual (R = 0.40 to 0.57) as well as seasonal data, with R values typically ranging from 0.28 to 0.40 (autumn (R = 0.28 to 0.33), winter (R = 0.39), and spring (R = 0.28 to 0.40)) indicating that with an increase (decrease) in the SOI, air temperatures tend to increase (decrease). Precipitation shows a small but significant correlation with the SOI. The relationship is positive for total precipitation in winter (R = 0.30), and negative for the number of days with snow in autumn (R = -0.27), indicating that with an increase (decrease) in the SOI the total precipitation increases (decreases) in winter and the number of days with snow decreases (increases) in autumn. Wind variables showed no correlation to the SOI. Principal components analysis of a data set of annual averages indicated that the SOI has a positive relationship with temperatures, a negative relationship with the number of days with snow, and no apparent relationship with wind. In terms of ski field management, negative or zero annual SOI values have coincided with a 60% chance of "good" skiing conditions or an 80% chance of "good" to "fair" skiing conditions at Mt. Ruapehu. Positive SOIs have been associated with only a 32% chance of good skiing. Given future reliable predictions of the SOI, the likelihood of a good ski season can be predicted.