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BAMOS Dec 2017
Figure 4. Number of tornadoes reported in 30-year periods in Tasmania, Australia, between 1927 and 2016( Bureau of Meteorology, 2016b).
wind speed trends remained relatively unaltered( Figure 1)( Bureau of Meteorology 2016a). Contrary to this, although the Orford( Aubin Court) site also displayed a steady trend in long-term wind speeds( Figure 1), it did not appear to have the similar wind speed monitoring equipment upgrades as did the previous sites( Bureau of Meteorology 2016a). Although this in itself is not a guarantee that equipment upgrades over time have not had an effect on wind speed measurement records, for the purpose of studying the generalised long-term negative( decreasing) and positive( increasing) trends in wind speeds across Tasmania, any measured effects of change induced by equipment upgrades is hereby considered as being marginal.
intensifying westerlies. McKendry et al.( 1986) had also found that the Southern Alps, and surrounding land and sea features of Canterbury, New Zealand, affected localised airflow patterns, and thus localised wind regimes. Using the International Pacific Research Center regional climate model, a study by Sen et al.( 2004) found that deforestation of the Indochina Peninsula has far-reaching effects on the East Asian summer monsoon, significantly altering rainfall distribution patterns while also increasing local westerly wind speeds. Climate change, the Tasmanian geomorphology, and deforestation practices in Tasmania are all therefore potential contributive factors of the wind speed features currently observed in Tasmania.
3.2 The zone of increasing wind speeds
Flanked on the east and west sides by decreasing wind speeds, the zone of increasing wind speeds was observed to extend from central northern Tasmania, through to southeastern Tasmania, appearing to form a central‘ corridor’ of increasing wind speeds( Figure 3). Increasing wind speeds range from an average of 1.12 % to 20.78 % every decade( Figure 3). Outside of the zone, the average decreasing wind speeds vary from 0.26 % to 11.99 % every decade( Figure 3). As 30 % of the sites used in Figure 3 only have two data points( Figure 2), the zone may not be validated by future recorded wind speed measurements. If wind speed measurements across the current Tasmanian sites are maintained, future thirty-year mean annual wind speed data sets available at the end of 2020 and beyond, may either enhance or negate the currently observed zone.
Due to a changing climate, Böning et al.( 2008) found a significant intensification of the Southern Hemisphere prevailing winds( westerlies) between the latitudes of 30 ° and 60 ° S, over the past few decades. Tasmania is geographically located within those
3.3 Tornadoes
Since records have begun, the frequency of tornadoes observed in Tasmania have steadily increased by 2 – 3 per decade( R 2 = 0.98)( Figure 4).
Over 86 % of recorded tornadoes occurred within the zone. However, due to Tasmania’ s relatively small population and large areas of remoteness, tornado events located outside of the zone may not have been adequately accounted for, therefore contributing towards a level of uncertainty in the actual number and distribution of tornadoes that occur across Tasmania, and its potential correlation with the zone. The population density of people living in various locations around Tasmania has also changed over time( ABS 2017). As the population density in areas change, the probability that tornadoes are observed and reported depending on a particular location may over time also be significantly affected. As this study did not include an analysis of the potential population density effects on tornado sightings over time, it must therefore be acknowledged that