Applying the Palaeo-tropical Cyclone Record
Palaeo-tropical cyclone records have to date been predominantly used to depict long-term trends as well as attempting to understand the causes of these trends. These records can also be useful for more immediate timescales such a reliably deriving the frequency and magnitude of events for present day planning purposes and also for assessing whether tropical cyclones are responding to global climate change.
Two examples of these uses of long-term cyclone records are presented here. The first […].
The second application is the use of high-resolution isotope records to assess whether tropical cyclone (TC) activity over the past few decades has changed substantially compared to the past 1,500 years.
High-resolution isotope records of TCs can be preserved within limestone stalagmites. Two records, one from Western Australia [since 500AD] and the other from Queensland [since 1400AD], provide insight into the nature of landfalling TC activity across the Australian continent. These records can be used to assess the role of humans in influencing the behavior of TCs […]. We developed a new index (Cyclone Activity Index – CAI), which calibrates the high-resolution, long-term isotope record of TC activity against the instrument TC record. The CAI allows for a direct comparison between the past and the present, and enables an examination of TC climatology at higher temporal resolution and on annual, decadal or millennial scales simultaneously, without the need to interpolate or extrapolate to account for missing data, which is a problem with the existing record of TCs. The CAI is the average accumulated energy expended over the TC season within range of the site, accounting for the number of days since genesis [of the storm] and the intensity and size of the storm relative to its distance from the site at each point along its track.
Our CAI for Australia shows that seasonal TC activity is at its lowest level since the year 500AD in Western Australia and 1400AD in Queensland and this decline in activity has been most pronounced since about 1960AD. This reduction in activity reflects the forecasts of TC behaviour for the Australian region from a suite of the most recent global climate models except this decrease appears to be occurring many decades earlier than expected.
h/t to Dr. Leif Svalgaard