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Seasonal forecasting of tropical cyclone formation in the Australian region

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posted on 28.03.2022, 03:10 by Angelika Werner
The hazard of tropical cyclones (TCs) is a very relevant topic to the Australian economy and to the welfare of its northern population. Australia's climate and the interannual variability of Australian region TC formation (genesis; TCG) is strongly dominated by the ocean-atmosphere interannual climate pattern El Niño-Southern Oscillation (ENSO) and to a lesser extent by other climate modes of variability. This thesis investigates new ways of seasonal forecasting Australian region TCG counts and distribution by identifying potentially skilful climatological predictors and applying more advanced statistical modelling methods than previous models for the region. ENSO is known to be the most important predictor of seasonal variations in TCG for the Australian region. To investigate the ENSO-independent effects of the Indian Ocean Dipole (IOD) on Australian TCG, a simple, but effective method has been developed to separate the IOD from ENSO. Results demonstrate, that there is reasonable individual forecast skill afforded by the influence of the isolated IOD. In combination with common ENSO metrics, however, the IOD does not significantly improve seasonal forecasting of seasonal TCG counts in the Australian region or subregions. A Poisson regression model using Bayesian inference and the Markov chain Monte Carlo (MCMC) method was developed to forecast seasonal TCG counts in the Australian region. The final three-predictor model based on derived indices of subtropical Central Pacific June-July-August average convective available potential energy (CAPE), the tropical northeast Pacific May-June-July average meridional winds at 850 hPa (v850) and subtropical central South Pacific June-July-August geopotential height at 500 hPa performs best with the corresponding correlation coefficient between observed annual TCG totals and cross-validated model hindcasts of r = 0.73 over the 40-year record between 1968/89-2007/08. The model is adaptable for hindcasting seasonal TCG totals in Australia's Eastern (Coral Sea) TC subregion, while it lacks skill in the Western (eastern Indian Ocean) TC subregion (r = 0.79 and r = 0.38 respectively). To improve forecasts of annual TCG counts in the Western region (90⁰-135⁰E), a separate model was developed with correlations between cross-validated hindcasts and observed annual TCG count of r = 0.67 using the June-July-August tropical Central Pacific sea level pressure (SLP) and the above used index of v850 as predictors. A logistic regression approach applied in the Bayesian seasonal forecast model was found to be successful in forecasting spatial probabilities of Australian region TCG on a 2.5⁰ x 2.5⁰ grid for the upcoming season. The most skilful model is based on the SLP, NINO4 and v850 indices, combined with spatial information from CAPE and shows an average improvement over the climatological average of 25%. The average distribution of TCG probabilities over the study period, as well as the hindcasted strong variations of probabilities and distribution of TCG during ENSO events match remarkably well against observations over most of the study domain. Results demonstrate that the combination of dynamic with synoptic and/or thermodynamic features is most useful to identify climatic influences on the seasonal frequency and spatial distribution of TC development in the Australian region. Independent forecasts using the three introduced models and comparisons with current operational models demonstrate the relatively high skill of the models presented in this thesis.

History

Table of Contents

I. Introduction and methodology. 1. Introduction -- 2. Statistical tools. II. Papers. 3. The separated effects of the El Nino-Southern Oscillation and Indian dipole on Australian region tropical cyclone counts -- 4. Development of statistical seasonal forecast models for tropical cyclone occurrences in the Australian region and subregions -- 5. Development of a seasonal forecast model for the spatial probability of tropical cyclones occurrences in the Australian region. III. Discussion and summary. 6. Discussion of results.

Notes

"A thesis submitted in fulfilment of the requirements for the degree of Doctor of Philosophy (PhD)". "May 2011". Bibliography: p. 220-231

Awarding Institution

Macquarie University

Degree Type

Thesis PhD

Degree

Thesis (PhD) , Macquarie University, Faculty of Science, Dept. of Environment and Geography

Department, Centre or School

Dept. of Environment and Geography

Year of Award

2011

Principal Supervisor

Neil Holbrook

Additional Supervisor 1

Angela Maharaj

Additional Supervisor 2

Kevin Cheung

Rights

Copyright disclaimer: http://www.copyright.mq.edu.au Copyright Angelika Werner 2011

Language

English

Jurisdiction

Australia

Extent

viii, 232 p. ill. (some col.)

Former Identifiers

mq:31325 http://hdl.handle.net/1959.14/291287 1617364