Characterizing Australia's east coast cyclones (1950–2019)
- Gray, Jessie, Verdon-Kidd, Danielle, Jaffrés, Jasmine, Hewson, Michael, Clarke, John, Sharma, Krishneel, English, Nathan
- Authors: Gray, Jessie , Verdon-Kidd, Danielle , Jaffrés, Jasmine , Hewson, Michael , Clarke, John , Sharma, Krishneel , English, Nathan
- Date: 2023
- Type: Text , Journal article
- Relation: International Journal of Climatology Vol. 43, no. 7 (2023), p. 3324-3352
- Full Text:
- Reviewed:
- Description: East coast cyclones (ECCs) provide an essential reprieve from dry periods across eastern Australia. They also deliver flood-producing rains with significant economic, social and environmental impacts. Assessing and comparing the influence of different types of cyclones is hindered by an incomplete understanding of ECC typology, given their widely variable spatial and temporal characteristics. This study employs a track-clustering method (probabilistic, curve-aligned regression model) to identify key cyclonic pathways for ECCs from 1950 to 2019. Six spatially independent clusters were successfully distinguished and further sub-classified (coastal, continental and tropical) based on their genesis location. The seasonality and long-term variability, intensity (maximum Laplacian value ± 2 days) and event-based rainfall were then evaluated for each cluster to quantify the impact of these lows on Australia. The highest quantity of land-based rainfall per event is associated with the tropical cluster (Cluster 6), whereas widespread rainfall was also found to occur in the two continental clusters (clusters 4 and 5). Cyclone tracks orientated close to the coast (clusters 1, 2 and 3) were determined to be the least impactful in terms of rainfall and intensity, despite being the most common cyclone type. In terms of interannual variability, sea surface temperature anomalies suggest an increased cyclone frequency for clusters 1 (austral winter) and 4 (austral spring) during a central Pacific El Niño. Furthermore, cyclone incidence during IOD-negative conditions was more pronounced in winter for clusters 1, 2, 3— and clusters 4 and 5 in spring. All cyclones also predominantly occurred in SAM-positive conditions. However, winter ECCs for clusters 1 and 3 had a higher frequency in SAM-negative. This new typology of ECCs via spatial clustering provides crucial insights into the systems that produce extreme rainfall across eastern Australia and should be used to inform future hazard management of cyclone events. © 2023 The Authors. International Journal of Climatology published by John Wiley & Sons Ltd on behalf of Royal Meteorological Society.
- Authors: Gray, Jessie , Verdon-Kidd, Danielle , Jaffrés, Jasmine , Hewson, Michael , Clarke, John , Sharma, Krishneel , English, Nathan
- Date: 2023
- Type: Text , Journal article
- Relation: International Journal of Climatology Vol. 43, no. 7 (2023), p. 3324-3352
- Full Text:
- Reviewed:
- Description: East coast cyclones (ECCs) provide an essential reprieve from dry periods across eastern Australia. They also deliver flood-producing rains with significant economic, social and environmental impacts. Assessing and comparing the influence of different types of cyclones is hindered by an incomplete understanding of ECC typology, given their widely variable spatial and temporal characteristics. This study employs a track-clustering method (probabilistic, curve-aligned regression model) to identify key cyclonic pathways for ECCs from 1950 to 2019. Six spatially independent clusters were successfully distinguished and further sub-classified (coastal, continental and tropical) based on their genesis location. The seasonality and long-term variability, intensity (maximum Laplacian value ± 2 days) and event-based rainfall were then evaluated for each cluster to quantify the impact of these lows on Australia. The highest quantity of land-based rainfall per event is associated with the tropical cluster (Cluster 6), whereas widespread rainfall was also found to occur in the two continental clusters (clusters 4 and 5). Cyclone tracks orientated close to the coast (clusters 1, 2 and 3) were determined to be the least impactful in terms of rainfall and intensity, despite being the most common cyclone type. In terms of interannual variability, sea surface temperature anomalies suggest an increased cyclone frequency for clusters 1 (austral winter) and 4 (austral spring) during a central Pacific El Niño. Furthermore, cyclone incidence during IOD-negative conditions was more pronounced in winter for clusters 1, 2, 3— and clusters 4 and 5 in spring. All cyclones also predominantly occurred in SAM-positive conditions. However, winter ECCs for clusters 1 and 3 had a higher frequency in SAM-negative. This new typology of ECCs via spatial clustering provides crucial insights into the systems that produce extreme rainfall across eastern Australia and should be used to inform future hazard management of cyclone events. © 2023 The Authors. International Journal of Climatology published by John Wiley & Sons Ltd on behalf of Royal Meteorological Society.
Influence of the Madden–Julian Oscillation (MJO) on tropical cyclones affecting Tonga in the Southwest Pacific
- Tu’uholoaki, Moleni, Espejo, Antonio, Sharma, Krishneel, Singh, Awnesh, Wandres, Moritz, Damlamian, Herve, Chand, Savin
- Authors: Tu’uholoaki, Moleni , Espejo, Antonio , Sharma, Krishneel , Singh, Awnesh , Wandres, Moritz , Damlamian, Herve , Chand, Savin
- Date: 2023
- Type: Text , Journal article
- Relation: Atmosphere Vol. 14, no. 7 (2023), p.
- Full Text:
- Reviewed:
- Description: The modulating influence of the Madden–Julian oscillation (MJO) on tropical cyclones (TCs) has been examined globally, regionally, and subregionally, but its impact on the island scale remains unclear. This study investigates how TC activity affecting the Tonga region is being modulated by the MJO, using the Southwest Pacific Enhanced Archive of Tropical Cyclones (SPEArTC) and the MJO index. In particular, this study investigates how the MJO modulates the frequency and intensity of TCs affecting the Tonga region relative to the entire study period (1970–2019; hereafter referred to as all years), as well as to different phases of the El Niño southern oscillation (ENSO) phenomenon. Results suggest that the MJO strongly modulates TC activity affecting the Tonga region. The frequency and intensity of TCs is enhanced during the active phases (phases six to eight) in all years, including El Niño and ENSO-neutral years. The MJO also strongly influences the climatological pattern of genesis of TCs affecting the Tonga region, where more (fewer) cyclones form in the active (inactive) phases of the MJO and more genesis points are clustered (scattered) near (away from) the Tonga region. There were three regression curves that best described the movement of TCs in the region matching the dominant steering mechanisms in the Southwest Pacific region. The findings of this study can provide climatological information for the Tonga Meteorological Service (TMS) and disaster managers to better understand the TC risk associated with the impact of the MJO on TCs affecting the Tonga region and support its TC early warning system. © 2023 by the authors.
- Authors: Tu’uholoaki, Moleni , Espejo, Antonio , Sharma, Krishneel , Singh, Awnesh , Wandres, Moritz , Damlamian, Herve , Chand, Savin
- Date: 2023
- Type: Text , Journal article
- Relation: Atmosphere Vol. 14, no. 7 (2023), p.
- Full Text:
- Reviewed:
- Description: The modulating influence of the Madden–Julian oscillation (MJO) on tropical cyclones (TCs) has been examined globally, regionally, and subregionally, but its impact on the island scale remains unclear. This study investigates how TC activity affecting the Tonga region is being modulated by the MJO, using the Southwest Pacific Enhanced Archive of Tropical Cyclones (SPEArTC) and the MJO index. In particular, this study investigates how the MJO modulates the frequency and intensity of TCs affecting the Tonga region relative to the entire study period (1970–2019; hereafter referred to as all years), as well as to different phases of the El Niño southern oscillation (ENSO) phenomenon. Results suggest that the MJO strongly modulates TC activity affecting the Tonga region. The frequency and intensity of TCs is enhanced during the active phases (phases six to eight) in all years, including El Niño and ENSO-neutral years. The MJO also strongly influences the climatological pattern of genesis of TCs affecting the Tonga region, where more (fewer) cyclones form in the active (inactive) phases of the MJO and more genesis points are clustered (scattered) near (away from) the Tonga region. There were three regression curves that best described the movement of TCs in the region matching the dominant steering mechanisms in the Southwest Pacific region. The findings of this study can provide climatological information for the Tonga Meteorological Service (TMS) and disaster managers to better understand the TC risk associated with the impact of the MJO on TCs affecting the Tonga region and support its TC early warning system. © 2023 by the authors.
Statistical assessment of Australian bushfire conditions : long-term changes and variability
- Authors: Biswas, Soubhik
- Date: 2023
- Type: Text , Thesis , PhD
- Full Text:
- Description: In the wake of increasing bushfire impacts in recent decades across the Australian landscape, questions arise regarding the role played by weather conditions, climate variability and long-term climate change. This thesis seeks to quantify the following components that can influence fire risk: (1) the effects of weather and mean climate conditions, (2) large-scale drivers of natural climate variability, (3) the influence of extreme weather events and (4) the contribution of long-term anthropogenic climate change. Bushfire risks associated with weather and climate factors in Australia are generally assessed using indices such as the Forest Fire Danger Index (FFDI). The FFDI is used in this study, calculated from daily values of rainfall, relative humidity, temperature and wind speed, providing a generalised approach for combining those four weather factors known to influence fire behaviour. This study also aims to fill several knowledge gaps in the literature. For example, a comprehensive study of climatology, variability and trends in Australia's fire weather conditions was never attempted before using a high-resolution and a very long-term fire weather dataset. The fire weather conditions were analysed using a long-term FFDI dataset constructed from 20th Century reanalysis climatic data with bias correction applied because reconstructed weather datasets like 20th Century reanalysis products often show systemic biases. Various statistical bias correction approaches based on quantile-quantile matching were compared, and a spline-based method was selected due to its higher precision in correcting a distribution for the purposes of this study. The relationship of this calibrated FFDI dataset with the climate drivers of El Niño-Southern Oscillation (ENSO), Indian Ocean Dipole (IOD), Southern Annular Mode (SAM) and Interdecadal Pacific Oscillation (IPO) was analysed. Results are mapped to show the regional and seasonal fluctuations in the severe fire weather across Australia during different combinations of ENSO, IOD, and SAM phases. During the austral spring and summer seasons, the highest frequency of severe fire weather conditions occurred for the combination of positive ENSO (i.e., El Nino), positive IOD and negative SAM. The calibrated FFDI dataset derived from bias-corrected Twentieth Century Reanalysis data was further used to study the long-term climate change trends in Australian fire weather conditions. A general positive trend in the number of extreme FFDI days was reported across Australia, except for New South Wales in Spring where a statistically non-significant negative trend was observed. Temperature and relative humidity were found to be the most critical climatic variables influencing fire weather trends across the country, noting that relative humidity is partly based on temperature. The applications of this work range from being useful for various stakeholders in framing new climate change adaptation policies to being used for seasonal outlooks and planning by fire management teams.
- Description: Doctor of Philosophy
- Authors: Biswas, Soubhik
- Date: 2023
- Type: Text , Thesis , PhD
- Full Text:
- Description: In the wake of increasing bushfire impacts in recent decades across the Australian landscape, questions arise regarding the role played by weather conditions, climate variability and long-term climate change. This thesis seeks to quantify the following components that can influence fire risk: (1) the effects of weather and mean climate conditions, (2) large-scale drivers of natural climate variability, (3) the influence of extreme weather events and (4) the contribution of long-term anthropogenic climate change. Bushfire risks associated with weather and climate factors in Australia are generally assessed using indices such as the Forest Fire Danger Index (FFDI). The FFDI is used in this study, calculated from daily values of rainfall, relative humidity, temperature and wind speed, providing a generalised approach for combining those four weather factors known to influence fire behaviour. This study also aims to fill several knowledge gaps in the literature. For example, a comprehensive study of climatology, variability and trends in Australia's fire weather conditions was never attempted before using a high-resolution and a very long-term fire weather dataset. The fire weather conditions were analysed using a long-term FFDI dataset constructed from 20th Century reanalysis climatic data with bias correction applied because reconstructed weather datasets like 20th Century reanalysis products often show systemic biases. Various statistical bias correction approaches based on quantile-quantile matching were compared, and a spline-based method was selected due to its higher precision in correcting a distribution for the purposes of this study. The relationship of this calibrated FFDI dataset with the climate drivers of El Niño-Southern Oscillation (ENSO), Indian Ocean Dipole (IOD), Southern Annular Mode (SAM) and Interdecadal Pacific Oscillation (IPO) was analysed. Results are mapped to show the regional and seasonal fluctuations in the severe fire weather across Australia during different combinations of ENSO, IOD, and SAM phases. During the austral spring and summer seasons, the highest frequency of severe fire weather conditions occurred for the combination of positive ENSO (i.e., El Nino), positive IOD and negative SAM. The calibrated FFDI dataset derived from bias-corrected Twentieth Century Reanalysis data was further used to study the long-term climate change trends in Australian fire weather conditions. A general positive trend in the number of extreme FFDI days was reported across Australia, except for New South Wales in Spring where a statistically non-significant negative trend was observed. Temperature and relative humidity were found to be the most critical climatic variables influencing fire weather trends across the country, noting that relative humidity is partly based on temperature. The applications of this work range from being useful for various stakeholders in framing new climate change adaptation policies to being used for seasonal outlooks and planning by fire management teams.
- Description: Doctor of Philosophy
Tropical cyclone climatology, variability, and trends in the Tonga region, Southwest Pacific
- Tu'uholoaki, Moleni, Singh, Awnesh, Espejo, Antonio, Chand, Savin, Damlamian, Herve
- Authors: Tu'uholoaki, Moleni , Singh, Awnesh , Espejo, Antonio , Chand, Savin , Damlamian, Herve
- Date: 2022
- Type: Text , Journal article
- Relation: Weather and Climate Extremes Vol. 37, no. (2022), p.
- Full Text:
- Reviewed:
- Description: The focus of several past tropical cyclone (TC) studies in the Southwest Pacific (SWP) had been primarily at the regional scale, with little or no attention to the local-scale TC activity (i.e., at the country level). With the growing coastal population in the South Pacific Island countries, as well as increasing threats from and exposure to climate extremes mostly affecting vulnerable communities, examining TC-related risks at the country level is more imperative now than before. This study catalogues for the first time the climatology, variability and trends of TCs affecting Nuku'alofa, the capital of Tonga using the Southwest Pacific Enhanced Archived for Tropical Cyclone (SPEArTC) dataset for the period between 1970 and 2019. The variability is examined in relation to the El Niño–Southern Oscillation (ENSO) phenomenon, which is the major driver of the year-to-year variability of TC activity in the SWP. A total of 128 TC tracks affected the Tonga region over the study period, with a seasonal average of
- Authors: Tu'uholoaki, Moleni , Singh, Awnesh , Espejo, Antonio , Chand, Savin , Damlamian, Herve
- Date: 2022
- Type: Text , Journal article
- Relation: Weather and Climate Extremes Vol. 37, no. (2022), p.
- Full Text:
- Reviewed:
- Description: The focus of several past tropical cyclone (TC) studies in the Southwest Pacific (SWP) had been primarily at the regional scale, with little or no attention to the local-scale TC activity (i.e., at the country level). With the growing coastal population in the South Pacific Island countries, as well as increasing threats from and exposure to climate extremes mostly affecting vulnerable communities, examining TC-related risks at the country level is more imperative now than before. This study catalogues for the first time the climatology, variability and trends of TCs affecting Nuku'alofa, the capital of Tonga using the Southwest Pacific Enhanced Archived for Tropical Cyclone (SPEArTC) dataset for the period between 1970 and 2019. The variability is examined in relation to the El Niño–Southern Oscillation (ENSO) phenomenon, which is the major driver of the year-to-year variability of TC activity in the SWP. A total of 128 TC tracks affected the Tonga region over the study period, with a seasonal average of
- Chand, Savin, Tory, Kevin, McBride, John, Wheeler, Matthew, Dare, Richard, Walsh, Kevin
- Authors: Chand, Savin , Tory, Kevin , McBride, John , Wheeler, Matthew , Dare, Richard , Walsh, Kevin
- Date: 2013
- Type: Text , Journal article
- Relation: Journal of Climate Vol. 26, no. 20 (October 2013), p. 8008-8016
- Full Text: false
- Reviewed:
- Description: The number of tropical cyclones (TCs) in the Australian region exhibits a large variation between different ENSO regimes. While the difference in TC numbers and spatial distribution of genesis locations between the canonical El Nino and La Nina regimes is well known, the authors demonstrate that a statistically significant difference in TC numbers also exists between the recently identified negative-neutral and positive-neutral regimes. Compared to the negative-neutral and La Nina regimes, significantly fewer TCs form in the Australian region during the positive-neutral regime, particularly in the eastern subregion. This difference is attributed to concomitant changes in various large-scale environmental conditions such as sea level pressure, relative vorticity, vertical motion, and sea surface temperature.
Modeling seasonal tropical cyclone activity in the Fiji region as a binary classification problem
- Authors: Chand, Savin , Walsh, Kevin
- Date: 2012
- Type: Text , Journal article
- Relation: Journal of Climate Vol. 25, no. 14 (2012), p. 5057-5071
- Full Text: false
- Reviewed:
- Description: This study presents a binary classification model for the prediction of tropical cyclone (TC) activity in the Fiji, Samoa, and Tonga regions (the FST region) using the accumulated cyclone energy (ACE) as a proxy of TC activity. A probit regression model, which is a suitable probabilitymodel for describing binary response data, is developed to determine at least a fewmonths in advance (by July in this case) the probability that an upcoming TC season may have for high or low TC activity. Years of "high TC activity" are defined as those years when ACE values exceeded the sample climatology (i.e., the 1985-2008 mean value). Model parameters are determined using the Bayesian method. Various combinations of the El Nin{ogonek} o-Southern Oscillation (ENSO) indices and large-scale environmental conditions that are known to affect TCs in the FST region are examined as potential predictors. It was found that a set of predictors comprising low-level relative vorticity, upper-level divergence, and midtropspheric relative humidity provided the best skill in terms of minimum hindcast error. Results based on hindcast verification clearly suggest that the model predicts TC activity in the FST region with substantial skill up to the May-July preseason for all years considered in the analysis, in particular for ENSO-neutral years when TC activity is known to show large variations. © 2012 American Meteorological Society.
Influence of ENSO on tropical cyclone intensity in the Fiji region
- Authors: Chand, Savin , Walsh, Kevin
- Date: 2011
- Type: Text , Journal article
- Relation: Journal of Climate Vol. 24, no. 15 (2011), p. 4096-4108
- Full Text: false
- Reviewed:
- Description: This study examines the variation in tropical cyclone (TC) intensity for different phases of the El Niño-Southern Oscillation (ENSO) phenomenon in the Fiji, Samoa, and Tonga (FST) region. The variation in TC intensity is inferred from the accumulated cyclone energy (ACE), which is constructed from the 6-hourly Joint Typhoon Warning Center best-track data for the period 1985-2006. Overall, results suggest that ACE in the FST region is considerably influenced by the ENSO signal. A substantial contribution to this ENSO signal in ACE comes from the region equatorward of 15°S where TC numbers, lifetime, and intensity all play a significant role. However, the ACE-ENSO relationship weakens substantially poleward of 15°S where large-scale environmental variables affecting TC intensity are found to be less favorable during El Niño years than during La Niña years; in the region equatorward of 15°S, the reverse is true. Therefore, TCs entering this region poleward of 15°S are able to sustain their intensity for a longer period of time during La Niña years as opposed to TCs entering the region during El Niñao years, when they decay more rapidly. © 2011 American Meteorological Society.
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