Projections of southern hemisphere tropical cyclone track density using CMIP5 models
- Bell, Samuel, Chand, Savin, Tory, Kevin, Dowdy, Andrew, Turville, Christopher, Ye, Harvey
- Authors: Bell, Samuel , Chand, Savin , Tory, Kevin , Dowdy, Andrew , Turville, Christopher , Ye, Harvey
- Date: 2019
- Type: Text , Journal article
- Relation: Climate Dynamics Vol. 52, no. 9-10 (2019), p. 6065-6079
- Full Text:
- Reviewed:
- Description: A recently validated algorithm for detecting and tracking tropical cyclones (TCs) in coarse resolution climate models was applied to a selected group of 12 models from the Coupled Model Intercomparison Project (CMIP5) to assess potential changes in TC track characteristics in the Southern Hemisphere (SH) due to greenhouse warming. Current-climate simulations over the period 1970–2000 are first evaluated against observations using measures of TC genesis location and frequency, as well as track trajectory and lifetime in seven objectively defined genesis regions. The 12-model (12-M) ensemble showed substantial skill in reproducing a realistic TC climatology over the evaluation period. To address potential biases associated with model interdependency, analyses were repeated with an ensemble of five independent models (5-M). Results from both the 12-M and 5-M ensembles were very similar, instilling confidence in the models for climate projections if the current TC-climate relationship is to remain stationary. Projected changes in TC track density between the current- and future-climate (2070–2100) simulations under the Representatives Concentration 8.5 Pathways (RCP8.5) are also assessed. Overall, projection results showed a substantial decrease (~ 1–3 per decade) in track density over most parts of the SH by the end of the twenty-first century. This decrease is attributed to a significant reduction in TC numbers (~ 15–42%) consistent with changes in large-scale environmental parameters such as relative vorticity, environmental vertical wind shear and relative humidity. This study may assist with adaption pathways and implications for regional-scale climate change for vulnerable regions in the SH.
- Authors: Bell, Samuel , Chand, Savin , Tory, Kevin , Dowdy, Andrew , Turville, Christopher , Ye, Harvey
- Date: 2019
- Type: Text , Journal article
- Relation: Climate Dynamics Vol. 52, no. 9-10 (2019), p. 6065-6079
- Full Text:
- Reviewed:
- Description: A recently validated algorithm for detecting and tracking tropical cyclones (TCs) in coarse resolution climate models was applied to a selected group of 12 models from the Coupled Model Intercomparison Project (CMIP5) to assess potential changes in TC track characteristics in the Southern Hemisphere (SH) due to greenhouse warming. Current-climate simulations over the period 1970–2000 are first evaluated against observations using measures of TC genesis location and frequency, as well as track trajectory and lifetime in seven objectively defined genesis regions. The 12-model (12-M) ensemble showed substantial skill in reproducing a realistic TC climatology over the evaluation period. To address potential biases associated with model interdependency, analyses were repeated with an ensemble of five independent models (5-M). Results from both the 12-M and 5-M ensembles were very similar, instilling confidence in the models for climate projections if the current TC-climate relationship is to remain stationary. Projected changes in TC track density between the current- and future-climate (2070–2100) simulations under the Representatives Concentration 8.5 Pathways (RCP8.5) are also assessed. Overall, projection results showed a substantial decrease (~ 1–3 per decade) in track density over most parts of the SH by the end of the twenty-first century. This decrease is attributed to a significant reduction in TC numbers (~ 15–42%) consistent with changes in large-scale environmental parameters such as relative vorticity, environmental vertical wind shear and relative humidity. This study may assist with adaption pathways and implications for regional-scale climate change for vulnerable regions in the SH.
Impact of different ENSO regimes on southwest pacific tropical cyclones
- Chand, Savin, McBride, John, Tory, Kevin, Wheeler, Matthew, Walsh, Kevin
- Authors: Chand, Savin , McBride, John , Tory, Kevin , Wheeler, Matthew , Walsh, Kevin
- Date: 2013
- Type: Text , Journal article
- Relation: Journal of Climate Vol. 26, no. 2 (2013), p. 600-608
- Full Text: false
- Reviewed:
- Description: The influence of different types of ENSO on tropical cyclone (TC) interannual variability in the central southwest Pacific region (58-258S, 1708E-1708W) is investigated. Using empirical orthogonal function analysis and an agglomerative hierarchical clustering of early tropical cyclone season Pacific sea surface temperature, years are classified into four separate regimes (i.e., canonical El Niño, canonical La Niña, positive-neutral, and negative-neutral) for the period between 1970 and 2009.These regimes are found to have a large impact on TC genesis over the central southwest Pacific region. Both the canonical El Niño and the positive-neutral years have increased numbers of cyclones, with an average of 4.3 yr-1 for positive-neutral and 4 yr-1 for canonical El Niño. In contrast, during a La Niña and negative-neutral events, substantially fewer TCs (averages of ;2.2 and 2.4 yr-1, respectively) are observed in the central southwest Pacific. The enhancement of TC numbers in both canonical El Niño and positive-neutral years is associated with the extension of favorable low-level cyclonic relative vorticity, and low vertical wind shear eastward across the date line. Relative humidity and SST are also very conducive forgenesis in this region during canonical El Niño and positiveneutral events. The patterns are quite different, however, with the favorable conditions concentrated in the date line region for the positive-neutral, as compared with conditions farther eastward for the canonical El Niño regime. A significant result of the study is the demonstration that ENSO-neutralevents can be objectively clustered into two separate regimes, each with very different impacts on TCgenesis. © 2013 American Meteorological Society.
- Authors: Chand, Savin , McBride, John , Tory, Kevin , Wheeler, Matthew , Walsh, Kevin
- Date: 2013
- Type: Text , Journal article
- Relation: Journal of Climate Vol. 26, no. 2 (2013), p. 600-608
- Full Text: false
- Reviewed:
- Description: The influence of different types of ENSO on tropical cyclone (TC) interannual variability in the central southwest Pacific region (58-258S, 1708E-1708W) is investigated. Using empirical orthogonal function analysis and an agglomerative hierarchical clustering of early tropical cyclone season Pacific sea surface temperature, years are classified into four separate regimes (i.e., canonical El Niño, canonical La Niña, positive-neutral, and negative-neutral) for the period between 1970 and 2009.These regimes are found to have a large impact on TC genesis over the central southwest Pacific region. Both the canonical El Niño and the positive-neutral years have increased numbers of cyclones, with an average of 4.3 yr-1 for positive-neutral and 4 yr-1 for canonical El Niño. In contrast, during a La Niña and negative-neutral events, substantially fewer TCs (averages of ;2.2 and 2.4 yr-1, respectively) are observed in the central southwest Pacific. The enhancement of TC numbers in both canonical El Niño and positive-neutral years is associated with the extension of favorable low-level cyclonic relative vorticity, and low vertical wind shear eastward across the date line. Relative humidity and SST are also very conducive forgenesis in this region during canonical El Niño and positiveneutral events. The patterns are quite different, however, with the favorable conditions concentrated in the date line region for the positive-neutral, as compared with conditions farther eastward for the canonical El Niño regime. A significant result of the study is the demonstration that ENSO-neutralevents can be objectively clustered into two separate regimes, each with very different impacts on TCgenesis. © 2013 American Meteorological Society.
- Bell, Samuel, Chand, Savin, Tory, Kevin, Turville, Christopher, Ye, Harvey
- Authors: Bell, Samuel , Chand, Savin , Tory, Kevin , Turville, Christopher , Ye, Harvey
- Date: 2019
- Type: Text , Journal article
- Relation: Climate Dynamics Vol. 53, no. 7-8 (2019), p. 4841-4855
- Full Text: false
- Reviewed:
- Description: The sensitivity of tropical cyclone (TC) projection results to different models and the detection and tracking scheme used is well established in the literature. Here, future climate projections of TC activity in the Eastern North Pacific basin (ENP, defined from 0 degrees to 40 degrees N and 180 degrees to similar to 75 degrees W) are assessed with a model- and basin-independent detection and tracking scheme that was trained in reanalysis data. The scheme is applied to models from the Coupled Model Intercomparison Project Phase 5 (CMIP5) experiments forced under the historical and Representative Concentration Pathway 8.5 (RCP8.5) conditions. TC tracks from the observed records and models are analysed simultaneously with a curve-clustering algorithm, allowing observed and model tracks to be projected onto the same set of clusters. The ENP is divided into three clusters, one in the Central North Pacific (CNP) and two off the Mexican coast, as in prior studies. After accounting for model biases and auto-correlation, projection results under RCP8.5 indicated TC genesis to be significantly suppressed east of 125 degrees W, and significantly enhanced west of 145 degrees W by the end of the twenty-first century. Regional TC track exposure was found to significantly increase around Hawaii (similar to 86%), as shown in earlier studies, owing to increased TC genesis, particularly to the south-east of the island nation. TC exposure to Southern Mexico was shown to decrease (similar to 4%), owing to a south-westward displacement of TCs and overall suppression of genesis near the Mexican coastline. The large-scale environmental conditions most consistent with these projected changes were vertical wind shear and relative humidity.
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