Louis-Philippe Caron | IC3 Institute (original) (raw)

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Papers by Louis-Philippe Caron

Research paper thumbnail of Multi-year prediction skill of Atlantic hurricane activity in CMIP5 decadal hindcasts

Using a statistical relationship between simulated sea surface temperature and Atlantic hurricane... more Using a statistical relationship between simulated sea surface temperature and Atlantic hurricane activity, we estimate the skill of a CMIP5 multi-model ensemble at predicting multi-annual level of Atlantic hurricane activity. The series of yearly-initialized hindcasts show positive skill compared to simpler forecasts such as persistence and climatology as well as non-initialized forecasts and return anomaly correlation coefficients of ∼0.6 and ∼0.8 for five and nine year forecasts, respectively. Some skill is shown to remain in the later years and making use of those later years to create a lagged-ensemble yields, for individual models, results that approach that obtained by the multi-model ensemble. Some of the skill is shown to come from persisting rather than predicting the climate shift that occur in 1994–1995. After accounting for that shift, the anomaly correlation coefficient for five-year forecasts is estimated to drop to 0.4, but remains statistically significant up to lead years 3–7. Most of the skill is shown to come from the ability of the forecast systems at capturing change in Atlantic sea surface temperature, although the failure of most systems at reproducing the observed slow down in warming over the tropics in recent years leads to an underestimation of hurricane activity in the later period.

Research paper thumbnail of On the relationship between cloud–radiation interaction, atmospheric stability and Atlantic tropical cyclones in a variable-resolution climate model

We compare two 28-year simulations performed with two versions of the Global Environmental Multis... more We compare two 28-year simulations performed with two versions of the Global Environmental Multiscale model run in variable-resolution mode. The two versions differ only by small differences in their radiation scheme. The most significant modification introduced is a reduction in the ice effective radius, which is observed to increase absorption of upwelling infrared radiation and increase temperature in the upper troposphere. The resulting change in vertical lapse rate is then observed to drive a resolution-dependent response of convection, which in turn modifies the zonal circulation and induces significant changes in simulated Atlantic tropical cyclone activity. The resulting change in vertical lapse rate and its implication in the context of anthropogenic climate change are discussed.

Research paper thumbnail of Understanding and simulating the link between African easterly waves and Atlantic tropical cyclones using a regional climate model: the role of domain size and lateral boundary conditions

Climate Dynamics

Using a suite of lateral boundary conditions, we investigate the impact of domain size and bounda... more Using a suite of lateral boundary conditions, we investigate the impact of domain size and boundary conditions on the Atlantic tropical cyclone and african easterly Wave activity simulated by a regional climate model. Irrespective of boundary conditions, simulations closest to observed climatology are obtained using a domain covering both the entire tropical Atlantic and northern African region. There is a clear degradation when the high-resolution model domain is diminished to cover only part of the African continent or only the tropical Atlantic. This is found to be the result of biases in the boundary data, which for the smaller domains, have a large impact on TC activity. In this series of simulations, the large-scale Atlantic atmospheric environment appears to be the primary control on simulated TC activity. Weaker wave activity is usually accompanied by a shift in cyclogenesis location, from the MDR to the subtropics. All ERA40-driven integrations manage to capture the observed interannual variability and to reproduce most of the upward trend in tropical cyclone activity observed during that period. When driven by low-resolution global climate model (GCM) integrations, the regional climate model captures interannual variability (albeit with lower correlation coefficients) only if tropical cyclones form in sufficient numbers in the main development region. However, all GCM-driven integrations fail to capture the upward trend in Atlantic tropical cyclone activity. In most integrations, variations in Atlantic tropical cyclone activity appear uncorrelated with variations in African easterly wave activity.

Research paper thumbnail of Impact of resolution and downscaling technique in simulating recent Atlantic tropical cylone activity

Climate Dynamics, 2011

Using the global environmental multiscale (GEM) model, we investigate the impact of increasing mo... more Using the global environmental multiscale (GEM) model, we investigate the impact of increasing model resolution from 2° to 0.3° on Atlantic tropical cyclone activity. There is a clear improvement in the realism of Atlantic storms with increased resolution, in part, linked to a better representation of African easterly waves. The geographical distribution of a Genesis Potential Index, composed of large-scales fields known to impact cyclone formation, coincides closely in the model with areas of high cyclogenesis. The geographical distribution of this index also improves with resolution. We then compare two techniques for achieving local high resolution over the tropical Atlantic: a limited-area model driven at the boundaries by the global 2° GEM simulation and a global variable resolution model (GVAR). The limited-area domain and high-resolution part of the GVAR model coincide geographically, allowing a direct comparison between these two downscaling options. These integrations are further compared with a set of limited-area simulations employing the same domain and resolution, but driven at the boundaries by reanalysis. The limited-area model driven by reanalysis produces the most realistic Atlantic tropical cyclone variability. The GVAR simulation is clearly more accurate than the limited-area version driven by GEM-Global. Degradation in the simulated interannual variability is partly linked to the models failure to accurately reproduce the impact of atmospheric teleconnections from the equatorial Pacific and Sahel on Atlantic cyclogenesis. Through the use of a smaller limited-area grid, driven by GEM-Global 2°, we show that an accurate representation of African Easterly Waves is crucial for simulating Atlantic tropical cyclone variability.

Research paper thumbnail of Analysing present, past and future tropical cyclone activity as inferred from an ensemble of Coupled Global Climate Models

Tellus Series A-dynamic Meteorology and Oceanography, 2008

Using the Yearly Genesis Parameter (YGP) and the Convective-YGP (CYGP), the main large-scale clim... more Using the Yearly Genesis Parameter (YGP) and the Convective-YGP (CYGP), the main large-scale climatic fields controlling tropical cyclone (TC) formation are analysed and used to infer the number of TCs in a given basin using ERA40 reanalyses for the period 1983-2002. Both indices show a reasonable global number and spatial distribution of implied TCs compared to observations. Using the same approach, we evaluate TC activity in the last 20-yr period of the 20th century in an ensemble of nine Coupled Global Climate Model simulations submitted to the IPCC AR4. We extend this analysis backwards in time, through the 20th century, and find the ensemble derived CYGP suggests no trend in inferred TC numbers while the YGP, after applying a correction to compensate for its oversensitivity to sea surface temperature, suggests a small upward trend. Both indices give a fair geographical distribution of cyclogenesis. Finally, we assess future TC trends using three emission scenarios. Using the CYGP, which appears the most robust index for application to climate change, a small increase is predicted in the northwestern Pacific in the A1B and A2 scenarios.

Research paper thumbnail of Multi-year prediction skill of Atlantic hurricane activity in CMIP5 decadal hindcasts

Using a statistical relationship between simulated sea surface temperature and Atlantic hurricane... more Using a statistical relationship between simulated sea surface temperature and Atlantic hurricane activity, we estimate the skill of a CMIP5 multi-model ensemble at predicting multi-annual level of Atlantic hurricane activity. The series of yearly-initialized hindcasts show positive skill compared to simpler forecasts such as persistence and climatology as well as non-initialized forecasts and return anomaly correlation coefficients of ∼0.6 and ∼0.8 for five and nine year forecasts, respectively. Some skill is shown to remain in the later years and making use of those later years to create a lagged-ensemble yields, for individual models, results that approach that obtained by the multi-model ensemble. Some of the skill is shown to come from persisting rather than predicting the climate shift that occur in 1994–1995. After accounting for that shift, the anomaly correlation coefficient for five-year forecasts is estimated to drop to 0.4, but remains statistically significant up to lead years 3–7. Most of the skill is shown to come from the ability of the forecast systems at capturing change in Atlantic sea surface temperature, although the failure of most systems at reproducing the observed slow down in warming over the tropics in recent years leads to an underestimation of hurricane activity in the later period.

Research paper thumbnail of On the relationship between cloud–radiation interaction, atmospheric stability and Atlantic tropical cyclones in a variable-resolution climate model

We compare two 28-year simulations performed with two versions of the Global Environmental Multis... more We compare two 28-year simulations performed with two versions of the Global Environmental Multiscale model run in variable-resolution mode. The two versions differ only by small differences in their radiation scheme. The most significant modification introduced is a reduction in the ice effective radius, which is observed to increase absorption of upwelling infrared radiation and increase temperature in the upper troposphere. The resulting change in vertical lapse rate is then observed to drive a resolution-dependent response of convection, which in turn modifies the zonal circulation and induces significant changes in simulated Atlantic tropical cyclone activity. The resulting change in vertical lapse rate and its implication in the context of anthropogenic climate change are discussed.

Research paper thumbnail of Understanding and simulating the link between African easterly waves and Atlantic tropical cyclones using a regional climate model: the role of domain size and lateral boundary conditions

Climate Dynamics

Using a suite of lateral boundary conditions, we investigate the impact of domain size and bounda... more Using a suite of lateral boundary conditions, we investigate the impact of domain size and boundary conditions on the Atlantic tropical cyclone and african easterly Wave activity simulated by a regional climate model. Irrespective of boundary conditions, simulations closest to observed climatology are obtained using a domain covering both the entire tropical Atlantic and northern African region. There is a clear degradation when the high-resolution model domain is diminished to cover only part of the African continent or only the tropical Atlantic. This is found to be the result of biases in the boundary data, which for the smaller domains, have a large impact on TC activity. In this series of simulations, the large-scale Atlantic atmospheric environment appears to be the primary control on simulated TC activity. Weaker wave activity is usually accompanied by a shift in cyclogenesis location, from the MDR to the subtropics. All ERA40-driven integrations manage to capture the observed interannual variability and to reproduce most of the upward trend in tropical cyclone activity observed during that period. When driven by low-resolution global climate model (GCM) integrations, the regional climate model captures interannual variability (albeit with lower correlation coefficients) only if tropical cyclones form in sufficient numbers in the main development region. However, all GCM-driven integrations fail to capture the upward trend in Atlantic tropical cyclone activity. In most integrations, variations in Atlantic tropical cyclone activity appear uncorrelated with variations in African easterly wave activity.

Research paper thumbnail of Impact of resolution and downscaling technique in simulating recent Atlantic tropical cylone activity

Climate Dynamics, 2011

Using the global environmental multiscale (GEM) model, we investigate the impact of increasing mo... more Using the global environmental multiscale (GEM) model, we investigate the impact of increasing model resolution from 2° to 0.3° on Atlantic tropical cyclone activity. There is a clear improvement in the realism of Atlantic storms with increased resolution, in part, linked to a better representation of African easterly waves. The geographical distribution of a Genesis Potential Index, composed of large-scales fields known to impact cyclone formation, coincides closely in the model with areas of high cyclogenesis. The geographical distribution of this index also improves with resolution. We then compare two techniques for achieving local high resolution over the tropical Atlantic: a limited-area model driven at the boundaries by the global 2° GEM simulation and a global variable resolution model (GVAR). The limited-area domain and high-resolution part of the GVAR model coincide geographically, allowing a direct comparison between these two downscaling options. These integrations are further compared with a set of limited-area simulations employing the same domain and resolution, but driven at the boundaries by reanalysis. The limited-area model driven by reanalysis produces the most realistic Atlantic tropical cyclone variability. The GVAR simulation is clearly more accurate than the limited-area version driven by GEM-Global. Degradation in the simulated interannual variability is partly linked to the models failure to accurately reproduce the impact of atmospheric teleconnections from the equatorial Pacific and Sahel on Atlantic cyclogenesis. Through the use of a smaller limited-area grid, driven by GEM-Global 2°, we show that an accurate representation of African Easterly Waves is crucial for simulating Atlantic tropical cyclone variability.

Research paper thumbnail of Analysing present, past and future tropical cyclone activity as inferred from an ensemble of Coupled Global Climate Models

Tellus Series A-dynamic Meteorology and Oceanography, 2008

Using the Yearly Genesis Parameter (YGP) and the Convective-YGP (CYGP), the main large-scale clim... more Using the Yearly Genesis Parameter (YGP) and the Convective-YGP (CYGP), the main large-scale climatic fields controlling tropical cyclone (TC) formation are analysed and used to infer the number of TCs in a given basin using ERA40 reanalyses for the period 1983-2002. Both indices show a reasonable global number and spatial distribution of implied TCs compared to observations. Using the same approach, we evaluate TC activity in the last 20-yr period of the 20th century in an ensemble of nine Coupled Global Climate Model simulations submitted to the IPCC AR4. We extend this analysis backwards in time, through the 20th century, and find the ensemble derived CYGP suggests no trend in inferred TC numbers while the YGP, after applying a correction to compensate for its oversensitivity to sea surface temperature, suggests a small upward trend. Both indices give a fair geographical distribution of cyclogenesis. Finally, we assess future TC trends using three emission scenarios. Using the CYGP, which appears the most robust index for application to climate change, a small increase is predicted in the northwestern Pacific in the A1B and A2 scenarios.