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Analysis of Inferred Tropical Cyclones Frequency in ERA-40 Reanalysis and in an Ensemble of Models

Analysis of Inferred Tropical Cyclones Frequency in ERA-40 Reanalysis and in an Ensemble of Models. Louis-Philippe Caron and Colin Jones. Objectives:

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Analysis of Inferred Tropical Cyclones Frequency in ERA-40 Reanalysis and in an Ensemble of Models

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  1. Analysis of Inferred Tropical Cyclones Frequency in ERA-40 Reanalysis and in an Ensemble of Models Louis-Philippe Caron and Colin Jones

  2. Objectives: • Evaluate and compare tropical cyclone frequency based on oceanic and atmospheric conditions favorable to their development in ERA-40 reanalysis data and in an ensemble of IPCC models. • Estimate tropical cyclone activity in future climate scenarios. • Two indices are used to estimate tropical cyclone activity per 20 years period: • The Yearly Genesis Parameter (YGP) based on mid-tropospheric humidity, ocean temperature, atmospheric stability, difference in wind shear between low and high troposphere, low relative vorticity and the coriolis parameter. • The Convective YGP, based on convective precipitation, difference in wind shear between low and high troposphere, low relative vorticity and the coriolis parameter.

  3. The first figure represents the number of tropical cyclones for the period 1983-2002, while the other two represent the inferred tropical cyclone activity derived from the reanalysis data for the same period and the ensemble of IPCC models, using the YGP index • We notice that they both compare favorably to the observations, even if the ensemble tends to underestimate the frequency of formation in almost all basins. • The average annual number of cyclones for the period was 86. ERA-40 predicts 83 and the ensemble, 58.

  4. The first figure represents the tropical cyclone activity for the period 1983-2002, while the other two represent the inferred tropical cyclone activity derived from the reanalysis data for the same period and the ensemble of IPCC models, using the CYGP index. • Again, we notice that they both compare favorably to the observations. The ensemble however predicts unrealistic activity off the coast of South America and a shortage in the North Atlantic. • The average annual number of cyclones for the period was 86. ERA-40 predicts 83 and the ensemble, 85.

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