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- Author or Editor: Samson Hagos x
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ABSTRACT
Sea surface temperature (SST) is one of the most important parameters for tropical cyclone (TC) intensification. Here, it is shown that the relationship between SST and TC intensification varies considerably from basin to basin, with SST explaining less than 4% of the variance in TC intensification rates in the Atlantic, 12% in the western North Pacific, and 23% in the eastern Pacific. Several factors are shown to be responsible for these interbasin differences. First, variability of SST along TCs’ tracks is lower in the Atlantic. This is due to smaller horizontal SST gradients in the Atlantic, compared to the Pacific, and stronger damping of prestorm SST’s contribution to TC intensification by the storm-induced cold SST wake in the Atlantic. The damping occurs because SST tends to vary in phase with TC-induced SST cooling: in the Gulf of Mexico and northwestern Atlantic, where SSTs are highest, TCs tend to be strongest and their translations slowest, resulting in the strongest storm-induced cooling. The tendency for TCs to be more intense over the warmest SST in the Atlantic also limits the usefulness of SST as a predictor since stronger storms are less likely to experience intensification. Finally, SST tends to vary out of phase with vertical wind shear and outflow temperature in the western Pacific. This strengthens the relationship between SST and TC intensification more in the western Pacific than in the eastern Pacific or Atlantic. Combined, these factors explain why prestorm SST is such a poor predictor of TC intensification in the Atlantic, compared to the eastern and western North Pacific.
ABSTRACT
Sea surface temperature (SST) is one of the most important parameters for tropical cyclone (TC) intensification. Here, it is shown that the relationship between SST and TC intensification varies considerably from basin to basin, with SST explaining less than 4% of the variance in TC intensification rates in the Atlantic, 12% in the western North Pacific, and 23% in the eastern Pacific. Several factors are shown to be responsible for these interbasin differences. First, variability of SST along TCs’ tracks is lower in the Atlantic. This is due to smaller horizontal SST gradients in the Atlantic, compared to the Pacific, and stronger damping of prestorm SST’s contribution to TC intensification by the storm-induced cold SST wake in the Atlantic. The damping occurs because SST tends to vary in phase with TC-induced SST cooling: in the Gulf of Mexico and northwestern Atlantic, where SSTs are highest, TCs tend to be strongest and their translations slowest, resulting in the strongest storm-induced cooling. The tendency for TCs to be more intense over the warmest SST in the Atlantic also limits the usefulness of SST as a predictor since stronger storms are less likely to experience intensification. Finally, SST tends to vary out of phase with vertical wind shear and outflow temperature in the western Pacific. This strengthens the relationship between SST and TC intensification more in the western Pacific than in the eastern Pacific or Atlantic. Combined, these factors explain why prestorm SST is such a poor predictor of TC intensification in the Atlantic, compared to the eastern and western North Pacific.
Abstract
This study compares the error characteristics associated with two grid refinement approaches including global variable resolution and nesting for high-resolution regional climate modeling. The global variable-resolution model, Model for Prediction Across Scales-Atmosphere (MPAS-A), and the limited-area model, Weather Research and Forecasting Model (WRF), are compared in an idealized aquaplanet context. For MPAS-A, simulations have been performed with a quasi-uniform-resolution global domain at coarse (1°) and high (0.25°) resolution, and a variable-resolution domain with a high-resolution region at 0.25° configured inside a coarse-resolution global domain at 1° resolution. Similarly, WRF has been configured to run on a coarse (1°) and high (0.25°) tropical channel domain as well as a nested domain with a high-resolution region at 0.25° nested two-way inside the coarse-resolution (1°) tropical channel. The variable-resolution or nested simulations are compared against the high-resolution simulations. Both models respond to increased resolution with enhanced precipitation and significant reduction in the ratio of convective to nonconvective precipitation. The limited-area grid refinement induces zonal asymmetry in precipitation (heating), accompanied by zonal anomalous Walker-like circulations and standing Rossby wave signals. Within the high-resolution limited area, the zonal distribution of precipitation is affected by advection in MPAS-A and by the nesting strategy in WRF. In both models, the propagation characteristics of equatorial waves are not significantly affected by the variations in resolution.
Abstract
This study compares the error characteristics associated with two grid refinement approaches including global variable resolution and nesting for high-resolution regional climate modeling. The global variable-resolution model, Model for Prediction Across Scales-Atmosphere (MPAS-A), and the limited-area model, Weather Research and Forecasting Model (WRF), are compared in an idealized aquaplanet context. For MPAS-A, simulations have been performed with a quasi-uniform-resolution global domain at coarse (1°) and high (0.25°) resolution, and a variable-resolution domain with a high-resolution region at 0.25° configured inside a coarse-resolution global domain at 1° resolution. Similarly, WRF has been configured to run on a coarse (1°) and high (0.25°) tropical channel domain as well as a nested domain with a high-resolution region at 0.25° nested two-way inside the coarse-resolution (1°) tropical channel. The variable-resolution or nested simulations are compared against the high-resolution simulations. Both models respond to increased resolution with enhanced precipitation and significant reduction in the ratio of convective to nonconvective precipitation. The limited-area grid refinement induces zonal asymmetry in precipitation (heating), accompanied by zonal anomalous Walker-like circulations and standing Rossby wave signals. Within the high-resolution limited area, the zonal distribution of precipitation is affected by advection in MPAS-A and by the nesting strategy in WRF. In both models, the propagation characteristics of equatorial waves are not significantly affected by the variations in resolution.
