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Weixing Shen
,
Robert E. Tuleya
, and
Isaac Ginis

Abstract

In this study, the effect of thermodynamic environmental changes on hurricane intensity is extensively investigated with the National Oceanic and Atmospheric Administration Geophysical Fluid Dynamics Laboratory hurricane model for a suite of experiments with different initial upper-tropospheric temperature anomalies up to ±4°C and sea surface temperatures ranging from 26° to 31°C given the same relative humidity profile.

The results indicate that stabilization in the environmental atmosphere and sea surface temperature (SST) increase cause opposing effects on hurricane intensity. The offsetting relationship between the effects of atmospheric stability increase (decrease) and SST increase (decrease) is monotonic and systematic in the parameter space. This implies that hurricane intensity increase due to a possible global warming associated with increased CO2 is considerably smaller than that expected from warming of the oceanic waters alone. The results also indicate that the intensity of stronger (weaker) hurricanes is more (less) sensitive to atmospheric stability and SST changes. The model-attained hurricane intensity is found to be well correlated with the maximum surface evaporation and the large-scale environmental convective available potential energy. The model-attained hurricane intensity is highly correlated with the energy available from wet-adiabatic ascent near the eyewall relative to a reference sounding in the undisturbed environment for all the experiments. Coupled hurricane–ocean experiments show that hurricane intensity becomes less sensitive to atmospheric stability and SST changes since the ocean coupling causes larger (smaller) intensity reduction for stronger (weaker) hurricanes. This implies less increase of hurricane intensity related to a possible global warming due to increased CO2.

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Thomas R. Knutson
,
Robert E. Tuleya
,
Weixing Shen
, and
Isaac Ginis

Abstract

This study explores how a carbon dioxide (CO2) warming–induced enhancement of hurricane intensity could be altered by the inclusion of hurricane–ocean coupling. Simulations are performed using a coupled version of the Geophysical Fluid Dynamics Laboratory hurricane prediction system in an idealized setting with highly simplified background flow fields. The large-scale atmospheric boundary conditions for these high-resolution experiments (atmospheric temperature and moisture profiles and SSTs) are derived from control and high-CO2 climatologies obtained from a low-resolution (R30) global coupled ocean–atmosphere climate model. The high-CO2 conditions are obtained from years 71–120 of a transient +1% yr−1 CO2-increase experiment with the global model. The CO2-induced SST changes from the global climate model range from +2.2° to +2.7°C in the six tropical storm basins studied. In the storm simulations, ocean coupling significantly reduces the intensity of simulated tropical cyclones, in accord with previous studies. However, the net impact of ocean coupling on the simulated CO2 warming–induced intensification of tropical cyclones is relatively minor. For both coupled and uncoupled simulations, the percentage increase in maximum surface wind speeds averages about 5%–6% over the six basins and varies from about 3% to 10% across the different basins. Both coupled and uncoupled simulations also show strong increases of near-storm precipitation under high-CO2 climate conditions, relative to control (present day) conditions.

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Michael R. Bueti
,
Isaac Ginis
,
Lewis M. Rothstein
, and
Stephen M. Griffies

Abstract

Strong surface winds of a hurricane locally cool the surface and warm the subsurface waters via turbulent mixing processes. While the surface cool anomalies generally decay in roughly a month, the warm subsurface anomalies can persist over a seasonal cycle. The authors examine questions related to the magnitude and cumulative footprint of subsurface warm anomalies forced by tropical cyclones during the combined global tropical cyclone seasons, making use of a global ocean model forced by tropical cyclones.

Simulations of the 2004/05 tropical cyclone season are conducted with and without tropical cyclone wind forcing, blended with the daily Coordinated Ocean-Ice Reference Experiments (COREs) atmospheric state. Physical characteristics of cyclone-forced surface and subsurface anomalies are elucidated. In particular, the spatial extent and magnitude of tropical cyclone–forced subsurface warm anomalies over the course of an entire season are examined. This analysis permits the estimation of the contribution of cyclone-induced anomalies to the ocean heat content and sea surface temperature, aiding in understanding anomalous meridional heat transport.

Globally, there is a maximum accumulated heat uptake 4.1 × 1021 J, with the greatest regional contributions in the North Atlantic (1.7 × 1021 J), west Pacific (1.5 × 1021 J), and east Pacific (1.7 × 1021 J). An export of heat from the subtropics to the tropics via rapid advective pathways is found, most notably in the west Pacific. These warm anomalies tend to remain in the equatorial band, with potential implications for the tropical climate system.

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