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Analyzing Relationships Between Tropical Cyclone Intensity and Rain Rate over the Ocean Using Numerical Simulations

Dazhi XiDepartment of Civil and Environmental Engineering, Princeton University

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Shuai WangDepartment of Civil and Environmental Engineering, Princeton University

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Ning LinDepartment of Civil and Environmental Engineering, Princeton University

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Abstract

In this study, the relationship between tropical cyclone (TC) intensity and rain rate over the ocean is investigated using a full-physics numerical model (WRF) and a physics-based TC rainfall model (TCR). TC intensity is found to be nearly linearly correlated with the average rain rate in the inner core (~ 0.97 (mm × h−1 × m−2)/(m × s−1)), while the correlation is weak at outer radii. This difference is induced because TC intensity is significantly correlated with both the vertical velocity and specific humidity in the inner core but is not significantly correlated with the vertical velocity in outer radii. Further investigation shows that the intensity-rain rate relationship at outer radii is influenced by the evolution stage of TCs. Outer radii rain rate is positively correlated with TC intensity for non-decaying TCs, while this correlation is reduced for decaying TCs due to systematic downdrafts in the outer radii. In the context of climate change, sensitivity of TC rain rate to sea surface temperature (SST) is found to be +9% per K increase of SST, roughly the product of the sensitivity of TC intensity to SST (+3%) and the Clausius-Clapeyron scaling (+7%). Coupled with synthetic storms, evolutions of TC rain rate over the 21st century under the SSP5 8.5 scenario are projected by the TCR (calibrated with the WRF simulations). The annual increase rates of averaged TC rain rate are 0.17% and 0.20% for inner core and outer radii, respectively, larger than the annual increase rate of TC intensity (0.046%) but comparable to that of cube of intensity (0.18%).

Corresponding Author: Dazhi Xi Email: dxi@princeton.edu

Abstract

In this study, the relationship between tropical cyclone (TC) intensity and rain rate over the ocean is investigated using a full-physics numerical model (WRF) and a physics-based TC rainfall model (TCR). TC intensity is found to be nearly linearly correlated with the average rain rate in the inner core (~ 0.97 (mm × h−1 × m−2)/(m × s−1)), while the correlation is weak at outer radii. This difference is induced because TC intensity is significantly correlated with both the vertical velocity and specific humidity in the inner core but is not significantly correlated with the vertical velocity in outer radii. Further investigation shows that the intensity-rain rate relationship at outer radii is influenced by the evolution stage of TCs. Outer radii rain rate is positively correlated with TC intensity for non-decaying TCs, while this correlation is reduced for decaying TCs due to systematic downdrafts in the outer radii. In the context of climate change, sensitivity of TC rain rate to sea surface temperature (SST) is found to be +9% per K increase of SST, roughly the product of the sensitivity of TC intensity to SST (+3%) and the Clausius-Clapeyron scaling (+7%). Coupled with synthetic storms, evolutions of TC rain rate over the 21st century under the SSP5 8.5 scenario are projected by the TCR (calibrated with the WRF simulations). The annual increase rates of averaged TC rain rate are 0.17% and 0.20% for inner core and outer radii, respectively, larger than the annual increase rate of TC intensity (0.046%) but comparable to that of cube of intensity (0.18%).

Corresponding Author: Dazhi Xi Email: dxi@princeton.edu
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