Assessing the oceanic control on the amplitude of sea surface cooling induced by tropical cyclones

Abstract

[1] Tropical cyclones (TCs) induce sea surface cooling that feeds back negatively on their intensity. Previous studies indicate that the cooling magnitude depends on oceanic conditions as well as TC characteristics, but this oceanic control has been poorly documented. We investigate the oceanic influence on TC-induced cooling using a global ocean model experiment that realistically samples the ocean response to more than 3,000 TCs over the last 30 years. We derive a physically grounded oceanic parameter, the Cooling Inhibition index (CI), which measures the potential energy input required to cool the ocean surface through vertical mixing, and hence accounts for the pre-storm upper-ocean stratification resistance to TC-induced cooling. The atmospheric control is described using the wind power index (WPi), a proxy of the kinetic energy transferred to the ocean by a TC, which accounts for both the effects of maximum winds and translation speed. The cooling amplitude increases almost linearly with WPi. For a given WPi, the cooling amplitude can however vary by an order of magnitude: a strong wind energy input can either result in a 0.5 C or 5 C cooling, depending on oceanic background state. Using an oceanic parameter such as CI in addition to wind energy input improves statistical hindcasts of the cold wake amplitude by $40%. Deriving an oceanic parameter based on the potential energy required to cool the ocean surface through vertical mixing is thus a promising way to better account for ocean characteristics in TCs studies.

Observation-Based Estimates of Surface Cooling Inhibition by Heavy Rainfall under Tropical Cyclones

“…This vertical mixing largely results from the intense vertical shear related to the strong inertial currents driven by TCs (Price 1983;Greatbatch 1984;D'Asaro 1985;Shay et al 1989;Price et al 1994;D'Asaro et al 1995;Crawford and Large 1996;Tsai et al 2008;Samson et al 2009;Jullien et al 2012). Recently, Vincent et al (2012a) have confirmed that vertical mixing is the dominant cooling process close to cyclone tracks and for strong cyclones by using an ocean general circulation model to study the cold wake of more than 3000 TCs over the last 30 years. Airsea fluxes (i.e., strong latent and sensible heat fluxes due to intense TC winds) nonetheless contribute in a nonnegligible way along the track of weaker storms, and lateral advection can contribute to up to 15% of the cooling for most intense TCs (Vincent et al 2012a).…”

Dynamic Potential Intensity: An improved representation of the ocean's impact on tropical cyclones

“…While the forecast of a TC's path has improved substantially over the past few decades, the prediction of its intensity remains challenging [Rappaport et al, 2012]. When over the ocean, vertical mixing induced by a TC entrains colder, deeper water into the relatively warm near-surface mixed layer, resulting in a cooling of the sea surface temperature (SST) [Price, 1981;Bender and Ginis, 2000;D'Asaro et al, 2007;Vincent et al, 2012aVincent et al, , 2012b. The decrease in SST is a negative feedback on the TC's intensity through its reduction in the flux of heat from the ocean to the atmosphere [Shay et al, 2000;Cione and Uhlhorn, 2003;Lloyd and Vecchi, 2011;Balaguru et al, 2012].…”

Ocean barrier layers’ effect on tropical cyclone intensification

“…The intensity of a TC is critically dependent on the air-sea enthalpy difference (9). Thus, any process or feature that can affect the TC-induced sea surface temperature (SST) change due to entrainment caused by wind mixing or upwelling (10) may play a role in TC intensification (11)(12)(13), making it critical to understand the factors controlling the upper-ocean response to TCs (14).…”