Processes setting the characteristics of sea surface cooling induced by tropical cyclones

Abstract

[1] A 1/2°resolution global ocean general circulation model is used to investigate the processes controlling sea surface cooling in the wake of tropical cyclones (TCs). Wind forcing related to more than 3000 TCs occurring during the 1978-2007 period is blended with the CORE II interannual forcing, using an idealized TC wind pattern with observed magnitude and track. The amplitude and spatial characteristics of the TC-induced cooling are consistent with satellite observations, with an average cooling of $1°C that typically extends over 5 radii of maximum wind. A Wind power index (WPi) is used to discriminate cooling processes under TCs with high-energy transfer to the upper ocean (strong and/or slow cyclones) from the others (weak and/or fast cyclones). Surface heat fluxes contribute to $50 to 80% of the cooling for weak WPi as well as away from the cyclone track. Within 200 km of the track, mixing-induced cooling increases linearly with WPi, explaining $30% of the cooling for weak WPis and up to $80% for large ones. Mixing-induced cooling is strongly modulated by pre-storm oceanic conditions. For a given WPi, vertical processes can induce up to 8 times more cooling for shallow mixed layer and steep temperature stratification than for a deep mixed layer. Vertical mixing is the main source of rightward bias of the cold wake for weak and moderate WPi, but along-track advection becomes the main contributor to the asymmetry for the largest WPis.

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

“…A fixed depth average has been justified by its simplicity and because the depth of mixing is only a weak function of the TC strength for strong storms [Lloyd and Vecchi, 2011;Vincent et al, 2012a]. However, we will show here that using a variable L leads to significant improvements in terms of variance explained in TC intensification.…”

“…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].…”

Modeling Interaction of a Tropical Cyclone with Its Cold Wake

“…What is not shown in Shay's figure is the horizontal advection by the ocean currents that move cold water from the rear part of the wake to the front and extend the width of the wake (Chen et al 2010: Vincent et al 2012. Using a two-way coupled model, Chen et al (2010) showed the distinct spatial separation among these three primary forcing terms that are generating the bulk of the cooling (Figure 2).…”

Sea surface height evidence for long-term warming effects of tropical cyclones on the ocean

“…S trong winds associated with tropical cyclones (TCs) increase air-sea heat fluxes, favoring the intensification of storms, and generate vigorous vertical mixing in the upper ocean, stirring warm surface waters with colder waters below (1)(2)(3)(4)(5)(6). The wake produced by the passage of TCs is thus characterized by a surface cold anomaly and a subsurface warm anomaly (1-3, 6, 7).…”