3 years ago

Advection by the North Equatorial Current of a cold wake due to multiple typhoons in the western Pacific: Measurements from a profiling float array

T.M. Shaun Johnston, Daniel L. Rudnick, Noel Brizuela, James N. Moum

Cold wakes of previous tropical cyclones (TC) affect the development of subsequent TCs, but few subsurface datasets have sufficient persistence and spatial coverage to follow a cold wake as it is advected by currents. For >2 months in 2018, an array of 8 floats obtained >20,000 temperature profiles from the surface to <200 m every <40 minutes before, during, and after Super Typhoons Mangkhut, Trami, Kong‐Rey, and Yutu. Two floats were in/near Mangkhut's eye; experienced gale‐force winds during Trami and Kong‐Rey; drifted over 1000 km westward with the North Equatorial Current; and tracked the advection of the weakly‐stratified, cold wake produced by the sequence of TCs. Sea surface temperature (SST) shows the westward advection of the cumulative cold wake. While causation cannot be established, since atmospheric measurements were not made, Yutu weakened as it passed over the cold wake.

The stratification and the energy needed to mix the water column in the cold wake decreased with each TC. One float directly in the path of Yutu showed mixing to 125‐‐150 m was likely, corresponding to a cooling of 0.5‐‐1°C under the eye. SST in the cold wake cooled by 1°C within a 150 km radius of Yutu's eye, where the effect on air‐sea heat fluxes is maximal. A cold wake can remain weakly stratified for many weeks during a sequence of TCs. These results also suggest an advected cold wake from previous TCs may contribute many weeks later to the arrested development of a subsequent TC at a distant location.

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