The e-Folding Recovery Time of Tropical Cyclones’ Cold Wakes

Abstract Tropical cyclones’ (TCs) cold wakes can persist from days to weeks after TC passage, giving potentially important feedback to the local atmosphere and subsequent TCs. The e -folding recovery time of TCs’ cold wakes is revisited in this study based on theoretical analysis, observational statistics, and idealized numerical simulations. Statistical results for global TCs from 2002 to 2021 reveal that the cold anomaly experiences an exponential decay, with an average e -folding time of ∼14 days. The warm rate of cold wakes depends on the magnitude of sea surface temperature anomaly (SSTA), and the e -folding time tends to be shorter for larger SSTA when it is over ∼1°C. Observations show that the mixed layer is roughly doubled of the originally estimated trapping depth, indicating that there is nonnegligible heat exchange at the base of the trapped layer. The previous e -folding time equation is modified to incorporate surface heat flux dependence on wind speed and extension of the trapping depth to be approximately the mixed layer depth. Diagnosis based on numerical simulations suggests that the thinner trapping depth than the mixed layer depth has underestimated the layer to be warmed up. As a consequence, the modified equation has extended the e -folding time recovery noticeably and has performed reasonably well in predicting the recovery time of observed and modeled cold wakes.