Impact of Rapid Change in the Rain-Formed Barrier Layer on the Upper Ocean Thermal Response to Typhoon Kalmaegi (2014)

Abstract High temporal resolution in situ observations measured by cross-shaped arrays of buoys and moorings are used to investigate the rapid variation characteristics of the rain-formed barrier layer (BL) and further to elucidate its influence on the upper ocean thermal response to Typhoon Kalmaegi. The barrier layer thickness (BLT) is shown to undergo rapid changes, reaching two close peak values (31.6 and 30.6 m) within just one hour at buoy observations on Kalmaegi’s right side. Although both BLTs are very similar, the barrier layer potential energy (BLPE) of the first BLT peak is almost three times greater than that of the second BLT peak. This discrepancy is due to strong density stratification playing a more crucial role than the isothermal layer depth in determining the barrier layer’s ability to suppress the upper ocean mixing. Consequently, the first BLT peak significantly inhibits 91% of entrainment mixing cooling, which is 3.8 times greater than that of the inhibition effect induced by the second BLT peak. Furthermore, the BL on Kalmaegi’s right side is deeper and more persistent, being twice as great as that on the left side. Throughout Kalmaegi’s passage, cooling due to entrainment mixing is reduced by 32.2% due to the BL effect at buoy observations on Kalmaegi’s right side, while the reductions are 18.9% and 14.6% at buoys on the left side, respectively. Significance Statement The study aims to illustrate that the rain-formed barrier layer should not be a slow process, where the barrier layer thickness (BLT) reaches two close peaks within just one hour at buoy observations on Kalmaegi’s right side. Although BLT peaks are very similar, which have extremely different inhibition effect on the upper ocean entrainment mixing and ocean cooling depending on BLT, isothermal layer depth (ILD), and barrier layer potential energy (BLPE). The rapid change in the rain-formed barrier layer is significantly important to provide a new guidance for analyzing the role of barrier layer.