Upper ocean response to typhoon Kalmaegi (2014)

Abstract

Typhoon Kalmaegi passed over an array of buoys and moorings in the northern South China Sea in September 2014, leaving a rare set of observations on typhoon‐induced dynamical and thermohaline responses in the upper ocean. The dynamical response was characterized by strong near‐inertial currents with opposite phases in the surface mixed layer and in the thermocline, indicating the dominance of the response by the excitation of the first baroclinic mode. The thermohaline response showed considerable changes in the mean fields in addition to a near‐inertial oscillation. In particular, temperature and salinity anomalies generally exhibited a three‐layer vertical structure, with the surface layer becoming cooler and saltier, the subsurface layer warmer and fresher, and the lower layer cooler and saltier again. The response in the surface and subsurface layers was much stronger to the right of the typhoon track, while that in the lower layer was stronger along the track and to the left. These features of the upper ocean response were grossly reproduced by a three‐dimensional numerical model. A model‐based heat budget analysis suggests that vertical mixing was mainly responsible for the surface cooling and subsurface warming, while upwelling was the cause of cooling from below. Both observations and model results indicate that the whole upper ocean experienced an overall cooling in the wake of typhoon Kalmaegi.

A New Coupled Ocean‐Waves‐Atmosphere Model Designed for Tropical Storm Studies: Example of Tropical Cyclone Bejisa (2013–2014) in the South‐West Indian Ocean

“…Temperature decreases by more than 3°C over 75 m. After the passage of the cyclone, the depth of the OBL decreases by strong advection (dark gray in Figure a) showing that Bejisa was not strong enough to entirely erode the thermocline (Zambon et al, ). This behavior is similar to the upper ocean response during typhoon Kalmaegi (2014) (Zhang et al, ).…”

Rapid shelf‐wide cooling response of a stratified coastal ocean to hurricanes

“…Upon storm forcing, the ROMS thermocline deepens to the correct depth, but the surface does not sufficiently cool, likely due to the inadequate supply of cold bottom water at the start. Insufficient surface ocean cooling in model simulations due to an excessively thick surface layer has also been found to occur in other recent TC studies [e.g., Zhang et al ., ], and is likely a common deficiency in numerical model simulations of TC ocean response. Despite deficiencies in the details, the overall storm response characteristics—two‐layer structure at the start, deepening of the thermocline, and rapid and intense cooling of the surface mixed layer—are present and adequate for determining dominant force balances and diagnosing the causes of SST cooling.…”

Hurricanes Enhance Labile Carbon Export to the Deep Ocean

“…Tropical cyclones (hurricanes) are the most extreme episodic weather event affecting the subtropical and temperate ocean. Hurricanes generate strong near-inertial waves and mixing impact air-sea heat and carbon dioxide fluxes (Bates et al, 1998;Black & Dickey, 2008;Brink, 1989;Price, 1981;Price et al, 2008;Zhang et al, 2016). Surface mixed layer deepening and upwelling generated by Ekman pumping during hurricane passage upwells nutrients into the euphotic zone which induces transient phytoplankton blooms, visible by satellite (Babin et al, 2004;Foltz et al, 2015;Lin et al, 2003;Platt et al, 2005;Son et al, 2006).…”