Shallow ocean response to tropical cyclones observed on the continental shelf of the northwestern South China Sea

Abstract

Based on observed temperature and velocity in 2005 in northwestern South China Sea, the shallow ocean responses to three tropical cyclones were examined. The oceanic response to Washi was similar to common observations with 2°C cooling of the ocean surface and slight warming of the thermocline resulted from vertical entrainment. Moreover, the wavefield was dominated by first mode near‐inertial oscillations, which were red‐shifted and trapped by negative background vorticity leading to an e‐folding timescale of 12 days. The repeated reflections by the surface and bottom boundaries were thought to yield the successive emergence of higher modes. The oceanic responses to Vicente appeared to be insignificant with cooling of the ocean surface by only 0.5°C and near‐inertial currents no larger than 0.10 m/s as a result of a deepened surface mixed layer. However, the oceanic responses to Typhoon Damrey were drastic with cooling of 4.5°C near the surface and successive barotropic‐like near‐inertial oscillations. During the forced stage, the upper ocean heat content decreased conspicuously by 11.65% and the stratification was thoroughly destroyed by vertical mixing. In the relaxation stage, the water particle had vertical displacement of 20–30 m generated by inertial pumping. The current response to Damrey was weaker than Washi due to the deepened mixed layer and the destroyed stratification. Our results suggested that the shallow water oceanic responses to tropical cyclones varied significantly with the intensity of tropical cyclones, and was affected by local stratification and background vorticity.

Contributions of physical and biogeochemical processes to phytoplankton biomass enhancement in the surface and subsurface layers during the passage of Typhoon Damrey

“…Observed vertical profiles of the water temperature during Typhoon Damrey at Station A were not available. The temperature profiles observed in a mooring station on the continental shelf of the northwestern SCS (Station B in Figure ) indicated that Typhoon Damrey caused a cooling of 4.5°C in the surface layer and a warming of 1.2°C in the subsurface layer (75 m depth) [ Yang et al ., ], which were comparable to our results in which the surface temperature decreased by 4.0°C while the water temperature at 75 m depth increased by 1.0°C (Figure c).…”

“…Typhoon Damrey happened to pass by a mooring station (19°35′N, 112°E) (Station B in Figure ) on the continental shelf of the northwestern SCS. The observed variation of temperature caused by the Typhoon Damrey [ Yang et al ., ] was used to compare with and validate the model results. The daily SST and sea surface Chl a time series during the passage of the typhoon were validated by using daily Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) SST data (http://www.remss.com/) and Chl a values derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) onboard Aqua (http://oceandata.sci.gsfc.nasa.gov/MODISa/Mapped/Daily/9 km/) and Sea‐viewing Wide Field‐of‐view Sensor (SeaWiFS) (http://oceandata.sci.gsfc.nasa.gov/SeaWiFS/Mapped/Daily/9km/), respectively.…”

“…Typhoons are intense atmospheric events with strong effects on the physical and biogeochemical processes in oceans [Tang et al, 2014;Guan et al, 2014;Yang et al, 2015]. Many studies have suggested that typhoons can enhance the chlorophyll a concentration (Chl a) in the upper water layer, as well as causing phytoplankton blooms via nutrient pumping to the surface [Zheng and Tang, 2007;Shan et al, 2014;Zhao et al, 2015].…”

“…However, due to the rough sea conditions associated with typhoon events, only a few shipboard observations are available to study typhoons and their oceanic impacts [Zheng and Tang, 2007;Zhao et al, 2009;Ye et al, 2013]. In addition, observations collected by moorings during typhoon events can only be captured by chance [Dickey et al, 1998;Zedler et al, 2002;Guan et al, 2014;Yang et al, 2015]. Thus, the responses of Chl a have been analyzed mainly at the surface based on satellite data [Babin et al, 2004;Tang et al, 2004a;Walker et al, 2005;Zhao et al, 2008;Zhao et al, 2013].…”

Observation of Tropical Cyclone‐Induced Shallow Water Currents in Taiwan Strait

“…The reasons underlying such large differences in NIOs among the three stations are further explored. Apart from the bottom friction which is the general dominated dissipation factors for the NIOs in this shallow water, the deepened mixed layers and the destruction of the stratification would further weaken the NICs to some extent [ Yang et al ., ]. As noted by Zhu et al .…”