The biophysical responses of the upper ocean to the typhoons Namtheun and Malou in 2004

Yuan-Jian Yang,Liang Sun,Qi Liu,Tao Xian,Yun-Fei Fu

doi:10.1080/01431161.2010.485140

Abstract

The responses of the upper ocean to typhoons were investigated by the observations of sea surface wind (SSW), sea surface temperature (SST), sea surface height anomaly (SSHA), chlorophyll-a (Chl-a) and Argo floats. Typhoon Namtheun had notable impacts on the upper ocean along its track from July to August 2004. The local processes (entrainment and upwelling) dominated the upper ocean responses in the regions of the pre-existing cold eddy and beneath the typhoon track, where the observed locations of upwelling, SSHA changes, SST cooling, and Chl-a enhancement were consistent with each other. Besides, there were cold tongues extending from the cold centres. The trajectories of Argo floats, along with the cold tongues, indicated that the surface advections induced such non-local responses. On the other hand, the following weak typhoon Malou had few impacts on the upper ocean. Finally, the mechanisms of the Chl-a concentration enhancement were sketched as the effects of both the local upwelling and the non-local advection. This study implies that some non-local processes, e.g. horizontal advections, may play a notable role in the upper ocean responses to the typhoons.

Highlights

Chlorophyll-a enhancement, appeared accompanied with sea surface cooling after typhoon, the inverse correlation ship between SST cooling and chl-a enhancement has been widely documented [Subrahmanyam et al, 2002; Lin et al, 2003; Babin et al, 2004; Walker et al, 2005], and the SST cooling was even taken as a proxy of phytoplankton blooming [Gierach and Subrahmanyam, 2008]
It is obvious that entrainment couldn’t change the vertical average chl-a alone, especially when the mixing zone depth was significantly shallower than euphotic zone depth (Fig 3), which might be the stories happened at wakes of typhoon Hai-Tang [Chang et al, 2008] and Wilma [Gierach and Subrahmanyam, 2008]
Noting that the upwelling was quite stronger at A (Fig. 2a), it seems that the pre-existed cyclonic eddy at region

Summary

Introduction

Typhoon (or hurricane, tropical cyclone), when passing over the ocean, has both physical [Price 1981; Stramma et al 1986; Price 1994; Emanuel, 1999; Chen et al, 2003; Liu et al, 2008] and biophysical [Behrenfeld et al., 1997; McGillicuddy et al, 1999; Subrahmanyam et al, 2002; Lin et al, 2003; Babin et al, 2004] impacts on the ocean. Vertical mixing, entrainment and upwelling injured colder subsurface water [Price, 1981; D’Asaro, 2002; Walker et al, 2005], made cold wake at sea surface, and leaded to phytoplankton blooming along typhoon track, especially in oligotrophic waters [Babin et al, 2004]. 2004; Walker et al, 2005; Gierach and Subrahmanyam, 2008] Such guess has not been clearly concluded, due to the lack of interdisciplinary subsurface data sets [Babin et al, 2004]. Both the invalid concept about ocean response and the uncertain guess about chl-a enhancements imply that further investigation on ocean response is required. It is found that pre-typhoon ocean environment played an important role in the ocean responses to typhoon

Observation Data and Background

Results

Discussion

Conclusion