On the Response of the Ocean to the Tropical Typhoon Nanmadol
Lin, Jingrou1; Tang, DanLing1; Alpers, Werner2; Wang, Sufen1
1South China Sea Institute of Oceanology, Guangzhou, CHINA; 2University of Hamburg, Institute of Oceanography, Hamburg, GERMANY
A super-typhoon, called Nanmadol, crossed the Luzon Strait, which separates the Philippine island of Luzon and the island of Taiwan, between on 27 and 28 August 2011 from south to north. The associated cloud pattern was captured by the MERIS sensor onboard the Envisat satellite on 27 and 29 August, and part of the sea surface roughness pattern also by the Advanced Synthetic Aperture Radar (ASAR) onboard the same satellite on 28 August in the Global Mode (GM). Furthermore, radar backscatter data were acquired by the Advanced Scatterometer (ASCAT) onboard the MetOp satellite on 28 August when the eye of the super-typhoon was located over the northern section of the Luzon Strait. The near-surface wind field derived from the ASCAT data shows the typical typhoon pattern.
One week after Nanmadol crossed the Luzon Strait, the research vessel (RV) Shiyan 3 of the South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou, reached the Luzon Strait. Measurements of the depth profiles of water temperature, salinity, and chlorophyll-a (Chl-a) and dissolved oxygen (DO) concentrations were carried out from this RV at different locations. Despite of the time delay of one week, the in-situ data still show distinct signals of the typhoon. They show close to the typhoon track a decrease of water temperature and a strong increase in Chl-a and DO concentrations. These values differ significantly from the values measured further away from the typhoon track. Maximum Chl-a concentration is found at depths between 50 m and 75 m and maximum DO concentration at depth around 5 m. The layer of high DO concentration extends from the surface down to a depth of 35 m and is strongly mixed. We explain the strong increase in DO concentration and the strong vertical mixing being caused by the typhoon wind, which gave rise to increased entrainment of oxygen from the air.