Daily Variation of Chlorophyll-A Concentration Increased by Typhoon Activity

Abstract

The chlorophyll-a (Chla) concentration product of the Himawari-8 geostationary meteorological satellite is used to show the temporal variation of Chla owing to the passage of typhoons, namely, tropical cyclones in the western North Pacific Ocean. The daily Chla variation shows that Chla usually increases along the paths of typhoons, whereas the same observations are almost impossible when using the data of polar-orbiting satellites as shown in previous studies. This is because the temporal resolution of Himawari-8 is ten times more than that of polar-orbiting satellites, and the daily Chla distribution contains a few disturbances attributed to clouds after compositing cloud-free data. Chla usually increases on the day of typhoon arrival, but mostly, the ratio of Chla increased by a typhoon to the background Chla, R Chla HIMA , is less than 2. Only a few typhoons considerably increased Chla. As a whole, R Chla HIMA is proportional to the maximum 10-min sustained wind speed up to 85 knots (44 m s−1), namely, 0.01 mg m−3 knot−1 (0.019 mg s m−4). However, there is no clear dependence between Chla and the wind speed in seas with higher Chla, such as the South China Sea. The result that typhoons are usually cultivating the ocean is important for studies of primary ocean productivity and carbon flux between the atmosphere and ocean.

Keywords

• phytoplankton bloom
• enhancement of chlorophyll-a concentration
• tropical cyclone
• Himawari-8
• daily variation