Fig. 1

The study area (the sea area inside the red line) and the location of the CTD stations. Yellow markers are the CTD stations in summer 2008, and magenta dots are the CTD stations in summer 2015"

Fig. 2

Scatter plots of satellite SST and in situ CTD data"

Fig. 3

Working processes for obtaining upwelling: calculating TPI from SST image (a); obtaining background temperature of upwelling (b); carrying out multi-scale segmentation of SST and TPI layers (c); merging upwelling objects (d); removing non-upwelling objects and finding the center (e); and calculating the upwelling intensity (UPI) (f)"

Fig. 4

The CTD stations, temperature and salinity profiles of the section on 1 July 2015 (a~c), and on 30 August 2008 (d~f). The blue line is the range of extracted upwelling area"

Fig. 5

A complete upwelling process off eastern Hainan Island and its time series of area and UPI between 18 June and 4 July 2017"

Fig. 6

Dates (a) and number of occurrence days (b) of the upwelling off eastern Hainan Island in 2008~2017"

Fig. 7

The statistical results of area and UPI and their correlation coefficient of the upwelling off eastern Hainan Island in 2008~2017"

Fig. 8

Frequency distribution of summer upwelling off eastern Hainan Island"

Fig. 9

Time series of offshore wind and UPI between 18 June and 4 August 2008 (a), and time series of wind stress curl and UPI between 28 July and 4 September 2014 (b)"

Tab. 1

Information of tropical cyclones landing in eastern Hainan Island during 2008~2017"

Fig. 10

The trajectories and strength of the typhoons passing through the Qiongdong area. The green, blue and red lines represent the northern, central and southern landing typhoons, respectively (a); wind field of typhoon passage (b~k); time series of wind vector (red arrows represent the northerly wind, black arrows represent the other wind directions) (l), upwelling area and UPI (m)"