2. Cruise observation

A hydrographic cruise survey for collecting in situ data of marine environmental parameters in the PRE was conducted during the period between May 3, 2014 and May 11, 2014. The instruments used to collect the in situ data in this cruise survey were a sea surface sampling Seabird CTD (conductivity, temperature, and depth) for sea surface sampling, an RDI 600 kHz acoustic Doppler current profiler (ADCP), and a Sea and Sun Technology CTD. The RDI ADCP was mounted on the right side of the cruise ship. With these instruments, the underway surface

Time periods of cruise transects together with the sea level at the Shek Pik Station (the location is shown in Figure 3c) (a). The 6-hourly wind condition from the NCEP/NCAR reanalysis data over the PRE (b).

salinity, temperature, density, and underway profiles of currents were collected, and additionally, the CTD profiles at a number of CTD cast stations along the cruise transects were also collected. Figure 2a displays the tidal conditions at the Shek Pik Station, located in the south of the Lantau Island near the mouth of the PRE (as shown in Figure 3c), and the observed periods of different transects. The 6-hourly wind conditions from the NCEP/NCAR reanalysis data over the PRE region during the cruise period are shown in Figure 2b. The cruise transects and CTD cast stations across the PRE are illustrated in Figure 3. During this cruise, a typical East Asian monsoon transition process happened with relatively weak wind strength. The northeasterly/easterly winds prevailed during a spring to neap tide transition from May 4, 2014 to May 6, 2014 (Figure 3a). From May 7, 2014 to May 9, 2014, the winds turned to be the easterly/southeasterly and the spring tide changed to neap tide (Figure 3b), and the southerly/southwesterly winds prevailed during a neap tide from May 10, 2014 to May 11, 2014 (Figure 3c).

Table 1 lists the tidal phases and wind conditions during different observed transects. Transects B and D were in flood phases during the spring tide under northeasterly winds, whereas transects C and F were in ebb phases. Transect H was during the flood under the easterly wind. In the neap tide period, transect I was during ebb under the southeasterly wind, whereas Transect J was during on the flood tide. Under the southerly wind, transect M was from flood to ebb, whereas transects N and O were during ebb. This data set has high sampling spatial resolution coverage over the PRE in a spring-neap cycle, which is particularly useful to identify the salinity and circulation characteristics and to validate model results.

#### Figure 3.

The cruise transects and the CTD cast stations: Under northeasterly/easterly winds (a), under easterly/ southeasterly winds (b), under southerly/southwesterly winds (c). The red pentagram shows the location of the Shek Pik tide gauge station.

Circulations in the Pearl River Estuary: Observation and Modeling DOI: http://dx.doi.org/10.5772/intechopen.91058


### Table 1.

Observed tidal phases and wind conditions for different transects.
