# Underwater Optical Path Loss after Passage of a Tropical Storm
## 3 IOPs with and without Typhoon Passage  
A glider is a remote operator programmed to perform a series of downward and upward tracks while collecting various oceanographic parameter data using various installed sensor packages. It can position itself at the ocean surface with a 45\({}^{\circ}\) downward angle to present the antenna array skyward to facilitate two-way satellite communications. The NAVOCEANO Seaglider has the Seabird Electronics SBE 41 CP CTD sensor (hydrographic measurement) and WET Labs' Beam Attenuation Meter (BAM) (optical measurement) [13]. The technical details about the BAM can be found in [14]. The Seaglider measures temperature, salinity, and beam attenuation coefficient (c) down to 100 m in depth. NAVOCEANO has routine quality control procedures on all raw observational data. Bad profiles were removed due to obviously erroneous locations, large spikes, and mismatches of characteristics with the surrounding profiles. NAVOCEANO provided the profile data of three Seagliders inside the area 124\({}^{\circ}\) E-134\({}^{\circ}\) E, 15\({}^{\circ}\) N-27\({}^{\circ}\) N after quality control with high transparency and low seasonal variability. Among them, two Seagliders (NG226 and NG232) were in the area where Super Typhoon Guchol passed by seven days ago. The two Seagliders were deployed from a survey ship 15 min and 223 m apart: 03:19 UTC, June 25, 2012 at 25\({}^{\circ}\)30\({}^{\prime}\)20\({}^{\prime\prime}\) N, 131\({}^{\circ}\)59\({}^{\prime}\)51\({}^{\prime\prime}\) E for NG226 (blue trajectory in Figure 2a,b), and 03:34  
Figure 1: Geography of the Western Pacific Ocean and track of Super Typhoon Guchol (2012) with strength. UTC, June 25, 2012 at 25\({}^{\circ}\)30\({}^{\prime}\)27\({}^{\prime\prime}\) N, 131\({}^{\circ}\)59\({}^{\prime}\)55\({}^{\prime\prime}\) E for NG232 (red trajectory in Figure 2a,b). The two Seagliders took very different trajectories despite being very close (only 223 m apart) initially, with NG226 drifting southwestward and then southward and then southward and NG232 drifting southeastward and then northeastward. On June 30, 2012, NG226 was located at 24\({}^{\circ}\)59\({}^{\prime}\)27\({}^{\prime\prime}\) N, 131\({}^{\circ}\)59\({}^{\prime}\)26\({}^{\prime\prime}\) E at 17:24 UTC. However, NG232 was located at 25\({}^{\circ}\)34\({}^{\prime}\)50\({}^{\prime\prime}\) N, 132\({}^{\circ}\)10\({}^{\prime}\)20\({}^{\prime\prime}\) E at 17:51 UTC. Such strong bifurcation of ocean currents was generated in the wake of Super Typhoon Guchol. The third Seaglider (NG270) was underwater from January 6 to February 28, 2014 without any typhoon activities (magenta trajectory in Figure 2a). We used IOP data from the two Seagliders for comparison: NG226 with a typhoon and NG270 without a typhoon. The beam attenuation coefficient \(c\) (470 nm), measured by NG226 (59 profiles) from June 25 to June 30, 2012 after Super Typhoon Guchol's passage (See Figure 5a in [6].) is large with horizontally averaged values (red solid profiles) generally greater than 0.8 m\({}^{-1}\). The beam attenuation coefficient \(c\) (470 nm) measured by NG270 (825 profiles) from January 6 to February 28, 2014 with no typhoon activity (see Figure 6 in [6]) is much smaller with horizontally averaged values less than 0.05 m\({}^{-1}\). The difference in \(c\)(\(z\)) between with and without typhoon passage is huge. During Super Typhoon Guchol's passage, high winds generated strong upwelling in the upper ocean and pumped rich nutrients upward from the subsurface layer to the euphotic layer. This would induce the phytoplankton chlorophyll-_a_ (Chl-_a_) to breed and grow rapidly. The Chl-_a_ concentration (C) is directly related to the beam attenuation coefficient by a classic least-square fitted formula for the wavelength of 490 nm [15],  
\[c(z)=c_{w}(z)+0.39[C(z)]^{0.57} \tag{1}\]  
where \(c_{w}(z)\) is the beam attenuation coefficient for the pure water.