On the Predictability of Sea Surface Height around Palau

Abstract

As part of the Flow Encountering Abrupt Topography (FLEAT) program, an array of pressure-sensor equipped inverted echo sounders (PIESs) was deployed north of Palau where the westward-flowing North Equatorial Current encounters the southern end of the Kyushu-Palau Ridge in the tropical North Pacific. Capitalizing on concurrent observations from satellite altimetry, FLEAT Spray gliders and shipboard hydrography, the PIESs’ 10-month duration hourly bottom pressure (p) and round-trip acoustic travel time (τ) records are used to examine the magnitude and predictability of sea level and pycnocline depth changes and to track signal propagations through the array. Sea level and pycnocline depth are found to vary in response to a range of ocean processes, with their magnitude and predictability strongly process-dependent. Signals characterized here comprise the barotropic tides, semidiurnal and diurnal internal tides, southeastward propagating super-inertial waves, westward propagating mesoscale eddies, and a strong signature of sea level increase and pycnocline deepening associated with the region’s relaxation from El Niño to La Niña conditions. The presence of a broad band of super-inertial waves just above the inertial frequency was unexpected and the FLEAT observations and output from a numerical model suggest that these waves detected near Palau are forced by remote winds east of the Philippines. The PIES-based estimates of pycnocline displacement are found to have large uncertainties relative to overall variability in pycnocline depth, as localized deep current variations arising from interactions of the large-scale currents with the abrupt topography around Palau have significant travel time variability.

Stirring and Mixing in the Wake of Angaur and Peleliu Islands, Palau

“…Palau is well suited for studies of such processes because its islands and submarine ridges are situated between the westward North Equatorial Current (NEC) and the eastward North Equatorial Countercurrent (NECC; Figure 1a). In Palau, wake eddies from 1 to 100 km scales and lee waves at 1‐km scales have been observed and modeled at the north and south points along with some estimates of their dissipation and drag on the total flow, which is often a combination of tidal, inertial, and lower‐frequency flows (Andres et al., 2020; Gopalakrishnan & Cornuelle, 2019; Johnston, MacKinnon, et al., 2019; MacKinnon et al., 2019; Merrifield et al., 2019; Rudnick et al., 2019; Siegelman et al., 2019; Simmons et al., 2019; St. Laurent et al., 2019; Voet et al., 2020; Wijesekera et al., 2020; Zedler et al., 2019; Zeiden et al., 2019, 2021).…”

Forecasting tropical ENSO-induced drought conditions using sea surface height in the Western Pacific

“…Independent assessments of altimetry data saw global bias estimates from each satellite mission 22,23 . In previous works, satellite altimetry data have shown great utility in various sea level applications across different study sites, such as the Palau Islands, Malaysia, West Philippine Sea, and Argentina [24][25][26][27] .…”

Advanced Remote Data Acquisition Using a Pop-Up Data Shuttle (PDS) to Report Data From Current- and Pressure-Recording Inverted Echo Sounders (CPIES)

“…The PIES or CPIES-measured variables have been used to investigate oceanic barotropic and baroclinic variabilities. For example, in low-and mid-latitude oceans, acoustic travel time has been used to estimate, with remarkable accuracy, time-varying vertical profiles of temperature (Watts and Rossby, 1977;Watts et al, 2001a;Park et al, 2005) and geopotential height (Chiswell et al, 1988;Baker-Yeboah et al, 2009;Park et al, 2012;Behnisch et al, 2013;Donohue et al, 2016;Jeon et al, 2018;Andres et al, 2020). Moreover, a recent field experiment in Sermilik Fjord in Greenland showed the possibility of detecting ice thickness variations using τ (Andres et al, 2015).…”