Abstract
Abstract. A 10-year reanalysis of the PacIOOS Hawaiian Island Ocean Forecast System was produced using an incremental strong-constraint 4-D variational data assimilation with the Regional Ocean Modeling System (ROMS v3.6). Observations were assimilated from a range of sources: satellite-derived sea surface temperature (SST), salinity (SSS), and height anomalies (SSHAs); depth profiles of temperature and salinity from Argo floats, autonomous Seagliders, and shipboard conductivity–temperature–depth (CTD); and surface velocity measurements from high-frequency radar (HFR). The performance of the state estimate is examined against a forecast showing an improved representation of the observations, especially the realization of HFR surface currents. EOFs of the increments made during the assimilation to the initial conditions and atmospheric forcing components are computed, revealing the variables that are influential in producing the state-estimate solution and the spatial structure the increments form.
Highlights
The Pacific Integrated Ocean Observing System (PacIOOS, 2018) has produced daily forecasts of the ocean state surrounding the Hawaiian Islands since 2009
We have presented a 10-year reanalysis of the PacIOOS Hawaiian Island Ocean Forecast System and assessed the performance of the state-estimate solution and freerunning forecasts
Using a time-dependent incremental strong-constraint four-dimensional variational data assimilation (I4D-Var) scheme, we show that the model represents the observational data well over the time period
Summary
The Pacific Integrated Ocean Observing System (PacIOOS, 2018) has produced daily forecasts of the ocean state surrounding the Hawaiian Islands since 2009. There are persistent trade winds from the northeast that, combined with steep mountainous terrain on the islands, cause wind wakes in lee of the peaks, on the islands of Hawai‘i and Maui This introduces strong temperature gradients, increases the seasonal variability (Sasaki and Klein, 2012), and drives currents such as the Hawaiian Lee Countercurrent (HLCC) (Smith and Grubišic, 1993; Xie et al, 2001; Chavanne et al, 2002). There are two main objectives to this study: to assess the skill and performance of the state-estimation model and to analyze the increments made to the initial, boundary, and atmospheric forcing terms. The first station was constructed in 2010, with the remaining six becoming operational over the period from 2011 to 2015 These instruments produce high-resolution (both spatially and temporally) surface current velocities in the vicinity of the islands of O‘ahu and Hawai‘i.
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