Abstract
Abstract. Canada has the longest coastline in the world and includes diverse ocean environments, from the frozen waters of the Canadian Arctic Archipelago to the confluence region of Labrador and Gulf Stream waters on the east coast. There is a strong need for a pan-Canadian operational regional ocean prediction capacity covering all Canadian coastal areas in support of marine activities including emergency response, search and rescue, and safe navigation in ice-infested waters. Here we present the first pan-Canadian operational regional ocean analysis system developed as part of the Regional Ice Ocean Prediction System version 2 (RIOPSv2) running in operations at the Canadian Centre for Meteorological and Environmental Prediction (CCMEP). The RIOPSv2 domain extends from 26∘ N in the Atlantic Ocean through the Arctic Ocean to 44∘ N in the Pacific Ocean, with a model grid resolution that varies between 3 and 8 km. RIOPSv2 includes a multivariate data assimilation system based on a reduced-order extended Kalman filter together with a 3D-Var bias correction system for water mass properties. The analysis system assimilates satellite observations of sea level anomaly and sea surface temperature, as well as in situ temperature and salinity measurements. Background model error is specified in terms of seasonally varying model anomalies from a 10-year forced model integration, allowing inhomogeneous anisotropic multivariate error covariances. A novel online tidal harmonic analysis method is introduced that uses a sliding-window approach to reduce numerical costs and allow for the time-varying harmonic constants necessary in seasonally ice-infested waters. Compared to the Global Ice Ocean Prediction System (GIOPS) running at CCMEP, RIOPSv2 also includes a spatial filtering of model fields as part of the observation operator for sea surface temperature (SST). In addition to the tidal harmonic analysis, the observation operator for sea level anomaly (SLA) is also modified to remove the inverse barometer effect due to the application of atmospheric pressure forcing fields. RIOPSv2 is compared to GIOPS and shown to provide similar innovation statistics over a 3-year evaluation period. Specific improvements are found near the Gulf Stream for all model fields due to the higher model grid resolution, with smaller root mean squared (rms) innovations for RIOPSv2 of about 5 cm for SLA and 0.5 ∘C for SST. Verification against along-track satellite observations demonstrates the improved representation of mesoscale features in RIOPSv2 compared to GIOPS, with increased correlations of SLA (0.83 compared to 0.73) and reduced rms differences (12 cm compared to 14 cm). While the RIOPSv2 grid resolution is 3 times higher than GIOPS, the power spectral density of surface kinetic energy provides an indication that the effective resolution of RIOPSv2 is roughly double that of the global system (35 km compared to 66 km). Observations made as part of the Year of Polar Prediction (2017–2019) provide a rare glimpse at errors in Arctic water mass properties and show average salinity biases over the upper 500 m of 0.3–0.4 psu in the eastern Beaufort Sea in RIOPSv2.
Highlights
Over recent years, there has been a growing number of regional ocean prediction systems developed and being run operationally (Kourafalou et al, 2015; Tonani et al, 2015)
An evaluation of the innovations will be presented for both Regional Ice Ocean Prediction System version 2 (RIOPSv2) and GIOPSv3 to demonstrate that the adaptations of SAM2 for the RIOPSv2 system are performing well and to highlight the areas of improvement and degraded performance
We assess the variations in sea level anomaly along a particular Jason satellite altimetry track over the 3-year evaluation period to show specific differences in the quality of the two analysis systems
Summary
There has been a growing number of regional ocean prediction systems developed and being run operationally (Kourafalou et al, 2015; Tonani et al, 2015). A particular challenge for regional ocean prediction systems is the assimilation of sea level anomaly (SLA) observations into an ocean model that includes tidal forcing. The approach taken in the IBI system is to perform an offline harmonic analysis and apply a static set of harmonic coefficients for the primary tidal constituents to remove tidal signals during the online assimilation step. This approach neglects nonstationary effects such as seasonally varying interactions between barotropic and baroclinic tidal modes. Tides are removed from the SSH field using the online harmonic analysis described below prior to calculation of the sea surface height anomaly. As error modes are produced every 3 d, this provides roughly 300 error modes available for each analysis cycle
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