The Regional Ice Ocean Prediction System v2: a pan-Canadian ocean analysis system using an online tidal harmonic analysis

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.

Presentation and evaluation of the Arctic sea ice forecasting system neXtSIM-F

“…The official European forecast for the Arctic is developed and run by the CMEMS Arc-MFC (Arctic Monitoring and Forecasting Centre) 5 . This uses the TOPAZ system (Simonsen et al, 2018;Sakov et al, 2012), which uses version 2.2.37 of the Hybrid Coordinate Ocean Model (HYCOM) (Bleck, 2002). In the current version (4) of TOPAZ, HY-COM is coupled to a sea ice model derived from version 4.1 of the Community Ice CodE (CICE: Hunke and Lipscomb, 2010); ice thermodynamics are described in Drange and Simonsen (1996), while the dynamics are based on the viscous-plastic (VP) sea ice rheology (implemented with the elastic-viscous-plastic (EVP) solver of Hunke and Dukowicz, 1997).…”

“…Another relevant example is the replacement of RIPS 3 (Lemieux et al, 2016a) by RIOPS 4 in 2016, having NEMO coupled to the system (Smith et al, 2021). The move was partly motivated by wishing to have detailed currents forecast around the Canadian coast for search-and-rescue purposes, including tidal forecasts.…”

“…The BBM's main physical achievement has been to stabilise the thickness for decadal-scale simulations; computationally it is also 5-6 times faster, since it is able to be solved explicitly, unlike our version of the MEB. It also kept the improvements in the model's representation of the main spatial and temporal characteristics of observed deformation that were gained by MEB -strain localisation and scaling (Marsan et al, 2004;Rampal et al, 2008;Stern and Lindsay, 2009), as well as multifractality and intermittency in time (Rampal et al, 2019) meaning that higher deformations are more localised in space and more intermittent in time than smaller ones. These properties have strong implications for things like distribution and size of lead openings and how long they will stay open, which controls the heat and salt fluxes across the ocean-iceatmosphere coupled system.…”

Arctic sea ice and snow from different ice models: A CICE–SI3 intercomparison study

“…CICE is coupled to NEMO based on a set up used in Smith et al (2021). Changes made from Smith et al (2021) to the present setup are the update of the model versions from NEMOv3.6 to NEMOv4 and CICEv4 to CICEv6.2.…”

“…CICE is coupled to NEMO based on a set up used in Smith et al (2021). Changes made from Smith et al (2021) to the present setup are the update of the model versions from NEMOv3.6 to NEMOv4 and CICEv4 to CICEv6.2. As a difference to the standard setting the freezing and the melt temperature has been differentiated in order to account for salinity difference of sea ice and the ocean.…”