Abstract
In numerical ocean modeling, dynamical downscaling is the approach consisting in generating high-resolution regional simulations exploiting the information from coarser resolution models for initial and boundary conditions. Here we evaluate the impacts of downscaling the 1/16o (~ 6–7 km) CMEMS Mediterranean reanalysis model solution into a high-resolution 2-km free-run simulation over the Western Mediterranean basin, focusing on the surface circulation and mesoscale activity. Multi-platform observations from satellite-borne altimeters, high-frequency radar, fixed moorings, and gliders are used for this evaluation, providing insights into the variability from basin to coastal scales. Results show that the downscaling leads to an improvement of the time-averaged surface circulation, especially in the topographically complex area of the Balearic Sea. In particular, the path of the Balearic current is improved in the high-resolution model, also positively affecting transports through the Ibiza Channel. While the high-resolution model produces a similar number of large eddies as CMEMS Med Rea and altimetry, it generates a much larger number of small-scale eddies. Looking into the variability, in the absence of data assimilation, the high-resolution model is not able to properly reproduce the observed phases of mesoscale structures, especially in the southern part of the domain. This negatively affects the representation of the variability of the surface currents interacting with these eddies, highlighting the importance of data assimilation in the high-resolution ocean model in this region to constrain the evolution of these mesoscale structures.
Highlights
Monitoring and modeling the ocean and coastal areas are crucial for both society and science (Visbeck 2018), with uses that include safety-at-sea, economicsThis article is part of the Topical Collection on Coastal Ocean Forecasting Science supported by the GODAE OceanView Coastal Oceans and Shelf Seas Task Team (COSS-TT) - Part IIResponsible Editor: Pierre De Mey-Frémaux, and the environment
The spatial patterns show good consistency between them, with velocities of the same order of magnitude. Both models represent reasonably the mean flows (NC, Algerian current, Balearic current, exit flow south of Sardinia) and the permanent WAG structures in the Alboran Sea. Both models describe quite well the Northern Current (NC) along the French shelf break until reaching the latitude of Barcelona around 41.5o N, with two acceleration zones at both ends of the Gulf of Lions, the amplification produced at 7° E is a bit underestimated in WMOP
In the CMEMS Med Rea model, this pattern is marked by a strong time-averaged current with a detachment from the Iberian shelf break which occurs around 2o E, before reaching the Tarragona mooring location. This retroflection is too intense and too far to the east compared with altimetry and to the WMOP model
Summary
Monitoring and modeling the ocean and coastal areas are crucial for both society and science (Visbeck 2018), with uses that include safety-at-sea (e.g., ocean-rescue, storm surges), economicsThis article is part of the Topical Collection on Coastal Ocean Forecasting Science supported by the GODAE OceanView Coastal Oceans and Shelf Seas Task Team (COSS-TT) - Part IIResponsible Editor: Pierre De Mey-Frémaux (e.g., sustainable fisheries, offshore energy designs, support to navigation), and the environment (e.g., oil spill tracking, plastic debris control). Monitoring and modeling the ocean and coastal areas are crucial for both society and science (Visbeck 2018), with uses that include safety-at-sea (e.g., ocean-rescue, storm surges), economics. This article is part of the Topical Collection on Coastal Ocean Forecasting Science supported by the GODAE OceanView Coastal Oceans and Shelf Seas Task Team (COSS-TT) - Part II. Numerical models are essential tools since they cover a wide range of spatial and temporal scales and are complementary to ocean observations, which are generally sparse. The spatial scales of the monitoring and modeling system must match the end-user requirements as much as possible. High-resolution models are required for regional and local applications and for the understanding of processes over a wide range of scales. In order to reach the required small scales, the “downscaling” approach is employed to generate high-resolution regional simulations. The downscaling techniques, widely used in atmospheric sciences (Navon, 2009), use initial and boundary conditions from a lower resolution model previously
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