Impact of Ocean Model Resolution on Temperature Inversions in the Northeast Pacific Ocean

Temperature inversions are a local vertical minimum in temperature located at a shallower depth than a local maximum. In the Northeast Pacific, several water masses are present as well as multiple mechanisms for transforming or adverting ocean temperature (cold air events, upwelling, river discharge, cross-shelf eddy transport), thus creating favorable conditions for the presence of temperature inversions. For these reasons, modeling temperature inversions is challenging. This work analyzes observations from 2020 and 2021 to characterize real inversions in the Northeast Pacific and then compares observations and model results from the U.S. Navy's Global Ocean Forecast System version 3.1 (GOFS 3.1) and two instances of the Navy Coastal Ocean Model (both with 3 km-50 level configurations and either with or without data assimilation). Temperature inversions are observed to be present in about 45% of profiles with temperature minimums between 50–150 m, temperature maximums between 75–175 m, and inversion thickness almost entirely less than 40 m. Modeled temperature inversions are present in about 5% of model-observations comparisons, with modeled minimums shallower than 50 m, modeled maximum shallower than 100 m, and inversion thickness broadly distributed between 20 m and 60 m. The models' vertical grid have coarse resolution at the depths where inversions occur. The assimilation process also low-pass filters temperature, making inversions weaker. Additional work is identified to test the impact of vertical grids on modeled inversions.