Quantifying Gravity Wave Forcing Using Scale Invariance

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Thursday, June 13, 2019

Despite the increasing resolution, forcing on the mean circulation by resolved waves in general circulation models is not yet converging. Parameterization of the forcing remains a major source of model uncertainty.

Graph depicting Gravity Wave Forcing
Comparing zonal forcing by resolved waves, unresolved waves, and parameterization. a Color contour: zonal forcing by unresolved gravity waves, deduced from the forcing by resolved gravity waves based on scale invariance. Line contours: parameterized zonal gravity wave forcing. Solid lines: eastward forcing, and contour intervals are 20 ms−1 day−1. b–d Vertical profiles of zonal forcing by resolved gravity waves (dotted lines), unresolved gravity waves (solid lines), and parameterized gravity waves (dashed lines), averaged over 40–50°N, 10°S–10°N, and 60–50°S. Base 10 logarithmic scale is used in a

This study examines the scale invariance of zonal spectra of momentum flux and wave forcing, and shows that it can be used to quantify the forcing by unresolved waves with knowledge of the resolved ones in global models. The result reveals the leading order importance of the small-scale wave forcing, which is in general agreement with that required for obtaining the zonal mean wind climatology. It is also found that wave and mean flow interaction is important in maintaining the robust spectral structure. This method may provide a strategy to design physically consistent and scale-aware parameterization schemes for scale invariant quantities, when a model has sufficient resolution to partially resolve their spectra.

Liu, H.-L., (2019), Quantifying gravity wave forcing using scale invariance, Nature Communications, (2019), 10, 2605, doi: 10.1038/s41467-019-10527-z.

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