Effects of Resolution‐Dependent Excitation of Parameterized Frontal Gravity Waves on the Middle Atmosphere Circulation in the Korean Integrated Model

The middle atmosphere circulation in the Korean Integrated Model (KIM) was evaluated at various horizontal resolutions and integration timescales. It was found that the intensities of the polar night jet and summer hemisphere easterly jet are underestimated. Consistent with the zonal wind, a warm (cold) bias in the mesosphere was found in the winter (summer) hemisphere high latitudes. This suggests that the gravity wave drag (GWD) is generally overestimated in KIM. The GWD in the mesosphere is dominated by the frontal GWD in the present simulations. In the frontal GWD parameterization, it was found that waves are launched more frequently and over a wider area at higher horizontal resolutions. To prevent the excessive generation of frontal gravity waves in the parameterization, the frontogenesis threshold used to diagnose the wave‐launching region was revised. Instead of a constant threshold across different resolutions, the threshold value was modified to depend on the horizontal grid size so that wave regions are diagnosed similarly regardless of the horizontal resolution. Using a modified threshold decreases the GWD, which induces mesospheric cooling (warming) in the winter (summer) hemisphere high latitudes. As a result, the biases are alleviated in the mesosphere. The responses are extended to the lower stratosphere over an extended medium‐range timescale. Lower stratospheric biases are reduced overall, but increase slightly in winter. Since the GWD is reduced to a greater degree at higher resolutions, biases are less reduced at lower resolutions, suggesting that the parameters for scale awareness in the GWD parameterization require further revisions.