Response of the resolved planetary wave activity and amplitude to turned off gravity waves in the UA-ICON general circulation model

Abstract

The interaction between the resolved waves and parameterized gravity wave (GW) drag in the upper atmosphere extension of the ICON model (UA-ICON) are investigated. To this end, we performed a set of 30-year long time slice UA-ICON runs with two sensitivity simulations where either the subgrid-scale orographic (SSO) or non-orographic GW drag parameterizations are switched off (noSSO and noGWD, respectively), and compare them against a control (CTL) simulation where both GWs parameterizations are active. The stratospheric polar vortex accelerates, cools and shifts poleward in both sensitivity runs. The frequency of sudden stratospheric warmings in the CTL simulation is 5.7 events per decade and drops to 1.7 and 4 events per decade in the noSSO and noGWD, respectively. In both sensitivity runs (particularly in noGWD), an enhancement in the resolved wave amplitude is found in the high latitude stratosphere and in the mesosphere and lower thermosphere (MLT) region in all latitudes. The magnitudes of the resolved waves responses are generally larger for noGWD than noSSO. Our results confirm the compensation mechanism in the UA-ICON model, whereby the perturbed forcings in the GW parameterization drag are often canceled or partly compensated by a resolved large-scale wave driving of opposite sign. In addition, evidence is presented that the compensation mechanism is not always operative everywhere. For example, we found a suppression of the upward propagation of the resolved waves in the cold seasons in the noSSO experiment, which is likely linked to a significant reduction of the favorable propagation conditions in the upper stratosphere.