Parametric Gravity Wave Forcings in the Stratocumulus-Topped Boundary Layer under a Prescribed Radiative-Convective Equilibrium

This work studies the breakup propensity of the stratocumulus-topped boundary layer (STBL) interacting with gravity waves using large-eddy simulation with a uniform vertical grid of 5 m and horizontal spacing of 30 m. A radiative-convective equilibrium (RCE) state is constructed to enforce stationarity in the STBL, and the gravity waves are introduced via a vertical momentum forcing mimicking a packet of waves. A nondimensionalization involving the inversion height ( z i ) and mean horizontal base wind as length and velocity scales is proposed to provide a framework to analyze the forcing parameter space. The magnitude of the scaled forcing amplitude (𝒜) is critical in understanding various STBL breakup conditions. Classification of breakup was based on the reduction of the liquid water path for each forced STBL case. For 𝒜 < 1, breakup did not occur, while we observed modest cloud reductions for 1 < 𝒜 < 2. However, STBL-stationarity was gradually reestablished after the single-period forcing ceased. Fixing 𝒜 ∼ 2 showed that forcings with longer duration and an o ( z i ) vertical length scale promoted breakup. When the forcing has two intrinsic periods, the percentage of cleared cloud dramatically increased, though recovery towards RCE is still observed. 𝒜 ≥ 2.5 marks a critical threshold by which the STBL broke up entirely, but this is sensitive to the imposed longwave cooling time scale. We explore the connection between these bulk breakup results and the turbulent state by examining energy budgets and the anisotropy induced by the forcing.