Unexpected 10-Hour Oscillation in Convectively Aggregated State in Cloud-Resolving Model

Abstract:

While investigating the relationship between atmospheric radiative cooling and latent heating—specifically how convective self-aggregation impacts this relationship—in a cloud-resolving model, an unexpected process was observed: a strong 10-hour periodic oscillation. The simulations were run using the System for Atmospheric Modeling for a period of 120 days over a 768 km square domain with no large-scale forcing and no rotation. Once convection aggregates and precipitation reaches a sustained increased level, the precipitation rate fluctuates so that the minimum is approximately 20% of the maximum within each period. The same pattern is observed in moisture and energy fields, though the strongest fluctuations occur in the precipitation rate. These simulations were run using both single and double-moment microphysics and this trend is insensitive to the microphysics. This oscillation has also been tested for sensitivities to resolution, domain size, and sea surface temperature.