The Time Scale of Shallow Convective Self-Aggregation in Large-Eddy Simulations Is Sensitive to Numerics

Area of Science:

• Atmospheric Science
• Cloud Physics
• Tropical Meteorology

Background:

• Tropical mesoscale simulations often show cloud self-aggregation driven by convection-circulation feedback.
• This phenomenon leads to the formation of large cloud clusters in the tropics.

Purpose of the Study:

• To evaluate if large-eddy simulations (LESs) can accurately represent the self-aggregation of tropical clouds.
• To investigate the impact of numerical settings on capturing this feedback mechanism.

Main Methods:

• Simulated the non-precipitating, cumulus-topped boundary layer using the BOMEX case.
• Employed a range of numerical configurations across two different LES models.
• Tested resolutions below 100 meters.

Main Results:

• Aggregation timescales did not converge even at high resolutions (<100 m).
• The energetic scales of convection are only slightly larger than typical LES grid spacings.
• LES models may not fully capture the self-aggregation process at current resolutions.

Conclusions:

• Faithful representation of tropical mesoscale cloud patterns and self-aggregating convection in LESs requires higher resolutions or improved sub-filter scale models.
• Further research is needed to understand the significance of these processes in organizing tropical mesoscales.