Sensitivity of Convective Self-Aggrgation to Bulk Microphysics Schemes Across Sea Surface Temperatures

Convective self-aggregation (CSA) is an atmospheric phenomenon where small scale convections are spontaneously reorganized into a single group of convection without the influence of an external atmospheric driver. Idealized studies of CSA have identified cloud radiative feedback as an imperative development mechanism, and cloud microphysical processes directly influence this, as atmospheric radiative transfer relies heavily on the overall properties of clouds. So far, systematic sensitivity study of convective self-aggregation in cloud microphysical schemes has not been conducted. In order to investigate this we conducted a set of sensitivity experiments with System for Atmospheric Modeling (SAM; Khairoutdinov and Randall, 2003) using four bulk microphysical schemes (Khairoutdinov and Randall, 2003; Morrison et al., 2005; Thompson et al., 2008; Morrison and Milbrandt, 2015) employing a wide range of sea surface temperatures (SST), different domain sizes (dx = 72 km - 576 km) and grid spacings (2 km and 4 km). All four microphysical schemes favored larger grid size (dx ≥ 288 km) for the CSA to develop, and the time for a simulation to reach a steady state (τs) was reduced with grid size. CSA development and τs dependency on SST is not clear, as each cloud microphysical scheme showed different trends with SST. Also, our findings show enhanced low-level clouds and a higher magnitude of radiative cooling at the same level in the drier regions for simulations that produced the convective self-aggregation, which is consistent with previous studies.