Convective aggregation in realistic convective‐scale simulations

Abstract

To investigate the real‐world relevance of idealized‐model convective self‐aggregation, five 15 day cases of real organized convection in the tropics are simulated. These include multiple simulations of each case to test sensitivities of the convective organization and mean states to interactive radiation, interactive surface fluxes, and evaporation of rain. These simulations are compared to self‐aggregation seen in the same model configured to run in idealized radiative‐convective equilibrium. Analysis of the budget of the spatial variance of column‐integrated frozen moist static energy shows that control runs have significant positive contributions to organization from radiation and negative contributions from surface fluxes and transport, similar to idealized runs once they become aggregated. Despite identical lateral boundary conditions for all experiments in each case, systematic differences in mean column water vapor (CWV), CWV distribution shape, and CWV autocorrelation length scale are found between the different sensitivity runs, particularly for those without interactive radiation, showing that there are at least some similarities in sensitivities to these feedbacks in both idealized and realistic simulations (although the organization of precipitation shows less sensitivity to interactive radiation). The magnitudes and signs of these systematic differences are consistent with a rough equilibrium between (1) equalization due to advection from the lateral boundaries and (2) disaggregation due to the absence of interactive radiation, implying disaggregation rates comparable to those in idealized runs with aggregated initial conditions and noninteractive radiation. This points to a plausible similarity in the way that radiation feedbacks maintain aggregated convection in both idealized simulations and the real world.

Convective Aggregation and Indices Examined from CERES Cloud Object Data

“…The domain mean CWV/CRH is lower, precipitation is stronger while outgoing longwave radiation (OLR) is higher, compared to non‐aggregated convection. These relationships are observationally verified (Tobin et al, ) and agree with a CRM simulation under a more realistic setting (Holloway, ). But the sensitivity of top‐of‐the‐atmosphere net radiation budget and surface turbulent fluxes to aggregation is not as strong as that found in idealized RCE simulations (Tobin et al, , ).…”

Observing Convective Aggregation

“…performed global aquaplanet simulations (using a superparameterization setup in which 2D CRMs are embedded in each large-scale model grid cell) with uniform SST both with and without rotation and found similarities in diabatic feedbacks between the self-aggregation in the non-rotating setup and the MJO in the rotating setup. Holloway (2017) found that simulations of real nearequatorial case studies using a limited-area CRM setup also showed similarities to idealized self-aggregation, although the effects of suppressing interactive radiation were constrained by the imposed lateral boundary conditions. More studies are needed to probe links between self-aggregation and convective organization that interacts with equatorial wave dynamics.…”

Circling in on Convective Organization

“…Observed maximal radii in fact vary by an order of magnitude, between 10 and 100 km (Black, 1978;Feng et al, 2015;Zuidema et al, 2012). This may also help to better assess models of self-organization, such as those employed in the idealized self-aggregation case (Holloway, 2017;Holloway et al, 2017;Wing & Cronin, 2016;Wing et al, 2017;Yang, 2018). This may also help to better assess models of self-organization, such as those employed in the idealized self-aggregation case (Holloway, 2017;Holloway et al, 2017;Wing & Cronin, 2016;Wing et al, 2017;Yang, 2018).…”