Effects of Rotation on the Multiscale Organization of Convection in a Global 2D Cloud-Resolving Model

Abstract

Atmospheric convection exhibits distinct spatiotemporal variability at different latitudes. A good understanding of the effects of rotation on the multiscale organization of convection from the mesoscale to synoptic scale to planetary scale is still lacking. Here cloud-resolving simulations with fixed surface fluxes and radiative cooling are implemented with constant rotation in a two-dimensional (2D) planetary domain to simulate multiscale organization of convection from the tropics to midlatitudes. All scenarios are divided into three rotation regimes (weak, order-one, and strong) to represent the idealized ITCZ region (0°–6°N), the Indian monsoon region (6°–20°N), and the midlatitude region (20°–45°N), respectively. In each rotation regime, a multiscale asymptotic model is derived systematically and used as a diagnostic framework for energy budget analysis. The results show that planetary-scale organization of convection only arises in the weak rotation regime, while synoptic-scale organization dominates (vanishes) in the order-one (strong) rotation regime. The depletion of planetary-scale organization of convection as the magnitude of rotation increases is attributed to the reduced planetary kinetic energy of zonal winds, mainly due to the decreasing acceleration effect by eddy zonal momentum transfer from mesoscale convective systems (MCSs) and the increasing deceleration effect by the Coriolis force. Similarly, the maintenance of synoptic-scale organization is related to the acceleration effect by MCSs. Such decreasing acceleration effects by MCSs on both planetary and synoptic scales are further attributed to less favorable conditions for convection provided by weaker background vertical shear of the zonal winds, resulting from the increasing magnitude of rotation.

Convective Momentum Transport and Its Impact on the Madden‐Julian Oscillation in E3SM‐MMF

“…In particular, the CMT with lower-tropospheric eastward MF and upper-tropospheric westward MF has the same sign as both the background zonal winds and the MJO wind fields, thus accelerating the large-scale zonal winds. This is consistent with the conclusion of Brenowitz et al (2018) and Yang, Majda, and Brenowitz (2019) that the CMT promotes planetary-scale organization of convection by serving as the dominant kinetic energy source.…”

“…This is consistent with the conclusion of Brenowitz et al. (2018) and Yang, Majda, and Brenowitz (2019) that the CMT promotes planetary‐scale organization of convection by serving as the dominant kinetic energy source.…”

“…The central role of CMT in interactions across multiple space and time scales was further studied in a simple dynamical model (Majda & Stechmann, 2009) and an idealized multicloud model (Majda & Stechmann, 2008). Recently, Brenowitz et al (2018) and Yang, Majda, and Brenowitz (2019) used a two-dimensional (2-D) global CRM to simulate multiscale organization of convection and concluded that CMT from MCSs is the dominant kinetic energy source for planetary-scale zonal winds, promoting planetary-scale organization of convection in the tropics. From a theoretical perspective, Yang and Majda (2017) used a multiscale model to study the upscale impact of MCSs on synoptic-scale equatorial waves in 2-D flows, and extended the results for modeling convectively coupled Kelvin waves and two-day waves .…”