Modulation of Tropical Convection-circulation Interaction by Aerosol
Indirect Effects in Idealized Simulations of a Global
Convection-permitting Model
Abstract
Observations suggest tropical convection intensifies when aerosol
concentrations enhance, but quantitative estimations of this effect
remain highly uncertain. Leading theories for explaining the influence
of aerosol concentrations on tropical convection are based on the
dynamical response of convection to changes in cloud microphysics,
neglecting possible changes in the environment. In recent years, global
convection-permitting models (GCPM) have been developed to circumvent
problems arising from imposing artificial scale separation on physical
processes associated with deep convection. Here, we use a GCPM to
investigate how enhanced concentrations of aerosols that act as cloud
condensate nuclei (CCN) impact tropical convection features by
modulating the convection-circulation interaction. Results from a pair
of idealized non-rotating radiative-convective equilibrium simulations
show that the enhanced CCN concentration leads to weaker large-scale
circulation, the closeness of deep convective systems to the moist
cluster edges, and more mid-level cloud water at an equilibrium state in
which convective self-aggregation occurred. Correspondingly, the
enhanced CCN concentration modulates how the diabatic processes that
support or oppose convective aggregation maintain the aggregated state
at equilibrium. Overall, the enhanced CCN concentration facilitates the
development of deep convection in a drier environment but reduces the
large-scale instability and the convection intensity. Our results
emphasize the importance of allowing atmospheric phenomena to evolve
continuously across spatial and temporal scales in simulations when
investigating the response of tropical convection to changes in cloud
microphysics.