The Life Cycle and Net Radiative Effect of Tropical Anvil Clouds

Abstract

We explore the importance of the life cycle of detrained tropical anvil clouds in producing a weak net cloud radiative effect (NCRE) by tropical convective systems. We simulate a horizontally homogeneous elevated ice cloud in a 2‐D framework using the System for Atmospheric Modeling cloud‐resolving model. The initially thick cloud produces a negative NCRE, which is later canceled by a positive NCRE as the cloud thins and rises. Turning off interactive cloud radiation reveals that cloud radiative heating and in‐cloud convection are fundamental in driving net radiative neutrality. In‐cloud convection acts to thin initially thick anvil clouds and loft and maintain thin cirrus. The maintenance of anvil clouds is tied to the recycling of water vapor and cloud ice through sublimation, nucleation, and deposition as air parcels circulate vertically within the cloud layer. Without interactive radiation, the cloud sediments and sublimates away, producing a large negative NCRE. The specification of cloud microphysics substantially influences the cloud's behavior and life cycle , but the tendency of the life cycle to produce compensating cloud radiative effects is robust to substantial changes in the microphysics. Our study shows that small‐scale processes within upper level ice clouds likely have a strong influence on the NCRE associated with tropical convective cloud systems.

What Drives the Life Cycle of Tropical Anvil Clouds?

“…Simulations without the effects of ACRE could not achieve a near cancelation of the SW and LW CRE as observed in the deep tropics, leading instead to a strongly negative net CRE. Radiative heating promotes the formation and maintentance of thin anvils, which is similar to the results by Hartmann et al (2018) who used a very simple cloud geometry. We find the horizontal spreading of the cloud to be the key feature influencing the radiative effects integrated over the whole convective life cycle.…”

“…Such clouds contain IWP of 5 to 150 g/m 2 and have COD between 1 and 6, and net CRE of about +5 to −25 W/m 2 . The upper tropospheric cloud peak spreads toward higher altitudes when transiting to lower IWP values due to either the in situ formation of new ice clouds or by lofting of anvil remains, as suggested by Hartmann and Berry (2017) and modeled by Hartmann et al (2018). Remarkably, the net CRE shifts from values around −100 W/m 2 for the highest percentiles, toward +15 to +30 W/m 2 for the 40th to 70th percentiles.…”

“…Moreover, tropical anvil cloud properties were found to be very sensitive to the level of turbulent mixing simulated by the model (Ohno et al, ). Hartmann et al () found that ACRE promote the formation and maintenance of thin anvils with the help of two‐dimensional cloud‐resolving model simulations. ACREs increase the longevity of thin anvils by microphysical cycling of water vapor and ICs within the in‐cloud convective mixed layer.…”

Impact of Cloud Ice Particle Size Uncertainty in a Climate Model and Implications for Future Satellite Missions

“…Note that such an alteration is only applied to the radiation calculation. We found that changing RR ei exerts negligible effect on the ice mass and number concentrations, so the proposed enhanced turbulence and cirrus cloud vertical development by in-cloud radiative heating (Hartmann et al, 2018) does not occur in such a large-scale model. The same magnitude of perturbations was applied to RR ei in the radiation scheme.…”

Statistically Steady State Large‐Eddy Simulations Forced by an Idealized GCM: 1. Forcing Framework and Simulation Characteristics

“…The vertical profile of cloud water specific humidity is more bottom heavy than that of cloud fraction, with a more obvious peak near the melting level. In general, the LES produce little cloud ice in the upper troposphere in deep convection regions, which may be related to the relatively simple microphysics scheme and the lack of cloud-radiation interactions (Hartmann et al, 2018) in this study.…”