Diabatic heating and mesoscale vertical motion in cumulus anvils

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Description

Areally extensive cumulus anvil clouds dominate tropical cloud forcing and account for ~30–70% of the total rainfall in convective systems. Given the different heating profiles of convective cores and stratiform anvils, errors in convective-stratiform rain partitioning in a GCM imply errors in its tropical circulation. Most GCM cumulus parameterizations include the effect of stratiform anvils only via the condensate detrained from the convective updraft. However, anvils create their own mesoscale updrafts in response to diabatic (radiative plus latent) heating, and the properties of the anvils can be expected to evolve over their life cycle. To place some observational constraints on mesoscale vertical motions in convective clusters, we are combining geostationary satellite data and ASR data for the SGP and TWP. The ISCCP Convection Colocator, which identifies convective systems in IR data and tracks their propagation and evolution, is first used to select times when a convective cluster passed over one of the sites. Each system is classified as being in either the developing, mature, or decaying stage of its lifecycle at the time of ASR observation. Radiative heating profiles are obtained from either the BBHRP product (at SGP) or the Mather-McFarlane product (at Manus), and composite profiles for the various life cycle stages are created. Initial results for the SGP suggest that longwave cooling peaks near 13 km during the developing stage, but descends to 10 km by the time systems decay; that shortwave heating is strong between 5–10 km during the developing stage, creating a net cooling/heating dipole above/below 10 km during the developing stage; and that shortwave heating is weaker later in the life cycle, creating little net heating/cooling below 8 km. Manus storms also show the net cooling/heating dipole during the developing stage but differ from the SGP in several ways, e.g., stronger longwave and shortwave heating during the developing and mature stages and heating extending to higher levels during the mature stage.