Increases in moist‐convective updraught velocities with warming in radiative‐convective equilibrium

Abstract

The scaling of updraft velocities over a wide range of surface temperatures is investigated in simulations of radiative-convective equilibrium with a cloud-system resolving model. The updraft velocities increase with warming, with the largest fractional increases occurring in the upper troposphere and for the highest percentile updrafts. A plume model approximately reproduces the increases in updraft velocities if the plume environment is prescribed as the mean profile in each simulation while holding the entrainment and microphysical assumptions fixed. Convective available potential energy (CAPE) also increases with warming in the simulations but at a much faster fractional rate when compared with the square of the updraft velocities. This discrepancy is investigated with a two-plume model in which a weakly-entraining plume represents the most intense updrafts, and the environment is assumed to adjust so that a more strongly-entraining plume has negligible buoyancy. The two-plume model suggests that updraft velocities increase with warming at a lower rate than implied by the CAPE because of the influence of entrainment on both the mean stratification and the updrafts themselves.

FAT or FiTT: Are Anvil Clouds or the Tropopause Temperature Invariant?

“…In the first paper on this topic, the FAT hypothesis was tested in simulations of RCE with parameterized convection (Hartmann & Larson, 2002). The most compelling evidence for a FAT appeared in a paper that was not about FAT (Singh & O'Gorman, 2015); that study showed a 6-K change in T a when the surface temperature was increased from 281 to 311 K, which is a slightly larger spread in T a than we find in our full-complexity simulations over the same temperature range. Subsequent results from CRMs found a 0.5 K change in T a for a 2 K change in surface temperature (Kuang & Hartmann, 2007), a 1-K change in T a for a 4-K change in surface temperature (Harrop & Hartmann, 2012), an 8-K change in T a for a 15-K change in surface temperature (Khairoutdinov & Emanuel, 2013), and a 2-K change in T a for a 4-K change in surface temperature (Thompson et al, 2017).…”

“…Since a fixed emission temperature for anvil clouds would tend to decouple the outgoing longwave radiation of convecting regions from the underlying surface temperature, a FAT would provide a positive feedback during global warming. Results from multiple cloud-resolving models (CRMs) have also appeared to support the existence of a FAT (Harrop & Hartmann, 2012;Khairoutdinov & Emanuel, 2013;Kuang & Hartmann, 2007;Singh & O'Gorman, 2015). Results from multiple cloud-resolving models (CRMs) have also appeared to support the existence of a FAT (Harrop & Hartmann, 2012;Khairoutdinov & Emanuel, 2013;Kuang & Hartmann, 2007;Singh & O'Gorman, 2015).…”

Simultaneous characterization of mesoscale and convective‐scale tropical rainfall extremes and their dynamical and thermodynamic modes of change

“…Contributions from the upward shift of the ω profile (Figure ) are negative on both scales ( %/K and −1.8%/K for meso‐ and convective scales respectively). This finding is consistent with the upward shift in the radiative cooling profile [ Hartmann , ; Singh and Gorman , ], and it is consistent in sign and magnitude with the behavior inferred from CRM studies in RCE (MOE11).…”

Radiative-Convective Equilibrium Model Intercomparison Project

“…For instance, recent work has suggested a thermodynamic mechanism for a decrease in anvil cloud fraction with warming in several GCMs (Bony et al, 2016) and a CRM (Cronin and Wing, 2017), but the robustness of this response across 25 a wider range of models has yet to be determined. For example, one other CRM finds the opposite response, an increase in anvil cloud fraction with warming (Singh and O'Gorman, 2015). Changes in the amount and height of anvil clouds with warming have strong implications for cloud feedbacks, and the coupling between temperature, cloud amount, and circulation may contribute to a narrowing of convective areas -both of which could lead to a type of iris effect (Mauritsen and Stevens, 2015;Bony et al, 2016;Schneider, 2016, 2017).…”