Shifting the diurnal cycle of parameterized deep convection over land

Abstract

[1] In most atmospheric circulation models used for climate projections, cloud and convective processes are not explicitly resolved but parameterized. Such models are known to produce a diurnal cycle of continental thunderstorms in phase with insolation, while observed precipitation peaks in late afternoon. We propose a new approach which corrects this long standing bias of parameterized convection. In this approach, deep convection triggering and intensity are controlled by subcloud processes: here boundary layer thermals and gust fronts, and potentially orography or surface heterogeneities. The representation of the diurnal cycle of deep convection is greatly improved in 1D mode, with rainfall maximum delayed from midday to late afternoon, provided parameterizations account for the key role played by shallow cumulus in preconditioning deep convection and by gust fronts in the self-sustaining of thunderstorms in the afternoon. Citation: Rio, C., F. Hourdin, J.-Y. Grandpeix, and J.-P. Lafore (2009), Shifting the diurnal cycle of parameterized deep convection over land, Geophys. Res. Lett., 36, L07809,

Simulating deep convection with a shallow convection scheme

“…This increase is driven by rain evaporation, which generates cold pools that induce horizontal flows. Together with the associated organized surface convergence along cold pool boundaries, it represents a supplementary energy source for lifting an air parcel and thus favors the development of convection, as is apparent in our SAM simulations and many past studies of deep convection (see e.g., Rio et al, 2009;Khairoutdinov and Randall, 2006).…”

“…Rio et al (2009) represented this effect by implementing a density current parameterization and coupling it to Emanuel (1991)'s scheme. Here we follow a simpler, more empirical, approach to parameterize this effect.…”

“…Rio et al (2009) were able to simulate a realistic diurnal cycle of convection for an idealized case of mid-latitude continental convection by adding a density current parameterization to Emanuel (1991)'s convection scheme. Grandpeix et al (2010) investigated this approach for the Hydrology-Atmosphere Pilot Experiment in the Sahel (HAPEX-Sahel) and the Tropical Ocean Global…”

Radiative convective equilibrium as a framework for studying the interaction between convection and its large‐scale environment

“…These changes led to significant improvements in the representation of the atmospheric variability in the ECMWF model. Simulations of the diurnal timing of precipitation have also benefited from comparisons between convection-resolving idealized models and global, highly parameterized models [Rio et al, 2009;Bechtold et al, 2014].…”

On the impact of recent developments of an atmospheric general circulation model on the simulation of CO<sub>2</sub> transport

“…The convective onset is now controlled by the thermal 10 plume variables and the maintenance of deep convection after its onset is operated by the cold pools. In better agreement with observations, the main results are a delay of the convective initiation, a self-sustainment of convection through the afternoon (Rio and Hourdin, 2008;Rio et al, 2009) and a drastic increase of the tropical variability of precipitations (Hourdin et al, 2013). This version has not been implemented in the above-mentioned inversion system for CO 2 because preliminary CO 2 transport simulations showed unrealistically large seasonal cycles at some southern stations like Palmer Station (PSA) in 15 Antarctica (unpublished results).…”