Convective response to changes in the thermodynamic environment in idealized weak temperature gradient simulations

• Published in: Journal of advances in modeling earth systems 2015-06, Vol.7 (2), p.712-738
• Main Authors: Sessions, Sharon L., Herman, Michael J., Sentić, Stipo
• Format: Article
• Language: English
• Subjects: Advection; Anomalies; Approximation; Atmospheric precipitations; Atmospheric stability; Convection; Drying; Entrainment; Environmental conditions; Horizontal advection; horizontal moisture advection; Moisture; multiple equilibria; Parameterization; Permits; Perturbations; Precipitation; Profiles; Rainfall; Shape; Studies; Temperature; Temperature gradients; Temperature profile; Temperature profiles; thermodynamic environment; Thermodynamics; Tropical climate; Tropical convection; Troposphere; Vertical advection; Vertical motion; weak temperature gradient approximation (WTG)
• ISSN: 1942-2466; 1942-2466
• DOI: 10.1002/2015MS000446

We investigate the response of convection to idealized perturbations in the thermodynamic environment in simulations which parameterize the large‐scale circulations using the weak temperature gradient (WTG) approximation. The perturbations include a combination of modifying the environmental moisture and atmospheric stability via imposing anomalies in reference moisture and temperature profiles. We find that changes in atmospheric stability strongly influence the character of convection by drastically modifying the vertical motion profile, whereas changes to atmospheric moisture modulate the intensity of precipitation produced by the convection, but do not qualitatively change the shape of the vertical motion profile. An important question is how does horizontal moisture advection into the domain affect convection? We test several different parameterizations of this process; these include lateral entrainment by circulations induced by enforcing WTG, a moisture relaxation which parameterizes the advection of moisture by large‐scale nondivergent circulations, and control simulations in which both of these mechanisms are turned off so horizontal advection is assumed negligible compared to vertical advection. Interestingly, the most significant differences resulting from the choice of horizontal moisture advection scheme appear in environmental conditions which suppress–rather than support–the development of deep tropical convection. In this case, lateral entrainment related to WTG circulations is the only parameterization which results in extreme drying of the troposphere in environments which suppress convection. Consequently, this is the only parameterization which permits multiple equilibria—dry or precipitating steady states—in convection. Key Points: Deep tropical convection is sensitive to the thermodynamic environment Atmospheric stability determines the convective profile in WTG simulations Parameterization scheme for horizontal moisture advection modifies convection