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

Abstract

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.

The role of radiation in organizing convection in weak temperature gradient simulations

“…In this work, we utilize the strategy of Sessions et al . [], but rather than investigating the additional role of horizontal moisture advection (as in Sessions et al . []), we consider how interactive versus noninteractive radiative cooling affects convection in different thermodynamic environments.…”

“…In addition to identifying conditions which support or suppress convection, WTG is also an efficient method for characterizing convection in different thermodynamic environments, as was demonstrated in Sessions et al . []. In this work, we utilize the strategy of Sessions et al .…”

“…[], but rather than investigating the additional role of horizontal moisture advection (as in Sessions et al . []), we consider how interactive versus noninteractive radiative cooling affects convection in different thermodynamic environments. Given that nearly all three‐dimensional RCE simulations of convective organization require interactive radiation for spontaneous organization [e.g., Bretherton et al ., ; Muller and Held , ]—the notable exception being Tompkins []—we hope to elucidate the role of interactive radiation in the organization of tropical convection.…”

Modeling the MJO in a cloud‐resolving model with parameterized large‐scale dynamics: Vertical structure, radiation, and horizontal advection of dry air

“…Under the influence of strong drying by horizontal advection in the first week of DYNAMO and strong temperature anomalies in the lower levels, which effectively suppress convection [e.g., Sessions et al ., ], our model simulations with interactive radiation (described in detail in section 3.2) settle into a dry state which is either permanent, or from which the simulation takes a long time to recover, and in either case in disagreement with observations. It is possible that this is in part due to the moist static energy bias in the forcing data set during that period [e.g., Johnson et al ., ].…”

Forcings and feedbacks on convection in the 2010 Pakistan flood: Modeling extreme precipitation with interactive large‐scale ascent

“…This modeling framework extends the notion of ''parameterization of large-scale dynamics'' previously applied in the tropics-including the weak-temperature-gradient method [e.g., Sobel and Bretherton, 2000;Raymond and Zeng, 2005;Daleu et al, 2015], the damped-gravity-wave method [e.g., Kuang, 2008;Blossey et al, 2009;Romps, 2012;Daleu et al, 2015], and related others [e.g., Mapes, 2004;Bergman and Sardeshmukh, 2004]-to parameterize large-scale vertical motion. These methods allow attribution of precipitation to environmental factors such as the sea surface temperature (SST) or the large-scale tropospheric temperature profile, and have been used to aid understanding of a variety of phenomena in the tropics [e.g., Chiang and Sobel, 2002;Wang et al, 2013Wang et al, , 2015Nie and Sobel, 2015;Sessions et al, 2015]. In the extratropics, quasi-balanced dry adiabatic PV dynamics, captured in an approximate way by the QG system [e.g., Charney, 1948;Phillips, 1951;Hoskins et al, 1985] plays a larger role in inducing large-scale vertical motion than it does in the tropics.…”