Generalization and application of the flux-conservative thermodynamic equations in the AROME model of the ALADIN system

Abstract

Abstract. General yet compact equations are presented to express the thermodynamic impact of physical parameterizations in a NWP or climate model. By expressing the equations in a flux-conservative formulation, the conservation of mass and energy by the physics parameterizations is a builtin feature of the system. Moreover, the centralization of all thermodynamic calculations guarantees a consistent thermodynamical treatment of the different processes. The generality of this physics-dynamics interface is illustrated by applying it in the AROME NWP model. The physics-dynamics interface of this model currently makes some approximations, which typically consist of neglecting some terms in the total energy budget, such as the transport of heat by falling precipitation, or the effect of diffusive moisture transport. Although these terms are usually quite small, omitting them from the energy budget breaks the constraint of energy conservation. The presented set of equations provides the opportunity to get rid of these approximations, in order to arrive at a consistent and energy-conservative model. A verification in an operational setting shows that the impact on monthlyaveraged, domain-wide meteorological scores is quite neutral. However, under specific circumstances, the supposedly small terms may turn out not to be entirely negligible. A detailed study of a case with heavy precipitation shows that the heat transport by precipitation contributes to the formation of a region of relatively cold air near the surface, the so-called cold pool. Given the importance of this cold pool mechanism in the life cycle of convective events, it is advisable not to neglect phenomena that may enhance it.

Simulating model uncertainty of subgrid-scale processes by sampling model errors at convective scales

“…The coupling between physics and dynamics is handled by an interface based on a flux-conservative formulation developed in Catry et al (2007) and further generalized in Degrauwe et al (2016). The interface transforms the fluxes coming from the parameterizations to tendencies using a clean description of the thermodynamic and continuity equations, ensuring the conservation of heat, mass and momentum.…”

“…The simulations are performed over the tropics during a period of enhanced convective activity on a grid with a horizontal grid spacing of 4 km. This resolution lies on the verge of what is considered the convection-permitting scale, where it has been demonstrated (Deng and Stauffer, 2006;Lean et al, 2008;Roberts and Lean, 2008) that non-parameterized convection often shows unrealistically strong updrafts and density currents as well as overestimated precipitation rates.…”

Response to the comments of reviewer 1

“…It is a regular 1.3 km grid on a Lambert projection, with its center at 50.57 • N, 4.55 • E, with 588 physical grid points in the east-west and north-south directions, and with 87 vertical layers. This ALARO CMC run on a kilometer scale was evaluated for a severe convective storm of 18 August 2011 causing casualties at the Pukkelpop mu- (Delobbe and Holleman, 2006). The red dot presents the location of the Pukkelpop music festival.…”

The ALADIN System and its canonical model configurations AROME CY41T1 and ALARO CY40T1

“…The coupling of the physics to the dynamics (step 4 in Table 1) is based on a flux-conservative formulation developed by Catry et al (2007). A flexible version of this physics-dynamics interface, called INTFLEX, has been recently implemented and validated in the common code by Degrauwe et al (2016) that facilitates the implementation of new species and processes. The use of INTFLEX for the AROME configuration has improved the life-cycle dynamics of the cold pool mechanism in deep convective systems.…”