MS Teams
Speaker
Eric Bembenek | McGill University
Title
Effects of Precipitation in Idealized Models of the Atmosphere
Abstract
Idealized models help to gain a fundamental understanding of geophysical fluid dynamics. One common idealization in these models is to assume a dry atmosphere. However, moisture can play an important role in affecting the dynamics. For example, precipitation involves a release of latent heat that forces the fluid. Moreover, in a warming climate, precipitation is projected to increase so that its effects can become more pronounced in the future. In this talk, we consider the effects of precipitation in idealized models of barotropic, baroclinic, and static/conditional instabilities.
First, we use a one-layer shallow water model to examine precipitation’s impact on the barotropic breakdown of the intertropical convergence zone (ITCZ). The ITCZ is an important generator of tropical cyclones (TCs) and aquaplanet simulations have shown that a more poleward ITCZ produces a higher frequency of TCs. In our model, we produce ITCZ-like winds using a prescribed forcing and quantify how the barotropic growth rate changes when the forcing shifts to higher latitudes. Next, we consider how precipitation affects the growth rate. To parameterize precipitation, we include a moisture variable that releases latent heat when supersaturation occurs, and this results in a thinning of the layer. We show an ITCZ produced at higher latitudes has a faster growth rate and that precipitation leads to a reduction in the growth rate.
Second, we use a two-layer shallow water model to investigate the effect of precipitation on the energetics of the midlatitude jet stream. Energy is input into the system by a relaxation of the temperature field towards a baroclinically unstable profile and removed via bottom drag. As in the one-layer model, precipitation occurs when moisture in the lower layer supersaturates and results in a mass transfer from the lower to the upper layer. To replenish moisture, we include an evaporative source in the lower layer. We show that precipitation leads to a reduction in the eddy energy of the system compared to a dry atmosphere.
Finally, we use a Rayleigh-Benard setup in a moist Boussinesq model as an idealized representation of tropical convection. The dynamics are forced by the diffusion of heat and moisture across the upper and lower boundaries. We consider the parameter space spanned by variations in the bottom and top temperatures. Here, we explore two regimes of interest: a statically and conditionally unstable regime. In the statically unstable regime, we will show the precipitation reduces kinetic energy and in the conditionally unstable regime, precipitation enhances kinetic energy.