Moisture Transport due to Baroclinic Waves: Linear Analysis of Precipitating Quasi-Geostrophic Dynamics

Abstract

Abstract:The e ects of rainfall speed, V T , and meridional/vertical moisture gradients on the meridional moisture transport are examined in the context of mid-latitude baroclinic waves. These e ects are investigated in an idealized model that can be solved analytically. The model is systematically derived in a precipitating quasi-geostrophic limit, starting from a moist atmospheric model with minimal representation of cloud microphysics. Single-phase dynamics are considered, with a comparison of three cases: unsaturated, saturated with V T = , and saturated with V T > . The Eady problem for linear baroclinic waves is analyzed, with modi cations to incorporate moisture. As a preliminary step, the moist waves are shown to have properties consistent with prior studies, including larger growth rates and smaller spatial scales in the saturated cases in comparison to the classic dry Eady problem. Then, in addition, it is shown that the meridional moisture ux, as a function of height, has a mid-tropospheric maximum in the case of V T = , and a maximum in the lower troposphere or at the surface for su ciently large values of V T . These results for di erent V T values are discussed in the context of meridional moisture transport in observational data.

Interactions between Water Vapor, Potential Vorticity, and Vertical Wind Shear in Quasi-Geostrophic Motions: Implications for Rotational Tropical Motion Systems

“…Gross PV is nearly identical to the ''moist'' PV discussed by Lapeyre and Held (2004). Additionally, as noted by AM18, the gross PV equation bears resemblance to the precipitating QG equations discussed by Smith and Stechmann (2017), and some of the results discussed here resemble studies that use these equations (Wetzel et al 2017(Wetzel et al , 2020. The gross PV equation also bears resemblance to the ''equivalent'' Ertel PV employed by some studies (Rotunno and Klemp 1985;Martin et al 1992;Cao and Cho 1995;Marquet 2014).…”

“…Relative to dry baroclinic instability alone, growth between m 5 0 and m 5 1 exhibits a larger amplitude due to the contribution from moist processes. This larger amplitude was noted in the diabatic Rossby waves examined by de Vries et al (2010), and by the balanced moist waves examined by Wetzel et al (2017). In the case of b 5 0 and b q 5 0 we find that baroclinic instability occurs when k , k d m 21/2 .…”

Estimated Impacts of Climate Change on Eddy Meridional Moisture Transport in the Atmosphere

“…Numerous studies involving the evaluation of the right-hand side of Equation (4) with observations datasets and CGCM-simulated data (Coupled atmosphere-ocean general circulation model) have shown that transient eddies dominate meridional moisture transport at mid-latitudes:~80% between 30 • and 40 • north and south latitudes (e.g., [20,40,41,68,[73][74][75][76][77]). One can easily show that for the plane wave solutions (A15), the TE meridional moisture flux is exponentially dependent on the growth rate χ k = kc i of unstable modes [78]. Let L w be the wavelength of a baroclinic unstable wave and k = 2π/L w its wavenumber.…”

Effects of clouds and phase changes on fast-wave averaging: a numerical assessment

“…While much is known about dry dynamics without moisture (for either balanced or unbalanced initial conditions), much less is known about moist dynamics with phase changes. In the case of balanced initial conditions, with moisture, a formal asymptotic derivation of precipitating QG (PQG) equations has been presented (Smith & Stechmann 2017), and some properties of the PQG equations have been investigated (Wetzel, Smith & Stechmann 2017, 2019 a ; Edwards, Smith & Stechmann 2020 a , b ), but no rigorous proofs have been shown. Unbalanced initial conditions, on the other hand, are the topic of the present paper.…”