Modeling Responses of Polar Mesospheric Clouds to Gravity Wave and Instability Dynamics and Induced Large‐Scale Motions

Abstract

A gravity wave (GW) model that includes influences of temperature variations and large‐scale advection on polar mesospheric cloud (PMC) brightness having variable dependence on particle radius is developed. This Complex Geometry Compressible Atmosphere Model for PMCs (CGCAM‐PMC) is described and applied here for three‐dimensional (3‐D) GW packets undergoing self‐acceleration (SA) dynamics, breaking, momentum deposition, and secondary GW (SGW) generation below and at PMC altitudes. Results reveal that GW packets exhibiting strong SA and instability dynamics can induce significant PMC advection and large‐scale transport, and cause partial or total PMC sublimation. Responses modeled include PMC signatures of GW propagation and SA dynamics, “voids” having diameters of ∼500–1,200 km, and “fronts” with horizontal extents of ∼400–800 km. A number of these features closely resemble PMC imaging by the Cloud Imaging and Particle Size (CIPS) instrument aboard the Aeronomy of Ice in the Mesosphere (AIM) satellite. Specifically, initial CGCAM‐PMC results closely approximate various CIPS images of large voids surrounded by smaller void(s) for which dynamical explanations have not been offered to date. In these cases, the GW and instabilities dynamics of the initial GW packet are responsible for formation of the large void. The smaller void(s) at the trailing edge of a large void is (are) linked to the lower‐ or higher‐altitude SGW generation and primary mean‐flow forcing. We expect an important benefit of such modeling to be the ability to infer local forcing of the mesosphere and lower thermosphere (MLT) over significant depths when CGCAM‐PMC modeling is able to reasonably replicate PMC responses.

Impacts of Limited Model Resolution on the Representation of Mountain Wave and Secondary Wave Dynamics in Local and Global Models: 2. Mountain Wave and Secondary Wave Evolutions in the Thermosphere

“…Our results discussed here and by F22 will hopefully prove beneficial in guiding developments and evaluations of new parameterizations of these various dynamics in middle and whole atmosphere GCMs. One example that is clearly of major importance is SGW generation, given its demonstrated roles in KMCM, despite coarse resolution, and regional models revealing these dynamics to arise easily and naturally for localized GWs (Dong et al., 2020, 2021; Fritts et al., 2020; L20, F21). Initial approximations to SGW generation due to 3‐D body forcing (i.e., Luo & Fritts, 1993; Vadas & Fritts, 2001, 2002; Vadas et al., 2003) were based on linear theory that captures an important element of these dynamics, specifically forcing by induced local mean winds.…”

“…KMCM, HIAMCM, WACCM, and WACCM-X resolutions enable SGW generation due to large-scale body forcing accompanying nonlinear interactions among large-scale GWs having their amplitudes constrained by parameterization of dissipation due to smaller-scale, unresolved instability dynamics at lower altitudes. However, these model resolutions currently preclude descriptions of much stronger body forcing of SGWs by small-scale GW packets, and their SA dynamics, often occurring on spatial scales of ∼70-200 km in the thermosphere accompanying high-resolution modeling (e.g., Dong et al, 2020Dong et al, , 2021Fritts et al, 2020;L20) and seen for smaller Δx in Figures 6-8.…”

“…These SA dynamics are especially important for GWs having small horizontal wavelengths, λ h , large c i , and large vertical group velocities, c gz , because these exhibit the fastest and strongest evolutions. There is also now significant direct and indirect observational evidence for SGWs in the MLT that emphasizes their increasing importance at higher altitudes (Becker & Vadas, 2018, 2020; de Wit et al., 2017; Dong et al., 2021; Smith et al., 2013).…”

“…Additional SGWs and acoustic waves (AWs) are generated at smaller spatial scales due to GW breaking driven by large GW amplitudes accompanying SA dynamics. Specific evidence of 3-D responses to such SA dynamics in the PMC layer at ∼82 km, including larger-and smaller-scale SGWs, is provided by Dong et al (2021). Importantly, the initial excitation of SGWs at larger scales precedes instabilities and breaking.…”

Impacts of Limited Model Resolution on the Representation of Mountain Wave and Secondary Gravity Wave Dynamics in Local and Global Models. 1: Mountain Waves in the Stratosphere and Mesosphere

“…Also addressed by a broad community spanning many years were interactions and instabilities accounting for GW dissipation driving energy and pseudo‐momentum flux divergence enabling these influences (e.g., Achatz, 2005, 2007; Andreassen et al., 1998, 1994; Bourgeat et al., 2013; Fritts & Rastogi, 1985; Fritts et al., 2017, 2009; Sutherland, 2013). Among the more recent results of such studies was the recognition of strong GW/mean‐flow interactions yielding “self‐acceleration” (SA) dynamics (Dong et al., 2020, 2021; Fritts et al., 2020, 2015; Scinocca & Sutherland, 2010). These comprise strong local body forcing and SA instabilities that drive secondary GWs (SGWs) arising at larger and smaller scales at higher altitudes, for which there is now additional modeling and observational evidence (Becker & Vadas, 2018, 2020; Dong et al., 2021; Lund et al., 2020).…”