Propagation Paths and Source Distributions of Resolved Gravity Waves in ECMWF-IFS analysis fields around the Southern Polar Night Jet

Abstract

Abstract. In the southern winter polar stratosphere the distribution of gravity wave momentum flux in many state-of-the-art climate simulations is inconsistent with long-time satellite and superpressure balloon observations around 60° S. Recent studies hint that a lateral shift between prominent gravity wave sources in the tropospheric mid-latitudes and the location where gravity wave activity is present in the stratosphere causes at least parts of the discrepancy. This lateral shift cannot be represented by the column-based gravity wave drag parametrisations used in most general circulation models. However, recent high-resolution analysis and re-analysis products of the ECMWF-IFS show good agreement to observations and allow for a detailed investigation of resolved gravity waves, their sources and propagation paths. In this paper, we identify resolved gravity waves in the ECMWF-IFS analyses for a case of high gravity wave activity in the lower stratosphere using small-volume sinusoidal fits to characterise these gravity waves. The 3D wave vector together with perturbation amplitudes, wave frequency and a fully described background atmosphere are then used to initialise the GROGRAT gravity wave ray-tracer and follow the gravity waves backwards from the stratosphere. Finally, we check for indication of source processes on the path of each ray and thus quantitatively attribute gravity waves to sources that are represented within the model. We find that stratospheric gravity waves are indeed subject to far (> 1000 km) lateral displacement from their sources, taking place already at low altitudes (

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

“…Rather, they typically employ parameterizations relying on linear theory and discrete or idealized GW spectral forms (Kim et al, 2003). Our results provide quantitative insights into, and confirmation of, significant deficiencies, especially large-scale circulation biases, in current parameterizations of orographic GW drag (GWD; Sandu et al, 2019;Strube et al, 2021;van Niekerk et al, 2020;Vosper et al, 2019) and of non-orographic GWD (Geller et al, 2013;Müller et al, 2018;Stephan et al, 2019).…”

Towards a more “scale‐aware” orographic gravity wave drag parametrization: Description and initial testing

“…There have been a number of studies indicating that the gravity wave dynamics within the Southern Hemisphere stratosphere could be more complex than in the Northern Hemisphere and that not representing this complexity in models is the cause of the bias at 60°S. Observations (Wright et al ., 2017), high‐resolution models (Sato et al ., 2012), and ray‐tracing theory (Perrett et al ., 2021; Strube et al ., 2021) all suggest that the lateral propagation of gravity waves, a process not accounted for in parametrizations, could be the cause of the missing drag at 60°S. Poor representation of other gravity wave processes, such as nonorographic gravity wave generation (Garcia et al ., 2017), could also contribute to this bias.…”

“…However, this bias still remains large and is consistent with the ubiquitous lack of parametrized gravity wave drag at 60 • S (McLandress et al, 2012), evident from Figure 11b,d. There have been a number of studies indicating that the gravity wave dynamics within the Southern Hemisphere stratosphere could be more complex than in the Northern Hemisphere and that not representing this complexity in models is the cause of the bias at 60 • S. Observations (Wright et al, 2017), high-resolution models (Sato et al, 2012), and ray-tracing theory (Perrett et al, 2021;Strube et al, 2021) all suggest that the lateral propagation of gravity waves, a process not accounted for in parametrizations, could be the cause of the missing drag at 60 • S. Poor representation of other gravity wave processes, such as nonorographic gravity wave generation (Garcia et al, 2017), could also contribute to this bias. It is interesting that the error remains large even in the N1280 grid case studies, implying that the processes contributing to this error are still not adequately represented even at this relatively fine grid spacing.…”