Gravity wave reflection and its influence on the consistency of temperature- and wind-based momentum fluxes simulated above Typhoon Ewiniar

Abstract

Abstract. For a case study of Typhoon Ewiniar performed with a mesoscale model, we compare stratospheric gravity wave (GW) momentum flux determined from temperature variances by applying GW polarization relations and by assuming upward propagating waves, with GW momentum flux calculated from model winds which is considered as a reference. The temperature-based momentum-flux profile exhibits positive biases relative to the reference, which fluctuate significantly with altitude. The vertically-averaged magnitude of the positive biases is about 14 % of the reference momentum flux. We found that this deviation from the reference stems from the interference between upward and downward propagating waves. The downward propagating GWs are due mainly to partial reflections of upward propagating waves at altitudes where the background wind and stability change with height. When the upward and downward propagating waves are decomposed and their momentum fluxes are calculated separately from temperature perturbations, the fraction of the momentum flux arising from the downward propagating waves is about 4.5-8.2 % of that from the upward propagating waves. The net momentum flux of upward and downward propagating GWs agrees well with the reference from the model wind perturbations. The implications of this study for the GW momentum-flux observations from satellites are discussed.

Characteristics of gravity waves resolved by ECMWF

“…This is mainly due to the fact that the effects of GWs are global, but that GWs are of small scales and mesoscales, and that even smaller scales are involved in their forcing, propagation and dissipation. In particular, for studying the interaction of GWs with the global circulation, general circulation models (GCMs) are required, in which GWs are not well represented (for overviews on GWs, their measurement and their implementation in global models see, for instance, Fritts and Alexander, 2003;Kim et al, 2003;Geller et al, 2013). There are two lines which can be followed for improving this situation: by enhanced understanding we may explicitly improve our representation of GWs in global models, or by enhanced resolution we may implicitly describe GWs correctly also on the global scale.…”

Characteristics of gravity waves generated in the jet-front system in a baroclinic instability simulation

“…The node structure can also be partly attributed to the partial reflection of waves. A partial reflection occurs where the wind or stability of the background flow changes significantly, and it causes interference between the primary wave and reflected wave in perturbation fields (e.g., Gossard and Hooke, 1975;Kim et al, 2012). The background wind for W3 has a large gradient in the vertical and horizontal directions in the lower and middle troposphere (Fig.…”

Observations of Inertia Gravity Waves in the Western Pacific and Their Characteristic in the 2015/2016 Quasi‐Biennial Oscillation Disruption

“…Most of the stratospheric GWs are generated in the troposphere (upward‐propagating waves), with significantly less downward‐propagating waves than upward‐propagating waves. However, if similar trends can still be seen in the average values of the four sites with sufficient samples, the downward‐propagating waves may be due to wave reflection occurred at the critical layer (Kim et al., 2012; Wüst & Bittner, 2008). The enhanced easterly wind with altitude in the stratosphere over four stations also indicates that wave reflection by jet stream may occur above the analyzed altitude (Figure S2 in the Supporting Information ).…”