Contribution of Gravity Waves to Universal Vertical Wavenumber (∼m⁻³) Spectra Revealed by a Gravity‐Wave‐Permitting General Circulation Model

Abstract

Observations with high vertical resolution have revealed that power spectra of horizontal wind and temperature fluctuations versus vertical wavenumber m $m$ have a universal shape with a steep slope in a high m $m$ range, approximately proportional to m−3 ${m}^{-3}$. Several theoretical models explaining this spectral slope were proposed under an assumption of gravity wave (GW) saturation. However, little evidence has been obtained to show that these universal spectra are fully composed of GWs. To confirm the validity of this assumption, two kinds of m $m$ spectra are calculated using outputs from a GW‐permitting high‐top general circulation model. One is the spectra for GWs designated by fluctuations having total horizontal wavenumbers of 21–639. The other is the spectra of fluctuations unfiltered except extracting the linear trend in each vertical profile that were often analyzed in the observational studies. A comparison between the two shows that GWs dominate the observed spectra only in a higher m $m$ part of the steep slope, whereas disturbances other than GWs significantly contribute to its lower m $m$ part. Moreover, geographical distributions of the characteristic wavenumbers, slopes, and spectral densities of GW spectra are examined for several divided height regions of the whole middle atmosphere. It is shown that strong vertical shear below the zonal wind jets as well as wave saturation are responsible for the formation of the steep slopes of GW spectra.

Gravity Wave Morphology During the 2018 Sudden Stratospheric Warming Simulated by a Whole Neutral Atmosphere General Circulation Model

“…The dependency of GW morphology on the model's horizontal resolution is briefly discussed in this study. Okui et al (2022) examined vertical wavenumber (m) spectra in the same GCM and showed that characteristics of the model-simulated m spectra of GWs were broadly consistent with observations. These earlier studies support the reality of GWs in our GCM simulations.…”

Roles of Gravity Waves in Preconditioning of a Stratospheric Sudden Warming

“…The details of the model are described by Watanabe and Miyahara (2009) and Okui et al. (2021, 2022). Here we shortly present the configuration of the model and simulations.…”

“…The DJF of 2018/2019 includes an SSW event that occurred in January 2019. The details of the model are described by Journal of Geophysical Research: Atmospheres 10.1029/2023JD039881 Watanabe and Miyahara (2009) and Okui et al (2021Okui et al ( , 2022. Here we shortly present the configuration of the model and simulations.…”

A Comparison of Stratospheric Gravity Waves in a High-Resolution General Circulation Model with 3-D Satellite Observations

“…In this sense, intercomparison of satellite observations is worthwhile. .g., VanZandt, 1985;Tsuda et al, 1989;Sato et al, 2003) , which is characterized by a steep slope of vertical wavenumber (𝑚) spectra (∝ ~𝑚 ) at high wavenumbers of 𝑚= ~10 -4 -10 -3 m -1 (Okui et al, 2022). Kruse et al (2022) (Becker et al, 2022;Kruse et al, 2022).…”