11:00 AM - 11:15 AM
[AAS06-07] A study on characteristics of gravity waves based on a whole neutral atmosphere GW-permitting GCM
Keywords:Gravity wave, middle atmosphere
Gravity waves (GWs) play a crucial role in the dynamics of the mesosphere and lower thermosphere (MLT). A residual mean circulation from the summer pole to the winter pole in the mesosphere is considered to be primarily driven by the wave forcing due to GWs through breaking and/or critical level absorption. GWs in the middle atmosphere originate mainly from the troposphere. The main tropospheric sources of GWs suggested by the theoretical, observational, and numerical studies are strong convection in the vicinity of the monsoon region in the summer hemisphere, topography and jet-front systems in the winter hemisphere. Although quantitative studies of stratospheric GWs have been conducted using observations and/or climate models (e.g. Geller et al., 2013) so far, studies on the GWs in the MLT region are limited, because observations are difficult for such a remote distance from the ground and the top of most climate models does not reach the MLT region. Therefore, the global aspects of GW dynamical characteristics in the entire middle atmosphere including the MLT region still remain unclear.
To tackle this issue, we utilized a high-resolution GW-permitting GCM, JAGUAR, which covers from the surface to the lower thermosphere (e.g., Okui et al., 2021). The model resolution is T639 and the number of vertical layers is 340. We conducted hindcasts over a whole year of 2022 using the high-resolution JAGUAR and analyzed the outputs. This simulation was initialized with reanalysis, JAWARA (Koshin et al., 2025), which covers from the surface to the lower thermosphere. GWs were designated as fluctuations having total horizontal wavenumbers of 21-639 (horizontal wavelengths λh< 2,000 km). It has been confirmed that the variability of the simulated GWs by the model is almost quantitatively consistent with atmospheric radar observations for respective height regions of the troposphere, lower stratosphere, and upper mesosphere (Sato et al., 2023).
First, the global mean GW kinetic energy (GM-GWKE) is calculated as a function of time and altitude. The GM-GWKE is maximized in summer and winter and minimized in spring and autumn for the stratosphere and mesosphere. Closer inspection shows that GM-GWKE is stronger in the JJA than in the DJF for the solstitial seasons and in the SON than in the MAM for the equinoctial seasons. The difference between the two equinoctial seasons is consistent with the results by Sato and Hirano (2019) who estimated GW contributions to the residual mean circulation in the stratosphere and lower mesosphere by a diagnostic method using reanalysis datasets. In contrast, seasonal changes of GM-GWKE are quite weak in the lower thermosphere compared with those in the stratosphere and mesosphere. Next, the GW kinetic energy is averaged over the NH and SH separately. The GWKE is stronger in winter than in summer for both hemispheres, and focusing on the winter season, GWKE is stronger in the SH than in the NH. This feature explains that the JJA is the strongest season for GM-GWKE. The altitude range of the GWKE maximum is higher in summer than in winter for both hemispheres. The vertical flux of zonal momentum associated with GWs is also analyzed in the meridional cross section for the solstitial seasons. The GW propagation focusing into the central latitude of the westerly (easterly) jet in the winter (summer) hemisphere that was shown by Sato et al. (2009) up to the altitude of 72 km is also clearly observed. This GW focusing on the jet is observed only below an altitude of about 90 km where the weak wind layer is situated. The mean winds in the equatorial region are easterly in the lower thermosphere throughout the year. It is observed that GWs with positive momentum fluxes propagate from the subtropical region into the equatorial easterly winds.
To tackle this issue, we utilized a high-resolution GW-permitting GCM, JAGUAR, which covers from the surface to the lower thermosphere (e.g., Okui et al., 2021). The model resolution is T639 and the number of vertical layers is 340. We conducted hindcasts over a whole year of 2022 using the high-resolution JAGUAR and analyzed the outputs. This simulation was initialized with reanalysis, JAWARA (Koshin et al., 2025), which covers from the surface to the lower thermosphere. GWs were designated as fluctuations having total horizontal wavenumbers of 21-639 (horizontal wavelengths λh< 2,000 km). It has been confirmed that the variability of the simulated GWs by the model is almost quantitatively consistent with atmospheric radar observations for respective height regions of the troposphere, lower stratosphere, and upper mesosphere (Sato et al., 2023).
First, the global mean GW kinetic energy (GM-GWKE) is calculated as a function of time and altitude. The GM-GWKE is maximized in summer and winter and minimized in spring and autumn for the stratosphere and mesosphere. Closer inspection shows that GM-GWKE is stronger in the JJA than in the DJF for the solstitial seasons and in the SON than in the MAM for the equinoctial seasons. The difference between the two equinoctial seasons is consistent with the results by Sato and Hirano (2019) who estimated GW contributions to the residual mean circulation in the stratosphere and lower mesosphere by a diagnostic method using reanalysis datasets. In contrast, seasonal changes of GM-GWKE are quite weak in the lower thermosphere compared with those in the stratosphere and mesosphere. Next, the GW kinetic energy is averaged over the NH and SH separately. The GWKE is stronger in winter than in summer for both hemispheres, and focusing on the winter season, GWKE is stronger in the SH than in the NH. This feature explains that the JJA is the strongest season for GM-GWKE. The altitude range of the GWKE maximum is higher in summer than in winter for both hemispheres. The vertical flux of zonal momentum associated with GWs is also analyzed in the meridional cross section for the solstitial seasons. The GW propagation focusing into the central latitude of the westerly (easterly) jet in the winter (summer) hemisphere that was shown by Sato et al. (2009) up to the altitude of 72 km is also clearly observed. This GW focusing on the jet is observed only below an altitude of about 90 km where the weak wind layer is situated. The mean winds in the equatorial region are easterly in the lower thermosphere throughout the year. It is observed that GWs with positive momentum fluxes propagate from the subtropical region into the equatorial easterly winds.