14:15 〜 14:30
[PEM12-33] Propagation characteristics of gravity waves over the Andes, observed by OH arirglow imaging at Rio Gallegos: horizontal phase velocity spectrum analysis.
キーワード：大気重力波、アンデス山脈、OH 大気光、大気上下結合
Atmospheric gravity waves, generated near the earth surface and in the troposphere, have been known as the main driver of the global general circulation in the middle atmosphere above the stratosphere since 1980’s. However, their role in the whole atmospheric system is not fully understood yet because of their complicated behavior during their generation, propagation and breaking. The wide-spread spectral range in temporal scale (~5 min to 10-20 hours in period), spatial scales (10 – 1,000s of km in horizontal wavelength, a few to a hundred of km in vertical wavelength) and the significantly transient characteristics are likely to cause difficulty in observational studies.
Recently the secondary wave generation caused by breaking gravity waves in the middle atmosphere has been recognized as a very important process because those waves can propagate into higher altitudes and play a great role of transporting momentum and energy to higher altitudes and furthermore efficiently propagate beyond the MLT region into the thermosphere/ionosphere to causes disturbances there.
Since late 2017, we have been carrying out OH airglow imaging observations (~87 km altitude) at Rio Gallegos, Patagonia, Argentine (51.6S, 69.3W) near the Andes, one of the hotspots of the gravity waves. In this study, we report the gravity wave activity in one year in 2018. The characteristics of the airglow images at Rio Gallegos were the quasi-stationary waves, suggesting the effect of mountain wave, and the wave breaking events, suggesting large amplitude of the waves. These are probably due to the intense gravity wave excitation over the Andes mountains. These characteristics show similarity with the finding by Pautet et al., (2021) by winter-time observation at Rio Grande (54S, 68W), but the quasi-stationary waves by our observation seem to be less frequent over Rio Gallegos.
Horizontal phase velocity spectral analysis (M-transform, Matsuda et al., 2014) has been applied to pick up the waves with periods of 5-60 min, and with horizontal wavelengths of 10-100 km. We found that the spectrum was very widespread up to 150 m/s, and very frequently clear signal of wind filtering (wind blocking) due to the stratospheric zonal wind, in early (Mar-April) and late (ASO) winter. In mid-winter, spectral peaks spreads to E-W around zero, and the wind blocking is not clearly seen, which suggests significant secondary wave generations above the stratopause and possibility of penetration into the thermosphere/ionosphere. Gravity wave energy (I’/I) seems to be the largest around August-September. In summer (Nov-Feb) primary propagation was eastward.
Our observational results indicate that the horizontal phase velocity spectrum is a useful way to investigate to identify the altitude range of the generation of the gravity waves observed in the airglow layer at around 85-90 km height. We also report the difference of the gravity wave characteristics between the observations near the Andes and at Syowa station, the Antarctic (69S, 40E).
Recently the secondary wave generation caused by breaking gravity waves in the middle atmosphere has been recognized as a very important process because those waves can propagate into higher altitudes and play a great role of transporting momentum and energy to higher altitudes and furthermore efficiently propagate beyond the MLT region into the thermosphere/ionosphere to causes disturbances there.
Since late 2017, we have been carrying out OH airglow imaging observations (~87 km altitude) at Rio Gallegos, Patagonia, Argentine (51.6S, 69.3W) near the Andes, one of the hotspots of the gravity waves. In this study, we report the gravity wave activity in one year in 2018. The characteristics of the airglow images at Rio Gallegos were the quasi-stationary waves, suggesting the effect of mountain wave, and the wave breaking events, suggesting large amplitude of the waves. These are probably due to the intense gravity wave excitation over the Andes mountains. These characteristics show similarity with the finding by Pautet et al., (2021) by winter-time observation at Rio Grande (54S, 68W), but the quasi-stationary waves by our observation seem to be less frequent over Rio Gallegos.
Horizontal phase velocity spectral analysis (M-transform, Matsuda et al., 2014) has been applied to pick up the waves with periods of 5-60 min, and with horizontal wavelengths of 10-100 km. We found that the spectrum was very widespread up to 150 m/s, and very frequently clear signal of wind filtering (wind blocking) due to the stratospheric zonal wind, in early (Mar-April) and late (ASO) winter. In mid-winter, spectral peaks spreads to E-W around zero, and the wind blocking is not clearly seen, which suggests significant secondary wave generations above the stratopause and possibility of penetration into the thermosphere/ionosphere. Gravity wave energy (I’/I) seems to be the largest around August-September. In summer (Nov-Feb) primary propagation was eastward.
Our observational results indicate that the horizontal phase velocity spectrum is a useful way to investigate to identify the altitude range of the generation of the gravity waves observed in the airglow layer at around 85-90 km height. We also report the difference of the gravity wave characteristics between the observations near the Andes and at Syowa station, the Antarctic (69S, 40E).