Statistical Comparison of Gravity Wave Characteristics Obtained from Airglow All-Sky Observation at Mt. Bohyun, Korea and Shigaraki, Japan

Abstract

Previously, all-sky airglow images observed at Shigaraki (34.9° N, 136.1° E), Japan, during 2004 and2005 were analyzed in relation to those observed at Mt. Bohyun (36.2° N, 128.9° E) for a comparison of their gravity wave characteristics (Kim et al. 2010). By applying the same selection criteria of waves and cloud coverages as in the case of Mt. Bohyun all-sky images, we derived apparent wavelengths, periods, phase velocities, and monthly occurrence rates of gravity waves at Shigaraki in this study. The distributions of wavelengths, periods, and speeds derived for Shigaraki were found to be roughly similar to those for Mt. Bohyun. However, the overall occurrence rates of gravity waves at Shigaraki were 36% and 34% for OI 557.7 nm and OH Meinel band airglow layers, respectively, which were significantly higher than those at Mt. Bohyun. The monthly occurrence rates did not show minima near equinox months, unlike those for Mt. Bohyun. Furthermore, the seasonal preferential directions that were clearly apparent for Mt. Bohyun were not seen in the wave propagation trends for Shigaraki. These differences between the two sites imply different origins of the gravity waves near the Korean peninsula and the Japanese islands. The gravity waves over the Japanese islands may originate from sources at various altitudes; therefore, wind filtering may not be effective in causing any seasonal preferential directions in the waves in the airglow layers. Our analysis of the Shigaraki data supports recent theoretical studies, according to which gravity waves can be generated from in situ sources, such as mesosphere wind shear or secondary wave formation, in the mesosphere.

Propagating characteristics of mesospheric gravity waves observed by an OI 557.7 nm airglow all-sky camera at Mt. Bohyun (36.2° N, 128.9° E)

“…Previous studies of mid-latitude gravity waves have reported that gravity waves in eastward and northward propagations dominate most of the summer (Taylor et al, 1993;Nakamura et al, 1999;Walterscheid et al, 1999;Hecht et al, 2001;Ejiri et al, 2003;Tang et al, 2005). Observations at BHO have confirmed the similar tendency of propagation in summer Yang et al, 2015). The summer bias of wave propagation can be distinctly due to the criticallevel filtering by the prevailing zonal and meridional winds in the lower atmosphere.…”

“…All-sky images were obtained with 4 × 4 binning to increase signal-to-noise ratios. A detailed description of the all-sky camera at BHO is given in Yang et al (2015). The OI 557.7 nm filter has a central wavelength of 557.81 nm with a full width at half maximum of 1.53 nm.…”

“…An all-sky imager had been deployed at Bohyun observatory (BHO; 36.2 • N, 128.9 • E) to observe various airglows, including OH Meinel 720-910 nm, O 2 atmospheric band near 865.7 nm, OI 630 nm and OI 557.7 nm in the pilot period 2002-2005. Later, the all-sky camera at BHO focused on the OI 557.7 airglow observation, because the throughput of the OI 557.7 filter is far more efficient than other filters. The previous studies with the all-sky observation at BHO have reported seasonal variation of wave parameters and horizontal propagation directions Yang et al, 2015).…”

Comment on angeo-2021-65

“…The previous studies for mid-latitude gravity waves have reported in the majority the dominance of eastward and northward propagations during summer (Taylor et al, 1993;Nakamura et al, 1999;Walterscheid et al, 1999;Hecht et al, 2001;Ejiri et al, 2003;Tang et al, 2005). Observations at BHO have confirmed the similar tendency of propagation in summer Yang et al, 2015). The summer bias of wave propagation can be distinctly due to the critical level filtering by the prevailing zonal and meridional winds in the lower atmosphere.…”

“…camera at BHO is an ultra-high speed (f/0.95) 3-inch camera composed of a fisheye lens with a viewing angle of 180°, telecentric lens to adjust airglow emission light path for parallel incident to filter, a 6-position filter wheel installed with two narrowband filters (OI-557.7, OI-630.0), and a 1024×1025 CCD detector. The detail description of the all-sky camera at BHO has been given in Yang et al (2015). The images with the OI 557.7 filter were obtained continuously at intervals of 5 minute with an exposure time of 90-150 seconds and a spatial resolution of 500 km radial region.…”