Statistical study of short‐period gravity waves in OH and OI nightglow images at two separated sites

Abstract

[1] Using airglow images of the near-infrared OH band (720-910 nm) and OI (557.7 nm) line, we investigated seasonal, latitudinal, and local time variations of short-period gravity waves. The images were obtained at two locations in Japan that are $1200 km apart, Rikubetsu (43.5°N, 143.8°E) and Shigaraki (34.9°N, 136.1°E), between October 1998 and October 1999. Our analysis has focused on small-scale gravity waves with wavelengths less than 40 km and dominant phase speeds of $20-50 m/s. Wave occurrences for both OH and OI at Rikubetsu and Shigaraki are significantly higher than 60%, with a slightly larger value in summer. The occurrences increase from evening to midnight. There are no obvious local time dependencies in horizontal wavelength, propagation direction, and phase speed. The propagation directions in summer are either northward or northeastward at both locations. However, in winter the propagation directions at Rikubetsu are generally westward (NW, W, and SW), whereas those at Shigaraki are only southwestward. From simultaneous wind observation by the MF radars at Wakkanai (45.4°N, 141.7°E) and Yamagawa (31.2°N, 130.6°E), we discuss possible influences of Doppler and thermal ducting, wind filtering, and source distribution of gravity waves propagating from the lower atmosphere to the airglow heights in the mesopause region.

Characteristics and sources of gravity waves observed in noctilucent cloud over Norway

“…Correspondingly, the observed periods found in these studies are typically on the order of 8-10 min. However, Ejiri et al (2003) found an average value of 35 m s −1 at mid latitude (40 • N), similar to this work. This wide range of values could be due to different gravity wave sources, for example orographic versus frontal generation, where the observed phase speeds would be Doppler shifted due to speed of the source relative to the observer.…”

An investigation of long-distance propagation of gravity waves under CAWSES India Phase II Programme

“…The ducts due to the variations in the mean wind field are called Doppler ducts, while those associated with strong discontinuities in the temperature field are called thermal ducts. And gravity waves trapped in these ducts can travel (without being considerably attenuated) to large horizontal distances before dissipating their energy and momentum to the background atmosphere; hence, these ducted waves are more likely to be detectable at large distance from their origin (Chimonas and Hines, 1986;Fritts and Yuan, 1989;Isler et al, 1997;Ding et al, 2003;Snively et al, 2007;Bageston et al, 2011). At low latitudes, such waves are more common in occurrence compared to those freely propagating (Isler et al, 1997).…”

“…Using a tri-station airglow network between 42 and 44 • N, Stockwell and Lowe (2001) investigated the gravity wave field and found striking similarity in the characteristics of observed gravity wave spectrum. Ejiri et al (2003) studied the propagation characteristics of gravity at two locations, Rikubetsu (43.5 • N, 143.8 • E) and Shigaraki (34.9 • N, 136.1 • E), Japan, separated by ∼ 1200 km. Authors observed the poleward propagation of gravity waves during summer at both the sites and conjectured that the waves at the two sites were the same waves that possibly travelled in thermal ducts.…”

“…GWs are created in the lower atmosphere by wind flow over uneven topography, convective activity, jet streams, geostrophic adjustments and other sources. GWs have periods of few minutes to hours, and their wavelengths range from tens of kilometres to hundreds of kilometres (Fritts and Alexander, 2003 and references cited therein). GWs propagate vertically as well as horizontally, and in the course of their vertical propagation from the lower atmosphere, their amplitude grows manifold (due to decreasing density).…”

MLT gravity wave climatology in the South America equatorial region observed by airglow imager

“…Nakamura et al (1999) observed spatial scales for these waves around 5-60 km. Ejiri et al (2003) found that the gravity waves observed in OI images have longer wavelengths (around 27 km) than those seen in OH images (around 21 km). In our previous studies (Medeiros et al, , 2004a, we reported that the averaged band wavelength was 23 km, approximately twice that of the ripples (13 km).…”