Lidar observations of the mesospheric sodium layer at Syowa Station, Antarctica

Abstract

The mesospheric sodium layer was measured for 42 nights during the period from April to October, 1985, at Syowa Station (69°00′ S, 39°35′ E), Antarctica, by using a dye laser radar (lidar) tuned to the D2 line of sodium. This observation was made as part of the Middle Atmosphere Program (MAP). In contrast to the results obtained at mid‐latitudes in the northern hemisphere, the seasonal variation in abundance showed no significant winter maximum. Further, there was no apparent seasonal variation in the vertical distribution of sodium density. However, we observed oscillatory variations in abundance with a period of about 40 days. The nocturnal variations in the sodium density profile have a wavelike structure with a vertical wavelength of 10 to 16 km and a period of 3 to 8 hours, which suggests strongly that gravity waves are propagating upward through the sodium layer. The sodium lidar measurements during auroral activity give evidence that the layer is disturbed associated with the auroral breakup event.

Simultaneous measurements of Antarctic mesospheric gravity waves by meteor radar and lidar.

“…These longer waves may correspond to the dashed curve of the sodium abundance in Fig. 1 and also to the wave found by NOMURA et al (1987). These points will be discussed later in more detail.…”

“…On the other hand, the lidar measurements were made on 42 nights during the period from April to October (NOMURA et al, 1987). As a result, the number of simultaneous measurements was not large.…”

“…For this observation (see Fig. 2), by calculating the difference between the normalized sodium profile averaged over one hour and the profile averaged over the night, NOMURA et al (1987) have found upward-propagating, monochromatic gravity waves with a period of 3 to 4 hours and with a vertical wavelength of about 10km, accordingly with a vertical phase velocity of about 0.8m/s.…”

“…The detailed description of the system and some results, including temporal and seasonal variations of the sodium layer and gravity wave activities, have been presented by NOMURA et al (1987NOMURA et al ( , 1988NOMURA et al ( , 1989. Briefly, the system consists of a transmitter based on a coaxial flashlamp pumped dye laser tuned to the sodium D2 line (589.0nm), a Cassegrainian-type telescope of 50cm in diameter, photon detection and counting circuits, and a data processing computer.…”

Lidar Observations of Sporadic Fe and Na Layers in the Mesopause Region over Equator

“…The Shigaraki Na lidar was operated at the Shigaraki MU observatory in September 1995 by Shinshu University. The basic system of this lidar was the same that used by Nomura et al (1987). A Shumidt-Cassegrainian telescope with a diameter of 35.5 cm was used.…”