The mesospheric sodium layer at 23°S: Nocturnal and seasonal variations

Abstract

The vertical profile of mesospheric sodium has been measured by laser radar at São José dos Campos (23°S, 46°W) on 344 nights since 1972. Large day‐to‐day variations are observed, but averaging over a large number of measurements consistently shows an annual variation by a factor of 2 in the sodium abundance, with maximum in local winter. The average nocturnal variation is consistent with photochemical control of the bottomside of the layer and diffusive control of the topside. Variations observed on individual nights appear to be mainly dynamic in origin. Vertical structure with a characteristic wavelength of the order of 10 km is frequently seen to propagate downward through the layer at rates between 1 and 4 km h−1. Comparison of our results with twilight and daytime absorption abundances suggests a latitudinal asymmetry in the seasonal variation of abundance.

Summer sudden Na number density enhancements measured with the ALOMAR Weber Na Lidar

“…In polar regions the winter Na number density is a factor of 10 larger than during summer (Gardner et al, 1988;Kurzawa and von Zahn, 1990). Towards lower latitudes this factor is smaller and at low latitudes it is about 1.3 (Simonich et al, 1979). This seems to indicate the sensitivity of the Na abundance to temperature as the mesosphere is coldest during summer in polar regions (Plane et al, 2003).…”

Statistics of the sodium layer parameters at low geographic latitude and its impact on adaptive-optics sodium laser guide star characteristics

“…1 shows a simplified diagram of the INPE Lidar in its present configuration. A description of the Lidar can be found in Clemesha et al (2001) and in Simonich et al (1979). Over the many years during which the system has operated, it has undergone considerable modifications, and only the 75 cm receiving telescope and the 120 cm turning mirror have remained unchanged.…”

“…The Lidar (Light Detection And Ranging) technique was used to measure the evolution of the mesospheric sodium layer over a long period . A description of the measurement technique and discussion of the measurement precision can be found in Simonich et al (1979) and in Clemesha et al (1992). The data used in this study consists of the height of the maximum sodium concentration, the centroid height, the full width at half maximum (FWHM) of the equivalent Gaussian of the mesospheric sodium layer thickness, the peak of the sodium concentration, and the column abundance.…”

A statistical study of sporadic sodium layer observed by Sodium lidar at Hefei (31.8° N, 117.3° E)

“…Many researchers consider that in the interpretation of the short-time scales atmospheric dynamics (such as gravity waves and tides), the sodium layer can be regarded as a passive tracer (Gardner and Shelton, 1985;Gardner and Voelz, 1987;Kwon et al, 1987;Bills and Gardner, 1993), due to the longer lifetime of sodium atoms above 85 km (Xu and Smith, 2003). Extensive lidar studies of the seasonal variations of the sodium layer were conducted at different latitudes in the 1970s (Gibson and Sandford, 1971;Megie and Blamont, 1977;Simonich et al, 1979;States and Gardner, 1999;Plane et al, 1999;She et al, 2000;Gardner et al, 2005;Yi et al, 2009). With the development of narrowband lidars (Bills et al, 1991;She et al, 1992;Bills and Gardner, 1993;Papen et al, 1995), the mesospheric temperature and wind measurements has complemented sodium observations and helped to us understand the dynamical process in the MLT region.…”