Lidar studies of the nighttime sodium layer over Urbana, Illinois: 1. Seasonal and nocturnal variations

Abstract

Sodium lidar measurements obtained between December 1980 and May 1986 at Urbana, Illinois, are compared with other reported lidar measurements and with recently developed models of the layer. Sodium abundance at Urbana reaches a maximum value in November, December and January which is approximately 4.5 times larger than the June minimum value of 2.15 x 109 cm -2. Also in November and December, the layer centroid height is about 1.5 km lower than the yearly average value of 92 km. There is no significant seasonal variation of the rms layer width whi•ch• has an average value of approximately 4.25 km. The peak-to-peak variations of the centroid height and rms width of the average nocturnal layer are 1 km and 600 m, respectively. The semidiurnal tide is primarily responsible for a 36% peak-to-peak abundance variation in the average nocturnal layer which is compatible with a 20 cm s-x amplitude for the vertical wind velocity. The vertical phase velocity of the density perturbations is approximately 1 m s-x which implies a 45 km vertical wavelength for the semidiurnal tide. Because of gravity waves and tides the structure of the nocturnal layer changes substantially throughout the night. Variations of over 200% in abundance, 2 km in centroid height, and 1 km in rms width have been observed within the time span of a few hours. 109-10 •ø m -3. Before lidar systems became available, sodium measurements were largely restricted to studying resonantly scattered sunlight. Groundbased observations of this type were able to define seasonal variations in column abundance [Blamont and Donahue, 1961; Gadsden and Purdy, 1970], but the sharp layer boundaries were not revealed until rocketborne dayglow measurements were made [Hunten and Wallace, 1967]. Lidar observations of the vertical structure of the layer were first made in England [Bowman et al., 1969]. Since then similar measurements have been reported from a variety of locations including France [Me•lie and Blamont, 1977], Brazil [Simonich et al., 1979], Japan [Aru•la et al., 1974], Illinois [Richter et al., 1981], California [Hake et al., 1972] and at the high latitudes of Franz Joseph Land, USSR [Juramy et al., 1981] and Andoya, Norway [Fricke and yon Zahn, 1985]. During the past few years numerous chemical and dynamical processes have been proposed in an attempt to explain the general characteristics of the seasonal, diurnal and geographical variations of the layer structure. Sodium chloride from the oceans and volcanic eruptions have been discussed as possible sodium sources. However, meteoric ablation is generally regarded as the dominant source of all the alkali metal layers including sodium [Clemesha et al., 1978; Richter and Sechrist, 1979a, b; Je•lou et al., 1985a, b]. Much of the intrinsic character of the layer is apparently governed by a complex chemistry involving many reactions among numerous neutral and ionic species [e.g., Sze et al., 1982; Kirchhoff, 1983; Jegou, 1985a]. The dominant loss mechanisms are believed to include the conversion of neutral sodium to t...

Development of the mesospheric Na layer at 69° N during the Geminids meteor shower 2010

“…This parameter is rather insensitive to wave perturbations and therefore a good indicator of the Na layer state (Gardner et al, 1986). Assuming a Gaussian profile for each of the recorded Na density profiles, the FWHM of the Na layer can be calculated, which is related to the RMS width (Gardner et al, 1986). Lidar specifications during the ECOMA campaign 2010 are given in Table 1.…”

The first lidar observations of the nighttime sodium layer at low latitudes Gadanki (13.5°N, 79.2°E), India

“…The mean rms widths of the layer vary between 4.3 and 4.9 km. The mean layer width has a peak-to-peak variation of about 600 m. It appears that the layer width has an inphase relation with the sodium column abundance, but an anti-phase relation with the centroid height (Gardner et al, 1986). However, there is a significant wave nature appeared in mean layer width variation.…”

“…• S. Gardner et al (1986) reported more than 200 percent variation in abundance over a midlatitude site. The best part of the lidar measurements at Gadanki site shows a steady fall in mean column abundance after sunset and a slow raise towards early hours of the day.…”

“…The layer parameters are calculated from the different moments of the mesospheric Na layer as given by Gardner et al (1986). Figure 6 shows the average column abundance, centroid position and width of the Na layer for the entire observational period.…”

ELP-OA : status report of the setup of the demonstrator of the polychromatic laser guide star at Observatoire de Haute Provence

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