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AIR GLOW

The various nightglow emissions (OI 630 nm, OI 557.7 nm, OI 777.4 nm, 589.3 nm, OH (7,2), OH (8,3), OH (6,2) and O2 Atmospheric (0,1) band emissions (862.0 nm – 865.9 nm)) are being monitored from the ground by ground-based high resolution airglow equipments (All-sky Imager, three tilting photometers, all-sky scanning photometers, Fabry-Perot Interferometer) to retrieve key parameters such as chemical composition of the neutral and ionized species, meridional and zonal components of wind velocity and temperature of the different layers of the ionosphere-thermosphere system at a given location during geomagnetically quiet and disturbed period. Knowledge of neutral (and ion) composition, temperature and input energy fluxes will provide critical tests of global models. The horizontal propagation characteristics (phase velocity, wavelength, period and direction) of the short period atmospheric gravity waves (AGW) are also being studied through OI 557.7 nm, 589.3 nm and OH (715 nm - 900 nm) imaging.

A CCD based all-sky imager with 180 0 field of view was operated from the top of a hill (3200 feet above sea level) at Panhala near Kolhapur( 16.8 0 N, 74.2 0 E) in India during January, February and March, 2001 on clear moonless nights to study the characteristics of atmospheric gravity waves and F-region irregularities. Simultaneous photometric data (OI 630 nm, 557.7 nm, OH (8,3)) were also used to examine the wave characteristics linking the two mesospheric regions at 86 km and 96 km. The phase velocity, oscillation periods and direction of propagation of the gravity waves were inferred from the analysis of successive OH and 557.7 nm images. The large scale size ‘band` structures as well as small scale ‘row’ like structures as observed in the OH images were found to propagate predominantly towards north-east and South ward direction during 21:00 to 22: 00 hrs with phase velocity of 40-70 m/s. The signature of north-south aligned ionospheric plasma bubbles moving towards east as observed in the three oxygen emission lines( 630 nm, 557.7nm and 777.4 nm) were seen on ninety percent of the nights. The bifurcation of the structures were complex and their inter seperation was estimated to be 150-200 km at F-region height.

Measurements of the hydroxyl rotational temperature for the (8,3) Meinel band have been carried out from the observations of the ratio of the relative intensities of P1(2) and P1(4) lines of the OH (8,3) band at Kolhapur (16.8°N,74.2°E, dip lat. 10.6º N) in India during the period 1 November 2002- 29 April 2003 using tilting photometers. Mean values of rotational temperature have been computed for 60 nights. The monthly mean value of temperature lies in the range 194 (±11)-208 (±18)K. The mean rotational temperature obtained from all the measurements was found to be 202 ± 15 K. The results agree with other low latitude measurements of rotational temperature using photometric airglow technique. Quasi periodic fluctuations with period of about one-two hours have been prominent on many nights. Furthermore, the results show the general agreement between observations and model (MSIS-86) predictions.

A CCD based Imaging Fabry-Perot Interferometer was developed and tested in the laboratory to study the dynamics of the F – region parameters (temperature and wind velocity).

Navin Parihar, P. T. Patil



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