Articles | Volume 35, issue 2
Ann. Geophys., 35, 227–237, 2017

Special issue: The 14th International Symposium on Equatorial Aeronomy

Ann. Geophys., 35, 227–237, 2017

Regular paper 21 Feb 2017

Regular paper | 21 Feb 2017

Large- and small-scale periodicities in the mesosphere as obtained from variations in O2 and OH nightglow emissions

Ravindra P. Singh1,2 and Duggirala Pallamraju1 Ravindra P. Singh and Duggirala Pallamraju
  • 1Space and Atmospheric Sciences Division, Physical Research Laboratory, Ahmedabad, India
  • 2Department of Physics, Sardar Patel University, Vallabh Vidyanagar, India

Abstract. Using 3 years (2013–2015) of O2(0–1) and OH(6–2) band nightglow emission intensities and corresponding rotational temperatures as tracers of mesospheric dynamics, we have investigated large- and small-timescale variations in the mesosphere over a low-latitude location, Gurushikhar, Mount Abu (24.6° N, 72.8° E), in India. Both O2 and OH intensities show variations similar to those of the number of sunspots and F10.7 cm radio flux with coherent periodicities of 150 ± 2.1, 195 ± 3.6, 270 ± 6.4, and 420 ± 14.8 days, indicating a strong solar influence on mesospheric dynamics. In addition, both mesospheric airglow intensities also showed periodicities of 84 ± 0.6, 95 ± 0.9, and 122 ± 1.3 days which are of atmospheric origin. With regard to the variability of the order of a few days, O2 and OH intensities were found to be correlated, in general, except when altitude-dependent atmospheric processes were operative. To understand mesospheric gravity wave behavior over the long term, we have carried out a statistical study using the periodicities derived from the nocturnal variations in all four parameters (O2 and OH intensities and their respective temperatures). It was found that the major wave periodicity of around 2 h duration is present in all the four parameters. Our analyses also reveal that the range of periods in O2 and OH intensities and temperatures is 11 to 24 and 20 to 60 min, respectively. Periods less than 15 min were not present in the temperatures but were prevalent in both emission intensities. No seasonal dependence was found in either the wave periodicities or the number of their occurrence.

Short summary
A near-infrared imaging spectrograph (NIRIS) has been developed in-house and is being operated from a low-latitude location, Gurushikhar, Mount Abu (24.6° N, 72.8° E), in India. The results presented in this study provide us with a comprehensive picture of mesospheric wave dynamics in terms of characterizing their response to various sources (solar and atmospheric) that give rise to the variability in the mesospheric intensities and temperatures.